Transfer molding differes from compression molding in that a runner and gate system are used to convey the plastic to the mold cavity. Typically, a preheated prform is placed in the transfer pot, and the mold is clamped shut by a hydraulic ram. The transfer ram then compress the pellet, forcing the material through the runner and gate system, filling the mold cavities. Like compression molding, mold temperature is maintained constant, typically with electric heaters, although hot oil and steam are still used.
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Transfer Molding Advantages
- Reduced cycle time
- Reduced Wear in the cavity
Runners and gates may erode.
- Delicate inserts and complex mold geometry are practical.
- Tight dimensional control across the parting line is acheiveable.
- Transfer molding hyeilds better tensile and felxural and impact strength than injection molding.
- Flash is very thin and easily removed.
Transfer Molding Limitations
- Mold ed in stress is greater than with compression molding.
- Knit lines may form in thin sections.
- Weasted material due to cull and runner system.
- Long fiber reinforced materials are not suitable for this process.
- Higher molding pressuires are required so fewer cavities can be run in a press of the same tonnage than with compression.
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