Angular Contact Ball Bearings Combination

1 Part 1 Part 2 Part 3 Part 4 Part5 Part 6 Part 7 Part Contact ball bearing COMBINATIONS148 Angular Contact BallBearing CombinationsAngular Contact ball bearing Combinations AvailableNormally, NSK supplies matched super precision Angular Contact ball Bearings as 2, 3, and 4 row combinations. The combinationsavailable for the fixed end of spindles are usually 2 rows (DB), 3 rows (DBD), and 4 rows (DBB) sets. However, in the case of 3 rowcombinations, since the preload distribution to each bearing is not equal, the optimum preload setting range is very limited, makingthem unsuitable for high speed Bearings are manufactured as sets, so when they are mounted adjacent to each other, a given preload is automaticallyobtained. The variation per pair of matched Bearings for bore and outer diameters is adjusted to less than 1/3 of the of Each Combination Back-to-back Arrangement, DBAxial loads in both directions and radial loads can besustained.

2 Since the distance between the effective loadcenters is large, this type is suitable if moments are , if accuracy of housing is not enough and there is amisalignment in the spindle, internal loads of Bearings couldbe large enough to possibly cause premature failure due togreater moment stiffness. Face-to-face Arrangement, DFCompared with the DB type, the distance between theeffective load centers is small, so the capacity to sustainmoments is inferior to the DB the other hand, this type is suitable for using withhousings that have less accuracy or larger shaft deflectionsdue to low bending stiffness of shaft. Tandem Arrangement, DTAxial loads in one direction and radial loads can besustained.

3 Since axial stiffness of this type is twice the valueof a single row type, this arrangement is used when the axialload in one direction is heavy. 3 rows Arrangement, DBDA xial loads in both directions and radial loads can , the preload distribution to each bearing is notequal, and preload on the counter side (single side) is twicethat of other , this type is unsuitable for high speedoperation because of the large increase of internal load ofthe single side which could lead to bearing failure. 4 rows Arrangement, DBBA xial loads in both directions and radial loads can situations that have the same axial clearance as DBarrangement, preload and stiffness are twice that of the DBarrangement. Also, the permissible axial load of a 4 rowarrangement is larger than that of a DB Bending Comparison between Back-to-backand Face-to-face ArrangementsMoment stiffness is different between Back-to-back and Face-to-face arrangements as shown in the shaft bendingcomparison calculation example below.

4 In this example, Angular Contact ball Bearings (75 BNR10 XET) are used in thefront side and the typical shaft deflections are shown for bothDB and DF configurations. When 1 000 N of radial load isapplied on the spindle nose, radial displacements on thespindle nose are calculated as follows. DB= 10 2 DF= 10 2 This demonstrates the effect of the distance between effectiveload centers on spindle Instructions for Angular Contact BallBearings Matching MethodDirection of MatchingFor matched Bearings , the mounting order and loadapplication direction are very V is marked on the outer diameter surfaces of the bearingsas shown in the figure on the right. When the Bearings aremounted so their marks correctly form a V , they are properlymatched and the side surface or chamfered part of the inner rings, thesymbol is marked to indicate the position of maximumradial runout.

5 Optimum accuracy is achieved when the bearingis mounted so the symbol is placed just opposite theposition of shaft maximum distance between the effective load centersThe distance between the effective load centersDBDFDTDB250 N250 N 500 NPreload=500 NDF ArrangementDB ArrangementRadial Load:1 000 NDBDFDTDBDDTDDFDDBBDFFDBTDFTDTTFig. Spindle Displacement CurveFig. The Distance between the Effective Load Centers ofBack-to-back and Face-to-face ArrangementsFig. Combinations of Angular Contact ball BearingsFig. Direction in Back-to-Back and Tandem ArrangementsFig. Internal Preload in DBD ArrangementDBDFDTDBDDBBLoad directionMoment stiffnessSpeed capabilityHeat generationStiffnessTable Features of Each CombinationFig. Symbol for the Position of Maximum Radial Runoutof Inner RingExcellent Very good Good Fair One direction only Two directionsPart 1 Part 2 Part 3 Part 4 Part5 Part 6 Part 7 Part Contact ball bearing COMBINATIONS150 Angular Contact BallBearing CombinationsDBDFDTDBDDTDDFDDBBDFFDBTDFTD TTU niversal CombinationNSK supplies universal Combination Angular Contact ball Bearings that have the same amount of stand out on both the front andback face.

6 This means that when Bearings that have the same reference number are combined, they have the specified amount foreach standard universal Combination Bearings , the V Combination marks on the outer diameter surface of outer ring prevent direction mistakes, ensure correct matching when they are mounted, and indicate the direction of the Contact between SU and DU BearingsThere are 2 types of NSK universal Combination Bearings as shown in the table for Use of Single Universal (SU) Bearings When these Bearings are used as part of multiple combined Bearings , it is recommended that the variation of bore andouter diameter tolerance is within 1/3 of tolerance range. There are also special Bearings with special accuracy Class 4Y that can accommodate small variations of bore and outerdiameter tolerance.

7 Class 4Y tolerance has the same running accuracy as Class 4 but has a narrower tolerance range ofbore and outer diameter than Class 4. It is suitable for random matching method universal Combination Bearings . Class 4Y is suitable for use random matching method universal Combination Bearings . However, when thesebearings are operated over 1 500 000 dmn, there is a possibility that this very small variation of fits with either the shaft orthe housing can cause bearing failure because of imbalance of internal load in each row. If these Bearings areconsidered for such high speed applications, this issue should be taken into of bore toleranceVariation of outer diameter toleranceTolerance Range of P4 Tolerance Range of P4 YTolerance Range of P4 YTolerance Range of P4 Negative Clearance: 2fNegative Clearance: 2bDB arrangementPreload is stand out ofback face x 2 = 2b(=2f) and it is the specifiedamount for each Bearings are mounted in random matchingmethod, variation of tolerance should be Tolerance of P4 and P4Y AccuracyFig.

8 Universal Bearings CombinationsDF arrangementPreload is stand out offront face x 2 = 2f(=2b) and it is the specifiedamount for each arrangementThere is no clearance on DT surfacebecause stand out of front face f issame as stand out of back face b .This situation is the same asbearings combined as to anyarrangement because f (stand out of front face)is same as b (stand outof back face).Fig. Universal CombinationSUDURow of bearings12 Variation of bore andouter diameter tolerance Controlled in 1/3 of toleranceTable Features of SU and DU BearingsCombination Mark and Matching Method for Universal Combination BearingsBore and Outer Diameter Tolerance (Class 4Y)Bore diameterClass 4 Class 4Y (Controlled to medium value)OverInclHighLowHighLow30500 6 1 350800 7 2 5801200 8 3 61201500 10 3 7 Table Tolerance of Bore Diameter of Inner Ring Tolerances for Bearings under 30 mm bore are the same as valuesquoted between 30 50 mm diameterClass 4 Class 4Y (Controlled to medium value)

9 OverInclHighLowHighLow50800 7 2 6801200 8 2 61201500 9 3 71501800 10 3 71802000 11 4 9200 Under 2150 11 2 9 Table Tolerance of Outer Diameter of Outer Ring Tolerances for Bearings under 50 mm outer diameter are the same asvalues quoted between 50 80 mm outer : mUnit: m