Lubrication limitations: The starting torque of rolling bearings in grease-lubricated applications generally increases significantly at lower temperatures. The starting torque is not mainly determined by the stability of the grease, but is usually determined by the rheological properties of the grease. The high temperature limit of a grease is generally determined by the thermal stability, oxidative stability and antioxidant efficacy of the base oil. Refer to the Lubrication section on page 39 for details on lubrication limitations. Device Requirements: Device designers must evaluate the effect of temperature on device performance. For example, precision machine tool spindle bearings can be very sensitive to thermal expansion. For some spindles, special attention is required when operating temperatures are 20C to 35C above ambient. Most industrial equipment can operate at fairly high temperatures. For example, transmission gears can withstand high temperatures of 93C. Equipment such as gas turbines can work continuously at temperatures above 100C. However, if the shaft and housing are not properly machined and heat treated for extended periods of time at high temperatures, the fit may be affected. Although bearings can operate normally at temperatures up to 120C, an upper temperature limit of 80C to 95C is more realistic. Higher operating temperatures increase transient temperature peaks, increasing the likelihood of damage to TIMKEN bearings. Sample testing based on the specific application can help determine the operating temperature range. Equipment designers should weigh all relevant factors and ultimately determine a satisfactory operating temperature.