Reply To: Furnace: cast iron from ferrous tin cans?

[PatJParticipant @patj87806]

Posted by Bazyle on 20/08/2022 22:52:10:

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.

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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