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| Foundry hints and tips for a noob on a budget, please! |
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| vtsteam:
Also, David, you asked about a translation of "drywall compound" or "mud" (US) for lost foam casting -- a look-up revealed it is: "Joint filler” in the UK “Drywall filler” in Canada “Fugenmasse” in Germany “Joint finish” in Australia “Voegenmiddel” in Holland “Wall putty” in India “Pasta de Tablayesero” in Guatemala I've done both lost foam and greensand casting, and I much prefer the latter. But there are some things you can do with lost foam that are complicated or impossible to do with greensand. Zero draft requirement and undercuts and complex shapes are no problem in lost foam. But the pour temp must be very high, thin sections tend to choke, pattern preparation is time consuming (it has to be dipped and then dry thoroughly), sprue usage and aluminum waste tends to be high because of contamination by dry sand, plaster and foam. If a pour fails, you need to make a complete new pattern, coat it and dry it again. With a regular greensand pattern, you can ram up and re-cast immediately if a pour is bad. While it's often stated that lost foam is ideal for one-off complex stuff, the problem is that often it is not actually one-off -- since the first pour may not be perfect, and then you are faced with making a new complex pattern. It's fun and everybody who likes casting should try it. But I find myself returning to regular pattern work where possible. But then I enjoy making wood patterns. I also tend to re-use my wooden patterns -- sometimes modifying them for parts built years later -- sometimes adding loose pieces, etc. I consider patterns part of a permanent library of casting tools. Oh, and no, don't coat the foam with wax. You're confusing lost foam with lost wax casting. Adding wax will greatly increase the amount of flammable material, and evolved gas -- possibly even to a dangerous level. In lost wax casting, the wax is melted out of a mold by baking before casting. In lost foam casting, the heat of the melt burns up the foam -- but to work, this depends on a very small amount of burnable material, since foam is mostly air. Increasing the amount of burnable material isn't a good idea. Surface finish on a lost foam casting tends to be excellent anyway, since the actual molding surface is the wallboard plaster shell. |
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