The Shop > Metal Stuff

A Tale of Two Castings

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vtsteam:
Well it can be easily, you just watch the exhaust flare and adjust. I tend favor very slightly toward rich. Not enough to smoke or soot up tools held above to pre-heat (a good idea btw, to ensure there is no moisture on them before plunging into metal). But that wouldn't affect the cardboard carbon, since it's without air under the crucible, and a slight richness in flame wouldn't oxidize it faster anyway.

But imagine: if cardboard would burn anywhere else in the furnace -- which it will instantly -- there's enough oxygen in the fireball even in a neutral flame to burn it anywhere in the furnace that's exposed. Beneath the crucible isn't exposed -- one hopes. Obviously with rough and rounded surfaces that's not a perfect seal. And the furnace bottom wasn't perfectly smooth.

I think that one of the main causes of sticking is that the pasty ceramic crucible glaze and drips of slag move down the outside and find there way to the bottom and "braze" the crucible to what it's standing on. That happens at the perimeter of the crucible bottom, which, because it is necessarily exposed, can't maintain cardboard carbon as a release agent.

Well that's my theory anyway.   :smart:

vtsteam:
Third time's the charm!  :ddb:

This one looks free of flaws, and the sawdust facing sand worked pretty well. I drilled a hole in one of the gates and it drilled easily and produced good-looking gray iron swarf, so I'm hopeful the main casting is free of chill and machinable.

Differences: I did use my new short handled slagging tool after pulling the crucible out of the furnace, and the mold had the 2% sawdust facing sand. The facing was a little dry (I think sawdust draws moisture out of the clay binder), so I lost a little bit of definition from crumbling at the edges of the pattern - thus the small amount of finning at at the parting line. No problem to clean off with an angle grinder.

This casting is only about 7mm thick -- really pleased with how metal filled the mold completely. Surface finish is greatly improved, it looks to be sand inclusion-free -- though not quite up to the shiny casting level yet. More sawdust would undoubtedly help, but there's a tradeoff in bond strength of the facing sand  -- the finning here illustrates that.

tom osselton:
Thatís a beautiful casting! I wonder how long it would have to sit in order to have the sawdust and sand moisture balance out.

krv3000:
just my bit well dune  in the uk leave any bit of steel lying abawt it will soon go rusty one of the old tips regarding small castings was to dig a hole and bury it but make sure you make where you have burred it the other methera it to put it in a bucket and pee on it and leev it to soke  i have never tried the last one but at present i have a set of castings of a Stuart turner   S50  just siting in the garden waiting for spring to cum si i can dig them up lol

vtsteam:
Thanks Tom! :beer: I did another iron pour this afternoon, same pattern (I need 3), I hope it came out as well -- don't know yet because I need to let it cool for 4 hours (I think that's minimum for iron of this size even though it's winter.)

Bob, why would it be good to bury a casting -- or put it in a bucket of pee? What does that do?  :scratch:

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