Spindle sliding bearing

Sliding bearings are used in high-speed or low-speed precision and high-precision CNC machine tools because of their good vibration resistance, high rotation accuracy and smooth motion.

The main shaft sliding bearing can be divided into dynamic pressure bearing and hydrostatic bearing according to the way of producing oil film. According to different fluid media, it can be divided into liquid sliding bearing and pneumatic sliding bearing.

(1) Hydrodynamic bearing

When the dynamic pressure bearing is rotated by the main shaft at a certain rotation speed, lubricating oil flows from a large gap to a small gap to form a pressure oil film, and the main shaft is floated and loaded.

(2) Hydrostatic bearing

The hydrostatic bearing consists of a special oil supply system, a throttle and a bearing. Compared with dynamic pressure bearings, hydrostatic bearings have the following advantages: high bearing capacity, high rotation precision, oil film homogenization error, improved machining accuracy, good vibration resistance, stable operation, and can work at very low speeds. It can also work at extremely high speeds with low friction and long bearing life.

The main disadvantage of hydrostatic bearings is that they require a special set of oil supply equipment, which is complicated in manufacturing process and high in cost.

(3) Hydrostatic bearings using air as a medium are called hydrostatic bearings, also known as air bearing or air bearing, and their working principle is the same as that of hydrostatic shaft. Because the viscosity of air is much smaller than that of liquid, the friction is small, the power loss is small, it can work at very high speed or very low temperature, vibration, noise is very small, rotation precision is high, life is long, basically no maintenance is needed, High-speed, ultra-high-speed, high-precision CNC machine tool spindle assembly.

(4) Magnetic bearing is a new type of high-performance bearing with special properties that cannot be compared with various conventional bearings. The magnetic bearing does not contact the surface of the journal, there is no mechanical friction and wear, no lubrication and sealing, low temperature rise, small thermal deformation, high speed, long life and low energy consumption. The basic electromagnetic feedback control system of the magnetic bearing guarantees the spindle. Rotational accuracy, stiffness and resistance can be adjusted to eliminate rotor mass balance. Rotation characteristics can be obtained by sensors and control systems for condition monitoring and diagnosis. Magnetic bearings are mainly used in the spindle assembly of the machining center.
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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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What are the daily maintenance of bearings?

First, keep the bearings lubricated and clean

Before inspecting the bearing, the surface of the bearing should be cleaned before the parts around the NSK bearing are removed. Pay special attention to the fact that the oil seal is a very fragile part, so do not apply excessive force when inspecting and disassembling the bearing to avoid damage to the part. If you have been experiencing bad symptoms when inspecting the oil seal of the NSK bearing and its surrounding parts, be sure to replace it to avoid damage to the bearing caused by a bad oil seal.



Second, to ensure the quality of bearing lubricants

Many later found that the bearing life is too short, except for other factors, the quality of the lubricant is also directly affected. The inspection method for the bearing lubricant is: rubbing the point lubricant to rub between the two fingers, if there is any contaminant, it can be felt; or apply a thin layer of lubricant on the back of the hand, and then seal the light. Then it is to replace the lubricant of the NSK bearing.



Third, the working environment of the bearing

When inspecting bearings, never expose them to contaminants or moisture. If the work is interrupted, cover the machine with a piece of oil-paper plastic or similar material. The working environment of the bearing is also very important. Many imported bearings in the machine are not working because of the working environment, which leads to the end of the life of the imported bearings.


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