Abstract
The application of polymers in power-transmitting machine elements, e.g., gears, is limited by moderate thermo-mechanical properties and the detrimental accumulation of contact heat, even with external lubrication. Hence, polymer rolling–sliding elements are often prone to thermo-mechanical overload or abrasive wear. Diamond-like carbon (DLC) coatings are well known from steel applications for enhancing wear resistance and reducing friction. Since preliminary results indicate promising results for such coatings for polymers as well, their influence on the behavior of lubricated polymer contacts is investigated by numerical simulation. For polymer–steel contacts, the mechanical and thermophysical properties of coating and polymer are varied. The contact geometry is dominated by a local conformity, in which most of the deformation is related to the polymer. The DLC coatings affect film thickness and hydrodynamic pressure only little even for untypical high coating thicknesses. In contrast, the contact temperature decreases already for very thin coatings due to enhanced heat removal. Hence, DLC coatings can act as a thermal barrier protecting the polymer from detrimental heat and protecting the polymer from abrasive wear.
Highlights
Moderate thermo-mechanical properties and detrimental accumulation of contact heat inhibit the application of polymers to power-transmitting machine elements, e.g., gears
Thermo-elastohydrodynamically lubricated (TEHL) simulation results of uncoated and Diamondlike carbon (DLC)-coated polymer–steel contacts are presented followed by a discussion of the main findings
To classify polymer–steel TEHL contacts, the hydrodynamic pressure p and the film thickness h are compared in Fig. 2 for a polymer–steel, polymer–polymer and steel–steel material paring at the same line load
Summary
Moderate thermo-mechanical properties and detrimental accumulation of contact heat inhibit the application of polymers to power-transmitting machine elements, e.g., gears. Typical lubricated steel contacts are hard TEHL contacts because the rolling elements are deformed, and the lubricant acts in a piezoviscous manner at high hydrodynamic pressure. Soft TEHL contacts, on the other hand, behave in an almost incompressible and isoviscous manner because of low hydrodynamic pressure [3] They exhibit large deformations which can be greater than the film thickness [4]. DLC coatings on rolling elements are well known in hard TEHL contacts They can improve wear resistance and reduce solid and fluid friction [16,17,18,19,20,21]. The mechanical properties of coatings can influence the hydrodynamic pressure and deformation, whereas the thermophysical properties influence the contact temperature, affecting the effective viscosity in the TEHL contact and influencing fluid friction. Thereby, the thickness of the coating as well as the mechanical and thermophysical properties of the coating and the polymer is investigated
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