Bearings are an important component in contemporary machinery, and their quality is related to the operation of the entire equipment. This article introduces the installation, maintenance, disassembly and common problems of bearings. I hope it will be helpful to everyone.
Bearing installation
The installation of bearings directly affects the accuracy, life and performance. Therefore, the design and assembly department must fully study the installation of bearings and proceed according to the following operating standards:
(1) Clean the bearings and bearing related parts;
(2) Check the size and finishing of related components;
(3) Installation (open the bearing package before installation);
(4) Inspection after installing the bearing;
(5) Supply lubricant.
General grease lubrication, no cleaning, directly filled with grease. Lubricating oil lubrication generally does not need to be cleaned. However, bearings for instruments or high speeds must be washed with clean oil to remove the anti-rust agent coated on the bearings. Bearings with the anti-rust agent removed are prone to rust, so they cannot be left alone. Furthermore, bearings that have been filled with grease can be used directly without cleaning. The installation method of bearings varies depending on the bearing structure, fit and other conditions. Generally speaking, since most of the shafts rotate, the inner ring requires an interference fit. Cylindrical bore bearings are usually pressed in with a press or hot-fitted. 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) Press in with a press
The pressing method of press is widely used for small bearings. Insert the pad into the inner ring and use a press to press it quietly until the inner ring is in close contact with the shaft shoulder. Installing the inner ring with spacers on the outer ring will cause indentations and bruises on the raceway, so it is absolutely prohibited. During operation, you can apply oil on the mating surface in advance. If it is absolutely necessary to use a hammer for installation, a spacer should be placed on the inner ring. This approach is limited to situations where the interference is small, and cannot be used for bearings with large interference, or medium or large bearings.
For non-separable bearings such as deep groove ball bearings, when both the inner and outer rings need to be installed with interference, use spacers to pad them, and use screws or oil pressure to press in the inner and outer rings at the same time. The outer ring of the self-aligning ball bearing is easy to tilt. 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 ring and outer ring can be installed on the shaft and housing respectively. When combining the separately installed inner and outer rings, the key is to stabilize them Close the two so that the centers of the two do not deviate. Forcibly pressing in will cause jamming of the raceway surface.
(2) Hot loading method
Large bearings require a lot of force when pressed in, so they are difficult to press in. Therefore, the hot-fitting method of heating the bearing in oil to expand it and then mounting it on the shaft is widely used. Using this method, the job can be completed in a short time without adding undue force to the bearing. The heating temperature of the bearing is based on the bearing size and required interference amount. Precautions related to hot loading operations are as follows:
(a) Bearings must not be heated above 120°C;
(b) In order to prevent the bearing from directly contacting the bottom of the oil tank, you can consider placing the bearing on a metal mesh table or lifting the bearing;
(c) Heat the bearing to a temperature 20°C to 30°C higher than the required temperature so that the inner ring does not become cold during operation, making installation difficult;
(d) After installation, the bearing cools down and shrinks in the width direction, so it is necessary to use a shaft nut or other appropriate method to tighten it to prevent a gap between the inner ring and the bearing shoulder.
02. Installation of tapered bore bearings
Most of the inner rings of bearings with tapered holes are installed with an interference fit. The amount of interference is determined by the axial advancement distance of the inner ring on the conical shaft diameter, adapter sleeve or withdrawal sleeve.
For small and medium-sized bearings, you can use bearing installation tools or locking nuts to push the inner ring into the appropriate position on the conical shaft diameter. When using an adapter sleeve, use a socket nut that can be tightened with a hook or impact wrench. Use the bearing installation tool or the end plate to push the withdrawal sleeve into the bearing inner hole.
Larger bearings require greater force to install, so hydraulic nuts should be used. Hydraulic nuts can install tapered bore bearings on conical shaft diameters, adapter sleeves and withdrawal sleeves.
When installing the shell, there is generally a lot of clearance fit and there is interference in the outer ring. It is usually pressed in with a press, or there is also a shrink fit method of installing after cooling. When dry ice is used as the coolant and shrink fit is installed, moisture in the air will condense on the surface of the bearing. Therefore, appropriate rust prevention measures are required.
Operation inspection After the bearing installation is completed, in order to check whether the installation is correct, an operation inspection is required. Small machines can be rotated by hand to confirm whether the rotation is smooth. Check whether there are any irregularities in operation caused by foreign matter, scars and indentations, uneven rotational torque caused by poor installation and poor machining of the mounting base, large torque caused by too small clearance, installation errors, sealing friction, etc. . If there is no abnormality, the power operation can be started. Since large machinery cannot be rotated manually, the power should be turned off immediately after starting without load, and the machine should perform inertial operation. Check whether there is any vibration, sound, and contact between rotating parts. After confirming that there are no abnormalities, enter power operation.
Bearing disassembly
Disassembly must follow basic rules, and different disassembly tools and methods must be used for different bearings. When the bearing has a tight fit with the shaft but a loose fit with the seat hole, the bearing and shaft can be removed from the housing together, and then the bearing can be removed from the shaft with a press or other disassembly tools.
Here are some common bearing disassembly methods:
1. Disassembly of the outer ring
To disassemble the interference-fit outer ring, set several screws for extruding the outer ring screw on the circumference of the casing in advance, and tighten the screws evenly while disassembling. These screw holes are usually covered with blind plugs, separable bearings such as tapered roller bearings, and several notches are set on the housing shoulders. Use spacers to disassemble them with a press or tap them lightly.
2. Disassembly of the inner ring
The inner ring can be removed using a press. At this time, attention should be paid to allowing the inner ring to withstand its pulling force. Furthermore, no matter what kind of clamp, it must be firmly stuck on the side of the inner ring. For this reason, 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 a drawing fixture.
The inner ring of large bearings is disassembled using the oil pressure method. Oil pressure is applied through the oil hole provided in the bearing to make it easy to pull out. For large-width bearings, the hydraulic method and the drawing fixture are used together for disassembly.
Induction heating can be used to disassemble the inner ring of cylindrical roller bearings. This is a method of heating a local area in a short period of time to expand the inner ring and then drawing it. Induction heating is also used where a large number of such bearing inner rings need to be installed.
3. Dismantle
Knocking off is a simple and common disassembly method. It is a method that uses the power of hammering to displace the matching parts and separate them from each other to achieve the purpose of disassembly. The commonly used tools for demolition are hand hammers, namely ordinary fitter's hand hammers, punches and spacers.
When disassembling, different methods and steps should be adopted according to different machine parts structures:
Both the sliding bearing bushing and the rolling bearing outer sleeve have an interference fit in the hole. To remove them from the hole, the method of disassembly is also commonly used. When dismantling, the hammered end face of the bushing should be padded with pads. When removing a bushing with a small diameter, it is better to use a step punch. The small diameter of the punch just matches the inner hole of the bushing, and 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.
When disassembling ordinary small bearing caps, the method of symmetrically driving in inclined pads is often used to open the bearing caps.
Precautions for using bearings
Bearings are precision components, but no matter how high-performance the bearings are, if used improperly, the expected results will not be achieved. Precautions regarding the use of bearings are as follows:
1. Keep the bearing and its surrounding environment clean. Even if tiny dust invisible to the naked eye enters the bearing, it will increase the wear, vibration and noise of the bearing. Bearings and surrounding accessories should be kept clean, especially dust and dirt. Tools and working environment must also be kept clean.
2. Be careful when using and installing. Strong stamping is not allowed, direct knocking of the bearing is not allowed, and pressure is not allowed to be transmitted through rolling elements.
3. Use appropriate and accurate installation tools, try to use special tools, and avoid using things like cloth and short fibers.
4. To prevent bearing corrosion, avoid taking the bearing directly with your hands. Wash off the sweat on your hands and apply high-quality mineral oil before operation. Pay special attention to rust prevention during the rainy season and summer.
However, under certain special operating conditions, bearings can obtain a longer life than conventional calculations, especially under light loads. These special operating conditions are when the rolling surfaces (rails and rolling elements) are effectively separated by a lubricating oil film and limit possible surface damage caused by contaminants. In fact, under ideal conditions, so-called permanent bearing life is possible.
Common problems and countermeasures in the use of bearings
Strong metallic sound
1. Abnormal load: Choose appropriate assembly clearance and preload;
2. Poor assembly: Improve shaft processing accuracy and improve installation methods;
3. Insufficient lubricant: replenish or use appropriate lubricant.
regular tone
1. Foreign matter causes channel corrosion, indentations and scars: Clean related parts and use clean grease;
2. Channel peeling: fatigue wear, replace the bearing.
Irregular sounds
1. Foreign matter intrusion: Clean related parts and use clean grease;
2. The clearance is too large: pay attention to coordination and choose the appropriate clearance;
3. Steel ball scars: The steel ball is peeled off due to fatigue or damaged by foreign matter. Replace the bearing.
Abnormal temperature rise
1. Too much lubricant: reduce lubricant;
2. The lubricant is insufficient or unsuitable: add more lubricant or choose a suitable lubricant;
3. The mating surface creeps or the sealing device is too large: the bearing outer diameter or inner diameter mating surface is corrected, and the sealing form is changed.
The rotational vibration of the shaft is large
1. Peeling: fatigue peeling, replace the bearing;
2. Poor assembly: Improve the machining accuracy of the shaft and improve the installation method;
3. Foreign matter intrusion: Clean related parts and use clean grease.
Large discoloration due to lubricant leakage
1. Too much lubricant: reduce lubricant;
2. Foreign matter invasion: Clean related parts.
