Molding

Thermoforming

Extrusion

Coating

Processing Wiki

In this process, a thermosetting charge (preform) is loaded into a chamber immediately ahead of the mold cavity, where it is heated; pressure is then applied to force the softened polymer to flow into the heated mold where curing occurs. There are two variants of the process: (a) pot transfer molding, in which the charge is injected from a "pot" through a vertical sprue channel into the cavity; and (b) plunger transfer molding, in which the charge is injected by means of a plunger from a heated well through lateral channels into the mold cavity. In both cases, scrap is produced each cycle in the form of the leftover material in the base of the well and lateral channels, called the cull. In addition, the sprue in pot transfer is scrap material. Because the polymers are thermosetting, the scrap cannot be recovered.

	Step #1 - A piece of uncured rubber is placed into a portion of the mold called the "pot." The plunger (on the top-most part of the mold) fits snugly into the "pot."
	Step #2 - The mold is closed up and under hydraulic pressure the rubber is forced through the small hole (the "gate") into the cavity. The mold is held closed while the rubber cures.
	Step #3 - The plunger is raised up and the "transfer pad" material may be removed and thrown away.
	Step #4 - Mold is opened and the part is removed. The flash and the gate may need to be trimmed.

Advantages:

• Loading a preform into the pot takesless time than loading preforms intoeach mold cavity.
• Tool maintenance is generally low, although gates and runners aresusceptible to normal wear.
• Longer core pins can be used and canbe supported on both ends, allowingsmaller diameters.
• Because the mold is closed before theprocess begins, delicate inserts andsections can be molded.
• Higher tensile and flexural strengths areeasier to obtain with transfer molding.
• Automatic de-gating of the mold's tunnelgates provides cosmetic advantages.

Disadvantages:

• Molded parts may contain knit lines in back of pins and inserts.
• The cull and runner system of transfer molding leaves waste material, but this scrap can be greatly reduced by injection molding with live sprues and Runnerless Injection Compression (RIC).
• Fiber degradation of orientation occurring in the gate and runner system reduces the molded part's impact strength.
• Compared to compression molding, high molding pressures are required for the transfer process, so fewer cavities can be put into a press of the same tonnage