Bearings are used to constraint relative motion between two parts or more and carry load during operation. There are many bearing types and each type has its own use. For example, thrust bearing is used to carry load in axial direction, while ball bearing is used to carry load in transverse direction. Multiple bearing arrangements are commonly used in rotating equipment. Bearings play an important role in reducing friction between two rotating parts. Incorrect lubrication can account for more than 30 percent of bearing failures. Hence proper lubrication for bearings is crucial in reliability operation.
Bearing lubricant provides a thin film between the bearing rolling elements, raceways and cages to prevent metal-to-metal contact. Proper lubricant minimizes the effect of surface contact or friction that would generate excessive heat, metal fatigue, and wear. The lubricant must also prevent rust, corrosion, and contamination damage.
Bearing lubricant contains base oil (mineral or synthetic), thickeners (soap), and other additives. Base oil separates and protects surfaces under operation conditions. Thickeners stiffen the mixture enable it to influence temperature resistance (relating to the viscosity) and chemical stability. Additives are used to inhibit oxidation, corrosions, prevent wear, and change viscosity.
Performance characteristics are derived mostly from the oil and additive mixture, but in some cases the thickener also provides unique performance enhancement. By varying oil viscosities, thickeners, and additives, lubricant manufacturers can make a lubricant that is suitable to predefined applications and operating conditions.
When selecting bearing lubrication, other conditions should be considered in addition to load, speed and temperature. For example, when bearings are subject to vibrations if lubricant with low mechanical stability were to apply, the lubricant matrix may be destroyed by the vibrations. This can cause premature bearing failure.
The following factors are important in selecting the proper bearing lubrication:
• Bearing type and size
• Load conditions
• Machine type
• Speed range
• Operating conditions such as temperature and humidity
• Machine orientation, vertical or horizontal and other external factors such as such as vibration
• Bearing sealing requirement in dusty environment
It is advised to follow bearing manufacturer’s recommendations for selecting bearing lubricant