Ball Bearings: Guide to selection, applications & calculations

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,

  • Rolling Element radial and Thrust.
  • Hydrodynamic radial and rolling element thrust.
  • Hydrodynamic radial and thrust.

Deep Groove Ball Bearings

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

Deep-Groove-Ball-Bearing-16001-RMS10-

Fig.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:- 626z – here, 6mm is the I.D. and 6 mm is the thickness, with single shield.
627-2z – here, 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. K – Roller and Cage assembly of a cylindrical roller thrust bearing. Example:- KNU07.
  2. L – Removable inner and outer ring of a separate ring. Example – LNU207.
  3. R – Separate bearing without removable inner and outer ring.

Suffixes:

A, B, C, D, E – Differed 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
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 bounting

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 molded cage of glass fibre reinforced plastic
TH Snap type of fabric reinforced phenolic plastic
IH Injection molded cage of plastic
V Full component bearing
VH Full component bearing with non-separable roller component

Other Bearing Features:

Accuracy:
a. P6 – ISO clearance class 6.
b. P5 – ISO clearance class 5.
c. CLN – ISO clearance of class 6X for taper roller bearings.

Relubrication Feature:
Classification as holes provided in the bearings to lubricate.

a. W 20 – 3 Holes in outer Ring.
b. W 26 – 6 Holes in inner Ring.
c. W 33 – Lubrication Groove and 3 holes in the outer ring.
d. W 33X – Lubrication Groove and 6 holes in the outer ring.
e. W 5/3 – This class has combined features of class W 26 and W 33.
f. W 5/8 – This class has combined features of class W 20 and W 26.
g. Q E5 – Special Electric motor quality, dimensional and running accuracy to P6 for high demands of silent running.
h. Q E6 – Normal Electric motor quality, for quiet running application.
i. Q 05 – Vibration peaks extra low.
j. Q 06 – Vibration peaks lower than normal.
k. Q 5 – Vibration level extra low (supersedes C6).
l. Q 6 – Vibration lower level than normal (supersedes C6).
m. Q 55 – This class has combined features of class Q 5 and Q 05.
n. W 66 – This class has combined features of class Q 6 and Q 06.

Classification as per temperature.
a. MT – Grease for medium temperature. (-30°C to 110°C)
b. LT – Grease for medium temperature. (-50°C to 80°C)
c. HT – Grease for medium temperature. (-20°C to 130°C)

Stabilization Feature:
Bearing rings are dimensionally stabilized for operating temperature.
a. S0 – Up to +150°C
b. S1 – Up to +200°C
c. S3 – Up to +250°C
b. S4 – Up to +300°C
c. S5 – Up to +350°C

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.

self_align

Fig.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.

fag-single-row-angular-contact-ball-bearingsFig.3: Single row angular contact bearings

Double row angular contact bearings:- These bearings correspond in function to two single row contact bearings arranged back to back. These bearings can also accommodate axial loads in both directions as well as tittling moments, but are narrower.

Automotive-Bearing-Double-Row-Angular-Contact-Ball-Bearing
Fig.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.

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.

359308301_205

Fig.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.

2000-a1365_cat_9_large_img2_2

Fig.6: Double ball thrust bearing

Calculations

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).
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:
Let’s understand, what does system bearing life mean. This can be clarified and understood as the criteria that apply to the bearing “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.
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,
L10hA is the basic rating life, L10h, per ISO 281 for bearing A;
L10hB is the basic rating life, L10h, per ISO 281 for bearing B;
L10hN is the basic rating life, L10h, per ISO 281 for bearing N;
N is the number of bearings

27 Responses to Ball Bearings: Guide to selection, applications & calculations

  1. GarethW says:

    nikhil – many thanks for your contribution. An excellent article.

    Got any more? 🙂

  2. nikhil3586 says:

    Re:- Ball Bearings

    I will definitely look into my stuff of articles into my laptop and will definitely post in the same style I did this.

  3. SCIYER says:

    A very good work done. I would recommend that readers study the bearing application notes available on SKF site. This would give a wealth of information on Bearing construction and assembly and dismantling methodology.
    Readers from India are requested to study CMTI handbook for additional bearing arrangement.

  4. Yogesh Joshi says:

    awesome article….. definitely helpful for us….. 🙂

  5. k.udhay says:

    Good work, friend! I have forwarded the link to all my colleagues. 🙂

  6. lynx001 says:

    Thank you! Great job 😀

  7. nikhil3586 says:

    Thanks guys for giving me a support and encouragment to some more articles like this. Thanks a lot.

  8. vashi says:

    Realy good work… dude….. the id. Consept is realy good……

  9. GarethW says:

    nikhil – thanks for updating the article.

    DETAILS OF ARTICLE REVISION (4th Dec 2012): Additional content content and corrections. Now conforms to the ASME, ANSI and API Standards.

  10. craff says:

    Hi nikhil
    thanks for your excellent artical. could you please show some examples of bearing life calculation?

    Thanks.

  11. nikhil3586 says:

    Re: Craff

    Hello,

    Thanks for the appreciation. I want you to be more precise in context with your reply. I will definitely be obliged to reply to your question.

    Thanks.

  12. lumagm says:

    Thank you for this article

  13. rdpatel90s says:

    i wants to know about how produce steel ball and which machinery is used?

  14. nikhil3586 says:

    Making of Steel Ball Bearings

    Plz follow the link;

    [url]http://www.abbottball.com/about-abbott/today/manufacturing.php[/url]

  15. Datonginc says:

    Hello friend, Your post is so informative post, i have learn many such kind of data about ball bearing. I suggest all to read your post. because generally people have doesn’t know basic idea about this ball bearing. Thank you

  16. Datonginc says:

    Where is Single row angular contact bearings using, I want know more.

  17. nikhil3586 says:

    [COLOR=#404547][FONT=Verdana]Dear[/FONT][/COLOR][FONT=Verdana] [/FONT][URL=”http://www.mechanicaldesignforum.com/member.php?21054-Datonginc”]Datonginc[/URL],[COLOR=#404547][FONT=Verdana]

    Single row angular contact ball bearings are self-retaining units with solid inner and outer rings and ball and cage assemblies with polyamide, sheet steel or brass cages. The raceways of the inner and outer rings are offset in relation to each other in the direction of the bearing axis. The bearings are available in open and sealed versions. Their self-alignment capacity is very small.

    [/FONT][/COLOR][COLOR=#404547][FONT=Verdana]Many sizes of angular contact ball bearings are supplied in X-life design. These bearings are indicated in the dimension tables. Bearings of X-life quality have an improved raceway geometry as well as optimised surfaces. This gives a significant increase in the fatigue limit load of the bearings. In calculation of the expanded adjusted rating life, values up to 50% higher are achieved. In certain applications, a smaller design of bearing arrangement can therefore be used if necessary.

    Now it is important that you realise your need and do the needful.[/FONT][/COLOR]

  18. lucabianchi says:

    article very useful to understand how it is done.
    someone can tell me where I can buy large quantities of industrial bearings?

  19. lucabianchi says:

    among the best producers i find this German website [URL=”http://www.omniabearings.com/bearings/ball_bearings/”]http://www.omniabearings.com/bearings/ball_bearings[/URL] .
    but in another topic spoke of the difference between those in ceramic and steel ones.
    I should buy an industrial quantities for my project but I have not figured out yet what differences there are between those of ceramic and steel ones and why should I choose one or the other.
    could you help me?

  20. Great post, please read [URL=”http://www.mymachineinfo.com/2015/07/ball-bearing-selection-guide.html”]ball bearings selection guide[/URL] to complement this info, thanks.

  21. Sudharshan says:

    Good one & can you please post any article on "Bearing Housing Selection"

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