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Essentials of bearing installation, maintenance and disassembly

Bearing is an important part of contemporary machinery, and its quality is related to the operating condition of the entire equipment. This article introduces the installation, maintenance, disassembly and common problems of bearings. I hope it will be helpful to everyone's production.


Bearing installation

The installation of the bearing directly affects the accuracy, life and performance. Therefore, the design and assembly department must fully study the installation of the bearing and proceed in accordance with the following operating standards:

(1) Clean the bearing and its related parts;

(2) Check the size and finishing of related parts;

(3) Installation (just before opening the bearing package);

(4) Inspection after the bearing is installed;

(5) Supply lubricant.


General grease lubrication, do not clean, directly fill with grease. Lubricating oil is lubricated, and cleaning is not usually necessary. However, the bearings for instruments or high-speed applications should be washed with clean oil to remove the anti-rust agent coated on the bearings. Bearings with anti-rust agent removed are easy to rust, so they should not be left alone. In addition, bearings that have been packed with grease can be used directly without cleaning. The installation method of the bearing varies depending on the bearing structure, fit and other conditions. Generally speaking, because most of the shaft rotates, the inner ring needs an interference fit. Bearings with cylindrical bores are usually pressed in with a press or hot-fitting methods are often used. In the case of a tapered hole, install it directly on the tapered shaft or install it with a sleeve.


01. Installation of cylindrical bore bearings

(1) The method of pressing in with a press

Small bearings are widely used in press-fitting methods. Pad the spacer block into the inner ring, and press it statically with a press until the inner ring is in close contact with the shoulder of the shaft. Mounting the outer ring with a spacer block to install the inner ring is the cause of indentation and crushing on the raceway, so it is forbidden. During operation, you can apply oil to the mating surface in advance. When installing with a hammer as a last resort, put a block on the inner ring. This method is only limited to the case of small interference, and cannot be used for large interference, or medium and large bearings.


For non-separable bearings such as deep groove ball bearings, where the inner ring and outer ring need to be installed with interference, use a cushion block to pad, use a screw or oil pressure to press in the inner ring and the outer ring at the same time. The outer ring of self-aligning ball bearing is easy to tilt, even if it is not an interference fit, it should be installed with a pad.


For separable bearings such as cylindrical roller bearings and tapered roller bearings, the inner ring and outer ring can be installed on the shaft and housing respectively. When combining the installed inner ring and outer ring, the key is to be stable Ground the two together so that the center of the two does not deviate, and pressing in will cause the raceway surface to jam.


(2) Hot loading method

Large bearings require a lot of force to press in, so it is difficult to press in. Therefore, the hot fitting method of heating the bearing in oil to expand it and then installing it on the shaft is widely used. Using this method, the operation can be completed in a short time without adding improper force to the bearing. The heating temperature of the bearing is based on the bearing size and the required interference. The precautions for hot loading are as follows:


(a) Do not heat the bearing above 120C;

(b) In order to prevent the bearing from directly contacting the bottom of the oil tank, consider placing the bearing on a metal mesh table or hoisting the bearing;

(c) Heat the bearing to 20C-30C higher than the required temperature, so that the inner ring does not become cold during operation and it is difficult to install;

(d) After installation, the bearing cools down and shrinks in the width direction. Therefore, use a shaft nut or other suitable method to tighten it to prevent a gap between the inner ring and the bearing shoulder.


02. Installation of tapered bore bearings

For bearings with tapered bores, most of their inner rings are installed in an interference fit. The amount of interference is determined by the axial advancing distance of the inner ring on the conical shaft diameter, adapter sleeve or withdrawal sleeve.

Small and medium-sized bearings can use bearing installation tools or lock nuts to push the inner ring to the appropriate position on the conical shaft diameter. In the case of an adapter sleeve, use a sleeve nut that can be locked with a hook wrench or an impact wrench. For the withdrawal sleeve, a bearing installation tool or an end plate can be used to push it into the inner hole of the bearing.


Larger bearings require more force to install, so hydraulic nuts should be used. The hydraulic nut can install the tapered bore bearing on the tapered shaft diameter, the adapter sleeve, and the withdrawal sleeve.


03. Installation of the shell When installing the shell to the shell, there is generally a lot of clearance fit, and the outer ring has interference. It is usually pressed in by a press, or there is also a shrink fit method for installation after cooling. When dry ice is used as the coolant, the moisture in the air will condense on the surface of the bearing when the shrink fit is installed. Therefore, proper anti-rust measures are required


04. Operation check After the bearing is installed, in order to check whether the installation is correct, it is necessary to check the operation. The small machine can be rotated by hand to confirm whether the rotation is smooth. Check if there is any improper operation caused by foreign objects, scars, indentation, uneven rotation torque caused by poor installation, poor processing of the mounting seat, large torque caused by too small clearance, installation error, seal friction, etc. . If there is no abnormality, power operation can be started. Because large machinery cannot be rotated manually, immediately turn off the power after starting without load, perform inertial operation, check for vibration, sound, and whether there is contact with rotating parts, etc., and enter power operation after confirming that there is no abnormality.


Disassembly of the bearing

The disassembly must follow the basic rules, and different disassembly tools and disassembly methods must be used for different bearings. When the bearing and the shaft are in a tight fit, and the seat hole is in a loose fit, the bearing and the shaft can be removed from the housing together, and then the bearing can be removed from the shaft with a press or other removal tools.


Here are some common methods of bearing disassembly:


1. Disassembly of the outer ring

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 screw evenly on one side, and remove it at the same time. These screw holes are usually covered with blind plugs and separable bearings such as tapered roller bearings. Several cuts are provided on the housing shoulders. Use spacers to remove them with a press or gently tap them to remove them.


2. Disassembly of the inner ring

The inner ring can be pulled out with a press for disassembly. At this time, pay attention to let the inner ring bear its pulling force. Furthermore, no matter what kind of fixture, it must be firmly clamped to the side of the inner ring. For this reason, it is necessary to consider the size of the shoulder of the shaft, or study the processing of the upper groove at the shoulder in order to use the drawing fixture.


The oil pressure method is adopted for the inner ring disassembly of the large bearing. Oil pressure is applied through the oil hole provided in the bearing to make it easy to draw. For bearings with a large width, the hydraulic method and the drawing fixture are used together for disassembly operations.


Induction heating can be used to disassemble the inner ring of cylindrical roller bearings. It is a method to heat the part in a short time to expand the inner ring and then pull it out. Where a large number of these bearing inner rings need to be installed, induction heating is also used.


3. Unloading

Knock-off is a simple and common method of disassembly. It is a method to achieve the purpose of disassembly by using the power of hammering to displace the mating parts and separate them from each other. Commonly used tools for demolition are hand hammers, that is, ordinary fitter's hand hammers, punches and spacers.


When unloading, different methods and steps should be adopted according to different machine structure:


Sliding bearing bushings and rolling bearing jackets are interference fits in the holes. To remove them from the holes, the method of knocking and unloading is also commonly used. When unloading, the hammered end face of the bushing should be cushioned. When unloading a small-diameter bushing, it is better to use a stepped punch. The small diameter of the punch matches the inner hole of the bushing. The large diameter of the punch is about 0.5mm smaller than the outer diameter of the bushing.


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


The disassembly of ordinary small bearing caps often adopts the method of symmetrically driving in the oblique pads to open the bearing caps.


Precautions for bearing use


Bearings are precision parts, but no matter how high-performance bearings are used, if they are used improperly, the expected results will not be obtained. Precautions concerning the use of bearings are as follows:


1. Keep the bearing and its surrounding environment clean. Even if tiny dust that is invisible to the naked eye enters the bearing, it will increase the wear, vibration and noise of the bearing. Bearings and their surrounding accessories should be kept clean, especially dust and dirt. Tools and working environment must also be kept clean.


2. When using and installing, it is necessary to be careful not to force punching, to directly hit the bearing with a hammer, and not to transmit pressure through the rolling elements.


3. Use appropriate and accurate installation tools as much as possible to use special tools, and try to avoid the use of cloth and short fibers.


4. Prevent the rust of the bearing. When directly picking up the bearing by hand, wash away the sweat from your hands and apply high-quality mineral oil before proceeding. Pay special attention to rust prevention in the rainy season and summer.


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


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