Ball Bearings - New Edition

8/12/2019 Ball Bearings - New Edition

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Preface

This article helps mechanical engineers understand the selection of ball bearings depending

upon the application and load conditions. Primarily the article helps you calculate the

minimum and maximum load bearing capacity of bearing and most importantly... life of the

bearing as an individual. Here the designation number of the ball bearing helps you know the

design, working nature and the physical property of the bearings.

In this new edition, I have come up with accuracy, operating temperatures, re-lubrication

features along with applications, utility and system of operations recommended by American

Society of Mechanical Engineers (ASME). You can also observe reflections of rules abiding

ANSI/API standards putting a significant relevance with bearing operations from

maintenance point of view.

Introduction

For Pumps used in Petroleum Industries and Gas Industries, we have some standard

statements meant to be followed:-

Each Shaft shall be supported by two radial bearings and one double acting Thrust Bearing

which may or may not be combined with one of the radial bearings. This means, The thrust

bearing may or may not be in the same axis as the rest of the two radial bearings. In other

words, it can also said as, the thrust bearing can be arranged in such an order that, it may or

may not be a part of the system bearing calculation although supporting the shaft.

Here, there can be only three possible system of arrangements,

1. Rolling Element radial and Thrust.

2.

Hydrodynamic radial and rolling element thrust.

3. Hydrodynamic radial and thrust.

Deep Groove Ball Bearings

Application: Deep Groove Bearings are used for small diameters with radial and axial loads.


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Figure 1:- Deep groove ball bearings

Bearings I.D: For any designated no. in any bearing company, the bearing I.D. is equal to 5

times the last two digits.

For example,6208 = I.D. 40mm

2313 = I.D. 65mm

But things change when suffixes are added beyond the designation no. of the bearings.

Example:- 626zhere, 6mm is the I.D. and 6 mm is the thickness, with single shield.627-2zhere, 7mm is the I.D. and 7 mm is the thickness, with double shield.

NOTE: For the selection of the bearing, C is important. If it is equivalent to C/P x Fr, in

terms of Newtons, then bearing matching the load bearing capacity will be suitable.

Supplementry Designations:

1. KRoller and Cage assembly of a cylindrical roller thrust bearing. Example:-

KNU07.

2. LRemovable inner and outer ring of a separate ring. ExampleLNU207.

3. RSeparate bearing without removable inner and outer ring.

Suffixes:

A, B, C, D, EDiffered or modified internal design .

External Design:

Ref Description

X Boundary dimensions altered to conform to ISO standards.

RS and

LS

Rubbing seals at one side of the bearing

2RS

and 2LS

Rubbing seals at both sides of the bearing


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Z Shield (Non-rubbing seals) at one end of the bearing

2Z Shield (Non-rubbing Seals) at both sides of the bearing

K Tapered Bore, 1:12 on diameter

K30 Tapered bore, 1:30 on diameter

N Snap ring groove in outer ring

NR Snap ring groove in outer ring, with snap ring

ZN Shield at one side of the bearing and snap ring groove in

outer ring at other side

ZNR As ZN, with snap ring

N2 Two locating slots in outer ring

G Single row angular contact ball bearing for paired mounting,

back to back or face to face mounting

Cage:

Ref Description

J Pressed Steel Cage

Y Pressed Brass Cage

M Machined Brass Cage

F Machined steel or spheroidal graphite cast iron cage

L Machined light alloy cage

P Injection moulded cage of glass fibre reinforced plastic

TH Snap type of fabric reinforced phenolic plastic

IH Injection moulded cage of plastic

V Full component bearing

VH Full component bearing with non-separable roller component

Other Bearing Features:

Accuracy:

a. P6ISO clearance class 6.


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b. P5ISO clearance class 5.

c. CLNISO clearance of class 6X for taper roller bearings.

Relubrication Feature:

Classification as holes provided in the bearings to lubricate.

a. W 203 Holes in outer Ring.

b. W 266 Holes in inner Ring.

c. W 33Lubrication Groove and 3 holes in the outer ring.

d. W 33XLubrication Groove and 6 holes in the outer ring.

e. W 5/3This class has combined features of class W 26 and W 33.

f. W 5/8This class has combined features of class W 20 and W 26.

Classification as per temperature.

a. LTGrease for medium temperature. (-50C to 80C)

b. MTGrease for medium temperature. (-30C to 110C)

c. HTGrease for medium temperature. (-20C to 130C)

Stabilization Feature:

Bearing rings are dimensionally stabilized for operating temperature.

a. S0 Upto +150C

b. S1 Upto +200C

c. S3 Upto +250C

b. S4 Upto +300C

c. S5Upto +350C

Relubrication Feature:

Classification as holes provided in the bearings to lubricate.

a. Q E5Special Electric motor quality, dimensional and running accuracy to P6 for high

demands of silent running.

b. Q E6Normal Electric motor quality, for quiet running application.


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c. Q 05Vibration peaks extra low.

d. Q 06Vibration peaks lower than normal.

e. Q 5 Vibration level extra low (supersedes C6).

f. Q 6 Vibration lower level than normal (supersedes C6).

g. Q 55This class has combined features of class Q 5 and Q 05.

h. W 66This class has combined features of class Q 6 and Q 06.

Self-Aligning Ball Bearings

Self-aligning ball bearings have two rows of ball bearings and common sphered raceway in

the outer ring, permitting minor angular misalignment of the shaft relative to housing. Thus,

they are perfect where misalignment arise. These bearings have a tapered bore to

automatically permit minor angular misalignments.

Figure 2:- Self-aligning ball bearings

Angular Contact Ball Bearings

In angular contact bearings, the line of action of the load (load line), at the contacts between

balls and raceways forms an angle with the bearing axis. The bearings are therefore

particularly suitable for combined loads.

Single row angular contact bearings: These bearings can carry axial loads acting in one

direction only. The radial load imposed on the bearing induces an axial force in the bearing

which must be counteracted. Consequently, the bearings are normally adjusted against the

second bearing.
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Figure 3:- Single row angular contact bearings

Double row angular contact bearings: - These bearings correspond in function to twosingle row contact bearings arranged back to back. These bearings can also accommodate

axial loads in both directions as well as titling moments, but are narrower.

Figure 4:- Double row angular contact bearings

Thrust Ball Bearings

Thrust bearings are also called as axial bearings. These bearings are used where high axial

loadings are operated under tougher conditions of operations in terms of Temperature, RPM,

etc.

In accordance with API 610, the thrust bearings, shall be sized for a continuous operation

under all specified conditions, including maximum differential pressures. All loads shall be

determined at design internal clearances and also twice design internal clearances. Thrust

bearings should provide full-load capacities if the direction of rotation is reversed.
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Single Ball bearings:Bearings of this type are suitable for all the accommodation of axial

loads in one direction and can locate a shaft in one direction. They must not however be

subjected to radial loads.

Figure 5:- Single ball thrust bearing:-

Double Ball bearings:This kind of ball bearings can bear axial loads from both sides and

thus can be used to locate shaft in both directions. They should not be subjected to radial

loads.

Figure 6:- Double ball thrust bearing

Calculation of bearing life:-

The bearing life calculations means, the life of an individual bearing in terms of revolutions

that can be utilized under continuous operating conditions designed to specific system

operating conditions.

L10= (106/60n) x (C/P)3

Where,

L10= Life of an individual bearing in hours under continuous run.

C = Dynamic load in Newtons

n = No. of Rotations / Minute.

P = Applied Load (effective).

XFr + YFa(3 for ball bearings and 10/3 for roller bearings)

( X = 1 and Y = 0 always).
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X and Y are factors required for the calculation of equivalent dynamic bearing load for single

and double row deep groove ball bearing, dependent upon axial load (Fa) and radial load (Fr).

Therefore, if Po< Fr, P = Po= Fr.

Po= Axial load and is equal to Po= 0.6Fr + 0.5Fa.

Where, Fr is the radial force and Fa is the Axial Force.

Calculation of maximum permissible axial load in Newtons:

Fap= 3Bd

Where,

B = Bearing Width.

d = Bearing bore diameter.

Fap= Max. Permissible Load.

Calculation of minimum Loads:

The calculation of Minimum Loads in a bearing under operating conditions

means to calculation the loads acting over a bearing under static or dynamic

conditions.

Fam= A (n/1000)2

Where,

Fam = Minimum Loads in Newtons.

n = No. of Rotations per Minute.

A = Cross-sectional Area of Bore.

Calculation for System Bearing Life:

Lets understand, what does system bearing life mean. This can be clarified and

understood as the criteria that apply to thebearing system and not to the individual

bearings alone, which should be a general practice in the industry. That means, an individual

lige of one bearing may be 100000 Revolutions and the other may juat have 26500

revolutions. But, if the value is put, the system bearing life becomes 25000 Revolutions. This

means, a combined effect of life of all the employed bearings in a system should perform

atleast 25000 revolutions at continuous run.


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As per API Standards, The system bearing life value should be less than the life of

any individual bearing having the shortest span of life. The formula for System Bearing Life

is:-

L10h= [(1/L10hA) + (1/L10hB) + (1/L10hB) + ........ + (1/L10hN)]

Where,

L10hAis the basic rating life,L10h, per ISO 281 for bearing A;

L10hBis the basic rating life,L10h, per ISO 281 for bearing B;

L10hN is the basic rating life,L10h, per ISO 281 for bearingN;

N is the number of bearings

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Ball Bearings - New Edition