Silicone Rubber Molding
Silicone rubber is one of many synthetic rubbers available for use in a variety of commercial and industrial manufacturing processes. It is created using a mixture of silicon, hydrogen, oxygen, and carbon. Other additives may be included, but this varies on a case to case basis.
Quick links to Silicone Rubber Molding Information
Applications of Silicone Rubber
- Silicone Rubber is Used in Many Industries, Including:
- Automotive Manufacturing
- Appliance Manufacturing
- Medical Device Manufacturing
Products range from small, practical, semi-universal components (like shaft sealing rings, door seals, gaskets, grommets, and o-rings) to application-specific products (like automotive heating hoses, spark plug caps, lab instruments, and medical devices).
- Other Products Made via Silicone Rubber Molding Include:
- Syringe Pistons
- Respiratory Masks
- Implantable Chambers for IV Administration
- Lipstick Molds
- Makeup Brushes
- Circular Lenses
- Freeform Lenses
- Cooking Aids
- Food Containers
- Non-Flammable Tape for Electronic Components
- Home Repair Products
Material Properties of Silicone Rubber
Silicone rubber is generally known for its chemical inertness, resistance to the negative impact of harsh environments, temperature resistance, and high electrical insulation abilities. However, individual grades, like medical grade silicone or RTV silicone, vary in levels of qualities like flame resistance, steam resistance, chemical resistance, metal detectability, and electrical conductivity. Though it is technically a polymer, silicone acts more like an elastomer in that it is quite elastic and flexible. In addition, unlike other polymers, which have a carbon backbone, silicone rubber has a Si-O-Si backbone.
Some special silicone rubber grades include metal detectable, high tear strength, metal detectable, low smoke emitting, flame retardant, and steam resistant. In addition, material used for silicone rubber molding can be placed on a hardness scale, using Shore A (durometers) or IRHD (International Rubber Hardness Degrees) as units of measurement. These range from 10 to 100, with one 100 being the hardest.
Manufacturing Process of Molded Silicone Rubber
There are five major methods by which silicone rubber molding may be achieved: injection molding, cast molding, transfer molding, compression molding, and dip molding. Injection molding begins with a batch of raw silicone rubber being placed in a long channel, where it is melted by the friction generated by the turning of a large screw. After this rubber has become molten, the process continues with the molten rubber being injected into a mold cavity that is preformed into the desired final shape. Allowed to cool and harden there, the rubber fills up the mold and takes on its shape. Similarly, in cast molding, silicone rubber is poured into an open mold, or hollow cavity, where it takes on the shape of the mold, cools, and hardens.
The transfer molding process is somewhat unique from the two before it. To work, either liquid silicone rubber or a piece of preheated, uncured rubber is placed into a chamber (called the pot). Once there, it is forced into a heated mold cavity by a plunger or ram. If the material is already liquid, it will then simply take the shape of the mold, but if it is solid, it will melt under the influence of the mold temperature and forcing pressure. Either way, the rubber material will be and remain liquid while inside the mold. Once it has uniformly taken on its shape, the rubber is cooled at a control rate that ensures optimal thermoset curing.
Compression molding also employs a heated mold. However, in this case, hydraulic pressure forces the rubber material, which is preheated, into the mold, which is closed, via a small hole. Once inside, the pressure ensures that the material is forced to contact every mold surface and take its shape. It stays there, with the mold closed, until it cures. Finally, dip molding is a process used to coat metal molds in silicone rubber rather than shape silicone rubber inside metal molds. In this case, the rubber is melted and held in a molten state so that steel and/or aluminum molds, which are primed and heated, may be dipped into it from an overhanging rack. In addition to primary molding, silicone rubber can also be dyed, cured and/or manipulated into different grades.