Accurately grasping the process concept of clearance adjustment and pre-tightening, and correctly applying this process in assembly work is the guarantee of the quality of bearing assembly work. In order to properly adjust and pre-tighten the bearing clearance, we must first have a full understanding of the clearance of the rolling bearing. In addition, we must know the concept of rolling bearing clearance and what kind of situation is the clearance?
The clearance of the rolling bearing refers to the large amount of movement of the other ferrule in the radial or axial direction when the ferrule is fixed, so the clearance is divided into radial clearance and axial clearance. When the rolling bearing is assembled, its play should not be too large or too small. If the clearance is too large, the number of rolling bodies that can bear the load at the same time is reduced, so that the load of the single rolling body is increased, thereby reducing the rotation precision of the bearing and reducing the service life; if the clearance is too small, the frictional force is increased, resulting in an increase The increased heat, which exacerbates wear and tear, also reduces the service life of the bearing. Therefore, many bearings must be tightly controlled and adjusted during assembly.
Preloading is the axial force of the inner or outer ring of the bearing during assembly to eliminate bearing clearance and cause initial deformation of the rolling element in contact with the inner and outer rings. Preloading can improve the stiffness and rotation accuracy of the bearing under working conditions. For bearings with large load and high rotational accuracy, most of them work without clearance or even a small amount of interference. In this case, the bearings need to be pre-tensioned during assembly.
Through the adjustment of the rolling bearing clearance, the bearing capacity and rotation precision of the bearing can be improved, and the service life of the bearing can be improved. At the same time, the bearing friction will be intensified and the heat generation will increase. Therefore, it is necessary to ensure good lubrication and heat dissipation while adjusting the clearance or pre-tightening. If improperly adjusted or poorly lubricated, it will in turn increase bearing wear and reduce life. Therefore, the correct adjustment and preloading of the rolling bearing clearance requires the following:
1. Assembly technical requirements are the fundamental basis for selecting assembly process methods
The adjustment of the rolling bearing clearance can improve the rotation precision of the bearing, improve the bearing capacity of the bearing, prolong the service life of the bearing, and also reduce the vibration and noise, but not all rolling bearings need to be installed during assembly. Adjustment. The pre-fastening can improve the bearing rigidity and the precision of the rotation, but at the same time, the friction is intensified, the lubricating oil film is destroyed and a large amount of heat is generated. Therefore, the pre-tightened bearing must be forcedly lubricated and cooled. This method is limited to It is a special method for the bearing rigidity and rotation precision. It is only used in the machine tool spindle assembly in production. The bearing assembly of other transmission mechanisms is almost invisible.
Whether to adjust and pre-tighten the clearance in the rolling bearing assembly is determined according to the assembly technical requirements of the technical documents. Specifically, in the assembly technical requirements, the bearings with high requirements for high speed, heavy load or rotation accuracy are required to adjust the bearing clearance or preloading. Otherwise, the bearing clearance is maintained, and only the shaft is assembled during assembly. Just fix it. From the perspective of the type of bearing, it is necessary to adjust the clearance for tapered roller bearings, angular contact bearings and thrust bearings; for normal low-speed, light-load radial ball bearings, in most cases, it is not necessary to carry out the play. Adjusted and only fixed axially.
2. To achieve clearance adjustment and preload requirements under thermal equilibrium conditions
The actual ideal working clearance of the rolling bearing is the clearance adjusted after the bearing temperature rises. Therefore, the adjustment of bearing clearance should be carried out in two stages: firstly adjust the bearing clearance according to the relevant operating specifications and technical requirements at normal temperature, and the rotation should be flexible when the clearance is appropriate and rotated by hand; then, the adjustment mechanism is appropriate Return to loose (to prevent sudden bearing lock due to temperature rise during test drive), carry out dry running test, from low speed to high speed idle running time not more than 2 hours, at high speed idle running time not less than 30 minutes, bearing should run Flexible, low noise, working temperature does not exceed 50 °C, then the adjustment mechanism is reset and locked.
3. Maintain good lubrication
Good lubrication not only reduces friction, but also cools the bearings and on-axis parts. After the rolling bearing clearance is adjusted, the friction will be aggravated and the heat generated will increase the temperature of the entire transmission system. If it is not possible to dissipate heat in time, this heat will change the size of the transmission parts, which will affect the change of the rolling bearing clearance, generate more heat, and form a vicious circle. Therefore, for the rolling bearing adjusted by the clearance, it is necessary to maintain good lubrication to reduce friction, and more importantly, to take away a large amount of heat with the circulating lubricating oil, control the temperature rise, and realize the heat balance of the transmission system.
The rolling bearing is correctly assembled according to the process, rationally used, and carefully adjusts the rolling bearing clearance and pre-tightening process. It is a means to improve the bearing rotation precision and bearing capacity, and reduce the vibration and noise of the transmission system. In addition to the general technology of rolling bearing assembly. In addition to the requirements, we must also consider the influence of bearing temperature rise and lubrication on the adjustment work, and carry out detailed inspection and secondary adjustment after the dry running test. The patient and meticulous work attitude is also indispensable good quality for assembly and maintenance fitters.
