The Most Common Causes of Bearing Failure and the Importance of Bearing Lubrication

Time:2021.01.04  Source:Roller Bearings Suppliers

The Most Common Causes of Bearing Failure and the Importance of Bearing Lubrication

Bearing grease is widely used in the industrial production of rolling bearings, and bearings are the basic parts of mechanical equipment. In the operation of the rolling bearing, the rolling friction will cause the heating and wear of the bearing, reducing friction and damage, so the operation of the rolling bearing requires lubrication. Generally, under special conditions of low speed and heavy load, sliding bearings require more lubricant supply and a more thorough lubrication guarantee. In many cases, the screening and increasing methods of rolling bearing lubricants are the most important factors affecting the life and working functions of sliding bearings.

Lubrication of rolling bearings

The rolling bearing is a machinery component that plays a very important role since it dominates the machine performance. If one of the bearings fails, not only the machine but also the assembly line stops and the deriving costs may be extremely high. For this reason, every bearing manufacturer should make every effort to ensure the highest quality for each bearing and the most careful use and maintenance on behalf of the user.

Lubricants are used between contact surfaces to keep the parts in continuous motion. The main purpose of rolling bearing lubrication is to avoid or reduce the metal-to-metal friction between the rolling and sliding contact surfaces. This is not the only function of rolling bearing lubrication. The supplementary functions are heat dissipation from the bearing, removal of solid wear particles and contaminants from the rolling contact surfaces, corrosion protection, increase of the sealing effect of the bearing seals. WSBC 22205 CC/W33 bearings online, pls click here :

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Lubrication is crucial for bearing life. In heavy-duty applications, such as rolling mill machines, furnaces, ovens or high-temperature fans, rolling bearings may be exposed to higher-than-normal temperatures. For these applications, the appropriate selection of the lubricant and lubrication method is very important [13]. In industrial applications, there are two types of lubricants suitable for high-temperature use: grease and oil. In special cases, bearings are lubricated with solid dry lubricants.

Grease lubricant is used for 90% of all rolling bearings. The amount of grease to be used will depend on many factors relating to the dimensional and geometrical parameters of the housing, space limitations, bearing working speed and type of grease used. As a general rule, rolling bearings and their housings should be filled from 30 to 60% of their total capacity. If working speed and temperature rise, then a reduced amount of grease should be used. If the amount of grease is excessive, temperature rises, which may cause the grease to soften and local leakage may appear. With the passage of time grease loses its properties and fresh grease must be resupplied at proper intervals. The relubricating interval depends on the bearing type, dimensional parameters, bearing working speed and temperature.

In industrial applications, oil lubrication is used if adjacent machine components are supplied with oil as well, or if generated heat must be dissipated by the lubricant. The heat dissipation is necessary if high rotating speeds and/or high loads are involved or if the bearing is exposed to high temperatures. In this case, the relubricating interval depends on bearing operational conditions (temperature, speed, load, etc.), oil quantity and type of oil used. If an oil bath lubrication method is used when operating temperatures are around 50 °C, then the relubricating interval should be one year. For operating conditions of 70 to 100 °C, the oil should be replaced every three months. Anyway, it is important that lubrication system and deterioration be verified regularly to determine oil replacement.WSBC 22206 CC/W33 bearings online, pls click here :

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Another type of bearing lubrication is solid or dry lubrication. This method is used in industrial applications, where rolling bearings are subjected to heavy loads, slow relative movements and high working temperature. Solid lubrication is very effective and yields relatively long running times. The most commonly used solid lubricants are graphite and molybdenum disulfide. These solid lubricants are applied to the raceway surfaces in the form of powder loose, sliding lacquer or paste. Graphite and molybdenum disulfide lubricants can be used for high operating temperatures of up to 450 °C.

The most common causes of bearing failure

The failure of a bearing is the result of the comprehensive effects of various aspects such as design, manufacturing, installation, operation and maintenance, and it is often difficult to determine the initial cause of its failure. In the process of bearing use, some users will also raise some non-failure phenomena. The non-failure phenomenon of the bearing will not have any influence on the use, but it is caused by the difference in the process of different manufacturers.

In practice, damage or failure of a bearing are often the results of several mechanisms operating simultaneously. The failure can result from improper assembly or maintenance or from faulty manufacture of the bearing or of its adjacent parts. In some instances, failure is due to a design compromise made in the interests of the economy or from unforeseen operating conditions. It is the complex combination of design, manufacture, assembly, operation and maintenance that often causes difficulty in establishing the primary cause of failure. Consideration of each feature is required for reliable determination of the cause of bearing failure. Since more than one process may cause similar effects to these surfaces, a simple description of the appearance is usually inadequate to determine the reason for the failure.

In the event of extensive damage to or catastrophic failure of the bearing, the evidence is likely to be lost and then it will be impossible to identify the primary cause of failure. In all cases, knowledge of the actual operating conditions of the assembly and the maintenance history is of the utmost importance. 

The evolution of tribological research during recent decades has led to a remarkable increase of new knowledge describing failure mechanisms. The data from this research field show that improper lubrication is the most commonly cited cause of bearing failure and accounts for approximately 80% of breakdowns. Naturally, these percentages may vary from application to application depending on operating conditions and maintenance practices.

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