Lubrication limitations and equipment requirements for cylindrical roller bearings

Lubrication limitations: The starting torque of flanged linear bearings in grease lubricated applications usually increases significantly at lower temperatures. The starting torque is not primarily determined by the stability of the grease, but usually by the rheological properties of the grease. The high temperature limit of a grease is generally determined by the base oil's thermal stability, oxidation stability, and antioxidant effectiveness.

Equipment Requirements: Equipment designers must evaluate the effect of temperature on equipment performance. For example, precision machine tool spindle bearings can be very sensitive to thermal expansion. For some spindles, special care needs to be taken when operating at temperatures 20°C to 35°C above ambient. Most industrial equipment can operate at fairly high temperatures. For example, transmission gears can withstand temperatures as high as 93°C. Equipment such as gas turbines can operate continuously at temperatures above 100°C. However, when running at high temperature for a long time, if the shaft and housing are not properly processed and heat treated, the fit may be affected. Although wholesale bearings can function well at temperatures up to 120°C, an upper temperature limit of 80°C to 95°C is more realistic. Higher operating temperatures increase transient temperature peaks, increasing the likelihood of bearing damage. Sample testing based on the specific application will help determine the operating temperature range. Equipment designers should weigh all relevant factors and ultimately determine an acceptable operating temperature.

Heating and cooling of cylindrical roller bearings

The operating temperature of a cylindrical roller bearing depends on many factors, including the heat generation of all relevant heat sources, the rate of heat flow between heat sources, and the system's ability to dissipate heat. Heat sources include bearings, seals, gears, clutches, and oil supplies, among others. Heat dissipation depends on many factors, including shaft and housing material and design, circulation of lubricating oil, and external environmental conditions. These factors will be introduced separately in later chapters. Heat generation Under normal operating conditions, most of the torque and heat in a bearing type comes from elastohydrodynamic losses at the roller/ring contact. Heat generation is a product of bearing torque and speed.

Heat dissipation: How to determine the heat flow of custom bearings in special applications is a complex issue. In general, factors that can be considered to affect the rate of heat dissipation include: 1. Temperature gradient from bearing to housing. This factor is influenced by the size of the housing as well as external cooling devices (eg fans, water cooling, etc.). 2. Temperature gradient from bearing to shaft. All other heat sources such as gears and other bearings and adjacent components will affect the temperature of the shaft. 3. The heat removed by the circulating oil lubrication system. To some extent, factors 1 and 2 can vary by application. Heat dissipation modes include heat conduction in the system, convection between internal and external surfaces, and heat radiation between adjacent structures. In many applications, heat dissipation can be broken down into two parts – heat removed by the circulating oil and heat dissipated through the structure. The heat taken away by the lubricating oil through the circulating oil system is easier to control. In splash lubrication systems, cooling coils can be used to control the lubricating oil temperature.