Shaped polymer fabrication extrusion molding

S3mthetic polymers can be fabricated by molding, extrusion, and solvent processing into reproducible shapes and sizes with little batch-to-batch variation. 

What makes plastics the most versatile of all materials is the ease with which they can be given any desired shape and form. Molding and fabrication processes, however, vary depending on the type of polymers to be processed and the end products to be made. Chapter 2, which deals with polymer fabrication processes for plastics, rubber and fiber, has been thoroughly revised in the new edition to include recent developments in the respective fields and a number of processes not covered in the previous edition. Particularly, the discussion on plastic foams and foam extrusion processes has been further broadened. 

Consideration of orientation and fiber length for a particular composite depends on the level and nature of the applied stress as well as on the fabrication cost. Production rates for short-fiber composites (both aligned and randomly oriented) are rapid, and intricate shapes can be formed that are not possible with continuous fiber reinforcement. Furthermore, fabrication costs are considerably lower than for continuous and aligned fibers fabrication techniques applied to short-fiber composite materials include compression, injection, and extrusion molding, which are described for unreinforced polymers in Section 15.22. 

Structural Foams. Structural foams are usually produced as fabricated articles in injection molding or extrusion processes. The optimum product and process match differs for each fabricated article, so there are no standard commercial products for one to characterize. Rather there are a number of foams with varying properties. The properties of typical structural foams of different compositions are reported in Table 4. The most important structural variables are again polymer composition, density, and cell size and shape. 

Matrix-type implants are fabricated by physically mixing the drag with a polymer powder and shaping the mixture into various geometries (e.g. rod, cylinder, or film) by solvent casting, compiession/injection molding or screw extrusion. 

Polyethylene is the least costly of the major synthetic polymers. It has excellent chemical resistance and can be processed in a variety of ways (blown film, pipe extrusion, blow molding, injection molding, etc.) into myriad shapes and devices. Fabrication methods will be briefly discussed in Chapter 8. 

This is the primaiy processing technique used to fabricate hollow plastic objects, particularly bottles, which do not need a very uniform distribution of wall thickness. It is a secondary shaping technique that inflates the preprocessed plastic (usually extruded) against the inside walls of the mold with a blow pin. In addition to extrusion blow molding, injection blow molding and stretch blow molding are commonly employed. With most polymers, especially when the product size is... 

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