Basic Bearing Technology document provides an overview of bearing fundamentals: - Friction occurs between two contact surfaces and generates heat, excessive torque, wear and tear. There are two types of friction - sliding and rolling. - A rolling bearing uses rolling elements like balls or rollers to reduce friction and support loads. It has lower friction than plain bearings. - Bearing components include an inner ring, outer ring, rolling elements, and a cage. The cage holds the rolling elements and provides space for lubrication. - Bearings can experience radial, axial or combined loads. Internal clearance is maintained to account for fits, tolerances and thermal expansion. The load zone is the area where load

1. Basic Bearing Technology

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3. What is friction?
• Friction is a resistance force acting between two relatively moving contact surfaces
• Friction generates
• Heat
• Excessive torque
• Wear and tear
• There are two types of friction;
• Sliding friction – Surface to surface contact
• Rolling friction – Surface to rolling element contact
Bearing Fundamentals - Introduction
Pulling force
Motion of the body
Pulling force
Motion of the body
Sliding friction Rolling friction

4. What is a rolling bearing?
• Rolling bearing is a rotating component which is used to reduce friction and bear or support the load
• There are two main category of bearings
• Plain or bush bearing
• Rolling bearing
•Absence of rolling elements
•Friction type - Sliding friction
•Higher friction
•Presence of rolling elements
•Friction type - Rolling friction
•Lower friction
Rolling bearingsPlain or Bush bearings
Bearing Fundamentals - Introduction

5. Merits and Demerits
• Point contact is made by a ball
• Lower contact area
• Lower friction
• Lower heat generation
• Higher speed capability
• Lower load carrying capability
• Line contact is made by a roller
• Higher contact area
• Higher friction
• Higher heat generation
• Lower speed capability
• Higher load carrying capability
Bearing Fundamentals – Point Contact & Line Contact

6. Basic components of a bearing
Outer ring
Inner ring
Rolling element
Cage
• Inner ring fits on to the shaft
• Outer ring fits in to the housing
• During operation inner and outer rings are either
in stationary or rotating condition depending on the application
Ex: Electric motor
Inner ring is rotating
Outer ring is stationary
Ex: Motorcycle wheel
Inner ring is stationary
Outer ring is rotating
Bearing Fundamentals – Bearing Components

7. Functions & Types
Functions:
• The main function of a cage is to hold, separate and guide the rolling elements in a bearing
• They are also designed to provide space for lubricant
• They are sensitive to the bearing loads and are prone to damage.
• Bearing loads are taken care by the rings and rolling elements
Types of cages
• Cages are made of different types – Prong cage / Rivet cage / Pin type cage / Machined cage / Moulded cage etc
• Cages are made of different materials – Steel / Brass / Polyamide etc
Bearing Fundamentals – Cages

8. Pure radial load
• Load is acting perpendicular to the shaft axis
• Load from the shaft passes through inner ring,
rolling element, outer ring and to the housing
Shaft
Cross section of a ball bearing
Radial loadRadial load
Bearing Fundamentals – Bearing Loads

9. Pure axial load
• Load is acting parallel to the shaft axis
• Axial load can be in either direction; left to right or right to left
• Load from the shaft passes through inner ring,
rolling element, outer ring and to the housing in axial direction
Shaft
Cross section of a ball bearing
Axial load
Bearing Fundamentals – Bearing Loads

10. Combined load
• Combination of radial and axial loads
• Resultant combined load depends on the magnitude
of radial and axial loads
• Load from the shaft passes through inner ring,
rolling element, outer ring and to the housing
Shaft
Cross section of a ball bearing
Radial load
Axial load
Combined load
Bearing Fundamentals – Bearing Loads

11. Radial Internal Clearance - RIC
• It is an internal clearance between inner ring track, outer ring track and rolling elements
measured in radial direction
• Generally, the internal clearances are measured in microns.
• Internal clearance is a design feature of a bearing to take care of expansion of rings
due to fits & tolerances and thermal effects.
• Using a bearing with a recommended clearance is of utmost importance to get a satisfactory performance
• Always select, procure and install a bearing with a right internal clearance.
• Using a bearing with a wrong clearance can be detrimental to the bearing life
• Remember, Internal clearance is not a quality feature of a bearing.
Bearing Fundamentals – Bearing Internal Clearances

12. Radial Internal Clearance - RIC
• Radial internal clearance are maintained during bearing assembly stage
• Clearance are maintained as per ISO 5753:1991 for Deep Groove Ball Bearings
• Clearance are of five category; C2/CN/C3/C4/C5
• CN and C3 bearings are most widely used for general applications
• C2, C4 & C5 bearings are used for special applications
• Refer Product catalogue to select a bearing with a right clearance
Example:
RIC is maintained as per ISO 5753:1991
C2 CN C3 C4 C5
Ball Bearing 6205
25*52*15
C2 0.001 / 0.011
CN 0.005 / 0.020
C3 0.013 / 0.028
C4 0.023 / 0.041
C5 0.030 / 0.053
Units : mm
D1 D2
d
RIC = D2-D1-(2d)
Bearing Fundamentals – Bearing Internal Clearances

13. Load zone in a bearing
• Load zone is an area or sector in a bearing where the load is shared by the rolling elements.
• Load zone or clearance adjustment is of utmost importance to have satisfactory bearing performance
• Select and maintain the right recommended load zone by adjusting the internal clearance
• Always contact NEI for guidance to select the right load zone
Pure radial load
Load zone
Bearing Fundamentals – Load Zone

14. Bearing life vs Load zone
Load zone
Influence of bearing setting on life !
Ratedlife(percent)
100°
100
0
EndplayPreload
Axial clearance
210°– 220°
360° 180° 135°
• Load zone is adjusted depending on the application
• Bearings are set either in clearance zone or preloaded zone
• Bearing life will be maximum at slight pre loaded condition
i.e. load zone angle between 210 – 220 degrees
Bearing Fundamentals – Load Zone

15. Bearing Life
• Bearing L10 life is given by an equation as follows;
• Bearing life depends on load / speed / lubrication / Operating temperature / Contamination level etc
• As the speed doubles, bearing life will reduce by 50%
• As the load doubles, bearing life will reduce by almost 90 %
• Excessive load will have more detrimental effect on bearing life
• Up to 50 % bearing failures are due to improper lubrication. Focus on right quality and right quantity
C = Dynamic load rating in N
P = Equivalent dynamic load in N
P = Life exponent
p = 3 for ball bearings
p = 10/3 for roller bearings
L10 = L = (C/P)p (106 revolutions) Lh10 = Lh = L.106 / n.60 (h)
n = speed in rpm
Bearing Fundamentals – Bearing Life

16. Bearing Raw Materials
Rings and Rolling elements
• Bearing rings and rolling elements are made of bearing steel with main composition of 1% Carbon and 1.5 % Chromium
• The most widely used steel specifications are SAE 52100 / 100Cr6 / SUJ 2
• Heat treatment is the most critical process to maintain the right hardness and the required microstructure
• Inner and outer rings are either through hardened or case hardened.
• In through hardened bearings, same hardness is maintained across the cross section
• In case hardened bearings, case is hardened (60 – 64 HRc) and core is slightly softer (@ 40 HRc)
• Ring hardness is maintained between 60 to 64 HRc and Rolling element hardness is maintained between 62 to 66 HRc
Bearing Fundamentals – Raw Materials

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