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This paper will examine the effect that PTFE, silicone and other internal lubricants have on the mold shrink rate of thermoplastic gear materials and the resulting effect on the accuracy of the molded gear. “Standard” thermoplastic mold shrinkage data is generated on relatively large test samples which do not represent the flow, orientation and heat transfer seen in a typical molded gear. Additionally, different parts of the gear can be expected to shrink at different rates, leading to potential errors if a single “generic” mold shrink rate is used to design and machine the gear mold cavity. Using a single cavity gear mold, the shrink rate of different internally lubricated gear materials is measured and compared to the unlubricated base resin. The shrink rate of individual parts of the gear are compared, as well as the resultant total composite variation.

This paper investigates the use of internally lubricated and reinforced thermoplastic compounds in tribological applications requiring high pressure-velocity (P-V) performance. Elevated temperature wear testing, limiting P-V testing and elevated temperature mechanical testing demonstrate the feasibility of using internally lubricated and reinforced Polyetheretherketone and thermoplastic Polyimides in high P-V applications. The data also suggest that reinforced and lubricated Polyphenylene Sulfide and Polyphthalamide may be worth investigating as even lower cost alternatives.