The injections presses are more automated than the hydraulic presses. The press opens the mold. The operator removes the parts from the cavities, often using compressed air to separate the part from the mold. The mold is closed by the press and the fully automated injection cycle begins. A large screw and ram assembly forces preheated uncured rubber through the injection nozzle, through the mold's runner system, and into the cavities. The uncured rubber is then forced into the shape of the cavity in the mold. The mold remains closed until the rubber is cured. The injection procedure is used for large parts, particularly part with thin walls and large surface areas.
The mold used in this process consists of a cavity shaped like the part to be produced and a top plate that presses down to form out the part. The heated mold is removed from the press and opened. A precut and weighed piece of custom mixed uncured rubber, is placed into the cavity. If the rubber is to be bonded to metal, the metal piece is placed into the cavity at the same time. The loaded mold is returned to the press and the press is then closed. The pressure exerted by the press pushes the plates together and forces the uncured rubber to flow into the shape of the cavity in the mold. The mold remains closed until the rubber is cured. A compression mold may have many cavities.
A variation on the compression mold is the transfer ...
