Thermoset Conversion

Many molders would like the flexibility of molding thermoset materials on their thermoplastic injection molding machine. Converting their existing machine can be done successfully by changing injection unit components manufactured from highly wear resistant tool steels:

Component Modifications

BARREL: Because thermoset materials melt and cure at a very low heat, temperature control is critical. This is better accomplished utilizing a new water jacketed barrel rather than conductive heater band heat. A short barrel or L/D ratio is also recommended to reduce residence time.

SCREW: Heat can be generated by shear from standard screws. To avoid excessive shear rates, it is necessary to change the compression ratio to approximately 1.15:1.

SMEAR TIP: In phenolics, a smear tip with the proper nose angel is required. A free flow valve assembly may be used for polyester.

END CAP: Clearance between the smear tip and end cap angle is critical. Too much and the material can cure and block flow. Incorporating the end cap and nozzle as one unit is usually required.

ADDITIONAL EQUIPMENT: A support bracket may be necessary to relocate the hopper opening closer to the output end when reducing the L/D ratio.

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