The content covers information about basic bearing fundamentals, components, bearing life, 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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