Spindle rolling bearing
(1) Type of rolling bearing
The rolling bearing has small frictional resistance, can be pre-tightened, has simple lubrication and maintenance, and can work stably within a certain range of speed and load variation. Rolling bearings are produced by specialized factories, and are easy to purchase and maintain. However, compared with plain bearings, the rolling bearing has a large noise, the number of rolling elements is limited, the stiffness is varied, the vibration resistance is slightly poor, and the rotational speed is greatly limited. The rolling bearing is divided into a ball bearing and a cylindrical roller bearing according to the structure of the rolling element. Ceramic bearings mean that the bearing rolling elements are made of ceramic material, while the inner and outer rings are still made of bearing steel. The reason why the rolling element is selected is mainly because it has the following characteristics: one is light weight, the other is small thermal expansion coefficient, and the third is large elastic modulus. Therefore, it has the characteristics of small centrifugal force, small dynamic friction force, stable pre-tightening force, small elastic deformation and high rigidity.
(2) Reasonable arrangement of spindle bearings
1) Selection and configuration of spindle bearings
The machine tool spindle has two front and rear supports and three front, middle and rear supports. The former is more common. The configuration of the two-bearing spindle bearings, including the selection, combination and arrangement of the spindle bearings, is mainly based on the requirements of the spindle components involved in the rotational speed, load carrying capacity, rigidity and accuracy.
The following general principles should be followed when determining the two-bearing spindle bearing configuration:
1 Adaptation to the requirements of stiffness and load carrying capacity: The choice of the configuration of the spindle bearing should first meet the required stiffness and load carrying capacity.
2 Adaptation speed requirements: The maximum speed allowed by bearings of different models, specifications and accuracy grades is different. Under the same conditions, the point contact is higher than the line contact; the cylindrical roller is higher than the tapered roller.
3 Adaptation accuracy requirements: The thrust bearing configuration of the spindle assembly to withstand the axial force directly affects the axial position accuracy of the spindle.
2) Three-bearing spindle assembly
Due to the structural design of some machine tools, the length of the headstock is long, and the bearing span between the two bearings of the main shaft is much larger than the optimal span. In this case, the intermediate support should be considered to increase the rigidity of the spindle assembly. Vibration resistance.
3) Application design of spindle rolling bearing
1 spindle rolling bearing stiffness and bearing capacity
The stiffness of a rolling bearing is mainly determined by the contact stiffness between the rolling element and the raceway. The stiffness of a moving bearing is related to bearing type, load and preload, and is nonlinear as the load increases.
2 lubrication of the spindle bearing
Lubrication has a large impact on the performance of the spindle assembly and the life of the bearing. Unreasonable lubrication may cause heat to increase, reduce spindle work accuracy, and accelerate bearing wear. Lubricants for rolling bearings can be divided into two broad categories, namely grease lubricants and liquid lubricants.
3 spindle rolling bearing seal
The function of the rolling bearing seal device prevents the coolant, chips, dust, debris, etc. from entering the bearing, and keeps the lubricant in the bearing without leakage, thereby fully exerting the performance of the bearing and ensuring the service life of the bearing. The requirements for the seal of the spindle assembly are: suitable for the speed of the spindle, adapt to the working environment, and tight structure. The bearings of the spindle bearings are contact-contact and non-contact. The former can be divided into a radial seal ring seal box felt ring seal, generally suitable for low speed spindle. Non-contact seals can be divided into gap seals and curved seal gasket seals. To ensure the sealing effect, the radial clearance between the rotating part and the fixed part should be less than 0.2-0.3mm, and there should be oil return control at the seal. In case of oil leakage.
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