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Materials Processes

Processes

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Air-Slip Forming

A vacuum forming process in which a male mold in enclosed in a box which forms an air cushion as the mold advances toward the hot plastic sheet, this keeping the mold from contacting the sheet until the end of its travel.  At this point, vacuum is applied to destroy the air cushion and pull the sheet against the mold (see thermoforming)

Source: Whittington, Lloyd R.  Whittington's Dictionary of Plastics (Stamford, CT: Technomic, 1968).

 

Annealing

The process of relieving stresses in molded plastic articles by heating to a predetermined temperature, maintaining this temperature for a predetermined length of time, and slowly cooling the articles.  The process is used to relieve stresses in articles to be painted which might craze due to solvent attack.

Source: Whittington, Lloyd R.  Whittington's Dictionary of Plastics (Stamford, CT: Technomic, 1968).

 

Assembly

Plastic parts are joined to other articles by many methods. Self-tapping screws are made with special thread configurations to suit specific resins.  Threaded inserts to receive mounting screws may be molded or installed by press-fitting or by self-tapping external threads.  Press fitting is used to join plastics to similar or dissimilar materials.  Snap fitting joints are made by molding or machining an undercut in one part, and providing a lip to engage this undercut in a mating component.  Other methods are cementing, heat sealing, staking, ultrasonic inserting and welding.

Source: Whittington, Lloyd R.  Whittington's Dictionary of Plastics (Stamford, CT: Technomic, 1968).