Pitting load carrying capacity under increased thermal conditions

• Published in: Industrial lubrication and tribology 2011-01, Vol.63 (1), p.11-16
• Main Authors: Höhn, Bernd-Robert, Michaelis, Klaus, Otto, Hans-Philipp
• Format: Article
• Language: English
• Subjects: Algorithms; Applied sciences; Bearing strength; Case hardenability; Cooling; Efficiency; Exact sciences and technology; Fracture mechanics (crack, fatigue, damage...); Friction; Friction, wear, lubrication; Fundamental areas of phenomenology (including applications); Gears; Load; Load carrying capacity; Lubricants; Lubricants & lubrication; Lubrication; Machine components; Mathematical analysis; Mechanical engineering. Machine design; Metal fatigue; Mineral oils; Physics; Pitting tests; Shear stress; Solid mechanics; Strength; Structural and continuum mechanics; Studies; Temperature; Thermal energy; Thickness; Viscosity
• ISSN: 0036-8792; 1758-5775
• DOI: 10.1108/00368791111101795

Purpose - The purpose of this paper is to make an attempt to evaluate the pitting load carrying capacity under increased thermal conditions. This is the basis for an estimated lifetime which is one of the most important parameters defining transmission reliability.Design methodology approach - Recommendations related to pitting load carrying capacity calculation of case hardened gears running at high gear bulk temperatures are formulated. These factors are based on extensive experimental data, obtained in pitting tests with high oil injection temperatures, high oil sump temperatures or high operational gear bulk temperatures due to a lack of heat dissipation caused by minimised lubrication.Findings - Testing of gear type C-PT on FZG back-to-back test rig at high gear bulk temperatures by either heating up the lubricant or caused by a lack of heat dissipation as it appears with poor lubrication conditions resulted in a decrease of up to 30 per cent of the endurance strength in various investigations. This results in a reduction of the material strength due to tempering effects and high surface shear stress due to low oil film thicknesses caused by low operating oil viscosities.Originality value - The present calculation method in the standard DIN ISO is not valid for high gear bulk temperatures. Nevertheless, the present calculation algorithms of the standards DIN ISO are valid for low and moderate thermal operating conditions when using oil temperatures of up to 80 (90)°C in the case of a sufficient cooling oil supply to the gear mesh. With the presented modifications higher gear bulk temperatures (>120°C) can be taken into account.