Re: silicon mold, polyurethane resin pressure cast question

First, make sure you keep mold under vacuum for an hour or so when you make it, that should get all the bubbles out. Second, 65 PSI is plenty of pressure for resin. Third, tin ot platinum care has nothing to do with mold life; durometer, tear index, elongation index, etc. do. I use either 18 Shore A or 30 Shore A rubbers and have no problems with either. The softer rubber doesn't last for as many casts (20-30 on average) but that's because I use it for parts with severe undercuts. The other rubber (G-1000 by the way) will give 50-60 really good casts before showing significant wear. I do not use release agent with either rubber. The softer one doesn't work well for multipart molds.

So yes, I think you screwed your mold. Call Polymer Tooling Systems in Pennsylvania and get some G-1000 rubber. Keep it under vacuum until all the bubbles are out. Cast at 60-65 PSI and no higher.

> Hi I did my first pressure casting in a pressure pot @ 80 PSI with > silicone RTV 1621 rubber (rubber was degassed when made, it has 23 > Shore A hardness)...I noticed that end result damaged my mold...it > seems the resin tried to push out in weak spots or areas where there > was a air bubble deep in the rubber... the end result was my resin > piece have several outward points and now the mold seems to have been > comprised b/c of these indentations... Just curious if anyone has any > tips on how I can not have this happen again ?? Maybe I should have > cast at 60 PSI or with a rubber that is Shore A 40 hardness instead or > a platinum cure silicone instead ? > > Any help would be appreciated ! > > Thanks, > > Jack
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Ron
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