Materials compression molding

Materials. Compression molding is primarily nsed with thermosetting plastics that crosslink nnder heat and pressure. Special compounds based on thermosetting polyester (SMC), phenolics, epoxies, and alkyls are commonly used. Care must be taken to insure material consistency, becanse this is the major source of variation in the process. 

Cathode electrode assembly, electrode panel between compression molded gaskets. A range of gasket, electrode materials, and electrode geometries is available... 

TS plastic products that are injection, transfer, or compression molded combine thick and thin sections relatively easily since the hardening process is a chemical reaction (Chapter 6). Annular shapes are best made by compression to gain best dimensional control and freedom from distortion. In the compression process, the molding compound is compressed and reduced to the plastic state in the mold. During this process, portions of the material may lie in hard forms in the mold while other portions are flowing rapidly with great force. 

Samples of /the polymers for physical evaluation were prepared by film casting from toluene solution at 90°C. and allowing the crystallization to occur by cooling the melt. It was observed that phase separation occurred in the melt in the case of the H2-BIB but not for the H2-BBB. These materials could also be compression molded at 1<40°C., but optimum results appeared to be obtained with the film-cast samples. 

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

Compression molding is one of the oldest materials handling processes. Ancient Chinese employed compression molding to form articles from paper Mache. Rubber articles were made in the early 19th century from composites of woody fibers and gum shellac. Baekeland used compression molding to make many of his early PF products. 

Figure 7.77 Schematic illustration of compression molding process with mold open (left) and mold closed (right). From Z. Tadmor and C. G. Gogos, Principles of Polymer Processing. Copyright 1979 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

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