Bearing mounting

15-3-1 Recommended preparation prior to mounting

1) Preparation of bearings

Wait until just before mounting before removing the bearings from their packaging to prevent contamination and rust.
Since the anti-corrosion oil covering bearings is a highly capable lubricant, the oil should not be cleaned off if the bearings are pre-lubricated, or when the bearings are used for normal operation. However, if the bearings are used in measuring instruments or at high rotation speed, the anti-corrosion oil should be removed using a clean detergent oil. After removal of the anti-corrosion oil, bearings should not be left for a long time because they rust easily.

2) Inspection of shafts and housings

Clean up the shaft and housing to check whether it has flaws or burrs as a result of machining.
Be very careful to completely remove lapping agents (SiC, Al2O3, etc.), casting sands, and chips from inside the housing.
Next, check that the dimensions, forms, and finish conditions of the shaft and the housing are accurate to those specified on the drawing.
The shaft diameter and housing bore diameter should be measured at the several points as shown in Figs. 15-1 and 15-2.

Fig. 15-1 Measuring points on shaft diameter

Fig. 15-2 Measuring points on housing bore diameter

Furthermore, fillet radius of shaft and housing, and the squareness of shoulders should be checked.

When using shaft and housing which have passed inspection, it is advisable to apply machine oil to each fitting surface just before mounting.

15-3-2 Bearing mounting

Mounting procedures depend on the type and fitting conditions of bearings.
For general bearings in which the shaft rotates, an interference fit is applied to inner rings, while a clearance fit is applied to outer rings.
For bearings in which the outer rings rotate, an interference fit is applied to the outer rings.
Interference fitting is roughly classified as shown here. The detailed mounting processes are described in Tables 15-1 to 15-3.
"Table 15-1 Press fit of bearings with cylindrical bores"
"Table 15-2 Shrink fit of cylindrical bore bearings"
"Table 15-3 Mounting bearings with tapered bores"
"Table 15-4 Mounting tapered bore spherical roller bearings"

ReferenceForce is necessary to press fit or remove bearings.

The force necessary to press fit or remove inner rings of bearings differs depending on the finish of shafts and how much interference the bearings allow.
The standard values can be obtained by using the following equations.

In equations (15-1) and (15-2),

Value of resistance coefficient ƒ_k

Table 15-1 Press fit of bearings with cylindrical bores

Mounting methods

Descriptions

(a) Using press fit (the most widely used method) (b) Using bolts and nuts (screw hole should be provided at the shaft end) (c) Using hammers (only when there is no alternative measure)

As shown in the Fig., a bearing should be mounted slowly with care, by using a fixture to apply force evenly to the bearing. When mounting the inner ring, apply pressure to the inner ring only. Similarly, in mounting the outer ring, press only the outer ring. If interference is required on both the inner and outer ring of non-separable bearings, use two kinds of fixtures as shown in the Fig. and apply force carefully, as rolling elements are easily damaged. Be sure never to use a hammer in such cases. Simultaneous press fit of inner ring and outer ring

Table 15-2 Shrink fit of cylindrical bore bearings

Shrink fit

Descriptions

(a) Heating in an oil bath (b) Induction heater

This method, which expands bearings by heating them in oil, has the advantage of not applying too much force to bearings and taking only a short time. [Notes] Oil temperature should not be higher than 100℃, because bearings heated at higher than 120℃ lose hardness. Heating temperature can be determined from the bore diameter of a bearing and the interference by referring to Fig. 15-3. Use nets or a lifting device to prevent the bearing from resting directly on the bottom of the oil container. Since bearings shrink in the radial direction as well as the axial direction while cooling down, fix the inner ring and shaft shoulder tightly with the shaft nut before shrinking, so that no space is left between them. Shrink fit proves to be clean and effective since, by this method,the ring can be provided with even heat in a short time using neitherfire nor oil. (When electricity is being conducted, the bearing itself generates heat by its electrical resistance, aided by the built-in exciting coil.)

Fig. 15-3 Heating temperature and expansion of inner rings

[Remarks]

1. Thick solid lines show the maximum interference value between bearings (class 0) and shafts (r6, p6, n6, m5, k5, j5) at normal temperature.
2. Therefore, the heating temperature should be selected to gain a larger "expansion of the bore diameter" than the maximum interference values.

(When fitting class 0 bearings having a 90mm bore diameter to m5 shafts, this figure shows that heating temperature should be 40℃ higher than room temperature to produce expansion larger than the maximum interference value of 48μm. However, taking cooling during mounting into consideration, the temperature should be set 20 to 30℃ higher than the temperature initially required.)

Table 15-3 Mounting bearings with tapered bores

Mounting methods

Descriptions

(a) Mounting on tapered shafts (b) Mounting by use of an adapter sleeve (c) Mounting by use of a withdrawal sleeve (d) Measuring clearances

When mounting bearings directly on tapered shafts, provide oil holes and grooves on the shaft and inject high pressure oil into the space between the fitting surfaces (oil injection). Such oil injection can reduce tightening torque of locknut by lessening friction between the fitting surfaces. When exact positioning is required in mounting a bearing on a shaft with no shoulder, use a clamp to help determine the position of the bearing. Locating bearing by use of a clamp When mounting bearings on shafts, locknuts are generally used. Special spanners are used to tighten them. Bearings can also be mounted using hydraulic nuts. When mounting tapered bore spherical roller bearings, the reduction in the radial internal clearance which gradually occurs during operation should be taken into consideration as well as the push-in depth described in Table 15-4. Clearance reduction can be measured by a thickness gage. First, stabilize the roller in the proper position and then insert the gage into the space between the rollers and the outer ring. Be careful that the clearance between both roller rows and the outer rings is roughly the same (e≒e'). Since the clearance may differ at different measuring points, take measurements at several positions. When mounting self-aligning ball bearings, leave enough clearance to allow easy aligning of the outer ring.

Table 15-4 Mounting tapered bore spherical roller bearings

[Remark]
The values for reduction of radial internal clearance listed above are values obtained when mounting bearings with CN clearance on solid shafts. In mounting bearings with C3 clearance, the maximum value listed above should be taken as the standard.