Why bearing temperature increases

Friction results in wear on a broad range of components, and bearings are no exception. Friction can directly cause thousands of dollars in damage to systems and machinery. Provided bearings are working under normal operating conditions, rolling bearings offer much lower friction coefficients than their slide counterparts—especially starting friction. A bearing's operating temperature hinges on equilibrium between two factors: the amount of heat that a bearing generates and the amount of heat that's conducted away from that bearing.

The amount of time that it takes a system to reach a stable state varies based on several factors, such as:. In events where temperatures continue rising for inordinate amounts of time, it must be assumed that a malfunction is occurring. Non-constant temperatures are red flags and should be assessed immediately.

Rolling bearings cannot operate reliably without adequate lubricant, which helps reduce friction and cut down on wear and tear.

In some cases, lubricant aids the cooling a system as well. When friction is converted into heat, that heat must be dissipated to avoid the risk of damage to the bearing.

Selecting the proper lubricating oil can help dissipate a portion of the heat. Recirculating oil lubrication with additional cooling features implemented can be an effective cooling method. While grease does not offer any benefit in heat dissipation it is still the most popular form of lubrication.

Viscosity in a synthetic oil does not vary as much with temperature as in a standard mineral oil, and the rate of oxidation is much slower. These systems pump clean, cool oil through a bearing arrangement. The oil is then cooled in a reservoir before returning to the bearing. In hot-gas fans, special measures must be taken to protect bearings from high temperatures. In virtually all cases, an aluminum disk or flinger placed on the shaft between the bearing and the fan casing can act as a heat shield.

Often, a blower wheel or compressed air can be used to direct cooling air across the bearing housing or the shaft. Although grease is used in some vertical pumps, oil is the preferred lubricant in the majority of pump applications. As in other bearing applications, higher-than-normal operating temperatures in pumps can be caused by bearing overlubrication. Overheating can also be caused by bearing misalignment or ball skidding within the bearing. Specially designed bearings are available to eliminate ball skidding.

Ideally, bearing temperatures in pumps, especially those in critical applications, should be regularly monitored. Gear Drives. As improved technology permits reductions in the size of gear drives, there is a growing trend to transmit more power through a given size drive than ever before. This practice can cause bearings in gear drives to run hotter and may necessitate the use of alternative cooling methods.

If these approaches are not feasible, a synthetic oil approved by the gear drive manufacturer may permit reasonable oil change intervals at the higher operating temperatures. Bearing installation problems can also lead to overheating in gear drive bearings. When tapered roller bearings are replaced, they can be excessively preloaded or misaligned during mounting, resulting in high bearing temperatures.

To minimize overheating, make sure bearings are installed correctly. Kiln and Furnace Applications. Here, specially designed deep groove ball bearings are often used in the wheel assemblies of carts and vehicles conveying material through furnaces and ovens.

Most precision installed and lubricated equipment will operate at less than degrees F. A bearing temperature that is less than degrees F is typically considered acceptable see the chart below. A higher operating temperature will cause the bearing lubricant to deteriorate at a faster rate. At more than degrees F, the lubricant life can be cut by 50 percent for every additional 18 degrees F.

A higher operating temperature also means a lower operating viscosity for the lubricant, which may hurt the overall reliability of the equipment. The diagram below shows how the maximum temperature for a specific lubricant viscosity index and bearing type may limit the maximum operating temperatures. Bearing temperature condition chart. In a caution condition, the bearing temperature may be between and degrees F.

While this is slightly higher than desired, it may be a typical operating temperature for some equipment. Therefore, it is essential to have an operating temperature history for equipment in this range to determine if the temperature is normal.

A C3 clearance bearing is typically considered for this operating temperature. Continue regular monitoring and watch for any significant changes in temperature. Another factor that is just as critical as the absolute bearing temperature is a change in temperature, which is an indication of a condition change. A temperature change of more than 50 degrees F is of concern no matter what condition range in which the absolute temperature falls. Increased monitoring and investigating should be required with this type of change.

Small temperature changes are generally of little concern. It may be normal for a recently greased bearing to increase in temperature degrees F. Other factors that can cause higher temperatures include increased bearing friction poor lubrication, high load, high speed, etc. In an alert condition, the bearing temperature may be between and degrees F.

These elevated temperatures may be due to a heated application, a recently greased bearing, oil level issues, early stages of bearing failure, etc. Be sure to verify the process conditions, recent greasing cycle or oil level. You may also need to increase the frequency of monitoring the temperature changes.

The safe operating temperature for grease is typically 75 percent of the dropping point. If the bearing is running in an application with heat through the journal, this elevated temperature range may be normal for operation. This would also call for a C4 clearance bearing. In an alarm condition, the bearing temperature may be between and degrees F. Bearings operating in this temperature range likely are in some stage of failure. The amount of life left can be highly variable.

Employ other predictive technologies vibration, infrared, ultrasonic testing, etc.