Angular contact ballbearings - SeekPartfile.seekpart.com/keywordpdf/2010/11/22/20101122142232328.pdf · Angular contact ballbearings ... Designation systems of single bearings

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Angular contactball bearings

Angular contact ball bearings 112Four different designs 112Standard high-precision angular contactball bearings 114High speed high-precision angular contactball bearings 114Hybrid high-precision angular contactball bearings 115Hybrid high speed high-precisionangular contact ball bearings 115Universally matchable bearings 116Matched bearing sets 117General bearing data 122Factors affecting the preload 127Cages 135Speed ratings 136Equivalent dynamic bearing load 137Equivalent static bearing load 137Calculation of equivalent bearing load for preloaded angular contact ball bearings 139Designation systems of single bearingsand matched sets 139

Product tables 141Standard high-precision angular contactball bearings 142High speed high-precision angular contactball bearings 156Hybrid high-precision angular contact ball bearings 162Hybrid high speed high-precision angular contactball bearings 172

Contents

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2 Angular contact ball bearings

Four different designsSKF high-precision angular contact ballbearings (➔ fig ) are available in threedimension series: bearing series 719,70 and 72 with a contact angle of 15°(designation suffix CD or CX and CE)or 25° (designation suffix ACD or ACXand ACE) (➔ fig ).Bearings with the greater contact angle arerecommended for applications where highaxial stiffness and high axial load carryingcapacity are required.

The CX and ACX suffixes identify thesmall bearing sizes belonging to the CDand ACD design and stand for revisedinternal geometry.

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The CE and ACE design bearings havea larger number of small diameter ballscompared with the standard CD or CXand ACD or ACX designs.

Summing up, SKF high-precision angularcontact ball bearings are available in fourdifferent designs and three dimensionseries (➔ fig ).

Clearly the space requirements aredifferent and arrangements can be more orless radially compact. Each bearing serieshas characteristic features that makes itsuitable for particular applications.

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Angular contactball bearings

For higher speeds, or where little radialspace is available, bearings of series 719 or70 should be chosen. For heavy loads atrelatively moderate speeds, bearings ofseries 72 are more appropriate. Wherestiffness requirements are paramount,bearings of series 719 incorporate a largenumber of balls and have the advantagethat large spindle diameters can be used.Both these factors contribute to highstiffness of the spindle system: spindlerigidity increases with increasing spindlediameter and bearing stiffness is morestrongly influenced by the number than bythe size of the balls. In fact, the rigidity ofthese light series bearings is greater thanthat, of comparable bearings from theheavier series.

15°15° 25°25°

3

Different designs of SKF high-precisionangular contact ball bearings series 70

Single row high-precision angular contactball bearing

A cross section of the three dimension series

ACD, ACX CD, CX ACE CEdesign design design design

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719 70 72

1Fig

Fig

Fig

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Standard high-precisionangular contact ball bearings

SKF standard high-precision angularcontact ball bearings are non-separable,having one reduced height flange on theouter ring, in order to allow the introductionof a large number of balls, using a one-piece cage and an optimised internaldesign. Thanks to this, they representthe best solution in terms of load carryingcapacity, rigidity and speed.

The bearings are manufacturedaccording to 719, 70 and 72 series, witha choice of two different contact angles:15 degrees (CX and CD) or 25 degrees(ACX and ACD).

The basic design is the same for CX(ACX) and CD (ACD) series. The CX andACX series covering the small bearing sizeshave recently been reviewed, offeringimproved dynamic and static load ratings,which have been increased by approx. 15 %and 30 % respectively. An enhanced levelof radial and axial rigidity has also beenobtained without compromising the speedratings.

The range of standard high-precisionangular contact ball bearings covers borediameters from 8 to 240 mm. Dimensionsand technical data can be found in therelevant product tables.

High-speed high-precisionangular contact ball bearings

In addition to the standard series, SKFoffers a series of high-speed bearingsto meet the highest demands in respectof speed capability and running accuracy.

These bearings belong to the series70 CE (ACE) and 719 CE (ACE) and arecharacterised by following features:● smaller balls● a contact angle of 15° (CE suffixes) or

25° (ACE suffix)● both outer and inner ring shoulders

of reduced height for better lubricationconditions

● an outer ring centred cage● optimised internal design for enhanced

speed capability● an extremely high running accuracy.

The CE and ACE design bearings have alarger number of small diameter ballscompared with the standard CD, CX, ACDand ACX designs. Centrifugal forces fromcontact between the balls and the outer ringraceway are therefore further reduced, as isalso the contact pressure. Because of thesmaller balls of the CE and ACE designs,they occupy less of the bearing cross-section. The rings are thereforecorrespondingly thicker. This means thatany form errors of shaft or housing borehave less influence on the roundness of thebearing rings. As a result the runningaccuracy is enhanced.

The range of very high-speed bearingscovers bore diameters from 20 to 120 mm.Technical data and dimensions can befound in the tables. Details concerningtechnical data and availability of other sizeswill be supplied on request.

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Hybrid high-speedhigh-precision angularcontact ball bearingsThese bearings have smaller ceramic balls,inner and outer ring shoulders of reducedheight, outer ring centred cage, optimisedinternal design, and are suitable for evenmore demanding applications than thosecovered by hybrid precision angular contactball bearings. With proper lubricationconditions and with moderate loadingrotational speeds can go up to 3 millionn × dm. By using specially designed hybridbearings, the spindle speed can be furtherincreased.

The SKF range comprises two series ofhybrid high-speed high-precision angularcontact ball bearings of series 719 (CE andACE) and 70 (CE and ACE). The bearingsare identified by the suffix HC in thedesignations, e.g. 7014 CEGA/HCP4A.

Hybrid high-precisionangular contact ball bearings

If the performance required is close tothe limits for all-steel bearings, or if higherrigidity or longer life are needed, analternative may be to select SKF hybridbearings. These bearings have steel ringsand ceramic balls. The advantages offeredby ceramic material versus steel are shownin chapter 1: “Principles of bearing selectionand application”, section “material for high-precision bearings”.

Hybrid high-precision angular contact ballbearings offer the following advantagesversus all-steel bearings:● lasting up to four to six times longer● achieving up to 20 % higher speed● lower temperature rise in the system● obtaining higher rigidity● fewer problems with lubrication and

vibration.● less sensible to speed accelerations

and decelerations.

Hybrid high-precision angular contact ballbearings are offered in the same executionas all-steel high-precision angular contactball bearings, series 719, 70 and 72 witheither 15 (CD and CX) or 25 (ACD andACX) degrees contact angle. Hybrid high-precision angular contact ball bearingsare identified by the suffix HC in thedesignation, e.g. 7014 CDGA/HCP4A.

117

Table shows some possiblecombinations and the correspondingnumber of matched sets, single bearingsor duplex sets to be ordered.

Marking of universally matchablebearingsThe bearing rings have several markings foridentification purposes. Each bearing ismarked with the complete designation onthe outer ring face. To facilitate the selectionof the actual bore and outside diameters inorder to obtain the desired fits aftermounting, the actual deviation of the innerbore diameter and outside diameter fromnominal, are marked on the inner ring/outerring respectively. An asterisk marks theposition of the greatest out-of-round on theinner and outer ring side-faces. This iswhere the greatest wall thickness betweenthe base of the raceway and the bore or theoutside diameter surface can be found.

A “chevron V” is marked on the outer ringoutside diameter indicating the contactangle direction. This allows the users tocheck that universally matchable bearings,once fitted on the shaft, are correctlypositioned according to the desiredcombination, i.e. back-to-back, face-to-face,etc. (➔ fig page 121).8

2 Matched bearing setsSKF high-precision angular contact ballbearings are also supplied as complete setsof two, three or four bearings. They arematched during manufacturing so that whenthe bearings are mounted immediately nextto each other, the predetermined value ofthe preload will be obtained, or the load willbe evenly distributed. The bore and outsidediameters do not differ by more than onethird of the permissible diameter tolerance.There is even less difference between thediameters of matched bearingsmanufactured to tolerance class PA9A.

The most popular set arrangementsare shown in figs , , andpages 118 – 119.

The load lines of bearings arranged back-to-back diverge towards the bearing axis.Axial load can be accommodated in bothdirections, although only by one bearing (orbearings in tandem) at a time. The back-to-back arrangement is relatively stiff and canalso take up tilting moments.

7654

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116


Universally matchablebearings

Universally matchable angular contact ballbearings are adjusted during manufactureso that they may be mounted immediatelyadjacent to each other in a back-to-back,face-to-face or tandem arrangement, asdesired. When arranged back-to-back orface-to-face the bearings will have a light,medium or heavy preload depending on therequirements. Basic features such asaccuracy, preload class, speed capabilityetc. of universally matchable angularcontact ball bearings are the same as thoseof the pre-matched sets.

Universally matchable bearings may beuseful in reducing stock holding and improvingavailability. Several specific matched setsmay be obtained by stocking the correctuniversal bearings.

Universal bearings can be supplied in twobasic executions: single universal bearingsfor mounting in any combination, or duplexsets with matched bore and outside diameters.

The designations for single universalbearings are explained in Table .

Customers need to order the samenumber of single universal bearings as thenumber of bearings in a set, e.g. to replacea set 7014 CD/P4ATBTA, three bearings7014 CDGA/P4A are required.

Alternatively, duplex sets of universallymatchable bearings can be chosen. Duplexuniversal bearings can either be used assets, or each bearing used to form othergroups of bearings, with the only limitationbeing the contact angle and the preloadclass. Universal bearings with light preloadmust not be paired against bearings with adifferent contact angle or preload class. Forsuch special cases, please consult the SKFapplication engineering service.

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Original Qty Single universal Qty Duplex universal Qtymatched set bearing bearing sets

7010 CD/P4ATBTA 2 7010 CDGA/P4A 6 7010 CD/P4ADGA 3

7010 CD/P4AQBCA 2 7010 CDGA/P4A 8 7010 CD/P4ADGA 4

7010 CD/P4ADT 5 7010 CDGA/P4A 10 7010 CD/P4ADGA 5

7010 CD/P4ADBA 15 7010 CDGA/P4A 30 7010 CD/P4ADGA 15

7010 CD/P4ADFA 4 7010 CDGA/P4A 8 7010 CD/P4ADGA 4

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See Table for more details17

Tolerance classP4A or PA9A

Preload classA: light, B: medium, C: heavy

Universally matchable execution

Contact angle and internal designCD, CE, CX = 15 degreesACD, ACE, ACX = 25 degrees

Bore diameter

Bearing series

70 10 CD / P4AAG

Designation of single universal high-precisionangular contact ball bearings

Table

Table

118


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Face-to-face arrangementfor axial load in both directions

Face-to-face arrangementDesignation suffix DF

5Fig

Back-to-back arrangementfor axial load in both directions

Back-to-back arrangementDesignation suffix DB

4Fig

Tandem arrangementfor axial load in one direction

Tandem arrangementDesignation suffix DT

6Fig

The load lines of bearings arranged face-to-face converge towards the bearing axis.Axial loads can be accommodated in bothdirections, although again only by onebearing (or bearings in tandem) at a time.The arrangement is not so stiff as theback-to-back arrangement and is lesssuitable for tilting moments.

In a tandem arrangement the load linesof the bearings are parallel. Radial andaxial loads are equally distributed over thebearings but axial loads can only be carriedin one direction. A set of bearings in tandemis therefore generally adjusted againstanother bearing that can take the axialloads acting in the opposite direction.

Combinations of tandem and back-to-back, or tandem and face-to-face arenormally used when the design makes itimpossible to adjust a further bearing,or bearing set against the tandem set.

7Fig

Combination of tandem and back-to-back arrangement

Designation suffix TBT

Combination of tandem and face-to-face arrangement

Designation suffix TFT

Combination of tandem and back-to-backarrangement

Designation suffix QBC

Combination of tandem and face-to-facearrangement

Designation suffix QFC

Tandem arrangement Designation suffix QT

Combination of tandem and back-to-backarrangement

Designation suffix QBT

Combination of tandem and face-to-facearrangement

Designation suffix QFT

Tandem arrangementDesignation suffix TT

120


Marking of bearing setsBearing sets not only have the markings ofsingle bearings; but also have additionalmarkings for identification purposes and toindicate how the bearings of a matched setshould be correctly mounted.

A ‘V’-shaped marking is to be found onthe outside diameter of the bearings. Thebearings need to be mounted in the ordershown by this marking to obtain the correctpreload. It also indicates how the set shouldbe mounted compared with the axial load.The point of the ‘V’ gives the direction inwhich the axial load should act on the innerring(s). Where axial loads act in bothdirections, the ‘V’ point gives the directionof the greater axial load.

Each bearing of a matched set is markedwith the complete designation of the bearingset. The same serial number is shown on theface of the outer ring (➔ figs and ).109

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“V” – shaped marking on outside diameter ofuniversally matchable bearings for paired mountingExample of a set of three universally matchablebearings combined in TBT arrangement

Marking of bearing sets

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Complete bearing designation:71916 ACE/HCP4ADBA

Serial number (for sets only):916

Country of origin:Italy V

Manufacturing date:W41Y

Chevron V

Bore diameter deviation from nominal: –5;and position of the point of maximuneccentricity of the inner ring: *

Outside diameter deviation from nominal:–4; and position of the point of maximuneccentricity of the outer ring: *

Fig

“V” – shaped marking on outside diameter of highprecision angular contact ball bearing sets

9Fig

Fig

123

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122


General bearing dataDimensionsSKF high-precision angular contact ballbearings conform to ISO 15:1998, DiameterSeries 9, 0 and 2.

TolerancesSKF high-precision angular contact ballbearings are manufactured to toleranceclass P4A specifications as standard. Onrequest, bearings can be made accordingto class PA9A or other specifications.

The values for P4A and PA9A toleranceclasses are given in Tables and .Hybrid bearings are made to the sametolerances as the corresponding all-steelbearings.

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PreloadTo meet varying customer needs in terms ofspeed, heat generation and rigidity, SKFoffers standard high-precision angularcontact ball bearings (identified by suffixesCX, CD, ACX and ACD), universallymatchable and matched back-to-back orface-to-face in groups of two or morebearings per set, with three differentpreload classes as standard:Class A: light preloadClass B: medium preloadClass C: heavy preload

Hybrid high-precision angular contact ballbearings (identified by the suffix HC) arenormally supplied either with preload classA or B since the heavy preload is notrecommended for high-speed operations.For the same reason preload classes A andB are usually applied to the high-speedhigh-precision angular contact ball bearings(identified by suffixes CE and ACE), fittedeither with steel or ceramic balls.

Tables page 124, page 125 andpage 126 show preload values for bearingpairs arranged either back-to-back or face-to-face prior to mounting.

765

Inner ring

d ∆dmp ∆ds Vdp Vdmp ∆Bs ∆B1s VBs Kia Sd Siaover incl. high low high low max max high low high low max max max max

mm µm µm µm µm µm µm µm µm µm µm

2,5 10 0 –4 0 –4 1,3 1 0 –40 0 –250 1,3 1,3 1,3 1,310 18 0 –4 0 –4 1,3 1 0 –80 0 –250 1,3 1,3 1,3 1,318 30 0 –5 0 –5 1,3 1 0 –120 0 –250 1,3 2,5 1,3 2,5

30 50 0 –6 0 –6 1,3 1 0 –120 0 –250 1,3 2,5 1,3 2,550 80 0 –7 0 –7 2 1,3 0 –150 0 –250 1,3 2,5 1,3 2,580 120 0 –8 0 –8 2,5 1,5 0 –200 0 –250 2,5 2,5 2,5 2,5

120 150 0 –10 0 –10 6 3 0 –250 0 –380 4 4 4 4150 180 0 –10 0 –10 6 3 0 –250 0 –380 4 6 5 6180 250 0 –12 0 –12 7 4 0 –300 0 –500 5 7 6 7

Outer ring

D ∆Dmp ∆Ds VDp VDmp ∆Cs, ∆C1s VCs Kea SD Seaover incl. high low high low max max max max max max

mm µm µm µm µm µm µm µm µm

18 30 0 –5 0 –5 2 1,3 Values are 1,3 2,5 1,3 2,530 50 0 –6 0 –6 2 1,3 identical to 1,3 2,5 1,3 2,550 80 0 –7 0 –7 2 1,3 those for 1,3 3,8 1,3 3,8

inner ring80 120 0 –8 0 –8 2,5 1,3 of same 2,5 5 2,5 5120 150 0 –9 0 –9 2,5 1,5 bearing 2,5 5 2,5 5150 180 0 –10 0 –10 6 3 4 6 4 6

180 250 0 –11 0 –11 6 4 5 8 5 8250 315 0 –13 0 –13 8 5 5 9 6 8315 400 0 –15 0 –15 9 6 7 10 8 10

3Table

Class P4A tolerances for radial bearings

Inner ring

d ∆ds Vdp Vdmp ∆Bs ∆B1s VBs Kia Sd Siaover incl. high low max max high low high low max max max max

mm µm µm µm µm µm µm µm µm µm

2,5 10 0 –2,5 1,3 1 0 –25 0 –250 1,3 1,3 1,3 1,310 18 0 –2,5 1,3 1 0 –80 0 –250 1,3 1,3 1,3 1,318 30 0 –2,5 1,3 1 0 –120 0 –250 1,3 2,5 1,3 2,5

30 50 0 –2,5 1,3 1 0 –120 0 –250 1,3 2,5 1,3 2,550 80 0 –3,8 2 1,3 0 –150 0 –250 1,3 2,5 1,3 2,580 120 0 –5 2,5 1,5 0 –200 0 –380 2,5 2,5 2,5 2,5

120 150 0 –6,5 3 2 0 –250 0 –380 2,5 2,5 2,5 2,5150 180 0 –6,5 3 2 0 –300 0 –500 3,8 5 3,8 5180 250 0 –7,5 4 2,5 0 –350 0 –500 3,8 5 3,8 5

Outer ring

D ∆Ds VDp VDmp ∆Cs, ∆C1s VCs Kea SD Seaover incl. high low max max max max max max

mm µm µm µm µm µm µm µm µm

18 30 0 –3,8 2 1,3 Values are 1,3 2,5 1,3 2,530 50 0 –3,8 2 1,3 identical to 1,3 2,5 1,3 2,550 80 0 –3,8 2 1,3 those for 1,3 3,8 1,3 3,8

inner ring80 120 0 –5 2,5 1,3 of same 2,5 5 2,5 5120 150 0 –5 2,5 1,5 bearing 2,5 5 2,5 5150 180 0 –6,5 3 2 (∆Bs, ∆B1s) 2,5 5 2,5 5

180 250 0 –7,5 4 2,5 3,8 6,5 3,8 6,5250 315 0 –7,5 4 3,5 3,8 6,5 3,8 6,5315 400 0 –10 5 5 6,5 7,5 6,5 7,5

4Table

Class PA9A tolerances for radial bearings

125

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124


Bearing Axial preloadSeries 719 ACD Series 719 CD Series 719 ACE Series 719 CE719 ACD/HC 719 CD/HC and 719 ACE/HC and 719 CE/HC719 ACX 719 CX and 719 ACX/HC and 719 CX/HCClass Class Class Class

Bore Size A B C1) A B C1) A B A Bdiameter

mm N

10 00 15 30 60 10 20 40 – – – –12 01 15 30 60 10 20 40 – – – –15 02 25 50 100 15 30 60 – – – –17 03 25 50 100 15 30 60 – – – –20 04 35 70 140 25 50 100 35 105 20 6025 05 40 80 160 25 50 100 40 120 25 75

30 06 40 80 160 25 50 100 40 120 25 7535 07 60 120 240 35 70 140 55 165 35 10540 08 70 140 280 45 90 180 75 225 45 13545 09 80 160 320 50 100 200 80 240 50 15050 10 80 160 320 50 100 200 80 240 50 15055 11 120 240 480 70 140 280 120 360 75 225

60 12 120 240 480 70 140 280 120 360 75 22565 13 120 240 480 80 160 320 130 390 80 24070 14 200 400 800 130 260 520 170 510 105 31575 15 210 420 840 130 260 520 180 540 110 33080 16 220 440 880 140 280 560 180 540 110 33085 17 270 540 1 080 170 340 680 230 690 140 420

90 18 280 560 1 120 180 360 720 230 690 140 42095 19 290 580 1 160 190 380 760 245 735 150 450100 20 360 720 1 440 230 460 920 295 885 180 540105 21 360 720 1 440 230 460 920 300 900 185 555110 22 370 740 1 480 230 460 920 310 930 190 570120 24 450 900 1 800 290 580 1 160 385 1 155 235 705

130 26 540 1 080 2 160 350 700 1 400 – – – –140 28 560 1 120 2 240 360 720 1 440 – – – –150 30 740 1 480 960 470 940 1 880 – – – –160 32 800 1 600 3 200 490 980 1 960 – – – –

170 34 800 1 600 3 200 500 1 000 2 000 – – – –180 36 1 000 2 000 4 000 630 1 260 2 520 – – – –190 38 1 000 2 000 4 000 640 1 280 2 560 – – – –200 40 1 250 2 500 5 000 800 1 600 3 200 – – – –220 44 1 300 2 600 5 200 850 1 700 3 400 – – – –

1) All-steel bearings only

5Table

Series 719Preload in bearings for universal pairing andbearing sets arranged back-to-back or face-to-face

Bearing Axial preloadSeries 70 ACD Series 70 CD Series 70 ACE Series 70 CE70 ACD/HC 70 CD/HC and 70 ACE/HC and 70 CE/HC70 ACX 70 CXand 70 ACX/HC and 70 CX/HCClass Class

Bore Size A B C1) A B C1) A B A Bdiameter

mm N

8 8 20 40 80 10 20 40 – – – –9 9 20 40 80 10 20 40 – – – –10 00 25 50 100 15 30 60 – – – –12 01 25 50 100 15 30 60 – – – –15 02 30 60 120 20 40 80 – – – –17 03 40 80 160 25 50 100 – – – –

20 04 50 100 200 35 70 140 55 165 35 10525 05 60 120 240 35 70 140 55 165 35 10530 06 90 180 360 50 100 200 80 240 50 15035 07 90 180 360 60 120 240 80 240 50 15040 08 100 200 400 60 120 240 90 270 55 16545 09 170 340 680 110 220 440 105 315 65 195

50 10 180 360 720 110 220 440 115 345 70 21055 11 230 460 920 150 300 600 120 360 75 22560 12 240 480 960 150 300 600 130 390 80 24065 13 240 480 960 160 320 640 130 390 80 24070 14 300 600 1 200 200 400 800 180 540 110 33075 15 310 620 1 240 200 400 800 180 540 110 330

80 16 390 780 1 560 240 480 960 230 690 140 42085 17 400 800 1 600 250 500 1 000 230 690 140 42090 18 460 920 1 840 300 600 1 200 295 885 180 54095 19 480 960 1 920 310 620 1 240 295 885 180 540100 20 500 1 000 2 000 310 620 1 240 300 900 185 555105 21 560 1 180 2 360 360 720 1 440 – – – –

110 22 650 1 300 2 600 420 840 1 680 – – – –120 24 690 1 380 2 760 430 860 1 720 – – – –130 26 900 1 800 3 600 560 1 120 2 240 – – – –140 28 900 1 800 3 600 570 1 140 2 280 – – – –150 30 1 000 2 000 4 000 650 1 300 2 600 – – – –160 32 1 150 2 300 4 600 730 1 460 2 920 – – – –

170 34 1 250 2 500 5 000 800 1 600 3 200 – – – –180 36 1 450 2 900 5 800 900 1 800 3 600 – – – –190 38 1 450 2 900 5 800 950 1 900 3 800 – – – –200 40 1 750 3 500 7 000 1 100 2 200 4 400 – – – –220 44 2 000 4 000 8 000 1 250 2 500 5 000 – – – –240 48 2 050 4 100 8 200 1 300 2 600 5 200 – – – –


6Table

Series 70 ➤Preload in bearings for universal pairing and bearing sets arranged back-to-back or face-to-face

127

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Factors affecting the preloadPreload on bearing systems is influencedby several factors under static and dynamicconditions.

The actual preload value on the bearingsfitted in a system differs from the pre-determined preload value in themanufacturing process, depending on:● the actual fits between the bearing inner

rings and the shaft, and between thebearing outer rings and the housing

● the system speed for constant positionarrangements.

Other effects may influence the actualpreload of angular contact ball bearingssystems while operating such as:● temperature differences in operation

between the bearing inner ring andouter rings and the rolling elements

● the shaft and housing materials (i.e.different materials may show varyingthermal expansion coefficients, resultingin a differential deformation of the matingpart while the system is operating).

● geometric errors (e.g. imposedmisalignment, cylindricity and conicityerrors, coaxiality errors between front andrear housing).

In case of applications where the abovepoints may be important please contactthe SKF application engineering servicefor advice.

Influence of the fit on the preloadWhen a bearing is mounted with aninterference fit on the shaft, the inner ringwill expand, increasing the racewaydiameter. Conversely, an interference fit inthe housing will compress the outer ring,reducing the raceway diameter.

One of these conditions alone or bothtogether, will reduce the space for therolling elements and thus increase thepreload of the bearing set.

The preload change thus depends on thereal fit between bearings and mating parts.When mating parts are made to tolerancesaccording to the recommendations given inTables and pages 42 – 43 (e.g. js4for shafts and JS5 for housings for bearingsof P4A precision class) the preloadincrease can then be calculated from thefollowing equation with reasonableaccuracy.

Gm = f f1 f2 fHC GA, B, C

whereGm = preload of the mounted bearing

sets, NGA, B, C = preload of bearing sets prior to

mounting, see Tables , andpages 124 – 126

f = bearing factor, see Diagrampage 129

f1 = correction factor depending oncontact angle, see Tablepage 128

f2 = correction factor depending onpreload class, see Table

fHC = correction factor for hybridbearings where applicable,see Table 8

8

8

17

65

21

126


Sets of three or more bearings have ahigher preload than sets of two bearings.The relevant preload value can becalculated by multiplying the preload valuesof pairs reported in the tables by thefollowing factors:1,35 for TBT and TFT sets1,60 for QBT and QFT sets2,00 for QBC and QFC sets.

To calculate preload for sets of bearingsinvolving more than four bearings, or forsets incorporating bearings of differentdesigns, size and contact angle, pleasecontact SKF application engineeringservice.

Bearing Axial preloadSeries 72 ACD Series 72 CD72 ACD/HC 72 CD/HC72 ACX 72 CXand 72 ACX/HC and 72 CX/HC

Bore Size Class Classdiameter A B C1) A B C1)

mm – N

10 00 35 70 140 20 40 8012 01 35 70 140 20 40 8015 02 45 90 180 30 60 12017 03 60 120 240 35 70 14020 04 70 140 280 45 90 18025 05 80 160 320 50 100 200

30 06 150 300 600 90 180 36035 07 190 380 760 120 240 48040 08 240 480 960 150 300 60045 09 260 520 1 040 160 320 64050 10 260 520 1 040 170 340 68055 11 330 660 1 320 210 420 840

60 12 400 800 1 600 250 500 1 00065 13 450 900 1 800 290 580 1 16070 14 480 960 1 920 300 600 1 20075 15 500 1 000 2 000 310 620 1 24080 16 580 1 160 2 320 370 740 1 48085 17 600 1 200 2 400 370 740 1 480

90 18 750 1 500 3 000 480 960 1 92095 19 850 1 700 3 400 520 1 040 2 080100 20 950 1 900 3 800 590 1 180 2 360105 21 1 000 2 000 4 000 650 1 300 2 600110 22 1 050 2 100 4 200 670 1 340 2 680120 24 1 200 2 400 4 800 750 1 500 3 000


7Table

Series 72Preload in bearings for universal pairing andbearing sets arranged back-to-back or face-to-face

129

2

128


Influence of speed on preloadA drastic increase in preload may alsooccur when approaching very high-speeds.The increase is mostly due to thecentrifugal load affecting the position of therolling elements. Thus, adoption of ceramicballs allows much higher rotational speeds,while maintaining low heat generation and

Bore diameter, mm

0

Bearing factor f

2,2

280

2,4

2

1,8

1,6

1,4

1,2

1

20 40 60 80 100 120 140 160 180 200 220 240 260

70 CD, ACDCX and ACX 70 CE 719 CD, ACD

CX and ACX 719 CE 72 CD, ACDCX and ACX

1Diagram

Bearing factor f

ExampleWhat will be the preload of the bearingpair 71924 CD/P4ADBC when mounted?

From Table page 124, the value ofGC is 1 160 N. The value of the bearingfactor f = 2,2 according to Diagram .The correction factors obtained fromTable are f1 = 1 and f2 = 1,24.Therefore,

Gm = f f1 f2 GC

Gm = 2,2 × 1 × 1,24 × 1 160 N = 3 165 N

In other cases the fits may have to besignificantly higher, for instance in veryhigh-speed spindles, to avoid the bearinginner ring from loosening its contact withthe shaft as a result of the centrifugalforce. The effect of fits must then becalculated in more detail. For specialcases such as these, please consult theSKF application engineering service.

The relationship between bearing fits,shafts, housing proportions and preloadincreases can be studied according toDiagram .1

8

1

5

Bearing fHC1) f1

2) f23) f2

3) f23)

series Preload A Preload B Preload C

719 CD and CX 1 1 1 1,12 1,24719 ACD and ACX 1 0,92 1 1,1 1,21719 CE 1 1 1 1,14 –719 ACE 1 0,92 1 1,14 –719 CD/HC and CX/HC 1,08 1 1 1,12 –719 ACD/HC and ACX/HC 1,08 0,92 1 1,12 –719 CE/HC 1,06 1 1 1,14 –719 ACE/HC 1,05 0,92 1 1,14 –

70 CD and CX 1 1 1 1,1 1,270 ACD and ACX 1 0,92 1 1,09 1,1870 CE 1 1 1 1,08 –70 ACE 1 0,96 1 1,08 –70 CD/HC and CX/HC 1,07 1 1 1,1 –70 ACD/HC and ACX/HC 1,06 0,92 1 1,09 –70 CE/HC 1,02 1 1 1,09 –70 ACE/HC 1,03 0,96 1 1,07 –

72 CD and CX 1 1 1 1,04 1,172 ACD and ACX 1 0,95 1 1,05 1,172 CD/HC and CX/HC 1,04 1 1 1,04 –72 ACD/HC and ACX/HC 1,02 0,95 1 1,04 –

1) fHC = correction factor for ceramic balls2) f1 = correction factor for contact angle3) f2 = correction factor dependent on preload

8Table

List of correction factors for preload calculation

131

2

130


spindles, the preload is often given througha set of elastic calibrated springs (➔ fig ),or alternatively hydraulic preload is used.

Table gives guideline values for thespring force to be applied on bearings inconstant load arrangements. The valuesrefer to single bearings with 15 degreescontact angle (suffixes CX, CD and CE),both all-steel and hybrid, of the mostpopular sizes used with spring preload

9

11systems. If bearings are paired in tandem,the value in the table needs to be multipliedby the number of single bearings in the set.

The above values are calculated tominimise the difference in contact anglebetween outer and inner raceway contacts,and to retain a certain axial rigidity of thebearing at high speed. However, it shouldbe noted that additional preload isdetrimental to performance becauseof heat generation.

Bearing Speed factorsize (n dm × 106)

2,25 2,0 1,75 1,5 1,25Preload

N

7000 150 150 150 125 1007001 150 150 150 125 1007002 160 160 160 125 1007003 175 175 150 125 1007004 250 250 200 150 1507005 280 280 250 200 175

7006 350 350 300 200 1757007 400 400 350 300 2007008 400 400 350 300 2007009 750 750 650 500 4007010 750 750 650 500 4007011 1 000 1 000 900 800 6007012 1 000 1 000 900 800 600

9

For applications where extremely high speedis required preloading should be done throughcalibrated springs acting against a bearing ring

Guideline valuesfor the spring forcein constant loadbearing arrangements

adequate stiffness. In Diagram thepreload variation versus speed for differentexecutions of basic bearing type 7014 isshown. For applications where speed is inexcess of 1 – 1,2 million n dm and constantposition preload is necessary, pleaseconsult the SKF Application EngineeringService for more details.

For high-speed applications like internalgrinding spindles and high-frequency milling

2

0

1

2

3

4

5

6

7

8

CD(all-steel)

CD/HC(hybrid)

0 0,45 0,9 1,35 1,8

Preload increase factor

Speed factor, n dm (× 106)

Constant load

CE(all-steel)

CE/HC(hybrid)

15°

15°

15°

15°

2

Preload increase factor for differentbearing designsReference base type 7014

11Fig

Diagram

Table

133

2

132


Bearing Spacer adjustmentsize Series 719 CD Series 70 CD Series 72 CD Series 719 CE Series 70 CE

719 CD/HC 70 CD/HC 72 CD/HC and 719 CE/HC and 70 CE/HC719 CX 70 CX 72 CXand 719 CX/HC and 70 CX/HC and 72 CX/HC

Bore Sizediameter a b a b a b a a

mm – µm

8 8 – – 4 6 – – – –9 9 – – 4 6 – – – –10 00 4 6 5 7 6 9 – –12 01 4 6 5 7 6 9 – –15 02 5 7 5 8 7 11 – –17 03 5 7 6 9 8 11 – –

20 04 5 8 7 10 8 12 10 1425 05 5 8 7 10 8 12 11 1330 06 5 8 8 13 11 15 11 1635 07 6 10 8 13 12 17 13 1540 08 7 11 8 13 13 21 14 1545 09 7 11 12 17 14 21 15 16

50 10 7 12 12 17 14 21 15 1755 11 10 15 14 19 16 24 21 1560 12 10 15 14 19 18 26 21 1665 13 10 18 14 20 20 29 22 1670 14 13 19 15 23 20 29 25 1975 15 13 19 15 23 20 29 25 19

80 16 13 20 17 25 20 32 26 2285 17 15 22 17 25 20 32 29 2290 18 15 23 18 29 25 36 29 2695 19 16 23 19 29 25 39 30 26100 20 17 26 19 29 27 41 33 26105 21 17 26 21 32 28 42 34

110 22 17 26 23 34 28 42 35 –120 24 19 29 23 35 30 46 38 –130 26 21 31 26 39 – – – –140 28 21 33 26 39 – – – –150 30 25 38 27 43 – – – –160 32 26 39 29 45 – – – –

170 34 26 40 29 45 – – – –180 36 28 44 30 47 – – – –190 38 29 44 31 49 – – – –200 40 31 49 34 54 – – – –220 44 33 51 37 56 – – – –240 48 38 59 – – – –

12

Spacer width reduction for changing preloadsin matched sets, CD, CX and CE designs

Preload for customised needsMost often, intermediate rings (spacers)are inserted between the bearings of aset (➔ fig page 135). When a specialpreload may be required to achieve thebest performance, it is possible to changepreload by face grinding the inner or outerspacer. It is not advisable to modify thebearings in any way.

12

Tables and show which spacer(s)should be ground to increase or decreasethe preload. Tables and , page 134show the necessary width reduction to beachieved by face grinding.

Spacers are not only used to customisethe preload but to improve the systemrigidity, and sometimes to bring the oil pipesas close as possible to the raceways. In

1312

1110

Bearing The part to be Amount to be ground off arrangement face ground to increase preload from

A up to B B up to C A up to C

Back-to-back Inner spacer a b a + b

Face-to-face Outer spacer a b a + b

10

Bearing The part to be Amount to be ground off arrangement face ground to decrease preload from

B down to A C down to B C down to A

Back-to-back Outer spacer a b a + b

Face-to-face Inner spacer a b a + b

11 Spacer(s) to be groundto decrease preload

Spacer(s) to be groundto increase preload

Table

Table

Table

135

2

134


other cases, especially in grease-lubricatedspindles, it is necessary to have spacers toallow grease to escape from the contactzone to reduce running temperature.

In order to get the best performance fromthe bearings, spacers should not deformunder load, and form errors should not beintroduced, as these would affect thepreload of the bearing sets. In general, theguidelines given in the form tolerancerequirements for shaft and housing can befollowed. For spacers in particular, thematerial should be hard enough to resistdamage during handling, preferably thesame hardness as bearing rings(i.e. around 60 HRC), but materials with45 – 50 HRC would be adequate.

The most important point concerns theparallelism of the faces and the widthdifference between the outer and innerspacer, in the same set of bearings. Theparallelism should be kept within 1 – 2 µm.To obtain the lowest possible differencein width of the inner and outer spacer,the two spacers should be face groundtogether (one placed inside the other).

CagesHigh-precision angular contact ball bearingsare as standard equipped with outer ringland riding fabric-reinforced phenolic resincages. The cages are lightweight anddesigned to minimise centrifugal force,while ensuring an optimum lubricant flowthroughout the ball-raceway contact. Theyare not identified in the bearing designation.New, better performance cages now beingintroduced are made of PEEK (polyetherether ketone) and are identified in thebearing designation by the suffix “TNH”.Fabric-reinforced phenolic resin ball guidedcages and metallic machined cages arealso available on request.

Bearing Spacer adjustmentsize Series 719 ACD Series 70 ACD Series 72 ACD Series 719 ACE Series 70 ACE

719 ACD/HC 70 ACD/HC 72 ACD/HC and 719 ACE/HC and 70 ACE/HC719 ACX 70 ACX 72 ACXand 719 ACX/HC and 70 ACX/HC and 72 ACX/HC

Bore Sizediameter a b a b a b a a

mm – µm

8 8 – – 3 4 – – – –9 9 – – 3 4 – – – –10 00 2 4 3 5 3 6 – –12 01 2 4 3 5 3 6 – –15 02 3 5 3 5 5 7 – –17 03 3 5 4 6 5 8 – –

20 04 4 5 4 7 5 8 7 925 05 4 5 5 7 5 8 7 830 06 4 5 6 9 7 11 7 1035 07 5 6 6 9 9 12 8 940 08 5 7 6 9 10 14 9 945 09 5 7 7 12 10 14 9 10

50 10 5 7 8 12 10 14 9 1055 11 6 10 8 14 11 17 13 1060 12 6 10 8 14 12 18 13 1065 13 6 10 8 14 13 20 14 1070 14 8 13 10 15 13 21 15 1275 15 9 13 10 15 13 21 15 12

80 16 9 13 12 18 13 22 15 1485 17 10 15 12 18 13 22 17 1490 18 10 16 12 19 16 25 18 1695 19 10 16 12 20 17 27 18 16100 20 11 18 13 21 18 29 20 16105 21 11 18 13 22 18 30 20

110 22 11 18 15 23 18 30 21 –120 24 12 21 15 24 20 32 23 –130 26 14 22 17 27 – – – –140 28 14 23 17 27 – – – –150 30 16 26 18 28 – – – –160 32 17 27 18 30 – – – –

170 34 17 27 18 30 – – – –180 36 18 30 19 33 – – – –190 38 18 30 19 33 – – – –200 40 20 33 22 37 – – – –220 44 21 34 24 38 – – – –240 48 24 39 – – – –

13

Spacer width reduction for changing preloads inmatched sets, ACD, ACX and ACE designs

Example of spacers in between a group of twohigh-precision angular contact ball bearingsmatched back-to-back

12Fig

Table

137

Equivalent dynamicbearing load

For bearings arranged singly or paired intandem

P = Fr when Fa/Fr � eP = XFr + YFa when Fa/Fr > e

Factor values are given in Tablepage 138.

When calculating bearing pairs, Fr and Farepresent the forces acting on the bearingpair.

For bearings paired back-to-back orface-to-face

P = Fr + Y1Fa when Fa/Fr � eP = XFr + Y2Fa when Fa/Fr > e

Factor values are given in Tablepage 138. When calculating bearing pairs,Fr and Fa represent the forces acting on thebearing pair.

16

15

Equivalent staticbearing load

For bearings arranged singly or paired intandem

P0 = 0,5 Fr + Y0Fa

when P0 < Fr, P0 = Fr should be used.

For bearings paired back-to-backor face-to-face

P0 = Fr + Y0Fa

The value of factor Y0 depends on thecontact angle and can be obtained fromTables and . When calculatingbearing pairs, Fr and Fa are the forcesacting on the bearing pair.

1615

2

136


Speed ratingsThe limiting speeds quoted in the bearingtables are guideline values and are validprovided that the bearings are lightly loaded(P � 0,06 C), that they are lightly preloadedby means of springs, and that the transportof heat away from the bearing position isgood.

The values for oil spot lubrication aremaximum values and should be reduced forcertain other methods of oil lubrication asmentioned in the chapter Speed (➔ page 23).The values for grease lubrication are alsomaximum values. Both apply to singlebearings.

When single bearings are adjustedagainst each other to a greater degree, e.g.to increase spindle stiffness, or if matchedsets of two, three or four bearings are to beused, the speed rating values given in thetables must be reduced.

Reduction factors to obtain guidelinevalues for the appropriate conditions aregiven in Table .14

For special preloads please contact SKF.If the speed rating obtained from the

above for matched bearing sets is inadequate,a simple design change, such as theinclusion of intermediate rings betweenthe bearings will allow appreciableincreases to be made (➔ fig page 135).For sets of three bearings, for example, itshould then be possible to run at the speedrating for paired bearings. Springs topreload the bearings may be beneficial.This type of preload is generally used forhigh-speed operation in order to obtainan even preload over the whole operatingrange of the machine.

12

Bearing Bearing designarrangement CD, CD/HC, ACD All CE, CE/HC, ACE

ACD/HC and ACE/HCCX, CX/HC,ACX and ACX/HCPreload Special Preload

preloadA B C A B

Set of 2 bearings paired in tandem 0,90 0,80 0,65 0,90 0,70

Set of 2 bearings paired back-to-back or face-to-face 0,80 0,70 0,55 Call SKF 0,75 0,60

Set of 3 bearings 0,70 0,55 0,35 0,65 0,40

Set of 4 bearings 0,65 0,45 0,25 0,55 0,30

14Table

Speed reduction factors for preloaded bearingsets of angular contact ball bearings

139

2

138


Calculation of equivalentbearing load for preloadedangular contact ball bearingsWhen calculating the equivalent bearingload for preloaded bearings, it is necessaryto take the preload into account. The axialcomponent of the load (Fa) is needed forthe equivalent load calculation. It is obtainedusing the following equations when actualoperating conditions are considered (thevalues obtained will be approximate).

For bearing pairs under radial loadand axially secured

Fa = Gm

For bearing pairs under radial loadand preloaded by springs

Fa = GA, B

For bearing pairs under axial loadand axially secured

Fa = Gm + 0,67 Ka when Ka � 3 GmFa = Ka when Ka > 3 Gm

For bearing pairs under axial loadand preloaded by springs

Fa = GA, B + Ka

whereFa = axial component of a bearing load, NGA, B = preload of a bearing pair, NGm = preload on a mounted bearing pair, NKa = external axial force acting on single

bearing, N

Designation systems of singlebearings and matched sets

The complete designation of a singlebearing identifies the series, bore diameter,contact angle, and design, as well as thesuffix indicating the tolerance class e.g.71914 CD/P4A. The designation of bearingsets also includes suffixes indicating thenumber of bearings in the set, theirarrangement and preload. Additionalsuffixes may be added to identify bearingsincorporating special features, such asgreases, special tolerances, etc. Pleaseconsult SKF for precise information.

The designation scheme of SKFhigh-precision angular contact ballbearings is shown in Table page 140.17

Vibration from other machinery, traffic orduring transportation may cause damage tobearings. In such cases, bearing life is notlimited by the material fatigue, but by thepermanent deformation produced in thecontact between balls and raceways. A ballmay be driven into the surface of the ringsby the applied load. The same may happenfor bearings sustaining heavy shock loadsduring a fraction of a revolution.

As demands are high for runningproperties and life, permanent deformationof the bearing parts should be avoided at alltimes. The maximum load should therefore

not exceed the equivalent static loadobtained from the equation:

P0 = C0/s0

whereP0 = equivalent static bearing load, NC0 = basic static load rating, Ns0 = static safety factor.

For all-steel high-precision angular contactball bearings, a minimum safety factor s0of 3 is recommended. For hybrid bearings,a safety factor s0 of 3,4 can be used.

f0 Fa/C0 e X Y Y0

Contact angle 15 degrees (suffix CD, CX and CE)

< 0,178 0,38 0,44 1,47 0,460,357 0,4 0,44 1,40 0,460,714 0,43 0,44 1,30 0,461,07 0,46 0,44 1,23 0,461,43 0,47 0,44 1,19 0,462,14 0,5 0,44 1,12 0,463,57 0,55 0,44 1,02 0,465,35 0,56 0,44 1,00 0,46> 7,14 0,56 0,44 1,00 0,46

Contact angle 25 degrees (suffix ACD, ACX and ACE)

– 0,68 0,41 0,87 0,38

Values of f0 are given in the bearing tables

15Table

Calculation factors for single bearingsand bearings paired in tandem

2 f0 Fa/C0 e X Y1 Y2 Y0

Contact angle 15 degrees (suffix CD, CX and CE)

< 0,178 0,38 0,72 1,65 2,39 0,920,357 0,4 0,72 1,57 2,28 0,920,714 0,43 0,72 1,46 2,11 0,921,07 0,46 0,72 1,38 2,00 0,921,43 0,47 0,72 1,34 1,93 0,922,14 0,5 0,72 1,26 1,82 0,923,57 0,55 0,72 1,14 1,66 0,925,35 0,56 0,72 1,12 1,63 0,92> 7,14 0,56 0,72 1,12 1,63 0,92

Contact angle 25 degrees (suffix ACD, ACX and ACE)

– 0,68 0,67 0,92 1,41 0,76

Values of f0 are given in the bearing tables

16Table

Calculation factors for bearings paired back-to-back or face-to-face

141

2

140


17

719 10 ACE Q A/ P4A BCHCTNH

Bearing series719 Single row angular contact ball bearing,

ISO Dimension Series 1970 Single row angular contact ball bearing,

ISO Dimension Series 1072 Single row angular contact ball bearing,

ISO Dimension Series 02

Bore diameter8 8 mm bore diameter9 9 mm bore diameter00 10 mm bore diameter01 12 mm bore diameter02 15 mm bore diameter03 17 mm bore diameter04 (×5) 20 mm bore diameterI48 (×5) 240 mm bore diameter

Contact angle and internal designACD, ACX 25°CD,CX 15°ACE 25°CE 15°

Cage design and material— Outer ring land riding, fabric reinforced phenolic resinTNH Rolling element riding, glass fibre reinforced PEEK

Rolling element material— SteelHC Silicon nitride (ceramic)

Tolerance classP4A Dimensional accuracy to ISO class 4,

running accuracy better than ISO class 4PA9A Accuracy to ABMA class ABEC 9

Number of bearings in setD 2 bearings in matched setT 3 bearings in matched setQ 4 bearings in matched set

Bearing arrangement in matched setB Back-to-backF Face-to-faceT TandemBT Back-to-back/tandemFT Face-to-face/tandemBC Back-to-back of pairs in tandemFC Face-to-face of pairs in tandemG For universal pairing

PreloadA Light preloadB Medium preloadC Heavy preloadG.. Special preload, value in daN, e.g. G240

Product tablesTable

Documents

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