The most comprehensive introduction to bearings, bearing knowledge

As an important component of contemporary machinery, bearings are widely used. We have some understanding and understanding of it to some extent. How much do you know specifically?








Bearings generally consist of inner rings, outer rings, rolling elements, and cages. For sealed bearings, add lubricant and sealing rings (or dust covers). This is the entire composition of the bearing.





picture




Different types of bearings can be selected based on their working conditions in order to better utilize their functions and extend their service life. We need to consider the following factors when selecting bearings:





·Radial load



·Axial load



·Speed requirements

·Radial runout

·Axial runout

·Working temperature

·Noise requirements

·Lubrication condition








picture







The bearing model generally consists of a pre code, a basic code, and a post code. In general, the bearing model is only represented by the basic model. The basic model generally consists of three parts: type code, size code, and inner diameter code. Post code refers to the use of letters and numbers to indicate the structure, tolerances, and special requirements for materials of bearings. The prefix is used to represent the sub components of the bearing, represented by letters.





picture



1. Basic code





The basic code is used to indicate the inner diameter, diameter series, width series, and type of the bearing, usually with a maximum of five digits. It is described as follows:




(1) The inner diameter of the bearing is represented by the first digit from the right of the basic code.




For bearings with a commonly used inner diameter of d=20-480mm, the inner diameter is generally a multiple of 5. These two numbers represent the quotient obtained by dividing the inner diameter size of the bearing by 5. For example, 04 represents d=20mm; 12 represents d=60mm, etc. For bearings with inner diameters of 10mm, 12mm, 15mm, and 17mm, the inner diameter codes are 00, 01, 02, and 03 in sequence. For bearings with an inner diameter of less than 10mm and greater than 500mm, the method for expressing the inner diameter has other regulations, which can be found in GB/T272-93.





(2) The diameter series of bearings (i.e. the series of changes in outer diameter and width of bearings with the same structure and 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 the extra light series; 2 represents the light series; 3 represents the middle series; 4 represents a heavy series. The size comparison between each series is shown in the following figure. Thrust bearings are consistent with radial bearings, except for using 1 to represent the extra light series.



(3) The width series of bearings (i.e. the series of changes in the width of 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 comparison column 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 indicated in the code for most bearings, but for self-aligning roller bearings and tapered roller bearings, the width series code 0 should be indicated. The diameter series code and 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 (using letters for type codes such as cylindrical roller bearings and needle roller bearings).




2. Post code





The post code of bearings refers to the use of letters and numbers to indicate the structure, tolerances, and special requirements for materials of bearings. There are many contents of post codes, and the following are some commonly used codes.





(1) The internal structure code refers to the different internal structures of the same type of bearing, represented by letters followed by the basic code. For example, angular contact ball bearings with contact angles of 15 °, 25 °, and 40 ° are represented by C, AC, and B for their internal structures.



(2) The tolerance levels of bearings are divided into 6 levels, namely 2, 4, 5, 6, 6X, and 0, from high to low. The codes are/PZ,/P4,/PS,/P6,/P6X, and/PO, respectively. Among the tolerance levels, level 6X is only applicable to tapered roller bearings; Level 0 is a regular level and is not indicated in the wheel bearing code.





(3) The commonly used radial clearance series of bearings are divided into 6 groups, including 1 group, 2 groups, 0 group, 3 groups, 4 groups, and 5 groups. The radial clearance ranges from small to large. O group clearance is a commonly used clearance group and is not indicated in the bearing code. The remaining clearance groups are represented by/CI,/CZ,/C3,/C4, and/CS respectively in the bearing code.





3. Pre code





The prefix of the bearing is used to represent the sub components of the bearing, represented by letters. If L is used to represent the separable ring of a separable bearing; K represents the rolling element and cage components of the bearing, etc.





There are many types of rolling bearings in practical applications, and the corresponding bearing codes are also quite complex. The codes introduced above are the most basic and commonly used parts of bearing codes. Once you are familiar with these codes, you can identify and select commonly used bearings. For detailed coding methods for rolling bearings, please refer to GBT272.








When selecting bearings, it is generally considered that the arrangement, installation, and ease of disassembly of the bearings as a shaft system, the allowed space and size of the bearings, and the marketability of the bearings roughly determine the bearing structure.



Secondly, while comparing and studying the design life of various machinery using bearings and the different durability limits of bearings, the bearing size is determined.



Furthermore, according to different applications, it is necessary to choose bearings with special design requirements for accuracy, clearance, cage structure, lubricating grease, etc. However, there is no specific order or rule for selecting bearings. Priority should be given to the conditions, performance, and most relevant options required for the bearings, which is particularly practical.







Rolling bearings are precision components, and their use must also be carried out with corresponding caution. Precautions for use are as follows:




(1) Keep the bearings and their surroundings clean





Even small dust that cannot be seen by the eyes can have a negative impact on the bearings. So, it is important to keep the surroundings clean to prevent dust from entering the bearings.




(2) Use with caution and caution





If the shaft is subjected to strong impact during use, it can cause scars and indentations, which can become the cause of accidents. In severe cases, cracks and fractures may occur, so attention must be paid.




(3) Use appropriate operating tools





To avoid using existing tools instead, it is necessary to use appropriate tools.




(4) Pay attention to the corrosion of bearings





When operating bearings, sweat on the hands can become the cause of rust. Pay attention to using clean hands for operation, and it is best to wear gloves as much as possible.








Before installation, open the packaging. Generally lubricated with grease, without cleaning, directly filled with grease. Lubricating oil lubrication is not necessary for regular cleaning, but for instrument or high-speed bearings, clean them with clean oil to remove rust inhibitors applied to the bearings. Bearings without rust inhibitors are prone to rust, so they cannot be left unattended. Furthermore, bearings that have been sealed with lubricating grease can be used directly without cleaning.




The installation method of bearing varies with the bearing structure, fit and condition. Generally, the inner ring needs interference fit because it is mostly shaft rotation. Cylindrical hole bearings are often pressed in with a press or hot assembled. In the case of a tapered hole, it can be directly installed on the tapered shaft or installed with a sleeve. When installing to the casing, there is usually a lot of clearance fit, and the outer ring has interference. Usually, a press is used to press it in, or there is also a cold shrink fit method for installation after cooling. When dry ice is used as a coolant and cold shrink is used for installation, moisture in the air will condense on the surface of the bearing. So, appropriate rust prevention measures are needed.







In order to maintain the original performance of bearings in good condition for as long as possible, maintenance and repair are necessary to prevent accidents, ensure reliability of operation, and improve productivity and economy. The maintenance should be carried out regularly according to the operating standards of the corresponding machinery operating conditions. The content includes monitoring the operating status, supplementing or replacing lubricants, and conducting regular disassembly inspections. As maintenance items during operation, there are bearing rotation sounds, vibrations, temperatures, lubricant status, and so on.








The lubrication purpose of rolling bearings is to reduce internal friction and wear of bearings, prevent burning and sticking, and their lubrication effects are as follows:



(1) Reduce friction and wear





To prevent metal contact and reduce friction and wear in the contact parts of the ring, rolling element, and retainer that make up the bearing.




(2) Extend fatigue life





The rolling fatigue life of bearings is extended when the rolling contact surface is well lubricated during rotation. On the contrary, if the viscosity of the oil is low and the thickness of the lubricating oil film is not good, it will be shortened.




(3) Discharging frictional heat and cooling





The method of circulating oil can use oil to remove heat generated by friction or heat transmitted from the outside for cooling. Prevent bearing overheating and prevent lubricating oil from aging.




(4) Other





It also has the effect of preventing foreign objects from entering the interior of bearings, or preventing rust and corrosion.




Lubrication method:





The lubrication methods for bearings are divided into grease lubrication and oil lubrication. In order to make the bearings function well, first of all, it is necessary to choose a lubrication method that is suitable for the conditions and purpose of use.







Cleaning of bearings: When disassembling the bearings for maintenance, first record the appearance of the bearings, confirm the residual amount of lubricants, sample and inspect the lubricants used, and then wash the bearings. As a cleaning agent, commonly used cleaning agents and kerosene.



The dismantled bearings are cleaned in coarse and fine ways, and each is placed in a container. First, a metal mesh pad is placed on the bottom to prevent the bearings from directly contacting the dirt in the container. During rough cleaning, if the bearing rotates with dirt, it can damage the rolling surface of the bearing and should be taken care of. In the coarse cleaning oil, use a brush to remove lubricating grease and adhesive substances. After roughly cleaning, proceed to fine cleaning. Fine cleaning refers to carefully cleaning the bearings while rotating them in cleaning oil. In addition, cleaning oil should also be kept clean regularly.





Maintenance and judgment of bearings: In order to determine whether the dismantled bearings can be used, it is necessary to inspect them after cleaning them. Check the condition of the raceway surface, rolling surface, and mating surface, the wear of the cage, the increase in bearing clearance, and any unrelated damage with decreased dimensional accuracy, and any abnormalities.



For non separable small ball bearings, use one hand to support the inner ring horizontally and rotate the outer ring to confirm smoothness.



Tapered roller bearings can be used to inspect the raceway surfaces of the rolling element and outer ring separately.



Due to the inability to rotate large bearings by hand, attention should be paid to inspecting the appearance of the rolling element, raceway surface, retainer, and retaining surface. The higher the importance of bearings, the more careful they need to be inspected