Characterization of TEHL contacts of thermoplastic gears

Abstract

Thermoplastic materials generally show low specific weight, low coefficients of friction, noise damping behavior and demonstrate low-cost manufacturing by injection molding. This qualifies thermoplastics for the use in lightweight gear design and more generally for an increase in resource efficiency. However, moderate thermo-mechanical material properties and detrimental accumulation of contact heat limit its applications to lowly loaded machine elements. Lubrication allows pushing these boundaries. In this work, the thermo-elastohydrodynamically lubricated (TEHL) contact of steel-thermoplastic material pairings (hybrids) is analyzed by tribosimulation and at the FZG twin-disk test rig for representative thermoplastic gear operating conditions. After a comparison to plain steel TEHL contacts, the focus is on friction, film thickness and heat management. Results show that high surface conformity leads to low hydrodynamic pressures and thus very low friction. Furthermore, local contact temperatures affect tribological performance. The considered steel-thermoplastic TEHL contact operates in the transition region between hard TEHL and soft EHL.