WHAT IS LIQUID SILICONE RUBBER (LSR)
Liquid Silicone Rubber(LSR) is a high performance, two-part, thermoset elastomer, that exhibit both organic and inorganic characteristics (watch this video). With typical viscosities of 500,000 – 2,000,000 cps, silicone elastomers are utilized due to their process versatility, with high temperature stability, low temperature flexibility, excellent weatherability, long life services, excellent sealing properties, easily pigmentable and inertness. Due to their proven application performance, LSR’s are often utilized in aerospace, automotive, consumer goods, health care & textiles.
Made from Silicon, a non-metal found in the earth’s crust, which does not occur free in nature, but a major constituent of clays, quartz, rocks and sands. Manufactured in an internal planetary mixer, adding in methyl vinyl polymer, silica fillers & additives. The orbital movements create a high shear, providing a homogeneous mix to the polyvinylsiloxane base. After a relatively long mix time, the base is separated into equal amounts, with different additives, creating the “A” and “B” components:
- Component A: Platinum Catalyst
- Component B: Hydride crosslinker, inhibitor
Material is then volume filled into lot matched containers, either 200L (55gal) or 20L (5gal)
Automated process, fast cure cycles – excellent productivity, multi-cavity molds, extremely low flash tolerances, high strength products, low viscosity = low injection pressures. Overmold and two shot capabilities, make Liquid Silicone Rubber one of the fastest growing Technologies in the industry.
LSR Molding Process:
The LSR molding process vs. the thermoplastic molding process is always referred to as a “reversed situation”, where is the mold is actually hot and the screw/barrel are cooled. This is actually the 30,000-foot view, as there are many differences with the LSR process that will have to be specified out properly, to be successful. LSR, when mixed together at a 1:1 ratio, will start to cure at room temperature. Adding heat to the equation will create a faster curing curve, so after the two components are introduced, a proper chilled water system is needed to retard the cure cycle. Approximate cooling temperature for equipment is 70°F.