Polyurethane Mold Rubber Spray Applied
Polytek®'s Polygel® Spray 50 Mold Rubber was
selected by master moldmakers Angelo and Joe Carolfi as the mold material
of choice for such a delicate and exacting job. Angelo said, "Heavier
brush-on mold rubbers could have damaged the fragile zinc, which varied
from 1/8-inch thickness to paper-thin in some spots where corrosion was
extreme. In addition, spray application was the fastest and most economical
way to cover such a large surface with mold rubber. Spray application
of Polygel® allowed the thinnest possible mold so the zinc would be stressed
as little as possible as the mold was being removed."
Half the Cost of Silicone Mold Rubber
Joe added, "Although only one polyester and fiberglass
casting was going to be made from these molds, Polygel® Spray 50 molds
often are used to make many polyester/fiberglass castings from one mold.
Polygel® Spray 50, a patented poly urethane rubber from Polytek®, is half
the cost of silicone rubbers, and the spray equipment is 1/4 the price
of silicone sprayers."
Low-Cost Sprayer Mixes and Applies Mold Rubber
The molds were made using the Polygel® Spray
Unit Model VS-3000 to mix the low-viscosity liquid rubber in the proper
1:1 ratio and to spray the mixed rubber onto the statue. The delicate,
gold-leafed statue had been prepared with two coats of PVA (polyvinyl
alcohol) to protect the gold leaf. A coat of release agent like Pol-Ease®
2450 was applied prior to application of the rubber. Plasticene flanges
were used to create parting line seams in the mold. One side of the flange
was sprayed first, the plasticene was removed, release agent was applied
to the cured half of the flange, and the other mold section was then sprayed
right against the first.
Hyperset Cure Speed Achieved with Polygel® Part X
The Carolfis accelerate the cure of the Polygel®
Spray 50 to yield about 30 seconds working time. This is just enough time
to saturate the reinforcing fabric and allow some tooling, if necessary
to adjust the surface of the Polygel® before it sets. With a fast cure
like this, additional coats can be built up immediately to any thickness
without any problems with sagging, dripping, or separating from the model.
Once all the mold rubber was in place, the mother mold was built from
the bottom up, self-supporting, so as not to place any weight from the
mother mold on the delicate statue.
Fabric Stiffens and Reinforces
The Carolfis have discovered a fabric, Tietex,
that absorbs and wets out with the Polygel® more rapidly than burlap or
any other reinforcing fabric. Tietex is used to stiffen the flanges and
to stiffen and bridge over undercuts. The mold collapses when withdrawn
from the undercut, yet is stiff enough to maintain shape when the casting
is made. Tietex will be sold as a Polytek® accessory by the yard to accommodate
moldmakers that cannot purchase a whole roll.
Master Moldmakers Partner with Polytek®
The Carolfi Studio, now operated by brothers
Joe and Angelo, is typical of many master moldmakers who have worked closely
with Polytek's founder and chemists for over 25 years, developing new
cutting-edge techniques and polymers that have changed the world of moldmaking.
During these many years of cooperation, progress has resulted from this
alliance, from little hints like the use of Tietex fabric to the development
of major new moldmaking rubbers and techniques. These innovations could
be the subject of another article—or even a book. Perhaps we will tackle
the story of these contributions in a future issue of Developments™. |
