by Peter Kunisch
I do not make any recommendations at any time. I have used this material and I am satisfied. Others make molding silicone as well and I have tried them. It should be noted that Micro-Mark had a molding flexible foam but no longer stock it. I have talked to the Rep and was told that they may at a later date have it again but to date it is not in their catalog. A good instruction sheet on “How to build a mold” is included with each Silicone set.
- #82083 Liquid Silicone Rubber for making molds: I use this stuff, it works well and has a 4 hours cure time.
- #80475 Rubber to Rubber Mold Release: needed to make 2 part molds, first you make one half and after curing you paint it with this mold release and pour and cure the second half.
- #82664 Rubber to Resin Mold Release: needed so that the resin or foam doesn’t stick. Other companies have it as well.
FlexFoam-it X flexible foam is from Smooth-On. It will expand up to 10 times its volume. In an open mold, I use a topper plate (Plexiglas or Lexan) with a vent hole. Make sure that you use a mold release spray. First I pour the mix until it fills about 25% of the mold but the full length of the part. Then I place the topper plate on the mold, holding the vent hole shut (use a pencil) until I see the foam expanded to fill the mold. I now open the vent and let the excess foam bubble out of the hole. To hold the topper down during curing, I place 1lb. lead weights (2) on the topper. Do not open too soon rather give added time. After removing from mold but attached to the topper, let it be for one or two hours. I you touch it too soon, it will shrink and shrivel like a soufflé. After full cure, I use a knife to lift the part of the topper cutting the vent (sprue).
It is good for many applications but I wish it would be more dense. In a high pressure mold it could be cured to a much higher density but I do not have the equipment or the patience.
I have used many different moldable plastics and for different uses Smooth-on has many and a good example is my Arado airplane. The body and floats are flexible foam, the wings are light weight rigid foam, the prop and struts are solid resin.