Specialized Tools Simplifies Bearing Works

The days of makeshift methods for mounting and dismounting bearings are gone. Today's specially designed mechanical and hydraulic bearing tools allow workers to remove bearings without damaging raceways and adjacent components and to mount bearings with precision. Successful bearing removal and mounting, in turn facilitates trouble-free operation.

Modern bearing tools range from impact rings to hook spanners, from bearing pullers to the hydraulic nut. Each tool is designed to be effective in a specific set of applications with particular bearing types and sizes.

Fitting tools and spanners

For cold-mounting small- and medium-sized bearings in bore sizes up 50 mm (about 2 in.), most experts recommend bearing-fitting tools. Fitting tool kits usually contain everything necessary for mounting a bearing. A typical kit includes a dead-blow hammer and several high-strength sleeves. It also includes a selection of impact rings that correspond closely in size to the bore and outside diameter (OD) of commonly used bearings. Then, for example, your technician would use a fitting tool ring with a 25 mm bore and 52 mm OD to install a bearing with those same dimensions. Ideally, for long service life, the rings are made of a durable material, such as acetal resin.

To mount bearings with rings designed for interference fits, fitting tools apply force via a sleeve-and-ring combination directly through the bearing ring. In most cases, the inner ring provides the interference fit. A fitting tool allows the user to distribute the mounting force around the bearing ring and against the central axis of the shaft. Doing so prevents damage to the bearing rings and rolling elements.

Technicians can mount small tapered-bore bearings on a tapered shaft using a lock nut and hook spanner. The spanner is a wrench that fits into slots on a lock nut. Hammer blows to the spanner’s handle transmit torque to the nut, driving the bearing onto the shaft. The spanner is preferable to using a drift or chisel to advance the lock nut because these methods can damage the lock nut and contaminate the bearing with debris.

Medium-sized tapered-bore bearings require greater mounting force. Typically, the best tool for this job is an impact spanner. This tool has a large cast-iron head, which provides an easy striking area for a sledgehammer. By hitting the striking area, a technician generates the required mounting force. Each impact spanner fits a range of lock nut sizes.

The hydraulic nut

The larger the bearing the more difficult it is for a technician to mount it using impact force. To do the job properly, it might take several hours and the attention of two or more technicians. In these cases, using a hydraulic nut with an oil pump considerably reduces the time and effort involved. This method is ideally suited for mounting tapered-bore bearings on an adapter sleeve or directly onto a tapered journal.

The hydraulic nut threads onto the shaft, replacing the lock nut for purposes of installation. The hydraulic nut consists of a steel ring with a groove in one side face and an annular piston that sits in the groove. When oil is pumped into the nut, the piston is pushed out with a force sufficient to mount a large bearing.

A hand pump supplies oil to the nut. Do not use an electric pump. An electric pump may generate excessive pressure and quickly overdrive the bearing.

Mechanical pullers

Although tools designed specifically for bearing removal are readily available, an unfortunately large number of technicians continue to employ outdated methods. These include knocking a bearing off with a hammer, heating it with a torch or cutting it off with a grinder. These methods can have damaging results. For one thing, they make the bearing unsuitable for reconditioning and reuse. But even in situations where the bearing is not targeted for reconditioning, other harmful effects make these practices unacceptable. Temperature-sensitive components can be weakened, for example, by a torch’s heat. Also, pounding and cutting can damage the shaft, housing, end covers, seal rings and spacers.

Mechanical pullers reduce the labor involved in dismount bearings. At the same time, they lessen the risk of damage to important components. Pullers generally consist of two or three gripping arms positioned around a central spindle. When the spindle is turned, the arms retract, engaging and withdrawing the bearing. There are a variety of different pullers designed for different bearing arrangements.

Jaw pullers have grip widths ranging from several inches to more than a foot across. They are intended for removing small- to medium-sized bearings. Jaw pullers work by grasping and pulling through the bearing’s outer ring. A recent innovation incorporates a hydraulic cylinder in a jaw puller’s spindle. There is no need for a hand pump; simply tightening the spindle initiates the hydraulic action.

By contrast, strong back pullers apply force to a bearing’s inner ring. Two plates bolt together immediately behind the bearing. Then, as the spindle is tightened against the end face of the shaft, force is applied from behind the bearing against the inner ring.

A specially designed internal puller will extract deep-groove ball bearings in cases where the bearing’s back or outer ring is not accessible. Puller arms, inserted between the bearing’s inner and outer rings, grasp onto the outer ring raceway from the inside. This tool is useful in applications with tight clearances.

Oil Injection

Oil injection is the most effective method of dismounting bearings. Use the technique to remove either straight bore or tapered-bore bearings. Of all dismounting techniques, oil injection poses the lease risk of bearing damage. In addition, it is the preferred method if you want to recondition the bearing.

Oil injection requires modifications to the shaft before installation of the bearing. You must drill and oil duct through the shaft and machine an oil distribution groove about one third of the bearing’s width from the end of the seating. During removal, inject oil under pressure though the duct into the distribution groove. The oil creates a film that reduces the friction of the interference fit and separates the bearing from the shaft.

Bearing installation and removal tools reduce the time and labor involved in handling bearings on site. They make the technicians’ job safer and easier to protect a company’s long-term investments in components and machinery.