Casting with rubber molds


jstewartdunn
 

Could you use a silicon rubber mold to cast a wax part instead of using
resin? You would then use the wax part to produce a lost wax part in
brass.

J

J Stewart Dunn
Windham, NH


Bruce Smith
 

On Dec 15, 2005, at 8:50 AM, jstewartdunn wrote:

Could you use a silicon rubber mold to cast a wax part instead of using
resin? You would then use the wax part to produce a lost wax part in
brass.
Indeed you could, although it does seem more complicated that just casting it in resin <G>. In addition, many RTV rubber molds can be used with low melting temp metal alloys to cast parts in metal. My general impresession has been that for ease and accuracy of reproduction, it is hard to beat resin.

BTW, my favorite casting resin is Railroad Resin, from Trainstuff
http://www.trainstuffllc.com/public_html/tips%20&%20clinics/Resin% 20Clinic/railroad%20resin.htm


Regards
Bruce

Bruce F. Smith
Auburn, AL
http://www.vetmed.auburn.edu/~smithbf/

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Gary Mittner
 

I agree with Bruce on Railroad Resin by Trainstuff. I have used it in G
scale for parts for the B6sb I did as well as making full copies of the
PRR Scale Test cars in G scale. I think their website is
http://www.trainstuffllc.com If not, do a google search.......Gary





Come visit my PRR Pages:

http://www.angelfire.com/film/prrpics/PRR-Pages.html


Ken Hough <k4sb@...>
 

Of first concern is shrink. If you make a silicone mold (there are nearly
50 different compounds) you need a no or low shrink mold compound.
Second, lost wax shrinks about 7%. All metal shrinks when cooling. Some
resins do not shrink at all.
I use Alumilite. Why? Because I always have after I experimented.It is
very low shrink. I sold a resin O scale PCC car 20 yrs ago. I made the
master exact size. Using Alumilite silicone and their resin my castings
had just a 1-2% shrink. No one noticed. Neither did I. NOW however there
are many others worth a look. Look for linear shrinkage.
Ken

Could you use a silicon rubber mold to cast a wax part instead of using
resin? You would then use the wax part to produce a lost wax part in
brass.

J

J Stewart Dunn
Windham, NH






SPONSORED LINKS
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Specializing in the Complete restoration of
Deardorff View Cameras
Est 1982
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219 462 0281


J W Box
 

Ken:

My firm has been using silicone rubber molds to make wax patterns for
investment castings for years. We have a small in-house casting foundry that
casts aerospace alloys exclusively - exclusively, that is, except for my
brass engine parts that I sneak in periodically. Rubber mold techniques were
pioneered by the jewelry making industry decades ago.

Choose an RTV compound that has zero (< 0.1%) shrinkage. I like an old
Dow-Corning silastic compound called Silastic E, but it is getting hard to
find and there are many others that work fine. If you control wax injection
temperatures, metal melt temperatures and mold temperatures closely, you can
make castings with an overall shrinkage of less than 2% from pattern to
part. That's a lot of "ifs", but any caster with his process under control
can do this.

If you really want to get into this, buy the book Centrifugal or Lost Wax
Jewelry Casting for Schools, Tradesmen, Craftsmen
by Murray Bovin. It's an old book that concentrates on the casting part of
the process, not mold making, but the concepts are all there. I bought it
over 25 years ago when I wanted to make parts for Bob Smith of Central
Locomotive Works in my garage. I never did make parts for Bob, but I used
the experience to cast several million small parts for the medical and
aerospace industry.

There's new technology on the immediate horizon that may change pattern
making. Rapid prototyping machines (rp) now exist that can take a 3D
computer model and make the pattern. Once you have drawn a part, you can
simply scale it in software and make the pattern in any scale. I showed a
bunch of PRR parts in my preferred scale of 1/32 at my table at Cocoa Beach
Prototype Modelers show last January. No one seemed interested, go figure.

I have some photos at:

www.galtran.com/PRR_L2_Construction_Information/pennsylvania_railroad_l2s_cl
ass_3.htm

Bill Box


Judd Barton <NNNPRRJRB@...>
 

Group
A small operation that is using the rapid prototyping machines is
Mark4design <www.mark4design.com>. He is presently working on a PRR X23
in N scale his company and a few other projects for other firms. He is
open for ideas in for other projects.

Judd Barton


J W Box wrote:


Ken:

My firm has been using silicone rubber molds to make wax patterns for
investment castings for years. We have a small in-house casting
foundry that
casts aerospace alloys exclusively - exclusively, that is, except for my
brass engine parts that I sneak in periodically. Rubber mold
techniques were
pioneered by the jewelry making industry decades ago.

Choose an RTV compound that has zero (< 0.1%) shrinkage. I like an old
Dow-Corning silastic compound called Silastic E, but it is getting hard to
find and there are many others that work fine. If you control wax
injection
temperatures, metal melt temperatures and mold temperatures closely,
you can
make castings with an overall shrinkage of less than 2% from pattern to
part. That's a lot of "ifs", but any caster with his process under control
can do this.

If you really want to get into this, buy the book Centrifugal or Lost Wax
Jewelry Casting for Schools, Tradesmen, Craftsmen
by Murray Bovin. It's an old book that concentrates on the casting part of
the process, not mold making, but the concepts are all there. I bought it
over 25 years ago when I wanted to make parts for Bob Smith of Central
Locomotive Works in my garage. I never did make parts for Bob, but I used
the experience to cast several million small parts for the medical and
aerospace industry.

There's new technology on the immediate horizon that may change pattern
making. Rapid prototyping machines (rp) now exist that can take a 3D
computer model and make the pattern. Once you have drawn a part, you can
simply scale it in software and make the pattern in any scale. I showed a
bunch of PRR parts in my preferred scale of 1/32 at my table at Cocoa
Beach
Prototype Modelers show last January. No one seemed interested, go figure.

I have some photos at:

www.galtran.com/PRR_L2_Construction_Information/pennsylvania_railroad_l2s_cl
ass_3.htm

Bill Box




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Ken Hough <k4sb@...>
 

You did not say your company did lost wax! I built a centrifugal caster 20
years ago. I used a 24 in dia feed pot for a farm as the base. Been there
and still at times do it. My newest project is the wire support arms for
the cantenary on our clubs layout. I need hundreds of them.. What's with
Dows Silastic E anyway? I used it for molds too and it is tough to get. I
contacted Dow last year and was told I could not get an account and they
would not tell me of a distributor. For really flexible delicate molds I
Castaldo Econosil Mold Rubber. I have a friend who bought a 3 axis laser
RP machine. I've done some neat "one offs" on it.
Thanks for the book hint.
Ken

Ken:

My firm has been using silicone rubber molds to make wax patterns for
investment castings for years. We have a small in-house casting foundry
that
casts aerospace alloys exclusively - exclusively, that is, except for my
brass engine parts that I sneak in periodically. Rubber mold techniques
were
pioneered by the jewelry making industry decades ago.

Choose an RTV compound that has zero (< 0.1%) shrinkage. I like an old
Dow-Corning silastic compound called Silastic E, but it is getting hard to
find and there are many others that work fine. If you control wax injection
temperatures, metal melt temperatures and mold temperatures closely, you
can
make castings with an overall shrinkage of less than 2% from pattern to
part. That's a lot of "ifs", but any caster with his process under control
can do this.

If you really want to get into this, buy the book Centrifugal or Lost Wax
Jewelry Casting for Schools, Tradesmen, Craftsmen
by Murray Bovin. It's an old book that concentrates on the casting part of
the process, not mold making, but the concepts are all there. I bought it
over 25 years ago when I wanted to make parts for Bob Smith of Central
Locomotive Works in my garage. I never did make parts for Bob, but I used
the experience to cast several million small parts for the medical and
aerospace industry.

There's new technology on the immediate horizon that may change pattern
making. Rapid prototyping machines (rp) now exist that can take a 3D
computer model and make the pattern. Once you have drawn a part, you can
simply scale it in software and make the pattern in any scale. I showed a
bunch of PRR parts in my preferred scale of 1/32 at my table at Cocoa Beach
Prototype Modelers show last January. No one seemed interested, go figure.

I have some photos at:

www.galtran.com/PRR_L2_Construction_Information/pennsylvania_railroad_l2s_c
l
ass_3.htm

Bill Box




SPONSORED LINKS
Ken Hough Photographic Repair Service
Specializing in the Complete restoration of
Deardorff View Cameras
Est 1982
www.deardorffcameras.0catch.com
219 462 0281