Bearing fit and clearance

It is very important to match the bearing inner diameter with the shaft and outer diameter with the housing when the bearing is installed. If the fit is too loose, the mating surface will produce relative sliding, which is called creep. Once creep occurs, it will wear out the mating surface, damage the shaft or housing, and wear powder will invade into the bearing, causing heat, vibration and damage. Excessive interference will lead to smaller outer diameter of the outer ring or larger inner diameter of the inner ring, which will reduce the internal clearance of the bearing. In addition, the geometric accuracy of shaft and shell processing will also affect the original accuracy of the bearing ring, thus affecting the performance of the bearing.

1.1 Selection of Fit 1.1.1 The nature of load and selection of fit are determined according to the bearing bearing load direction and the rotation status of inner and outer rings, generally referring to Table 1. Table 1 and load and load bearing rotating conditions illustrations with inner ring: negative turns: static load direction: fixed inner ring spinning load inner ring, outer ring static load USES the interference fit (interference fit) outer ring: available running fit (clearance) inner ring: static negative circle: the rotation direction of the load, and the outer ring and spin inner ring: negative turns: static load direction: fixed inner ring static load inner ring, outer ring spinning load available running fit (clearance) outer ring: USES the interference fit (interference fit) inner ring: static negative circle: rotary load direction: with the inner ring spinning at the same time. 2) Recommended fit To select suitable fit, bearing load characteristics, size, temperature conditions, bearing installation, removal of various conditions. When the bearing is mounted to the thin-walled shell and hollow shaft, the interference amount needs to be larger than that of ordinary ones. The separated shell can easily deform the outer ring of the bearing, so the outer ring should be used carefully under the condition of static coordination. In the case of large vibration, the inner ring and the outer ring should adopt static coordination.

Cooperate with the most general recommendation, refer to table 2, table 3 table 2 centripetal bearing and shaft with the conditions applicable cases (reference) the diameter of axle (mm) spherical roller bearing remark ball bearings cylindrical roller bearings taper roller bearings automatic self-aligning roller bearing cylindrical hole bearing outer ring and shaft rotation load need inner ring on the shaft is easy to move static axle wheels all size g6 precision requirements, With g5, h5, bearing and facilitate mobile required h6 is also available without inner ring is easy to move the shaft tension wheel h6 inner ring spinning frame, rope round or direction of variable load under light load 0.06 Cr (1) load varying load appliances, pump, blower, truck, precision machinery, machine tool under 18 — Js5 accuracy when required by the level of the p5, inner diameter using precision ball bearing under 18 mm h5. Common load (0.06~0.13) Cr (1) General bearing part of medium and large motor turbine, pump, engine spindle, gear transmission device, woodworking machinery under 18 — N6 single-row tapered roller bearings and single-row radial thrust ball bearings can be used k6, M6 instead of K5, M5. P6 140-200 40-65 R6 200-280 100-140 N6 — 200-400 140-280 P6 — 280-500 R6 — Over 500 R7 heavy load (over 0.13Cr (1)) railway and industrial vehicles electric vehicle owners electric motor construction machinery crusher — 50-140 50-100 N6 Need is greater than the clearance of the bearing – p6, 140-200, 100-140 – more than 200, 140-200 r6 — 200-500 r7 only carry axial load of parts of structure bearing use location all dimensions Js6 (j6) – table 3 centripetal bearing with shell hole conditions applicable cases (reference) the movement of the outer ring hole tolerance range grade note overall shell hole wall bearing outer ring spinning load heavy duty automobile wheel roller bearings (crane) walk road wheel P7 outer ring to the axial direction.

Normal load, heavy load automobile wheel (ball bearings) shaker N7 light load or changing load conveyor belt tension pulley wheel, pulley M7 not the host of directional load large impact load trolley load or light load of pump crankshaft spindle large motor K7 outer ring in principle not to the axial direction of outer ring does not need to the axial direction integral type shell holes or separation type shell hole normal load or light load JS7 (J7) outer ring will be able to be moved to the axial need outer ring to the axial direction of inner ring spinning load of all kinds of load bearing part of the general bearing box of railway vehicle H7 outer ring to the axial direction easily – normal load or light load arrange ushering in shell shaft and bearing H8 whole circle into general load, high temperature of paper making dryer G7 light load, especially need precision grinding spindle rotation at the back of the ball bearing high-speed centrifugal compressor fixed side bearing JS6 (J6) outer ring to the axial direction – not directed the direction load at the back of the ball bearing grinding spindle high-speed centrifugal compressor K6 fixed side bearing outer ring fixed in the axial direction of the load in principle, applicable to the amount of interference with larger than K, special requirements under the condition of high precision, Small allowable fits should be further used for each purpose.

Inner ring spinning load varying load, especially need precision rotation and large rigidity of machine tool spindle with M6 or N6 cylindrical roller bearing outer ring fixed in the axial direction for noiseless operating household appliances H6 outer ring to the axial direction – 3), the precision of the axis, a hood, and the surface roughness axis, a hood precision is not good situation, bearing affected by its can’t display the required performance. For example, the installation of part of the shoulder if the accuracy is not good, the inner and outer rings will be inclined. In addition to the bearing load, combined with the concentrated load at the end, the bearing fatigue life will be reduced, and more seriously, it will become the cause of cage damage and sintering. In addition, the shell deformation due to external load is not large. It is necessary to fully support the rigidity of the bearing. The higher the rigidity, the better the noise and load distribution of the bearing.

In general conditions of use, turning end machining or precision boring machine processing can be. However, for the occasions with strict requirements of rotation runout and noise and the load conditions are too harsh, the final grinding shall be used. When more than 2 bearings are arranged in the whole housing, the housing mating surfaces should be designed to be machined and perforated. In general conditions of use, shaft, housing precision and finish can be as shown in Table 4 below. Table 4 Axis and Housing Accuracy and Finish Of bearings – Class AXIS enclosure roundedness tolerances – class 0, class 6, class 5, Class 4 IT3 ~ IT42 2IT3 ~ IT42 2 IT4 ~ IT52 2IT2 ~ IT42 2 Cylindricity tolerances – class 0, class 6, class 5, class 4 IT3 ~ IT42 2IT2 ~ IT32 2 IT4 ~ IT52 2IT2 ~ IT32 2 Shoulder runout tolerances – class 0, class 6, class 5, class 4 IT3IT3 IT3~IT4IT3 Matching surface finish Rmax small bearing large bearing 3.2 S6.3s 6.3 S12.5s.

The so-called internal clearance of the bearing refers to the amount of movement when the inner or outer ring of the bearing is fixed before the bearing is mounted on the shaft or bearing box, and then the unfixed side is moved in radial or axial direction. According to the movement direction, it can be divided into radial clearance and axial clearance. When measuring the internal clearance of the bearing, in order to keep the measured value stable, the test load is generally applied on the ring. Therefore, the test value is larger than the actual clearance value, that is, an additional amount of elastic deformation caused by applying the test load. The actual value of bearing internal clearance is shown in Table 4.5. The increase of clearance caused by the above elastic deformation is corrected. The elastic deformation of roller bearings is negligible. Table 4.5 to eliminate influence of radial clearance test load correction (deep groove ball bearing) units: um nominal bearing model diameter d (mm) (N) clearance test load correction over to C2 C3 C4 C510 ordinary (including) 18 24.549 147 3 ~ 4 4 ~ 5 6 ~ 8 45 8 4 6 9 April 9 April 6 92.2 the selection of the bearing clearance bearing running clearance, due to the bearing fit and temperature difference on inner and outer reasons, generally are smaller than the initial clearance. The operating clearance is closely related to the bearing life, temperature rise, vibration and noise, so it must be set to the optimal state.

Theoretically speaking, when the bearing is in operation, with slightly negative running clearance, the bearing life is maximum. But it is very difficult to maintain this optimal clearance. With the change of service conditions, the negative clearance of the bearing will increase correspondingly, which will lead to the significant decrease of bearing life or the generation of heat. Therefore, the initial clearance of the bearing is generally set to be slightly greater than zero. FIG. 2 variation of bearing radial clearance 2.3 Selection criteria for Bearing clearance Theoretically, bearing life is maximized when there is a slightly negative operating clearance under safe operation conditions. But in practice, it is very difficult to maintain this optimum condition. Once certain service conditions change, the negative clearance will increase, resulting in a significant decline in bearing life or heating. Therefore, when the initial clearance is usually selected, the operating clearance is required to be only slightly greater than zero.

For bearings under normal conditions, the coordination of common loads will be adopted. When the speed and temperature are normal, the corresponding common clearance should be selected to obtain the appropriate operating clearance. Table 6 very ordinary clearance for example using conditions applicable occasion clearance under heavy load, impact load, interference with large amount of railway vehicle axle C3 vibrating screen C3 and C4 cannot afford the directional load, inside and outside the circle of C4 tractor adopt static with railway vehicle traction motor, reducer or C4 bearing inner ring heat paper machine, dryer C3 and C4 mill roller kun C3 to reduce rotational vibration and noise of micro-motor C2 clearance adjustment and control the vibration of the shaft NTN spindle (double row cylindrical roller bearing) C9NA, C0NA.