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Materials Processes

Processes

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Slush Molding

Method for casting either heat hardening or heat softening plastics, in which the resin in liquid form is poured into a mold, allowed to cure or cool until the required wall thickness is obtained, after which the remaining liquid is poured out.

 

Spinning

Process for producing synthetic fibers and filaments by forcing a viscous resin solution through sine holes in a spinneret.

 

Spray-Up

A general term covering several processes using a spray gun.  In reinforced plastics, the term applies to the simultaneous spraying of resin and chopped reinforcing fibers onto the mold or mandrel.  In the foamed plastics field, the term refers to the spraying of fast-reacting polyurethane or epoxy resin systems onto a surface where they react to foam and cure.  In both processes, resins and catalysts are usually sprayed through separate nozzles so that they become mixed externally, thus avoiding pot life problems in the spray equipment and tanks. [LW]

 

Steam Molding

A process for molding parts of pre-expanded beads of polystyrene, using steam as a source of heat to further expand the blowing agent in the materials. The steam in most cases is contacted intimately with the beads directly or may be used to heat mold surfaces which are in contact with the beads. [LW]

 

Stretch Blow Molding

The main applications of stretch blow molding includes jars, bottles, and similar containers because it produces items of excellent visual and dimensional quality compared to extrusion blow molding. The process first requires the plastic to be injection molded into a 'preform' with the finished necks (threads) of the bottles on one end.  The preform is then heated above its glass transition temperature and blown, using high pressure air, into bottles using metal blow molds. At the same time the preform is stretched with a core rod to fill inside of the mold. Strain hardening occurs as part of the stretching process of some polymers (such as Polyethylene Terepthalate) which allows the bottles to resist deforming under the pressures resulting from carbonated beverages (typically around 60 psi).