Silicone rubber differs from other polymers in that it does not have a carbon backbone, but a Si-O-Si backbone. Also, even though it is a polymer, silicone rubber acts like an elastomer; it can be very flexible and elastic.
Silicone rubber can be engineered in many different grades. These grades distinguish themselves from each other in terms of their respective qualities of steam resistance, electrical conductivity, flame resistance, metal detectability, chemical resistance and other physical properties.
Most silicone rubber varieties share in common naturally-occurring qualities of high electrical insulation, resistance to extreme temperatures, chemical inertness and resilience in harsh environments.
Silicone rubber can be molded into an unending list of indispensable products that are used across industry and commerce; medical devices, gaskets, lab instruments, automotive heating hoses, shaft sealing rings, door seals, o-rings, spark plug caps and rubber grommets can all be made using the silicone rubber molding process.
The aerospace, medical, automotive, construction, electronics, appliance manufacturing, architecture, petrochemical and pharmaceutical industries all make use of silicone rubber products.
Silicone rubber molding is accomplished in five different ways: cast molding, injection molding, compression molding, transfer molding and dip molding.
The cast molding process involves pouring silicone rubber in its liquid form into an open mold, which is a hollow cavity in which the silicone rubber solidifies and takes shape.
The injection molding process involves a collection of raw silicone rubber, which is melted in a long channel by friction caused by a large, turning screw. Once molten, the silicone rubber is injected into a mold cavity that gives the rubber its shape, after which the silicone rubber cools and hardens.
In compression molding, silicone rubber is preheated and squeezed into a heated mold cavity. Pressure is then applied to force the silicone rubber into contact with every mold surface, which creates a precisely-molded finished product.
The transfer molding process involves a plunger-like device built into a mold. First, the silicone rubber is injected into the mold’s cavity through small holes, after which a piece of uncured silicone rubber is placed in a chamber.
The mold is closed and hydraulic pressure is used to force the silicone rubber through a small hole into the cavity. The mold is held closed while the silicone rubber cures.
Lastly, in dip molding silicone rubber is kept in a liquid state while heated and primed aluminum or steel molds are dipped into the liquid silicone rubber from an overhanging rack.