Close this search box.
Home » Blog » How thermosetting plastics are injection molded?

How thermosetting plastics are injection molded?

Thermoset injection molding uses a screw or a plunger to pass the polymer through a heated barrel (120-260°F) to reduce density and fit it into the heated earth (300-450 °F). Once the material fills the world, it’s held under pressure. 

At this point, chemical cross-linking occurs, causing the polymer to harden. The complex (i.e., cured) product can be ejected from the earth while still hot, and it can not be remolded or remelted. 

The injection molding outfit has a hydraulically driven ending device to close the earth and an injection device to convey the material. Utmost thermoset plastics are used in bullet or distance form and can be fed into the screw injection unit from a graveness hopper. 

When recycling polyester monolithic molding composites (BMC), like” chuck dough,” a feed piston is used to press the material into a threaded groove. 

The polymers reused using this process are (in order of operation); phenolic plastics, polyester monolithic molding compounds, melamine, library paste resins, urea-formaldehyde plastics, vinyl ester polymers, and diallyl phthalate( DAP). 

Utmost thermoset plastics contain large quantities of paddings (up to 70 by weight) to reduce cost or ameliorate their low loss parcels and increase the strength of particular packages. 

Common paddings include glass filaments, mineral filaments, complexion, wood filaments, and carbon dark. These paddings can be veritably abrasive and produce high density, which the processing outfit must overcome. 




Both thermoplastics and thermosets will drop in density when hot. Still, the density thermosets increases with time and temperature due to the chemical cross-linking that occurs. The concerted result of these goods is a-shaped density wind with time and temperature. 

The purpose of thermoset injection molding is to complete the stuffing of the earth in the region of the most negligible density when the pressure needed to rot the material into the earth shape is the smallest. This also helps to minimize damage to the filaments in the polymer. 

The injection molding process uses a screw to flow the material through a heated barrel, circulated with water or canvas in a jacket around the barrel. The screw can be designed for each material type, compressed, slightly to remove air, and toast the material to gain a low density. Utmost thermosetting accouterments inflow relatively well then. 

The operation to get the material into the earth is to stop the screw gyration and push the screw forward at high speed with hydraulic pressure to press the plasticized low-density material into the earth. 

This rapid-fire inflow requires that the earth depression be filled in 0.5 seconds at a pressure of 193 MPa. Once the depression is filled, the high-speed inflow of the material generates lesser heat of mocha to accelerate the chemical response. Once the depression is filled, the injection pressure is reduced to a holding pressure of34.5-68.9 MPa. 

This holding pressure is maintained on the material for 5 – 10 seconds, followed by depressurization, and also the coming cycle of plasticization begins. 

The material is held in the hot earth until it hardens. Also, the earth-ending device is opened, and the product is ejected. 

The product can be smoothly uncured and kindly soft when first ejected, and the final cure is completed within 1 or 2 twinkles after junking using the heat retained inside the product. 

The entire production cycle of a thermoset product is 10 – 120 seconds, depending on the consistency of the product and the type of raw material. 

Numerous different and technical ways are used to ameliorate the quality and reproducibility of the product. Given that some thermoset polymers induce gas when hot, there’s frequently a deflation operation after the earth is incompletely filled. 

In this step, the earth is opened slightly to allow the gas to escape and closed snappily to refill the remaining material. 

Injection molding provides advanced strength, better dimensional control, and bettered face condition( appearance) due to the use of earth with a retractable depression and core, which can be opened 1/ 8- l/ 2 in during the injection process and also snappily compressed as if the earth were closed. 

Monolithic molding composites made of glass filaments, paddings, and polyester unsaturated resins can be injection moldered with the fresh technical outfit on the machine. 

A piston confluent is attached to the barrel to force the feed, which can also be operated differently. One with a conventional reciprocating screw, which pushes the material forward while mixing and hotting. This requires a stop-over stopcock at the end of the screw. 

This prevents the material from flowing back onto the screw vestments because of the material’s low density. Another way is to use a plunger or piston to press the material into the earth’s depression. 

The plunger is frequently used for accouterments containing further than 22 by weight of glass filaments, as it’s lower dangerous to the filaments and gives advanced strength.



Share this post