The Shop > Metal Stuff
Sawed off cupola
ironman:
vtssteam It is by weight. The coal dust burns and slightly lifts the metal of the sand to give it a smooth surface. Coal dust may be hard to find so you could use other things that burn ie. sawdust or wheat flour.
vtsteam:
Thank you Swarfing, I will look into that for silica sand.
Ironman, would powdered charcoal work? That would be easy to get/make. I'd prefer not to use other things like flour and sawdust that can decompose.
I could carbonize sawdust -- I have quite a bit of that from my homemade sawmill.
awemawson:
Recalling something I read in one of my early foundry books, I think the coal is added to stop 'blistering' where the sand fuses to the cast. If I remember correctly the coal dust breaks down forming a gas layer that cushions the sand from the metal. Also improves surface finish.
If the above is correct powdered charcoal wouldn't work as the gases have already been driven off.
vtsteam:
Thanks awemawson, I think the gas involved is CO2 or CO so any of the above might work.
awemawson:
Google "why is coal added to foundry sand" There are many references to the coal partially burning and off gassing organic compounds - here is one on wikipedia
http://en.wikipedia.org/wiki/Molding_sand
My feeling is charcoal won't work as the majority of the organic stuff has been driven off in the making process.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version