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Sawed off cupola

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vtsteam:
CO2 and CO are organic compounds that are off-gassed during partial combustion of coal. And charcoal.

Graphite has recently come into favor in commercial practice for replacing sea coal to reduce unwanted emissions. Graphite is pure carbon.

Most references I found online said seacoal was used to produce a reducing atmosphere. There was not specific mention of the need for VOCs to do that, just a reducing atmosphere,.....which a mix of CO2 and CO would produce, since they have absorbed and continue to actively absorb oxygen.

I'd still like to hear from Ironman on this, or anyone who has actual experience using charcoal in greensand for iron casting.

ironman:
vtsteam Charcoal will not do anything because as awemawson has said it burns and forms a gas  layer.

I used to add coal dust to my sand after every melt but I don't do it anymore. Each time the cast iron burns the coal dust it turns to coke which is an inert byproduct that I don't need or want in my sand. The sand becomes very brittle after a while and so more bentonite has to be added to give the sand more strength.

 I now make a facing sand with coal dust and use it to cover the pattern only so the sand lasts for many years. When I added coal dust to the sand after every melt I would throw out the sand about every 12 months.

If you want to don't use any additives and just wire brush or sand blast the castings

vtsteam:
Thanks Ironman, so coal only in the facing sand. That is easier for me to come by, since I have some coal that I can pulverize, and I wouldn't need much of it

I'm still confused about the charcoal since all of the online talk is that you want a reducing layer of gas between the metal and mold surface to get a good finish, and that seacoal produces it. But charcoal also seems to produce it, but now it is seen as a negative. Maybe because it burns more easily, and produces too much gas? Would reducing the amount help that?

Anyway experience is more important than theory, and you have that, more than most people doing iron on the scale we are interested in. So I won't add coal or charcoal to the molding sand, but only to facing sand.

I suppose I could do some small batch experiments with various amounts of ingredients just to satisfy my curiosity about all of the above. I also have some plumbago (graphite) that I could try. Since it doesn't have to be in my main casting sand, there's less of a concern that I'm going to wreck it all by mixing in the wrong ingredients right now at the start.

vtsteam:
One more accidental addition to the gear....the propane torch I'm experimenting with in another thread -- trying to get it to braze -- no good for that so far, but would probably work fine as a ladle heater.

ironman:
I was about to suggest doing experiments to see what works and what does'nt, that is  the way I learnt. We all come from different parts of the world so what we use may not the same and give a different result.

I have heard about this method but never tried it, is using CO2 gas from a bottle and filling up the mold so there is no oxygen left. The castings have a nice colour and skin because there is no air to oxidize the surface.

With your ladle heater it might be easier to place the ladle on top of your exhaust vent to recover the waste heat coming from your furnace. It also means you do not waste propane heating your ladle. I wanted to try this method with my own cupola but my the ladle was too heavy to lift to the top so I scrapped the idea because of safety concerns.

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