Friday, 29 January 2016

BEARING OPERATING CONDITION AND VARIOUS TERMINOLOGIES

BEARING OPERATING CONDITION AND VARIOUS TERMINOLOGIES

We were discussing in our previous post about the basic concept of bearings and also we have seen the various functions of a bearing. Today we will see here the various terms those are quite important to consider and study for securing the best operating condition of bearing.

Let us see, what we will understand after through reading this post.
  1. Tolerance in bearing dimensions
  2. Bearing internal clearance
  3. Bearing seats
  4. Alignment of bearing inner ring and outer ring
  5. Lubrication of bearing
  6. Condition of shaft and housing
  7. Operating temperature of bearing

Tolerance in bearing dimensions

Tolerance, in bearing dimensions, is basically defined as deviation amount from predefined nominal dimensions permissible by industries. In order to understand the tolerance in detail, let us consider one example of a bearing Y, which inner diameter of inner ring is 40 mm and tolerance is permissible as 0 to – 0.00762 mm. It means, bearing Y will permit inner diameter in a range of 40 mm to 39.99238 mm, but bearing Y will not permit inner diameter more than 40 mm or less than 39.99238 mm.

Bearing inner diameter as well as outer diameter is very important, these dimensions must be within tolerance limit as if any one diameter fails to follow the range of tolerance as prescribed by manufacturer; we will not be able to secure the better performance of bearing. Bearing inner ring must be fixed with shaft and bearing outer ring must be fixed with housing within prescribed interference.

Let bearing inner ring is slightly loose over bearing seat at shaft then in this condition bearing inner ring will also revolve during operation of bearing and we will have premature failure of bearing in short period of time.

Bearing internal clearance

Bearing internal clearance is very important in operation of bearing because there must be space or clearance for rolling elements to rotate or turn so that there will not be any creation of heat. If bearing internal clearance will not be available then in that case, there will be produce excessive heat due to friction during operation of bearings.


We must note it here that bearing internal clearance must be in limit and internal clearance limit or range of bearings could be seen in bearing hand book provided by the manufacturer of bearings as limit or range of allowable internal clearance also depends on bearing dimensions.

Bearing seats

Bearing inner ring and outer ring must be mounted over the specified area which is termed as bearing seat, bearing outer race will be fixed over area provided in housing and it is also termed as cup seat, while bearing inner ring will be fixed over the area provided on shaft which is termed as cone seat.

Alignment of bearing housing and shaft

Bearing outer ring and inner ring must be fixed over its specified area and bearing housing and shaft must be aligned properly because if there will be any misalignment between bearing housing and shaft then it will reduce the service life of bearing.

If there is misalignment between bearing housing and shaft then in that situation rolling element will not have suitable contact with outer and inner race and therefore load will not be distributed uniformly and chances of failure of bearing will be increased.

Lubrication of bearing

Lubrication is very important factor when we consider securing the better service life of bearing because correct quantity and type of lubricant avoid the generation of heat by reducing the friction between moving components in bearing.

We can follow post “8 ways to prevent the bearing failure” where we will see the importance of lubrication in bearing operation.

Condition of shaft and housing

As we know that bearing will be supported between housing and shaft and therefore the condition of area where bearing will be fixed i.e. bearing seat at shaft and housing must be smooth and there should not be any metal burr or any dent as bearing need better surface to surface contact between outer ring and housing and also between bearing inner ring and bearing seat over shaft for securing the better performance and service life of bearing.

There should not be any burr or dent or high spot over the bearing seat as it will restrict the surface to surface contact as we have discussed earlier and therefore there will be great probability of bearing failure before its service life and hence we will not be able to secure the better productivity and availability of our equipment.

Operating temperature of bearing

Bearing temperature is one of the most important conditioning monitoring parameter which could be measured during operation of bearing and by which we will be able to understand the condition of bearing.

There are following important contributors in abnormal temperature of bearing and these are as mentioned below.
  1. Overloading i.e. higher load as compared to rated load which will cause the deformation of bearing races, cages and rolling elements
  2. Absence of adequate lubrication i.e. lack of lubrication which will cause the excessive friction and hence excessive heat generation during operation of bearing.
  3. Excessive churning which is basically due to much lubrication.
Reference: SKF bearing maintenance manual
Image courtesy: Google

We will see the concept of roller bearing and its various types in our next post.

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