by paulson games » Mon Dec 05, 2011 10:32 pm
But what type of costs are you incurring for paying for the gas/electric for baking as well as buying the silicon oils? It may be fairly inexpensive for one or two molds, but you're running that oven for hundreds of hours if you're baking 100+ molds multiple times.
For my production molds on simple parts I'm usually getting upwards to 200 pulls from each mold, so with mold release they tend to last way longer than a few dozen pulls. Assuming it's all new material my average mold takes about 12oz so it's not quite $20, I find it easier to run it without baking and just recycle chunks of the old mold. (recycling has cut my silicone costs by about 50-60%)
Most of the wear and dry out will be at the outer surfaces so if you recycle the inner core you can stretch that silicon a long way. Each time you bake it it pulls the oils from the core out to the faces. I would suspect that you probably wouldn't want to recycle old baked molds as their internal oil level will have been significantly depleated.
Edit:
I found this on the tekcast site
10. Mold Life ExtensionBarrier Coating. The use of a barrier coat when casting polyurethanes can greatly extend mold life, in some cases up to 200 percent. The barrier coat should be sprayed into the silicone mold prior to each casting. When the cast part is removed from the mold, the barrier coat becomes the outer skin of the casting. The barrier coat can then be stained or painted, an important feature. Note that this type of barrier coat is different than the barrier coat mentioned in “Techniques to Prevent Inhibition.”
Reconditioning. Reconditioning can be accomplished by burnishing a low viscosity 200 Fluid into the surface. When the mold is to be put back in use, any excess fluid should be removed from the surface. This is necessary to ensure the cast parts will be paintable. Non-wetting or fisheyes can occur on the surface of the cast parts if all excess 200 Fluid is not removed.
Bake-Out. A bake-out is recommended to remove the hardeners, plasticizers and other materials that leech out of the casting materials and are gradually absorbed into silicone molds. A slow, gradual bake-out at 93°C (200°F) for eight hours or a rapid bake-out at 204°C (400°F) for two hours can be used.