Furnace: cast iron from ferrous tin cans?

I'm wondering if I could use tins of baked beans and such along with other iron scrap in my furnace to make cast iron?

I guess my main question is what they are made of? They're magnetic so I'm guessing they're mostly iron.

They are mild-steel, so "mostly iron" in the way all steels are "mostly iron", in this case iron plus a trace of carbon. (Other grades of steel are that alloy plus traces of other metals.)

If you succeeded in melting them without losing a lot of the metal by oxidation, and I think it requires a lot higher melting-point than for cast-iron, just to add to the fun, your resulting castings would be of steel. Not cast-iron.

You'd need a heck of a lot of "tins" to yield a useful volume of steel, too. Try calculating the volume of steel in a standard one, which is proportioned so as to give the required volume of contents with the minimum area of very thin sheet-steel. You may neglect the stiffening corrugations.

(That latter calculation - of area for volume - sometimes pops up in school mathematics text-books, as an application of Calculus.)

Cast-iron is iron with a higher proportion of carbon diffused through it than has mild-steel.

The refiners who melt vast tonnages of mixed iron and steel of all grades all mixed up have metallurgical laboratories in which they can analyse the melt, purify and modify it as required. I would think this a challenge in a home foundry!

If you want to make your own iron castings you are best using scrap cast-iron machinery parts as your raw material.

Not my first choice, they are tin plated. The big boys get the tin off chemically. Not sure what happens if you just melt them. You'll find plenty of scrap steel or even iron if you look around

Is the steel still tin-plated? I thought it was all some sort of lacquer now: the insides rust quite rapidly once opened and part-emptied; hence the advice on the label to transfer uneaten contents to a non-metallic container for storing in the fridge.

Lacquer would simply burn away. Tin might boil off well before the steel is anywhere near its melting-point.

Intensely heating such thin steel though risks losing a lot of it by oxidation, unless the furnace has a reducing atmosphere.

According to wikepedia cans are still tin plated. Those containing acidic foods are lacquered to stop the tin being attacked by the acid.

There is generally an abundance of scrap iron laying around.

I use electrical motor end bells, and they are very nice gray iron.

I tried melting 1/2" diameter mild steel rods in my furnace, with my oil burner, but after an hour on the highest heat, they were red hot, but still very solid.

I think the cans would melt, but you would have to submerge them in a pool of molten iron, making sure that every bit of moisture was out of the cans (such as baking the cans at 400 F for about an hour).

I am not sure raw cans would melt on their own, or perhaps with lots of oxidation.

I think the tin would vanish quickly at iron temperatures, or perhaps just mix in with the melt.

I personally would not use cans, just due to the moisture hazard.

And scrap iron can be rusty, or painted, and you don't have to clean that off before you melt the iron, since all that comes off as slag. You do have to make sure your scrap is very dry before you drop it into molten metal.

I hold my scrap pieces in tongs in the exhaust stream of the furnace for about 30 seconds per piece, to drive off any residual moisture.

The slightest amount of moisture (even if you can't see the moisture) will cause a violent reaction if dropped into molten iron.

Good luck.

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I was once invited to watch a pour of cast iron at an engineers a couple of years ago. He added glass, bits of broken bottles, to his crucible. He was advised to do it by a foundryman. Apparently the molten glass acts like a magnet to attract a lot of the dross. He used brake rotors, disc brakes, for his scrap. They must have been from a lorry or railway train by the looks of them.

Are ‘tins’ not coated with shellac, or similar, these days? The last time I went round a can factory, that is what they were using. Tin is an expensive commodity, these days. Lack of a really permanent coating is likely partly why tinned goods have a expiry date on all items.?

Completely forget cans, nails, bits of bar, springs, anything that looks like it was once a round or rectangular bar as they will be steel that has a much higher melting point than cast iron. If you can't tell cast iron just by looking at it step back for a few months and learn the difference. There have been quite a few threads on this forum even in the last year about casting. Find the search engine and have a nice long read.

Food cans are made of 'Dead Mild-Steel', which is almost entirely Iron with a smidge of Carbon. Dead Mild-Steel is slightly weaker than the usual structural mild-steels, but being more ductile, is good for being shaped with a press. Cheap, cuts easily, and can be tinned, soldered and folded.

The melting point of mild-steel is high, but I guess feeding strips into a pot of molten cast-iron would melt them. As adding what's close to pure Iron to the mix would reduce the Carbon percentage, it might be necessary add some Carbon if a high percentage of cans were added.

I think the Tin will end up in the alloy as well, and alter the properties of the cast-iron. Wikipedia says:

Chromium is added in small amounts to reduce free graphite, produce chill, and because it is a powerful carbide stabilizer; nickel is often added in conjunction. A small amount of tin can be added as a substitute for 0.5% chromium.

So although Tin in cast-iron isn't evil, the chill effect is slightly worrying if the castings are going to be machined, Try it and see.

Cast-iron is interesting because it ranges from really nasty to high-end. At least 30 cast-irons are made to a tight specification, quite different from what's knocked out in a jobbing foundry. For rough work cast-iron can be full of impurities: all that matters is it melts and flows. Old sash window weights and modern exercise bell-bars are notoriously horrible. At the other end of the spectrum there are many accurately specified cast-irons used for high-tech purposes.

For amateur purposes, I guess the goal is to make cast-iron significantly better than the worst a jobbing foundry would do but there's no need to fuss with exact proportions. Perhaps PatJ could comment, but I think he gets good results by selecting the metal he's going to melt rather than tossing random scrap into the pot. Clutch bell-housings rather than tin cans and old lamp posts!

Professional recycling is a different game. I believe the Tin coating is more valuable than the steel!

Dave

DO NOT waste your time or fuel trying to melt cans ! There is plenty of scrap cast iron available, most garages will have a pile of old brake discs, any thing that was fairly thin will be good. You will be looking at a temperature of about 1550*c white heat, tin vapourises at about 2500*c, only spot heats will reach this - may be ! There was an article in ME several years ago about making cast iron from steel. Noel.

Edited By noel shelley on 20/08/2022 10:28:53

I was going to suggest going to a scrapyard and buying some cast iron, but Noel's garage brake discs is an even easier source.

If you get a brake disc, bell housing or exhaust manifold whack it with a sledge hammer, If it bends rather than breaks or the fracture surface is not dull grey but shiny you have a ductile or spheroidal casting. Still potentially useable but will have different properties to grey iron. And yes, some special cast irons do bend - that's why they are called ductile.

Using glass on top of an iron melt achieves nothing (as far as any knowledge I have on that topic).

The slag from iron is easily skimmed off, and no additives are needed.

One large foundry (Lodge I think, the cast iron skillet folks) uses vermiculite as a slag coagulant, and they dump it on top of the melt, and then roll a rod in it, to wrap the slag around the rod, where it can be dragged out.

With a crucible melt, the crucible is not very large, and the area to be deslagged is small, so one or two passes with a skimmer is all it takes to remove the slag.

Iron slag is easily separated from the molten iron, and there is a very clear line of demarcation between the two.

I have seen more than one person who uses a method or material, and they create good castings, and thus they become convinced that the method/material that they used is the reason they have good castings.

Often the method or material that folks use has nothing to do with making a good casting, and they get good castings because the method or material had no effect on the melt.

One has to use a blind test to determine if something actually affects the melt, and often I see the wedge test used. There is another test that measures the fluidity of the melt.

I don't use any type of testing on my iron, but instead rely on the fact that my iron castings have no internal or external flaws, and no hard spots anywhere in the casting.

The art-iron folks sometimes use calcuim carbonate in their melts, I think for slag control and fluidity, but I don't use that. I never use any additive that is not required, ie: I don't try to fix problems that I don't have.

The instance I have heard about when using glass on top of a melt is with brass/bronze that has significant amounts of zinc in it.

The zinc tends to burn off before a brass melt is at pour temperature, and that is problematic.

My solution is to melt bronze mixtures that have little or no zinc in them.

If one does use a glass cover, one must be sure to skim it all off, else the glass will flow with the molten metal, just as slag will, and you will have glass inclusions in your casting.

.

Edited By PatJ on 20/08/2022 23:33:13

I have heard various comments on the suitability of disk brake rotors for making iron castings.

I know of one individual who uses disk rotors exclusively, but I have not had an opportunity to test any of his castings.

He does add the extra step of annealing (I think that is the correct term) all of his iron castings in a kiln.

I have never had to anneal any of my castings when using electric motor end bell housings.

Ferrosilicon can also improve the machinability of ductile iron, when ductile iron is used as scrap (so I have heard).

The amount of ferrosilicon that is added to an iron melt is critical.

Too much ferro and you get excessive shrinkage and hot tears.

The correct amount of ferrrosilicon improved fluidity, and prevents hard spots in thin sections of castings.

The correct amount of ferrosilicon to be used with iron is very small, such as 0.04-0.06 oz/lb of iron.

I add this amount of ferrosilicon to all my iron castings, but you only really need it for castings that are thinner than about 3/4".

As I understand it, when you melt ductile iron, it basically reverts back to gray iron (perhaps not entirely).

The difference between ductile iron and gray iron is the distribution of the graphite.

Chilled thin gray iron castings are basically the hardness of tool steel, and cannot be drilled with a normal twist drill.

Another secret to good machinable iron castings is to let the casting cool in the mold overnight, and cool as slowly as possible.

Aluminum 356 benefits from a water quench, but you never want to cool iron castings quickly, unless hardness is desired in the casting, such as in a high wear situation (such as the teeth on an earth moving bucket).

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I have read some old casting books, and also John Campbell's book on castings, and the No.1 rule of making quality castings is to start with quality scrap that is of a known composition.

Items like window sash weights are made from the discards from the casting process, and the old book specifically mentions avoiding junk metal like window sash weights at all cost.

I have heard that cast iron radiators should also be avoided in engine castings, due to the phosporus, but then I saw a fellow cast a model V-8 engine block in gray iron made from radiator iron.

The phosphorus gives the iron excellent fluidity, at the expense of I think strength.

It would appear that on a model engine scale, using phosphorus radiator iron does work ok, but I am not sure how you would test what "ok" is.

The V-8 does function well.

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It is an odd thing, but I cannot melt 1/2" mild steel rods in my crucible steel furnace.

But if I use a 1/2" mild steel rod as a skimmer, or stirring rod, and stir the melt while it is at pour temperature (pour temperature is between 2,500 and 2,600 F), if I leave the rod in the melt for more than about 30 seconds, the end of the rod almost completely melts off.

Someone mentioned that there is a chemical reaction between the mild steel rod and the molten iron, which is why the steel melts.

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Pure Iron melts at 1538°C, which requires a hot furnace. Adding a little Carbon (mild-steel is 0.05 to 0.25% Carbon) drops the melting point slightly to about 1500°C. Steel also requires a hot furnace. Adding a lot more Carbon (Cast-Iron is 2.5 to 5% Carbon) drops the melting point to about 1150°C, which can be achieved by a relatively low-tech furnace.

When a mild-steel rod stirs molten iron, Carbon in the Cast-Iron migrates into the rod, causing the melting point at the rod's surface to drop sufficient to melt in the mix.

Not a chemical reaction, it's one thing dissolving in another. Same phenomenon as when Common Salt is added to ice. The melting point at the junction drops and the ice melts into a solution of common salt in water. Not chemical because the salt and water are unchanged.

Ice/salt and Iron/carbon are examples of solutions that absorb heat. Thus a furnace requires more heat (fuel and air) to maintain the temperature at melting point as steel is dissolved in it. Other solutions release energy, such as adding water to concentrated Sulphuric Acid. Here the problem is removing heat, not providing it.

On the subject of Glass, plain glass is almost pure Silicon Dioxide. Up to 3% Silicon can be added to Cast-Iron, so that when the iron cools and solidifies Carbon comes out of solution first,. This creates a popular cast-iron (Gray) with a lot of free Graphite in it. Gray casts and machines well, and is a cheap way of providing bearings, but it's brittle with low tensile strength. My guess is glass was used as much to add Silicon as to remove impurities. And recycled glass must be cheaper than pure Silicon and cleaner and drier than sand.

Dave

Edited By SillyOldDuffer on 21/08/2022 11:15:03

Dave-

That is a great explanation.

Thanks for that.

Pat j