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Bearing Knowledge Encyclopedia (4)

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According to the application experience; the most suitable working clearance of the ball bearing is close to zero, the roller bearing should adhere to a small amount of working clearance. In the parts with excellent support rigidity, the bearing promises a certain value of pre-tightening force. Here is unique It is pointed out that the so-called working clearance refers to the clearance of the bearing under the practical working conditions. There is also a kind of clearance called the original clearance; it refers to the clearance before the bearing is installed. The original clearance is larger than the device clearance. Let's swim The choice of gap; the first is to choose the appropriate job clearance.
The clearance values ​​of the national normative rules are divided into three groups: basic group (0 group), small clearance auxiliary group (1, 2 group) and large clearance auxiliary group (3, 4, 5 groups). Under normal working conditions; the basic group should be preferred; the bearing can be properly operated. When the basic group is not satisfied with the demand; the auxiliary group clearance should be used. The large clearance auxiliary group is suitable for bearings and shafts. The outer hole of the shell is selected for interference cooperation; the temperature difference between the inner and outer rings of the bearing is large; the deep groove ball bearing needs to accept a large axial load or needs to improve the centering function; the heart and the demand increase the limit speed and the falling bearing conflict torque, etc. The group is suitable for high-precision rotation accuracy, strict control of the axial displacement of the housing hole, and occasions where oscillation and noise need to be reduced.
The radial clearance of various types of bearings can be found in the rules of national regulations.
1. The public service level selects the bearing's common grade; the first is based on the shaft's rotation accuracy requirements. In general, for example, a spur gear reducer with large meshing and public service; available PO grade bearings; but some pairs of rotation accuracy There are shafts with strict requirements or high speed; for high-precision, small-jumping machine spindles, bearings with higher than PO grades are used.
When selecting a bearing with a high level of public service; the production of the outer casing of the shaft should be compatible with the public service level of the bearing; and it should have a satisfactory layout stiffness. Table 1 3 lists examples of the selection of the bearing public service level; for reference.
2. The lifespan L of the calculation of the lifespan and reliability is determined according to the total accumulated time that the equipment is expected to operate; the common unit is the number of hours of operation; the calculation of the lifespan can also be indicated by the total number of revolutions of the bearing; In the process of lifespan; it is necessary to think about all kinds of work conditions. Is the equipment operation an eight-hour shift or an operating day? Can it be used all day long? Can it start and stop for a long time once it starts? Table 1 4 gives the general service life values ​​for various power transmission applications.
It is also necessary to think about the cost of repairing, the probability of life and the invalidation; it is the cost of the replacement of the equipment after the long-term use of the equipment is still timed repair (including replacement bearings).
Of course; the reliability of the bearing is a primary consideration when determining the number of life required for the resolution; the standard of reliability in the bearing industry is generally 90%; that is to say; a lot of work in the same use case In the bearing; 90% of the bearings are still indispensable when the selected bearing life (L life) is reached; if the demand power is low, the life L of the demand needs to be changed.
Improve bearing reliability; make it more reliable than 90%; can be treated with 10% loss of power to regulate the service life of the bearing. In other words; if you want to achieve higher reliability, it is necessary to reduce the life of the bearing. For example: for a bearing with a reliability of 96%; it is necessary to say that the bearing life is L; instead of L. Without increasing the bearing scale; you need to reduce the life of the original L bearing.
In the following we will give the dynamic bearing capacity of a given bearing; it is a function of speed, bearing practical load and lifespan. For a given use case; speed and practice load are given; thus dynamic loading Can be a function of the lifespan. In order to improve the reliability to 96%; you can increase the size of the bearing; then reach the same level of operational reliability of 90%; that is, you can improve its dynamic bearing capacity; Make it higher than the value required for 90% reliability; this requires picking a larger bearing.

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