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RTV rubber molds?


#1

Anyone had any luck with the room temperature vulcanizing
rubber? I would love to make a mold of a couple of wax pieces I
have carved so I can duplicate them. I am not ready to dump money
into a vulcanizer (yet). Also, anyway to improvize a wax
injector- how about a syringe? Any help will be greatly
appreciated. Thanks dave J


#2

Dave, I use a product from SWEST. Im not at my shop now, but I think it is
called RTV silicone rubber. It is pitch black and smells like rotten eggs,
but works beautifully. The only thing you have to be careful of is trapping
bubbles in it.
It seems to have a very long shelf life and has a built in release agent.
Good luck!
Ken
P.S. Its pretty expensive. I think about 80.00 for a quart


#3

In a message dated 97-06-12 13:34:03 EDT, davyjo@midcoast.com writes:

<< Anyone had any luck with the room temperature vulcanizing
rubber? I would love to make a mold of a couple of wax pieces I
have carved so I can duplicate them >>

We have used the RTV and if you mix it properly it works well ($$$ and you
need a vacume chamber). I sent a wax to Quality casting in NY to cast in
platinum and they molded the wax, the thing is they used a white rubber
(rather than the green). I am wondering what that is and if its better than
the green RTV we have been using. I would think that a huge casting house
like that would have found the better product as they do it so often.

Mark P.


#4

In a message dated 97-06-12 13:32:06 EDT, you write:

Anyone had any luck with the room temperature vulcanizing
rubber? I would love to make a mold of a couple of wax pieces I
have carved so I can duplicate them. I am not ready to dump money
into a vulcanizer (yet).

I use RTV regularly and thinks it works fine. I have had a number of molds
split excessively after a two or three thousand injections, but I don’t think
this is a problem, molds are not very difficult to remake. The life span will
vary with how much you have to flex the molds to release your injection.

Until recently I was using Silastic brand E-RTV by Dow Corning. Now I use a
product called Akron RTV Silicon Mold Rubber. I get it from Zero-D Products,
Inc., 800-382-3271. The Akron rubber is clear, which is nice for cutting, and
has a greater tear strength than the Silastic. There are two catalysts
available for the Akron rubber, one will give you a harder rubber, the other
will be softer. That’s a nice option.

 Also, anyway to improvize a wax
 injector- how about a syringe? Any help will be greatly
 appreciated. Thanks dave J

I’ve heard syringe’s suggested before, I imagine that could work. I had a
doctor use a nice stainless steel one of about five ounce capacity on me
once. I’ve often thought that one would work beautifully.

If there is a jewelry shop nearby you could probaly get a couple injections
from them.

Good luck:)

Dick Caverly
rcaverly@aol.com


#5

Anyone had any luck with the room temperature vulcanizing
rubber?
I have had good luck with a product called ditto3d avaliable from rio
grande. I almost prefer it over vulcanized rubber because it cuts silky
smooth and is very flexable allowing you to remove fine detailed objects
very easily. It dries at room temp in about 24 hours but you can speed
it up with a little heat. It is fairly expensive and you pretty much
need the teflon non stick spray, sold separatly, so it will not stick to
the model and the mold frame. I have used both for a few years now and
it look like it may not last as long as vulcanized rubber,tears easily
after a few years,but after that long you should be able to pull as many
waxes as you would ever need. It recomends that you vacume it after you
mix the two parts togrther and after you pour it around your mold. I
would agree with that too. Tried it a few times without doing so and
ended up with a few bubbles on the wax but were easy to remove.
Michael Chapman


#6

Dave,

I have been using Dow Corning Silastic RTV for about 18 years to do just
what you want. I often make molds of my waxes before i cast for
protection.

I usually use a Ferris mold frame for my set up. I like the shape and it
helps to conserve rubber as it is already the shape of injection molds.

I sprue the wax up with a wax sprue on the mold frame. Mix my RTV in a
plastic drinking cup and vacume it. This removes the air bubbles.(be
careful when vacumming the volume will expand by about 300%). I usually
bring the vacume up until the RTV rises to the top of the plastic glass
and then release it. repeating until the volume rise decreases enough to
run 27"mercury of vacume.

Next pour about 1/2 of the mold frame full of RTV and vacume the same
as before . Then add top half of mold and vacume lightly to remove large
bubbles. Let set overnight.

If you do not have a vacume table you can brush on a contact coat after
you sprue the wax and then just fill the mold. This reduceses the
strength and the life of the mold.

I usually use either the L or the E formulas. One is green and gives a
very rigged mold and one is white and gives a very flexable mold. I
believe the green is the L but check to be sure.

One caution. any petroleum based product will retard the catalyst so if
you polish your waxes with mineral spirits or use vasoline as a release
agent don’t.

As for using a syringe for a injector yes it works I did just that for a
a couple of years. I used a 50cc syringe and a crock pot to melt the
wax. you fill the syringe from the pot and inject. Wear gloves though, I
pulled the syringe apart one day while filling it and got second degree
burns from the hot wax. it sticks! so be careful. as an alternative to
aan expensive wax injector a friend of mine made one from an electric
pressue cooker. He bought the valves and had the cooker drilled and
tapped at a local machine shop. It worked great!

Frank.


#7

Dave,

I have been using Dow Corning Silastic RTV for about 18 years to do just
what you want. I often make molds of my waxes before i cast for
protection.

I usually use a Ferris mold frame for my set up. I like the shape and it
helps to conserve rubber as it is already the shape of injection molds.

I sprue the wax up with a wax sprue on the mold frame. Mix my RTV in a
plastic drinking cup and vacume it. This removes the air bubbles.(be
careful when vacumming the volume will expand by about 300%). I usually
bring the vacume up until the RTV rises to the top of the plastic glass
and then release it. repeating until the volume rise decreases enough to
run 27"mercury of vacume.

Next pour about 1/2 of the mold frame full of RTV and vacume the same
as before . Then add top half of mold and vacume lightly to remove large
bubbles. Let set overnight.

If you do not have a vacume table you can brush on a contact coat after
you sprue the wax and then just fill the mold. This reduceses the
strength and the life of the mold.

I usually use either the L or the E formulas. One is green and gives a
very rigged mold and one is white and gives a very flexable mold. I
believe the green is the L but check to be sure.

One caution. any petroleum based product will retard the catalyst so if
you polish your waxes with mineral spirits or use vasoline as a release
agent don’t.

As for using a syringe for a injector yes it works I did just that for a
a couple of years. I used a 50cc syringe and a crock pot to melt the
wax. you fill the syringe from the pot and inject. Wear gloves though, I
pulled the syringe apart one day while filling it and got second degree
burns from the hot wax. it sticks! so be careful. as an alternative to
aan expensive wax injector a friend of mine made one from an electric
pressue cooker. He bought the valves and had the cooker drilled and
tapped at a local machine shop. It worked great!

Frank.


#8

The RTV I use is under $30.00 for a 1.1lb. kit. A 3/4" thick
mold on an avarage ring will use about 70 gr. rubber.

Dick


#9

We have been using the RTV’s for a number of years now, I
really do not know why in the world anyone would go to the
trouble and expense of vulcanizing with the RTV choices
available. The silicones are very good but I do not like the
short shelf life of the hardners, the way the main part needs to
be stirred after sitting. I use polysulfides for the molds in
the foundry and make jewelry molds too. The new materials are
better than the old “black tuffy” used for many years. So I say
try it. You will save 100’s of $$$$ not buying a vulcanizer, and
you will be immediately ready to make molds as soon as you get
the rubber. I would ask the supplier you use what they
recommend. Also, call/write a couple of the RTV companies and
see what they recommend. A MAJOR advantage or most all RTV’s is
there is essentially NO shrinkage with RTV’s, it is a major
problem with most all vulcanized materials (less with the
silicons, but still a factor, and they are temp. touchy!!!)

If you are going to do much injecting, spend the money you were
going to spend on the vulcanizer and get a pressure pot. It is
worth it if you are going to do much. A syringe…
could/would work but how much is your time worth???

John

John and Cynthia/MidLife Crisis Enterprises
Maiden Metals/C. T. Designs/ Bloomin’ Wax Works. etc.
PO BX 44, Philo, Ca 95466
Ph 707-895-2635 FAX 707-895-9332
Don’t be afraid to go out on a limb… That’s where the fruit is!