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Rolling Contact Bearings(Chapter 11)

Dr Samir Mekid

Mechanical Engineering DepartmentKFUPM

ME 308 Machine Design II

Semester 131- 2013

http://upload.wikimedia.org/wikipedia/commons/3/30/BallBearing.gif

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Rolling Contact Bearings

2

1. Introduction

2. Bearing Types

3. Ball Bearing Nomenclature

4. Bearing Life

5. Bearing Loads6. Load-Life trade-off

7. Bearing Survival, Reliability and Goal

8. Equivalent Load

9. Ball and Roller Bearing Selection10. Selection of Tapered Roller Bearings

11. Lubrication Mounting and Enclosure

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Various types

http://images.google.com/imgres?imgurl=http://www.skf.com/images/cat/images/1/1_0/0008f01.gif&imgrefurl=http://www.skf.com/skf/productcatalogue/maincatalogueForwarder%3Fmaincatalogue%3D1%26newlink%3D1_0_71%26lang%3Den&usg=__P6pc83c038yGBm3oAc_a1lpkDCA=&h=270&w=308&sz=7&hl=en&start=41&um=1&itbs=1&tbnid=WL41z_CRNTip2M:&tbnh=103&tbnw=117&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.servosystems.co.nz/site/images/162462.jpg&imgrefurl=http://www.servosystems.co.nz/product-news-xidc44382.html&usg=__NAR_WhoDBxIRzGLNCoUqgYrvpH8=&h=333&w=300&sz=18&hl=en&start=4&um=1&itbs=1&tbnid=Nhx-OSrFFDJ30M:&tbnh=119&tbnw=107&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26um%3D1%26hl%3Den%26safe%3Dactive%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://news.thomasnet.com/images/large/027/27505.jpg&imgrefurl=http://news.thomasnet.com/fullstory/27505&usg=__yc8COuRVKOTplEUUl0c0RS4QY3w=&h=700&w=742&sz=39&hl=en&start=17&um=1&itbs=1&tbnid=h5_PSrgys4RCYM:&tbnh=133&tbnw=141&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26um%3D1%26hl%3Den%26safe%3Dactive%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.drives.co.uk/images/news/Schaeffler%2520ball%2520roller%2520bearing%2520small.jpg&imgrefurl=http://www.drives.co.uk/fullstory.asp%3Fid%3D1968&usg=__sUliLm51r2NXourpdcAIftcBi60=&h=399&w=400&sz=32&hl=en&start=86&um=1&itbs=1&tbnid=onqvxX15AO9xKM:&tbnh=124&tbnw=124&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D80%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.engineeringtalk.com/news/ine/ine287_01.jpeg&imgrefurl=http://www.engineeringtalk.com/news/ine/ine287.html&usg=__b_OrlWZIr8weBkzVZcEzgg0PwZY=&h=300&w=300&sz=30&hl=en&start=18&um=1&itbs=1&tbnid=IU5ElNFIk1cmxM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Drolling%2Bbearings%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.eworldtradefair.com/product_images/1248421455Dscn0328.gif&imgrefurl=http://www.eworldtradefair.com/oscarautocorp/manufacturer-exporter-distributor/&usg=__z5a7GAKUoiU1swBRt8m-ioLB9-w=&h=335&w=360&sz=19&hl=en&start=42&um=1&itbs=1&tbnid=auogWGtyactJCM:&tbnh=113&tbnw=121&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.industrysearch.com.au/products/images/p47988_9.jpg&imgrefurl=http://www.industrysearch.com.au/Suppliers/NSK-Australia&usg=__UYNXEBS5i1_HpaNDBoyx7ljdl6M=&h=302&w=302&sz=21&hl=en&start=48&um=1&itbs=1&tbnid=L1nHqDzHXKyJmM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.nskeurope.com/cps/nsk/eu_en/p/images/content/1.2.5.12_ACTBB_Ball_Screw_rgb_rdax_95.jpg&imgrefurl=http://www.nskeurope.com/cps/rde/xchg/eu_en/hs.xsl/super-precision-ball-bearings.html&usg=__oQXp_A7kliaey8klmyeEJjhtx9s=&h=500&w=500&sz=69&hl=en&start=54&um=1&itbs=1&tbnid=oi_L2LtlXaGOMM:&tbnh=130&tbnw=130&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1

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Objectives

1- Types of rolling bearings

2- How to choose them? (No design of RCB!)

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We will learn the following:

1. Types of bearings

2. How do we select them depending on application

3. Calculate forces applied to bearings in all directions

4. Estimate life time of bearings

5. Understand failure mechanisms in bearings

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Rolling Bearings

History:

1. As far back as 1100 BC the Assyrians andBabylonians used rollers inserted betweenenormous stones and ground to reducefriction.

2. The wheel based on sliding motion camelater.

3. The bicycle introduced the need for rolling

elements.

http://images.google.co.uk/imgres?imgurl=http://www.edupics.com/bicycle-silouette-t9835.jpg&imgrefurl=http://www.edupics.com/en-coloring-pictures-pages-photo-bicycle-silouette-i9835.html&usg=__j3NOYJDYHBGfd7m6XRiyB6O3Ucc=&h=531&w=750&sz=27&hl=en&start=57&um=1&tbnid=R054F6gBd03hFM:&tbnh=100&tbnw=141&prev=/images%3Fq%3Dbicycle%26start%3D40%26ndsp%3D20%26um%3D1%26hl%3Den%26safe%3Dactive%26rlz%3D1T4GGIH_en-GBGB279GB279%26sa%3DNhttp://www.artdiamondblog.com/WaterDrumRollingForPoor3.jpghttp://content.answers.com/main/content/wp/en-commons/thumb/2/2d/300px-Plutonium_ring.jpg

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Bearings

Journal (Sleeve) BearingsLoad is transferred through a lubricant in sliding contact

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Bearing Types

RollingElement

Pure radialload

(Cylindrical roller bearings)

Pure Thrustload

(Cylindrical and Ball)

Combination load

(Deep groove ball, Tapered

roller, Angular contactbearings)

Sliding (Journal)Bearings

Pure radialPure Thrust

Combination

In general

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Bearings

RCB

SCB

http://images.google.com/imgres?imgurl=http://www.designworldonline.com/uploads/ImageGallery/SKF%2520High%2520Temp%2520Ball%2520Bearings.jpg&imgrefurl=http://www.designworldonline.com/articles/2909/144/SKF%25C2%25AE-High-temperature-Ball-Bearings.aspx&usg=__pyfIRcSo40J_WiPZs0kHTkgxcLk=&h=458&w=500&sz=94&hl=en&start=4&um=1&itbs=1&tbnid=JFcCipBfqMsfSM:&tbnh=119&tbnw=130&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1

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Journal Bearings

Radial

(Plain Bearings, sleeves)

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Thrust Journal Bearing

Ch 11. Notes

Thrust

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Other Types

Magneticbearings

Air bearings

Micro/Nanobearings

13

Flat Pad air bearings

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Why Rolling-Contact Bearings?

RCB are used to minimize the frictionresulting

from relative motion performed under load.

RCB are used to describe bearings in which the

main load is transferred through rolling elements.

Typical applications include supporting shafts

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Design Considerations

Bearing life and reliability Bearing speed (rpm)

Space limitation

Accuracy

Bearing loadradial, thrust (axial) or both

Radial loadRadial load

Thrust load

Bearings are selected from catalogs, before referring to catalogs

you should know the followings:

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Bearing Nomenclature

Inner and outer races are typically pressed onto shafts or hubs with slight

interference fit to make them move with shafts (inner race) or remain stationary

(outer race)

Ball

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Ball Bearings

How are the balls introduced

between the races?

Expecting answers from you in the next

lecture !

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Assembly of single-row deep groove ball bearings

In the assembly of this type of bearing, the inner race is placedeccentric with the outer race, and then the balls are inserted in thecrescent shaped space.

The balls are then evenly spaced as the races are brought intoconcentric relation.

The halves of the retainers are then assembled so that the balls willremain evenly spaced but can rotate freely.

Even spacing of the balls is desirable from the standpoints of:

Distribution of the load and

Balance of the bearings.

The four steps in the assembly of the deep groove

type ball bearing

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http://images.google.com/imgres?imgurl=http://www.skf.com/images/cat/images/1/1_0/0008f01.gif&imgrefurl=http://www.skf.com/skf/productcatalogue/maincatalogueForwarder%3Fmaincatalogue%3D1%26newlink%3D1_0_71%26lang%3Den&usg=__P6pc83c038yGBm3oAc_a1lpkDCA=&h=270&w=308&sz=7&hl=en&start=41&um=1&itbs=1&tbnid=WL41z_CRNTip2M:&tbnh=103&tbnw=117&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.servosystems.co.nz/site/images/162462.jpg&imgrefurl=http://www.servosystems.co.nz/product-news-xidc44382.html&usg=__NAR_WhoDBxIRzGLNCoUqgYrvpH8=&h=333&w=300&sz=18&hl=en&start=4&um=1&itbs=1&tbnid=Nhx-OSrFFDJ30M:&tbnh=119&tbnw=107&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26um%3D1%26hl%3Den%26safe%3Dactive%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://news.thomasnet.com/images/large/027/27505.jpg&imgrefurl=http://news.thomasnet.com/fullstory/27505&usg=__yc8COuRVKOTplEUUl0c0RS4QY3w=&h=700&w=742&sz=39&hl=en&start=17&um=1&itbs=1&tbnid=h5_PSrgys4RCYM:&tbnh=133&tbnw=141&prev=/images%3Fq%3Dmechatronic%2Bball%2Bbearings%2Bapplications%26um%3D1%26hl%3Den%26safe%3Dactive%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.drives.co.uk/images/news/Schaeffler%2520ball%2520roller%2520bearing%2520small.jpg&imgrefurl=http://www.drives.co.uk/fullstory.asp%3Fid%3D1968&usg=__sUliLm51r2NXourpdcAIftcBi60=&h=399&w=400&sz=32&hl=en&start=86&um=1&itbs=1&tbnid=onqvxX15AO9xKM:&tbnh=124&tbnw=124&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D80%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.engineeringtalk.com/news/ine/ine287_01.jpeg&imgrefurl=http://www.engineeringtalk.com/news/ine/ine287.html&usg=__b_OrlWZIr8weBkzVZcEzgg0PwZY=&h=300&w=300&sz=30&hl=en&start=18&um=1&itbs=1&tbnid=IU5ElNFIk1cmxM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Drolling%2Bbearings%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.eworldtradefair.com/product_images/1248421455Dscn0328.gif&imgrefurl=http://www.eworldtradefair.com/oscarautocorp/manufacturer-exporter-distributor/&usg=__z5a7GAKUoiU1swBRt8m-ioLB9-w=&h=335&w=360&sz=19&hl=en&start=42&um=1&itbs=1&tbnid=auogWGtyactJCM:&tbnh=113&tbnw=121&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.industrysearch.com.au/products/images/p47988_9.jpg&imgrefurl=http://www.industrysearch.com.au/Suppliers/NSK-Australia&usg=__UYNXEBS5i1_HpaNDBoyx7ljdl6M=&h=302&w=302&sz=21&hl=en&start=48&um=1&itbs=1&tbnid=L1nHqDzHXKyJmM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1http://images.google.com/imgres?imgurl=http://www.nskeurope.com/cps/nsk/eu_en/p/images/content/1.2.5.12_ACTBB_Ball_Screw_rgb_rdax_95.jpg&imgrefurl=http://www.nskeurope.com/cps/rde/xchg/eu_en/hs.xsl/super-precision-ball-bearings.html&usg=__oQXp_A7kliaey8klmyeEJjhtx9s=&h=500&w=500&sz=69&hl=en&start=54&um=1&itbs=1&tbnid=oi_L2LtlXaGOMM:&tbnh=130&tbnw=130&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1

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Rolling Contact Bearings

Deep groove (Conrad) bearing

Filling notch ball bearing or maximum capacity bearing

Angular contact bearings (AC)

1. Ball bearings

3. Thrust bearings

4. Linear bearings

Cylindrical bearings

Needle bearings

Tapered bearings

Spherical bearings

2. Roller bearings

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Roller Bearings

Roller bearings have higher load capacity than ball bearings, load is

transmitted through line contact instead of point contact.Straight cylindrical roller Needle type

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Roller BearingsTapered bearings

Designed to withstand high radial loads, high thrust loads, and

combined loads at moderate to high speeds. They can also withstandrepeated shock loads.

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Ball Bearing Types

25

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Notes on Bearings Bearings maybe obtained with shieldson one or

both sides. Shields provide a degree of protectionagainst dirt.

Some bearings are manufactured with sealsin oneor both sides. If sealed on both sides, bearingsare lubricated at the factory.

Starting frictionis almost twicethe runningfriction. Bearings are manufactured to take either pure

radial load, pure thrust loador a combination ofboth.

Bearing makers usually provide manualstodescribe the various types. (www.skf.com,www.fag.com, www.timken.com)

http://www.skf.com/http://www.skf.com/http://www.skf.com/http://www.fag.com/http://www.timken.com/http://www.timken.com/http://www.skf.com/http://www.fag.com/http://www.timken.com/http://www.timken.com/http://www.fag.com/http://www.skf.com/

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Ball Bearings Forces

Angular ball bearings have higherthrust load capacity in

one direction than Radial ball bearings.

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Ball bearing self aligning

28

http://upload.wikimedia.org/wikipedia/commons/7/75/Ball_bearing_self_aligning.gif

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Mounting and Enclosure of Bearings

Duplex Mountingof angular contact bearings: Bearings manufactured for this purpose

have their rings ground with an offset so that they are tightly clamped together and

apreloadis automatically established (as you have seen on the animation).

a) Face to face mounting (DF)for heavy Frand Fafrom either directionb) Back to back mounting (DB)=a)+ aligning stiffness

c) Tandem arrangement (DT)for thrust which is always in the same direction. Preload

required.

http://images.google.com/imgres?imgurl=http://www.biztrademarket.com/User/177374/bb/self-aligning_ball_bearings1_6ao.jpg&imgrefurl=http://search.biztrademarket.com/SearchProduct%3Fq%3Dball%2520bearing%26sort%3Dmatch%26pageindex%3D1&usg=__Mn24v7tuoIgprfgVV_2IkVcLq-g=&h=474&w=496&sz=35&hl=en&start=28&um=1&itbs=1&tbnid=dg4AYFyx2sDxHM:&tbnh=124&tbnw=130&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D20%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1

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Characteristics of ball Bearings

30

Type Approximate range of bore sizes, mm

Relative capacity Limitingspeed

factor

Toleranceto mis-

alignment

Minimum Maximum Radial Thrust

Conrad or deep

groove

3 1060 1.00 a0.7 1.0 015

Maximum capacity

or filling notch

10 130 1.2-1.4 a0.2 1.0 03

Self-aligning

internal

5 120 0.7 b0.2 1.0 230

Self-aligning

external

- - 1.0 a0.7 1.0 High

Double row,

maximum

6 110 1.5 a0.2 1.0 0.3

Double row, deep

groove

6 110 1.5 a1.4 1.0 0

aTwo directionsbOne direction

http://images.google.com/imgres?imgurl=http://www.biztrademarket.com/User/177374/bb/self-aligning_ball_bearings1_6ao.jpg&imgrefurl=http://search.biztrademarket.com/SearchProduct%3Fq%3Dball%2520bearing%26sort%3Dmatch%26pageindex%3D1&usg=__Mn24v7tuoIgprfgVV_2IkVcLq-g=&h=474&w=496&sz=35&hl=en&start=28&um=1&itbs=1&tbnid=dg4AYFyx2sDxHM:&tbnh=124&tbnw=130&prev=/images%3Fq%3Ddesign%2Bball%2Bbearings%2Bapplications%26start%3D20%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-gb:IE-SearchBox%26rlz%3D1I7GGIT_en-GB%26ndsp%3D20%26tbs%3Disch:1

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Characteristics of Angular Contact BallBearings

31

Type Approximate

maximumsize, mm

Relative capacity Limiting

speed factor

Tolerance

to mis-alignment

Radial ThrustOne-directionalthrust

320b1.00-1.15

a,b1.5-2.3 b1.1-3.0 02

Duplex, back toback

320 1.85 c1.5 3.0 0

Duplex, face toface

320 1.85 c1.5 3.0 0

Duplex, tandem 320 1.85 a2.4 3.0 0Two directional orsplit ring

110 1.15 c1.5 3.0 02

Double row 140 1.5 c1.85 0.8 0a

One directionDepends on contact anglecTwo directions

dIn other direction

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Roller Bearings

32

Roller bearings have higher load capacity than ball bearings.Roller bearings require prefect geometry.

Straight roller bearing (radial cylindrical) cannot take thrust loads.

Tapered roller bearings combine the advantage of ball and straight

roller bearings, they take radial and thrust loadings.

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Roller bearings: Needle Bearings

33

Needle bearings have very high load ratings and require less space.

Needle bearings can be used with and without races.

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Characteristics of Cylindrical Roller Bearings

34

Type Approximate range of

bore sizes, mm

R elat ive capaci ty Limi ting

speed

factor

Tolerance

to mis-

alignment

Mi ni mum Max imum Radi al Thrus t

Seperable outer

ring, nonlocating

(N)

10 320 1.55 0 1.20 05

Seperable inner

ring, nonlocating

(NU)

12 500 1.55 0 1.20 05

Seperable inner

ring, one direction

locating (NJ)

12 320 1.55 aLocating 1.15 05

Seperable inner

ring, two-direction

locating (NUP)

20 320 1.55 bLocating 1.15 05

aOne direction

Two directions

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Characteristics of Spherical Roller Bearings

35

Type Approximate range of

bore sizes, mm

Relat ive capaci ty Limi ting

speed

factor

Tolerance

to mis-

alignment

Mi ni mum Max imum Radi al Thrus t

Single row, barrel

or convex

20 320 2.10 0.20 0.50 2

Double row, barrel

or convex

25 1250 2.40 0.70 0.50 130

Thrust 85 360 a0.10b0.10

a1.80b2.40

0.35-0.50 3

Double row,

concave

50 130 2.40 0.70 0.50 130

aSymmetric rollersbAsymmetric rollers

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Other Types of Bearings

36

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Rolling Contact Bearing Materials

37

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Rolling Contact Bearings

The designer should take into considerationthe following:

The available space

The load and its characteristics

The desired life

The required speed

The cost

38

Not to designrolling bearings but to selectproper

bearings for the application

Objective:

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Bearing Life

Assuming perfect mounting, adequatelubrication and protection thus failure willoccurby fatigue.

Bearings are subjected to millions ofrepeated contact stress (Hertezian) cycles

causing spalling (flaking or pitting) on ballor raceway. (Video 1& 3)

Failure Criteria:

1. SKF: failure happens when a pit ofdiameter 10-4diameterof ball or roller

2. Timken Co.: failure happens when 10-2in2of surface is spalled

39

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Simulation of progression of fatigue

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Simulation of progression of fatiguefailure

Fatigue Wear

Mc Graw Hill, Hamrock et al.: Figure 8.22, page 346

Flakepit

Spalling Surface Fatigue

Pitting Surface Fatigue

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Bearing Life

Definitions

1. Fatigue Life = Useful Life of a bearing = #revolutions (or Hrs @ a certain speed) of ringbefore evidence of failure in ball or rings.

1. Rating Life (AFBMA= Anti-Friction BearingManufacturers Association)=Minimum Life =L10 = B10 = # revolutions (or Hrs @ a certainspeed) that 90% of a group of apparentlyidentical (2500 bearings) will complete or exceedbefore failure develops.

1. Median Life = Average Life = L50 = #revolutions completed or exceeded by 50% ofbearings.

L50= 4 to 5 times L10

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Bearing Load

Load Ratings:

1. Static Load Rating,

2. Dynamic Load Rating

Basic StaticLoad Rating (AFBMA)= C0

Radial load causing a total deformation of10-4of ball or roller diameter.

43

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Bearing Load

Dynamic Load Rating Basic Load Rating = Specific

Dynamic Capacity = Dynamic LoadCapacity = Basic Dynamic Capacity =C = C10 = AFBMA Catalog Load =

constant radial load resulting in L10= 106revolutions of inner ring or 500 hrs @33&1/3 rpm. (Companies e.g. SKF, FAG,NTN)

44

Other ratings: Companies such as Timken Co.use 90

x106revolutions or (3000h @ 500 rpm)

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Life & Load Calculation

a

F

CL

10

aFLC

/1

10

Life

Load Rating

L = Life (in Millionsof revolutions)C10= Basic Dynamic load rating

F = Design Load

a = 3 for ball and 10/3for roller bearings

Load F

Life L

a

D

D

F

C

L

L

10

10

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a

RR

DD

D

nLnLFC

/1

106060

LDand LRare in Hrsand nDand nRin rpmSub D is for design and R for rated (catalog)

Load Rating

xD =life multiplier

Load F

Life L

or

a

D

D

F

C

L

L

10

10When life is in Hours

Life & Load Calculation

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Example on load-life

A radial ball bearing has a basic dynamic load

rating of 2350 lb.-What would be its life when operating at a load 1675 lb?

Given

1. Ball bearing (a=3)2. C10= 2350 lb

3. FD= 1675 lb

4. L10= 106 revolutions

Required: LD?

Note: Loadreduced by 30%

Lifeincreased by 176%

Solution

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Load-Life and Reliability

The rel iabi l i ty used so far is the catalog rel iabi l i ty of 90%(R = 0.90)

In practice, a reliability of less than 90% is not desirable

because bearings are used in large numbers in assemblies

53.0)9.0(9.06

81.0)9.0(9.02

6

6

2

2

RRandN

RRandN

RR NN

Exampleif an assembly has N bearings

Load Life and Reliability

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Load-Life and Reliability

49

R=.9

xD=1

From Machine Design Handbook

RDGreater than 0.90

90%

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Load-Life and Reliability

a

R

DD

K

xFC

/1

10

To correct for reliabilities > 90%:

60

60/, 10

RR

DDD

nL

nLLLxmultiplierlife

483.1/1)1(439.402.0 DR RK

5.1/1))/1(ln(48.4 DR RK

The reliability correction factorKRforball and straight

(cylindrical) roller bearingsis:

and for tapered roller bearings:

In calculating FD it is important to take into account theLoad application factorgiven in table 11.5.Some recommended bearing life values(LD) are given in table 11.4