The objective of compression molding, in a general sense, is to make specimens that are both homogeneous and isotropic. The molds themselves are made from power, pellets, particles from recycling operations, or from preformed sheets. To produce the thermoplastic mold the beginning materials are melted and molded in a mold that is the desired geometry and thickness. Thermoplastic specimens can also be machined, punched, or cut from a uniform sheet of thermoplastic mold.

There are three pieces of equipment needed for compression molding thermoplastic materials into test specimens according to ASTM D4703. The first is a two-roll mill with chrome plated rolls. The second is a mold. The third is a thermal press. ASTM D4703 requires the press to be capable of 10 MPa (1450 psi) and to be able to heat up to 240 degrees Celsius.

The apparatus used to mold the thermoplastic test specimen is dependent on the type of thermoplastic being created. This means that many apparatus meet the requirements of ASTM D4703, however not all can be used to create a specific thermoplastic.

ASTM D4703 is reference my other ASTM plastic standards for sample preparation. These include:

  • ASTM D1248 Standard Specification for Polyethylene Plastics Extrusion Materials for Wire and Cable
  • ASTM D1693 Environmental Stress-Cracking of Plastics
  • ASTM D1784 Standard Specification for Rigid Poly(Vinyl Chloride (PVC) Compounds and Chlorinated Poly(Vinyl Chloride) (CPVC) Compounds
  • ASTM D3350 Standard Specification for Polyethylene Plastics Pipe and Fittings Materials
  • ASTM D4976 Standard Specification for Polyethylene Plastics Molding and Extrusion Materials
  • ASTM F2922 Standard Specification for Polyethylene (PE) Corrugated Wall Stormwater Collection Champers

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