Expanded thermoplastic extrusion - in foam head between die and sizing section, dimensional accuracy and control are increased

摘要

Expanded plastic extrusions, specially made of rigid PVC, are produced by passing the thermoplastic material, mixed with a chemical blowing agent, through a die as a strand into a foam head. This varies steadily over its length from the circular cross-section to the final profile of the desired extrusion. The temp in the foam head is controlled by passing a heating or cooling agent through internal bores. The extrusion then passes through a sizing section and a cooling section. The foam process is easy to control and the mfr. of the extrusion die is simplified. The same die can be used for different extrusions by changing the foam head. The new extrusions have excellent dimensional accuracy, a smooth shiny surface and a low unit wt.