Material Selection Guide
Plastics are increasingly being used to replace other materials like bronze, stainless steel, aluminum and ceramics. The most popular reasons for switching to plastics include:
With the many plastic materials available today, selecting the best one can be an intimidating proposition. Here are guidelines to assist those less familiar with these plastics.
Determine whether the component is a:
Determining the primary function of the finished component will direct you to a group of materials. For example, crystalline materials (i.e., Nylon, Acetal) outperform amorphous materials (i.e., Polysulfone, Duratron® PEI or Polycarbonate) in bearing and wear applications. Within the material groups, you can further reduce your choices by knowing what additives are best suited to your application.
Wear properties are enhanced by MoS2, graphite, carbon fiber and polymeric lubricants (i.e., PTFE, waxes).
Structural properties are enhanced by reinforcement fibres like glass or carbon.
Once you have determined the nature of the application (B&W or Structural), you can further reduce your material choices by determining the application's mechanical property requirements. For bearing and wear applications, the first consideration is wear performance expressed in PV and"k" -factor. Calculate the PV (pressure (psi) x velocity (m/min) required. Using Figure 1, select materials whose limiting PV's are above the PV you have calculated for the application. Further selection can be made by noting the "k" wear factor of your material choices. In general the lower the "k" factor, the longer the wear life of the material.
Structural components are commonly designed for maximum continuous operating stresses equal to 25% of their ultimate strength at a specific temperature. This guideline is meant to compensate for the viscoelastic behavior of plastics that result in creep. Isometric stress-time curves are provided here to help you characterize a material's strength behavior as a function of time at both room temperature (Figure 2) and at 150 °C (300 °F) (Figure 3).
Additional Information on Material Performance
Engineering Plastics are more or less flammable. Their flammability depends on the chemical structure, the fillers and additives, the environment - rich in oxygen or not, the ambient temperature, the part geometry, the presence or not of the ignition source, ect. Through the action of fire, certain polymers burn easily, others with difficulty or even not at all.
Note: These mostly estimated ratings, derived from raw material supplier data, are not intended to reflect hazards presented by materials under actual fire conditions.
In 1995, a number of Quadrant Engineering Plastic Products materials were tested according to the European Space Agency (ESA)-specification PSS-01-702 ("A thermal vacuum test for the screening of space materials"). Samples were heated to 125°C for 24 hours (Method "A"), collector plates kept at 25°C and the testing carried out in a vacuum of 10-3 P.
Steam sterilization is commonly used in the medical industry for sterilizing all kinds of reusable equipment, devices, instruments, trays, ect. and is conducted in a pressurized vessel that allows the presence of superheated saturated steam. The main purpose of sterilization is to kill all viable micro-organisms on a certain part.
Tests in which the effect of repeated steam sterilization on the charpy notched impact strength was measured according to ISO 179-1/1eA (measured on dry test specimens at 23°C) clearly show that :