The importance of motor bearings

Types of motor bearings

Bearing-related failures account for 51% of all motor failures. The more you know about the types of motor bearings, their failure modes, and how to maintain them, the better prepared you will be to take steps to help extend the life of motor bearings.

 

 

Rolling Bearings

Rolling bearings, also known as friction-reducing bearings, are an indispensable component of most electric motors. They allow shafts and axles to rotate at incredible speeds with minimal power loss, and they do so by greatly reducing friction by replacing sliding motion with rolling motion. Rolling bearings are usually classified by the type of element used, the most common being ball bearings and cylindrical bearings.

Ball Bearings

In a ball bearing, rolling motion is provided by balls that are held in place by raceways and cages. Ball bearings support high speeds and very low friction, and they can handle light to medium loads. Motor ball bearings are typically used in direct-coupled applications and can handle radial and axial loads.

Roller Bearings

As the name implies, roller bearings rely on a cylindrical rolling element. These bearings do not require a cage and seat ring as do ball bearings. Roller bearings for electric motors are used in belt applications for motors 150 HP and above. The cylindrical rolling element surface helps to address the high level of radial loads imposed on the bearing by the belt.

 

Types of seals for rolling bearings

Now that we have discussed the different seal types for rolling bearings, we should take a few minutes to discuss the type or style of bearing. The three most common types are sealed, shielded, and open, and each type has its advantages and disadvantages.

Sealed Bearings

In a sealed bearing, the bearing cavity is filled with grease and then sealed during the manufacturing process. This prevents any contaminants (e.g., dirt, dust, metal shavings) from being trapped in the grease and eliminates the need to relubricate the bearing. However, motor sealed bearings have a shorter life than other bearings and need to be completely replaced at the first sign of trouble.

Shielded Bearings

Shielded bearings are similar to sealed bearings in that the rolling elements are protected from contamination during mounting and use. However, unlike sealed bearings, they use a removable shield to retain the grease within the bearing chamber. Because it is removable, it allows relubrication of the bearing (something that sealed bearings cannot do). The ability to relubricate these bearings gives them a longer service life.

Open type bearings

The last type of rolling bearing is the open type bearing. These bearings are neither shielded nor sealed. This allows them to run cooler, with less friction, and they can be easily relubricated. However, the bearing system itself must be designed to protect the bearing from contamination and keep the grease where it is needed.

 

Sleeve Bearings

Another type of bearing you can find on electric motors is the sleeve bearing. These bearings are much simpler in design than friction-reducing bearings, and they rely more on proper lubrication to do the job. Sometimes called journal or barrel bearings, sleeve bearings usually consist only of a lubricated sleeve in which the shaft rotates.

 

Vertical Motor Bearings

There are also bearings for vertical motors that are oriented to run vertically, rather than horizontally. These include thrust bearings, which can include anti-friction bearings (such as ball bearings, roller bearings or cylindrical bearings). Stack multiple thrust bearings so that they can handle both upward and downward thrusts. You may also see bottom guide bearings on vertical motors. Guide bearings can take the form of sleeve bearings or rolling bearings and are located at the bottom of the motor.

 

Bearing care and maintenance

The main task in maintaining friction reducing bearings (especially ball bearings) is to properly lubricate them. It is important to keep the bearings properly lubricated because they are the number one cause of motor failure. The key to lubricating bearings is in using too much grease (more is not always better!) ) and too little grease (which can quickly damage bearings).

 

Motor Bearing Failure

Most bearing failures are related to one of two things: the root cause of the failure is lubrication (too much, too little, or contamination) or electrical damage (including grooves). The good news is that both of these failure modes are preventable.

Bearing failures related to lubrication and contamination

As mentioned earlier, it is critical to keep motor bearings properly lubricated. Too much grease can lead to cage failure or shield dislocation, and can even affect the motor winding temperature. On the other hand, not using enough grease can lead to metal-to-metal contact, which can damage bearings (and other components) if left unaddressed. Finally, another major problem with bearings is contamination. If the grease becomes contaminated with abrasive particles, it will accelerate wear and cause the bearing to fail to reach its expected life.

Electrical damage to bearings

Another common cause of motor bearing failure is electrical damage. One form of electrical damage is grooving, where electrical current passes through the bearing causing visible damage. The damage occurs on the surfaces of ball bearings (which may appear to be frosted or pitted) and roller bearings (which will have evenly spaced lines or patterns on the surface). Fortunately, the groove problem can be solved by electrically isolating the bearing or, in the case of VFD motors, by a shaft grounding ring.

 

Conclusion

If you are experiencing motor bearing problems and are looking for answers, contact Nicer. nicer offers powerful repair solutions that you won't find anywhere else. In addition, we have the equipment and expertise to help you track down the root cause of bearing problems, including grooves in VFD motors. We are EASA certified and follow strict repair and reconditioning procedures, allowing us to provide you with the highest quality repairs that will reduce the M&O costs of your motor power system.