View Full Version : Mystery cast

01-08-2010, 07:36 PM
Thought it was about time for another mystery metal question :)

Well, here it is. I picked up a grate today, looks like it might have been a curbside drain cover or something. It's 5 inches wide, and was about 24 inches long. Looks strong enough to drive a vehicle over. Anyway, it was broken at one end, so I figured what the hay, I can cut that part off and re-surface the thing, probably use it as a fixture somehow.

I very carefully nudged it into the bandsaw blade, and it seemed to cut just fine. I got through one side, then into the other side, then with about 1/16 left to go it got hard. Looks to be flame cut on that edge. I snapped the piece off and took it to the grinder. That edge portion gives dull red looking sparks, while the rest of the material gives a uniform bright orange spark, same as grinding ordinary steel.

Now I'm wondering how these things are made- would they actually be cast as much wider pieces, then flame cut apart? Doesn't seem realistic, somehow. If not, would I be right to assume that a hard edge or surface would be the result of the molten iron hitting a cold mold? The top surface is covered in little raised dots, presumably for traction, and if I grind on these dots, I get the same dull red sparks- once into the surface a ways, it's back to bright sparks. I've probably exposed about 3 or 4 sq in of fresh metal from bandsawing, and all that looks very uniform, no inclusions or pinholes have shown up, and it cut very smoothly. Cast into the piece is the word 'polycast'.

That's it. No answers required, just wondering if it's likely that this is made from a horrible mixture of unknownium, or if I might find that I can resurface it reasonably well with carbide.

Then there's this other grate- definitely a curbside drain cover, but larger and with very substantial thicknesses all around and in each cross piece. What are my chances of being able to make stuff out of that cast-

01-08-2010, 09:07 PM
I dunno. HSS makes dull red sparks.

01-09-2010, 01:18 AM
Well, I did some testing with one of the smaller pieces I had cut from this grate. Mystery metal is misery metal, yup- now you've heard it again :) From the looks of the surfaced piece, all the outer edges are hard, and where the casting is thinner, the metal is harder. You can see that pattern all over it. I had a lot closer look at the edges, and now it looks like maybe there was some grinding going on to roughly finish the outside edges, so it probably wasn't flame cut. At any rate, I'll be able to use a piece or two for some simple things, but the big piece will have to wait for some annealing or something before I touch it again. Or it will just lean somewhere until I forget what it's like to machine :) No loss anyway, it was cheap as a cup of coffee, and one piece is going to become a tool anyway.

01-09-2010, 01:29 AM
I've found that mild steel parts cut with plasma have a thin surface that's extremely hard to machine. It needs to be removed with a grinder before welding, too.

01-09-2010, 04:03 AM
cast iron for furnace bars and grates and such tends to be any old crap, it is fairly unusual to find a good bit, very high in Silicon tends to make the iron porus, massively high carbon to the point it cant fit in the matrix so comes off as flake graphite, ive destroyed dozens of angle grinders just getting a peice with a flat surface to analyse the stuff, sand cast isnt too bad but if they use chills or a metal mould then prepare for chill cast [tiny tiny grains of super hard cementite], virtually unmachinable, but not impossible, we get test buttons off 2 blast furnaces that are cast in a steel mould, these have to have a flat surface and the skin removed as it is not representative of the analysis, they get ground, there are a couple of machines on order from germany that the manufacturers rechon they can mill the samples [5 axis HAAS/Fanuc type mills] with ceramic tipped face mill, this i must see becase i reckon the things will do great on steel but i bet itll eat tips like wheatos.
A reheat >720 degrees and a very slow cool can help redistribute the carbon and soften the skin [partial decarb i suppose], you need to hold the temperature for a good hour min ive found
I often end up machining it with a 14lb sledgehammer to get a bit off!

01-09-2010, 10:04 AM
Considerring that these samples are from grates, they wern't to concerned about quality so they were probably made from assorted scrap. Engine blocks, steel scrap, mystery scrap. And they were not overly concerned about machineability so they didn't do much special with the molds to control moisture any more than necessary to be able to cast the parts, and then the molds were broke open about as soon as the parts were cooled enough not to bend when they were handled. Production rate was important as quality did not mean machineable.

Used to work for a company that made grates and manhole covers and rings and such. Real fum when we had to machine one of those castings because they were made to be driven on, not machined.

01-09-2010, 02:00 PM
Sounds like it's almost certain to be cast iron of some untraceable pedigree.

Chances are real good it was made by this company, or a subsidiary thereof.

Mueller has a plant not far from here that makes such as that, fire hydrants, etc..

I have a small piece of storm drain grating, that seems to be very high quality CI. ...at least it machines nicely and leaves a nice finish.

01-09-2010, 02:05 PM
Cast trash metal... one end may be a chrome moly something in the pot, another portion the engine block of a 59 chevy...

Sometimes it don't get all mixed up real good during a melt.. it's strong enough for the "desired" product..

01-09-2010, 04:12 PM
Agreed on the trash cast diagnosis. Many of these grates were made out of the tail end remelts from foundries or steel mills. Want some fun? try cutting old double hung window weights, they have about anything in them.

01-09-2010, 06:24 PM
As I thought. I took some care so I wouldn't destroy my bandsaw blade or the carbide fly cutter, and both survived. I guess I was taken in by the relative thickness of the material, hoping to be able to make something substantial out of it.

Maybe this experiment best serves as a reminder to newbies- this kind of scrap isn't worth trying to work with.

01-09-2010, 06:35 PM
Anyway, it was broken at one end, so I figured what the hay, I can cut that part off and re-surface the thing, probably use it as a fixture somehow.

Then there's this other grate- definitely a curbside drain cover, but larger and with very substantial thicknesses all around and in each cross piece. What are my chances of being able to make stuff out of that cast-

I wish I had some advice but unfortunately I can offer no help here however I just had to say that really admire your vision! Being a connoisseur of fine junk myself I just love it when someone can see worth in what others see only as a piece of scrap, the world would be a much better place if more people could think as you do! :)

01-09-2010, 09:21 PM
Thanks, Radkins. I am a scrap hound, and I do like to envision the 'project within'. That results in lots of scrapped projects, but that's ok. Sort of part of the territory, I guess. Not long ago I picked up something from liquidation world, and on my way to the checkout, I met one of the girls who works there. I showed here what I had found and told her what it was going to become. She just smiled and said 'that figures' :)

A few months ago I picked up a bolt cutter and told her it was a pex crimper. Now it is. She's starting to make a point of showing me odd stuff that comes in, wondering what I could dream of making from it-

I'm not so sure the world would be a better place if more people thought like me- maybe there's room for more like me, but too many and the economy would be in the dumpster. :)