Analysis of the ring mold granulator bearing

Rolling bearings can be divided into different conditions according to the working conditions of the bearing outer ring during use: the outer ring is stationary with respect to the load direction and the outer ring is rotated with respect to the load direction. In the latter case, the inner ring of the bearing is stationary with respect to the load direction, the rotational load acts on the outer ring of the bearing, and the bearing of the rotor of the ring die granulator is in this form of rotation. Figure 1 shows the rotor assembly of a ring die granulator in which the spindle is stationary, the rotor is rotated under power, and the rotational load acts on the outer ring of the bearing. For bearings of this type of transmission, the outer ring and the outer casing are usually in a tight fit or an interference fit. During the use of the ring die granulator, the rotor bearing may have excessive temperature rise, severe bearing wear and short life.

The fit of the inner and outer rings of the rolling bearing and the radial working clearance have a great influence on the bearing life, temperature rise and noise. The following is an analysis of the fit and radial working clearance of the inner and outer rings of the rolling bearing.

1 cooperation

1.1 Coupling of bearing outer ring and housing hole

The outer ring of the bearing and the hole of the outer casing are interference fit. However, when the outer ring is installed with a small interference, when the outer ring is rotated by the load, the rolling elements and the raceway of the bearing are rubbed. The bearing and the outer casing are subject to thermal expansion, but due to expansion. The coefficient and the heat dissipation speed are different. When the expansion degree of the outer casing is larger than the outer ring of the bearing, the interference will be reduced, and the relative sliding between the outer ring of the bearing and the hole of the outer casing will be harmful in the circumferential direction. This phenomenon is called creep phenomenon. Once creep occurs, significant wear and damage to the outer ring or casing of the bearing occurs on the mating surface. Therefore, the fit of the outer ring of the bearing to the bore of the housing must meet the minimum interference Ymin.

In addition, the interference should not be too large. Under the action of the working load, the bearing will reduce the radial clearance of the bearing. The reduction of the clearance will cause the bearing to heat up, the temperature will rise, and the interference will be too large. It is difficult to install and disassemble the bearing, so the appropriate interference should be selected according to the load conditions.

1.2 Bearing inner ring and shaft coordination

Usually, the inner ring of the bearing cooperates with the shaft to form a clearance fit. The size of the matching clearance depends on the bearing load, the fit of the outer ring of the bearing and the shell hole, and the choice of the bearing clearance. At the same time, the inner ring and the shaft also affect the bearing diameter. To work clearance.

2 radial working clearance

The clearance is an important parameter of the rolling bearing fit, which directly affects the bearing performance, vibration, noise, wear, temperature rise, service life and mechanical running accuracy. The basic dynamic load rating of the bearing varies with the size of the clearance. If the working clearance is too large, the number of rolling elements will be reduced, the bearing capacity will be reduced, the rolling contact surface stress will increase, the running accuracy of the bearing will decrease, the vibration and noise will increase, the bearing life will be shortened, and the working clearance will be too small. It will cause the bearing to heat up, the temperature rises, and even the bearing will die during operation.

Factors affecting the radial working clearance of rolling bearings:

1 The outer ring of the bearing and the hole of the outer casing are assembled by interference. Therefore, assembly stress is generated at the mating surface, the outer ring is elastically deformed, and the inner raceway of the outer ring is contracted inward, thereby causing the radial clearance to decrease;

2 Under the action of the working load, the rotating load acts on the outer ring of the bearing, and the radial force causes the outer ring to elastically deform and contract, thereby causing the radial working clearance to decrease;

3 When the bearing works due to the influence of temperature increase on the radial working clearance, the temperature rise causes the inner ring of the bearing to expand, so that the radial working clearance is reduced; the outer ring of the bearing and the outer casing are subject to thermal expansion, but due to the material Different causes different expansion coefficients, and the heat dissipation speed affects the degree of expansion of the two, the outer ring expands less than the outer casing, and the radial working clearance decreases, and vice versa, the radial working clearance increases;

4 When the bearing is in operation, the grease will form an elastic fluid dynamic pressure oil film in the rolling body and the inner and outer rings to bear the load. The existence of the oil film thickness will reduce the radial clearance, and the dynamic pressure oil film thickness is related to the viscosity of the grease.

3 example application

A certain type of ring die granulator, spindle journal d, inner casing diameter D, bearing SKF spherical roller bearing, bearing standard clearance 95~145 μm, spindle journal d upper deviation 0, lower deviation -25 μm, The upper deviation of the bore diameter D in the outer casing is -14 μm, and the lower deviation is -60 μm. The outer ring of the bearing and the inner hole of the outer casing are interference fit. The inner ring of the bearing and the shaft are over-matched. During the use of the equipment, the temperature rise of the bearing is too high and the service life of the bearing is short. The tolerance band of the rotor spindle journal d was corrected, and the clearance was matched. The situation was improved, the bearing temperature rise was in the normal range, and the bearing was running normally.

The reason analysis, because the initial bearing outer ring and the outer casing hole are interference fit, the inner ring and the shaft are over-fitted, and under the action of the bearing, the radial force causes the outer ring to elastically deform and contract, thereby causing radial working tour. The gap is reduced; the inner ring is contracted and deformed under the action of radial force, and the radial working clearance is increased, but since the initial over-coupling is small, the deformation is small, and the radial working clearance is small, and the radial working is performed at this time. The clearance is smaller than the minimum clearance required for the normal operation of the bearing, and therefore, the bearing temperature rise is too high. After increasing the clearance between the inner ring of the bearing and the journal, the inner ring is contracted and deformed under the action of radial force, and the radial working clearance is increased. At this time, the radial working clearance satisfies the minimum clearance required for the normal operation of the bearing. When the bearing runs through for a period of time, the temperature of the inner and outer ring shafts of the bearing is relatively stable, and the radial working clearance is also stabilized, and finally the bearing reaches stable operation. Therefore, it is necessary to select the proper bearing inner ring and the journal to match the gap size for the normal operation of the ring mold granulator rotor bearing.

4 Summary

The matching of the inner and outer rings of the rolling bearing and the radial working clearance play an important role in the normal operation of the ring mold granulator rotor bearing. The above influencing factors have mutual influence, so when doing similar structural design, according to the bearing Bearing capacity, determine the appropriate bearing radial clearance size, should consider the elastic deformation of the inner and outer rings of the bearing under the interference fit and the radial force, the expansion of the inner and outer rings of the bearing caused by the temperature rise, The influence of dynamic pressure film thickness and other factors on the radial clearance of the bearing, the fit of the outer ring of the bearing and the shell hole, and the cooperation of the inner ring of the bearing and the shaft are selected.