You may be unfamiliar with rolling mill bearings, so you don't know about the faults of rolling mill bearings. As a professional one-stop service website for bearings, Zhonghua bearing network will share with you how to analyze the faults of rolling mill bearings when rolling mill bearings fail, so as to make targeted methods to modify them. Through the understanding of rolling mill bearings, Inspection and maintenance are very important for the use of rolling mill bearings.

What is rolling mill bearing?

Rolling mill bearings are used in the rolling industry, i.e. rolling of non-ferrous metals, ferrous metals and non-metallic products. It is used for the bearing at the roll diameter of calendering roll system and on the drum. Generally, four row cylindrical roller bearings are used to bear radial load, while thrust roller or thrust ball bearings and centripetal angular contact ball or centripetal roller bearings bear axial load. At present, oil-gas lubrication or oil mist lubrication and grease are mostly used for lubrication and cooling.

Structural features of rolling mill bearings

Rolling mill bearings usually use cylindrical roller bearings to bear radial load, deep groove ball bearings or angular contact ball bearings, or tapered roller bearings with radial design or thrust design to bear axial load.

Four row cylindrical roller bearings and six row cylindrical roller bearings are almost all used for roll neck, drum and rolling press of steel rolling frame. Compared with other roller bearings, these bearings have low friction. Because these bearings are usually installed on the roll neck with interference fit, they are especially suitable for the application of rolling mill with high rolling speed. The low cross-section of these bearings allows the use of a relatively large roll neck diameter compared to the roll diameter. Because many rollers can be installed, its radial load capacity is very high.

Multi row cylindrical roller bearings can only bear radial load. Therefore, these bearings are installed with deep groove ball bearings or angular contact ball bearings, or tapered roller bearings of radial design or thrust design, which bear axial load. The four row and six row tapered roller bearings are of separate design, that is, the bearing ring with integral flange and roller and cage components can be installed separately from the separate bearing ring, or all bearing components can be installed separately. This simplifies the installation, maintenance and inspection of bearings to a considerable extent. The bearing can bear a certain limit of axial displacement of the shaft relative to the bearing seat. Four row cylindrical roller bearings have a cylindrical hole, and some sizes of bearings can also be supplied with conical holes. The bearing with tapered holes can be adjusted during installation to obtain certain radial internal clearance or predefined load.

Fault analysis of rolling mill bearing

The service life and reliability of the bearing are closely related to the installation and design of the bearing. Improper design and manufacture of the bearing seat will lead to uneven bearing force and reduce the service life of the bearing. The bearing seat should be self-aligning to avoid eccentric load on the bearing due to roll burning, deflection and deformation. Due to the particularity of its process, all the rolling mills of MPM continuous rolling mill in hot rolled seamless steel pipe plant are installed obliquely at 45 ℃. Under the working conditions of high temperature, roll cooling water spray and large impact load, the service life of imported bearings is generally about 2 years. If domestic bearings are used, the service life of bearings will be further reduced, and the faults will be concentrated, which will seriously affect the production. According to statistical analysis, the bearing failure is mainly caused by the following reasons: ① the field assembly accuracy and installation process of the bearing; ② Unreasonable assembly of bearing seals; ③ Poor working conditions and poor lubrication.

1. Bearing design calculation

The service life of the bearing is inseparable from the reasonable design of the bearing. The equivalent load of the bearing must be calculated for the selection of the bearing. Bearing load can be roughly divided into radial load, axial load and composite load according to the direction; According to the different properties in the process of load action, it can be divided into three forms: pulse, constant and alternating. The bearing rated load is the fixed value of the bearing, which depends on the characteristics of the material used. The static rated load is the maximum allowable static load that the rod end can bear on its weakest section without reaching permanent deformation. The ideal static load rating is based on the tensile stress test of a large number of rod ends with appropriate materials and appropriate ambient temperature. The service value is 80% of the test results, so it includes a safety factor of 1.25. Dynamic load rating is used to determine the service life of rod end plain bearings under dynamic load conditions. Dynamic loads include loads under swing, rotation and axial tilt.

2. Bearing assembly technology

The accuracy, assembly clearance and other technical characteristics of bearings directly affect the service life and reliability of bearings. Dimensional accuracy refers to the items necessary for installing the bearing on the shaft or bearing housing (box), which refers to the inner diameter, outer diameter, width, assembly width, chamfer size and taper tolerance or allowable value. Shape accuracy refers to the allowable values of inner diameter variation, average inner diameter variation, outer diameter variation and average outer diameter variation. Rotation accuracy refers to the deflection during specified rotation. It refers to the allowable values of radial deflection and axial deflection of inner ring and outer ring, side deflection of inner ring and outer diameter deflection of outer ring. The convexity of the bearing inner ring, outer ring and rolling element are not in the same circumference, resulting in uneven stress at both ends of the rolling element and local peeling; The main reason for the breakage of the small retaining edge of the inner ring is that the width of the over travel groove is too large; The depth machining of over pass groove is too deep, and there is a stress concentration area. It is necessary to optimize the machining tolerance of parts and control the machining and assembly quality. The radial clearance of rolling bearing refers to the movement amount of one ring fixed and the other ring moving from one extreme position to another in the direction perpendicular to the bearing axis. Whether the selection of bearing clearance is correct or not has a great impact on the mechanical operation accuracy, bearing life, friction resistance, temperature rise, vibration and noise. The field faults are counted and the factors affecting the quality of bearing spare parts are analyzed, including: the surface peeling of inner ring and rolling element and the fragmentation of small retaining edge of inner ring; The manufacturing and assembly deviation of cage is too large; Inaccurate assembly tolerance and clearance control.

Maintenance analysis of rolling mill bearing

1. Inspection of bearings during operation

According to the requirements of the service environment of the bearing, the bearing shall be listened to, observed and measured regularly. Listening is to use the specified instruments to face the radial shell of the axial end cover and bearing seat of the bearing, and the other end is close to the ear to listen to whether there is impact sound and mechanical friction sound during the operation of the bearing; Observation is to observe the operating environment, installation position, vibration offset, lubrication and other conditions to see if there is a bad environment; The measurement is to quantitatively detect the bearing seat with thermometer and vibration meter.

2. Inspection of bearings at rest

Check the fastening of relevant spare parts, and check whether all parts are in the correct position and loose. The bearing pedestal shall be checked frequently for tightness and looseness. In particular, there must be no axial clearance between the bearing seat on the operation side and the rolling frame, so as to reduce the matching clearance between the bearing seat on the transmission side and the window of the rolling frame as much as possible, so as to reduce the impact of the runout of the transmission shaft on the bearing. In addition, the bearing lubricant can be tested to check whether there are sundries, iron oxide scale, water, etc. in the lubricating oil. Rough rolling mill is usually subject to strong impact load, large bearing vibration and easy loss of lubricating grease. Therefore, the grease is required to have strong adhesion and can be firmly adhered to the surface of the parts. Part of the grease lubricates the bearing on the raceway and the rest is stored in the internal space of the bearing to play a sealing role. If external dirt intrudes into the bearing seat, the first pollution is the grease near the outside, causing wear on the surface of bearing parts. With the increase of dirt, the wear surface will increase. At the same time, the signal layer crack will gradually expand, and finally the ferrule will crack. In serious cases, the roll, bearing seat and other related parts will be scrapped.

3. Post disassembly inspection of bearing

After the roll is replaced, use cleaning agent to clean the bearing, dry it with compressed air, and then check the roller, cage and roll. If the roller and raceway have dents, pitting corrosion and other phenomena, replace them according to the specific situation. At the same time, check the radial clearance of the axial seal box. After checking, add lubricant for standby. In short, the bearing of rolling mill has its unique service environment, characteristics and requirements. When the rolling force is small, the cracking of the inner and outer rings of the bearing and the fragmentation of the rolling element caused by excessive load are very few. Therefore, we should focus on the correct installation, inspection and maintenance of the bearing, and formulate corresponding process procedures to reduce the accident rate of bearing burning of the rolling mill. There are many factors affecting the service life of bearings. Therefore, a comprehensive management system and process regulations should be formulated in order to prolong the service life of bearings and ensure smooth production.

4. Maintenance, overhaul and abnormal treatment of rolling mill bearing

In order to maintain the original performance of the bearing in good condition for as long as possible, it is necessary to maintain and repair in order to prevent accidents, ensure the reliability of operation and improve productivity and economy. The maintenance should be carried out regularly according to the operation standard of the corresponding mechanical operation conditions. The contents include monitoring the operation status, replenishing or changing the lubricant, and regular disassembly inspection.

How to deal with frequent failure of rolling mill bearing? Inspection and maintenance are indispensable. There is no doubt about the importance of bearing maintenance. For the use of bearings, we must carry out regular inspection and maintenance, which can not only improve the service efficiency of bearings, but also prolong the service life of bearings.