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 and is 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 representation method is specified separately, please refer to GB/T272-93.
(2) The diameter series of the bearing (i.e., the series of changes 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 extra-light series represented by 1, the rest are the same as those for radial bearings.
(3) The width series of the bearing (i.e., the series with different widths of the bearings with the same structure, inner diameter, and diameter series) is represented 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 size 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 a bearing is a letter and number indicating the structure, tolerance and special material requirements of the bearing. 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, and is indicated 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 levels, from high to low, and their codes are /P2, /P4, /P5, /P6, /P6X and /PO. Among the tolerance grades, 6X is only applicable to tapered roller bearings; 0 is a normal grade and is not marked in the wheel 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, radial clearance from small to large. 0 group clearance is a common clearance group, which 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, represented by letters. For example, L represents the separable ring of a separable bearing; K represents the rolling element and cage assembly of the 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 for rolling bearings, please refer to GBT272-93.
How to select 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 removal difficulty of the shaft system, the space allowed by the bearing, the size, and the marketability of the bearing are considered, and the bearing structure is roughly determined. Secondly, the design life of various machines using bearings and the various different durability limits of bearings are compared and studied, and the bearing size is determined. When selecting bearings, people tend to only consider the fatigue life of the bearings, and the grease life, wear, and noise 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 fixed order or rule for selecting bearings. The conditions, performance, and most relevant matters required for the bearing should be given priority, which is particularly practical.
Precautions for the use of bearings
Rolling bearings are precision components, and their use must also be carried out with corresponding caution. No matter how high-performance the bearing is, if it is used improperly, the expected high performance will not be achieved.
The following are the precautions for using bearings.
(1) Keep the bearing and its surroundings clean.
Even small dust particles that cannot be seen by the naked eye can have a bad effect on the bearing. Therefore, keep the surroundings clean to prevent dust from entering the bearing.
(2) Use with caution.
Strong impact on the bearing during use will cause scratches and indentations, which may cause accidents. In severe cases, cracks and breaks may occur, so care must be taken.
(3) Use appropriate operating tools.
Avoid replacing existing tools with appropriate tools.
(4) Pay attention to bearing rust.
When operating the bearing, sweat on the hands may cause rust. Be careful to operate with clean hands, and it is best to wear gloves as much as possible.
Correct installation of bearings
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 recommended that the installation be carried out in accordance with the operating standards.
The standard operation items 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 the bearing is installed
(5) Supply lubricant
Before installation, open the package. For general grease lubrication, do not clean and fill with grease directly. For oil lubrication, it is not necessary to clean it. However, for instrument or high-speed bearings, etc., they should be cleaned with clean oil to remove the rust inhibitor applied to the bearing. 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 tapered bores, they are directly installed on the tapered shaft or installed with a sleeve. When installed in the housing, there is usually 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 and shrink fit installation, moisture in the air will condense on the surface of the bearing. 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 the reliability of operation, 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 rings, rolling elements and retainers that constitute the bearing.
(2) Extend fatigue life.
The rolling fatigue life of a bearing is extended if the rolling contact surface is well lubricated during rotation. On the contrary, if the oil viscosity is low and the lubricating film thickness is poor, the life is shortened.
(3) Discharge friction heat and cool.
The circulating oiling method can use oil to discharge the heat generated by friction or the heat transmitted from the outside and cool it. Prevent the bearing from overheating and prevent the lubricating oil 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 bearings 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. The advantages and disadvantages of grease lubrication and oil lubrication are compared.
Bearing maintenance method
Bearing cleaning: When disassembling the bearing for maintenance, first record the appearance of the bearing, confirm the remaining amount of lubricant, take a sample of the lubricant to be inspected, and then wash the bearing. As cleaning agents, cleaning agents and kerosene are commonly used. The cleaning of disassembled bearings is divided into rough cleaning and fine cleaning. They are placed in containers respectively, and a metal mesh pad is placed at the bottom first to prevent the bearings 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 inspection 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, matching surface, wear of the cage, increase in bearing clearance, and damage and abnormalities 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. Since large bearings cannot be rotated by hand, pay attention to check the appearance of the rolling elements, raceway surfaces, cages, rib surfaces, etc. The more important the bearing is, the more careful the inspection must be.
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