The Installation and Maintenance of Four Row Cylindrical Roller Bearings for Rolling Mill

Jun 16, 2023

1.Preface

The rolling mill four-row cylindrical roller bearing is a kind of bearing which is widely used in rolling mill system. The support roller of the hot rolling mill set adopts the type of four-row cylindrical roller bearing and thrust bearing. The four-row cylindrical roller bearing can bear large radial force, and the axial force is borne by a single thrust bearing. Compared with ordinary rolling bearings, the working environment of roll bearings is harsh, and the working load is large. Most of the damaged roll bearings in the early days are not due to their own quality defects, but in most cases are caused by incorrect installation and unnecessary maintenance. According to statistics, Among the reasons for bearing failure, poor bearing lubrication accounts for 35%, bearing pollution accounts for 15%, poor installation accounts for 20%, and fatigue failure of materials accounts for 30%. Therefore, the correct installation and maintenance of roll bearing is an important factor for the life of roll bearing.

2. Installation of four row cylindrical roller bearings

2.1 Preparation before installation

(1) The installation environment should be a clean and dry working place, all tools should be ready and kept clean, and the installation should not be near the welding site to prevent debris or dust from entering the bearing. Before installation, the instructions or drawings should be carefully checked, and the installation sequence and working steps of bearing components should be clear, so as to save the assembly time and reduce bearing pollution in the air.

(2) Before installation, all parts, including roll neck and bearing box, must be inspected on the surface, and the specifications, status, precision and tolerance of the parts must be inspected to determine whether they meet the standards required by the design. If the precision of the parts combined with the bearing fails to meet the design requirements, the precision of the bearing will be changed.

(3) For the area combined with the bearing surface, including roll neck, each hole and its corner and burr need to be properly removed. Otherwise, it will affect the bearing installation and scratch the bearing surface, and then debris falls into the bearing, directly causing the early damage of the bearing.

(4) After the new bearing is unpacked, it should check whether its assembly size meets the installation requirements, and check whether the appearance has rust, bump, burr and other defects, as well as whether the ring number is correct.  If there is any objection, it should contact the supplier or return the product. 

2.2 Install the roller ring and inner ring

The roller ring and the inner ring are generally combined by the roll factory for debugging, in which two inner rings are installed in each four row cylindrical roller bearing, and the inner ring and the roller diameter are combined by interference. Before the combination debugging, the inner ring needs to undergo necessary temperature treatment, and the inner ring can be installed on the roller diameter after expansion to the required size, and then the outer diameter of the inner ring is grinded.

Before installation, the actual size of bearing inner diameter and roll diameter should be reviewed first. In order to confirm whether the two sizes meet the interference requirements of the design, after heating is completed, the bearing inner diameter should be checked quickly to see whether it can meet the installation requirements. Otherwise, the inner ring may be installed to half and hold the shaft, unable to push the inner ring to the required position, thus wasting the inner ring resources. In four-row cylindrical roller bearings, the inner ring is combined with the roll neck by interference, and in the specific installation process, the inner ring must be heated, so that the temperature rises to about 100℃, but not more than 150℃, within 2 hours, otherwise the inner ring material organization may be changed, the inner ring can not shrink to the original size after cooling. As a result, the interference of the fit can not meet the design requirements. Temperature rise, can be through the oil tank or induction temperature increase, never through the way of open flame heating treatment.

In the process of heating by the oil tank method, its inner diameter expansion increment must be calculated according to the following formula:

In the formula:

△d: represents the increase of the inner diameter of the inner ring (mm) after the temperature rises;

△t: is the difference between the liquid oil temperature and the room temperature (℃), assuming the room temperature is 20℃;

D: represents the inner diameter of the initial inner ring (mm).

In the process of installing the double inner ring, the inner ring needs to be cooled along the direction of the bearing so that the inner ring and its end face are closely combined together, so as to ensure that there is no gap, and through the feeler ruler expansion test. (See Figure 1 for details)

3) Installation of outer ring and rollers

The outer ring and the inner hole of the bearing seat are generally transitional. Firstly, the roundness of the bearing seat should be checked, and the bearing seat should be thoroughly cleaned before measurement. The inner diameter micrometer should be used to measure the four positions of the inner hole of the bearing seat, and each position should be measured twice, 90° apart, to ensure that the roundness meets the requirements of the drawing. The same set of four columns of cylindrical roller bearings, the compound size of the outer ring and roller components is matched out, so as far as possible do not mix, in order to ensure the original processing accuracy of bearings. Install the skeleton seal, water seal and O-ring on the end cover of the bearing seat near the roll body, and then install the end cover on the bearing seat. Install the side ring, outer ring and its accessories, retainer ring, etc., in accordance with the order. The thread hole on the holding frame is used for lifting, and the spare mounting hole on the outer ring can be used to lift the outer ring and its accessories and vertically put into the bearing box. The outer ring, roller and cage can be slowly knocked into the bearing with a copper hammer. In addition, in the process of installing the outer ring, it is necessary to always pay attention to whether there is a mark on the surface and cage surface. If there is, it is necessary to maintain the identity of the mark in the process of installation; For the four row cylindrical roller bearings with movable gears, the accessories must be installed in the order marked on the end face of the ring, and do not be mixed (see Figure 2 for details).

If the surface of the parts do not have any mark, or only one of them has, then in order to prevent, it must be installed according to the order of the initial state of the disassembly of the bearing packaging, that is to say, it is not wrong to install a set of bearing parts and outer ring raceway, otherwise the bearing roller will be damaged because it can not get uniform force.

The outer ring end face is divided into four equal sections and marked with four load zones (1, 2, 3, and 4) (see Figure 3 for details). During the first installation, load zone 1 should be used. After every certain operating cycle, the bearing should be thoroughly checked, cleaned and checked, and the load zone should be replaced. To this end, the service life of each part of the bearing can be extended to the maximum extent, and the problem of premature damage and falling off in some areas of the raceway can be effectively avoided. When the bearing is removed, the fastening device used to locate the bearing seat to prevent its axial movement is removed, and the internal bearing of the bearing seat can be removed as a whole. In the process of roll replacement, the bearing seat can be installed directly to the inner ring roll already set. (See Figure 1, Figure 2, Figure 3)

3. The lubrication of four rows of cylindrical roller bearings

In the actual use of bearings, in order to ensure the normal operation of bearings to the maximum extent, complete lubrication is needed.

First, avoid or minimize the contact between bearing and rolling body, raceway and cage, so as to reduce the loss caused by friction;

Secondly, the oil film is molded on the friction surface. After the oil film is molded, the contact area of each part can be effectively expanded, so as to reduce the tensile stress of the contact surface to a certain extent, and thus realize the service time of extending the contact surface.

Third, after the use of lubricant, can play a certain degree of corrosion prevention effect.

Fourth, the lubricant can achieve heat dissipation, and remove the particles that occur in the use of bearings.

Fifth, the lubricant can improve the sealing performance of the appliance, so as to avoid the pollution of external particles.

Sixth, it can reduce vibration and noise to a large extent.

The bearing of the support roll of normal aluminum hot mill is lubricated by oil and gas. Oil and gas lubrication is a newly developed lubrication method in recent years. It is a process of mixing lubricating oil and compressed air supplied separately intermittently and forming a flock-like oil and gas mixing flow. Because oil and gas lubrication has no oil and thin oil spill, less pollution, low oil consumption and good cooling effect, it can effectively reduce the working temperature of bearings. Prolong the service life of bearings and other advantages. It is widely used in roll bearing of heavy duty rolling mill.

4. Four row cylindrical roller bearing maintenance

The service life of bearings largely depends on the maintenance of bearings. Bearings must be removed from the roll regularly for inspection, to discover the problem load area as early as possible in order to prevent it from further expanding, and thus to ensure the longest running time of bearings to the maximum extent.

Build bearing documents, clean and test bearing parts on time, observe the damage of running surface and rolling surface of raceway, and replace them in time if they exceed the specified standards. In the process of using bearings, the original bearing parts must be used first, and other accessories can be selected and used only after secondary measurement.

Change the bearing load area, such as the initial use of load area 1, the next maintenance and cleaning can use the relative direction of the load area 3, then load area 2, load area 4 and so on, so that in the bearing operation process can automatically correct the deformation of the bearing outer ring, maintain the load area stress Angle, reduce fatigue damage stress, make full use of the use value of each surface, Effectively prolong the service life of bearings.

Regularly check and adjust the side slide of the bearing seat of the support roll to ensure that the axis of each roll is parallel. In addition, it is necessary to replace the connecting shaft of the transmission system on time, otherwise the gap will be too large and lead to additional axial force, and eventually lead to bearing damage.

5. Preservation of rolling mill bearings

As a bearing component with high tightness, its preservation environment has a very high demand.

First, storage temperature and humidity. First of all, it is necessary to maintain the air in the warehouse is highly fluid, and the temperature is maintained at more than 25℃. Secondly, too much humidity will cause rust and corrosion of bearings, so the humidity of the warehouse needs to be maintained below 70%.

Second, the placement of the warehouse. Bearings need to be kept separately, when placed in the same place with other goods, other goods can not be chemical products.

Third, bearing placement. Bearings must be kept above 3cm and flat with the ground when placed, and keep a certain distance from the radiator.

Fourth, regular inspection. According to the corrosion prevention specifications of bearing goods, inspection should be carried out every once in a while. If rust is detected in the packaging, it is necessary to repackage in time.

6. Conclusion

Practice has proved that if the installation and maintenance of the four-row cylindrical roller bearings are proper, the service life of the bearings will be greatly extended. The average service life of the four-row cylindrical roller bearings is 15000 hours, and the longest service life has reached more than 20000 hours, far exceeding the expected life of the manufacturer of 8000 ~ 12000 hours. It reduces the use of new bearing spare parts, greatly reduces the production cost of enterprises, reduces the frequency of enterprise shutdown to replace bearings, improves production efficiency and creates good earnings for enterprises.