Thermoset Molding

The Thermoset family of plastic materials harden and cure in the molding process as the molecules actually crosslink in a chemical reaction and set into a final shape. No addition of heat will soften or melt the material. As a result, thermosets have their advantage in any high heat environment where softening or melting cannot be tolerated. Domestically products such as ash trays, cooking utensils and cookware handles are produced from thermosets. Industrially thermosets are used in electrical, electronic and military applications. Some examples of thermoset materials are phenolics, epoxys, melamines and diallylphthalates.

Thermosets can be molded using the compression, transfer or injection molding processes. Southwest Plastics has extensive capabilities in molding thermoset materials using all three of these processes.

Compression Molding is the first technique developed in the early 1900s to mold Bakelite (phenolic) molding compounds. It is used today to process many varieties of thermoset plastics and composites including phenolic, epoxy, melamine, and diallyl phthalate. The compression molding press is simply a vertically oriented hydraulic press. The compression mold is clamped into the compression molding press, and is simple in that it consists of two halves: the cavity and the force or core on the opposite side. The mold is heated to the temperature as specified by the material manufacturer which is usually around 300° F, and the material is placed directly in the cavity. The mold is then closed under pressure compressing the material and causing it to flow into the void between the cavity and the core. The mold is held closed for several minutes (depending on the material used and the wall thickness of the part) while the material is curing or “setting” into the form of the mold surface. The mold is then opened and the part ejected from the mold cavity. Compression molding lends itself to relatively simple parts, but since there are no sprues, runners or gates through which the material must flow, the material can be heavily loaded with a composite of fillers and fibrous reinforcements which remain in a random orientation in the molded part resulting in superior strength properties.

Transfer Molding is another method for molding thermoset materials where the design of the part is too complicated or unsuitable for compression molding. Transfer molding is often used when metal inserts, studs, connector pins wear plates, electronic components or other parts are molded into the part. With transfer molding, the mold is clamped closed first. The material charge is then loaded into a loading “pot” which is connected to the cavity with a short runner. The material is then “transferred” from the pot to the cavity via the runner under pressure exerted from a plunger which is hydraulically actuated against the material which has been loaded in the pot.

Thermoset Injection

In order to shorten cycles and lower costs, some thermoset materials have been developed which can be injection molded. The standard injection molding machine must be modified by way of the use of a specialized screw and barrel in order to injection mold thermoset materials. Southwest Plastics has been injection molding thermoset materials for many years and have the expertise to make your next project a success.

Thermoset Materials