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Making Bad molds


#1

I’m sorry to put a negative spin on the “Making good molds” thread
[ http://www.ganoksin.com/orchid/archive/200507/msg00622.htm ], but
I’ve been making molds for over 30 years and have made thousands of
them.

My intent is to save anyone some grief for trying a new product. I
made the mistake of ordering some “Choice” brand mold rubber from a
very “Grande” company that most of us deal with.

When it arrived, I was surprised that it was made in Mexico. Not that
this would make any difference, but my first thought was, I hope this
is quality stuff.

This is the worse rubber I have ever used. Not that the final molds
are that bad, but the molds are so sticky when they come out of the
vulcanizer, you have rubber sticking everywhere. I use the same tongs
to remove the mold frames from the vulcanizer as I do to take hot
flasks out of the oven. The rubber sticking to the tongs against the
flasks stink up the whole shop. My bench pin where I cut the molds is
sticky too.

This is not an issue of vulcanizer temperature. This is just bad
rubber. Has anyone else experienced this?


#2
   This is not an issue of vulcanizer temperature. This is just
bad rubber. Has anyone else experienced this? 

That’s EXACTLY what you get if you use silicone based rubbers in
mold frames or with mold plates that were previously used with
natural rubbers, or vice versa. Cleaning the frames and plates well
enough to switch rubber types without problems is actually trickier
than it would seem. The amount of residue needed to interfere with
proper vulcanization of the other type of rubber in both cases seems
very small, and not visible to the eye. Literature with the rubbers
suggested cleaning with solvents like naptha, but I have found even
that to not be quite enough. Now I simply have a set of mold frames
and plates for silicone, and another set for natural rubbers, and I
make sure not to mix them up. You can get a bit of this interference
as well, with natural rubbers, if you use a silicone based mold
release spray, and some of the spray gets on your mold frames for
natural rubber. This seems less consistant, but seems to have
happened to me once or twice.

HTH
Peter


#3
    Not that the final molds are that bad, but the molds are so
sticky when they come out of the vulcanizer, you have rubber
sticking everywhere. 

Richard,

Not taking the time to look up in the catalog the "Choice "rubber
you refer to, it sounds very much like it is a silicone based
vulcanizing rubber. These silicone rubbers will react with the
natural rubber residues remaining on your mold frames and plates in
such a way as to not “cure” ; thus remaining very sticky. These
synthetic rubbers need their own frames and mold plates, or to have
your existing frames and plates very well cleaned prior to using the
with them. Clean the frames and plates outdoors with steel wool and
xylene (xylol) as a solvent. This should “cure” your symptoms.

Paul Reilly


#4

You know, I think that is the same stuff that I bought from Rio
Grande, and it caused a nasty allergic reaction for me. When I cut
the warm mold, bright yellow water started running out of my nose,
and I had burning and coughing symptoms that lasted overnight. I
offered to send the rest of the box back to Rio, so they could
donate it to a school or something, but when I did send it they
actually credited my account for the whole thing, even though the six
pre-cut pieces I’d used were missing. That was really nice! I guess
most folks are not allergic to this rubber, but I sure am. I went
back to my old standby, Castaldo Gold. From what I have been hearing
lately on Orchid, there may now be better rubbers out there, but
Castaldo Gold works for me, and my urge to experiment has been
tempered by the experience I had with the Yellow Nose Faucet, as I
call it, rubber.

So…I didn’t like the product, but, as always, I loved, loved, loved
the Rio Grande service! They sure were nice to me.

M’lou Brubaker, Jeweler


#5

Richard,

I have used Castaldo Gold rubber for twenty-five years or more, but
the last batch or two have acted just as you described, stickey and
clinging to the vulcanizer, the mold frames, and even the hand tools
that come into contact. Thought it was something only I experienced.

Jon Michael Fuja


#6
So...I didn't like the product, but, as always, I loved, loved,
loved the Rio Grande service! They sure were nice to me.

I use Zero D mold rubber, firm grade, for about 6 years. I have
made 600-1000 molds and no problems. I use their wax, rubber, and
silicone spray.

They have great customer service and technical support.

Richard Hart


#7

M’lou:

Romoff rubber CO in my opinion is the best for rubber 2 piece molds.
Progress Has the same thing. It us gray looking. A caser in La years
ago used it for their molding rubber.

The trouble with Romoff in N.Y is you have to buy 50 lbs. of the
rubber and that was too much for me.

Yours :

Billy S. Bates
royalminiatures.com


#8

Dear Richard,

This is Michael Knight at CASTALDO.

The problem you are describing sounds much more like a bad
vulcanizer heating element or thermostat than the kind of chemical
contamination Richard was talking about.

You’d get that kind of contamination only if you were using silicone
vulcanizing rubbers at some point and did not wash off your frames,
tools, etc later with solvent.

Jewelry vulcanizers can go on without problems for decades. As a
result they are often taken for granted and given little attention.
When there is a problem, the typical first reaction is to blame the
rubber because the vulcanizer is just assumed to be the same as
always. Kind of below the radar, so to speak.

Try measuring the temperature of both the top and bottom plates
separately using a small block of wood as a separator first above
and then below your thermometer. Odds are that you’ll find one or
both plates well below the 307F / 153C recommended temp.

If that doesn’t do the trick, please let me know so that I can send
you a replacement batch of rubber.

Michael Knight
CASTALDO
& F.E. Knight Inc.
120 Constitution Blvd.
Franklin, MA 02038 U.S.A


#9

Castaldo is not consistent. It is one time too soft, next time too
hard and the shrink is all over the place. I switched to Akron
Jewelry Rubber a couple of years ago and have had perfect results.
Their number is 440-942-1150.

Lori


#10

Thats funny, we have been using and selling Castaldo for a long
time, and have never had a problem or complaint. Go figure.


#11

Can eat you up. After you have it, it becomes your problem. Time is
so precious that to waste it on low grade materials would not make
any sense.

Mass advertised products of all kinds are so consumed with
advertising and dealer profits that there is not much left for the
actual product. Those are the pressures of living large.

When you can buy a product from every corner of the country you have
to know that every distributer is doubling the price and you lose on
product… Some cut on volume some cut on quality. You are buying
their advertising, the product is secondary.

I would compare it to the different grades of steel tools, a low
grade (Dollar Store) soft steel tool; to a high grade tempered steel
tool is the WOW Factor!

The best quality of anything in life gives the best results with
ease.

I never had anything but the best results with Akron Jewelry Rubber.
It is smooth to cut, yet tough to break any thin strands in the
mold.

They know their business.
We love quality,

Allan Creates
superringfit.com
Perfectly Fabulous Fit, Hinged ring Shanks


#12
       You'd get that kind of contamination only if you were using
silicone vulcanizing rubbers at some point and did not wash off
your frames, tools, etc later with solvent. 

Michael,

Can you say more about this? This is the first I’ve heard of the need
to wash frames and tools with solvent after using the silicone
rubbers!

Thanks!
Karen Goeller
@Karen_Goeller


#13

Dear Karen,

    Can you say more about this? This is the first I've heard of
the need to wash frames and tools with solvent after using the
silicone rubbers! 

The chemistry needed to cure natural rubber (such as our White
Label & Gold Label) doesn’t get along with the chemistry needed to
cure our Silicone rubbers.

You can’t mix the two for that reason. But even without mixing them
there can be trace amounts of either type of chemical on anything
that touches them. For your purposes that means the model itself,
the sprue rod, the sprue button former, the inside of the mold frame
and the mold plates.

Contamination of this sort won’t ruin your mold but will make any
affected areas soft, sticky & gooey. The effect is limited to just a
few 1,000/ths of an inch deep, but it’s enough to be unpleasant.

Almost any solvent – from acetone to paint thinner to gasoline –
can be used to clean affected parts.

As a practical matter I keep one set of plates, frames, etc for
silicone rubber and another set for natural rubber. It’s easier than
cleaning, cleaning and cleaning again.

Michael Knight
CASTALDO
& F.E. Knight Inc
120 Constitution Blvd
Franklin, MA 02038 U.S.A
www.castaldo.com