The Thermoset injection molding process is the process of thermoset injection molding using a screw or a plunger to put the polymer into a heated barrel to reduce viscosity and then into a heated mold. Once the material fills the mold, pressure should be maintained. Chemical crosslinking occurs at present to harden the polymer. The solidified product can be pushed out of the mold while it is hot. It cannot be shaped or melted again.
The equipment of the thermoset injection molding process includes a hydraulically driven die closing device for closing the mold and an injection device for conveying the material. Injection molding of thermosets is mostly used in granular states or sheets and can be sent into a screw injection device by a gravity hopper. When processing polyester integral mold plastic, it will be like bread balls, a feeding piston is used to press the material into threaded slots.
The polymers processed by the thermosetting plastic injection molding process are phenolic plastics, polyester integral mold plastics, melamine, epoxy resin, urea-formaldehyde plastics, vinyl ester polymers, and diallyl phthalate.
Most injection molding of thermosets contains a large number of fillers to reduce costs or improve their low shrinkage properties and increase strength or special properties. Common fillers include glass fiber, mineral fiber, clay, wood fiber, and carbon black. These fillers can be very wear-resistant and produce high viscosity, which must be overcome by the processing equipment.
Important factors in the selection of equipment for thermoset injection molding include the capacity of mold clamping equipment and injection molding as well as the control system and barrel temperature.
Thermoset injection molding will reduce viscosity when heated. However, the viscosity of injection molding of thermosets increases with time and temperature due to chemical crosslinking reactions. The comprehensive result of these actions is a U-shaped viscosity curve with time and temperature.