Uneven cured Silastic J RTV


Andy Carlson
 

Your problem of uneven curing is probably related to the uneven mixing
you encountered with the troubled batch you had. My guess is that the
stuff will never cure, and that you will have a big ugly mess to
retrieve your pattern from this Goo. However, you might have a
contamination problem, as well.

Many of the better RTVs today (The Platinum based formulas, not the
cheaper tin-based ones) are better than earlier formulas in avoiding
partial un-curing by reformulations of their chemistry make-up,
providing a less sensitive rubber. If you have a problem in having wet,
un-cured areas limited to the contact zone of your fabricated styrene
patterns, you are probably having solvent contamination. I absolutely
avoid Testors, which seemed to be the worst solvent for RTV solvent
contamination ( I suspect because it was slower than most solvents in
flashing off, plus it seems to have some "fillers" which are left
behind). There are still RTVs which are sensitive to solvents, and to
assure that this is not a problem, glue your patterns with MEK
(available in paint stores) which flashes off 100%, leaving absolutely
nothing behind.

Andy Carlson

Message: 23
Date: Fri, 30 Aug 2002 19:02:26 -0500
From: lawrence Jackman <ljack70117@adelphia.net>
Subject: Re: RTV Rubber and Detailing Questions

It should not. Use 125 degrees. I used to use Dow "J" rubber. Once in a
while
one would screw up. I do not know which one you are using. But if the
oven saves
yours, do not demold or cut it open for 72 hours. If before 72 hours
you will
have shrinkage if you are using the "J". I just remembered some of my
Patterns
were plastic. I would force a cure in 4 hours at 150 degrees. No
problem using
the "J". Remember that the rubber heats up while curing by itself..
Thank you
Larry Jackman

Paul LaCiura wrote:

Larry, my forms and much of my masters are styrene plastic, will the
150
degrees melt that?

Thanks,

Paul

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Message: 24
Date: Fri, 30 Aug 2002 19:41:02 -0400
From: James D Thompson <jaydeet@inna.net>
Subject: Re: Rutland gondolas/empties

Later, however (and I would have to research dates to say exactly
when),
the Rutland did have a fleet of USRA-type ribbed twin hoppers (CDS also
makes lettering sets for them) and, in its last few years, even bought
some second-hand triple offset-side hoppers.
Rutland 10000-10099 were built by SSC in 1/1915, off the drawings for
the
C&O's 57000-58999 "early standard" hoppers of 1912.

David Thompson




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Message: 25
Date: Fri, 30 Aug 2002 15:54:54 -0800
From: "JGG KahnSr" <jacekahn@hotmail.com>
Subject: Rutland Steel Hoppers

Thanks, David
I have that somewhere in my books and files, but no longer at the top
of my
head; the USRA-cars are pretty close for us "85-90% accuracy is good
enough"
types. I did up a re-build of a museum-era ScaleCraft car with the CDS
set
and it satisfies me when I look at photos in Shaughnessy and Nimke.
Jace Kahn

the Rutland did have a fleet of USRA-type ribbed twin hoppers (CDS
also
makes lettering sets for them) and, in its last few years, even bought
some second-hand triple offset-side hoppers.
Rutland 10000-10099 were built by SSC in 1/1915, off the drawings for
the
C&O's 57000-58999 "early standard" hoppers of 1912.

David Thompson




Jace Kahn
Mostly Fairbanks


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