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Vulcanized vs. RTV


#1

Materials improve with time. I have seen a few posts which suggest
that RTV in general is not as strong as vulcanized natural rubber.
That was an accurate generalization eight or more years ago.

Although we manufacture natural mold rubber, back in 1993, I saw a
clear need for a high tear strength RTV silicone. Silicones were
noted for very low tear strength. That was true of both the RTV and
the heat cured silicones of the day.

It took us about a year to develop the characteristics jewelers
needed. We introduced high tear strength heat cured silicones (4X
Gold), and a little later, Akron RTV Silicone (clear).

Today, a lot of jewelry manufacturers are using Akron RTV Silicone to
make production molds directly from original waxes, thus completely
eliminating the model making step. Silicone RTV is initially costly,
but it makes a permanent mold (unlike the less costly urethane RTV
which tends to revert over time, especially in moist regions).

Manufacturers find that skipping the model making step easily
underwrites the higher cost of the mold. In addition, throughput
increases with silicone because of the easy release character. There
is very little tinkering involved in getting the wax out of the
mold. Some folks claim to have doubled speed at the pot.

I am available at any time to answer questions relative to how
Silicone RTV can best be used. As with any material, there are some
limitations, but it is a new day and these products currently save a
lot of money for the manufacturing jeweler.

Best wishes,

Bill Mull
Zero-D Products, Inc.
38285 North Lane. #103
Willoughby, OH 44094 USA
800-382-3271
440-942-1150
fax 440 942 2130
WWW.ZERODPRODUCTS.COM


#2
Today, a lot of jewelry manufacturers are using Akron RTV Silicone
to make production molds directly from original waxes, thus
completely eliminating the model making step. Silicone RTV is
initially costly, but it makes a permanent mold (unlike the less
costly urethane RTV which tends to revert over time, especially in
moist regions). Manufacturers find that skipping the model making
step easily underwrites the higher cost of the mold. 

I disagree only with this part of your statement above. Actually,
As a manufacturer for many different designers, I firmly believe that
a wax model or plastic model for production is not the way to go in
most cases.I have very good reasons for these thoughts. First, is
that the responsibility of making the mold from a wax pattern or
other non metallic part is the responsibility of the manufacturer…
So … what happens if the pattern is broken in the process? Oh
well… another patern may need to be made… and at what expense
!!! You can and should make a wax or SLA model with the intent of
having an RTV mold made and then castings made that will be cleaned
,perfected and used as your final production models. Next … make
sure you have calculated enough shrinkage as there will be shrinkage
in the process… RTV molds do have some small percentage of
shrinkage… the wax and casting process definitely has shrinkage

As a manufacturer, we often have to make multiple molds of the same
item. The weight and size of the final production pieces must be
very close. Can we use wax models or SLA models …yes,but not
easily . The reason being that if the pattern is broken , we can’t
go into production with multiple molds until a new pattern is created.

This next statement is important and has a lot to do with “why a
manufatcurer prefers a metal model for production” Are the wax
patterns perfect? Usually not… if there are minor defects in the
pattern, they are often not visible and if they are reproduced into
the production pieces, the cost of polishing out those defects is
expensive in a production run.Again, having metal models is and
advantage.

As I have mentioned in previous posts, make an RTV mold of your wax
or SLA patterns,( these are called master models/molds) then make a
few castings that are to be perfected in metal. These metal models
are to be called production models . They will last forever in any
kind of mold making process.

Now, if you wish to use RTV or heat cured silicone or organic
rubbers , you may do so without fear .

RTV’s and Silicone based rubbers are prefered for production for
many reasons so on this point , I agree wholeheartedly with Bill
from Zero D products.

Happy Thanksgiving to all, Daniel Grandi

Racecar Jewelry Co. Inc . We do casting and finisnishing for
designers , Jewelers, students and people in the trade. conatct:
sales@racecarjewelry.com or call 401-461-7803


#3
    Materials improve with time. I have seen a few posts which
suggest that RTV in general is not as strong as vulcanized natural
rubber. That was an accurate generalization eight or more years
ago. 

I read this with great interest as I am currently without a
vulcanizer and am always looking for new ways to do things. I went
to the web site and clicked on the instructions for using the RTV
referenced. It looked very familiar, so I checked my stock and it
was what I already have.

While this product may be stronger than older formulations, it is
far from vulcanized rubber as far as tear strength is concerned. It
is a useful addition to one’s arsenal but is not, in my opinion, a
replacement for vulcanized rubber.

– Spike Cornelius Portland, Or. RC ArtMetal