Mounting of Bearings with Cylindrical Bores
In the case of separable bearings, such as cylindrical roller bearings and tapered roller bearings, the inner and outer rings may be mounted separately. Assembly of the inner and outer rings, which were previously mounted separately, should be done carefully to align the inner and outer rings correctly. Careless or forced assembly may cause scratches on the rolling contact surfaces.
The expansion of the inner ring for various temperature differences and bearing sizes is shown in Fig. 3.
The precautions to follow when making shrink fits are as follows:
(a) Do not heat bearings to more than 120℃.
(b) Put the bearings on a wire net or suspend them in an oil tank in order to prevent them from touching the tank's bottom directly.
(c) Heat the bearings to a temperature 20℃ to 30℃ higher than the lowest temperature required for mounting without interference since the inner ring will cool a little during mounting.
(d) After mounting, the bearings will shrink in the axial direction as well as the radial direction while cooling. Therefore, press the bearing firmly against the shaft shoulder using locating methods to avoid a clearance between the bearing and shoulder.
NSK Bearing Induction Heaters
Besides heating in oil, NSK Bearing Heaters, which use electromagnetic induction to heat bearings, are widely used.
In NSK Bearing Heaters, electricity (AC) in a coil produces a magnetic field that induces a current inside the bearing that generates heat. Consequently, without using flames or oil uniform heating in a short time is possible, making bearing shrink fitting efficient and clean.
In the case of relatively frequent mounting and dismounting such as cylindrical roller bearings for roll necks of rolling mills and for railway journal boxes, induction heating should be used for mounting and dismounting inner rings.
Mounting of Bearings with Tapered Bores
Bearings with tapered bores are mounted on tapered shafts directly or on cylindrical shafts with adapters or withdrawal sleeves (Figs. 4 and 5). Large spherical roller bearings are often mounted using hydraulic pressure. Fig. 6 shows a bearing mounting utilizing a sleeve and hydraulic nut. Fig. 7 shows another mounting method. Holes are drilled in the sleeve which are used to feed oil under pressure to the bearing seat. As the bearing expands radially, the sleeve is inserted axially with adjusting bolts.
Spherical roller bearings should be mounted while checking their radial-clearance reduction and referring to the push-in amounts listed in Table 1. The radial clearance must be measured using clearance gauges. In this measurement, as shown in Fig. 8, the clearance for both rows of rollers must be measured simultaneously, and these two values should be kept roughly the same by adjusting the relative position of the outer and inner rings.
When a large bearing is mounted on a shaft, the outer ring may be deformed into an oval shape by its own weight. If the clearance is measured at the lowest part of the deformed bearing, the measured value may be bigger than the true value. If an incorrect radial internal clearance is obtained in this manner and the values in Table 1 are used, then the interference fit may become too tight and the true residual clearance may become too small. In this case, as shown in Fig. 9, one half of the total clearance at points and b (which are on a horizontal line passing through the bearing center) and c (which is at the lowest position of the bearing) may be used as the residual clearance.
When a self-aligning ball bearing is mounted on a shaft with an adapter, be sure that the residual clearance does not become too small. Sufficient clearance for easy alignment of the outer ring must be allowed.
Table 1 - Mounting of Spherical Roller Bearings with Tapered Bores
The values for reduction in radial internal clearance are for bearings with CN clearance.
For bearing with C3 Clearance,the maximum values listed should be used for the reduction in radial internal clearance.