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Oil fired crucible furnace

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awemawson:
I was thinking the same as I typed that. When the Traub lathe is finally tucked up and put to bed, maybe that'll be my next project - it's time I got round to it. I even put up a fireproof extension to house it then filled it with other stuff   :bang:

Mayhem:
What NeoTech said (with pictures, lots of pictures).

vtsteam:
Yes I'd like to see that, too.

Just as an explanation of what I've done so far and why, I'm going to quote here from C.W. Ammen's "The Complete Handbook of Sand Casting" 1979:

"Melting cast iron in a crucible is actually so simple, it's a wonder more people don't do it.

"The usual practice incorporates clay and graphite crucibles. The iron, free from contaminants (anything other than iron) is broken into small pieces, the size of walnuts or a little larger. The crucible is charged (filled) with alternate layers of charcoal and iron, to which is added about two handfuls of soda ash. The soda ash can be placed either below or on top of the charge. After you have gone this far with this process, cover the crucible with an old crucible bottom and place a circular piece of corrugated cardboard between the base and support block to prevent the crucible from sticking. Start the furnace with the flame set to slightly oxidizing.. Gray iron melts at about 2327 degrees Fahrenheit. Although this figure may look large compared to that for the melting point of brass, you will find that the layers of charcoal promote rapid melting that can be done in not much more than the time it takes for brass. With a little practice you can produce high grade iron castings. (Old cast-iron steam radiators can be easily broken up to produce an excellent source of very fluid iron.)"

My first casting, and the most successful so far, followed this procedure exactly - including making a clay cover for the recommended "clay/graphite" crucible and incorporating charcoal, and soda ash, as well as the radiator source metal. Unfortunately the soda ash seemed to soften the crucible after only a couple of melts.

I own and have read probably 10 books on casting, including the extensive online US naval casting manual. Almost all provide alternate and even opposing views on all aspects of casting, including casting flaws, sand recipes, etc.

It's clear to me that the truest line above is "With a little practice you can produce high grade iron castings."

A little practice....that's what's more commonly called experience. There are no absolute recipes for success. Only a process towards it, experience, where you learn and discover the special requirements of your own equipment and materials and your own capabilities.

tom osselton:
 I know I haven't cast anything but I have a theory :  The pics that you posted both look similar, as for your pic of the flow of the metal I think it is the position of the riser. I believe that the metal travels along the path you say but when they meet some goes into the riser (at a right angle) and some of it will go towards the center, the left side will circle clockwise and the right counterclockwise putting the defects basicaly in the same spot on both castings. You might want to try it with one gate and riser moving the riser to a corner so the flow is funneled into it. If you still want to use two gates you could have a main at the farthest point and another not as thick so it feeds at a slower rate. Like you said there are a lot of casting books but I can't  remember any that talked about the placement of sprue's or risers or the hydrodynamics that take place. I'd be interested to get Ironman's thought on this.

Tom

vtsteam:
Tom, my own understanding:

The main function of the riser is to feed metal to prevent shrink depressions or cavities. I haven't had a shrinkage problem since I started using one. But the riser does not reduce blow holes or slag inclusions.

Blow holes can be reduced by better sand permeability, lower sand moisture content, and venting.

Slag inclusions can be reduced by slagging the melt and gating. The ideal there is to prevent slag from entering the mold in the first place. Though once it is in a mold, gating can help trap it.

Excess or difficult slag in the melt can prevent complete slagging before the pour. Difficult slag can come from the metal used, excessively oxidizing furnace atmosphere, slow melting, and, in my opinion, the crucible materials.

Slag can be made easier to remove by fluxing the melt. But flux can deteriorate crucibles.

So, all of the above need to be juggled in relation to the materials and furnace you have, to give you the quality of casting you expect.

Not every casting purpose requires a perfectly cast part. I've seen casting flaws in commercial products, and in other individuals' work. A machining allowance is, in a sense, a way of dealing with the surface flaws and draft which are a necessary result of sand casting.

But in trying to learn how to cast iron, I want to try to achieve a no flaw casting, so I at least know the subject better. Or as well as I can.

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