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brunneng
03-16-2006, 12:55 AM
I know the has been bantered around before but a quick search didn't ring any bells.

If I were to have a project that required some aluminum casting but I was not setup to do that nor was I likely to be in the near future but wanted to have some pieces cast for making, say a small slant bed for a widdle cnc lathe to mount some THK linear bearings on that I happen to have for just such a use...

...are there any known people or groups out there that you know of that do that sort of thing just because they need to get some use of all the work they put into seting up a foundry and are not afraid of money...

Kevin

wierdscience
03-16-2006, 01:05 AM
If you were closer I would give you my old furnace.I never get to use it so why not.

My advice is hit the yellow pages and find somebody local that casts ornamental iron,if you do the patterns,most times they will cast what you need reasonable if you can wait until they are doing a pour.

I have taken the odd mould down to the local scrapyard and passed it under the spout of the're scrap smelter.They usually do a lot of tranny cases so the alloy ain't that bad and it only costs me $.51/lb

torker
03-16-2006, 08:10 AM
This is funny! I was just going to ask the same question.
I got a call from a steel supplier here wondering where to get some bigger chunks of aluminum. Seems a lot of retired guys are buying lathes etc. but large alu bits don't happen around here.
I'm thinking of building a furnace also. Did quite a bit of reading the last few days.
There is an old guy here who does some (this is the guy who doesn't use oil on the lathe ways).
He has legs welded onto a Chevy SB oil pan.
He uses a Tiger torch on the bottom and another on the top. When the mess is melted he grabs the oil pan with two sets of vicegrips and runs outside with the works and pours the alu into wooden boxes for moulds! Yikes!
The steel place is scared to deal with this guy so he asked me if I can do this.
A couple things I can't find in the stuff I found through Google...
He throws Borax into the melt to flux it...do I have to do that? I couldn't find it mentioned in any home foundry writeups.
I need to make some 6" and 8" round pieces.
Was thinking of using pipe for moulds but I'm wondering if they'd need to be split and use them as two piece moulds so I can get the pieces out.
Was going to use the bottom part of a propane cylinder for a melting pot and fire it with a forced air burner made for BBQ briquettes.
I've melted lots of lead but no alu.
I have some alu cylinder heads and some pistons already scrounged.
I've read about how to make moulds with lost wax, sand etc. but can't find what to use for simple mould for rough cylinders and squares.
Was the old guy right to use just wood?
I'm assuming you'd have to cover the wood with wax.
These guys are willing to pay a pretty good price for these pieces so I'd like to take a crack at it.
Thanks!
Russ


[This message has been edited by torker (edited 03-16-2006).]

railfancwb
03-16-2006, 08:26 AM
Get Gingrey's(sp?) book on the charcoal foundry. In the $10 range. It will give a practical BASIC discussion of the entire process, including pattern making. His other books go into more details. Charles

torker
03-16-2006, 08:31 AM
Charles, Thanks, I'm going to build roughly the same burner as a guy has on his foundry site. Well, maybe a little nicer than his, it's pretty crude.
I want a frame for the pot so it can swivel and a table on casters to move around under it for filling moulds etc.
The burner he made uses a small squirrel cage fan with a speed control. Seems awful simple to me.

PTSideshow
03-16-2006, 08:39 AM
Here is the site for casting.
http://www.backyardmetalcasting.com/forums/index.php
This is a totally amazing site. check out your local community college they may offer a casting class. Ours is going to offer one in the fall which is nice because i will be able to ask question and get answers that you can always get form a book.

------------------
Glen
Been there, probally broke it doing that

kf1002002
03-16-2006, 09:27 AM
I have melted up a batch of aluminum using a sawed off propane bottle for a crucble; it worked fine and shows no sign of serious burning but obviously will need replacement sometime; but there are lots of propane bottles around.
I use a 20 lb propane cylinder with the top cut off and a refractory lining burning charcoal for a furnace. My home made refractory is perlite with some stuff called "CPD" to hold it all together. The perlite is a good insulator and I found that after a run I could pick up my furnace with my bare hands--it was just comfortably warm. I've also wondered about borax flux but never tried it and I've heard of using sulphur.
One caution though: If you start cutting up propane bottles be sure to get all the propane out first. I fill them with water then empty them before cutting.

Ken

thistle
03-16-2006, 10:30 AM
a very good book to get before you go haring off melting stuff is Casting Aluminum" by C.W. Ammen.
Put out by TAB books. ISBN 0-8306-1910-0.

it goes in to the basic chemistry making furnaces burners ect .

PTSideshow
03-16-2006, 01:20 PM
Here is a hobby foundry supplier site I have a number of books from them the one on furnaces, forges and kilns and burners is well worth the price for any body planning on using old propane tanks and really great operating burners.
http://www.budgetcastingsupply.com/
somebody on this board has the book and has made up improved burners form this book and loves them

------------------
Glen
Been there, probally broke it doing that

Carl
03-16-2006, 01:52 PM
<font face="Verdana, Arial" size="2">Originally posted by railfancwb:
Get Gingrey's(sp?) book on the charcoal foundry. In the $10 range. It will give a practical BASIC discussion of the entire process, including pattern making. His other books go into more details. Charles</font>

http://img.photobucket.com/albums/v35/lathefan/The20Charcoal20Foundry.jpg

http://www.lindsaybks.com/dgjp/djgbk/char/163a.jpg

http://www.lindsaybks.com/dgjp/djgbk/char/163b.jpg



[This message has been edited by Carl (edited 03-16-2006).]

brunneng
03-16-2006, 04:14 PM
The Gingery books are a nice resource. I have most of them and quite a few of the foundry books from Lindseys include the big Navy book.

It looks like I'll have to setup my own foundry to do this. Looking around at the improvements made in propane burners it seems that they are quite viable for the small shop use.

This site shows the construction of a Reil EZ burner. http://metalcast.boorman.us/index.html and a foundry.

PTSideshow
03-16-2006, 04:33 PM
Lindsay Technical Books has added the Michael Poter book #1590 Gas Burners for Forges furances and kilns it is 19.95. Thier spring catalog #633 hit the mail box today.
http://www.lindsaybks.com/
This is were to get a current edition of C.W. Ammens book on casting. $23.95
http://www.edwardrhamilton.com/titles/0/1/9/0198315.html
They have an amazing assortment of books at great prices.

------------------
Glen
Been there, probally broke it doing that

Carl
03-16-2006, 04:39 PM
<font face="Verdana, Arial" size="2">Looking around at the improvements made in propane burners it seems that they are quite viable for the small shop use.</font>

I think Gingery used charcoal because it was the least expensive viable option.

TECHSHOP
03-16-2006, 06:19 PM
I have only cast lead and bronze.

Alcoa had a plant down the street from me, closed end of 2001, I think. One of the "new startup" companies in its place melts AL scrap just had a big dinner 1800hr last Thursday to tell the fifty workers, the place was closed, by 2000hrs the place was on fire.

That was one of the places I was looking for work. The other half of the building is where a friend has his biz. I was suppossed to start there next month.

Plenty of melted metal down the street, today. The place was stacked 10-12 high with "ingots" about 4x4x2 ft.

------------------
Today I will gladly share my experience and advice, for there no sweeter words than "I told you so."

Evan
03-16-2006, 07:35 PM
Russ,

Look around for some damaged irrigation pipe, maybe ask some farmers. They get run over by tractors and they are toast.

wierdscience
03-16-2006, 08:51 PM
Russ,checkout Steve Chistians tilting furnace sold by Linsay,it is the way to go for what your considering.The small crucible furnaces are too much work for too little reward.

cam m
03-16-2006, 08:55 PM
Russ
There was a local to me, and within shipping distance to you, Al foundry in Central Ab. They had capability to do permanent and sand molding. A school mate of mine took it over some years ago, but I don't know if they're still in business. If you're interested, I could check. On the other hand, charcoal or coal is relatively safe to transport and store (unlike propane), but smoke can be an issue. Coal should be available from Elkford?. Charcoal or coal also give enough heat to raise a 8" pipe crucible full of scrap Al to pouring temp in 25 or so minutes (been there, done it). You don't say how long/thick your 8" rounds are?
Borax is flux to deal with impurities. You may not need it if your scrap is clean enough. I never used any, but then my results weren't always flawless either.
Porosity is also a big issue.
The work may not shrink enough to release from a pipe mold. If finish is not critical sand molds are more versatile.

my $.02 cdn
Cam

[This message has been edited by cam m (edited 03-16-2006).]

wierdscience
03-16-2006, 09:05 PM
Here you go Russ-

http://www.lindsaybks.com/bks5/chalfur/index.html

uute
03-16-2006, 10:58 PM
I'm w/ cam on porisity, Your likely to get lots of little bubbles in your pour, machinists won't like that when their finished surfaces are pitted. If you try, split the pipe molds and use a degassing agent (salt & potasium cloride salt are often recomended, or commercial degassers are available). Gotta get the hydrogen out!

Borax is usually recomended for brass as a flux. Sounds like it may work w/ alum too, not tried that.

Good luck!

torker
03-17-2006, 12:03 AM
Thanks ALL! Great info.
weird...I'm going to see if Lindsay will ship up here by USPS. That's a bigger outfit than I had planned but the book would pay for itself in time saved I'm sure http://bbs.homeshopmachinist.net//biggrin.gif
Cam...check your mail!
Cam and uute, you bring up something(the ugly porosity word) that hasn't been mentioned in the stuff I've read but I wondered about.
I've turned some alu castings and welded even more that had porosity.
The "raw billets" I want to make can't have any of that. Well, I'm hoping.
I'll check out the degassing agents. Thanks...good one!
I'd like to make 6" and 8" rounds and a few different sizes of cubes. I'm mostly interested in lengths 3" and up to maybe 10".
As for scrap...I can get a lot of tranny cases, engine blocks, heads, pistons....and irrigation pipe for free or very little.
Cam again...good point about the coal. Geez, I never even give it a though. I read how much cheaper BBQ briquettes where than LPG and left it at that. When I have a mountain of coal an hour away!
Thanks again guys. Got more "learnin" to do!
Russ

torker
03-17-2006, 01:39 AM
Ahhhso...found a little more info!
Use chlorine tablets or nitrogen gas for "degassing"
Also, clean and degrease oily cast before melting.
Don't let the melted alu sit in the pot too long...it collects hydrogen.
Also collects more hydrogen on rainy days (duh)

[This message has been edited by torker (edited 03-17-2006).]

Tinkerer
03-17-2006, 02:06 AM
I've also read that you should melt and cast your scrap into ingots then remelt them and cast into final shape.... you'll get a better pour and finish this way.

david_r
03-17-2006, 02:20 AM
torker,
Can you clarify that? Hydrogen gas to degas but don't let it absorb hydrogen from the air?

torker
03-17-2006, 07:39 AM
<font face="Verdana, Arial" size="2">Originally posted by david_r:
torker,
Can you clarify that? Hydrogen gas to degas but don't let it absorb hydrogen from the air?</font>
Oh boy...the end of a looong day. Sorry should read nitrogen. Hope nobody was killed in the explosion http://bbs.homeshopmachinist.net//biggrin.gif

cam m
03-17-2006, 10:43 AM
Russ

I won't be able to check mail until mid next week. I'll try to find out if the local Al foundry is still in business.
My experience was strictly on a hobby basis. The castings I made were in the 1/2 - 3 qt range.
Here's what I found. YMMV.
Thin Al scrap and swarf is not preferable (in fact my last choice). While plentiful, it is very low yeild. For example, not only is the volume of beer cans (even crushed) relatively large for their weight, there is a lot of oxidized/painted/coated surface area relative to clean, pure Al. Besides, can you see to run up a fire after you've emptied enough beer cans to justify a fire?
Extrusions are second choice because the alloying elements that make it plastic enough to squirt out through a die are not the same as those for casting.
Die castings or sand castings are the most desireable. They are thicker and therefore have less oxidized surface to clean Al. The chemistry of the alloy is also closer to the optimum for casting less what ever might have been consumed last time it was cast.
The oxidized material forms a layer on top of the melt that protects it from the air and bits of steel like bolts, pins, and helicoils sink to the bottom of the pot.
As far as heat goes, I would, on occaision melt small quantities by laying an open steel pot directly on the coal bed in the old wood and coal furnace Dad heated his shop with. That furnace had no forced draft, just an induced draft from a 16 - 18' chimney. I've also melted Al with a 200,000 BTU Tiger torch. Simply stick the pot (4" pipe) in a sheild (8" pipe) and play the flame from the tiger torch on the pot. By far the quickest methiod I used was to line a piece of 16" pipe with fire brick, set up a salvaged 12v heater fan for draft, and set the pot (8" pipe) on a thick bed of local coal. By the time I had the sand mold rammed up, the Al would be melted. I didn't have a pyrometer to use, but I had the best results with the pot at a red glow in a shadow (not direct sun).
I got 2 - 20 l pails of casting sand from the steel foundry in Cowtown for a contribution to the coffee fund.
Degassing with gaseous media like N2 or Chlorine tabs relies on agitating the liquid metal in the melt (ever blown on a straw in a glass of milk?)
Because it is a vigorous process with lots of splashing, I'm frankly scared stiff of the process. (think molten Al at 1450 - 1500 F sticking to your skin, boots, or leather protective gear) Even if the molten Al doesn't contact skin, it will stick like S&%$# to a wool baby blanket to anything having a texture to it tranferring heat to that object until it cools. In addition Chlorine gas is an additional hazard.

Cam

Editted cause I can't type very good.

[This message has been edited by cam m (edited 03-17-2006).]

Schutzhund
03-17-2006, 10:21 PM
<font face="Verdana, Arial" size="2">Originally posted by torker:

Originally posted by david_r:
torker,
Can you clarify that? Hydrogen gas to degas but don't let it absorb hydrogen from the air?</font>
Oh boy...the end of a looong day. Sorry should read nitrogen. Hope nobody was killed in the explosion http://bbs.homeshopmachinist.net//biggrin.gif




It's all good torker. Doc says my eyebrows will grow back. Thats the last time I get destructions from the internet...

uute
03-18-2006, 01:20 AM
Cam brings up another great point!

While I've heard of guys pouring from a pipe crucible in shirt sleeves w/ channel-locks for a pouring shank, I wear all the leather welding gear HF sells (which itself is less than ideal, but much better than nothing) and a welding helmet - even when just adding to a charge in the pot. The shoe spads/chaps are about manditory in my book, on your feet is where that hot stuff will go when your pot springs a leak - and it Will, unless you buy a real crucible, then it is more likely to shatter or crumble when it fails.

I,ve had several pop & splatter events when adding to a charge, even w/ dry & preheated scrap, I think from corosion/forign matter hidden in recesses/holes in scrap castings. Be Alert & Careful. Allot an afternoon, this is no time to be in a hurry.

Keep everything DRY (don't want to mix molten Al w/ miosture of any kind - BOOM!!). Be fire concious & keep some sand handy to smother anything that might arise.

And I think its a derned lot of fun too! http://bbs.homeshopmachinist.net//smile.gif
(even when the pour fails) http://bbs.homeshopmachinist.net//biggrin.gif

uute

[This message has been edited by uute (edited 03-18-2006).]

torker
03-18-2006, 08:33 AM
Schutzhund...Sorry about the eyebrows! http://bbs.homeshopmachinist.net//biggrin.gif
Cam...I meant check your email,lol! I think I've forgotten how to write a real letter!
Cam and utte, Thanks for taking all the time to school us noobs!
I agree with the safety factor. I used to melt a lot of lead for the local shotmaker here.
Was getting way to cocky about the whole thing until one day I dipped the rake I made into the bucket of wheel weights and just fired them into the pot without looking.
There was some water in the bottom of the bucket and when the wet lead hit the melt it exploded!
I was really lucky. I'm always nursing some kind of second or third degree burn anyway (work as a weldor) but this would have been a whole new adventure if that hot lead had splashed in my face.
Some of it flew onto the side of the wifes car 20 feet away and took the paint off right now!
The remainder started a dozen little grass fires.
Introducing the degasser agents. I was thinking of piping the nitrogen into the bottom at low pressure through a flowmeter?
Or making a strainer type gadjet to put a chlorine tablet in. Lower it into the pot and push it to the bottom where it should melt. The chlorine thing doesn't really appeal to me. I've worked in pulpmills and know the dangers of this stuff. Sure seems easy though. Pop in a "pill" and you're done. Or so one would think.
And what about the crucible? I'm rethinking the propane bottle deal now. Wouldn't a piece of XXX heavywall pipe with an equally thick bottom last longer? This pipe is near 5/8" thick. I suppose it would take longer to heat up but if it lasted it may be worth it.
Today I'm going on a scavenger hunt to find a little squirrel cage fan for blower. And mounting my new DRO, and working on the old McDougal, and finishing the body work on my new truck, and finding one of them rountooit deals so I can get this all done.
I like weirds idea about making a big pre heat oven to help reduce the size of cylider heads and engine blocks etc.
Funny, i have an old Toyota engine I was going to sell for $50. Wonder how much alu is in that thing http://bbs.homeshopmachinist.net//biggrin.gif
Russ

SJorgensen
03-19-2006, 12:50 AM
Torker,

You've got a couple of errors in your last post. The first one is the idea for piping nitrogen into the bottom of the pot. Remember that it is nitrogen absorbtion that is the problem, and not the solution. Also the pellets that are the degassing agents are definately not clorine. Clorine tablets that I've had for swimming pools burn really good and I think introducing a strong oxidizer into molten metal might be an extreme mistake. Even worse than the first one you told about. I'm not sure what chemical the degassing tablets are but the smell reminds me of mothballs.

torker
03-19-2006, 07:14 AM
SJ...How do you figure the two are errors when they are questions. The first one is for sure...see the question mark.
I wasn't aware that nitrogen was the problem. I thought hydrogen was the problem.
As for the chlorine tablets, I have no idea....but you may want to read this....
http://www.chaski.org/homemachinist/viewtopic.php?t=47784&start=0

cam m
03-20-2006, 12:15 AM
Russ

For my pots I used old standard weight Oilwell casing roughly 3/16" thick with a 1/4 or 3/8 plate capping the end. My circumstances changed and I quit casting before either the 4" or 8" wore out or corroded through. The thicker the pot's metal, the slower the melt. All that heat has to be conducted though the pot. There was an old vet that lived in our neighborhood when I was a kid. He told tales of melting aircraft pistons down in tobacco tins for turning stock for government jobs in the machine shop he served in.
Cam

[This message has been edited by cam m (edited 03-20-2006).]

torker
03-20-2006, 12:41 AM
Cam...I wondered about that. A heavy pot would last longer but would cost more to heat in the end. After all the old guy here uses an oil pan http://bbs.homeshopmachinist.net//biggrin.gif
I think I'll just start out simple and go from there. Thanks! Oh yes...thanks also for the info in the emails!
Spence...you may want to read this
http://www.key-to-metals.com/Article83.htm
Note the part that says...
Hydrogen Removal....
"the most important....
use nitrogen, argon, chlorine, freon"
I've read several more articles and not one mentions that nitrogen absorbtion is a problem...it is the cure.
Russ

SJorgensen
03-20-2006, 02:57 AM
Dear Torker,

I'm no expert, and I could be wrong and I probably am. I recall nitrogen absorption from the books I read on the subject. Memory being what it is, and after all the beef I've been eating lately (mad cow), I'm probably wrong. Nitrogen is about 70% of our air. I know that Aluminum has a great affinity to carbon, and it robs carbon from the cast iron pots that I have used to melt in. Eventually the bottom will swell and the pot will get brittle. That is a side note. If aluminum has a great affinity for hydrogen, and if it is hydrogen absorption that causes the pin holes, then it has to absorb hydrogen from somewhere. There isn't likely to be very much free hydrogen available in the casting environment. This is because it is a very hot environment. I'm considering that hydrogen is both very light and very flammable and that the environment of molten aluminum is about 1220 degrees. Maybe it could be from the water vapor of combustion. I don't know. As I said, I'm not holding myself out as an expert. I look foreword to hearing more opinions from those here who are. Also I don't know if the degassing compounds are chlorine. The tablets that I bought didn't smell like chlorine and I don't know if clorine tablets work. You've raised some questions in my mind and I'm anxious to find out what is right.

torker
03-20-2006, 07:26 AM
Spence..I think the only way one will find out is to try it.
However, I'm starting to doubt that I can cast the type of pure pieces that I'd hoped for.
I'm still reading all I can find and it looks like the big dollar foundries have the porosity problem even with all their equipment.

gkman11
03-20-2006, 07:54 AM
Info on degassing from the pros.
http://www.palmermfg.com/aluminumdegas.htm

torker
03-20-2006, 08:12 AM
gkman...thanks for that!
They don't have a pirce for that unit but I'll have to check it out later after work.
I like the testing unit they have also. Probably worth its weight in aluminum http://bbs.homeshopmachinist.net//biggrin.gif

Rooter
03-20-2006, 08:42 AM
You might want to check in at some of the local High Schools. I went to a small town High School and our shop had a furnace for casting aluminum. That was 25+ years ago, but can't hurt to try and see if you could use their stuff or do it for you if they have the equipment.

5Bears
03-20-2006, 09:12 AM
Hi Guys, first post here! I've done a bit of aluminum casting, and the degassing part in my opinion is pretty critical. If you cast parts that require subsequent machining, and you don't degas, at a minimum you'll have a whole bunch of annoying pinholes... at worst, some big voids.

My understanding of degassing is that it is mechanical. Bubble any DRY gas through the melt, and it'll do the job. I had a small bottle of nitrogen, and created a stainless steel wand, cross drilled #60 at the end, with a trigger and flow valve at the handle end (modify a standard compressed-air blower) and this worked great. After the melt is fluid, the heat is turned off or lowered, and a very fine trickle of bubbles from the wand does a good job. BE VERY CAREFUL, as too much gas will cause serious splatter. Be sure you're fully protected at all times.

When the Nitrogen bottle ran out, and needing to degas a batch, I thought, "Hmmm, argon as used in TIG welding is totally inert, and bone dry." Argon is greatness. If you TIG weld, and have a bottle handy, go for it. I see no need to replenish the Nitrogen bottle so long as Argon is available. Argon is super-easy to find at any welder's supply.

The hydrogen comes from the inevitable moisture, which in turn comes from combustion gasses and the atmosphere itself.

Good luck, casting is a lot of fun.

torker
03-20-2006, 02:24 PM
Rooter...the high schools here started getting out of any of that kind of stuff years ago. Too many liabilities I guess.
5Bears...Welcome...but just where do you think you're going?
You do not have permission to leave this site yet http://bbs.homeshopmachinist.net//biggrin.gif
Us noobies have a bunch of dumm questions for you and Cam...we just haven't thought of them yet http://bbs.homeshopmachinist.net//biggrin.gif
BTW...thenks for the info.
I've read that you can use argon and I do have a big double fill bottle of it but it's very pricey up here ($320 to fill it).
I haven't checked on the price of nitrogen yet.
Any idea how much gas flow you would use for a certain size of melt?
I have an extra flowmeter that I use for back purging when I tig pipe and the wand sounds simple enough.
Thanks!
Russ

Evan
03-20-2006, 02:51 PM
Russ,

My wife sells 7.25 cubic meters of nitrogen (refill) for $113.00. That's a "large" bottle.

torker
03-20-2006, 03:03 PM
Evan..I get a pretty good break on gas here for my industrial account. I just phoned.
A 9 cubic m bottle of nitrogen is $79.
Ha....the same "high capacity" bottle that I use for argon (14 cm @ 4200 psi) is $78...go figure!

Evan
03-20-2006, 03:10 PM
It costs the same to fill either bottle as far as the gas is concerned. Nitrogen is "free" and is a byproduct of oxygen liquifaction.

kenrinc
03-20-2006, 06:20 PM
I use a comercial degassing flux which consists of sodium chloride, potasium chloride and some other flourides. It's a powder. You put a tsp in the crucible before your start and the other I just wrap up in some tin foil and put it in the end of a 1/4" rod and push it in. I do this a couple minutes before I skim the dross. Works well.

ken-

torker
03-20-2006, 06:37 PM
Ken, cna you explain something to me then.
I've read that you need a degasser AND a flux.
The degasser is for getting rid of the hydrogen and the flux is used to seperate the oxides from the melt.
Am I missing something (simple) here?

Evan
03-20-2006, 06:47 PM
The degasser gas removes dissolved gasses from the molten metal simply by agitating it and bringing new metal to the top. The flux prevents the metal from reacting with the oxygen in the air and all promptly turning to oxide.

[added]

Think what happens when you stir a soda.

[This message has been edited by Evan (edited 03-20-2006).]

5Bears
03-20-2006, 06:56 PM
Russ, it doesn't take much flow at all to degas say a 10 lb crucible of aluminum. When I first started casting, I was waaay overheating the melt. After a bit of experience, this is what I found worked for me. This was using a pyramid foundry - the basic small trash-can sized job that is typical of any home foundry.

When the scrap or ingots completely liquified, I'd leave the gas on for perhaps another 30 to 45 seconds, no more. For lack of a better term, the molten metal begins to "dance" a bit from the turbulence of the swirl. I'd kill the gas, but leave the crucible in the furnace. There's huge residual heat in the walls of the furnace... no fears that the melt will quickly cool. In fact, if you use a pyrometer, you'll find that the temp will continue to rise for a short time after the gas is off, at least with my furnace.

A couple tablespoons of flux goes in, stirred, and the dross skimmed. Another tablespoon - let it form a "skin" on the top of the melt. Now for the degas - I used a regulator capable of 0 to 30 psi, and found that setting 1 psi or less on the dial was more than enough. All you want to do is bubble the melt, not blow it out of the crucible. I'd first purge the hose leading to the wand by letting the argon flow for about 20 seconds... then, slowly lower the wand to the bottom. If the bubbling action is too vigorous, (al blowing out of the crucible) turn the argon down. For 5 pounds of metal, I'd probably degas 30 seconds.

After degas, one final skim of the oxides, and it's time to pour. I've never had a melt get too cool if I left the crucible in the furnace throughout his process.

These numbers are all what I came up with after doing a number of pours, and it is "rule of thumb" only and worked for me. I machined all of my aluminum, and without degassing, I had distinct porosity. Degassing really works well. Be safe and experiment a bit, that's what it's all about.

torker
03-20-2006, 07:30 PM
Thanks Guys! This just keeps getting better (unlike my oiler idea).
Glad I talked to you all before I barged into this.
This afternoon between coats of primer/surfacer on my truck, I got an old propane bottle cut up for a "trial" crucible.
What a disappointment that was. Thsy are far thinner than I thought they'd be and this one was full of rust in the bottom.
I don't have enough faith in it to pour any serious heat to it. Who knows what will flake off it just when you don't want it to.
I just got another treat...I got invited to a "pourin" this weekend.
I saw the old guy who melts alu in an oilpan.
He claims he just bought a crucible and a bunch of sand. Says he has a bunch of molds made up.
I asked him how he was degassing the melt.
He said "Huh"
But I'm going anyway. I'm sure to learn something http://bbs.homeshopmachinist.net//biggrin.gif
Russ

Evan
03-20-2006, 07:56 PM
You want your aluminum smelting crucible rust free. Although molten aluminum isn't hot enough to ignite it I still wouldn't want a chance of a thermite reaction.

torker
03-20-2006, 08:05 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
You want your aluminum smelting crucible rust free. Although molten aluminum isn't hot enough to ignite it I still wouldn't want a chance of a thermite reaction.</font>
That's why I'm not going to use it.
The rust is so bad I don't think there'd be much left if I put it in my rust buster http://bbs.homeshopmachinist.net//biggrin.gif

wierdscience
03-20-2006, 10:44 PM
Russ the crucible I use is nothing more than a section of 6" sch40 Stainless pipe.I welded a bottom in it(also ss)and a short section of 1-1/4"square tubing to the side near the top for a pouring handle socket.

gkman11
03-21-2006, 07:40 AM
Source of nitrogen gas?
I don't want to buy a cylinder plus $70 + for a supply of dry nitrogen for a hobby job. Googling for an alternative, I found that aircraft, racing and other high performance tires are filled with nitrogen to provide more stable pressure. So just steal a tire off a Cessna or top fueler...no that's another forum. Find a tire store to fill a spare tire with nitrogen and have a lifetime supply for a few bucks.

Your comments?

torker
03-21-2006, 08:03 AM
weird, that's what I was originaly thinking.
At least then I'd know what I had. The LPG cylinder was a waste of time. I still can't believe how thin them things are.
gkman...I don't mind the $70 bucks for gas...but I don't like the bottle rental idea either. I already have four bottles rented...don't need to pad their pockets any further.
The guy at Praxair told me they test and revalve old cylinders. Says he's seen bottles from the early sixties that are still in service. Hmmm...wonder how many dozens of times those bottles have paid for themselves. Anyone thinking that someone has a nice summer home by the lake?

Evan
03-21-2006, 08:53 AM
Look for someone that sells the bottles instead of renting them (not Praxair). My wife sells them with no strings or annual/hidden charges, any size. They are exchange filled and inspected/tested too. She is an agent for Northern Cylinder and Gas out of PG.

lynnl
03-21-2006, 12:11 PM
I have made maybe a dozen or so melts, and have only poured ingots up to this point. So I'm no expert. But none that I've cut open and machined have shown any signs of porosity, and I've taken no degassing measures at all. May be just luck, which will run out next time, but so far they've been nice and smoothly solid.

As for crucibles, the first few were done using 46 oz juice cans with the tops cut out. In fact the first can I got two melts from before deciding it looked too weak for another. Then I decided cans were cheap enough, so just used a new one each time.

Then I came across some 5" pipe, about 5/32" thick, and welded on a bottom and some lifting ears and forged a pouring lip. I thought that would last a long time. But after about 3 or 4 pours it was burned so bad I decided the juice cans worked just as well, with much less trouble.
(NOTE: my experience has all been with the charcoal fired furnace described by Mr. Gingery.)

I've read of ceramic coatings that can be applied which would help to protect the juice cans. Sometime in the future I intend to try that.

kenrinc
03-21-2006, 01:08 PM
Torker: the can of flux says it's a "degasser and a flux" so that's all I know. Evan had a good explanation.

gkman11: You don't need to steal a Cessna tire; the majority of tire shops now fill auto tires with nitrogen. I know the Costco down the street does this.

I've never noticed much porisity before I started using flux. I started using it because my steel pipe crucible is on about 20 melts and I just decided to start. Also I'm through my stockpile of excellent cast aluminum stock and am back to alloy wheels and valve covers :-) I coat the crucible with Gingery's glaze: smashed beer bottles, borax and fireclay. Works very well.

Ken-