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Evan
05-10-2010, 01:20 AM
We had a thread a while ago in which the principle of seasoning cast iron to relieve casting stress was discussed. Some maintained that it was a myth and some agreed that it must have some merit to be practised for as long as it has.

I am on the side that it does actually relieve the strains produced by cooling after casting. My reasoning is based on the fact that common cast iron undergoes a ductile to brittle transition at temperatures near freezing. By reducing the the amount of energy required to propagate a crack by as much as 90 percent the ordinary changes in size with temperature are enough to cause micro cracks that will reduce the strains built into the part during casting.

This "seasoning" usually involves leaving the cast piece outside in the weather for a full season so that it is exposed to a full range of temperatures from hot weather to below freezing. Of course this only works in a moderate climate where it does actually freeze in the winter. The part is not under any external load so that the formation of micro cracks does not result in a significant reduction in strength since the cracks do not propagate far. They also will "heal" somewhat as the molecules of iron and carbon rearrange positions to fill the voids left by the cracks.

At least, that is the conjecture.

I have inadvertently tested this theory. I left a pair of cast iron C clamps holding a 2x4 piece of lumber that was to become a hand rail on one of my sections of ornamental iron railing. That was a couple of years ago and I (ahem) have been too busy attending meetings of the procrastination society to complete the handrail installation.

The C clamps were used to hold the wooden rail in place on the top metal rail of the iron railing. They weren't clamped particularly tight because it would mark the wooden rail, but they were under moderate compression for two years. During that time the temperature has covered a range from -40F to +100F with many freeze/thaw cycles.

These particular C clamps are a 3" clamp sold by the local Canadian Tire store. They sell a wide variety of tools of decent quality, certainly not bottom of the line imports quality. I have at least 50 of this brand of clamps and have never had one fail, until now. The two clamps are from different batches and of considerably different age but they were both outside and under medium pressure for the same length of time.

When I removed them them the other day everything seemed fine. However, when I went to use them to clamp some parts for welding they both failed easily and in precisely the same way. They both cracked at the part of the clamp where the greatest stress is brought to bear under load. I repeat, I have never seen this sort of failure before regardless of how much I tighten these type of clamps.

The only reasonable explanation is that the seasoning process really does produce micro cracks that relieve casting stresses. In this case the cracks propagated because of the additional external stress cause by the clamping force.

http://ixian.ca/pics7/clamps.jpg

dp
05-10-2010, 01:33 AM
I'd have sworn this was a pretty well established fact. It's discussed here:
http://www.ehow.com/list_6045435_effects-freezing-cast-iron-radiators.html

It's not a new problem.

Astronowanabe
05-10-2010, 02:39 AM
could another possible culprit be the wood swelling

MuellerNick
05-10-2010, 02:49 AM
The old Romans knew a very simple technique to crack rocks:
Make a rectangular hole, drive wood in and then keep the wood whet.
That's how the C-clamps cracked.


Nick

Doc Nickel
05-10-2010, 02:52 AM
could another possible culprit be the wood swelling

-Doubtful the wood could produce sufficient force to stress the clamps that much. I've cranked down on those things before (not that exact brand, but similar midrange imports) and even after using cheater pipes to tighten and beating on the clamped part with heavy cudgels, they never failed. (Or at least, haven't failed yet.)

I'm not yet convinced of the "microcracks" theory, but I doubt it was swelling wood. I suppose I could see damp wood swelling from ice formation during the cold, combined with the cold-related contraction of the iron frame, combined with the cold-induced weakening of the metal, but even that's just a theory.

Doc.

Evan
05-10-2010, 03:21 AM
The wood was actually already fully finished and sealed. It is also softwood, pine to be exact and it can't exert enough force to break the clamps even if it did swell. This is a very dry climate, especially in the winter. Wood shrinks here.

Also, the clamps were not visibly cracked. They didn't fail until I applied significant force.

MuellerNick
05-10-2010, 03:38 AM
but they were under moderate compression for two years. During that time the temperature has covered a range from -40F to +100F with many freeze/thaw cycles.

The wood was actually already fully finished and sealed. It is also softwood, pine to be exact and it can't exert enough force to break the clamps even if it did swell. This is a very dry climate, especially in the winter. Wood shrinks here.

And in summer, it swells. It doesn't matter wether the wood was sealed, it still shrinks and swells. I once made a table with an iron flat underneath (my fault) and the wood cracked in winter. I needed a 10 ton press to get the crack back together. That wood was sealed.


Nick

Punkinhead
05-10-2010, 05:59 AM
The wood was actually already fully finished and sealed. It is also softwood, pine to be exact and it can't exert enough force to break the clamps even if it did swell.It was the wood swelling with moisture. "Sealing" doesn't really seal, especially outdoors. Finishes like varnish slow down the movement of moisture but don't stop it. You'd be astounded how much force swelling wood can produce. Like has already been mentioned, it was used to crack large slabs of rock in ancient times.

The labels "hard wood" and "soft wood" are misnomers - they're classified botanically rather than by hardness. Pine is labelled a soft wood because it comes from conifers. Hard woods come from deciduous trees. Pine is harder than many so called hard woods. Some varieties of pine are harder than oak. Balsa wood is a hard wood.

Evan
05-10-2010, 06:08 AM
Cast iron is well known for it inability to bend. If the swelling of the wood were sufficient alone to crack the cast iron it would have done so in a very obvious and visible failure. I challenge anybody to take a piece of cast iron and slowly apply stress so that it doesn't actually break the iron or produce visible damage yet reduces the strength by perhaps 50%.

Evan
05-10-2010, 06:24 AM
The labels "hard wood" and "soft wood" are misnomers - they're classified botanically rather than by hardness. Pine is labelled a soft wood because it comes from conifers. Hard woods come from deciduous trees. Pine is harder than many so called hard woods. Some varieties of pine are harder than oak. Balsa wood is a hard wood.

The softwoods are called softwoods because they are soft. There are very few exceptions regardless of the botanical distinctions. Jack Pine, which used to be the predominate species here is only about 1/3 as hard as the various species of Oak. There is only one species of pine that approaches the hardness of the average Oak variety and that is Caribbean Pine. We don't have that here. We also are VERY familiar with wood products here as we depend entirely on the forest industry for our livelihood. I say that personally as my wife is the general manager of a small business that supplies a wide range of products to the saw filing and planer rooms of many sawmills. Wood is our business.

If you check the Janka hardness for a wide variety of wood species you will find the species called hardwoods are consistently much harder than the softwoods.

Punkinhead
05-10-2010, 06:49 AM
Cast iron is well known for it inability to bend. If the swelling of the wood were sufficient alone to crack the cast iron it would have done so in a very obvious and visible failure.Magnaflux is used to check for cracks in cast iron that are undetectable by eye.

Evan
05-10-2010, 07:09 AM
This turns out to be pretty easy to settle. I broke the piece off completely so I could inspect it for evidence that the crack was pre existing. If there was any trace of a crack while the part was out in the weather the cracked area will be discoloured or rusted. There is no evidence of that. The cracked area is very fresh and all looks the same. If it had cracked from extreme pressure it would have started at the inside of the clamp so the inside would have been exposed to moisture ingress.

http://ixian.ca/pics7/clamp2.jpg

MuellerNick
05-10-2010, 07:26 AM
the cracked area will be discoloured or rusted.

a) I see 3 redish areas in the picture
b) The broken clamp in the second picture is the lower one from the first picture. It seems to have been painted. The paint didn't crack


Nick

Evan
05-10-2010, 07:43 AM
I have seen a lot of broken parts over the years Nick. If there is a pre existing crack it is easy to tell. That paint isn't the least bit elastic. The other clamp is exactly the same. As for the reddish area, either that is primer or the paint DID crack so the rest of the cracked area should also be discoloured.

However, I knew you would have some sort of objection so I am going to try to do a relative energy impact test later today. I will compare the seasoned clamps to a similar one that has led a sheltered life.

JoeFin
05-10-2010, 08:28 AM
Don't know how well this relates to "seasoned cast iron"

Used to be an old engine builder's trick to take a stripped engine block and bury it in the ground for a year. Then to dig it up and perform a complete rebuild on the engine. Theory being 2 fold. All the stresses would be relieved from the engine block and the molecules would "line up" with the earth's poles making for a stronger bond

J Tiers
05-10-2010, 08:30 AM
I have had cheap C-clamps crack in exactly the same way, ones which had never been out in the weather (at least while I had them, and they were "new").

The typical breakage was EXACTLY where yours broke, and EXACTLY the same sort of crack. it is a high stress area

Evidently there is no need for weathering to produce cracking.

If one were to ask me, I would have a very good look at the area that appears to be rusted on the "crossbar of theT". if it IS rusted, the crack did likely appear while out weathering.... Whether they were the result of weathering, or the result of the various temp and humidity changes, there is no real way to tell.

They might have seasoning cracks. Or they might have "had cracks", from the casting process, or whatever.

My suspicion is that those cheap clamps , if they ARE cast iron, as not MALLEABLE cast iron, as they should be, but were either not processed, or were only poorly processed through the heat treatment that makes malleable iron.

Tony Ennis
05-10-2010, 08:38 AM
Does the wood fence have indentations from the clamps? If it swelled enough to damage the clamp, I'd expect to see at least a little embossing on the fence.

I wanna see wood split rock. That would be interesting.

Evan
05-10-2010, 08:38 AM
Jerry,

As I said, I have at least 50 of these clamps and these are the only two that have ever broken. They have been selling the same clamps for a long time, maybe 20 years. Normally they will take whatever abuse I give them.

Another test will be to cut one cleanly and polish it up. Then acid etch to see what the crystal structure lookes like and compare it with an unweathered specimen. I now have a pair of cast iron samples that have a well documented interval outdoors. All I need to do is download the weather records to establish the seasoning history.

Mcgyver
05-10-2010, 08:39 AM
I have seen a lot of broken parts over the years Nick. If there is a pre existing crack it is easy to tell.

is that such a black and white thing? would it not depend on the size of the crack? what if the crack was a thou or a tenth....you wouldn't see it but it would still provide the stress raiser that would produce failure when the force got to a certain level

Evan
05-10-2010, 08:49 AM
Does the wood fence have indentations from the clamps? If it swelled enough to damage the clamp, I'd expect to see at least a little embossing on the fence.

I wanna see wood split rock. That would be interesting.


No dents because It had a small spacer to protect the finish. Rock has very poor tensile properties. It is generally easy to break, same as concrete if you can apply tensile forces.

If the crack is large enough to admit air it will discolour. That includes iron and aluminum, zinc, magnesium, and the various alloys of same. It is a very standard diagnostic to determine failure modes with aircraft aluminum.

BTW, I looked up the tensile strength of granite. It is surprisingly low, ranging from only 500 to 1000 psi. Grey cast iron is a minimum of 20,000 psi.

aboard_epsilon
05-10-2010, 09:07 AM
now lets see

1. they have been out in the weather for a long time.
2. they are not rusty .yet they are unpainted . ????

conclusion ..you you electro derusted them ..so now they have this enbrittlement.

all the best.markj

MuellerNick
05-10-2010, 09:08 AM
As for the reddish area, either that is primer or the paint DID crack so the rest of the cracked area should also be discoloured.


So if it is primer, there was already a crack. Even before they painted it. Or how does primer get into the iron?
And if it is rust and the paint cracked (paint still is by maginitues more elastic than CI) the crack in the iron makes a perfect stress kerf.
From the picture, the rusty part of the crack is smooth, so it is a crack that took longer (fatigue crack), the rest is rough, a force crack.


Nick

JoeBean
05-10-2010, 10:45 AM
I actually have a Mastercraft 6" C clamp lying around in one of my tool boxes that was left outdoors on the ground for about 2-3 years, connected to an engine block (long story). Anyway, when I finally went to dump the block I found the C clamp and retrieved it. It's still as strong as ever. In fact I had to remove the handle after I bent it around the screw trying to clamp something that it really wasn't big enough for. Since then I've used it a dozen or so times with a cheater bar, no breaks.

Mine is covered in surface rust btw. That may be due to various chemicals that got on it before it went out, or some abrasion from this-or-that, or maybe even coming in contact with a torch once or twice, as (if you can't tell already) I didn't take it easy on this poor tool.

I know CT's quality has been atrocious for the last few years. Maybe if these clamps are 'newer' the metal's makeup is different. Or maybe they just ship sh*tty tools out west and quality tools east :)

Evan
05-10-2010, 10:46 AM
Primer, thick enough to make for a smooth finish, is cheaper than polishing.

If it was just one clamp I would agree. But it is two clamps from entirely different batches and molds separated by years in time. It's too much of a coincidence to pass it off as a manufacturing defect of some sort.

I will be doing some more testing now that I have some verified seasoned samples to play with. Crystallographic analysis will be interesting. It may take a while as this time of year I have my hands full with outside chores but this is a good oppourtunity to learn something about materials, something I won't pass up.

Tony Ennis
05-10-2010, 11:03 AM
It's too much of a coincidence to pass it off as a manufacturing defect of some sort.

Yep. That was my thought. Is it possible they were damaged on a previous project?

metalmagpie
05-10-2010, 11:22 AM
Evan, you draw WAY too much out of some dimestore homeowner CSOs (clamp shaped objects) failing. Buy better clamps.

Your theories on metallurgy may or may not be valid - I don't consider myself an authority. But what happened to your clamps can not be globalized to cover all cast iron manufacturing.

metalmagpie

dian
05-10-2010, 11:43 AM
so did napoleon loose the war in russia because his cannons cracked? on second thought, they may still have been cast out of bronze at that time. but there are millions of cast iron parts doing service exposed to outdoor conditions. what about engine blocks/cylinder heads? or would it depend on the type of cast iron used?

dexter
05-10-2010, 12:14 PM
I only owned one of those Mastercraft clamps and it broke in the very same way under moderate force (I welded it back together and then lost it). I think the obvious answer is the stress inparted by the expansion of the wood caused a crack. It doesn't make any difference weather the wood is treated or not. it will move. That is why allowances must be made for expansion for finished interior wood projects.

When you hear hoof beats, think horses, not zebras.

strokersix
05-10-2010, 12:39 PM
I'll second the comment above regarding fatigue. Wood swelling with moisture and temperature changes will be cyclical. Add in the continuous tensile stress in a corrosive environment and you have favorable crack propagation conditions.

A low grade material clamp likely can compromise on fatigue properties based on expected usage. I think this is the explanation.

I had to take metallurgy twice. Got a "B" the second time but not sure I learned any more so take it for what it's worth.

interiorpainter
05-10-2010, 12:50 PM
From looking at the picture it apears that these clamps are not exact lookalikes but yet they broke at the same place, that is at the point of the biggest tensilestress.
Crudely said those are 3 beams welded together. Lenght is the biggest factor (3th power) in making it brake somehow. The biggest stress is near a corner.
I would guess cold weather in combination to swelling of the wood caused it.
A bit like the comination of tork and tensile stress make a lot of difference according to Huber and Henke.
Yes Strokersix, thats what i forgot. Ductile tensile stress is much higher than creaping tensilestress. Much like plastics.
But ahum then the stress would releave itselve and it did.

MuellerNick
05-10-2010, 12:50 PM
I wanna see wood split rock. That would be interesting.

Here is the modern version, based on the same principle: Video (http://www.youtube.com/watch?v=Qt3TzjTwhM0)

Nick

lynnl
05-10-2010, 12:51 PM
...
When you hear hoof beats, think horses, not zebras.

:D I like that!
Pretty much sums up Occam's Razor.

I too am inclined to believe the varying stresses imposed by the swelling/shrinking wood, during that period, when the cast iron clamp molecules were undergoing the seasoning realignment was detrimental to the final alignment.

And even though we tend to think of CI as been brittle/rigid/non-flexible, I'm sure that's not totally and absolutely true, but only in comparison to steel and other metals. So over an extended period of being under the stress of clamping, the alternating swell/shrink cycle would tend to fatigue the metal.

I also had a 6" C clamp break in the same way a few years back, but I was really cranking down on it ...tho not with a cheater. At the time I thought it was just a weak clamp. But now I think perhaps the fact that I store my C clamps clamped onto 2X4 shelf braces might have played a role in its failure.

Boucher
05-10-2010, 01:33 PM
Does the wood fence have indentations from the clamps? If it swelled enough to damage the clamp, I'd expect to see at least a little embossing on the fence.

I wanna see wood split rock. That would be interesting.
The early stone masons would drill a hole in rock. Pee in the hole tamp that with cotton. The Osmotic pressure differential would crack the rock.
Didn't mean to hijack this thread.

aboard_epsilon
05-10-2010, 03:01 PM
Blinking good primer if its been out there two years without rusting through the primer ..its aint that thick either ..or the lettering would be obscured a bit .

SORRY...still looks like youve had them in the electro bath to me .

all the best.markj

MuellerNick
05-10-2010, 03:52 PM
Evan could make a detailed picture of the questionable area. That would end any wild guessings (and start new ones ;) ).


Nick

MCS
05-10-2010, 04:04 PM
I would'nt call this a proof of any principle.

This is just a case of uncontrolled stress conditions, contrary to stress relief conditions, where both subjects fail at the same (predictable) place.

This test is not going to win the Noble price, although the topic will probably linger on for 50 pages.

JanvanSaane
05-10-2010, 04:14 PM
And remember free advice is worth what you pay for it. I would guess that is where most of the stress is and a small swelling of the wood would amplify where the most stress is. I have never heard of burying a race car engine block. But, we took a die grinder and sanding emery bits and cleaned up our race car blocks and epoxy coated the inside. The theory was oil got into the small imperfections when hot, then when the engine cooled this oil caused a hyd lock that actually made the cracks go deeper. It also helped the oil drain into the oil pan better. I don't know if it actually helped with cracking blocks or not but those polished rods sticking out of that nice polished block sure looked pretty. Jan

Alistair Hosie
05-10-2010, 04:17 PM
Evan there are cast iron clamps, then there are cast iron clamps.I have used them cheapotasic clamps the bend warp and fracture easy as lead.If you buy quality clamps and this will not happen.These clamps are not a good well known brand and even look like chinese junk or Schrott eisen as the Germans say.I bought copied bessey clamps and the failed first time I used them. so I feel with respect thats where your problem lies, as not all cast iron is the same quality .Alistair

Evan
05-10-2010, 04:22 PM
If you buy quality clamps and this will not happen.

It doesn't happen with exception of these two clamps. How many times do I have to say this?


I will take some micrographs as well as sacrifice an identical clamp that has never been left outside. I want to see how much it takes to actually break one of these clamps so I will see if I can break one by clamping it on the same piece of pine to find out just how much deformation it will produce before it breaks. These clamps weren't clamped that hard on the wood. I can't quantify it for you but for myself I can say categorically that expansion and contraction of the wood is not the culprit.

When I used the clamps to clamp parts for welding after removing them from the rail they were not already cracked. If they had been they would not have produced any significant clamping force. Instead, they acted normally up to a certain pressure and then suddenly cracked. That is why both did not fall apart because it was very clear that they had suddenly broken so I stopped twisting.

The force required to embed a 44 calibre ball 1/2 diameter in jack pine side grain is only around 390 lbs compared to thousands of pounds for many hardwoods. 390 lbs is nothing to a 3" C clamp. These are decent clamps. As I have said, these are the only ones that have ever failed and they are also the only ones that have been left outside while under clamping stress.

MuellerNick
05-10-2010, 04:35 PM
but for myself I can say categorically that expansion and contraction of the wood is not the culprit.

Why didn't you say in your first posting, that any discussion or contradiction is useless?


When I used the clamps to clamp parts for welding after removing them from the rail they were not already cracked.

They were cracked, but not fully. Or did I miss your posting, where you stated that you inspected them before clamping your weldments?


Useless discussion ...

Nick

Evan
05-10-2010, 04:45 PM
Perhaps you do not have a feel for the metal you work with but I do from many years of experience. I cannot for sure say why they cracked at this time but I can say what was not the cause. I can also say that they were not already failed when I used them again. That isn't the same as having my mind already made up as to the cause. It is made up as to what is not the cause.

The Artful Bodger
05-10-2010, 04:58 PM
I think they cracked when you dropped them on your really, really hard concrete floor.

interiorpainter
05-10-2010, 05:13 PM
Put a hydrolic jack between the c clamp and i will tell you where it is going to break!
Seasoning should not be biased to go to the same place over again.
Does not make much difference what type of material.
If this thing was made of sheet metal is warps under pressure. Theres your twist and pull and 60% increase in sigma.

beanbag
05-10-2010, 05:21 PM
Evan,

Your analysis is appreciated.

Will your acid etch test tell the difference between your theory of propagating micro-cracks vs micro-cracks due to fatigue cycling?

Punkinhead
05-10-2010, 05:25 PM
Breaking a 3rd clamp isn't going to tell you much given that you know virtually nothing about it's origins. Were they made on the same day or even in the same factory? Maybe some were made on the day that factory was melting down Bridgeports and others on the day they got a load of AMC Pacer engine blocks from Uncle Chu's scrap yard. So today you clamp one down on a piece of pine. Maybe it breaks, maybe it doesn't. Either way, that sample size of 1 hasn't given you anything useful and you certainly haven't gotten any closer to proving a theory about aging castings.

I personally wouldn't waste an otherwise serviceable clamp.

PeteM
05-10-2010, 06:52 PM
The three colored areas in the section also suggest stress corrosion -- slight crack initiation due to both stress (original clamping force plus the variously argued wood swelling and freezing trapped water options) PLUS corrosion.

Given any significant crack initiation, the clamp would show some strength and then sudden failure. Point being, pending Evan's microphotos, it looks to me that the evidence for initial stress/corrosion is stronger than evenly distributed microcracking from the clamps freezing their collective atoms off in Evan's variable climate.

Evan
05-10-2010, 07:19 PM
Will your acid etch test tell the difference between your theory of propagating micro-cracks vs micro-cracks due to fatigue cycling?


Good question. I plan to section the clamps very close to the point of failure and well away from it. I will do the same with an unbroken (but beat up) clamp. If there is a significant change in the structure due to thermal cycling I would expect it to be visible throughout the material of the seasoned clamps. It should also show some differences compared to the unseasoned clamp. I have no idea how much difference it takes to be visible so the test will only be conclusive if there is an easily observable and consistent change in structure. If there appears to be a major change then it is worth exploring further by examining yet another unseasoned clamp.

I do have a decent dual trace oscilloscope so another approach might be to measure the speed of sound in the material, or even the amount of dispersion in a conducted square wave. Another possibility is to try to measure the damping factor of the material. This would fit in with the claimed improvements in properties if the damping factor is improved since that would be expected if the crystal matrix is filled with tiny cracks.

Right now I am very busy so I probably won't be reporting any results in this thread. When I do some tests I will present the results regardless of the outcome, conclusive or not. I am going to do the simple wind it till it squeals test this evening. An uncalibrated relative energy Charpy impact test should also be fairly easy to set up.

jdunmyer
05-10-2010, 08:11 PM
Evan,
If I read this correctly, you're surmising that the heat/cold cycling of the clamp *while it was under a strain from clamping* caused some sort of micro-fracturing that resulted in later breakage. My question is, why wouldn't other cast iron parts such as engine blocks fail similarly? At least certain parts, where things are bolted together, are under some strain, yet they don't seem to break at random.

I'm also thinking that your clamps would not have failed had they been left outside, but not under strain, is that what you think?

FWIW: I worked at Toledo Scale Company in the mid-to-late 1960s and well remember stacks of cast iron scale levers sitting outside to weather before machining. Dunno how long they sat, but I believe it was at least over one entire Winter.

I'm much looking forward to further discussion and your experiments.

Evan
05-10-2010, 08:30 PM
My question is, why wouldn't other cast iron parts such as engine blocks fail similarly? At least certain parts, where things are bolted together, are under some strain, yet they don't seem to break at random.



I don't think you will find any instance of cast iron in an engine being placed under tensile strain. That isn't sound engineering practice. A C clamp places the inside of the lower corner under pretty severe tensile strain and that is the major difference. The rest of the clamp is also under tensile strain on the inner fibres but the corner is a stress concentration. Cast iron is much stronger in compression than it is in tension which sets it apart from most metals and alloys.

J Tiers
05-10-2010, 08:41 PM
Evan:

It is entirely possible that a weathering process initiated cracks..... I'm not actually discounting that at all.

But the usual way to "season" CI is to allow it to season outside with essentially no stresses

Clamps SHOULD be made with malleable iron. I believe the "seasoning" is basically never done with MALLEABLE CI, as that has been through a several day heat treatment that would be expected to substantially relieve the stresses.

Potentially, if those clamps were "leakers" and didn't get the heat treatment, they could have seasoned as you suggest.

An alternate suggestion is that the clamps were in fact malleable, fairly stress-free iron, and that they suffered stress corrosion cracking, as evidenced by the rusty edge (if it IS a rusty edge, which only you can tell for sure).

When you used them the already initiated crack (which is just where it would be expected in one of the highest stress areas), simply propagated across.

I really can't tell which. I suggest the latter because as I understand it, the heat treatment for malleable iron should not leave a highly internally stressed material. And those should have been malleable.

Why just those two? Well, how many others have had a similar treatment?

Robin R
05-10-2010, 08:51 PM
I think it would be safe to say that the clamps failed at their weakest point, so what ever other factors were at work, you could expect the failure point to be the same.
It would be easy to test the wood expansion theory, use another of the same clamps done up good and tight on a dry piece of the same wood, then throw it in a bucket of water for a couple of days. If it doesn't fail under those conditions, then that wouldn't have been the cause and my guess is that it wouldn't fail.
Evan could test his theory fairly reliably by buying say 3 more of the same clamps and clamp each in turn, at what would seem like a reasonable maximum pressure. After this set one aside, then clamp the other 2 onto blocks of something with the same rate of expansion and put them outside for a couple of years. After this treatment, test the 2 that had been outside and the one that hadn't in a similar way to the 2 that are the subject of this thread. If the 2 that have been left out fail with significantly less force than the control clamp, it would point to Evans theory as having some value.

Evan
05-10-2010, 08:56 PM
I should point out that this isn't my theory. It is a common explanation of why seasoning makes a difference. There is a measurable loss in tensile strength in samples that have been aged this way.

Evan
05-10-2010, 09:03 PM
Seasoning makes no sense with malleable cast iron. It is made by chilling the castings when they are poured which causes the formation of extremely hard white cast iron instead of grey cast iron. Then it is heat treated by raising it to the solution temperature and very slowly cooled which produces malleable cast iron. The size of malleable cast iron parts is limited by the rate at which a casting may be cooled to form white iron.

Robin R
05-10-2010, 09:11 PM
My apologies, let me revise that to, the theory presented by Evan.

J Tiers
05-10-2010, 09:26 PM
Seasoning makes no sense with malleable cast iron. It is made by chilling the castings when they are poured which causes the formation of extremely hard white cast iron instead of grey cast iron. Then it is heat treated by raising it to the solution temperature and very slowly cooled which produces malleable cast iron. The size of malleable cast iron parts is limited by the rate at which a casting may be cooled to form white iron.

precisely......... And those clamps ought to BE malleable iron...... I have lots of C-clamps, most of which are obviously cast.

Some have bent, which would not happen if they were untreated CI.... They HAVE to be malleable.

interiorpainter
05-11-2010, 03:28 AM
The sleeve (cylinder) of an Alfa engine is made of cast iron.
Hoop stress -> tensile stress.
But either way you are right Evan, Alfa is not called good engineering:D

jihe
05-11-2010, 04:04 AM
The force required to embed a 44 calibre ball 1/2 diameter in jack pine side grain is only around 390 lbs compared to thousands of pounds for many hardwoods.Even when frozen?

Black_Moons
05-11-2010, 05:03 AM
I think they cracked when you dropped them on your really, really hard concrete floor.

I vote for this awnser. That or some kinda intergrain corrosion. But thats just me clutching at straws.

Evan
05-11-2010, 05:14 AM
The clamps were applied in summer. Freezing dry wood causes it to contract slightly, not expand. The humidity here is very low all year long. Inside humidity never goes above 50% and when it is very cold the outside humidity can be as low as 20% or even lower. We only have an average of 15 inches rain per year (including snow).

Evan
05-11-2010, 05:19 AM
I have polished and etched a sample from one of the broken clamps. Under circularly polarized light it shows a very interesting and non uniform structure. However, without a reference to some sort of control that doesn't mean much so I will put up some pictures perhaps this evening when I have a chance to do a few more tests. What appeared to be either rust or primer seems to be neither. More later.

Punkinhead
05-11-2010, 05:44 AM
The clamps were applied in summer. Freezing dry wood causes it to contract slightly, not expand. The humidity here is very low all year long. Inside humidity never goes above 50% and when it is very cold the outside humidity can be as low as 20% or even lower. We only have an average of 15 inches rain per year (including snow).You said the clamp was outside, not inside. I couldn't find yearly relative humidity for Williams Lake, but I checked all the major cities in BC and the outside relative humidity (where your clamp was) varies from 20% to 100%. Here's Kamloops,BC:

http://kamloops.weatherstats.ca/relative_humidity-1year-500.png

You can go here and select BC, then a city, then "Relative Humidity" to see yearly trends: http://www.weatherstats.ca/

But really, whether swelling wood initiated a crack in your clamps isn't really relevant to the issue of whether microcracks due to aging took place. All we know is that you cranked down on a couple cheap clamps of unknown material, quality, and origin and they broke. That's not proof of any theory, whether it be aging, intermolecular breakdown due to moon beams, or that they were beaten on by a sasquatch.

Evan
05-11-2010, 06:57 AM
All we know is that you cranked down on a couple cheap clamps of unknown material, quality, and origin and they broke. That's not proof of any theory, whether it be aging, intermolecular breakdown due to moon beams, or that they were beaten on by a sasquatch.



Yes it is. The question is determining what caused the breakage. It's too cold here for Sasquatchii to survive so that's out. The energy density of a moonbeam is below the juxtaposition Heisenberg constant minimum threshold so that's out too.

As for aging, unlike wine most metals deteriorate with age in one way or several, so that is a possibility. It is a matter of determining if possible what role the conditions of aging might play. That is a very common question that often requires answering in materials science.

BTW, you need to learn the difference between relative humidity and specific humidity. It is a very big difference.

strokersix
05-11-2010, 07:24 AM
Or also known as stress corrosion cracking:

http://corrosion-doctors.org/Forms-SCC/scc.htm

I still think this explanation makes sense. Continous strain, cyclic or not, on a brittle material in an outdoor environment.

J Tiers
05-11-2010, 08:19 AM
Or also known as stress corrosion cracking:

http://corrosion-doctors.org/Forms-SCC/scc.htm

I still think this explanation makes sense. Continous strain, cyclic or not, on a brittle material in an outdoor environment.


Where do you get the "brittle material"? I see NO "brittle material".

strokersix
05-11-2010, 08:35 AM
The fracture does not appear to show much elongation at all. Therefore I think it can be characterized as a brittle failure. This type of sudden failure has been seen in fasteners and is sometimes traced back to hydrogen embrittlement. I think this possibility was mentioned above.

Microcracks under strain have high energy at the crack tip. Continuous strain in a corrosive environment will cause the crack to grow. Cyclic loading will also cause the crack to grow. Crack growth leads to sudden, brittle failure.

A ductile failure should show elongation or necking.

A higher grade clamp material would have better fatigue properties meaning resistance to crack growth. Low grade clamps probably compromise on material, heat treat, or other specs considering their intended low cycle loading.

But, as I mentioned earlier, I'm no metallurgist.

strokersix
05-11-2010, 08:42 AM
http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/exper/bailey/www/bailey.html

JCHannum
05-11-2010, 09:02 AM
The best c-clamps are of forged steel. Garden variety inexpensive clamps are of malleable iron. The cheapest clamps are made of cast iron. Add the known variability and lack of quality control in the batching and pouring of Chicom cast iron and you end up with a c-clamp that will fail. It will fail at the point of highest concentration of stresses. This is the only "proof" these clamps provide.

The only way to "prove" that any "seasoning" these clamps might have been exposed to would be to run a closely monitored control which "proves" that another set of identical clamps held under the same tension with no temperature cycles will retain their original, very questionable, strength and will not fail.

chrisfournier
05-11-2010, 10:04 AM
First,and not to alienate all the CTC fans out there, those clamps are not a quality item when it comes to C clamps. The square casting with pretty much 90 "bends" concentrates forces spot on the failures. I am not arguing that Evan's other clamps haven't failed but I believe that where they put under strain for two years, they too would fail when they were cranked up anew. I really don't think that the temperature got to the metal properties at all. Weather may have caused some corrosion around micro cracks.

Look at good quality C clamps and you'll notice that they're "rounder" than the clamps in question or if they're "square" like these they're likely made of steel. These clamps are really bottom of the barrel and their failure is no surprise to me. My wife was good enough to buy me a Mastercraft C clamp assortment once (I returned the favour with Pantsaver car mats on her birthday) and of the 6 clamps, two broke. I've never broken a Record, Jorgensen or Bessey clamp - ever.

Second, the seasonal movement of Evan's pine wooden rail had nothing to really add to this failure. For all those talking about the swelling of wood, there are formulas that allow you to claculate the dimnesional change of various wood species. These formulas take into account the starting moisture content of the wood and the target moisture content of the wood. Evan's pine likely only ranged from a MC of 4% in the dry summer to 17% in the wet fall spring. The dimensional change across the small cross section of Evan's railing given the above estimated MCs would have been miniscule.

ADGO_Racing
05-11-2010, 12:39 PM
Yes it is. The question is determining what caused the breakage. It's too cold here for Sasquatchii to survive so that's out.


How do you know it is too cold for Sasquatch to survive??? Maybe he is migratory, maybe he has an advanced heat source, maybe he hibernates in winter like a bear. As far as I know there are still many unanswered questions surrounding Sasquatch.:rolleyes:

Tony Ennis
05-11-2010, 01:54 PM
It's too cold here for Sasquatchii to survive so that's out.

African or European?

lynnl
05-11-2010, 02:17 PM
BTW, you need to learn the difference between relative humidity and specific humidity. It is a very big difference.

Who said anything about specific humidity? ...and what relevance does that have here anyway?

ADGO_Racing
05-11-2010, 02:50 PM
African or European?


Are the African ones called Sasquatch too, or do they have a different name, maybe a different species or subset of the same creature???

Although the African Sasquatches could possibly have advanced methods of cooling.

Of course, we also forgot about possible Alien (ET) abuse. I could see a possibility that a UFO landed out there in BC, needing some repairs. Scrounging for tools, found Evans C-Clamps, maybe over tightened them a little...
Not being familiar with the English language, didn't leave a note, and not having a currency they could exchange here on earth, just put them back where they found them and left.:D

gaston
05-11-2010, 03:57 PM
Aint it great that we can fill 8 pages of forum over a broken clamp, given all that is wrong with the world , and this all I have to do. I love it

ADGO_Racing
05-11-2010, 04:21 PM
Gaston:

There wouldn't happen to be a Dr. in front of that?

MuellerNick
05-11-2010, 04:34 PM
fill 8 pages of forum over a broken clamp

I only do have these Besseys (http://www.bessey.de/catalogue/catalogue.do?id=189&favOid=000000010003177f00060023&act=showBookmark). They never break, they never bend, they never fail. I love them!


Nick

John Stevenson
05-11-2010, 05:19 PM
I do have a decent dual trace oscilloscope so another approach might be to measure the speed of sound in the material, or even the amount of dispersion in a conducted square wave.
For fooks sake Evan it's only a $5 G clamp, not a treatise on
BioUnidirectionalLooseLinearitySafeHighIntegritySy stem
or B.U.L.L.S.H.I.T for short.

.

John Stevenson
05-11-2010, 05:22 PM
I only do have these Besseys (http://www.bessey.de/catalogue/catalogue.do?id=189&favOid=000000010003177f00060023&act=showBookmark). They never break, they never bend, they never fail. I love them!


Nick

Next time try these

http://www.lawson-his.co.uk/images/Carver/rack.jpg

.

Timleech
05-11-2010, 05:28 PM
I only do have these Besseys (http://www.bessey.de/catalogue/catalogue.do?id=189&favOid=000000010003177f00060023&act=showBookmark). They never break, they never bend, they never fail. I love them!


Nick

I had a couple of those for a while, until some toerag took a fancy to them. They're very good, but the Carver clamps which John shows are in another league - in terms of strength, durability, weight and price!

Tim

ADGO_Racing
05-11-2010, 05:51 PM
I see Enco is having a sale....Maybe Evan can get some good clamps cheap...:rolleyes:

JCHannum
05-11-2010, 08:41 PM
For fooks sake Evan it's only a $5 G clamp,
.

Actually, they are more like 2 for $3.00 Cdn. Two aisles over from the copper plated speaker cable.

oldtiffie
05-11-2010, 08:44 PM
Are/were they "Starrett" micrometers?

Evan
05-11-2010, 08:56 PM
I am curious. How much does a high quality cast steel 3" C clamp cost?

How much does it improve the finish on the work?

Does it improve the welding and is it immune to welding damage?

How often does it need sharpening?

In short, is it really worth the extra money in the same way that high quality cutters and measuring tools can be?

Thes clamps I buy are not bottom line. They give good service and are priced low enough that I don't mind if I have to use them in a way that might cause damage, when welding for instance. I do have some very good clamps that I bought many years ago and as far as I can tell they don't generate any more clamping force for the same size of clamp.

This isn't about clamps though. It seems that the usual suspects have forgotten that.

Rich Carlstedt
05-11-2010, 09:15 PM
Between Sir John, and JC, I am rolling on the floor laughing .
There has been so much conjecture here, I would like to throw this out.
I have worked with lots of CI in my life, and even poured it.
CI has tremendous compression strength , but almost nil in tensile
Temperature extremes stabilize CI, so the colder you can get it, the more the molecules lock in together which PREVENTS Subsequent WARPING and dimensional changes. Period !

now an analysis of the clamps.

All bets are off guys !
The clamps were exposed to welding heats, and we have no way of knowing to what extent. Look at the bottoms of those clamps. They are brown black, just likee my welding clamps. That means we have no idea of what heat treatment the clamps have seen in " real" life
When Evan clamped the wood, he probably had a light load on it, so the real test came when he brought them indoors and clamped on a welding project.

The cross-section shows two things, almost complete Tensile failure due to load. The even crystal structure of the upper right hand view ( the lower left "hump" and "rust" mark are from Evans final break..lets stay on the initial failure point) shows no adverse cross-sectionss. HOWEVER, there is a thin shiney line going around the cross-section on the outside and it goes in on both sides, about half way to the "hump" ( This is on the indside of the clamp cross-section !) This crack is almost "Round" in layout and you can see it has gone into the web section. It looks like a snap ring in shape !
This shows a fracture or crack around the part before total failure. Shiney marks are from the cracks rubbing on each other before failure. No shine would mean utter and total tensile failure
I would suggest that when used for welding, the welded material expanded tremendousely and cracked the clamps with that hairline mark.
The paint prevented rusting.
The wood did nothing, OR it pushed the clamp short of its tensile limit.
Evan probably did not tighten for fear of marking the wood
Normally you experience 'Yield" in metals, when the tensile limit is reached, as the ductility of the metal allows it to reform, or "Yield".
Cast Iron has no yield. when you reach it, it breaks
Rich




This turns out to be pretty easy to settle. I broke the piece off completely so I could inspect it for evidence that the crack was pre existing. If there was any trace of a crack while the part was out in the weather the cracked area will be discoloured or rusted. There is no evidence of that. The cracked area is very fresh and all looks the same. If it had cracked from extreme pressure it would have started at the inside of the clamp so the inside would have been exposed to moisture ingress.

http://ixian.ca/pics7/clamp2.jpg

Doc Nickel
05-11-2010, 09:25 PM
I have what might be a useful update for this little problem...

I was just as the local "flea market"/secondhand type store- the kind that not only sells used 'garage sale' type stuff, but also a liberal helping of "new", albeit cheap import, stuff. The usual bins full of crap folding knives, no-name wrench sets, that sort of thing.

Anyway, they have a bin the size of a washtub full of "new" C-clamps very much like the upper of Evan's two in the first pic-though like Evan's, they all clearly came out of a couple of different molds.

Unfortunately I didn't have a camera with me, but two of the five I picked up and looked at, had a faint but definite hairline crack in almost the exact same location as Evan's two examples- the inside edge of the first bend.

And since these were new- unless the factory had a worker clamp them really firmly to something in order to "test" them :D - it looks like the failure may be more due to shoddy manufacturing rather than weathering, wood swelling or seasoning.

I suspect it may have to do with the design of the mold, causing the arm to be stressed as the metal contracts.

I'll try to go back with a camera in the next few days, but the proprietor might not put up with that. :) He knows a lot of it is junk-barrel import crap, and somebody with a fancy camera might suggest "investigative reporter" to him... :D

Doc.

S_J_H
05-11-2010, 09:26 PM
I do have a decent dual trace oscilloscope so another approach might be to measure the speed of sound in the material, or even the amount of dispersion in a conducted square wave. Another possibility is to try to measure the damping factor of the material. This would fit in with the claimed improvements in properties if the damping factor is improved since that would be expected if the crystal matrix is filled with tiny cracks.


Please send me some of whatever drug you are on!!:D

Steve

Evan
05-11-2010, 09:32 PM
I just finished my supper and later will do some more analyzing of the specimens. The reddish zone on that broken part is not rust and it isn't primer either. It is metal but I don't know for sure what. I will post pictures later but it may be quite late. The weather is good now and the days are long so I am very busy with other things.

The broken clamps never made it to being exposed to welding heat (again). They failed before I started welding. It isn't likely that they have been exposed to high enough temperatures at any time to significantly alter the properties. The paint would be damaged in the HAZ and it isn't where the clamp broke.

Evan
05-11-2010, 09:37 PM
Please send me some of whatever drug you are on!!

B. V. Kovacs, "On the Interaction of Acoustic Waves with SG Iron Castings." Transactions, American Foundrymen's Society, Vol. 83, 1975, pp. 497-502.

B. V. Kovacs, "Quality Control and Assurance by Sonic Resonance in Ductile Iron Castings," Transactions, American Foundrymen's Society, Vol. 85, 1977, pp. 499-508.


K. B. Palmer, "The mechanical and physical properties of engineering grades of cast iron at subzero temperatures," British Cast Iron Research Association, Oct., 1988.

http://ixian.ca/pics7/ductilebrittleiron.jpg

Evan
05-11-2010, 09:56 PM
Doc, I have been using those clamps for years. The cracking is a recent development, not an original defect.

http://metalshopborealis.ca/pics2/shapsup2.jpg

JCHannum
05-11-2010, 10:07 PM
You can analyze the clamps until Hell freezes over, but you will never prove anything more than that they are broken. Most of us have arrived at that conclusion independently.

You cannot prove by any means that the failure has anything remotely to do with their "seasoning" for however many years until you can prove that similarly stressed clamps that have not been exposed to the temperature cycling will not fail.

ADGO_Racing
05-11-2010, 10:22 PM
I agree with Evan....His clamps do not get hot enough to significantly change their properties...

It is plainly evident in the photo, that he uses an advanced welding process which does not generate much if any heat. Otherwise that plastic clamp would MELT!:eek:

Which makes me wonder....How well does a plastic clamp weather? Obviously they don't rust, do they?

J Tiers
05-11-2010, 10:33 PM
I think you guys are dumping on Evan without cause here.......

I do not agree with his conclusions, at least as I understand what has been stated so far, but I have NO problem with someone being curious enough to look at it, and ingenious enough to find ways to examine it.

My own opinion here is that it's his time, his equipment, and if he wants to study them it's his business... And if he wants to report it here, I'll read it.... I may offer an alternate opinion, based on the info given, but I am N.O.T. going to dump on the idea of investigating it, reporting it, discussing it or whatever......

It IS after all machining-related, in that it is a properties of materials issue..... Fair game, in my book.

Some folks seem to be getting all "annealed" here, and may need to be quenched.......

Personally, I believe the material is, or should have been, malleable iron, and so it should NOT be subject to "seasoning" issues. I very much suspect a different cause, possibly stress corrosion cracking, or whatever....... It likely needs only a small crack to break them with the stress concentration at the 'corner". Maybe the cracks were started some time ago.

But, If Evan can find a different plausible explanation, I'm interested enough to read about it an maybe learn something.

gmatov
05-11-2010, 10:39 PM
3 dollar clamps which no one's life depends on do not merit a second page of argument.

Cast iron can be bent to a degree, as in an old issue of Fine Woodworking and witnessed being done by the mold master, or whatever, of the OLD Delta Woodworking Machinery Company.

All their castings were stored out in the weather to season. Iron clad rule, to them.

Bending, he would force such as a long bed jointer table just to the "there" point. Further force would cause it to crack or snap.

You can get more force from a "C" clamp if it is fitted with a standard thread than if fitted with an Acme or square thread of coarser pitch. Also why you can make a "nut cracker" with a fine thread, but not a coarse thread.

The inclined plane.

Cheers,

George

Sorry if this rains on any parades.

Rich Carlstedt
05-11-2010, 10:58 PM
I think some mis-understood the welding issue.
You have TWO variables.
First, is that the Cast Iron may have gotten too hot and anealled or chilled or whatever.. that is NOT the concern I have.
The darkening confirms that this has occured !

When you clamp two pieces of steel together, and tighten the clamp very tight, The act of welding the steel causes the steel to expand tremendousely
which in turn overloads the clamp from its original tightening and places unwanted stress on the clamp.

Just look at some welders sets of "C" clamps to confirm this phenomina.
Thats why many good welders use " Boiler Clamps" and not "C" clamps

Rich

J Tiers
05-11-2010, 11:22 PM
I think some mis-understood the welding issue.
You have TWO variables.
First, is that the Cast Iron may have gotten too hot and anealled or chilled or whatever.. that is NOT the concern I have.
The darkening confirms that this has occured !

When you clamp two pieces of steel together, and tighten the clamp very tight, The act of welding the steel causes the steel to expand tremendousely
which in turn overloads the clamp from its original tightening and places unwanted stress on the clamp.

Just look at some welders sets of "C" clamps to confirm this phenomina.
Thats why many good welders use " Boiler Clamps" and not "C" clamps

Rich

I suspect that the darkening is NOT from them getting hot enough to change properties...... Evan might possibly have noticed if they were bright orange......... and lesser "black" heat wouldn't bother them.

A year or two of weathering on what was originally dark gray paint is sufficient to explain darkening...... that and some just plain grunge...

Cast iron, or cast steel, both need some heat treatment to make them sufficiently ductile to stand up as clamps.... despite what the chinese may think.

I have C-clamps that have bent significantly. The expansion of welded steel would not break the clamp if it is made as it should be.

That may be too much to ask..... I had an arbor press with the "notch plate" made of cast iron :rolleyes: .... One fine day the %^%$#@! thing essentially exploded when under a load. maybe those clamps were really white iron and were missed out of the treatment........

RancherBill
05-12-2010, 12:17 AM
I am not a metallurgist in any way. Reading all the posts I have several comments.

First, Canadian Tire stuff is a solid medium quality tool brand as Evan states.

Second, I learned something in Mom's cooking class. You don't wash cast iron pans. The grease / oil goes into the "pores" and makes it non-stick. Stay with me for a minute, I know a frying pan is not the same Cast iron as is used in clamps. Cast iron is not perfectly smooth and has the ability to trap stuff, and it leads me to comment.

If there was any paint failure water could get into the metal. Simple freezing of the water would create the micro-cracks that Evan mentions.

It is not a question of relative humidity it is a question of absolute water content in or near the metal. To put it in a contest of Evan's situation, It rains for several days and gets the clamps wet. The next night it go to -5C. There will be freezing - it's been soaked for several days. There will be expansion causing micro-cracks. Repeat the process several time and you are on your way to the failure Evan describes.

The other clamps the Evan has that have not failed probably have not gotten really wet. They have had temperature cycling but not being wet and freezing.

Just a thought.

dp
05-12-2010, 12:21 AM
We all have freezers we can test this with. We probably all have some crappy cast c-clamps we can afford to brutalize. Put one in the freezer over night and take it out during the day just to simulate an overnight freeze. Dunk it in water to simulate Seattle weather most of the year :). Repeat several times for a month.

Then clamp the test unit and an unstressed unit and see what transpires.

Evan
05-12-2010, 12:22 AM
Which makes me wonder....How well does a plastic clamp weather? Obviously they don't rust, do they?


I have no idea. There are no plastic clamps in that picture.

Evan
05-12-2010, 12:35 AM
We all have freezers we can test this with. We probably all have some crappy cast c-clamps we can afford to brutalize. Put one in the freezer over night and take it out during the day just to simulate an overnight freeze. Dunk it in water to simulate Seattle weather most of the year

Then clamp the test unit and an unstressed unit and see what transpires.


You will need to do that every day for at least six months. A single such treatment has no measurable effect. That isn't surprising since the effects accumulate over time with repetition. Micro cracking of cast iron is a well proven and characterized effect that occurs when the melt is contaminated with traces of phosphorus or other similar elements. It may also happen when cast sections vary considerably in thickness in close proximity. It is called "cold shortness" or "cold cracking" and it demonstrates that the internal strains can be strong enough to cause failure on the scale of individual crystal boundaries.

The presence of micro cracks is also known to increase the damping factor in cast iron which is a desirable characteristic. In many applications the strength of the cast iron is only a minor consideration since the mass is great enough that a reduction in strength is irrelevant. That is obviously not the case for a clamp but that is also irrelevant to the point at hand. This isn't about clamps that break. It is about seasoning cast iron.

Evan
05-12-2010, 12:46 AM
It is not a question of relative humidity it is a question of absolute water content in or near the metal. To put it in a contest of Evan's situation, It rains for several days and gets the clamps wet. The next night it go to -5C. There will be freezing - it's been soaked for several days. There will be expansion causing micro-cracks. Repeat the process several time and you are on your way to the failure Evan describes.


Cast iron isn't porous. It does have a surface where the excess carbon in the form of graphite may be eroded from between crystal boundaries leaving a fine network of micro pits. Liquid water will not "soak" in to cast iron and cause cracking. There are numerous bridges that have been in service for many years that have major structural elements made from cast iron. If the process of microcracking were somehow developed to macro cracks by exposure to water and freezing weather the bridges would have long since failed.

dp
05-12-2010, 01:01 AM
You will need to do that every day for at least six months.

I'd edited my post but apparently not quick enough :) Anyway, I agree. I see it all the time. Seattle and surrounding areas have a habit of placing iron plaits around trees on downtown sidewalks. They have no stress on them - no pedestrian traffic, no mowers, no nothing, and yet they crack with great regularity. They don't winter over very well at all, in fact.

When I was a kid I sat on the frozen seat of my uncle's Ford tractor. It was an old cast iron seat with slots, wide like a Harley seat. It cracked in two places and a piece of the webbing fell out of it moments after my butt hit it. There was a lot of snow on the ground - we were within 20 miles of Mt. Hood in Oregon and it was winter.

I think the best time to buck up an old machine for scrap must be in the dead of winter - just keep your sledge hammer warm.

Evan
05-12-2010, 01:09 AM
If the option exists scrap iron breakers do indeed wait for cold weather to break up cast iron. A 90% reduction in impact strength makes a very big difference to the difficulty of the job.

ADGO_Racing
05-12-2010, 01:14 AM
I have no idea. There are no plastic clamps in that picture.


Whats the yellow thingy on the end of the long clamp???

Paint...Still it doesn't get hot enough to discolor. Matter of fact, all of those clamps look to be in mighty fine shape. Must be that advanced welding process.

We neanderthals still use stick, tig and occasionally mig processes. All of our clamps have long since lost their paint.:rolleyes:

Evan
05-12-2010, 01:32 AM
The yellow thing is a plastic foot to prevent the metal clamp from marring the work.


We neanderthals still use stick, tig and occasionally mig processes. All of our clamps have long since lost their paint.

Hint: Tack it together and remove the clamps one at a time before you weld each portion. The clamps last longer. :rolleyes:

Doc Nickel
05-12-2010, 03:06 AM
Doc, I have been using those clamps for years. The cracking is a recent development, not an original defect.

-And I never said otherwise. Nor is there any way to know whether these came out of similar molds, or from the same factory. They're almost certainly much more recent, and may well be the victim of additional cost-cutting.

However, it is undeniably telling that similar clamps have a similar failure (or the beginnings thereof) in basically the exact same spot as yours- which were themselves somewhat dissimilar castings (at least different molds), and which both failed in identical locations.

That tells me it's inherent to the design and/or how it's made, not due to any weathering, heat or cold, or in-use stress. (All of which may have led to the ultimate failure, but didn't form the weak point where the failure began.)

Doc.

Evan
05-12-2010, 03:45 AM
However, it is undeniably telling that similar clamps have a similar failure (or the beginnings thereof) in basically the exact same spot as yours- which were themselves somewhat dissimilar castings (at least different molds), and which both failed in identical locations.



It is telling indeed. What it tells is easy to deduce. That is the point of maximum stress regardless of what material the clamp is made from. It is no coincidence that both clamps failed at the same point. The point of failure doesn't inform us as to the quality or lack of same.

edit: what it might tell is that the clamps you observed are made with a contaminated batch of iron creating a condition of cold shortness. That also doesn't convey anything of use if it is the case.

RancherBill
05-12-2010, 11:19 AM
My standard disclaimer, I am not an Engineer and not a Metallurgist, as previously noted.


There are numerous bridges that have been in service for many years that have major structural elements made from cast iron. If the process of microcracking were somehow developed to macro cracks by exposure to water and freezing weather the bridges would have long since failed.

Bridges do fail. That is a fact.

Your reply goes to disprove the essence of your original post.


The only reasonable explanation is that the seasoning process really does produce micro cracks that relieve casting stresses. In this case the cracks propagated because of the additional external stress cause by the clamping force.

All of these old bridges have been "seasoned" and thus must be full of micro cracks. Your clamps failed in a year, thus, all these bridges should have fallen down within a year if the 'seasoning micro-crack' theory is valid.


What I had referred to as pores you have acknowledged as "micro-pits" Your clamps, even being medium quality, are not made by made by the finest English Mills by master craftsmen, then polished to mirror like finish by virgin apprentices. They are production castings done in high volume and painted heavily to cover the irregularities in the casting.

The combination of an irregular cast surface and your micro pits with produce interesting features. I am going to call them macro-pits.

Your specific situation is that you placed the clamp in tension, had wood clamped that increased tension as it increased in size when it froze and then had water freeze in the macro-pits. The three factors start the failure.

Your failure is situational - not seasoning. If it was seasoning, there would be LARGE warnings on all clamps to store in a temperature controlled space. This is clearly not the case.

aboard_epsilon
05-12-2010, 02:55 PM
this one has been up since 1779......hasnt fallen down yet ...and has, in those years experienced a couple of minus 30 degrees cycles

http://www.ask-irezalet.com/wordpress/wp-content/uploads/iron_bridge_ingiltere.jpg

all;l the best.markj

ADGO_Racing
05-12-2010, 05:00 PM
Hint: Tack it together and remove the clamps one at a time before you weld each portion. The clamps last longer. :rolleyes:[/QUOTE]


Gosh dang! I wish I had met you years ago! Maybe my clamps would still be as purdy as eurs....!:rolleyes:

Actually, most of mine are 20+ years old. Have I had them break, yes usually from abuse. Most of mine are a higher quality clamp. And even the ones that broke from abuse in the past were a "cheaper" clamp.

I couldn't really care less about the paint, as they have served their purpose and have probably paid for themselves more than 100 times over. Ours have been used outdoors for years, indoors, dropped on the floor, pushed around etc...Virtually no issues, but thats why I pay for good ones.

That being said, when one fails, especially a cheaper one, I am really not that concerned with why it failed. If I need another one I order it. I really don't have the time to waste with a simple C-Clamp failure. I could use that time much better by drinking a few beers, or even better yet sleeping.

I do not allow anyone here to use any c-clamps in any lifting activities. So if one fails nobody is at risk of being injured.

When I see one of mine or another manufacturer's chassis come through the shop where something broke, it is worth loosing sleep over and examining thoroughly, to know exactly what happened and why, so it can be redesigned and properly repaired if necessary. Peoples lives and well being are at stake in this sport.

I seriously doubt anyone will be basing any critical material decisions on the findings of some guy in his garage who came up with his own theory that seasoning is bad for Cast Iron and posts his garage findings on a forum.:rolleyes:

Evan
05-12-2010, 05:29 PM
I seriously doubt anyone will be basing any critical material decisions on the findings of some guy in his garage who came up with his own theory that seasoning is bad for Cast Iron and posts his garage findings on a forum

I seriously doubt that you have a clue what I am doing. Seasoning is not "bad for cast iron", it is done to achieve a particular modification of the physical properties that is desirable for certain purposes, but not in C clamps.

Exactly what is it about experiments carried out in a garage that makes them invalid? You also are very short on reading skills since you obviously did not understand my previous statement in post 52.

beanbag
05-12-2010, 08:10 PM
Evan's analysis on C Clamps will be yet another good case study on how flame wars get started.

J Tiers
05-12-2010, 08:10 PM
I seriously doubt that you have a clue what I am doing. Seasoning is not "bad for cast iron", it is done to achieve a particular modification of the physical properties that is desirable for certain purposes, but not in C clamps.

Exactly what is it about experiments carried out in a garage that makes them invalid? You also are very short on reading skills since you obviously did not understand my previous statement in post 52.

You know?

I am definitely going to have to "+1" this comment...... "+1"! There, it's done.....

BTW, if you ever used Apple or Hewlett-Packard equipment, those companies basically started in garages, so you may want to ditch your Mac.....

S_J_H
05-12-2010, 09:01 PM
Quote:
Please send me some of whatever drug you are on!!

B. V. Kovacs, "On the Interaction of Acoustic Waves with SG Iron Castings." Transactions, American Foundrymen's Society, Vol. 83, 1975, pp. 497-502.

B. V. Kovacs, "Quality Control and Assurance by Sonic Resonance in Ductile Iron Castings," Transactions, American Foundrymen's Society, Vol. 85, 1977, pp. 499-508.


K. B. Palmer, "The mechanical and physical properties of engineering grades of cast iron at subzero temperatures," British Cast Iron Research Association, Oct., 1988.


Actually I did not doubt you about that. The difference with me is I would have seen the cracked clamp and chucked it into the trash without a hesitation. You on the other hand see that crack and are ready to measure the speed of sound through it.:eek:
Like I said, pass it over here please!:D
J/K
Steve

oldtiffie
05-12-2010, 09:21 PM
OK.

Back to where it all - Evan - started.

Here are the clamps:
http://ixian.ca/pics7/clamps.jpg

The clamps are essentially a horizontal "U" shape. The arm under discussion is the "top" one and the opposite/bottom one is threaded with the fastening screw in it. Both are similar and are similarly connected to the "back/spine" of the clamp.

Other than the torsional screw load on the "bottom" clamp the forces pushing the arms apart are about equal as are the radii that connect both of them the the back/spine.

That being the case, the forces at the radius at each arm and spine should be about equal.

Assuming the metal - what-ever it is - is homogeneous - there should be an equal chance of the cracking either starting or being at either - or both - radii.

If that is the case then assuming and working on the basis that the fracture will only be at the top radius is a false or yet to be proved assumption.

It seems equally likely that the next two clamps could fracture at the bottom radius and the two after that fracture at both radii - and the rest of the lot not fracture at all.

Frankly I'd chuck both the clamps and the argument in the $hit bin.

J Tiers
05-12-2010, 09:54 PM
Looking again at the clamps, It appears to be nearly CERTAIN that any cracking would occur preferentially at the BOTTOM.

Look carefully at the shape.....

1) the bottom arm is deeper, with a curve to it

2) the width of the "T" is probably more on the lower arm, with no particular taper

3) the top arm does not have a wide "T" section, it is much more even, with even a taper from teh corner to the "nut barrel".

My conclusion is that these clamps are nearly certain to break at the bottom, because the lower arm is much more rigid than the top arm. That means the first weaker spot will have stresses concentrated due to the rigid lever action of the bottom arm.

The top arm, being more flexible, should not concentrate the stress at the "corner" the way the bottom one appears to.

reggie_obe
05-12-2010, 10:35 PM
3 dollar clamps which no one's life depends on do not merit a second page of argument.
George

Sorry if this rains on any parades.

Correction George, 12 pages of discussion for a $3 clamp.

oldtiffie
05-12-2010, 11:00 PM
Probably the best resolution of the "discussion" would be that Evan accurately measure and draw the clamp and either run a computerised "Finite Element Analysis" (FIE) or get some-one else to do it and let us all know what and where the stresses really are.

If this were done either properly or a bit better, a randomly selected number of clamps would be taken from a single large batch - with some used as reference pieces - and any testing taken from there - applying the engineering and statistical analysis at adequate levels of rigour.

This is a good example of a thread about not much at all that has a lot of unsubstantiated "proof" and just a little logic applied to it for no real measurable or tangible effect or knowledge for any useful purpose.

Its probably about time George either locked or deleted it.

ADGO_Racing
05-12-2010, 11:46 PM
It has been a while, I forget...Have we definitely ruled out Sasquatch and/or aliens???:D

gmatov
05-13-2010, 12:08 AM
Reggie,

I am set at 40 views per page. I was wrong, in that there were more than 80. So 3 pages.

Tiffie,

I have nothing to say as to locking it, or do you mean the other George?

I don't really consider those "C" clamps. What you WOULD call that square design, I don't know. My good clamps ARE actually "C" shaped, Deep "C" shape. Malleable iron or steel.

Some are UNC, some are Acme thread. I also have garbage clamps that twist like the dickens when you bear down on them. I don't depend on them more than to apply a bit of hold on light application.

That we are at XX pages of "Why Did a 3 Dollar Clamp Fail After Being Outside Through a Canadian Winter Fail?" is way beyond me.

I would pitch it in the trash and mutter something about "Chinese junk", except that some of my cheaper clamps are "Made in the USA". Lighter duty. Never meant to be squose that tight.

Regardless, if Evan wants to continue his metallurgy on HIS failure, more power to him.

Cheers,

George

dp
05-13-2010, 12:31 AM
Its probably about time George either locked or deleted it.

I hope never to be so incurious about something. Sure, it's a trivial thing to have a c-clamp shatter but I don't see a harm coming from the desire to know why these two of the many failed. I'd like to think there's some validity to all those alarm clocks that gave up their lives to my explorations, all the neon transformers that went up in smoke from the Jacobs ladders they were never meant to power, and all the other oddities of science I followed (or pushed) to dead and smoldering ends because I was curious and needed to know.

I think it's great that Evan's curiosity and tool suite allows him to consider sonic testing of these trivial and now broken implements. That curiosity is its own reward and I think cheated are those who have lost that need to know.

Evan's is a harmless path and were it not for the steady hammering of the incurious here, his would be a rather quiet stroll. I recall a similar situation when I chose to publicly explore the mysteries of the Blake coax indicator. You'd have thought I'd roused the seven hounds of hell and set them loose in a school house.

Ken_Shea
05-13-2010, 12:44 AM
Dang well said Dennis !

Evan
05-13-2010, 01:41 AM
I really don't understand all the ruckus. If you look at the title of this thread it isn't about clamps at all. They just happen to be the example that may help explain the reason that nearly every single foundry and foundryman believes that seasoning cast iron is beneficial.

Cast iron is a pretty unique metallic substance. It has a variety of forms with widely varying properties. Some of these forms are dependent on the way the material is prepared, cast and post processed rather than being dependent on variations in ingredients.

The difference between chilled iron and grey iron could not be greater but is only dependent on the rate of cooling. Malleable iron is very different again and is a result of mere application of heat to one of the previous forms. Grey cast iron undergoes a major change in properties at the temperature of freezing water. Below that temperature it is as brittle as glass and the normal contraction of the iron due to it's coefficient of linear expansion with temperature is in contrast with the very different behaviour of the sheets of graphite interspersed among the crystals of iron.

Some sort of effect must be expected in such circumstances. It has been argued that a material cannot exceed it's own rupture strength due to changes in dimension caused by temperature changes. That argument is demonstrably invalid as shown by the tendency of some alloys of steel to crack when quenched from red hot.

The transition of grey iron and ductile iron from the ductile state to the glassy state is both abrupt and severe in the change in properties. Unlike most other ferrous materials it occurs at a temperature commonly reached in temperate climates.

Early metal workers had little or no scientific knowledge to guide them in their craft but did have a large store of practical experience to draw on. It is absolutely possible to know what to do without knowing why to do it. I know what to do in many aspects of the craft of metal work but I also very much like to know why. I constantly experiment with materials to better understand their properties and this particular situation is no exception.

I will be doing some experiments on this over the next week or three as time permits (it doesn't permit right now) and will post my findings when I have something to report. I am particularly interested in the idea of characterizing the damping properties of the material via the dispersion of an acoustic impulse as well as the velocity of same in the material. It should be possible to make a test that is both easy to apply and non destructive so that an arbitrary number of specimens may be tested.

John Stevenson
05-13-2010, 03:53 AM
I recall a similar situation when I chose to publicly explore the mysteries of the Blake coax indicator. You'd have thought I'd roused the seven hounds of hell and set them loose in a school house.

Aaaahhhhh NOT the dreaded Blake [ making signs of the cross and goes looking for knurling tool ]

.......

.

Punkinhead
05-13-2010, 06:23 AM
I am particularly interested in the idea of characterizing the damping properties of the material via the dispersion of an acoustic impulse as well as the velocity of same in the material. It should be possible to make a test that is both easy to apply and non destructive so that an arbitrary number of specimens may be tested.Sounds like fun, but the problem is the lack of control samples. Without knowing the original material and history of other clamps in your collection you won't be able to learn anything meaningful. If you get a different acoustic signature between your broken clamps and others in your collection you can't chalk it up to the aging. If your goal is to see if the acoustic signal is different between regular and "aged" castings you'd have to purchase samples that all came from the same batch and age some while storing others then compare them. Although if you saw a difference you still wouldn't know why. Just the fact that the signals were different wouldn't be proof of the microcracks theory.

Weston Bye
05-13-2010, 08:17 AM
...I will be doing some experiments on this over the next week or three as time permits (it doesn't permit right now) and will post my findings when I have something to report. I am particularly interested in the idea of characterizing the damping properties of the material via the dispersion of an acoustic impulse as well as the velocity of same in the material. It should be possible to make a test that is both easy to apply and non destructive so that an arbitrary number of specimens may be tested.

Buy a bunch of new clamps, do a before and after measurement. 1 sample each, stressed and unstressed, but both "seasoned" as you described. Do the same with similarly stressed and unstressed samples in a "controlled" envioronment. Go away, do something else equally interesting and tell us about it, and report back about the clamps in a year or two.

J Tiers
05-13-2010, 08:25 AM
I hope never to be so incurious about something. Sure, it's a trivial thing to have a c-clamp shatter but I don't see a harm coming from the desire to know why these two of the many failed. I'd like to think there's some validity to all those alarm clocks that gave up their lives to my explorations, all the neon transformers that went up in smoke from the Jacobs ladders they were never meant to power, and all the other oddities of science I followed (or pushed) to dead and smoldering ends because I was curious and needed to know.

I think it's great that Evan's curiosity and tool suite allows him to consider sonic testing of these trivial and now broken implements. That curiosity is its own reward and I think cheated are those who have lost that need to know.

Evan's is a harmless path and were it not for the steady hammering of the incurious here, his would be a rather quiet stroll. I recall a similar situation when I chose to publicly explore the mysteries of the Blake coax indicator. You'd have thought I'd roused the seven hounds of hell and set them loose in a school house.

yep..... +100

Lock the thread?

OK, let's lock the next one of those "boring and disgusting" drawn-out and painful threads detailing the process of making a model pumpjack, or some other such totally useless and material-wasting "project".

I mean..... really.... who NEEDS one of those, and why should ANYONE be interested in the steps (and worse yet, MIS-steps) in the process of making one? When you are done making it, what do you have? Basically nothing.... so what is the point?

Lock those.... lock these........ lock lock lock..........!

Evan
05-13-2010, 09:09 AM
Buy a bunch of new clamps, do a before and after measurement. 1 sample each, stressed and unstressed, but both "seasoned" as you described. Do the same with similarly stressed and unstressed samples in a "controlled" envioronment. Go away, do something else equally interesting and tell us about it, and report back about the clamps in a year or two.


If, and it's a big if, if I can make it work by a simple acoustic measurement I intend to do just that. Except I don't need to use clamps. I have some nice pieces of grey cast iron including a chunk of Durabar. I can easily build a very simple jig that will hold pieces under a controlled amount of bending force next to a control that is relaxed along with an indoor control all cut from the same chunk of metal. Several sets of samples will serve to reduce the effect of any outliers and the entire experiment may shed some light on the subject of seasoning cast iron.

In my review of the available literature I cannot find any reference to actual testing that has duplicated the "real life" conditions of a season to season exposure to the elements. It would also be easy to prevent any confusion from corrosion processes by simply applying a corrosion resistant coating to all the pieces.

For now though I think there is something still to be learned by comparing all the clamps in my collection if a non destructive test can be developed. I have a feeling that magnetostriction might be a good way to test the damping properties.

lazlo
05-13-2010, 09:36 AM
Except I don't need to use clamps. I have some nice pieces of grey cast iron including a chunk of Durabar. I can easily build a very simple jig that will hold pieces under a controlled amount of bending force next to a control that is relaxed along with an indoor control all cut from the same chunk of metal.

Now you're talking Evan. Cut several test specimens from the same piece of DuraBar, and do a double-blind study of cold cycled versus ambient specimens.

DuraBar doesn't have any internal stresses, so I presume you're proposing to test for changed in ductility. So put each sample under shear and measure the deltas.

oldtiffie
05-13-2010, 09:58 AM
I went back to the OP at:
http://bbs.homeshopmachinist.net/showpost.php?p=548237&postcount=1
in which I rather understood that the main topic was about micro-cracking.

The thread seems to have deviated somewhat from that aim.

Why not just grind selected parts of one or several clamps and apply non-destructive dye-penetrant to see if there actually are any existing micro-cracks?

Why not apply that test to the cracked clamps - adjacent, near and remote from the fractures?

It may well give a reasonable indication of the "before" and "after" states.

And you will have the results as soon as the dye-penetrant process is complete.

Punkinhead
05-13-2010, 10:09 AM
Why not just grind selected parts of one or several clamps and apply non-destructive dye-penetrant to see if there actually are any existing micro-cracks?I'm not sure what micro-cracks are, but I assumed he was talking about cracks at grain boundaries, in which case dye penetrant wouldn't help. I do a lot of failure analysis of parts made from various alloys of tin, silver, lead, and copper and have to microsection, polish, and put them in a scanning electron microscope to see cracks at grain boundaries. They're very difficult (often impossible) to see with a normal optical microscope.

lazlo
05-13-2010, 10:09 AM
I went back to the OP at:
http://bbs.homeshopmachinist.net/showpost.php?p=548237&postcount=1
in which I rather understood that the main topic was about micro-cracking.

Why not just grind selected parts of one or several clamps and apply non-destructive dye-penetrant to see if there actually are any existing micro-cracks?.

That's actually a very good idea 'Tiff. The ultraviolet dye will find even the smallest cracks, and would be easy to instrument an overall luminance measurement.

dp
05-13-2010, 10:19 AM
Aaaahhhhh NOT the dreaded Blake [ making signs of the cross and goes looking for knurling tool ]

.......

.


Hey - looks like the Blake should be a new tool for the next Hannibal Lecter movie. Guaranteed to send grown men running from the theater!

lazlo
05-13-2010, 10:22 AM
Aaaahhhhh NOT the dreaded Blake [ making signs of the cross and goes looking for knurling tool ]

Yes, but you were largely responsible for that thread John :) You mentioned that you really liked your 3D Taster, which inspired some zealotry... :p

oldtiffie
05-13-2010, 10:48 AM
Originally Posted by John Stevenson
Aaaahhhhh NOT the dreaded Blake [ making signs of the cross and goes looking for knurling tool ]


Hey - looks like the Blake should be a new tool for the next Hannibal Lecter movie. Guaranteed to send grown men running from the theater!

So.

The (real?) "Blake" is cause for concern?

No mention of the "fake Blake" so I guess that is OK.

Further, as the "real" Blake is made in the USA it seems that the problem is with the USA-made tool.

As no mention or criticism has been made of the "China-made" "fake Blake" there are no concerns about it and by extension it gives a higher degree of satisfaction when used for its intended purpose.

That seems reasonable to me as even though I don't have a real USA-made Blake I am more than satisfied with my "fake Blake".

John S's "holy cross" is of no use as the serial number of my "Fake Blake" is 666!!!! but it sure does a devilishingly good job!!!

I can see that John has a genuflection coming on.

Well - I'll be damned.

Oh - I am already?

Fancy that!!!

Evan
05-13-2010, 12:18 PM
Dye penetrant won't reveal micro cracks. It might show microcracks that have propogated to the next discontinuity in a crystal field but I doubt it. Dye testing is intended to reveal macroscopic cracking only. The type of cracking that is posited as being responsible for the stress relief in unloaded seasoned cast iron is micro cracks that are the result of differential expansion and contraction of the binary composite material that is the structure of grey cast iron. If the iron is unloaded these cracks do not progress but allow redistribution of the strains in the crystal structure. These cracks will also create a higher damping constant for the material that is measurable as a reduction in ringing when the material is given a sudden impulse.

lazlo
05-13-2010, 12:22 PM
These cracks will also create a higher damping constant for the material that is measurable as a reduction in ringing when the material is given a sudden impulse.

Why? Grey cast iron damp so remarkably well because vibrations are absorbed by the laminations of flake graphite. That's why ductile cast iron isn't used in machine bases -- the spheroidal graphite inclusions don't damp vibration nearly as well.

Why would you think micro-cracks in the structure of grey cast iron would enhance vibration damping?

Evan
05-13-2010, 01:34 PM
Why would you think micro-cracks in the structure of grey cast iron would enhance vibration damping?

Two reasons. It makes sense since the stress/strain curve for cast iron shows a large amount of hysterisis because of the difference in compressive vs tensile strength.

The other reason is because other people think so too.




Fatigue properties in very high cycle regime were obtained for
cast iron at 20 kHz frequency, the fatigue strength decreased as
the applied stress levels increased. Comparing with the fatigue
test results obtained at 35Hz tests, there is no frequency effect.
The thermography detection has been applied to observe the
fatigue damage processes of cast iron GS51. The relationship
between the temperature evolution and fatigue damage were
analysed, the heat dissipation behaviour of the cast iron is depend
on not only the amplitude of cyclic loading but also the loading
frequency. Temperature increase at ultrasonic frequency was
considerably higher than that at 20Hz. The study of fractography
showed that fatigue crack initiation site from the surface graphite,
void or subsurface void for the cast iron GS51, fatigue crack
initiation site is predominated from the subsurface microstructure
defect under lower maximum cyclic stress. Temperature evolution
reflect the heat dissipation process, due to the damage phase
occurred in the microstructure of the cast iron GS51, local
temperature increase sharply in the fatigue test specimen, it also
reflected the micro crack growth processes. Micro crack growth
life is only a very small part of the total fatigue life for specimen
with very long fatigue life.
http://www.journalamme.org/papers_amme06/173.pdf

The increase in temperature reflects an increase in damping behaviour just before the failure of the specimen.

lazlo
05-13-2010, 01:43 PM
The other reason is because other people think so too.

http://www.journalamme.org/papers_amme06/173.pdf[

Temperature evolution reflect the heat dissipation process, due to the damage phase occurred in the microstructure of the cast iron GS51, local
temperature increase sharply in the fatigue test specimen, it also reflected the micro crack growth processes.

That quote makes no comment about vibration damping -- how are you making the leap from micro-cracks to vibration damping?

lazlo
05-13-2010, 01:44 PM
I posted these articles in the last thread about seasoning cast iron:

Metals Handbook, 8th Edition, Volume 1, published in 1961 by the American Society for Metals, pg 362 - 363:


"If residual stresses are high enough, they may relieve themselves slightly at a very slow rate at room temperature. This is the origin of the old practice of aging castings for three months to a year before machining.

However, modern methods of investigation indicate that a maximum of only 15% of the residual stress can be relieved by aging, and therefore the practice is seldom used today. Table 25 shows that aging for 84 days at room temperature had no stress relieving effect."

[Note 15% is the max theoretically *possible*, not the amount normally achieved.] "


In my review of the available literature I cannot find any reference to actual testing that has duplicated the "real life" conditions of a season to season exposure to the elements.

The Naval Research Lab paper I posted last time did test "outdoor aging":



http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD620556&Location=U2&doc=GetTRDoc.pdf

"The effect of outdoor Aging has been said to be due to the alternate heat and cooling of the casting. A rapid check on this theory was made by placing a stress wheel in a dry-ice box at 0F for two hours and then transferring it an oven at 220F for two hours. After four complete cycles of intermittent heating and cooling, the rim was sawed and 0.0191 inches of strain was measured. before this treatment, a duplicate wheel showed 0.0200 inches of strain.

Thus only a small amount of stress reduction wet obtained by this treatment.

Besides the temperature changes to which castings are subjected in outdoor aging, the possibility that corrosion relieves a part of the stresses locked in the outer -skin of the casting has been suggested. To determine the effectiveness of such corrosion, a rapid test was conducted by completely immersing a stress wheel in a 6 percent solution of sulfuric acid for 20 minutes at a temperature of 165 0 F. Sawing of the wheel revealed a residual strain of 0.0159 inches compared with the "as cast" strain of 0.0164 Inches.

From this observation, it is possible that corrosion might contribute slightly toward relief of casting stresses."

Rich Carlstedt
05-13-2010, 04:25 PM
Lazlo

Thanks for posting the Navy trials
They have one possible error.
We know for example, that when heat treating steel, "soak" time is extremely important . While normally this is considered for "Phase Change", it may also be a natural function of general molecular action as well.
Just as we know that Vibration is a great stress reliever....time span of vibration is very important to sucess in this venue.
We don't know what the cross-section area or density is in the Navy tests, so the only value it states is that some form or relief occurs. It would be a mistake to consider the percentage results as designated formulas without a comparitive "time" study

Thanks for posting
I have the book, but not read it since King Edward VIII Resigned.

( a Sir John pun)

Rich

Evan
05-13-2010, 04:54 PM
That quote makes no comment about vibration damping -- how are you making the leap from micro-cracks to vibration damping?


It isn't a leap at all. They are fatiguing the metal with ultrasonic vibrations. The formation of micro cracks coincides with a large increase in temperature. The only source of energy is the ultrasonic vibration. If that vibration is being converted to heat then it is an example of increased damping. All damping that occurs must result in an increase in temperature since energy is being absorbed. Correspondingly, in that test an increase in temperature can only be a result of increased damping.


"The effect of outdoor Aging has been said to be due to the alternate heat and cooling of the casting. A rapid check on this theory was made by placing a stress wheel in a dry-ice box at 0F for two hours and then transferring it an oven at 220F for two hours. After four complete cycles of intermittent heating and cooling, the rim was sawed and 0.0191 inches of strain was measured. before this treatment, a duplicate wheel showed 0.0200 inches of strain.



That isn't even slightly representative of a season to season exposure to numerous freeze/thaw cycles. The effect is certainly cumulative and 4 cycles is nothing.

Your quote of me:
"In my review of the available literature I cannot find any reference to actual testing that has duplicated the "real life" conditions of a season to season exposure to the elements. "

lazlo
05-13-2010, 06:12 PM
We know for example, that when heat treating steel, "soak" time is extremely important . While normally this is considered for "Phase Change", it may also be a natural function of general molecular action as well.
Just as we know that Vibration is a great stress reliever....time span of vibration is very important to sucess in this venue.

Very true. Vibratory stress relief is a mainstream industry process for skin stress, although I understand it's on giant vibrating tables with multiple G's.


We don't know what the cross-section area or density is in the Navy tests, so the only value it states is that some form or relief occurs.

They actually describe the test piece in detail -- it's a spoked wheel that they cast in a way that they can characterize the internal stress.

http://i164.photobucket.com/albums/u15/rtgeorge_album/NRLtestsample.png

oldtiffie
05-13-2010, 06:34 PM
Dye penetrant won't reveal micro cracks. It might show microcracks that have propogated to the next discontinuity in a crystal field but I doubt it. Dye testing is intended to reveal macroscopic cracking only. The type of cracking that is posited as being responsible for the stress relief in unloaded seasoned cast iron is micro cracks that are the result of differential expansion and contraction of the binary composite material that is the structure of grey cast iron. If the iron is unloaded these cracks do not progress but allow redistribution of the strains in the crystal structure. These cracks will also create a higher damping constant for the material that is measurable as a reduction in ringing when the material is given a sudden impulse.

My understanding of the OP is that the subject of the investigation is (was?) the localised failure that may be attributed to micro-cracks.

As both failed/fractured clamps are available(?), why not complete the fracture on one of them and then grind, polish, etch and dye-penetrate the surface and check/examine it on/under a good microscope?

That will give you the grain structure from which quite a of of data or further questions can be extracted and evaluated.

Similar grinding, polishing and dye-penetrant treatment on parts of a non-failed clamp will give an indication of a possible or probable state ex-foundry/casting as a reference.

J Tiers
05-13-2010, 11:03 PM
Can someone explain how the gray iron relates to C-clamps?

They should either be cast steel, or a malleable iron, both of which are rather different than gray cast iron. I'm not sure exactly how the seasoning process relates to either of them, as neither should need it, or benefit from it.

Now, cheap chinese C-Clamps may not BE anything other than CI, in which case it would become very relevant.

Evan
05-13-2010, 11:14 PM
Ductile iron is also subject to the same transition to the glassy state and at the same temperature as grey iron. Malleable iron exhibits shiny crystals at the fracture surface so the clamps are definitely not malleable iron, at least not entirely. Most likely they are cast with no special attention to ensuring that white chilled iron is formed. It will form in the thinner sections but may not in the heavier parts. If the clamp is then subsequently heat treated the white iron areas will form malleable iron but the remaining areas will simply be annealed grey iron. I will go down now and take a picture of the section I polished and etched to show what I mean. Back in a while.

Evan
05-14-2010, 12:54 AM
Here are some images. This section was cut about 1/2 inch from the fracture zone. The images are taken with circular polarized lighting and the polarization is different for each image.


http://ixian.ca/pics7/clampmicro0.jpg

The first pair show what certanly appear to be a fine network of cracks although they are much too large to be called "micro cracks".

The rest show different aspects of the distribution of various forms of iron. I won't attempt to characterize them as I am not very familiar with crystallography.

http://ixian.ca/pics7/clampmicro1.jpg

http://ixian.ca/pics7/clampmicro2.jpg

http://ixian.ca/pics7/clampmicro3.jpg

oldtiffie
05-14-2010, 07:20 AM
Evan.

Well done - that is very nice work indeed.

Just a couple of suggestions for other "cut and polish" work:

That sample was transverse. It would assist if a longitudinal section were take in the general area of that sample (or perhaps the sample itself or one that would be similar).

In that "U" shape, the maximum bending moment will be in the centre of the "back" (between the two "arms"). A transverse as well as a longitudinal section from that area will detail the granular structure/s at that point.

My guess is that while I think that the maximum stress was where the fracture occurred - ie at the ends of the corner inside radius, that as both "corners" are reasonably symmetrical that the stresses just before the fracture were pretty close to being equal, I'd suggest a transverse section through one end of the "blend" of the arc connecting the arm to the back as well as a longitudinal section through the "blend" (~90* arc) between - and including - the ends of the arc will be show any minor fracturing that may have been due to stress failure etc. may be evident.

I'd suggest that you retain and preserve your samples from the fractured clamp/s.

Perhaps similar samples from a clamp that had not failed will or may show a prior fault and/or the condition prior to fracture in ther fractured clamp/s.

If you were to post the results here, I would hope that experienced professional Structural, Civil and Mechanical Engineers or Metallurgists and associated technologists will assist with advice, comment and analysis as well. I think that you will be well able to be in that group as well.

That will get and keep it more in the "know so" than the "think so" or "saying so" categories and more toward the analytical and engineering - and perhaps scientific - categories where some definitive and structured answers to the discussion may well eventuate.

I think that George B will or should leave the thread to roll on as I am now rather looking forward to see how it goes and where it arrives.

J Tiers
05-14-2010, 08:32 AM
Looking at the sections, and admitting up-front that I am not a metallurgist, and am simply comparing to various remembered textbooks......

The distribution of apparent carbon in the material appears to confirm it is some form of cast iron. I am not entirely sure of the scale, but the yellow rectangle appears to be the outline of the next image.

I will want to look again at the books, but the distribution does NOT look so much like either entirely "spheroidized" as with malleable iron, OR the larger flakes seen in plain gray cast iron. It does appear to be towards "spheroidized, but BOTH seem to be present, as my recollection of pictures goes. I am going to work now, and won't be able to check until later.

lazlo
05-14-2010, 09:47 AM
Can someone explain how the gray iron relates to C-clamps?

I will want to look again at the books, but the distribution does NOT look so much like either entirely "spheroidized" as with malleable iron, OR the larger flakes seen in plain gray cast iron.

I don't understand that either Jerry. Evan is making a leap from a cracked pig iron clamp to stress relief of grey cast iron.

This is what spheroidal (ductile) cast iron looks like. Good quality clamps and vises are made from ductile, because the tensile strength is much higher than grey cast iron, and you don't care about vibration:

http://www.msm.cam.ac.uk/phasetrans/2001/adi/as-cast-200.jpg

Evan
05-14-2010, 09:59 AM
This is what spheroidal (ductile) cast iron looks like. Good quality clamps and vises are made from ductile, because the tensile strength is much higher than grey cast iron, and you don't care about vibration:


Ductile cast iron has the same response to cold as grey cast iron. It becomes as brittle as glass.

This is the graph I posted earlier. Perhaps you meant malleable iron, as Jerry has remarked.

http://ixian.ca/pics7/ductilebrittleiron.jpg

bborr01
05-14-2010, 10:03 AM
OK.

I have been following this thread since the beginning.

I think the clamps failed because the wood expanded in sub freezing temperatures as the moisture in the wood froze and expanded.

Lets see here.

2 out of 50 clamps fail.

Those 2 are left out in the cold for a couple years.

Does anyone here think that if the same 2 clamps had just been laying out on the railing instead of being clamped to something that they would have failed?

I don't.

The other thing about these clamps that has been mentioned here many times is that cast iron is not a real great material for making strong clamps.

I have seen clamps made of ductile iron that had been clearly abused with cheater bars and bent a long way but did not break.

Brian

lazlo
05-14-2010, 10:12 AM
Perhaps you meant malleable iron, as Jerry has remarked.

No, I mean ductile iron, which is what good quality clamps and vises are made from. Your clamps are made from pig (white) iron.

JCHannum
05-14-2010, 10:25 AM
The first pair show what certanly appear to be a fine network of cracks although they are much too large to be called "micro cracks".

http://ixian.ca/pics7/clampmicro1.jpg

That photo looks less like micro or macro cracks and more like porosity resulting from poor iron, poor casting technique, poor mold design or a combination of all three.

lazlo
05-14-2010, 10:36 AM
That photo looks less like micro or macro cracks and more like porosity resulting from poor iron, poor casting technique, poor mold design or a combination of all three.

You mean these guys Jim?

http://i164.photobucket.com/albums/u15/rtgeorge_album/IndiaFoundry.jpg

Evan
05-14-2010, 12:09 PM
No, I mean ductile iron, which is what good quality clamps and vises are made from. Your clamps are made from pig (white) iron.


Don't use ductile iron clamps in cold weather. They will snap.

Apparently you have no idea what pig iron is. Or for that matter white iron which is used to make malleable iron.



Merchant pig iron comprises three main types: BASIC PIG IRON, used mainly in electric arc steelmaking, HAEMATITE PIG IRON [also known as FOUNDRY PIG IRON], used in mainly in the manufacture of grey iron castings in cupola furnaces, and NODULAR PIG IRON, used in the manufacture of ductile [also known as nodular or spheroidal graphite - SG] iron castings. Pig iron contains at least 92% Fe. Other constituents are typically:

BASIC PIG IRON 3.5-4.5% carbon, <1.5% silicon, 0.5-1.0% manganese, <0.05% sulphur, <0.12% phosphorus

HAEMATITE PIG IRON 3.5-4.5% carbon, 1.5-3.5% silicon, 0.5-1.0% manganese, <0.05% sulphur, <0.12% phosphorus

NODULAR PIG IRON 3.5-4.5% carbon, <0.05% manganese, <0.05% sulphur, <0.05% phosphorus



http://www.pigiron.org.uk

BTW, you left off the attribution on that image.



Foundry workers, India (photo by J. A.dam Huggins)

http://www.honestfilms.net/index.php/tag/film

lazlo
05-14-2010, 12:26 PM
Apparently you have no idea what pig iron is. Or for that matter white iron which is used to make malleable iron.

I know more than enough that I don't have to Google a quote for it. Pig iron is the precursor material that's in the pig, prior to adding alloying elements to make it into ductile or grey cast iron.

As many others have posted, your clamp is made from crap iron, and you're trying to make the great leap from the fracture of a cheap pig iron clamp to seasoning grey and ductile cast iron, which every reputable metallurgy books says is a myth.


BTW, you left off the attribution on that image.

It's from the New York Times article about the abusive worker conditions in the cast iron foundries in India:

New York Manhole Covers, Forged Barefoot in India (http://www.nytimes.com/2007/11/26/nyregion/26manhole.html)

Evan
05-14-2010, 12:35 PM
As many others have posted, your clamp is made from crap iron, and you're trying to make the great leap from a cheap pig iron clamp to seasoning grey and ductile cast iron, which every reputable metallurgy books says is a myth.


There is no leap. Read the quote in my previous post. The clamp also is not White iron. It would have destroyed my bandsaw blade if it was.

Every metallurgy book? How about a few citations?

I'm going to town now. That should give you plenty of time to Google something up.

lazlo
05-14-2010, 12:46 PM
Don't need to Google it Evan -- I've posted several articles in this thread, and your previous cast iron threads, and you refuse to believe it:

http://bbs.homeshopmachinist.net/showpost.php?p=549277&postcount=138

But I'll leave you with a quote from Richard Moore, who admittedly was an academic with no first-hand knowledge of machine tool design :p


"'The theory that a cast iron part must be exposed to the weather to rust and 'age' in order to stabilize it is a carry-over from the past. In the absence of closer measuring facilities or adequate temperature control, the stability of the iron was blamed. Supposed cases of instability might have been traced to machining practices, deflection or, most often, to temperature variations"

Richard Moore, Foundations of Mechanical Accuracy, p. 19

John Stevenson
05-14-2010, 04:58 PM
But I'll leave you with a quote from Richard Moore, who admittedly was an academic with no first-hand knowledge of machine tool design :p


But did he have perfect pitch hearing, 20 / 20 eyesight and an acute sense of smell ?

MuellerNick
05-14-2010, 06:30 PM
Ductile cast iron has the same response to cold as grey cast iron. It becomes as brittle as glass.

I really can't understand why you over and over repeat that statement and, for the second time, quote a diagram that shows a dynamic property.
You you have the slightest idea of what you are talking about?
Static brittleness is what might have an infulence in the case of seasoning. Static brittleness is plastic elongation before failure.
Dynamic brittelness is also measured with an intentional stress-riser (a kerf)


Nick

boslab
05-14-2010, 08:51 PM
You could do a sulphur print of the offending lump of iron [originally called a Bauman print], machine if poss though not always needed, etch with 5% nitric acid [if diluting remember AAA, always add acid, to the water that is] for about 10 Min's, wash off and air blow dry, hairdryer will do, soak a piece of photographic paper [B&W multi grade is good] in 5% sulphuric for 2 to 3 Min's
Apply the wet paper to the piece of steel or iron your interested in, hold it in close contact with a bag of sand or heavy rubber mat for about 5 Min's.
once done remove to see all the internal structures like cracks,segregation and the like, also shows flow lines in sectioned forgings and the like, even welds but these are usually too small to be really useful except for HAZ measurement.
Metals do change with time, in some its quick and at room temp like lead where recrystallization is instant [almost], the changes are quicker in say an iron where there is a source of energy like strain, sometimes caused by irregular cooling, the stress will dissipate like a very slow thermal equilibrium,
It was common for iron castings to be buried but the practice has all but died out as post production heat treatments became more widely known about [dark secrets in the beginning] and better understanding of metallurgy, chemical elements being added improve the casting, like Calcium treated steels, Niobium stabilized steels, altering irons by Magnesium injection and lots of other ideas
Excuse the ramble the photo looks like macrosegrigation to me
regards
mark

Evan
05-14-2010, 08:53 PM
Static brittleness is what might have an infulence in the case of seasoning. Static brittleness is plastic elongation before failure.


Elongation before failure is one measure of the transition from ductile to glassy state. It is directly related to the impact energy required to cause rupture. The two are manifestations of the same change in properties.


Fracture Behaviour

Ductile Iron, like most ferrous materials, exhibits fracture behaviour which varies according to composition, microstructure, temperature, strain rate, and stress state. At low temperatures, brittle failure occurs by the formation of cleavage cracks, producing a facetted, shiny fracture surface. Very little deformation is associated with this type of fracture, resulting in low absorption of energy and low toughness. As the temperature increases, producing a decrease in flow stress, failure occurs by plastic deformation, primarily by the formation, growth and coalescence of voids. The resultant fracture surface will be dull gray, and the energy absorbed will be high, meaning very good fracture toughness. Fracture in ferrous materials traditionally has been characterized according to appearance and absorbed energy, with a Nil-Ductility-Transition (NDT) temperature quoted to indicate the change from brittle to ductile behaviour. In addition to transition temperature, upper shelf energies were quoted to define toughness in the ductile fracture region.



As for microcracks providing stress relief, that is well known and well accepted. The only question is how much does this depend on temperature, cooling rate and temperature cycles.

On the issue of whether microcracks improve damping of the material, that is also well known and accepted.



Effects of Microstructure

In addition to the general variations related to different types of material, damping capacity is also affected within a family of materials by applied stress state and microstructure. Figure 3.55 shows the variation in damping capacity with surface stress for Gray Iron, low carbon steel and ferritic and pearlitic Ductile Iron. Figures 3.56 and 3.57 illustrate the influence of microstructure on damping behaviour of Ductile Iron. As would be expected from the relative damping capacities of Gray and Ductile Irons, as the percentage of spherical graphite decreases ( and the amount of flake-like graphite increases), damping capacity increases significantly (see Figures 3.56). This Figure also shows that damping capacity is not affected strongly by carbide contents up to 14 volume per cent. Figure 3.57 shows that damping capacity generally decreases with increased matrix hardness and increases with carbon content. The only exception to the damping-hardness relationship is for as-quenched martensite, in which the internal stresses produced by the formation of martensite increase microplastic deformation and thus increase damping. As shown in Figure 3.55, ferritic and pearlitic Ductile Irons exhibit a transition in relative damping capacity as the applied stress is increased. At low stresses, the softer ferritic matrix has higher damping capacity, while at higher stresses, the damping capacity of the pearlitic matrix is greater.

http://www.ductile.org/didata/Section3/3part2.htm#Modified Charpy Test Results

boslab
05-14-2010, 09:11 PM
It seems the usual cut and paste war has broken out, Canada v the rest as usual, much better than the television,
Were the clamps ductile iron or is it a conspiracy, I rekon all irons have some ductility ? even glass has a little !

Evan
05-14-2010, 09:28 PM
It isn't a cut and paste war. Those are quotes from a very authoratative reference that say the same thing I have been saying.

For instance:


At low temperatures, brittle failure occurs by the formation of cleavage cracks, producing a facetted, shiny fracture surface...

Here is an example from the broken surface of the clamp. Note how the facetted region does NOT extend to the edges of the iron. This seems to indicate that the cracking remained internal to the clamp but did seriously weaken it so that when I applied it in warm weather the usual plastic fracture behaviour occured all around the internal glassy crack area.

http://ixian.ca/pics7/iron7.jpg



even glass has a little

Glass has exactly zero ductility. It is classed as a perfectly elastic material. That means that if it is deformed below the point of failure it will return completely to the previous shape.

boslab
05-15-2010, 02:54 PM
mon cherri, i was in fact agreeing with you, the works of griffiths fresh in my mind, almost, i very rarely refer to the google and for the most part rely on my own damaged thinking unit, refer to the directiom of the sand dunes, thats the key
mark

BarnyCarParts
05-19-2010, 07:26 PM
Hmmmm Seems to me I saw a show about the Titanic being made from Iron made in Scotland during the winter. Being such the Iron had low or higher cabon or sulpher content I don't recall which, but, when the Titanic pushed against the Iceberg the metal didn't sheer or rip, it cracked and shattered because brittleness in the cold.

J Tiers
05-19-2010, 11:47 PM
BTW, my copy of the American Foundry Association cast metals handbook specifically mentions that GRAY cast iron has little or no effect from low temperatures. They had the data to show it as well, illustrating possibly a 10% change or so.

I tried to find data for malleable/ductile iron, but no go in that source.

lazlo
05-19-2010, 11:53 PM
BTW, my copy of the American Foundry Association cast metals handbook specifically mentions that GRAY cast iron has little or no effect from low temperatures.

That's the LCE, but that's a good point -- that's why measuring standards (camelbacks, etc) were made from Grey cast iron -- because grey iron has a very low dimensional change due to temperature.

Don't know if that's related to brittleness, but I also don't follow the association of micro-cracks with seasoning. Stress relief is plastic deformation of the grains, which is why it works best at temperatures close to iron's transition temperature.

But I'm certainly willing to be convinced, if Evan can do a blind study with grey cast iron. Somehow generate test samples with internal stresses like the Navy Research Lab did, and subject them to hot/cold cycles like NRL did. According to Evan's theory, seasoning == microcracks == stress relief.

J Tiers
05-20-2010, 12:25 AM
Sorry, I meant cold brittleness...... gray CI has no big increase in brittleness per the handbook

There has been proven effect from cryogenic treatments of all sorts of things, including music wire guitar strings...... The opposite of transition temp......

possibly gives the effect of years of "seasoning"..... in one fell swoop.

boslab
05-20-2010, 05:06 AM
Hmmmm Seems to me I saw a show about the Titanic being made from Iron made in Scotland during the winter. Being such the Iron had low or higher cabon or sulpher content I don't recall which, but, when the Titanic pushed against the Iceberg the metal didn't sheer or rip, it cracked and shattered because brittleness in the cold.
It was due to phos, it depresse brittle ductile transition, and a bit of a bugger to remove from the metal when useing open hearth furnaces, multiple slagging off with lime is required as phos removal is a metal/slag reaction, it can go slag metal if temp is right, called phos reversion, P2O5 is the end product, phos pentoxide [mainly], all from my head not google! incidently the shell/hull was not cast, it was wrought [the stuff with the sringy slag inclusions, fiberous as they say, i think the rivets might have been brittle too!
mark

lazlo
05-20-2010, 08:41 AM
Sorry, I meant cold brittleness...... gray CI has no big increase in brittleness per the handbook

Ah, I didn't know that. Ignore what I wrote then :)

black powder
05-20-2010, 12:37 PM
I can remember a cast iron piston roughly 8" in dia. and having a buna polly pack piston seal that smelled up because the hyd.fluid used was phosphate ester . The bottom of the piston gland was broken off of the piston dew to the buna swelling . I didn't think the rubber could swell with enough force to break the cast piston.