Extrusion process materials handling

Part of the contaminants may be present in the pelletized raw materials, another part originates from material handling and processing. The extrusion process and the application of screens removes the larger particles or breaks them down. 

The extrusion of PVC is a field well adapted to use of microwave technology. Use of the chemically polar basic polymer means that microwave absorption within the polymer is possible. Nonpolar polyolefins, on the other hand, cannot be heated directly by microwaves. Since, however, the counter-rotating twin-screw extruders used in PVC extrusion process practically nothing besides PVC, use of the micro-wave does not amount to a loss of flexibility as far as the range of materials an aggregate is designed to handle. 

Web web [ME, fr. OE akin to ON ve web, OE wefan to weave] (before 12c) n. (1) A continuous film or fabric in process in a machine. In extrusion coating, the molten web is that which issues from the die and becomes the coating, and the substrate (web) is the material being coated. (2) A continuous length of sheet material handled in roll form as contrasted with the same material cut into short lengths. 

Cracks that are cause for concern are those that traverse completely through the hardfacing material and then turn in a circumferential direction. When such cracks occur, parts of the hardfacing may come loose. This may happen when the hard-facing is not properly applied. It may also occur when the screw is not handled properly before installation or if the screw is exposed to excessive stresses during the extrusion process. 

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