Making your own vulcanizer

Jewelry Discussion
1

Hi Kelvin,

Prior to designing a vulcanizer (assuming you’re only going to have 1
size) one of the things that has to be determined is what is the maximum
size of item you’ll be molding. The larger the mold size, the heavier the
vulcanizer needs to be.

Some typical sizes of mold frames can be found in most any jewelers tool
catalog. Rio Grande’s lists sizes with openings from 1 1/2 x 2 1/2 x 5/8"
to 3 1/2 x 4 3/4 x 1 3/4". The length & width of these dimensions must be
increased by 1 1/2" to allow for the frame wall thickness. Based on frames
with these dimensions you’d need a platen at least 5 x 6 1/4". These
dimensions don’t allow for any guide rods or clamping bolts on the sides
of the mold frames. If an allowance for a 1 " border is made, the platen
size becomes 7 x 8 1/4". The platens should be capable of opening at least
4" & closing to less than 5/8". If you make the platen too much larger,
it’ll take longer to heat up the excess metal mass.

For info on the temps required for the various mold rubbers check with the
supplier. Rubbers made by Castaldo vulcanize between 250 & 400F.

There are a number of videos & books on casting & mold making that may
give you some ideas for designing & building your own equipment. I’d
suggest getting a copy of Rio Grande’s (US,800-545-6566; Can,800-253-9738)
tool catalog. It has a good selection of tools, books & videos. Sometimes
better prices can be found elsewhere, but atleast you’ll have an idea of
what’s available & what the cost is.

Dave

2 
   I would think twice about using Aluminum, as it is soft and
isn't that good of a heat conductor.

I assume you’re talking about vulconizer platens. Several
commercial vulcanizers use aluminum platens, as it is, in fact,
and EXCELLENT heat conductor. Almost all commercial mold frames
are aluminum for the same reason. Almost as good as silver. As
to it’s softness, that depends on what you buy. You can get
rolled machining stock from metals suppliers that’s nicely work
hardened, and won’t easy deform, yet machines beautifully if
that’s how your planning to build your machine or part. It’s not
steel, of course, but then it doesn’t need to be to work well.
Use mold plates, 1/8th inch sheets of aluminum larger than your
mold frame to face the sides of the molds in vulcanizing, and
you’ve equalized both the heat transfer to the rubber surface
and any unequal pressure that might damage the vulcanizer.

I use only Castaldo mold rubber, gold to be exact. It
vulcanizes @ 307'f, and the instructions say 7 min. per slice,
I do 10, it has worked for me, with no problems. Your
vulcanizer needs to be as close to the 307'f as possiable with
no variations.

Agreed. Castaldo gold is good stuff. The white lable makes a
stiffer mold, though, which can be useful for flat items where
the soft gold might tend to make it harder to keep from
compressing the center of the mold cavity, and you don’t need the
flexibility of the gold label to pull your waxes. Both rubbers
make excellent molds that are very long lasting. but it should
be pointed out that in recent years, a number of other very
useful mold rubbers have come along as well. In particular, some
of the silicone rubber based vulcanizing products are very
interesting. Some of them produce molds that are just as
durable and flexible as the castaldo, yet are completely self
lubricating, with no need for sprays or other wax releases. Some
of them, if shaped to fit into a casting flask instead of a flat
injection mold, will even withstand the heat of white metals like
pewter, and can be directly used to cast such metals in your
centrifuge, with the mold being reusable for a great many such
castings. Still, for plain old wax injection rubber molds, few
pros use other than the Castaldo or the competing Kerr rubbers
(which are essentially similar).

You will also need pressure kinda like a press. Look at the
professional vulcanizers in the catalogs and you will
understand what I mean. When you put pressure and heat together
you vulcanize the raw rubber into a semi-solid form, or "cooked", rubber.

A vulcanizer is a great convenience for doing any appreciable
quantity of molds. But you can also use a home oven, if the
thermostat is accurate enough. The mold frame and rubber get
clamped between two sheets of steel plate (1/4 inch) instead of
the vulcanizer platens, with a C clamp or two to provide the
pressure. Sheets of aluminum between the steel and the rubber
will improve the even heating of the mold.

Peter Rowe

3

I have a friend who uses an old pizza toaster oven. Works just
fine for him. And he is a mold maker as a profession in his
job. Just uses the toaster at home.

4

Hi Matt,

I have since received Castaldo’s catalogue which is very
informative and they directed me to their agent Bedrock Supplies
right here in my city. The salesperson there was very helpful
and acutally inspecting the equipment and supplies gave me a lot
and ideas on how they work and the processes
involved. Ipicked up a whole stack of trade handouts. I
received another comprehensive catalogue from Eisinger
Enterprises of Canada.

I spent several hours reading through the books on casting and
jewelry making in a mega bookstore CHAPTERS which is our
Canadian equivalent of Barnes and Nobels. Bought a couple of
reference books. The public library and the university library
were deficient in this area. I am on the right track now and
have practically all the resources are close at hand.

As for, the homemade vulcaniser it will cost me around $20 (plus
scrap parts) to make it so its no big loss if it doesn’t work
but I think it should. The aluminium I will be using is of the
same or better grade than the clothes iron alloy. I think
making homemade equipment is going to be as much fun as metal
smithing itself. Next on the list will be a wax injector then a
kiln and a centrifugal caster.

Kelvin Mok (klmok@shaw.wave.ca)

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