Compression molding, which is the simplest form of rubber molding, is the process in which a pre-form is placed in or near a cavity. The tool plates are clamped together, forcing the elastomer to fill the cavity. The elastomer is vulcanized and removed from the tool.
Injection molding is the most precise way to shape rubber. The rubber is heated until it has a toothpaste-like consistency. Then the rubber is injected into a mold and allowed to harden. Rubber pieces created this way are strong and are unlikely to lose their shape.
Transfer molding is like a mix between compression and injection molding. A large slug of rubber is placed in a pit. A machine forces the slug into the mold, which causes the rubber to take the shape of the mold. Pieces made this way have higher quality than compression pieces, but less than injection pieces.
During the injection process, rubber compounds are subjected to more severe processing conditions than during compression or transfer molding. While the temperatures, pressures, and stress are higher, cure times are shorter. Control over variables in the process can be more precise.
Types of rubber used in the molding process include butyl rubber, EPDM, fluoroelastomer, neoprene, sponge rubber, nitrile, natural rubber, polyisoprene and silicone rubber.
Numerous influences fueled a change from natural rubber to synthetic rubber during the first half of the 20th century. Synthetic rubber began to replace natural rubber development, natural rubber only account for less than half of all the rubber materials produced worldwide. Neoprene was one of the first synthetic rubbers introduced on an industrial scale, it featured all of the desirable qualities of natural rubber, but few of its undesirable qualities. Synthetic rubber can be engineered to varying levels of resistance to corrosion, chemical inertness, heat resistance, ozone resistance, strength, durability, flexibility, rigidity and many other products.
Industries for which natural rubber products were not practical can now enjoy the benefits of rubber products without enduring the problems they can also cause. Health care facilities, for example, make extensive use of rubber tubing, must consider that some patients have a latex allergy (natural rubber is derived from rubber latex). Silicone tubing allows for the transmission of intravenous fluids without causing allergic reaction.
Uses for molded rubber products are almost endless. Almost every industry out there makes use of some sort of molded rubber product. Manufacturing machinery often have problems caused by vibration, but molded rubber parts can help protect workers, other machinery and the vibrating equipment itself. Other molded rubber products include hoses, seals, grommets, rollers, tubes, gears, valves and so many more.