When the temperature of a cylindrical rolling bearing system rises, lubricants are frequently the primary cause of failure.
When the temperature of their equipment is high or rising, maintenance staff frequently asks bearing companies: What is the highest temperature that the bearings can withstand? What is the highest temperature that the bearing system can withstand is a better question to ask.
It’s crucial to consider a whole cylindrical rolling bearing system while considering temperatures.
A rolling bearing, lubricant, and most often a lubrication system make up a full cylindrical rolling bearing system. Oils, greases, or dry solid films (graphite, polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2), oil-impregnated polymer oil, etc.) are used to lubricate ball and roller bearings.
Although rolling bearings support the weight of rotating machinery, they cannot operate for very long without oil. The bearing will fail soon after if the lubricant fails. When the temperature of a bearing system increases, lubricants are frequently the primary cause of failure.
Thinking of Temperatures
Instead of thinking of temperatures in relation to just a bearing, just the lubricant, and just the lubrication system, this article is meant to assist maintenance professionals in thinking of maximum temperatures that a bearing system can tolerate while in use.
Both through-hardened and case-carburized steels are treated to a minimum Rockwell C 60 hardness before being used in cylindrical bearings. The American Bearing Manufacturers Association (ABMA) states that the maximum operating temperature of through-hardened steels is 16O0C (32O0F), 18O0C (3560F), and 32O0C for AISI 52100, 440-C, and M50, respectively (60O0F). The hardness generally starts to decline when the temperature rises above 20O0C (3920F) for all steels. As temperatures climb above 20°C, rolling bearing life diminishes as a result (3920F).
Temperature at the Bearing Surface
It is crucial to keep in mind that the temperature at the bearing surface is 10 to 15 degrees Fahrenheit lower than bearing temperature since the most typical way to determine the temperature of a bearing is by reading the temperature on the outside of the housing.
Without oil, cylindrical rolling bearings are unable to operate consistently. A rolling bearing, an effective lubricant, and a lubrication system make up the rolling bearing system. Oils, greases, or dry solid films can be used to lubricate ball and roller bearings. The highest permitted temperature that the cylindrical rolling bearing can withstand shouldn’t be the maintenance team’s top priority when a machine’s temperature increases.
The maximum temperature that the entire bearing system can withstand should be the key consideration. The maximum temperature that the lubricant and/or the lubricating system can withstand should be the main concern since if either of these fails, the bearing will also fail. The failure of a lubricant brought on by a high temperature is challenging to identify. As a result, it’s critical to keep an eye on a lubricant’s temperature.
A cylindrical rolling bearing’s actual life (LO life) will be shortened by friction and wear between the rolling element and the raceways if there is insufficient oil supply. Oil minimizes wear and friction between the rolling element (ball, spherical roller, cylindrical roller, etc.) and the raceway, which lowers heat generation.
Either directly or via the use of grease, oil can be given to the bearing. Base oil and occasionally additives are among the oils used to lubricate rolling bearings. Base oil (65–95%), thickener (3–30%), and additives (0–15%) make up greases. Grease may occasionally have up to 5% of a solid lubricant added.
When used to lubricate cylindrical rolling bearings, oil and grease can only withstand so much heat before losing their effectiveness.
The maximum and minimum operating temperatures of lubricating greases are determined by the base oil type (mineral or synthetic oil) and its viscosity as well as the kind and quantity of thickening agent (organic, inorganic, metal soap) employed.
The viscosity of the oil is something else to take into account with high temperatures in a cylindrical rolling bearing. The relative reluctance of a fluid to flow at a specific temperature is measured by its viscosity; the higher the viscosity, the greater the resistance to flow. Either centistokes (cSt) or Saybolt Universal Seconds are used to quantify viscosity (SUS). The flow rate of the basic oil, not the thickening, determines the viscosity of greases.
Under operating conditions, a lubricant’s viscosity should be sufficient to separate the parts, but not too high to cause additional drag. Oils become less viscous as the temperature rises. A bearing system requires more viscosity as the temperature rises.
In high temperature situations, the bearing system will typically fail early if the employed oil or grease has a lower viscosity. As would be assumed, a higher viscosity oil or grease should often be utilized in high temperature applications.