Liquid Silicone Injection Molding, Custom Silicone Rubber Molding
Liquid silicone rubber injection molding is the fastest growing segment of Stockwell Elastomerics's molding operations. Liquid silicone rubber is often specified for gaskets, seals and cushioning pads in portable communications, data acquisition devices, sensing instruments and ruggedized electronic devices where outdoor conditions are demanding. Cured liquid silicone rubber does not out-gas volatiles and plasticizers; this has made it friendly to many electronics assemblies that were formerly required to be "silicone free".
The fast cure cycles and improved performance properties of liquid silicone rubber make it a good choice for small molded rubber components. Unlike most thermoplastic elastomers (TPRs and TPEs), liquid silicone rubber (LSR) remains flexible and elastic at -70°F and retains its properties up to 450°F. Since the major cost driver for molded components is labor, or time in the press, liquid silicone rubber is replacing gum base compression molded silicone in many applications.
In the liquid silicone injection molding process, a key advantage of liquid silicone rubber over gum based compression molding silicone compounds is the cure cycle. Depending on the catalyst and cross-section of the molded component, the actual cure cycle can take from 30 seconds up to 2 minutes - with our average cure time of 35 to 50 seconds. In contrast, gum base silicones may take from 5 to 15 minutes per cure cycle in a compression mold. Therefore, a single or two cavity injection mold will out-produce a multi-cavity compression mold. With fewer cavities needed to support production, tooling costs and lead times are reduced. Our tooling partner maintains an inventory of pre-cut steel plates to reduce lead time wherever possible - to facilitate fast design-to-production cycles.
A recent enhancement to our liquid silicone rubber molding capabilities has been the installation of our Cryogenic Systems Model SCC1505 cryogenic de-flashing system. Using liquid nitrogen and small tumbling beads, our new system can remove parting line flash from difficult to reach areas on both simple and complex molded parts. The typical flash condition is reduced from .010" to .015" long, down to .005" long maximum flash extension. Contact us for samples of silicone molded parts after cryogenic de-flashing - you will have to look very close for the parting lines.
Liquid Silicone Compound Suppliers
Liquid silicone molding compounds are purchased in Part A and Part B components from the major silicone producers such as Momentive (formerly GE Silicones) and Wacker Silicones. These compounds are usually mixed in a one to one ratio, with pigment added during the mixing process prior to injecting into the cavity and the cure. The elevated temperature and molding pressures of the liquid silicone injection molding (LIM molding) process enhance the cure. Liquid silicone rubber is supplied to us in airtight containers, pumped from the mix metering units into the tooling without exposure to the environment - therefore humidity is not a concern and generally the liquid silicone injection molding process is more consistent than rubber compression molding.
Tooling Considerations for Liquid Silicone Injection Molding
Liquid silicone rubber molding involves room temperature compounds mixed and pumped into a hot mold. Tooling designs are simplified as liquid silicone rubber flows readily into very thin cross sections, tight radii and thick / thin features. Tooling surfaces do not have to be highly polished, and draft angles are not required to facilitate removal of the finished component from the tooling. When the cure cycle is complete, the molded silicone gasket (LIM gasket) can be removed without concern of distortion or tearing as the silicone is fully cured. (TPRs and TPEs would require ejector pins and draft angles designed into the molds). Call to see samples of liquid silicone injection molding items containing undercuts, straight walls and similar design features that were produced from molds designed to utilize the unique properties of LSR.
Stockwell Elastomerics' latest developments in liquid silicone injection molding include increasing shot size (over 300 grams) to produce LSR molded gaskets as large as 8" wide x 18" long for analytical instrumentation, medical diagnostic equipment and and telecommunication equipment housings. This same capability allows liquid silicone molding of cured sheets, .020" thick through .188" thick in our 12" x 12" sheet mold.
Silicon Rubber or Silicone Rubber? Silicone Rubber Molding, Silicone Molding or LIM Molding?
Although silicon rubber is called out sometimes called out in specifications, silicone rubber is the widely accepted terminology used among in the synthetic rubber industry.
Similarly, terms liquid silicone rubber molding, liquid silicone rubber injection molding, liquid silicone molding, silicone liquid molding, liquid silicone injection molding, silicone injection molding, LIM molding, silicone rubber molding and silicone molding are all used frequently and mostly interchangeably.
Contact Stockwell Elastomerics for Liquid Silicone Injection Molding and Custom Liquid Silicone Molding
Contact Us for further assistance with your custom liquid silicone rubber molding needs.
Molded Silicone Gaskets with Adhesive
Injection Molded Silicone Rubber Components
LSR Force Deflection Curves
Large Shot Liquid Injection Molding (LIM)
Custom Colors for Silicone Liquid Injection Molding (LIM)