Transfer Molding Process / Advantages of Transfer Molding / Disadvantages of Transfer Molding
The transfer molding process can be used to produce both solid rubber parts and parts that require bonding rubber to a metal or non-metallic component. Examples of parts manufactured with transfer molding include vibration isolators and shock absorbers.
The Rubber Transfer Molding Process
Similar to compression molding, transfer molding requires raw material preparation into pellets and/or pre-forms. Rather than placing the preform in the mold cavity, the preformed material is placed in a “pot” located between the top plate and a plunger. In the pot, the material is compressed by the heated plunger and forced (transferred) through sprues into the cavity below. The plunger is kept in place until the preform takes on the shape of the mold and the cure is reached, vulcanized. The part is allowed to harden, cool, then is ejected. The cull pad, any cured rubber left in the pot, is removed, mold cavities are cleaned and the next molding cycle begins.
When used for rubber to metal bonding, the transfer molding process requires the components are loaded into a heated mold either by hand or using a loading fixture. Material is loaded into the well pot of the transfer mold. The mold closes and the heated rubber is then transferred through the runner and gate sprues into the mold cavities. Under pressure and elevated temperatures, the rubber cures/vulcanizes and parts are removed.
The rubber transfer mold consists of a piston, well pot, sprue plate, cavity plate, and a base plate with a knock-out system used to eject the parts after molding.