Installation of bearings

The installation of bearings directly affects their accuracy, lifespan and performance. Therefore, the design and assembly departments should conduct thorough research on the installation of bearings and follow the following operation standards:

(1) Clean the bearings and related parts of the bearings;

(2) Check the dimensions and finishing conditions of the related components;

(3) Installation (Just before installation, open the bearing packaging);

(4) Inspection after the bearings are installed;

(5) Supply lubricants.

General grease lubrication is used. No cleaning is required. Just fill the grease directly. Lubricating oil lubrication usually does not require cleaning. However, for bearings used in instruments or at high speeds, etc., they should be washed clean with clean oil to remove the anti-rust agent applied to the bearings. Bearings without rust inhibitors are prone to rust, so they cannot be left unattended. Furthermore, bearings that have been sealed with grease can be used directly without cleaning. The installation methods of bearings vary depending on their structure, fit and other conditions. Generally speaking, since it is mostly shaft rotation, the inner ring needs an interference fit. Cylindrical bore bearings are mostly pressed in by a press or installed by hot mounting methods. In the case of conical holes, it can be directly installed on the conical shaft or installed with a sleeve.

01. Installation of cylindrical bore bearings

(1) The method of pressing in with a press

Small bearings are widely pressed in by a press. Insert the spacer into the inner ring and press it quietly with a press until the inner ring is in close contact with the shaft shoulder. Placing spacers on the outer ring to install the inner ring is the cause of indentations and injuries on the raceway, so it must be absolutely prohibited. When operating, oil can be applied to the mating surfaces in advance. In cases where it is absolutely necessary to strike the installation with a hammer, spacers should be placed on the inner ring for the operation. This approach is only applicable in cases where the interference fit is small and cannot be used for bearings with a large interference fit or medium and large-sized ones.

For non-separable bearings such as deep groove ball bearings, in cases where both the inner and outer rings need to be installed with interference fit, spacers should be placed on them, and both the inner and outer rings should be pressed in simultaneously with a screw or hydraulic pressure. The outer ring of a self-aligning ball bearing is prone to tilting. Even if it is not an interference fit, it is best to install it with spacers.

For separable bearings such as cylindrical roller bearings and tapered roller bearings, the inner and outer rings can be respectively installed on the shaft and the housing. When combining the separately installed inner and outer rings, the key is to firmly close them so that the centers of the two do not deviate. Forcing them in will cause the raceway surface to be scratched.

(2) The method of hot mounting

Large bearings require a great deal of force when being pressed in, so it is very difficult to press them in. Therefore, the hot mounting method, which involves heating the bearing in oil to expand it and then installing it onto the shaft, is widely used. By using this method, no improper force can be applied to the bearing and the operation can be completed in a short time. The heating temperature of the bearing shall be based on the size of the bearing and the required interference fit. The relevant precautions for hot mounting operations are as follows:

(a) The bearing must not be heated above 120℃.

(b) To prevent the bearing from directly contacting the bottom of the oil tank, it can be considered to place the bearing on a metal mesh platform or lift it up.

(c) Heat the bearing to 20℃-30℃ higher than the required temperature to prevent the inner ring from getting cold during operation and becoming difficult to install.

(d) After installation, the bearing cools down and contracts in the width direction. Therefore, a shaft nut or other appropriate method should be used to tighten it to prevent a gap from forming between the inner ring and the bearing shoulder.

Disassembly of the bearing

Disassembly must follow the basic rules, and different disassembly tools and methods should be adopted for different bearings. When the bearing is in a tight fit with the shaft and in a relatively loose fit with the seat hole, the bearing and the shaft can be removed from the housing together, and then the bearing can be taken off the shaft with a press or other disassembly tools.

Here are several common methods for disassembling bearings for you:

1. Disassembly of the outer ring

To disassemble the outer ring of the interference fit, set several screws for the outer ring extrusion screw on the circumference of the housing in advance. Tighten the screws evenly while disassembling. These screw holes are usually covered with blind plugs. For separable bearings such as tapered roller bearings, several notches are set on the shoulder of the housing. They can be disassembled using spacers and a press or by gently tapping.

2. Disassembly of the inner ring

The inner ring can be removed by pulling it out with a press. At this point, it is important to ensure that the inner ring bears its pulling force. Furthermore, no matter what kind of fixture it is, it must be firmly clamped on the inner side of the ring. For this purpose, it is necessary to consider the size of the shaft shoulder or study the processing of an upper groove at the shoulder to facilitate the use of the drawing fixture.

The inner ring of large bearings is disassembled by hydraulic method. By applying oil pressure through the oil holes set in the bearing, it is made easy to draw. For wider bearings, the hydraulic method and the drawing fixture are used in combination for disassembly operations.

The inner ring of cylindrical roller bearings can be disassembled by induction heating. The method of heating a local area in a short time to make the inner ring expand and then pulling it out. Induction heating is also used in situations where a large number of such inner rings of bearings need to be installed.

3. Dismount

Disassembly is a simple and common method. It is a method that uses the force of hammering to cause the parts that fit together to shift and detach from each other, thereby achieving the purpose of disassembly. The commonly used tools for disassembly are hand hammers, that is, ordinary fitters' hand hammers, punches and spacers.

When unloading, different methods and steps should be adopted according to the different structures of the machine parts:

Both the bushings of sliding bearings and the outer sleeves of rolling bearings have interference fits in the holes. To remove them from the holes, the common method is to strike them off. When disassembling, the end face of the bushing that is hammered should be padded with spacers. When unloading small-diameter bushings, it is better to use a stepped punch. The small diameter of the punch exactly matches the inner hole of the bushing, and the large diameter of the punch is approximately 0.5mm smaller than the outer diameter of the bushing.

For the disassembly of large-diameter bushings and rolling bearings, bushings are mostly used.

The disassembly of a common small bearing cover is often carried out by symmetrically driving in inclined shims to open the bearing cover.

Precautions for bearing use

Bearings are precision components. However, no matter how high-performance the bearings are, if they are not used properly, the expected effect will not be achieved. The precautions for the use of bearings are as follows:

1. Keep the bearings and their surrounding environment clean. Even tiny dust invisible to the naked eye entering the bearings will increase their wear, vibration and noise. Bearings and their surrounding accessories should be kept clean, especially dust and dirt. Tools and the working environment must also be kept clean.

2. When using and installing, be careful and meticulous. Do not use strong stamping, do not directly strike the bearing with a hammer, and do not transmit pressure through the rolling elements.

3. Use appropriate and accurate installation tools. Try to use dedicated tools and avoid using materials like cloth and short fibers as much as possible.

4. To prevent rusting of bearings, when handling bearings directly by hand, thoroughly wash off the sweat on your hands and apply high-quality mineral oil before operation. Special attention should be paid to rust prevention during the rainy season and summer.

However, under certain special operating conditions, bearings can achieve a longer lifespan than traditionally calculated, especially under light loads. These special operating conditions are that when the rolling surfaces (tracks and rolling elements) are effectively separated by a lubricating oil film and the surface damage that may be caused by contaminants is restricted. In fact, under ideal conditions, the so-called permanent bearing life is possible.

Common Problems and Countermeasures in Bearing Use

Strong metallic sound

1. Abnormal load: Select the appropriate assembly clearance and preload

2. Poor assembly: Enhance the machining accuracy of the shaft and improve the installation method

3. Insufficient lubricant: Replenish or use appropriate lubricant

Regular sound

1. Rust, indentations and scratches on the channel caused by foreign objects: Clean the relevant parts and use clean grease

2. Raceway spalling: Fatigue wear, replace the bearing

Irregular abnormal sound

1. Foreign object intrusion: Clean the relevant parts and use clean grease

2. Excessive clearance: Pay attention to the fit and select the appropriate clearance

3. Steel ball scratches: If the steel balls peel off due to fatigue or are jammed by foreign objects, replace the bearing

Abnormal temperature rise

1. Excessive lubricant: Reduce the lubricant

2. Insufficient or unsuitable lubricant: Increase the lubricant or select an appropriate one

3. Creep at the mating surface or excessive sealing device: Correct the mating surface of the outer or inner diameter of the bearing and change the sealing form

The rotational vibration of the shaft is large

1. Spalling: Fatigue spalling, replace the bearing

2. Poor assembly: Enhance the machining accuracy of the shaft and improve the installation method

3. Foreign object intrusion: Clean the relevant parts and use clean grease

Lubricant leakage causes significant discoloration

1. Excessive lubricant: Reduce the lubricant

2. Foreign object intrusion: Clean the relevant parts