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Dow corning silastic RTV molds


#1

Was: [Looking4] Vulcanizer

Just a clarification:

Dow Corning Silastic J RTV Silicone mold color is GREEN. It is
firmer than Silastic E. While it has good tear strength for silicone
RTV molding materials, it is not as strong as a vulcanized rubber
like Castaldo Gold. If you are making pull out spiral coils or have a
lot of skinny rubber appendages in your mold, this material, while
providing a beautiful, self-releasing surface, may not last very
long. This material has very minimal shrinkage so it’s good for
making master molds. A downside, however, it that you can’t burn this
material to make modifications to your mold should you have thin
spots in your model.

Dow Corning Silastic E RTV Silicone mold color is WHITE. It is
softer than the green Silastic J so excessive clamping pressure will
distort your injection waxes. I prefer the green product.

If you store Silastic materials in an air conditioned environment
and take care not to contaminate them, they will last longer than 6
months to a year. I have had 4KG buckets of the base and the
corresponding bottle of catalyst last for more than 5 years. I
periodically shake the catalyst, but otherwise have left the base
alone. The main thing is to not buy an expired or nearly expired
product that may not have been properly stored prior to being sold to
you. Make sure that your supplier guarantees freshness. Old base is
thicker and doesn’t not flow as well. Old catalyst will settle and
start separating.

Be sure to test compatibility when trying to mold items. Besides
rubber and sulphur contamination, the silastic materials won’t cure
in contact with some of the rapid prototyping resins. Also, don’t
assume that E and J are compatible with the same materials.

Donna Shimazu


#2

Sorry my mistake yes the E silastic is white, the L silastic is green
as well as the J silastic. I have never used the J silastic the L has
always been my preference. Also yes there are certain things that
will retard the catalytic reaction, mostly (from my experience) it
has to do with organic oils. Oil is a real killer for all the
silicone rubbers that I have used both vulcanized and RTV and that
includes body fluids from biological specimens. Thanks for the
correction Donna, sometimes I get a little dyslexic. The shelf life
I mentioned is what Dow recommends or at least that is what I have
been told by the people I bought it from, could be wrong I only ever
ordered the 1/2 kilo kits so they got used up pretty quick. A four
or five year shelf life sounds pretty good to me maybe I should have
been ordering larger tubs all along. Frank Goss