How does Injection Molding work for thermoset resins like BMC?

While injection molding is widely known for thermoplastics, it is also a highly efficient process for thermosetting resins like Bulk Molding Compound (BMC).

The Thermoset Injection Molding Process:

  1. Feeding: The cold BMC material is fed into a hopper, which uses a stuffer mechanism to push the dense material into a heated barrel.
  2. Plasticizing: Inside the barrel, a rotating screw gently heats and mixes the BMC, reducing its viscosity until it becomes a flowable paste. *Crucially, the barrel is kept warm enough to melt the material, but cool enough to prevent it from curing prematurely.*
  3. Injection: The screw plunges forward, injecting the BMC under high pressure into a closed, hot mold cavity.
  4. Curing: The hot mold triggers a rapid cross-linking chemical reaction, solidifying the thermoset resin.
  5. Ejection: The mold opens, and the hardened, finished part is ejected. Unlike thermoplastics, the waste sprue and runners cannot be melted down and reused because the chemical change is permanent.

Injection molding for BMC is ideal for producing small to medium-sized intricate parts with high precision and fast cycle times, such as electrical contactors and motor brush holders.

Typical Processing

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Pultrusion

Pultruded Grating, Tent Poles, Solid Rod, Flat Strip, Square Tube, Hollow Round Tube.

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SMC/BMC

Insulating FRP Parts (Low Voltage), FRP Plates for Water Tanks, FRP Insulators (High Voltage), Sanitary Ware and Auto Parts

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Solid surface

Solid Surface And Artificial Marble Resins, Engineered Stone, Quartz Stone, Granite.

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Hand Lay-up

Chemical Resistance, Tanks & Pipes Resin