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SiliconesWhy silicones?
Silicone rubber is used most often for casting liquid plastic resins, such as polyurethane, epoxy or polyester because the resins or the barrier coats used with them do not require release agent. Thus, plastic parts from silicone molds are usually ready for finishing with no washing of release or surface imperfections due to release agents.
Silicone molds also withstand the high temperatures (above 250o F) of some polyester or acrylic resins or low melting metals better than any other rubber.Thus, silicones' non-stick quality makes short run resin casting easy.
High production of many parts per mold release agents are often used to prolong mold life, if this instance polyurethane rubber molds may perform nearly as well at half the price. If your mold costs are high, it may pay for you to review the possibilities of a lower cost rubber with a Polytek representative.
Silicone rubber molds are almost never used for cement casting and are only needed at foundries with the stickiest of foundry waxes.
Webster & Sons Ltd. offers four series of silicone rubber products that are perfect for all your casting and molding needs:
The 70 SeriesSilicones
TinSil® 70 Series rubbers consist of a liquid Part B base and Part A catalyst, which after mixing at the proper ratio by weight, cure at room temperature to flexible, high tear strength, RTV (room temperature vulcanizing) silicone rubbers.
All TinSil® 70 Series mold rubbers are tin-catalyzed, condensation-cure systems. They are ideal for molds where easy release or high temperature resistance is needed. They are recommended for evaluation as mold materials for polyester, epoxy and polyurethane resins and waxes. TinSil® 70-60 is useful with low melting metals.
TinSil® 70-25 cures to Shore A-25 hardness within 24-48 hours.
TinSil® 70-30 is slightly tougher and firmer than TinSil® 70-25.
TinSil® 70-11 is the new and improved version of TinSil 70-10. Higher strength formula, proven to have better chemical resistance and substantially longer mold life when performing high volume polyester/polyurethane resin casting. Will replace 70-10 from this point on.
TinSil® 70-60 is the hardest, highest heat resistant rubber for casting low melting metals.
Features:
The 71 Series Silicones
PlatSil® 71 Series RTV Silicone Rubbers are two-component, addition-cure, platinum-catalyzed, high tear strength, flexible mold compounds.
71-11 & 7-20 are easy 1:1 mix ratios with a 4 hour demold time.
Class B
Class 2They have tough knotty tear strength, which make them especially valuable to the mold making industry.
They are recommended for evaluation as mold materials for polyester, epoxy, polyurethane resins, waxes and many other materials.
PlatSil® 71 Series Silicones are preferred because on curing, they don't shrink, they don't produce alcohol like tin-catalyzed silicones which can inhibit urethane castings, and they can be heat accelerated to speed the cure.
Features:
The 73 Series Silicones
PlatSil® 73 Series RTV silicone rubbers are two-component, addition-cure, platinum-catalyzed, very high tear strength, flexible mold compounds.A tough, knotty tear strength is characteristic of the 73 Series systems making them especially valuable to the mold making industry.The 73 Series rubbers are recommended for evaluation as mold materials for polyester, epoxy and polyurethane resins, as well as for waxes and many other materials.PlatSil® 73 Series silicones offer advantages over tin-catalyzed systems in certain applications because on curing they don't shrink, they don't produce alcohol (like tin-catalyzed silicones) which can inhibit urethane castings, and they can be heat accelerated to speed the cure.
Features:
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