Assignment no.

Selection of Bearing
From Manufacturer’s Catalogue (SKF Bearings)

Presented by : Aakash Atul Virdhe (TME18250) (TE B)

 Bearing selection process
• When selecting bearings for any purpose, ultimately you want to be
certain of achieving the required level of equipment performance –
and at the lowest possible cost.

• Robustness also is very important because the conditions in which

your equipment is assembled, operated and maintained may not be
precisely known and may, in fact, vary over time.
In addition to the bearing rating life, there are key
factors you must consider when putting together the
bearing specifications for an application, including:

• Lubricant and supply method

• Shaft and housing fits
• Bearing clearance class
• Cage material and guidance
• Dimensional stability
• Precision requirements
• Bearing sealing
• Mounting method and maintenance
To help evaluate these key factors, we recommend following
this selection process:
Each icon represents a step in the process.
The first step in the bearing selection process is to understand
and document:
• The required performance
• The operating conditions and assumptions of them
• Any other application prerequisites

Common factors include:

• Bearing life
• Speed capability and ability to withstand applied acceleration levels
• Precision of the radial and axial position of the shaft
• Ability to cope with low or high temperatures or temperature gradients
• Generated noise and vibration levels
Bearing Size:
The size of a bearing must be sufficient to ensure that it is strong enough to
deliver the required/expected life under defined operating conditions.

The two main criteria that can be used for determining appropriate bearing size
are:
• Size selection based on rating life: This is based on the required bearing life,
taking into account the possible effects of rolling contact fatigue, and requires
calculation of the basic rating life L10, or SKF rating life L10m, for the bearing.
• Size selection based on static load: This is based on the static load that the
bearing can accommodate, taking into account the possible effects of permanent
deformation, and requires calculation of the static safety factor s 0 for the bearing.
Diagram shows these
selection criteria and
the related bearing
ratings and static
safety factor, which
are described in detail
in the relevant sub-
sections.

Which selection criteria you should use depends on the operating conditions of the
bearing:
• For applications where bearings are running in typical operating conditions – i.e. normal
speeds, good lubrication conditions and not highly or peak loaded – use 
Size selection based on rating life.
• For applications where bearings are running under very low speeds or which are used under
stationary conditions, very bad lubrication conditions or where occasional peak loads occur,
use Size selection based on static load.
Lubrication :
The lubricant is required to reduce friction, inhibit wear, protect the bearing
surfaces against corrosion and may also be needed to provide cooling.

How lubrication relates to other selection criteria :

Lubrication selection and lubricant properties greatly influence the 
operating temperature, which in turn influences:
• Whether you should use grease or oil
• The rel-ubrication interval required for grease
• Whether oil lubrication is necessary, because circulating oil can be used to
remove heat
• The lubrication condition – the viscosity ratio, κ, which influences the
bearing size selection based on SKF rating life
Operating temperature and speed :
The relationships between the temperature and power loss of components
within an application is complex and these factors, in turn, have
interdependencies with many others such as bearing sizes, loads and lubrication
conditions.

They influence many performance characteristics of an application and its parts,

and do so in various ways depending on the operational state, such as at start-up
or in normal operation, when steady-state conditions have been reached.

Estimating the operating temperature and verifying speed limitations is a critical

aspect of the analysis of an application.
Bearing operating temperature and heat flow :
• Temperature has a major influence on many performance characteristics of an
application. The heat flow to, from and within an application determines the
temperature of its parts.
• The operating temperature of a bearing is the steady state temperature it attains when
running and in thermal equilibrium with its surrounding elements. The operating
temperature results from (Diagram):
The operating temperature results from :
• The heat generated by the bearing, as a result of the combined bearing
and seal frictional power loss
• The heat from the application transferred to the bearing via the shaft,
housing, foundation and other elements in its surroundings
• The heat dissipated from the bearing via the shaft, housing, foundation,
lubricant cooling system (if used) and other cooling devices

The bearing operating temperature depends as much on the application

design as on the bearing generated friction. Therefore, the bearing, its
adjacent parts and the application should all be thermally analysed.
Bearing size, operating temperature and lubrication
conditions :
For a given bearing type, the bearing size, operating temperature and lubrication
conditions are interdependent as follows (Diagram - Dependencies between bearing
size, operating temperature and lubrication conditions):
• Bearing size is selected based on bearing load, speed and lubrication conditions.
• Operating temperature is a function of the bearing load, size, speed and
lubrication conditions.
• Lubrication conditions depend on the operating temperature, the viscosity of the
lubricant and the speed.
These interdependencies are dealt with by taking an iterative approach to the
analysis, in order to achieve an optimum design for a bearing arrangement and
select the most appropriate components for it.
Diagram - Dependencies between bearing size, operating temperature and lubrication conditions
Bearing interfaces :
In this section you can find recommendations and requirements for
designing bearing interfaces, including:
• Criteria when selecting bearing fits
• Recommended fits for standard conditions
• Tables to help determine minimum, maximum and probable values of
clearance or interference between the bearing and its seat
• Recommendations for specifying geometrical tolerances of bearing seats
• Recommendations for the axial support of bearing rings
• Further design considerations for bearing interfaces
Bearing execution :
As part of the bearing selection process, when the bearing type, size, and fit
have been determined, additional factors must be considered to enable you to
further define the final variant of the bearing.

In this section you can find recommendations and requirements for selecting:
• The bearing internal clearance or preload
• The bearing tolerances
• The appropriate cage (where applicable)
• Integral seals (where applicable)
• Additional options, such as coatings and other features to meet any special
needs/requirements
Sealing :
• Bearing arrangements generally include a shaft, bearings, housing(s),
lubricant, associated components, and seals. Seals are vital to the
cleanliness of the lubricant and the service life of the bearings.
• This section describes seals outside the bearing, and how they affect
bearing performance. Because of their importance for bearing
applications, this section deals exclusively with non-contact and contact
shaft seals, their various designs and executions.
• The purpose of a seal is to retain lubricant and prevent any contaminants
from entering into a controlled environment. There are several basic seal
types:
i. Non-contact seals
ii. Contact seals
iii. Static seals
Many factors must be considered when selecting the most suitable seal for a
particular bearing-shaft-housing system.
These include:
• The lubricant type: oil or grease
• The contaminant type: particles or fluid or both
• The circumferential speed at the seal lip
• The shaft arrangement: horizontal or vertical
• Possible shaft misalignment or deflection
• Run-out and concentricity
• Available space
• Seal friction and the resulting temperature increase
• Environmental influences
• Cost
• Required operating time
• Maintenance requirements