Tool for removing pressed-in bearings (12 4966)

A number of things can go wrong during a bearing change: damage to the shaft or bearing can occur due to improper handling or improper installation of the new bearing. Particularly on seized bearings, the question arises as to how to successfully remove the latter without damaging the surrounding components and the bearing itself. In this context, the appropriate tools are crucial for the successful disassembly and installation of pressed-in bearings. In this article, we present tools and methods to ensure that the next bearing change is guaranteed to succeed.

When to change bearings

Generally, bearings are removed if they have malfunctioned due to natural wear or excessive stress caused by high friction values/coefficients of friction, incorrect mounting or inadequate lubrication. Sometimes, bearings are also removed for routine maintenance and inspection and then reinstalled. Especially in these cases, it is important that the bearing is removed without problems and without damaging the bearing and adjacent components.

Bearing removal tools

Bearing pullers are specialized tools for precise and gentle removal of bearings. They are used for maintenance and replacement of damaged or worn bearings. Their design allows bearing pullers to distribute the force needed to uninstall the bearing evenly onto the shaft or components installed around the bearing to prevent misalignment. This purposeful and evenly aligned use of the tensile force allows the bearing to generally be dismantled in a controlled manner without damaging surrounding components or the bearing itself, provided the correct type of bearing puller is used.

Bearing puller types

Bearing pullers are principally differentiated into outer bearing pullers and inner bearing pullers. The outer bearing puller grabs and removes the bearing from the outside with two or three jaws. The jaws grip the bearing ring and extract it evenly to prevent damage. Inner bearing pullers pull the bearing out. Collets are introduced through the inner bearing ring. The bearing puller then spreads and the bearing can be pulled out. The pulling operation may also involve use of a slide hammer to generate the force necessary for pulling off, without stressing adjacent components. Bearing pullers are also available in a hydraulic version. A hydraulic cylinder is installed, which is controlled by a pump. The force required for pulling off the bearing is generated by the extending hydraulic cylinder. High pull-off forces can then be exerted with little physical effort. The blind hole puller is yet another form of inner bearing puller.   A blind hole is a bore that does not completely penetrate the material. The bearing is located in this blind hole. If it is not possible to reach through the bearing in the base hole, blind hole pullers are often clamped in the bearing inner ring by a cone. Blind hole pullers also generally work with a slide hammer or impact puller, which loosens and removes the bearing piece by piece. Other variants of bearing pullers include clamping pullers or impact pullers. There are also specialty pullers for sensitive bearings that use additional protective mechanisms to minimize damage.

When to use which bearing puller?

The type of bearing puller used depends on the size and design of the bearing in addition to the installation situation and accessibility of the bearing. Is the bearing installed on a shaft or in a housing? Is it easily accessible or is it concealed by other components? What tensile force is required? Is there a risk of misalignment? How and where can the puller be positioned?

Above all, it is also crucial whether and how easily the rear of the bearing is accessible. If this can be easily achieved, an external bearing puller (outer bearing puller) may be sufficient.

An inner bearing puller may be the best choice if the bearing is for example installed in a housing. The size of the bearing also influences the choice: hydraulic bearing pullers are the best choice for large bearings, for example. They also provide support when the bearing is already slightly rusted or is generally seated very firmly. It can also make sense to use triangular bearing pullers for larger bearings because they provide better support.

Auxiliary tools - Induction heaters

If a bearing is seated particularly tight, it may make sense to prepare the bearing before removing it. An induction heater is suited for this: They operate on the principle of electromagnetic induction. An electric coil generates a magnetic field into which the bearing is introduced. This results in eddy currents affecting the internal electrical resistance of the bearing. The bearing heats up evenly, quickly and without contact. The associated expansion of the bearing increases its inner diameter according to the thermal expansion coefficient of the material used, making it easier to extract the bearing from the shaft.

Properly changing bearings

A bearing is usually changed based on the following steps:

• Preparation: Lubricants, cleaning agents and spare parts must first be provided in addition to the bearing puller. The machine is switched off and disconnected from the power supply.
• Create access to the bearing: In the next step, all components that prevent access to the bearings must be removed. These can for example be protective caps or idlers in a motor. The area around the bearing change should be clean so that the new bearing is not contaminated.
• Position bearing puller: The bearing puller must be seated securely and firmly on the bearing. The correct position must be verified, e.g. the bearing puller must be seated on the inner ring to prevent damage.
• Remove bearing: Carefully remove the bearing while avoiding misalignment, if necessary with an auxiliary tool for bearing pullers, such as a slide hammer.
• Clean and check bearing seat: Remove all residue (grease, dirt) and check the bearing seat for damage.
• Prepare the new bearing: Most bearings are generally pre-lubricated (e.g. ball bearings). However, sometimes the bearing still needs to be lubricated before installation.
• Insert new bearing: Align the new bearing evenly while avoiding misalignment and press it into the bearing seat with a press-in tool. Any removed components must also be reinstalled.
• Check the new bearing: The proper fit and function should be checked as a final step. Does the bearing rotate without resistance? Do unusual noises occur when the machine is switched on?

Reasons why bearing changes fail (and what can be done about it)

There are various reasons why bearing changes fail, in the example here while using an external puller. The main cause is often that the bearing cannot be gripped on the inner ring and is thus pulled off on the outer ring. The inner cage breaks and the bearing is destroyed.

The wrong tool selection also has a significant influence on the success of the bearing change: An unsuitable bearing puller can slide off, thus damaging surrounding components, or the required force cannot be exerted to pull out the bearing. Always ask yourself the following questions before selecting the tool:

• Is an internal or external bearing installed?
• What type of bearing is it in general? For example, a clamping mechanism is installed on special ball bearing pullers in order to grip the inner ring securely and gently.
• How firmly is the bearing seated? A hydraulic puller or sliding hammer may be required for support.
• How much space is available for the bearing change? For example, a compact bearing puller should be used in confined spaces.
• Which gripping method minimizes the risk of damage? For example, an additional rubber guard is available when a two- or three-jaw gripper is used.