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Selection & Design Guidelines

With the many plastic materials available today, selecting the best one can be an intimidating proposition. Let us assist you in the selection of materials: stock shape availability; mechanical, chemical, thermal or electrical properties. Here are guidelines to assist those less familiar with plastics.

- Longer part life - Elimination of lubrication
- Reduced wear on mating parts - Faster operation of equipment / line speeds
- Less power needed to run equipment - Corrosion resistance and inertness

STEP 1 -- Determine whether the component is a:

Bearing and Wear Application (i.e., frictional forces) or Structural (static or dynamic) Application.

STEP 2 -- Consider the thermal requirements of your application using both typical and extreme conditions.

A material's heat resistance is characterized by both its heat deflection temperature (HDT) and continuous service temperature. HDT is an indication of a material's softening temperature and is generally accepted as a maximum temperature limit for moderately to highly stressed, unconstrained components. Continuous service temperature is generally reported as the temperature above which significant, permanent physical property degradation occurs after long term exposure. This guideline is not to be confused with continuous operation or use temperature reported by regulatory agencies such as Underwriters Laboratories (UL).

The melting point of crystalline materials and glass transition temperature of amorphous materials are the short-term temperature extremes to which form stability is maintained. For most engineering plastic materials, using them at or above these temperatures should be avoided.

STEP 3 -- Consider chemical exposure during use and cleaning.

Nylon, acetal and Ertalyte® PET-P are generally suitable for industrial environments. Crystalline high performance materials such as Fluorosint® filled PTFE, Techtron® PPS and Ketron® PEEK are more suitable for aggressive chemical environments (See Page 6). We strongly recommend that you test under end-use conditions.

STEP 4 -- Before proceeding to steps 5-7 itmay be appropriate to consider additionalmaterial characteristics including:

- Relative Impact Resistance/Toughness - Dimensional Stability - Regulatory/Agency Compliance

Materials with higher tensile elongation, Izod impact and tensile impact strengths are generally tougher and less notch sensitive for applications involving shock loading.

Engineering plastics can expand and contract with temperature changes 10 to 15 times more than many metals including steel. The coefficient of linear thermal expansion (CLTE) is used to estimate the expansion rate for engineering plastic materials. CLTE is reported both as a function of temperature and as an average value. Page 4 shows how many different engineering plastics react to increased temperature.

Modulus of elasticity and water absorption also contribute to the dimensional stability of a material. Be sure to consider the effects of humidity and steam.

Agencies such as the Food and Drug Administration (FDA), U.S. Department of Agriculture (USDA), Underwriters Laboratory (UL), 3A-Dairy Association and American Bureau of Shipping (ABS) commonly approve or set specific guidelines for material usage within their industrial segments.

STEP 5 -- Select the most cost-effective shape for your part.

Cope Plastics, Inc. offers designers broad size and configuration availability. Be sure to investigate all of the shape possibilities--you can reduce your fabrication costs by obtaining the most economical shape.

Note: From process to process, many material choices remain the same. However, there are physical property differences based upon the processing technique used to make the shape. For example:

  • Injection molded parts exhibit the greatest anisotropy (properties are directionally dependent).
  • Extruded products exhibit slightly anisotropic behavior.
  • Compression molded products are isotropic -- (equal properties in all directions.)

STEP 6 -- Determine the machinability of your material options.

Machinability can also be a material selection criterion. All of the Quadrant products are stress relieved to enhance machinability. In general, glass and carbon reinforced grades are considerably more abrasive on tooling and are more notch sensitive during machining than unfilled grades. Reinforced grades are
commonly more stable during machining.

Because of their extreme hardness, imidized materials (i.e., Torlon® PAI, Duratron® PI and Celazole® PBI) can be challenging to fabricate. Carbide and polycrystalline diamond tools should be used during machining of these materials. To aid you in assessing machinability, a relative rating for each material can be found on the property comparison charts. See line 42 under product description.

STEP 7 -- Make sure you receive what you specify.

The properties listed here are for Quadrant Engineering Plastic Products' materials only. Be sure you are not purchasing an inferior product. Request product certifications when you order.