Transfer Molding

In a transfer mold procedure, the mold is removed from the press and opened. First, a metal insert is placed into the cavity, and then a pre-cut piece of uncured rubber of pre-determined weight is placed into the transfer “pot.” The loaded mold is then placed back into the press and the press is then closed. The pressure forcing the plates together distributes or transfers the pre-cut piece of uncured rubber in the “pot” down through the “sprues” and into the cavities. The uncured rubber is then forced into the shape of the cavity in the mold. An excess of material flows out of the cavity along the gates and vents. The mold remains closed until the rubber is cured, completing the cycle.

Unlike compression molds, transfer molds consume additional rubber when filling the cavity in the “pot” and “sprues.” Because the cavity plates start out closed, however, less rubber escapes the cavity thereby limiting excess flash. This also makes it well-suited for molding delicately shaped parts and securing inserts that are embedded in a product. Since you work with a single piece of uncured rubber and not several individual pre-cut or shaped pieces of rubber for each cavity, the transfer mold is ideal for colored and translucent compounds. Transfer molds have a shorter cycle and cure time than compression molds. This is due to the rapid transfer of heat to the rubber while being forced from the “pot” through the “sprue” and into the cavity. It is also faster to load just one piece of rubber when running a multi-cavity mold. Due to the more complex design of a transfer mold, it is more expensive to purchase than a compression mold, but it may be better suited for your product design.

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