clear silicones for molds

From: Glyn Churchman (
Date: Tue Mar 31 1998 - 02:55:10 EEST

This may be a stretch for the purists on this RP BBS but I also know
that some of you do molding as well, so…….
I would like to know what others are experiencing when using the “clear”
silicones for molds. How is mold life and “real world” tear strength?
What is or has been your standard mold material and if you have tested
or switched to a clear what are the benefits? I am not really
interested in watching bubbles move around in a cavity, so is there more
to it than that? I know of Shin-Itsu 1300T, CIBA LST 30-616,
Rhone-Poulenc RTV-1556-57 and Dows’ Silastic T, but our experience with
them is limited. We use Dow M as our baseline machine dispensed
material. We did not need to push our 1-2 clear molds to the max and
wonder if anyone has. We get 30 to over a hundred parts with the Dow M
when we are using the CIBA 6450’S line of materials. We get similar
results with other fast urethanes. I know mold life can vary greatly
depending on tolerances held, complexity, material run in the mold-and
its’chemistry, how long the part stays in the mold, release agents, care
and other magical treatments and incantations that can be employed. I
am wondering if the additional cost of these clear/translucent silicones
infer that they are purer and are possibly more chemical resistant? One
non-clear platinum system we used had almost 35% crystalline silica in
it while the translucent Dow T and clear CIBA silicone have none. I’m
no chemist but there must be some differences.
Are they worth the extra cost?
Glyn Churchman, Prototech, Inc., 972-221-6599/ fax: 221-8579

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