1、 Preface

The four row cylindrical roller bearing used in rolling mills is a widely used bearing in the rolling mill roll system. The support roller of the hot rolling mill unit of Changshu Aluminum Industry Co., Ltd. adopts a combination of four row cylindrical roller bearing and thrust bearing. The four row cylindrical roller bearing can withstand large radial forces, and the axial force is borne by a separate thrust bearing. Compared with ordinary rolling bearings, the working environment of roller bearings is relatively harsh and the working load is also relatively large. Most of the roller bearings that were damaged earlier are not necessarily due to their own quality defects. In most cases, they are caused by incorrect installation methods and lack of necessary maintenance. According to statistics, poor bearing lubrication accounts for 35% of the reasons for bearing failure, while bearing pollution accounts for 15%, Poor installation accounts for 20%, and material fatigue failure accounts for 30%. Therefore, the correct installation and maintenance of roller bearings are important factors related to the lifespan of roller bearings.

2、 Installation of four row cylindrical roller bearings

（1） Preparation before installation

(1) The installation site should choose a clean and dry workplace, and all tools should be prepared and kept clean. The installation should not be near the welding site to prevent debris or dust from entering the bearings. Before installation, it is necessary to carefully refer to the instructions or drawings, and ensure that the installation sequence and work steps of the bearing components are clear and clear, thereby saving assembly time and reducing bearing pollution in the air;

(2) Before carrying out installation work, it is necessary to conduct surface inspection on various accessories, including roller necks, bearing boxes, etc., to inspect the specifications, status, precision, and tolerances of the accessories and determine whether they meet the standards required by the design. If the accuracy of the parts combined with bearings does not meet the design requirements, it will change the original accuracy of the bearings;

(3) For the area that combines with the surface of the bearing, including the roller neck, various holes, their edges, and burrs, appropriate cleaning is required. Otherwise, it will affect the installation of the bearing and scratch the bearing surface, causing debris to fall into the bearing interior, directly causing early damage to the bearing;

(4) After opening the packaging of the new bearing, the assembly dimensions should be checked to ensure they meet the installation requirements. At the same time, the appearance should be checked for defects such as rust, bumps, burrs, and the ring number should be correct. If there are any objections, the supplier should be contacted or returned.

（2） Install the roller ring and inner ring

The roller ring and inner ring are generally assembled and debugged by the roller processing factory. Two inner rings are installed in each four row cylindrical roller bearing, and the inner ring and roller diameter are combined through interference. Before assembly and debugging, the inner ring needs to be subjected to necessary temperature rise treatment. After expanding to the required size, it can be installed on the roller diameter, and then the outer diameter of the inner ring needs to be ground.

Before installation, first recheck the actual dimensions of the bearing inner diameter and roller diameter to confirm whether the two dimensions meet the interference requirements during design; After heating is completed, quickly check the inner diameter size of the bearing to see if it meets the installation requirements. Otherwise, the inner ring may be installed halfway 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 roller neck through interference. During the specific installation process, the inner ring must be heated to around 100 ℃, but not more than 150 ℃ for less than 2 hours. Otherwise, the material structure of the inner ring may change, and the inner ring cannot shrink to its original size after cooling, resulting in the interference amount not meeting the design requirements. Heating up can be achieved through oil tanks or induction, and heating treatment cannot be carried out through open flames.

During the heating process using the oil tank method, the inner diameter amplification amount must be calculated according to the following formula:

In the formula:

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

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

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

During the installation process of the double inner ring, the inner ring needs to be cooled in the direction of the bearing to ensure a close connection between the inner ring and its end face, ensuring that there is no gap, and tested using a feeler gauge. (See Figure 1 for details)

（3） Installation of outer ring and rolling element

The outer ring and the inner hole of the bearing seat are generally in a transitional fit. Firstly, the roundness of the bearing seat should be checked. Before measurement, the bearing seat should be thoroughly cleaned. Use an inner micrometer to measure at four positions of the bearing seat inner hole, with each position spaced 90 ° apart twice to ensure that the roundness meets the requirements of the drawing. The compound dimensions of the outer ring and roller components of the same set of four row cylindrical roller bearings are matched, so try not to mix them up as much as possible to ensure the original machining accuracy of the bearings. Install the skeleton seal, water seal, and O-ring on the end cover on the side near the roller body of the bearing seat, and then install the end cover on the bearing seat. Install the edge ring, outer ring, and its accessories, retaining ring, etc. in order. The threaded holes on the cage are used for lifting, and spare installation holes on the outer ring can be used to lift the outer ring and its accessories, and vertically place them in the bearing box. For small bearings, use a copper hammer to lift the outer ring Slowly tap the roller and cage into the bearing. In addition, during the installation process of the outer ring, it is necessary to always pay attention to whether there are signs on its surface and the surface of the cage. If there are signs, it is necessary to maintain the identity of the signs during the installation process; For four row cylindrical roller bearings with movable gears, all accessories must be installed in the order marked on the end face of the ring, and do not mix them (see Figure 2 for details).

If there are no markings on the surface of the accessories, or only one of them is present, in order to prevent unforeseen circumstances, installation must be carried out according to the initial state of disassembly and assembly of the bearing packaging. That is to say, a set of bearing accessories and outer ring raceways cannot be installed by mistake, otherwise the rollers of the bearing will be damaged due to the inability to receive uniform force.

The outer ring end face is divided into four equal parts and marked with four load zones 1, 2, 3, and 4 (see Figure 3 for details). During the first installation, load zone 1 is used. After each certain service cycle, the bearing should be thoroughly inspected, cleaned, and inspected, and the load zone should be replaced. To achieve this, the service life of each accessory part in the bearing can be extended to the maximum extent, while also effectively avoiding the problem of premature damage and detachment in some areas of the raceway. After removing the fastening device used to locate the bearing seat and prevent its axial movement when disassembling the bearing, the bearing seat and internal bearings can be removed as a whole. During the process of replacing the roller, the bearing seat can be directly installed on the already set inner ring roller. (See Figures 1, 2, and 3)

3、 Lubrication of four row cylindrical roller bearings

In the actual use process of bearings, in order to ensure the normal operation of the bearings to the greatest extent, it is necessary to carry out complete lubrication treatment;

Firstly, to avoid or minimize contact between bearings and rolling elements, raceways, and cages, thereby reducing losses caused by friction;

Secondly, shaping the oil film on the friction surface can effectively expand the contact area of each component after the oil film is molded, thereby reducing the tensile stress on the contact surface to a certain extent and extending the service life of the contact surface;

Thirdly, after using lubricants, it can have a certain degree of anti rust effect;

Fourthly, lubricants can achieve heat dissipation and remove particles that appear during the use of bearings;

Fifth, lubricants can improve the sealing performance of appliances, thereby avoiding pollution from external particles;

Sixth, it can greatly reduce vibration and noise.

The support roller bearings of the Chang Al hot rolling mill unit are lubricated by oil and gas. Oil gas lubrication is a newly developed lubrication method in recent years. It involves mixing separately intermittent lubricating oil and continuously supplied compressed air to form a flocculent flow of oil gas mixture for lubrication. Due to the advantages of oil gas lubrication, such as no oil and thin oil overflow, less pollution, low oil consumption, good cooling effect, effective reduction of bearing operating temperature, and extension of bearing service life. It is widely used in heavy load rolling mill roller bearings.

4、 Maintenance of Four Row Cylindrical Roller Bearings

The service life of bearings largely depends on their maintenance and upkeep. The bearing must be regularly removed from the roller for inspection, in order to identify the problem load area as soon as possible in order to prevent it from further expanding and thus ensure the maximum operating time of the bearing to the greatest extent possible.

Build bearing documents, clean and inspect bearing components on time, observe the damage to the running surface of the raceway and the surface of the rolling body, and replace them in a timely manner if they exceed the specified standards. During the use of bearings, original bearing components must be used first, and other accessories must undergo secondary measurements before they can be selected for use.

Change the bearing load zone, such as using load zone 1 at the beginning, using load zone 3 in the opposite direction after the next maintenance and cleaning, followed by load zone 2, load zone 4, and so on. This can automatically correct the deformation of the outer ring of the bearing during operation, maintain the force angle of the load zone, reduce fatigue failure stress, fully utilize the value of each surface, and effectively extend the service life of the bearing.

Regularly inspect and adjust the side sliding plates of the support roller bearing seat to ensure that the axes of each roller are parallel. In addition, it is also necessary to replace the connecting shaft of the transmission system on time, otherwise there may be too large a gap that leads to additional axial force, ultimately leading to bearing damage.

5、 Preservation of Rolling Mill Bearings

As a bearing component with high tightness, its storage environment has a very high demand:

Firstly, the temperature and humidity of the warehouse. Firstly, it is necessary to maintain that the air in the warehouse has high fluidity and the temperature is maintained above or below 25 ℃; Secondly, excessive humidity can cause rusting and corrosion of bearings, so the humidity in the warehouse needs to be maintained below 70%;

Secondly, the placement of the warehouse. Bearings need to be stored separately, and when placed in the same place as other goods, other goods cannot be chemicals;

Thirdly, the placement of bearings. When placing bearings, they must be kept at least 3cm above the ground and placed flat, with a certain distance from the radiator;

Fourth, conduct regular inspections. According to the rust prevention regulations for bearing goods, it is necessary to conduct inspections at regular intervals. If rust is detected in the packaging, it is necessary to repackage it in a timely manner.

6、 Conclusion

Practice has proven that if the installation and maintenance of four row cylindrical roller bearings are appropriate, the service life of the bearings will be greatly extended. The support roller of the hot rolling mill unit of Changshu Aluminum Industry Co., Ltd. currently uses four row cylindrical roller bearings with an average service life of 15000 hours, with the longest reaching over 20000 hours, far exceeding the manufacturer's expected life of 8000 to 12000 hours, reducing the use of new spare parts for bearings and greatly reducing enterprise production costs, Reduced the frequency of enterprise downtime to replace bearings, improved production efficiency, and created good profits for the enterprise.