Overview
The
recent introduction of Castaldo®’s VLT™ [Very Low Temperature] molding
rubber opens the way to a new time-saving process for jewelry molding
using Objet Eden™ 3-Dimensional Printing Systems. The new rubber allows
users Objet users to utilize their PolyJet™ patterns as master models
and mold them in as little as one hour. This eliminates the need to go
through the time-consuming process of creating a metal master model.
Direct casting of resin models made by most rapid prototyping
systems do not burn out cleanly. However, using cold-mold compounds
that do not damage the pattern and an RP system that supports the
specialized material offers the perfect alternative.
Another recently developed alternative method involved making a
liquid rubber mold of the model, curing it overnight, injecting the
wax, and then casting the wax (another overnight process) to get the
master model. Finally, they make a traditional rubber mold, shoot
waxes, and start production casting. All together, the process would
take more than two days.
Many casters, while still preferring to make a mold of the resin
model and shoot waxes are unhappy with the long curing times: quite
simply, they want to make their models as fast as possible.
New Methodology
Now
this entire process can be done rapidly – in less than half the
time. Rubber can be cured at temperatures ranging from 160°F (71°C) to
180°F (83°C), well below the softening point of most resin materials.
At a temperature of 160°F, a standard 3/4-inch mold will be cured and
ready for injection in 90 to 120 minutes. At 180°F, that time is
further reduced to just 30 to 45 minutes. However, as with traditional
casting rubbers, longer curing times mean better molds – the longer the
cure, the more likely it is that the rubber will flow into every nook
and cranny to provide detail. In addition, when VLT™ rubber cures, it
shrinks just 1.4 percent.
Perhaps one of the greatest benefits of VLT™ rubber is that it makes
rapid prototyping more useful for mass production. Specifically for the
jewelry industry, enabling PolyJet™ models to be used directly as
master models is a important development because it offers significant
time savings in a market where time can be a vital competitive edge.
On a practical level, it is too expensive and time consuming to run
a rapid prototyping machine a thousand times in order to create the
high number of castings needed. Now, with VLT™ rubber and PolyJet™, a
prototype piece can be directly molded, and the subsequent wax models
can be used to make thousands of castings.
VLT™ rubber also works well with traditional hand-carved waxes. And,
VLT™ rubber is designed specifically for molding – i.e. it acts like
any other molding rubber, only at much lower temperatures.
Essentially, the VLT™ and PolyJet™ methodology leverages traditional
technology, tools, and techniques. This means there is no one needs to
learn anything new, buy new equipment, or train people in new
techniques. If you are already doing lost-wax casting, the VLT™ and
PolyJet™ methodology fits right in.
How does it work?
Castaldo®
VLT™ Silicone Molding Rubber can be vulcanized at any of a wide range
of time and temperature combinations, depending on the characteristics
and requirements of the model material. Below are some suggested
combinations for a typical mold that is 3/4" / 19 mm thick
88° C / 190° F for 30 minutes
82° C / 180° F for 45 minutes
76° C / 170° F for 60 minutes
71° C / 160° F for 90 minutes
The only change from established mold making techniques required by
Castaldo® VLT™ Silicone Molding Rubber may be the need to coat the
plastic model with a release spray before vulcanizing to ensure easy
release of the model after vulcanization. Teflon® (PTFE) sprays work
very well, as do common household cooking oil sprays made with olive
oil or canola oil, such as PAM®. Wax models do not need to be sprayed.
Key Advantages
Tools and technology
The VLT™ and PolyJet™ methodology utilizes the simple tools and easy technologies you already have and know how to use.
Easy to work with
VLT™
Silicone Molding Rubber has the consistency of modeling clay or putty,
reducing mold packing time to a few minutes. There is no need to cut
and shape the pieces to fit the mold frame. Merely pull off a piece
with your fingers and push it into the mold frame as desired.
Easy to cut
Molds made of VLT™ rubber are firm, yet they “cut like butter”.
Minimal shrinkage
Rubber shrinkage is only 1.4%
Easy, spray-less release of wax injections
Finished
molds require no mold release spray. Wax patterns release easily
because the rubber already contains anti-stick compounds.
High-shine finish
Molds made of VLT™ rubber provides waxes with an extremely shiny finish, reducing the polishing work required on your casting.
High tear strength
For
a silicone rubber compound, VLT™ rubber is exceptionally high in tear
strength, meaning that molds made from it last for years.
Cheaper and easier than RTVs
Room
temperature vulcanizing (RTV) compounds require exact measuring and
exact mixing. They have limited working times and require vacuum
de-bubbling to provide usable molds.
VLT™ Rubber Specifications
Sizes:
Regular strips: 18" x 2 7/8 " x ~3/8" (45.7cm x 7.3cm x ~6mm). Packaged in 5lb (2.27kg) cartons.
Double-wide strips: 18" x 5 3/4" x ~3/8" (45.7cm x 14.5cm x ~6 mm). Packaged in 10Ib (4.5kg) boxes.
Storage:
As with any unvulcanized rubber
compound, store away from any source of heat and light. Unvulcanized
shelf life is at least one year if properly stored.
Processes
Castaldo® VLT™
Silicone Molding Rubber is compatible with all mold making techniques,
including mold cutting and powder and cream separation molds. It is
particularly adaptable to the powder and cream separation processes
since the parting line is so easily controlled. For patterns strong
enough to resist some pressure, merely push the model into rubber to
the desired point. If not satisfied with the results, remove the model,
smooth the rubber over with your finger or tool and re-insert the model.
Disclaimer
Objet
Geometries LTD is not responsible for misuse of our products or their
use in conjunction with unsafe or improperly maintained equipment or
for uses other than intended as jewelry casting mold making material.
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