The Shop > Metal Stuff
Oil fired crucible furnace
vtsteam:
Today I decided to "use up" my last small crucible before going to the new A6 Salamander Super.
Instead of trying to pour the same pattern again, I decided to just make ingots. And to do that I would use my old broken up radiator material, rather than cleaner thicker iron.
And I decided to use flux, since i didn't care about the crucible. I would do two melts, one with oyster shell, in the form of the ground up powder they feed chickens. it is supposed to be calcium carbonate -- as is limestone or agricultural lime.
And for the second melt, I would go back to good old sodium carbonate (soda ash).
This would at least do something useful with the old crucible and convert the radiator scrap into clean metal, plus give me a comparison with the two fluxes.
Well actually, there was no cmparison. The oyster shell did little to liquify the slag -- it was still really bad -- black cottage cheese taking up half the melt, and sticking tightly to the crucible. In fact after the crucible cooled I could see a few places where it insulated itself in a chunk and hadn't even melted. I don't actually know what that stuff is made of -- could have concrete floor sweepings in it -- who knows. It's just grit for the hens.
But since it didn't all melt, and thinking I might not have enough furnace heat, I decided to increase the air pressure to the burner nozzle. This had been at 45 psi lately, and I upped it to 60 psi.
That really did seem to make a difference -- probably atomized the fuel better, because I noticed that I actually ended up using less throttle, even thought there was more heat and flame height. And the flame burned cleaner -- quite visibly better.
So, second trial with the sodium carbonate went MUCH better -- a faster melt by about 20% but the slag was totally different. I was a bit cautious with the soda ash flux because it's supposed to be much more destructive to crucibles -- I used about an ounce. I'd used 2 ounces of calcium carbonate earlier.
But what a difference -- the slag was easily scooped off in one piece to leave a pool of clean shiny metal in the pot. While I won't say it liquified the slag, it did compact it into a single "chewey" crust that I could scoop off with a spoon. It was also much lighter in weight (less contained iron).
All in all, just what I would have liked in a pour.
So, it looks like the radiator iron can be used, but it definitely needs a flux to slag well. And it probably should be poured into ingots before use to clean it up.
Next pour will be with the new crucible....
vtsteam:
tom osselton:
Looks good!
vtsteam:
--- Quote from: tom osselton on July 31, 2013, 08:03:46 AM --- snip..... 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.
--- End quote ---
Tom, I forgot to answer this part of your earlier question -- most foundry books do talk about risers -- Terry Aspin's are very good casting books in general. Fewer talk about sprue placement. However, there is a lot of hands on specific placements in any of the machine building books that Gingery wrote -- most have 20 castings or more to build and all show sprue and riser placements for each casting,with notes and instructions where needed. These are the most complete and accurate of this type of thing because it is very specific per pour, and is tested to work, rather than generalized theory.
For detailed general/theoretical/technical discussions of placement shapes and sizes of sprues, risers, and gates, the US Navy Foundry Manual (available online here: http://www.hnsa.org/doc/foundry/ ) and Steve Chastain's Metal Casting: A Sand Casting Manual for the Small Foundry Vol 2. both go into it.
As usual with foundry books, however, you will find disagreement and inconsistency, or just downright impractical information for a small home metal casting operations. Technical books provide suggestions, but practice must prove their usefulness in real life in specific cases with specific materials and specific furnaces.
vtsteam:
Here is a comparison of the slag scraped from the melt before pouring radiator metal when fluxed with, left, ground oyster shell (calcium carbonate), and right, soda ash (sodium carbonate).
Besides the roughness of the slag on the left, notice the white specks of unmelted shell. The right hand slag is glass-like and iridescent -- not metallic in color, and weighs less than the slag on the left. The slag on the left is only part of what was removed, while the slag on the right was the full amount, which scooped off in one swipe.
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