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Mounting bearings with a tapered bore

Performance and operating conditionsBearing type and arrangementBearing sizeLubricationOperating temperature and speedBearing interfacesBearing executionSealing, mounting and dismounting

For bearings with a tapered bore, inner rings are always mounted with an interference fit. The degree of interference is determined by how far the bearing is driven up onto a tapered shaft seat or an adapter or withdrawal sleeve. As the bearing is driven up the tapered seat, its radial internal clearance is reduced. This reduction in clearance, or the axial drive-up distance, can be measured to determine the degree of interference and the proper fit. Recommended values of clearance reduction and axial drive-up are listed in the relevant product section.
The SKF Drive-up Method is a reliable and well-proven method for mounting SKF bearings on tapered seats. For additional information refer to the SKF Drive-up Method Program.

Small and medium-size bearings
Bearings with bore diameters up to 80 mm (d ≤ 80 mm), can be driven up onto a tapered seat using either a bearing fitting tool or, preferably, a lock nut. For adapter sleeves, use the sleeve nut that can be tightened with a hook or impact spanner. Withdrawal sleeves can be driven into the bearing bore using a bearing fitting tool or a nut. Starting from a 50 mm thread, SKF hydraulic nuts can also be used.

Medium-sized and large bearings
Larger bearings, with bore diameters greater than 80 mm (d > 80 mm), require considerably more force to mount, therefore, SKF hydraulic nuts should be used. Where applicable, SKF also recommends using shafts and sleeves with grooves and ducts for the oil injection method. When combining the two methods, bearing mounting and dismounting becomes much faster, easier and safer. For additional information about the oil injection equipment required for both the hydraulic nut and the oil injection method, refer to Maintenance products and skf.com/mount.

Mounting with SKF hydraulic nuts

Bearings with a tapered bore can be mounted with the aid of an SKF hydraulic nut:
  • on a tapered shaft seat (fig. 1)
  • on an adapter sleeve (fig. 2)
  • on a withdrawal sleeve (fig. 3)
The hydraulic nut can be positioned onto a threaded section of the shaft (fig. 1), or onto the thread of a sleeve (fig. 2 and fig. 3). The annular piston abuts the inner ring of the bearing (fig. 1 and fig. 2) or a stop on the shaft, which can be either a nut on a shaft thread (fig. 3) or a plate attached to the end of the shaft. Pumping oil into the hydraulic nut displaces the piston axially with the force needed to drive the inner ring up the taper for accurate and safe mounting.

Oil injection method

With the oil injection method, oil under high pressure is injected via ducts and distribution grooves between the bearing and bearing seat to form an oil film. This oil film separates the mating surfaces and considerably reduces the friction between them. This method is typically used when mounting bearings directly on tapered shaft seats (fig. 4). The necessary ducts and grooves should be an integral part of the shaft design. This method can also be used to mount bearings on adapter or withdrawal sleeves if they are equipped with the relevant features, ducts and grooves.

A spherical roller bearing mounted on a withdrawal sleeve with oil ducts is shown in fig. 5. Oil is injected between all mating surfaces so that the withdrawal sleeve can be pressed into the bearing bore as the bolts are tightened.

Verifying the interference fit
During mounting, the degree of interference is normally determined by one of the following methods:
  • measuring the clearance reduction
  • measuring the lock nut tightening angle
  • measuring the axial drive-up
  • measuring the inner ring expansion
For self-aligning ball bearings, feeling the clearance reduction by swiveling the outer ring is an additional method (→ Mounting).

Measuring the clearance reduction

A feeler gauge is most often used to measure the radial internal clearance in medium-sized and large spherical and CARB toroidal roller bearings. Recommended values for the reduction of radial internal clearance to obtain the correct interference fit are listed in the relevant product section.

Before mounting, measure the clearance between the outer ring and upper-most roller (fig. 6). During mounting, measure the clearance between the inner or outer ring and lowest roller, depending on the bearing internal design (fig. 7).

Before measuring, rotate the inner or outer ring a few times. Both bearing rings and the roller complement must be centrically arranged relative to each other.

For larger bearings, especially those with a thin-walled outer ring, the measurements are affected by the elastic deformation of the rings, caused by the weight of the bearing or the force to draw the feeler gauge blade through the gap between the raceway and an unloaded roller. To establish the “true” clearance before and after mounting, use the following procedure (fig. 8):
  1. Measure the clearance “c” at the 12 o’clock position for a standing bearing or at the 6 o’clock position for an unmounted bearing hanging from the shaft.
  2. Measure the clearance “a” at the 9 o’clock position and “b” at the 3 o’clock position without moving the bearing.
  3. Obtain the “true” radial internal clearance with relatively good accuracy from 0,5 (a + b + c).

Measuring the lock nut tightening angle

This method can be used when mounting bearings with a bore diameter d ≤ 120 mm. Recommended values for the tightening angle α are listed in the relevant product section.

Before starting the final tightening procedure, push the bearing up onto the tapered seat until it is firmly in position. By tightening the nut through the recommended angle α (fig. 9), the bearing is driven up over the proper distance on the tapered seat. The bearing inner ring then has the requisite interference fit. The residual clearance should be checked if possible.

Measuring the axial drive-up

Bearings with a tapered bore can be mounted by measuring the axial drive-up of the inner ring on its seat. Recommended values for the required axial drive-up are listed in the relevant product section.

However, the SKF Drive-up Method is recommended for medium-sized and large bearings. This method provides a reliable and easy way to determine the degree of interference. The correct fit is achieved by controlling the axial displacement of the bearing from a pre-determined position. The equipment for the SKF Drive-up Method is shown in fig. 10. It includes an SKF hydraulic nut (1) fitted with a dial indicator (2), and a hydraulic pump (3) fitted with a pressure gauge (4).

The SKF Drive-up Method is based on a two-step mounting procedure (fig. 11):
  • Step 1
    Push the bearing to its starting position by applying the prescribed pressure to the hydraulic nut.
  • Step 2
    Increase the pressure on the hydraulic nut so the bearing inner ring is pushed further on its tapered seat to its final position. The prescribed displacement is measured by the dial indicator.
Recommended values for the requisite oil pressure to reach the start position and the axial displacement to reach the final position for individual bearings are available from the SKF Drive-up Method Program.

Measuring the inner ring expansion

Measuring the inner ring expansion is a quick and accurate method for determining the correct position of large spherical and CARB toroidal roller bearings on their seats (d ≥ 340 mm, depending on the series). To apply this method, use common hydraulic mounting tools and a SensorMount, which consists of a bearing with a sensor embedded in the inner ring and a dedicated hand-held indicator (fig. 12). Aspects like bearing size, shaft material and design (solid or hollow), and surface finish do not need any special consideration.

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