Preforming

Precision preforms production requires homogeneous plasticizing, constant extrusion and precise cutting to length or weight. VMI COMBEX does this with a single cold feed plasticizing extruder screw, feeding the rubber to a volumetric operated gear pump.

A heavy duty servo driven rotating knife mounted in front of the head outlet, synchronized with the gear pump speed, cuts the extrudate to length or weight. This way, preform weight accuracies within +/- 0.5% are realized.

VMI COMBEX for efficient plasticization
The VMI COMBEX extruder screws guarantee an efficient plasticization, even with high Mooney compounds. The screw delivers the rubber, free of entrapped air, to the gear pump at an adjustable inlet pressure (P1). A gear pump can build up high extrusion pressures with relatively low energy input which results in a low compound temperature (P2).

The system software and display feature a preform set up recipe function. A unique shut down feature allows you to make good preforms up until the last remaining rubber in the extruder. Furthermore, the different sizes of extruder heads can be equipped with straining screens, enabling high pressure fine mesh straining in combination with preforming operation.

The machine design allows easy access for maintenance and cleaning, in particular between the screw and the gear pump. VMI COMBEX extruder gear pump systems, specially executed and without cutting unit are also very suitable – and often used for:

  • Hot and cold feed rubber compound straining
  • Special applications in direct mold filling
  • Endless high precision profile extrusion
  • Silicone rubber extrusion and straining

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