What You Should Know About PV Rating of Bearings

December 15, 2020

Bearings have been very useful for many pieces of equipment and devices. For one, bearings help them reduce friction whenever their parts or components rotate. Additionally, they are intended to protect the part that supports the rotation. Even the positioning of the rotating shaft is maintained through bearings. With these hardware devices, industries are guaranteed to perform optimally for a very long time.

To date, bearings can be classified according to their composition. Some of them have spherical rolling elements, while others have cylindrical rolling elements. But whatever their composition is, their performance is still determined by various elements. Some of these are pressure and velocity.

Overview of Bearing’s PV Rating

The pressure (P) imposed on the bearing and its velocity (V) can easily determine the longevity of the bearing. Both elements make up the PV rating, which is a rating that tells the highest combination of load and speed that the bearing can handle optimally during the actual operations. One factor that can be detrimental to the overall PV rating of bearing is the presence of heat.

With heat, it can easily deteriorate the lubricating properties of the bearing. Additionally, it can alter the clearance between the bearing and its housing. The clearance between the bearing and shaft can also be changed due to the presence of heat. As long as there is heat, bearings can easily be faced with increased friction, greater wear, and reduced service life.

The ability of a system to remove heat from the bearing depends on numerous factors. Some of these factors include thermal conductivity of the bearing and the shaft, difference between the maximum bearing temperature and the ambient temperature, bearing thickness, and coefficient of friction between the bearing and the shaft.

Increasing Permissible PV Rating

There are a lot of conditions that can increase the permissible PV rating of a bearing.

  • Shaft Hardness and Finish:A hardened or chrome-plated shaft that has a finish of 0.3 microns or better can yield much closer bearing clearances, decreased wear, and better performance.
  • Additional Lubrication: The addition of pressure lubrication or extra oil that comes from a reservoir or pump can easily result in a much higher PV rating.
  • Cooling: As mentioned, heat can affect the performance of bearing. With effective cooling such as forced air or oil circulation, the permissible PV rating of a bearing can easily increase.
  • Instantaneous Loads: Instantaneous loads or loads of short duration is known for increasing the permissible PV rating of a bearing.

Reducing Permissible PV Rating

A reduction in the permissible PV rating of a bearing can be caused by numerous conditions.

  • General Properties: A bearing that has poor shaft finish, out of round or soft material, a build-up of dust, grit, or moisture, and presence of corrosive fumes can affect its PV rating.
  • Overall Operations: Self-lubricated bearings that operate at low speeds, continual start-stop, or reciprocating motion can instantly reduce their permissible PV rating.
  • Extreme Elements: Other types of bearings that operate at high speeds, extreme temperatures, and extreme clearances can likewise reduce their overall PV rating. Operating under high or low temperatures can affect the actual shaft clearance and the lubricant properties.

Keeping the PV rating at the recommended value ensures that a bearing can work optimally for a long time. To know more about it, feel free to contact us at PM Distributors.


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