1. Preparation before installation
Precision spindle bearings must be unpacked immediately before installation.
Precision spindle bearings need to do the following preparations before installation:
(1) Bearing cleaning:
To prevent corrosion of precision bearings during transportation and storage, precision bearings are usually coated with a thin layer of anti-rust oil on the surface of the bearings when the finished product is packaged. In order to prevent poor bearing lubrication due to incompatibility between bearing lubricating oil or grease and anti-rust oil, it is recommended that precision bearings be carefully cleaned after opening the package. If conditions permit, the operator should wear a disposable Gloves, do not touch the bearings directly with your hands.
1. Clean/high-purity gasoline should be selected as the bearing cleaning fluid, preferably at least 90# gasoline, or even 120# white gasoline.
2. The cleaning of the bearing is completed in two steps: prepare 2 clean containers, pour enough cleaning liquid, and place a metal mesh pad in one of the containers, first place the bearing in the packaging box into the container with the metal mesh pad Soak in medium, or use a brush to remove the anti-rust oil film on the surface of the bearing, and then perform final cleaning on the bearing in the second container, cleaning while rotating. Note: During the cleaning process, the cleaning solution should be replaced in time to ensure that the cleaning solution is clean.
There is no need to clean the bearings with seals, and they can be installed and used directly.
3. After cleaning, the bearing should be air-dried or dried naturally. Do follow-up work after the residual cleaning fluid on the bearing is completely dried.
4. If the precision bearing is lubricated with oil, try to install it without rotating the bearing. If the bearing is grease lubricated, proceed with the subsequent greasing and mounting procedure.
5. In order to facilitate installation, it is recommended to apply a thin layer of lubricating oil on the surface of the outer diameter of the precision bearing.
(2) Injection of bearing grease:
For grease-lubricated bearings, if the grease is selected improperly, or the amount of grease injected is not appropriate, or even the method of injecting grease is incorrect, it will affect the working state of the bearing and even affect the service life of the bearing. Therefore, it is necessary to strictly formulate the injection procedures of grease.
1. Choose the right grease and prepare a syringe of the right size.
2. Fill the syringe with grease according to the amount of grease injected.
3. Use a syringe to evenly inject grease into the bearing raceway from between two adjacent rolling elements. For the grease of cylindrical roller bearings, 80% of the amount of grease injection should be injected into the raceway of the inner ring, the rolling surface of the roller and the end surface, and the pocket hole surface of the cage, and the remaining 20% should be injected into the raceway surface of the outer ring in the bearing housing. superior.
4. Gently rotate the bearing by hand, so that the grease is evenly distributed on the raceway of the bearing, the guide surface of the cage, the surface of the pocket hole of the cage and the surface of the rolling body.
2. Accuracy inspection of bearing related parts
1. The mating shaft and bearing seat should be cleaned and ensure that there are no obvious defects such as burrs, burrs and bumps on the shaft, bearing seat and spacer.
2. Check whether the size of the shaft and bearing seat matches the relevant size of the matching bearing.
3. Check whether the highest jumping point is marked at the shaft and bearing housing where the bearing fits.
4. Check the parallelism of the two ends of the sleeve or spacer and the perpendicularity of the end to the axis line. Generally, it is required to be controlled below 0.003mm.
3. Bearing installation
According to the structure type of the precision bearing, the conditions for matching with the shaft and the bearing seat, and the existing installation conditions, formulate the corresponding bearing installation method. No matter what method is used, a prerequisite is that during the entire installation process of the precision bearing, the rolling elements of the bearing must not be stressed.
The fit between the inner ring of the bearing and the shaft is generally an interference fit, while the outer ring and the bearing seat are mostly a clearance fit, and there is also a slight interference fit.
The installation methods of precision bearings are mainly as follows:
1. Using hammer and sleeve method
This method is mostly used for the installation of small and medium-sized bearings where the fit between the bearing ring and the journal or the housing hole is not too tight. When selecting a sleeve, its size corresponds to the size of the bearing ring to be assembled. The inner diameter of the sleeve used to install the inner ring is slightly larger than the diameter of the spindle shaft, and the outer diameter of the sleeve used to install the outer ring is slightly smaller than the bore diameter of the bearing housing. It is absolutely not allowed to hit the outer ring of the bearing when installing the inner ring of the bearing or the inner ring when installing the outer ring, so that the hammering force will be transmitted to the other ring through the rolling body and the raceway, resulting in damage to the raceway and rolling body . If the fit of the inner and outer rings of the separable bearing and the shaft journal and seat hole are tight, 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 using a hand hammer to hit the sleeve to install the bearing, on the one hand, the force on the bearing will not be stable, and on the other hand, it will produce an impact on the bearing. Therefore, unless the conditions are limited, this method is generally not recommended when installing precision bearings.
2. Using pressure device
The pressure devices mainly include presses, presses, hydraulic fixtures and hydraulic nuts. The characteristic of this installation method is that the bearing will not be directly hit, so the bearing will generally not be damaged. However, this installation method must ensure that the pressure line coincides with the axis of the bearing to prevent the bearing from tilting.
3. Use hot loading method
When the interference of the bearing fit is relatively large, it is difficult to install the bearing by means of a 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 will be easier to fit into the main shaft.
At present, the magnetic induction heater is often used to heat the inner ring of the bearing when the thermal charging method is adopted.
The heating temperature of precision bearings should not exceed 120°C. The specific heating temperature depends on the size and interference of the bearing.
Since the size of the outer ring of the bearing is also widening during the heating process of the bearing, it is easy to produce a gap with the shaft shoulder in the axial direction after the bearing is cooled, and the bearing is in an interference fit state with the main shaft after cooling, so the thermal heating method When the bearing is cooled, use nuts or other suitable methods to eliminate the axial clearance between the bearing and the shaft shoulder.
4. The method of injecting pressure oil between the mating surfaces
When there is interference between the shaft and the bearing, the friction of the mating surface is very large. When the interference is large, the mating surface may be damaged. 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 surfaces to form a layer of 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 relatively small force. This method is not only suitable for the installation of conical surface fittings, but also suitable for the assembly and disassembly of cylindrical surface fittings.
Fourth, the installation of paired angular contact ball bearings
Single row angular contact ball bearings can only bear axial load in one direction. Therefore, during installation and disassembly, attention must be paid to the direction of bearing force to avoid damage to precision bearing assets. Schematic diagram of the force direction of angular contact balls with different structures:
Illustration under page 58
Force direction of angular contact ball bearings
For paired bearings, the position of the preload gap is different when they are installed back-to-back and face-to-face, so pay attention to the compression position of the paired bearings. As shown below:
illustration on page 59
Preload clearance of matched bearings
In order to ensure the rotation accuracy of the main shaft assembly, it is recommended to adopt the installation method of directional assembly as much as possible when installing the precision bearing. Precision angular contact ball bearings are marked with the highest points (△ or ○) of the radial runout of the inner ring and outer ring on the end faces of the inner ring and outer ring respectively. When installing the bearing, firstly align the highest point of radial runout of the inner ring and the highest point of radial runout of the outer ring of the same group of bearings along the axial direction, and then, when the bearing is installed on the main shaft or the bearing seat, adjust the bearing group The axial position, so that the highest point of the radial runout of the inner ring of the bearing and the highest point of the radial runout of the spindle journal are in a symmetrical state in the radial position. Similarly, the highest point of the radial runout of the outer ring of the bearing and the highest point of the radial runout of the bearing seat are in a symmetrical state in the radial position, and finally adjust the preload of the paired bearing according to the design requirements.
Mounting of back-to-back paired bearings
1. Adjust the position of the highest point of radial runout of the inner ring of the bearing, and install it into the predetermined position of the main shaft.
2. Tighten the lock nut and apply the preload.
3. Adjust the axial position of the outer ring of the bearing, install the main shaft assembly into the bearing seat, and then perform operations such as installing and adjusting the end cover.
Mounting of face-to-face paired bearings
1. Adjust the position of the highest point of the radial runout of the outer ring of the bearing, and install it into the predetermined position of the bearing seat.
2. Install the end cap to preload the bearing.
3. Install the main shaft into the inner ring of the bearing, tighten the nut, and proceed to the follow-up operation.
5. Fastening of precision bearings
Tightening of the inner ring
In order to fasten the inner ring of the bearing on the main shaft, a thread is generally designed on the shaft, and a nut is used to position the bearing. The verticality between the thread axis and the end surface of the nut and the matching accuracy of the thread are very important. If the manufacturing accuracy of the nut is not high, the nut will tilt after locking, which will easily cause the main shaft to bend, and the bearing will not be preloaded uniformly. It affects the rotation accuracy, rigidity and load carrying capacity of the bearing. Therefore, in order to ensure the rotation accuracy of the shaft, the nut must be adjusted and tightened to prevent loosening.
Corresponding to different preloads, the locking force applied by the bearing lock nut should be determined according to the actual working conditions and through experiments.
In order to eliminate or reduce the influence of part positioning resistance during the assembly process, it is recommended that when locking the nut, first lock the nut with a torque of 2 to 3 times the normal locking force, then loosen the nut, and finally lock it with the normal locking force Tighten nuts and tighten.
To use lock nuts, on the one hand, it is necessary to process threads on the spindle, and on the other hand, it also requires high-precision nuts to match, plus the inevitable rotation imbalance of lock nuts. Therefore, on the main shaft of a high-precision numerical control machine tool or a machining center machine tool, an interference sleeve is used as an axial positioning element of the bearing on the main shaft.
Tightening of the outer ring
The outer ring of the bearing is positioned in the bearing housing hole with bolts by pressing the end cover. If the tightening force of the bolt is too large or the force on the end cover is uneven, the raceway of the outer ring of the bearing will be easily deformed. Therefore, the tightening force of the bolt must be controlled. In addition, in order to ensure the correct positioning of the bearing outer ring, it is necessary to control the axial preload clearance between the compression end cover and the end face of the bearing seat.
It is recommended that the axial preload gap between the compression end cover and the bearing seat be controlled within the range of 0.01-0.04mm.
6. Installation of cylindrical roller bearings with tapered bore
The radial clearance adjustment of tapered bore cylindrical roller bearings is controlled by the axial movement of the inner ring of the bearing on the tapered shaft. The methods mainly include empirical method, calculation method, direct control method of measuring instruments, etc. The most suitable method can be selected for installation adjustment.
1. Empirical method
According to one’s own assembly experience, the assembly adjustment of the spindle bearing is carried out by hand feeling and necessary inspection methods. For cylindrical roller bearings with tapered bore, firstly install the bearing inner ring, cage and roller assembly on the main shaft, tighten the lock nut so that the tapered hole of the bearing is closely attached to the tapered journal, and then install the main shaft assembly Insert it into the box hole and continue to adjust the nut so that the radial clearance of the bearing continues to decrease until interference occurs. Whether the clearance or interference of the bearing is appropriate is judged by the feel of the assembler when turning the main shaft. If the interference is large, it will feel more difficult when turning the main shaft; if the main shaft is turned too briskly, it means that the bearing clearance is large. Therefore, the key to the empirical method is to master the feel when turning the spindle.
The following method can also be used to judge whether there is a gap in the spindle bearing during the adjustment process: fix the dial indicator frame on the box, and the contacts of the gauge are pressed on the positioning surface of the front end of the spindle. Lift up the head of the main shaft with force. If the needle jumps, it means that there is radial clearance in the bearing. You can judge the size of the bearing clearance according to the jumping amount of the needle.
2. Calculation method
The inner bore of cylindrical roller bearings for machine tool spindles generally has a taper of 1:12. When the bearing is installed on the tapered shaft and moves along the axial direction, the tapered hole of the bearing will be expanded to varying degrees. The amount of expansion in this diameter direction is equivalent to the reduction in the internal clearance of the bearing. The reduction of bearing clearance is not only related to the amount of axial movement, but also related to the surface roughness of the journal, the wall thickness of the inner ring and the bore diameter of the shaft.
3. Instrument direct control method
The radial clearance of the bearing is controlled by using a special cylindrical roller bearing clearance measuring instrument to measure the diameter of the outer circle of the bearing rolling body and the diameter of the raceway of the outer ring of the bearing after it is installed in the box.