Speed - Bearings - Technical

Bearing Speed / Limiting Speed

Limiting speed is the speed at which a bearing can operate at light loads and normal operating conditions without failing prematurely. It is a guide only. Application speeds can vary greatly.

Bearings in dental handpieces often run at speeds of up to 3 times their limiting speed, however they are not expected to last as long as bearings in less demanding applications.

Published limiting speeds apply to applications involving a rotating shaft. Speeds for applications involving a rotating housing can be up 30% lower.

Many factors combine to affect the attainable speed and expected life of a bearing. Factors affecting speed and life include ...

• load
• vibration
• lubrication
• cage type
• operating temperature and internal clearance
• moisture / contaminants
• mounting
• precision
• closures

Load

The limiting speed of a bearing is based on lightly loaded running conditions. Increasing the load will adversely affect the attainable speed and/or bearing life. An increase in either load or speed may sometimes be compensated by a decrease in the other resulting in a similar life expectancy.

It is important to note that a deep groove radial ball bearing should not be subjected to undue axial loads, and axial type bearings (such as angular contact or thrust bearings) should not be subjected to undue radial loads.

Vibration

Vibration can be a major factor in bearing failure by causing brinelling or flaking of the races. If your bearings are operating under vibratory conditions you will not be able to achieve the same speeds that you could under perfectly smooth conditions. Attempting to increase speeds under vibratory conditions will quickly lead to bearing failure.

Lubrication

Lubrication is a major consideration with regards to bearing speed. We list a limiting speed for both standard oil and standard grease lubrication in our datasheets which are available by contacting our sales department.

Oil lubrication generally achieves higher speeds than grease lubrication. Increasing lubricant viscosity will reduce the permissible speed, whilst decreasing the viscosity will increase the permissible speed. Oil mists are used for very high speed applications. Use of silicone based oils and greases requires lower speed.

Cage Type

Often, the first part of a bearing to fail under high speed is the cage. The use of a synthetic cage designed for high speed helps to correct this. Synthetic cages are made from a variety of material including nylon, polyamide and phenolic. Our datasheets show the limiting speed allowing for each bearings cage type. These are available by contacting our sales department by email.

Temperature and Clearance

Low or high temperatures can adversely affect bearing life. Low temperatures can cause components to become brittle and lubricants to harden. High temperatures can cause parts to bind due to expansion and lubricants to melt and evacuate the bearing. These effects can be somewhat controlled by use of an adequate high or low temperature lubricant and purchasing bearings with increased internal clearance to allow for expansion.

Moisture and Contaminants

Strict cleanliness is essential to the correct functioning of bearings. Bearings requiring contact with excessive moisture or even lubrication by water should be made from 316 stainless steel, acetal or even full ceramic. These materials are only suitable for low speeds and loads.

Mounting

Correct mounting is essential to the correct running of the bearing. A poorly aligned assembly, or incorrect housing/shaft tolerances will result in slower attainable speeds and premature failure. Incorrect housing/shaft tolerances can result in a lessening of the bearing internal clearance.

Precision

The use of higher precision may be suggested if the bearing is to run at speeds above the standard limiting speed. Small Parts and Bearings limiting speeds are already adjusted to take consideration of this effect.

Closures

Contact seals reduce the speed capabilities of a bearing. Small Parts and Bearings limiting speeds are already adjusted to take consideration of this effect.

You can find many types of bearings in the Small Parts and Bearings Bearings Online Catalogue pages.

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