Fitting of Bearings

THE IMPORTANCE OF CORRECT FITTING

A bearing can only perform to its full capacity when it is correctly fitted on the shaft and in the housing. Insufficient interference on fitting surfaces could cause bearing rings to creep in a circumferential direction. Once this happens, considerable wear occurs on the fitting surface and both shaft and housing are damaged. Furthermore, abrasive particles may enter the bearing causing vibration, excessive heat and damage to raceways. It is therefore necessary to provide bearing rings under rotating load with an adequate interference fit to prevent creep. When using thin-type bearings under low load, the bearings should be fastened by a nut. Statically loaded bearings generally do not need to be fitted with an interference fit. Only when subject to a high degree of vibration do both inner and outer rings require fitting with an interference fit.


FITTING OF BEARING AND SHAFT

CONDITION
(STEEL SHAFT)
SHAFT BORE DIAMETERSHAFT TOLERANCE CLASS
THIN-TYPE
OTHERS
INNER RING ROTATING LOAD OR INDETERMINATE LOAD DIRECTIONLIGHT LOAD<=0.06Cr OR FLUCTUATING LOAD
10d18
18
d30
30
d50
h5
h5
h5
js5
js5
js5
STANDARD LOAD=0.06~0.12Cr
10d18
18
d30
30
d50
js5
js5
js5
j5
k5
k5
OUTER RING ROTATING LOADNECESSARY FOR INNER RING TURNING EASILY AROUND SHAFTALL BORE DIAMETERSg5g6
UNNECESSARY FOR INNER RING TURNING EASILY AROUND SHAFTALL BORE DIAMETERSh5h6

FITTING OF BEARING AND HOUSING

CONDITION
(ONE-PIECE HOUSING)
AXIAL DIRECTIONAL MOVEMENT OF OUTER RINGTOLERANCE CLASS OF SHAFT HOUSING SEATS
THIN-TYPE
OTHERS
INNER RING ROTATING LOADVARYING LOADS
EASY TO MOVE
H6
H7
LIGHT OR STANDARD LOAD
EASY TO MOVE
H7H8
HIGH TEMPERATURE OF INNER RING AND SHAFT
EASY TO MOVE
G6
G7
LIGHT OR STANDARD LOAD PRECISE ROTATIONAS A RULE, IMPOSSIBLE TO MOVEK5K6
POSSIBLE TO MOVEJS6J6
QUIET OPERATIONEASY TO MOVEH6H6
INDETERMINATE LOAD DIRECTIONLIGHT OR STANDARD LOADIN GENERAL, POSSIBLE TO MOVEJS6J7
STANDARD OR HEAVY LOADAS A RULE, IMPOSSIBLE TO MOVEK5K7
LARGE SHOCK LOADIMPOSSIBLE TO MOVEM5M7
LIGHT OR FLUCTUATING LOADIMPOSSIBLE TO MOVEM5M7
OUTER RING ROTATING LOADSTANDARD OR HEAVY LOADIMPOSSIBLTE TO MOVEN5N7
THIN-TYPE HOUSING SEATS HEAVY LOAD OR LARGE SHOCK LOADIMPOSSIBLE TO MOVEP6P7

CHARACTERISTICS OF LOAD AND FITTING

ROTATING RINGLOADLOAD CONDITIONFITTING
  INNER RING  STATICINNER RING ROTATING LOAD

OUTER RING STATIC LOAD
INTERFERENCE FIT FOR INNER RING

CLEARANCE FIT FOR OUTER RING
  OUTER RING  ROTATING
  OUTER RING  STATICOUTER RING ROTATING LOAD

INNER RING STATIC LOAD
CLEARANCE FIT FOR INNER RING

INTERFERENCE FIT FOR OUTER RING
  INNER RING  ROTATING
IN THE CASE OF FLUCTUATING LOAD
DIRECTION OR UNBALANCED LOAD
ROTATING OR STATICINDETERMINATE LOAD DIRECTIONINTERFERENCE FIT FOR INNER AND OUTER RING

CALCULATIONS OF FITS

  1. FITTING PRESSURE AND DIMENSIONAL CHANGES OF INNER AND OUTER RING
    The right fit for each application is established taking various condetions into consideration such as load, speed, temperature, mounting dismounting of the bearing. The interference fit should be greater than normal in thin housings, housings of soft material or on hollow shafts.
  2. LOAD OF INTERFERENCE
    The interference fit of shaft and inner ring decreases under radial load. The decrease in fit of shaft and inner ring is calculated by the following formula:
    LOAD OF INTERFERENCE
  3. INFLUENCE OF TEMPERATURE ON BEARINGS, SHAFTS AND HOUSINGS
    Each inner ring, outer ring or rolling element of a bearing rotating under load generates heat which will affect the interference fits of the shaft and the housing. Assuming a temperature difference within the bearing and the housing of T(), that of the mating surface of the shaft and of the bearing is (0.100~.15) T.
    Consequently, dr, the decrease of the inner ring interference fit due to temperature change, is calculated from the following formula:

    It should also be noted that fit can increase due to temperature changes.
  4. EFFECTIVE INTERFERENCE, SURFACE ROUGHNESS AND ACCURACY
    The surface is smoothed during fitting and the effective interference becomes smaller than the theoretical interference. The surface quality of a mating surface has an influence on how much this theoretical interference decreases. Effective interference can usually be calculated as follows:

    By combining these factors, the theoretical interference fit required for inner ring and shaft where the inner ring is subjected to rotating load is calculated as follows:

    Normally, shaft and housing seats have to meet the accuracy and roughness requirements as given below.

ACCURACY AND ROUGHNESS OF SHAFT AND HOUSING SEATS

  SHAFTHOUSING
ROUNDNESSBELOW 50% OF SHAFT DIAMETER TOLERANCEBELOW 50% OF HOUSING BORE DIAMETER TOLERANCE
CYLINDRICITYBELOW 50% OF SHAFT DIAMETER TOLERANCE WITHIN BEARING WIDTHBELOW 50% OF HOUSING BORE DIAMETER TOLERANCE WITHIN BEARING WIDTH
SQUARENESS3/1000(0.17)
ROUGHNESS OF MATING SURFACERmax 3.2
Rmax 6.3

Mountings bearing with extra tight or light interference fits can lead to early bearing failure. In order to ensure safe operating conditions the tolerance variations of shaft seats, housing bores and bearing bore and outside diameter need to be reduced.

We recommend the tolerance zones are divided into two bands and selective assembly is applied. Bearings sorted into two tolerance bands for inner and outer rings are available on request. These bearings are marked as follows:

SELECTIVE CLASSIFICATION OF OUTER AND BORE DIAMETER TOLERANCES AND INDICATION MARK


Note:

  1. THIS IS APPLIED TO BOTH BEARINGS OF ABEC 5P AND P5.
  2. UPON YOUR REQUEST, PLEASE SPECIFY THE MARK LISTED BELOW.
    ZC1…. 2 SELECTIVE CLASSIFICATIONS FOR BORE DIAMETER TOLERANCE (0-d/2,-d/2-d)
    1 SELECTIVE CLASSIFICATIONS FOR OUTER DIAMETER TOLERANCE (0-D)
    ZC2… 1 SELECTIVE CASSIFICATION FOR BORE DIAMETER TOLERANCE (0-d)
    2 SELECTIVE CASSIFICATION FOR OUTER DIAMETER TOLERANCE (0-D/2,-D/2-D)
    ZC3… 4 SELECTIVE CASSIFICATION FOR BOTH BORE DIAMETER TOLERANCE (0-d/2,-d/2-d,0-D/2,-D/2-D)
    D… MINIMUM VALUE OF OUTER DIAMETER TOLERANCE
    d… MINIMUM VALUE OF BORE DIAMETER TOLERANCE