NHML Resources - Proper Application of Engineering Plastics

The following outlines a few characteristics of plastics which must be considered in the design or application of a plastic part. Discuss your design expectations and constraints with your material advisors. Consider these:

Thermal Considerations

  • Temperature Resistance&Heat Deflection Temperature
      High temperature exposure can result in changes in the mechanical strength or life of a plastic part. It accelerates plastic deterioration and may cause colors to shift.
  • Thermal Conductivity
      This is especially important for a device that is heat generating. Modern electronics often need a method of heat dissipation.
  • Coefficient of Thermal Expansion
      Dimensional changes may introduce unplanned stresses into the part which could result in part failure.

Environmental Considerations

  • Operating Temperature
      Chemical resistance and mechanical strength can be affected by operating temperature. Operating temperatures (and time at those temperatures) must be assessed at the location of the part.
  • Internal&External Stress
      Residual (internal) stresses may be minimized by careful part design. Mechanical testing of the part may help to identify potential stress problems.
  • Chemical Exposure&Adjacent Materials
      Mechanical strength as well as appearance can be affected by chemical exposure. Reactions with organic chemicals are especially troublesome. Outgassing vapors or migrating chemicals can affect nearby parts. Review the chemical compatibility of nearby solids as well as liquids and lubricants.

Mechanical Properties

  • Tensile and impact strength, as well as elastic moduli, may be improved by the specification of fillers or fibrous reinforcements. For example, the base resin of PEEK plastic has a tensile strength of 13,000 psi. When reinforced with 40% short fibers, the tensile strength increases to 27,000 psi. When long fibers are used, the tensile strength is increased to 32,000 psi.
  • Some reinforcement fillers may affect the part's wear characteristics and flammability, as well as the tool choice and the ability to mold.
  • Consider the structural requirements of the part. The affects of loading (long-term, short-term, and impact) may drive your resin or filler choice.

Electrical Considerations

  • Most plastics are excellent insulators, however, their performance may vary with material thickness and temperature. Contact your material experts to confirm the expected performance of the material.
  • International regulations are calling for the increased control of EMI (Electro Magnetic Interference). Carbon and metal fibers are often added in order to change the electrical conductivity of the plastic, thereby increasing the shielding effects. Another effective method of shielding is plating the part with a zinc or other metal coating.

Contact your material advisor to discuss your specific needs. Engineering reference materials on plastics are available from ASM International in Materials Park, OH. For information on plastics and suppliers, contact Modern Plastics Magazine at Canon Communications LLC in Los Angeles, CA.

See our Industry Definitions for further insight.

 

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