The performance of the machine tool depends to a large extent on the accuracy and dynamic performance of the spindle assembly, which is directly related to the installation and adjustment of the spindle bearing.

Rolling bearings for machine tools are precision components that are particularly sensitive to improper handling during installation and adjustment. If the installation method is not appropriate, it may damage the bearing and damage the accuracy of the bearing. If the adjustment is not appropriate, there will be phenomena such as poor precision, low stiffness, high temperature rise, high noise or poor vibration resistance. Therefore, precision bearings must be installed and adjusted with a strict set of operating procedures and appropriate mounting and adjustment tools.

First, preparation before installation

The preparations for precision bearings before installation are mainly as follows:

1, the cleaning of the bearing

In order to prevent corrosion of the bearing during transportation and storage, precision bearings are usually coated with a thin layer of rust and oil on the bearing surface. In order to prevent the occurrence of poor lubrication of the bearing due to the incompatibility between lubricating oil or grease and rust preventive oil, it is recommended that the precision bearing be carefully cleaned after opening the package. If conditions permit, the operator can wear it once. Plastic gloves, do not touch the bearings directly with your hands. Bearing cleaning fluid should use clean, high-purity gasoline, it is best to choose at least 90 gasoline, or even 120 white gasoline.

The cleaning of the bearings can be done in two steps. Prepare two clean containers, pour in enough cleaning fluid, and place the metal mesh mat in one of the containers. First, the bearing taken out from the package is placed in a container with a mesh mat, or the anti-rust oil film on the bearing surface is removed by a brush, and then the bearing is finally cleaned in the second container and cleaned while rotating. Note that the cleaning solution should be replaced at the appropriate time during the cleaning process to ensure the cleaning fluid is clean.

Sealed bearings are not suitable for cleaning and can be installed directly.

After cleaning, the bearings are air dried or naturally dried. After the cleaning liquid remaining in the bearing is completely air-dried, the subsequent operation is performed.

If the bearing is oil lubricated, it should be installed without rotating the bearing as much as possible. If the bearing is greased, follow-up grease filling and installation procedures are performed.

In order to facilitate the smooth installation of the bearing, it is recommended to apply a thin layer of lubricating oil to the mounting surface of the bearing.

2, the injection of grease

For grease-lubricated bearings, if the grease is improperly selected, or the amount of grease injected is not appropriate, even if the grease is injected incorrectly, it will affect the working condition of the bearing until it affects the service life of the bearing. Therefore, it is necessary to strictly establish the injection procedure for grease.

Prepare a syringe of the right size with the right grease. The grease is uniformly injected into the bearing raceway between the adjacent two rolling bodies by a syringe. Gently rotate the bearing by hand to distribute the grease evenly over the bearing raceway, the cage guide surface, the cage pocket surface, and the rolling element surface.

3. Inspection of the accuracy of bearing related parts

The mating shaft and bearing housing should be cleaned and the shaft, bearing housing and spacer should be free from defects such as burrs, burrs and bumps. Check that the dimensions of the shaft and housing match the corresponding dimensions of the bearing. Check the parallelism of the ends of the sleeve or spacer and the perpendicularity of the end face to the axis, generally controlled below 0.003mm.

Second, the installation of the bearing

According to the type of structure of the bearing, the condition of the shaft and the bearing housing, and the existing installation conditions, the corresponding bearing installation method is formulated. Regardless of the installation method, one principle is that the rolling elements of the bearing must never be used during the entire installation of the precision bearing.

The inner ring of the bearing and the shaft are generally an interference fit, and the outer ring and the bearing seat are mostly gap-fitted, and there is also a slight interference fit.

There are several common methods for mounting bearings on the spindle:

1, using the hand hammer and sleeve

This method is mostly used for the installation of small and medium-sized bearings that are not tightly fitted between the bearing ring and the journal or housing bore. When selecting a sleeve. Its size corresponds to the size of the bearing ring installed. The inner diameter of the sleeve for the inner ring should be slightly larger than the diameter of the main shaft. The outer diameter of the sleeve for the outer ring should be slightly smaller than the outer diameter of the bearing housing. Never hit the inner ring when hitting the outer ring of the bearing or the outer ring when installing the inner ring of the bearing, so that the hammering force is transmitted to the other ring through the rolling body and the raceway, resulting in damage to the raceway and the rolling element. If the inner and outer rings of the split type bearing are tightly coupled with the journal and the seat hole, the end face of the sleeve needs to be in contact with the end faces of the inner and outer rings at the same time, and the end face of the sleeve must be flat and perpendicular to the center line of the sleeve.

When a hand is used to strike a sleeve to mount a bearing, on the one hand, the bearing is not stressed smoothly, and on the other hand, the bearing has an impact force. Therefore, unless the conditions are limited, the method is generally not recommended when installing a precision bearing.

2, the use of pressure devices

The pressure devices used in this installation method mainly include a press, a press, a hydraulic clamp, and a hydraulic nut. The feature of this method is that the bearing is not directly subjected to knocking, so the bearing is not easily damaged. However, in this method, it is necessary to ensure that the pressure line coincides with the bearing shaft line to prevent the bearing from tilting.

3, using the hot method

When the interference of the bearing fit is large, it is difficult to fit the bearing by the method of the pressure device, and it is easy to damage the mating surface of the bearing. Therefore, if the inner ring of the bearing is heated and expanded, the bearing can be easily loaded into the main shaft.

At present, the inner ring of the bearing is often heated by a magnetic induction heater using a hot charging method. The heating temperature of the bearing should not exceed 120 °C. The specific heating temperature depends on the size of the bearing and the amount of interference. Since the outer ring of the bearing is also widened during the heating process of the bearing, the bearing is likely to have a gap in the axial direction after the bearing is cooled, and the bearing is in an interference fit state after the bearing is cooled, so when using the hot mounting method After the bearing is cooled, the nut and other suitable methods are used to eliminate the axial clearance between the bearing and the shoulder.

4. Inject pressure oil between the mating surfaces

When there is interference between the shaft and the bearing, the friction of the mating surface is large, and the mating surface may be damaged when the interference is large. If the pressure oil is injected between the mating surfaces, the two mating parts are slightly deformed, and the pressure oil penetrates into the mating surface to form a lubricating oil film, which can greatly reduce the friction between the mating surfaces. In this way, the two mating parts can be relatively slid with a small force. This method is suitable for both the installation of conical fittings and the fitting of cylindrical fittings.

Third, the installation of the angular contact ball bearing

Single row angular contact ball bearings can only bear axial loads in one direction. Therefore, during the installation or disassembly process, the bearing force direction must be paid attention to. For the assembled bearings, the position of the pre-tightening gap is different when back-to-back and face-to-face mounting. Therefore, pay attention to the pressing position of the bearing set.

In addition, in order to ensure the rotation accuracy of the spindle assembly, it is recommended to use the directional assembly installation method when installing the precision bearing.

Fourth, the fastening of the bearing

In order to fasten the inner ring of the bearing to the main shaft, a thread is generally designed on the shaft, and the bearing is positioned with a nut. The perpendicularity between the thread axis and the end face of the nut and the matching accuracy of the thread are very important. If the manufacturing precision of the nut is not high, the nut is inclined after locking, which tends to cause the spindle to bend and the bearing load is uneven, which directly affects Rotational accuracy, rigidity and load carrying capacity to the bearing. Therefore, in order to ensure the rotation accuracy of the shaft, the lock nut must be adjusted and tightened to prevent loosening. Corresponding to different preloads, the locking force exerted by the bearing lock nut should be determined according to the actual working conditions.

In order to eliminate or reduce the influence of the positioning resistance of the parts during the assembly process, it is recommended to first lock the nut with a torque of 2 to 3 times the normal locking force, then loosen the nut and finally lock with the normal locking force. Nuts are tightened.

The use of a lock nut requires machining of the thread on the main shaft. On the other hand, a high-precision nut is required to match, and the rotation imbalance which is inevitably caused by the lock nut is added. Therefore, on the spindles of some high-speed precision CNC machine tools or machining centers, the interference sleeve is used as the axial positioning component of the bearing on the spindle.

Most of the outer ring of the bearing is positioned in the bearing housing hole by pressing the end cap. If the fastening of the bolt is too large or the end cover is unevenly stressed, the bearing outer ring raceway is easily deformed. Therefore, the tightening force of the bolt must be controlled. In addition, in order to ensure the correct positioning of the outer ring of the bearing, it is also necessary to control the axial pre-tightening gap between the pressing end cap and the end face of the bearing housing. It is recommended that the axial pre-tightening clearance between the compression end cap and the end face of the bearing housing be controlled within the range of 0.01 to 0.04 mm.