Thermoset injection moulding runs the thermal cycle backwards from thermoplastic moulding. The barrel is kept cool so the material does not cure on the way in, and the tool is hot because heat is what triggers the cure. The part is removed hot and rigid rather than cooled until rigid, and nothing can be remelted afterwards.
The inverted cycle
Material is fed as a granulate or a liquid, warmed only enough to flow, injected into a heated tool, and held while a chemical crosslinking reaction sets it permanently. Cure time depends on section thickness and tool temperature. Because the reaction is irreversible, sprues and runners cannot be reground, which makes runner design and cold runner systems a real economic consideration.
What thermosets give you
Dimensional stability at temperature, because a crosslinked network does not soften the way a thermoplastic does. Electrical insulation that holds up under heat, which is why so much electrical hardware is thermoset. Chemical resistance, creep resistance and low mould shrinkage. And, in filled grades, very high stiffness at a low material cost.
What the tool has to do
Run hot and evenly, since uneven temperature means uneven cure and uneven properties. Vent well, because the cure reaction can release volatiles that have to escape or they burn the part. Tolerate abrasive fillers, which many thermoset compounds contain and which wear cavities quickly. And handle flash, since low viscosity before cure means material finds every gap.
Where they are used
Electrical connectors, switchgear, commutators and insulators. Under bonnet automotive parts that see heat. Brake and friction components. Cookware handles. Anywhere a thermoplastic would soften or creep at the service temperature, which is the boundary that decides most thermoset selections.
Questions people ask about thermoset injection molding
How does thermoset moulding differ from thermoplastic moulding?
The barrel is cool and the tool is hot, because heat triggers a chemical cure rather than melting and cooling. The part is removed hot and rigid.
Can thermoset runners be reground?
No. The cure is irreversible, so sprues and runners are scrap. That is why cold runner systems are economically important on thermoset tools.
Why choose a thermoset?
Dimensional and electrical stability at temperature, creep and chemical resistance, and low shrinkage. Where a thermoplastic would soften, a thermoset holds.
Do thermoset tools wear faster?
Often yes, because many compounds contain abrasive fillers. Tool steel and coating choices reflect that, and the tool is quoted against a shot count accordingly.