Bearing clearance and equipment selection is an extremely important part of motor planning

  • 5-06-2019

Motor skill internal reference
The selection of bearing clearance and equipment is an extremely important part of motor planning. The plan chosen without knowing the function of the bearing is probably a kind of unplanned plan. Different working conditions, the requirements on the bearing will be different, Ms. Shen believes that it is necessary to carry out some study and discussion on the common sense of the bearing.
The relationship between various grooves of deep groove ball bearings
Bearing operation clearance calculation according to formula (1), the choice of bearing working clearance, theoretically speaking, in the smooth operation of the bearing, the bearing life is the longest when there is a slight negative working clearance.
△=△0-Δfi-δf0-δt+δw.....................(1)
In formula (1):
△0--original clearance
Δfi--the amount of clearance reduction caused by the cooperation between the inner ring and the shaft
Δf0--the amount of clearance reduction caused by the cooperation between the outer ring and the outer casing
Δt--the amount of clearance reduction caused by the temperature difference between the inner and outer rings
Δw--the increase in clearance caused by the load
About bearing smooth grease
The purpose of the smooth bearing is to separate the roll and the rolling surface with a thin oil film. During the operation, the rolling surface forms a uniform smooth oil film, and then the internal friction of the bearing and the wear of each component are prevented to prevent sintering. Outstanding smoothness is a necessary condition for bearing operation. Analysis of bearing damage indicates that about 40% of bearing damage is related to poor smoothness. The smooth way is divided into smooth grease and smooth oil.
●The smoothness of the grease has the advantages that it does not need to be compensated for a long time after filling with a smooth grease, and the sealing structure is relatively simple, so it is widely used. Smooth grease is a semi-solid smoothing agent based on a smooth oil-based oil blended with a strong lipophilic solid thickener. It is also used to improve certain properties and various additives.
●The oil is smooth, and the circulating oil is often smooth, the spray is smooth, and the oil mist is smooth. The smooth oil of the bearing is generally made of refined mineral oil with good oxidation stability and rust resistance and high oil film strength, but various constituent oils are also often used.
Bearing smooth grease high temperature failure feature picture
Motor bearing equipment
The bearing assembly of the rolling parts of the motor (such as the main shaft) generally requires two sets of bearings to support and the rolling parts are positioned radially and axially relative to the fixed part of the machine (such as the bearing housing). Bearing equipment can include the following methods according to different operating conditions, such as load, required rotation accuracy and cost requirements:
●Fixed end and floating bearing equipment
●Pre-adjusted bearing equipment (fixed at both ends)
● "Floating" fine-fitting equipment (both floats)
Fixed end and floating end bearing equipment
The fixed end bearing is radially supported at one end of the shaft for axial positioning in both directions. Therefore, it is necessary for the fixed end bearings to be fixed together on the shaft and the bearing housing. Suitable bearings for fixed ends are radial bearings capable of accepting combined loads, such as deep groove ball bearings, double row or paired single row angular contact ball bearings, self-aligning ball bearings, spherical and roller bearings or matched tapered rollers. Sub-bearing. Can only accept radial bearings with pure radial load, such as one-ring fixed-column roller bearings without ribs, and another type of bearing (such as deep groove ball bearings, four-point ball bearings or two-way thrust bearings) When used in groups, it can also be used on the fixed end. In this type of equipment, the other bearing is only used for axial positioning in both directions, and it is necessary to have a certain radial freedom in the bearing housing (ie, a clearance should be reserved with the bearing housing).
The floating bearing is only supported radially at the other end of the shaft, and it is necessary to allow the shaft to have a certain axial displacement so that the forces between the bearings do not occur, for example, when the bearing is inflated due to heat, the axial direction Displacement can be done inside certain types of bearings. The axial displacement can occur between one of the bearing rings and the component to which it is connected, preferably between the outer ring and the bearing housing bore.
The fixed end and the floating end bearing are equipped with many different combinations. The following are some of the more common combinations of rigid bearing equipment. The combination of axial displacement can be done in the bearing, for example:
(1) Deep groove ball shaft / cylindrical roller bearing
(2) Double row angular touch ball bearing / cylindrical roller bearing
(3) Paired single row tapered roller shaft/cylindrical roller bearing
(4) NUP cylindrical roller bearing / NU cylindrical roller bearing
(5) NU type cylindrical roller bearing + four point touch ball bearing / NU type cylindrical roller bearing
In the above combination, it is necessary to minimize the viewpoint error between the shaft and the bearing housing. If the operating conditions are not agreed, it is recommended to use a combination of self-aligning bearings that can accept larger viewpoint errors, for example:
(1) Self-aligning ball bearing / CARB toroidal roller bearing
(2) Spherical roller shaft / CARB toroidal roller bearing
These devices are capable of accepting certain visual point errors and axial displacements and are capable of preventing internal axial forces from occurring in the shafting.

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