Monday, October 21, 2013

Casting Grey Iron

This past Friday, I cast iron. A former student had a ceramic shell mold he wanted to cast in iron. Could he use one of our foundry furnaces? Yes, he could. All he need do is provide the crucible and the metal. Would we be able to cast at such a high temperature? Yes, we would. Our furnaces can make it up to temperature to cast iron, which, on the high end for pouring, is around 2650F.

My MIFCO B-150 furnace manual even has a chapter on casting iron. So, he shows the week before with a clay/graphite crucible and a couple of old steam radiators. I anneal the crucible in our kiln to red heat, to cure it nice and proper. But I send him away with the radiators to burn the paint off them, which obviously, given the thickness and age, has lead paint in there someplace. I don't want to know how or where he burns it off, it just can't be here. So, environmental no-no number one committed. I then tell him to break up the radiators with a sledge hammer, which he does.

Friday, he arrives with two pickle buckets filled with cast iron pieces. We load the crucible, add in two pounds of graphite, and crank up the furnace. Slowly, over the next two and a half hours, we load pieces into the crucible. The interior of the furnace quickly becomes impossible to look into with the naked eye. Environmental no-no number two: we are going through a huge amount of natural gas to heat up some fifty pounds of iron. Had we done bronze, we would have cast around 150 lbs in the same amount of time.

Problem: I cannot use our pyrometric lance on the molten metal to gauge the temperature. The tip of my lance, made of high temperature ceramic and platinum alloy, will melt and be destroyed if I do so. I am going to have to eyeball it. A difficult task to judge color while wearing cobalt blue welder's glasses.

Well, I let it cook, and check it now and again. Here's the weird thing. It's the color and brightness of the sun in that furnace, well not really, but seems like it. And I notice, with the swirling of the exhaust gases that a molten yellow fluffy egg white meringue is flopping around in there. It looks exactly like that. Wow.

So, my eyeball solution was to take a pencil rod of stainless, stick it down into the crucible, and pull it out. The first time I did it, the merinque (slag) stuck to the rod, and it looked like a red hot Q-tip. I banged the rod on the floor, and the slag broke off. I waited about ten minutes and repeated the procedure, and this time, there was red hot merinque ten inches up on the rod, and just a few yellow-white drops down by the tip of the bare rod. That meant, the rod had not wetted enough to attract molten metal, and the yellow drops were the kind of iron that we wanted.

After placing the pre-heated mold in the pouring box filled with sand, we pulled the crucible out of the furnace. The crucible was yellow-white and sending off a shower of sparks just like a sparkler. The meringue slag quickly cooled to red hot and looked exactly like the top of a key lime pie, but browned. I smashed through the slag to the get to the metal, added a few ounces of flux to make it less plastic (flux is equal parts washing and baking soda). The metal and flux fizzed up rather alarmingly, but only for a moment, and then we poured the metal.

You know, when working with bronze, it's all much cleaner and simpler - heat up, skim, pour. And the metal is gorgeous, but a pretty, kind of precious, kind of gorgeous. The metal is yellow-white to yellow-orange, but there is a nacreous quality to it, an iridescence, like mother-of-pearl. It's easy to get lost in it, and forget what you are doing and just watch the geometric cells form on the surface as the metal convects.

But with molten iron, it is a solid honest no-nonsense pure yellow-white about it. None of this fairy dust and glitter shit that bronze pulls. It says, "We got job to do and you better do it, and quick fucking around!"

So we did. The mold filled up very nicely indeed.

Sorry no pictures of the pour, but once you've seen molten poured, it's all about the same. Not happy with that? Here you go:

We had perhaps a third of a crucible left. which we dumped into the pouring box. The metal displaced the sand, sank down, and (later we found out) welded itself to the sheet metal bottom.
7 lbs of cast iron welded to the floor of the box

We had to cut the iron out of the box

Leftover stuff from the pour and cut from the mold

(It should be noted, having some knowledge of just how much iron loves carbon, that molten iron and steel are like the worst kind of acid when it comes to working on the flesh. I therefore made it very plain from the beginning that if ANYTHING went wrong, we were to RUN AWAY, and not worry about the equipment and facilities. In retrospect, it's a very good thing we came through okay. All in all, a very pleasing first time encounter with quasi-catastrophe. Everything went better than well, considering we knew only a little of what we were doing).


  1. beautiful handmade corn knives fall within this temperature range, fine edged weapons are an inevitable blip on your event horizon....,

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