Bearings are generally composed of inner rings, outer rings, rolling elements and cages. For sealed bearings, lubricants and seals (or dust covers) are added. This is all the components of the bearing.
Choose different types of bearings according to the working conditions of the bearings to better play the function of the bearings and extend the service life of the bearings.
We need to consider the following factors when selecting bearings: radial load, axial load, speed requirements, radial runout, axial runout, operating temperature, noise requirements, and lubrication conditions.
Bearing code
Bearing models generally consist of leading codes, basic codes and post-codes. Under normal circumstances, bearing models are only represented by basic models. The basic model generally contains three parts, type code, size code and inner diameter code. The post-code uses letters and numbers to represent the structure, tolerance and special requirements of materials of the bearing. The leading code is used to represent the sub-components of the bearing, which are represented by letters.
The general bearing (rolling bearing) code method is divided into: leading code, basic code and post-code.
1. Basic code (type code, size code, inner diameter code [2 digits])
The basic code is used to indicate the inner diameter, diameter series, width series and type of the bearing. It is generally up to five digits. They are described as follows:
(1) The inner diameter of the bearing is indicated by the first digit from the right of the basic code. For bearings with commonly used inner diameters d=20~480mm, the inner diameter is generally a multiple of 5. These two digits indicate the quotient of the bearing inner diameter size divided by 5, such as 04 for d=20mm; 12 for d=60mm, etc. For bearings with inner diameters of 10mm, 12mm, 15mm and 17mm, the inner diameter codes are 00, 01, 02 and 03 respectively. For bearings with inner diameters less than 10mm and greater than 500mm, the inner diameter indication method is specified separately. Please refer to GB/T272-93.
(2) The diameter series of a bearing (i.e., the series of variations in outer diameter and width of bearings with the same structure and inner diameter) is indicated by the third digit from the right of the basic code. For example, for radial bearings and radial thrust bearings, 0 and 1 represent the extra-light series; 2 represents the light series; 3 represents the medium series; and 4 represents the heavy series. The size comparison between the series is shown in the figure below. For thrust bearings, except for the use of 1 to represent the extra-light series, the other series are the same as those for radial bearings.
(3) The width series of a bearing (i.e., the series of variations in width of bearings with the same structure, inner diameter, and diameter series) is indicated by the fourth digit from the right of the basic code. When the width series is listed as the 0 series (normal series) in the comparison of the diameter series in Figure 13-4, 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 should 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 (the type code for cylindrical roller bearings and needle roller bearings is a letter).
2. Post-code
The post-code of the bearing is a letter and a number indicating the bearing structure, tolerance and special material requirements. There are many post-codes. Here are some commonly used codes.
(1) The internal structure code indicates the different internal structures of the same type of bearing. It is represented by a letter following the basic code. For example, angular contact ball bearings with contact angles of 15°, 25° and 40° are represented by C, AC and B respectively to indicate the different internal structures.
(2) The tolerance grades of bearings are divided into 2, 4, 5, 6, 6X and 0, a total of 6 grades, from high to low, and their codes are /P2, /P4, /P5, /P6, /P6X and /PO respectively. Among the tolerance grades, 6X is only applicable to tapered roller bearings; 0 is a common grade and is not marked in the bearing code.
(3) Common bearing radial clearance series are divided into 1 group, 2 group, 0 group, 3 group, 4 group and 5 group, a total of 6 groups, and the radial clearance is from small to large. Group 0 clearance is a common clearance group and is not marked in the bearing code. The remaining clearance groups are represented by /C1, /C2, /C3, /C4, and /C5 in the bearing code.
3. Prefix code
The prefix code of the bearing is used to indicate the sub-components of the bearing, and is represented by letters. For example, L represents the separable ring of a separable bearing; K represents the rolling element and cage assembly of a bearing, etc.
There are many types of rolling bearings in actual application, and the corresponding bearing codes are also relatively complex. The codes introduced above are the most basic and most commonly used parts of the bearing codes. Once you are familiar with this part of the codes, you can identify and select commonly used bearings. For detailed code methods of rolling bearings, please refer to GBT272-93.
How to choose bearings
The market requirements for various mechanical devices and instruments using rolling bearings are becoming increasingly stringent, and the conditions and performance required for bearings are becoming increasingly 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 bearings, generally, the bearing arrangement, installation, and disassembly difficulty of the shaft system, the space allowed by the bearing, the size, and the marketability of the bearing are considered to roughly determine the bearing structure. Secondly, while comparing and studying the design life of various machines using bearings and the various different durability limits of bearings, the bearing size is determined. When selecting bearings, people tend to only consider the fatigue life of the bearings, and the grease life, wear, noise, etc. caused by grease aging also need to be fully studied. Furthermore, according to different uses, it is necessary to select bearings that are specially designed for requirements such as accuracy, clearance, cage structure, grease, etc. However, there is no certain order or rule for selecting bearings. The priority should be given to the conditions, performance, and most relevant matters required for the bearings, which is particularly practical.
Precautions for using bearings
Rolling bearings are precision parts and their use must be handled with corresponding caution. No matter how high-performance the bearings are, if they are used improperly, the expected high performance will not be achieved.
Precautions for using bearings are as follows.
(1) Keep the bearings and their surroundings clean.
Even small dust particles that cannot be seen by the naked eye can have a bad effect on the bearings. Therefore, keep the surroundings clean to prevent dust from entering the bearings.
(2) Use with caution.
Strong impacts on the bearings during use can cause scratches and indentations, which can cause accidents. In severe cases, cracks and breaks can occur, so care must be taken.
(3) Use appropriate operating tools.
Avoid replacing existing tools and use appropriate tools.
(4) Pay attention to bearing rust.
When operating the bearings, sweat on the hands can cause rust. Be careful to operate with clean hands and wear gloves as much as possible.
Correct installation of bearings
Whether the bearings are installed correctly affects their accuracy, life, and performance. Therefore, the design and assembly departments should fully study the installation of bearings. It is hoped that the installation will be carried out in accordance with the operating standards.
The items of the operating standards are usually as follows:
(1) Clean the bearings and bearing-related parts
(2) Check the size and finishing of related parts
(3) Installation
(4) Inspection after the bearings are installed
(5) Supply lubricant
Before installation, open the package. Generally, grease lubrication is not cleaned and grease is directly filled. Lubricating oil lubrication does not need to be cleaned in general, but bearings for instruments or high-speed use should be cleaned with clean oil to remove the rust inhibitor applied to the bearings. Bearings with rust inhibitors removed are prone to rust, so they cannot be left alone. In addition, bearings that have been filled with grease should not be used directly without cleaning.
The installation method of bearings varies depending on the bearing structure, fit, and conditions. Generally, since the shaft rotates, the inner ring needs an interference fit. Cylindrical bore bearings are often pressed in with a press or hot-fitted. In the case of a tapered hole, it is directly installed on the tapered shaft or installed with a sleeve. When installed in the housing, there is generally a lot of clearance and the outer ring has an interference fit. It is usually pressed in with a press, or there is also a shrink fit method for installation after cooling. When using dry ice as a coolant, moisture in the air will condense on the surface of the bearing when shrink fitting is installed. Therefore, appropriate rust prevention measures are required.
Bearing maintenance methods
In order to maintain the original performance of the bearing in good condition for as long as possible, maintenance and inspection are required to prevent accidents before they happen, ensure operational reliability, and improve productivity and economy. Maintenance is best performed regularly according to the operating standards of the corresponding mechanical operating conditions. The content includes monitoring the operating status, replenishing or replacing lubricants, and regular disassembly inspections. As maintenance items during operation, there are bearing rotation noise, vibration, temperature, lubricant status, etc.
Bearing lubrication
The purpose of rolling bearing lubrication is to reduce internal friction and wear of the bearing and prevent burning and sticking. Its lubrication effects are as follows:
(1) Reduce friction and wear.
Prevent metal contact and reduce friction and wear in the contact parts of the bearing rings, rolling elements and retainers.
(2) Extend fatigue life.
The rolling fatigue life of the bearing is extended if the rolling contact surface is well lubricated during rotation. On the contrary, it is shortened if the oil viscosity is low and the lubricating film thickness is poor.
(3) Discharge friction heat and cool.
The circulating oil supply method can use oil to discharge the heat generated by friction or the heat transmitted from the outside and cool. Prevent the bearing from overheating and prevent the lubricant from aging.
(4) Others
It also has the effect of preventing foreign matter from invading the inside of the bearing or preventing rust and corrosion.
Lubrication method:
The lubrication method of the bearing is 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 that is suitable for the use conditions and purpose. If only lubrication is considered, the lubricity of oil lubrication is superior. However, grease lubrication has the advantage of simplifying the structure around the bearing. Compare the pros and cons of grease lubrication and oil lubrication.
Bearing maintenance method
Bearing cleaning: When disassembling the bearing for maintenance, first record the appearance of the bearing, confirm the remaining amount of lubricant, sample the lubricant for inspection, and then wash the bearing. As a cleaning agent, cleaning agent and kerosene are commonly used. The disassembled bearing is cleaned in two steps: rough cleaning and fine cleaning. Place them in containers respectively, and put a metal mesh pad on the bottom first to prevent the bearing from directly contacting 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 you should pay attention. In the rough cleaning oil, use a brush to remove grease and adhesives. After it is roughly clean, turn to fine cleaning. Fine cleaning is to rotate the bearing in the cleaning oil while carefully cleaning it. In addition, the cleaning oil should also be kept clean at all times.
Bearing maintenance and judgment: In order to determine 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, mating surface, wear of the cage, increase in bearing clearance, and damage and abnormality that are not related to the reduction of dimensional accuracy. For non-separable small ball bearings, use one hand to support the inner ring horizontally and rotate the outer ring to confirm whether it is smooth. For separable bearings such as tapered roller bearings, the rolling element and the raceway surface of the outer ring can be checked separately. Large bearings cannot be rotated by hand, so pay attention to checking the appearance of the rolling element, raceway surface, cage, flange surface, etc. The more important the bearing is, the more careful the inspection should be.
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