Blending

Blending the raw materials is one of the most underrated aspects of calendering technology. The reason, perhaps, is at U.S. manufacturers first concentrated on flexible compounds rather than rigid ones. Blending flexible compounds is done differently, usually in large batch blenders, first heated and then cooled for better absorption and storage of masterbatched plasticizer and pigment. So, when U.S. manufacturers finally under took compounding of rigid PVC formulas, there was a tendency not to spend capital dollars on the high-intensity mixers used extensively in Europe. Because of their high speed, not only do they blend thoroughly and quickly but fuse ingredients in place preventing separation. U.S. compounders had been relying on ribbon blenders, which are much less efficient. Banburys, from the Farrel Corp, were used to flux batch by batch and essential mixing was accomplished in the fluxing step. But with the newer continuous fluxing machines, little effective mixing is done after a compound leaves a blender.

A blender is essentially a very simple piece of equipment, it consists of a large container into which the plastic materials are fed, the bottom of which is conical in shape to aid with emptying the material out after the blending process is complete. A vertical screw feeds the plastic to the top of the blender where it then spays onto the sides of the blender where foils further disperse the material.How long this process takes depends on the quantity of material and the speed of the screw.