Bearings generally consist of inner rings, outer rings, rolling elements and cages. For sealed bearings, add lubricant and seals (or shields). This is what a bearing is all about.
According to the working conditions of the bearings, different types of bearings are selected to better play the function of the bearings and prolong the service life of the bearings. We choose bearings to consider the following factors:
1. Radial load 2. Axial load 3. Speed requirements 4. Radial runout
5. Axial runout 6. Working temperature 7. Noise requirement 8. Lubrication condition
Bearing Code
The bearing model generally has a pre-code, a basic code and a post-code. In general, the bearing model is only indicated by the basic model. The basic model generally consists of three parts, type code, size code and inner diameter code. The post code is to use letters and numbers to indicate the structure, tolerance and special requirements of materials of the bearing. The prefix code is used to indicate the sub-components of the bearing, which are represented by letters.
The general bearing (rolling bearing) code method is divided into: pre-code, basic code and post-code.
Basic code
The basic code is used to indicate the inner diameter, diameter series, width series and type of the bearing, generally up to five digits, firstly described as follows:
1) The inner diameter of the bearing is represented by the first digit from the right of the basic code. The inner diameter of bearings with commonly used inner diameter d=20~480mm is generally a multiple of 5. These two digits represent the quotient of the bearing inner diameter size divided by 5, such as 04 means d=20mm; 12 means d=60mm and so on. For bearings with inner diameters of 10mm, 12mm, 15mm and 17mm, the inner diameter codes are 00, 01, 02 and 03 in turn. For bearings with an inner diameter of less than 10mm and greater than 500mm, there are other regulations on the expression method of the inner diameter, see GB/T272-93.
2) The diameter series of the bearing (that is, the series of changes in the outer diameter and width of bearings with the same structure and the same inner diameter) is represented by the third digit from the right of the basic code. For example, for radial bearings and radial thrust bearings, 0 and 1 represent extra light series; 2 represent light series; 3 represent medium series; 4 represent heavy series. The size comparison between each series is shown in the figure below. Thrust bearings are the same as radial bearings, except that 1 is used to indicate the ultra-light series.
3) The width series of bearings (that is, the change series of bearing widths with the same structure, inner diameter and diameter series) are represented by the fourth digit from the right of the basic code. When the comparison of the diameter series in Figure 13-4 of the width series is 0 series (normal series), the width series code O may not be marked in the code for most bearings, but for spherical roller bearings and tapered roller bearings, the width series Code 0 shall be marked. The diameter series code and the width series code are collectively referred to as the dimension series code.
4) The bearing type code is represented by the fifth digit from the right of the basic code (for cylindrical roller bearings and needle roller bearings, the codes are letters).
postcode
The post code of the bearing is to use letters and numbers to indicate the structure, tolerance and special requirements of the material of the bearing, etc. There are a lot of postcodes, here are a few commonly used codenames.
1) The internal structure code indicates different internal structures of the same type of bearing, and is represented by letters followed by the basic code. For example: Angular contact ball bearings with contact angles of 15°, 25° and 40° respectively use C, AC and B to indicate the difference in internal structure.
2) The tolerance grades of bearings are divided into 2 grades, 4 grades, 5 grades, 6 grades, 6X grades and 0 grades, a total of 6 grades, from high to low, and their codes are /PZ, /P4, /PS, /P6, /P6X, and /PO. Among the tolerance grades, grade 6X is only applicable to tapered roller bearings; grade 0 is ordinary grade, which is not marked in the wheel bearing code.
3) The commonly used radial clearance series of bearings are divided into 1 group, 2 groups, 0 groups, 3 groups, 4 groups and 5 groups, a total of 6 groups, and the radial clearances are in order from small to large. The o group clearance is a commonly used clearance group, which is not marked in the bearing code, and the rest of the clearance groups are respectively represented by /CI, /CZ, /C3, /C4, /CS in the bearing code.
Front code
The prefix code of the bearing is used to indicate the sub-components of the bearing, which are represented by letters. For example, L represents the separable ring of the separable bearing; K represents the rolling body and cage assembly of the bearing, etc.
There are many types of rolling bearings used in practice, and the corresponding bearing codes are also relatively complicated. The codes introduced above are the most basic and commonly used parts of the bearing codes. If you are familiar with this part of the codes, you can identify and check the commonly used bearings. Please refer to GBT272-93 for the detailed code method of rolling bearings.
Bearing selection method
The market requirements for various mechanical devices and instruments using rolling bearings are becoming increasingly strict, and the conditions and performance required for bearings are also becoming more and more diverse. In order to select the most suitable bearing from a large number of structures and sizes, it is necessary to study from various angles. When selecting a bearing, generally, the bearing arrangement, the ease of installation and disassembly, the space allowed by the bearing, the size of the bearing, and the marketability of the bearing are generally considered to roughly determine the bearing structure. Next, determine the bearing size while comparing and studying the design life of various machines using bearings and the various durability limits of bearings. When selecting bearings, it is often biased to consider only the fatigue life of the bearing, and the grease life, wear, and noise caused by the aging of the grease also need to be fully studied. Furthermore, according to different uses, it is necessary to select bearings specially designed for the requirements of precision, clearance, cage structure, grease, etc. However, there is no certain order and rules for selecting bearings. The priority should be the conditions, performance, and most relevant matters required for the bearings, especially practical.
Precautions for the use of bearings
Rolling bearings are precision components and must be used with corresponding care. No matter how high-performance bearings are used, if they are not used properly, the expected high performance will not be obtained. The precautions for the use of bearings are as follows.
(1) Keep the bearing and its surroundings clean.
Even small dust, invisible to the eyes, can have a bad effect on bearings. Therefore, keep the surrounding clean so that dust does not invade the bearing.
(2) Use with caution.
If a bearing is subjected to a strong impact during use, scratches and indentations may occur, which may cause accidents. In severe cases, it will crack and break, so be careful.
(3) Use appropriate operating tools.
Avoid substituting existing tools, use the right tools.
(4) Pay attention to the corrosion of the bearing.
Sweat from hands when handling bearings can be the cause of rust. Pay attention to operate with clean hands, it is best to wear gloves as much as possible.
The correct way to install the bearing
Whether the bearing is installed correctly affects the accuracy, life and performance. Therefore, the design and assembly departments should fully study the installation of bearings. It is expected that the installation will be carried out according to the working standard. Items of working standards are usually as follows:
(1) Clean the bearing and bearing-related parts
(2) Check the size and finishing of related parts
(3) Installation
(4) Inspection after installing the bearing
(5) Lubricant supply
Before installation, unpack. General grease lubrication, no cleaning, directly filled with grease. Lubrication with lubricating oil generally does not need to be cleaned, but bearings for instruments or high speeds should be cleaned with clean oil to remove the rust inhibitor applied to the bearings. Bearings from which the anti-rust agent has been removed are prone to rust, so they cannot be left alone. Furthermore, bearings that have been sealed with grease can be used directly without cleaning.
The installation method of the bearing varies with the bearing structure, fit, and conditions. Generally, since the shaft is mostly rotated, the inner ring needs an interference fit. Cylindrical bore bearings are mostly pressed in with a press, or hot-packed. In the case of a tapered hole, install it directly on the tapered shaft, or install it with a sleeve. When installing to the shell, generally there is a lot of clearance fit, and the outer ring has an interference, which is usually pressed in with a press, or there is also a shrink fit method for installation after cooling. When dry ice is used as the coolant and the shrink fit is installed, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate anti-rust measures are required.
Bearing maintenance method
In order to maintain the original performance of the bearing in good condition for as long as possible, maintenance and repair are required to prevent accidents before they happen, ensure the reliability of operation, and improve productivity and economy. It is best to maintain the operating standards corresponding to the operating conditions of the machinery and carry out it regularly. The content includes monitoring the running status, replenishing or replacing lubricants, and regular disassembly inspections. The inspection items during operation include the rotation noise of the bearing, vibration, temperature, and the state of the lubricant.
bearing lubrication
The purpose of lubricating rolling bearings is to reduce the internal friction and wear of the bearings and prevent burning and sticking. The lubricating effects are as follows:
(1) Reduce friction and wear.
In the mutual contact parts of the rings, rolling elements and cages that make up the bearing, metal contact is prevented and friction and wear are reduced.
(2) Prolong fatigue life.
The rolling fatigue life of the bearing is extended when the rolling contact surface is well lubricated during rotation. Conversely, if the oil viscosity is low and the thickness of the lubricating oil film is not good, it will be shortened.
(3) Discharge frictional heat and cool down.
Circulating oil supply method, etc. can use oil to discharge heat generated by friction, or heat transmitted from the outside, for cooling. Prevent the bearing from overheating and prevent the lubricating oil itself from aging.
(4) Others
It also has the effect of preventing foreign matter from intruding into the bearing, or preventing rust and corrosion.
Bearing lubrication methods are divided into grease lubrication and oil lubrication. In order to make the bearing function well, first of all, it is necessary to select a lubrication method suitable for the conditions of use and the purpose of use. If only lubrication is considered, the lubricity of oil lubrication is dominant. However, grease lubrication has the advantage of simplifying the structure around the bearing. The advantages and disadvantages of grease lubrication and oil lubrication are compared.
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Bearing maintenance method
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Bearing cleaning: When disassembling the bearing for maintenance, first record the appearance of the bearing, confirm the remaining amount of lubricant, and wash the bearing after sampling the lubricant for inspection. As a cleaning agent, cleaning agent and kerosene are generally used. The disassembled bearings are cleaned, divided into coarse cleaning and fine cleaning, and placed in the container respectively, first put the bottom of the metal mesh pad so that the bearing does not directly contact the dirt in the container. During rough cleaning, if the bearing is rotated with dirt, it will damage the rolling surface of the bearing, so care should be taken. In the rough cleaning oil, use a brush to remove grease and stickies. After it is roughly clean, switch to fine cleaning. Fine cleaning is to carefully clean the bearing while rotating it in the cleaning oil. In addition, the cleaning oil should always be kept clean.
Bearing maintenance and judgment: In order to judge whether the disassembled bearing can be used, it should be checked after the bearing is cleaned. Check the state of the raceway surface, rolling surface, and mating surface, the wear of the cage, the increase of the bearing clearance, and the damage and abnormality that have nothing to do with the decrease in dimensional accuracy. For non-separable small ball bearings, use one hand to support the inner ring horizontally, and rotate the outer ring to check whether it is smooth. For separable bearings such as tapered roller bearings, the rolling elements and the raceway surfaces of the outer ring can be inspected separately. Because large bearings cannot be rotated by hand, pay attention to check the appearance of rolling elements, raceway surfaces, cages, rib surfaces, etc. The higher the importance of the bearing, the more carefully it must be inspected.
