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Where to get the base metal, specifically iron, for casting?

Q

qualitymachinetools

Stainless
Joined
Nov 18, 2004
Location
McDonald, Pennsylvania
I was at a foundry the other day, talking about having some castings made. I really did not see any raw material there, but a lot of finished products were there, so they are working. Some of these castings were 1000 pounds or larger, so its not like they could have been hiding it in a closet.
Nothing I could see, except maybe some piles out back which looked to me like what they would haul off and put in the dump.
What am I missing? Do they actually make their own iron as most foundries? Ir have it brought in as material, melt it, then pour it?
Not trying to sound stupid, and I have been around metal and machining all my life, but not really ever into much casting. Its probably something I should know.
I was too afraid to ask at the foundry, I hate to sound too dumb in person.
 
There is pig iron, or used to be, of MULTIPLE flavors. There is graded and sorted scrap cast ron, and graded and sorted STEEL scrap.

Pig is new. Used to be made largely in Blast Furnaces

All of this stuff is apt to be stored outside.

Any steel melted in a cast iron melting process completely loses its "steelness" and just becomes more cast iron. After all, "steel" is primarily iron.

Read it this way. In the old days, multiple varieties of pig was the norm with some scrap or foundry returns.

It is now mostly scrap, possibly some pig, and compounds to make the result what you want - such as ferro silicon

It is entirely feasible today to take a bunch of channel steel scrap, and make high grade ductile (nodular) cast iron from it - or with a few less additions and controls, plain ASTM A48 Class 30 gray iron.

John
 
John
Steel melts at about 1700dgr C and does not loose its steelness You get cast steel It does not become more cast iron which melts at about 1300dgr C
In electric ovens nowadays they often melt steel(sheetmetal St38) scrap and then add carbon(amongst others) to make it cast iron That can be done because in a induction oven it is simple to reach 1700dgr C This temperature can not or difficult be reached in a cupola oven There you need pig iron or cast iron scrapp
Peter
 
We could do with a little more multiplicity in language ablity ourselves. :D

I salute those Europeans that do us the great honor of communcating in our tongue.


John
 
John
You make me grab for the dictionary

Peter
 
An 83 year old machinist I know, ran a foundry in the 1950's locally in what was once a small town far from the industrial centers.

His main source of iron scrap was old steam engines which he used to shatter with gelignite. Over the years he built a centrifugal iron water pipe casting machine and was able to out-compete a very large pipe supplier that cast their pipes in green sand but had to ship their pipes in via sea. He supplied water pipes to the local council for most of this town's water supply at the time and there would still be some of these pipes in use.

The furnace ran most efficiently when fully charged with iron so he used to cast iron pipes to make up a full load when there was an excess capacity


His small furnace, which is still in use today:
http://www.turbofast.com.au/astrotel/furnace1.html

It's no good for melting steel as it's owner tells me the steel ignites and "foams up and sprays sparks everywhere" all you can do is take the crucible outside and let it burn out. Years ago this guy melted a batch of cast mower base plates and one turned out the be magnesium alloy not the usual aluminium this particular mower manufacturer normally used.

He got pretty good at sorting out the magnesium after that.
 
Qualitymachinetools,

thats a good question - I had assumed they used scrap cast iron (engine blocks etc), but on second thoughts.... a friend of mine owns a good-sized bronze casting foundry (for art work), they are very particular about raw material and only use new ingots of the silicone bronze they have found is best. (It pours well and welds without cracking).The only scrap comes from previous pours (risers etc. that get cut off), but definitely nothing unknown goes into the crucible. The ingots come by the pallet load from a non-ferrous specialist supplier.

So now I am wondering if cast iron foundries are just as careful, and possibly use only known raw materials (I am talking about commercial foundries). I can imagine in a large scale foundry they could test and alter the make-up of a each pour, (I have seen this done in steel making) but a small foundry might find it necessary to use only new or known material?

John or others, is it possible to buy a pallet of cast iron in ingot form just as you can buy non-ferrous metals eg. aluminium, bronze etc? Or what form is it supplied in?
 
As is well known, not many blast furnaces are still in operation making pig iron in whatever composition the foundryman could desire - as was the case long ago.

You can buy pig iron in the USA at such places as Tennessee Coal, Iron, and Railroad Company. I do not know if the many varieties of the old days are still aorund. They stated recently that they have booked orders totaling 450,000 tons.

Modern foundrymen have to make do with what is available and still make the castings meet specs.

I am sure they still pay attention to the cast iron scrap's former use. The reason for this is chemistry HAS TO CHANGE from thick to thin , light to heavy, strong to not so strong.

He has to be aware of what constituents are being lost in the melting process, and he has to know how to make up for their loss.

In the old days this was done with close attention to pig chemistry, close attention to what scrap was being charged, and then resorting to maybe a little ferro silicon added before the pour.

These days it cannot be as easy a proposition assuming pig of limited choice chemistry, so so scrap and plenty a steel scrap which is sort of a fixed chemistry item due to very little in it other than iron.

A good iron casting has to be CORRECT in silicon, sulphur, phosphorous, manganese, combined carbon and total carbon.

He has to make his ingredients right with multiple compounds that simply did not exist in the old days.

John
 
A bunch of us toured a mini-mill in Seattle that makes rebar and the like (low-grade steel). It was an amazing place: in comes scrap metal (stored in huge piles in a storage area) and out comes rebar and the like with very few people. What they seem to do is do a melt (I vaguely recall 120 tons) and then check the chemical composition. Then they add whatever they need to meet the spec of whatever they are making. I guess that this defines what low-grade is - the spec has to be loose enought that random junk pulled from the yard using a huge magnet can be turned into something useful.

Presumably, higher grade castings must have higher standards.

Cheers,
Bob Welland
 
as to how materials are purified
Click to expand...
Fairly easy. At around 2700° F. to 3000° F., the iron melts (steel too if sufficient carbon, such as cast iron scrap is present), the rust and trash goes into the slag bath and the small percentage constituents are either lost or add slightly to the needed end result.

If steel, the tiny bit of carbon is just added to the much larger percentage of carbon wanted in the cast iron.

Some of the Manganese is recovered and added to the wanted precentage of that element.

What is left is incinerated or becomes part of the slag.

John
 
Some impurities must be effectively impossible to remove from the melt, right?

The scrap industry is credited with 10,000 detections of radioactive scrap before it got in the mix; must be a little hard to get it out.

http://www.epa.gov/rpdweb00/source-reduction-management/international.html

Was looking for the story of lawn furniture made in Mexico from scrap including old medical irradiation internals; the chairs supposedly set off alarms when delivered to a power plant rec center. Might just be an urban myth.

Eventually, why wouldn't all recycled melt be some random witches' brew of various elements? At least the ones that melt roughly at iron temps.
 
:D
Eventually, why wouldn't all recycled melt be some random witches' brew of various elements?
Click to expand...
No.

For the reason that beyond "traces", any significant amount of things that were not supposed to be there would render the material not only out of spec., but incapable of doing the job for which it was bought.

Something as simple as too little silicon can make cast iron too hard to machine, or too much sulphur can make it both weak and too hard to machine.

John
 
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