Abstract:High performance greases, which are resistant to high temperature, high extreme pressure, large amount of water and impact load, are generally used for hot tandem rolling mill work roll bearing lubrication. Manual grease lubrication is the main lubrication method. Therefore, on the one hand, the lubrication management of bearings directly affects the operating status and life of bearings, and on the other hand, it also determines the level of operating costs. The lubricating oil quantity of each rolling mill and each bearing seat is determined by testing and tracking the lubrication condition of work roll bearings, and the lubrication system of roll bearings after rolling off the line is optimized, which not only ensures the normal use of roll bearings, but also greatly reduces the lubricating oil consumption of roll bearings and effectively controls the running cost of bearings.

Key words: roll bearing characteristics; Bearing lubrication method; To test; Lubrication system optimization

1 Introduction

As a key part of rolling mill, work roll bearing is widely used in all kinds of rolling mill work rolls. The lubrication management of roll bearing directly affects the running state and running life of the bearing, and determines the running cost of the bearing. Therefore, reasonable lubrication management of work roll bearings can not only ensure the service life of roll bearings, but also effectively control the running cost of bearings.

2 Working characteristics and typical structure of roll bearing

Hot tandem rolling mill is generally equipped with bending roll and axial channeling roll system, roll bearing design to withstand large radial load and multi-angle axial load, because of the four row tapered roller bearing outstanding load distribution and load area control, generally four row tapered roller bearings as radial bearings arranged in the roll drive side and operating side bearing housing. The double-row tapered roller bearing, which can bear the axial load in both directions, is installed in the bearing seat on the operating side of the roll.

(1) The radial load is mainly carried by four row tapered roller bearings installed on the roll drive side and the operating side of the bearing seat, and the double row tapered roller bearings in the roll operating side of the bearing seat also bear a small amount of radial load.

(2) The axial load is mainly carried by double-row tapered roller bearings installed in the bearing seat on the operating side of the roll.

(3) The bearing seat sealing device is mainly composed of oil seal, water seal, type 0 sealing ring, etc. The oil seal is used to prevent the lubricating dry oil from leaking from the bearing inside, and to prevent the cooling water, oxide sheet and other dirt from outside the bearing inside.

3 General lubrication methods for roll bearings

According to industry analysis statistics, improper bearing lubrication accounts for 36% of the causes of premature bearing failure, and selecting the right bearing grease for specific applications is the key to play the bearing performance. The use of the correct amount of grease at the right time interval is also important, too much or too little grease and incorrect lubrication methods will greatly shorten the service life of the bearing.

(1) Installation and initial lubrication: installation is one of the keys to the bearing life cycle, if the correct method and tools are not used to correctly install the bearing, the service life of the bearing will be greatly shortened. Primary lubrication is also an important step in the installation procedure, and the choice of grease suitable for the bearing application is a prerequisite for obtaining bearing performance. In addition, the amount of grease and lubrication method will also affect the service life of the bearing.

(2) Supplementary lubrication: During the operation of the bearing, the lubricating grease will produce emulsification and high-speed rotation and throw out the phenomenon, choosing the grease suitable for bearing applications and using the right amount of grease at the right time interval is the key to achieving the maximum service life of the bearing.

(3) Regular cleaning and inspection lubrication: After the bearing runs a stage, it is necessary to disassemble the inspection to check whether the bearing roller, inner and outer rings and cages have abnormal wear, so as to determine the actual lubrication effect of the bearing, and the bearing will be lubricated again according to the initial load after the inspection.

4 Original lubrication of roller bearing on site

4.1 Lubrication for initial assembly

When the bearing is installed, a layer of lubricating grease is applied between the bearing seat and the bearing roller to reduce the friction resistance and damage to the bearing during installation. After installation, the bearing is lubricated through each lubricating oil port on the bearing seat and two lubricating channels above and below the roll end until new oil is found between the roll neck and the bearing seat. Lubrication is manually operated, because there is no timing quantitative standard, the oil is basically filled with the inner cavity of the bearing seat, and the oil is thrown during the operation of the bearing upper machine, and the bearing has abnormal heat.

4.2 Supplementary lubrication

There is no specific lubrication cycle, as long as the machine is off, lubrication is carried out, see Figure 1. The lubricating oil quantity control is basically the same as that of the initial lubrication. The bearing is lubricated through the lubricating oil ports on the bearing seat and the two lubrication channels above and below the roll end. Until new oil is seen between the roll neck and the bearing seat, there is also a large amount of oil in the running process and abnormal heating during the running of the bearing, as shown in Figure 2.

4.3 Disassembly check lubrication

There is no reasonable disassembly inspection period, and the bearing lubrication effect is judged by field temperature measurement, and there is a large measurement error. Frequent disassembly of the bearing housing to check the lubrication effect increases the risk of bearing damage and grease contamination during installation on the one hand, and wastes manpower and oil quantity on the other hand.

According to the above three ways of lubrication, the average daily consumption of 1 barrel (180kg/ barrel) of lubricating oil, the annual consumption of about 360 barrels, and the roll bearing selection of imported high-performance grease, the price is higher (16,000 / barrel), the annual consumption of roll bearing grease is about 6 million yuan, which has become one of the main bottlenecks restricting the reduction of production costs.

5 Field roll bearing lubrication system test and optimization measures

5.1 Calculation of lubricating oil quantity

The field roll uses Timken and SKF bearings, which are tested according to the maintenance instructions of the two bearings.

(1) First calculate the free volume in the bearing, the formula is as follows:

Formula:

V -- free volume of bearing;

D -- outer diameter of outer ring (cm);

d -- inner ring aperture (cm);

T -- total width (cm);

M -- bearing quality;

A -- Average steel density, 7.8×10-3kg/cm3

(2) The amount of oil depends on the working conditions (such as speed, etc.), the recommended amount is: ordinary mineral oil is one-third to two-thirds of V.

(3) The density of grease is about 0.9g/cm3

F1-F2 roll: radial bearing NP814067/9A2A1, bearing total weight is about :327.48kg, the recommended amount of oil is about :3.2 ~ 6.4kg; Thrust bearing JM966748DW, bearing total weight is about :150kg, the recommended amount of oil is about :1.6 ~ 3.2kg.

F3-F4 roll: radial bearing M270448/9A2A4, bearing total weight is about :272.55kg, the recommended amount of oil is about :2.6 ~ 5.2kg; Thrust bearing JM966748DW, the recommended amount of oil is about :1.6 ~ 3.2kg.

F5-F6 roll: radial bearing LM763447DGW, bearing total weight is about :137.25kg, the recommended amount of oil is about :1.6 ~ 3.2kg; Thrust bearing JHM957540DW, bearing total weight is about :115.77kg, the recommended amount of oil is about :1.6 ~ 3.2kg.

5.2 Lubricating oil quantity on machine test

5.2.1 Test methods and procedures

(1) Grease according to the calculated amount to ensure the best lubrication effect.

(2) Test subjects: one set of rolls for F2, F4 and F6.

(3) Before loading the machine: grease, disassemble and check the lubrication.

(4) After loading: disassemble to check bearing lubrication; Refat.

(5) Fat control: control the pumping time.

(6) Real-time monitoring: Check the bearing temperature every two hours.

⑺ Record data: record bearing lubrication and bearing operating temperature.

5.2.2 Develop precautions for test operation

(1) Test roll :4F1 lower work roll, roll number :011111, upper F2 mill; 1F3 lower work roll, roll number :011205, upper F4 rolling mill; 5F6 lower work roll, roll number :051303, upper F6 rolling mill.

(2) Test site: assembly area of work roll bearing seat between rolling mill and roll.

(3) Test personnel: equipment management personnel, work roll bearing seat assembly shifts, roll management personnel, operation and maintenance personnel.

(4) Related responsibilities.

Equipment management: Select the test roll according to the actual situation on site; Make test plan and participate in the whole test process, coordinate the smooth test.

Each shift of work roll bearing seat assembly: grease the test roll bearing seat in strict accordance with the test plan; The test roll must be disassembled and checked after disassembling the machine, and the equipment management personnel should be notified 30min before disassembling the bearing seat to check the lubrication condition; Make relevant test records timely according to the requirements of test plan.

Note: In order to ensure the integrity of the test, the assembly of each shift must first confirm whether the test roll on the machine.

Roll management: the test roll loading machine shall be arranged according to the test requirements, and the test roll loading machine shall not be changed at will.

Operation and maintenance: According to the requirements of the test plan, it is necessary to ensure that the temperature of the tested roll bearing seat is measured and recorded every 2h.

Note: In order to ensure the integrity of the test, it is necessary to confirm whether there is a test roll on before running each shift.

5.2.3 Test process control

Multiple machine tests tracking lubrication grease and lubrication effect of the extension frame, see the following figures for details.

(1) F2 roll: A total of 4 tests, machine running 10 ~ 23h, bearing maximum temperature: operating side 49℃, transmission side 41℃, average 35 ℃, normal. Disassemble the machine and check, it is found that the operating side bearing lubrication is normal, and the transmission side bearing water, as shown in Figure 3-Figure 6.

(2) F4 roll: A total of 4 tests, machine running 6 ~ 16h, bearing maximum temperature: operating side 49℃, transmission side 45℃, average 45℃, normal. If no exception is found after dismounting, see Figure 7-Figure 10.

(3) F6 roll: A total of 6 tests, machine running 6 ~ 10h, bearing maximum temperature: 64℃ on the operating side, 46℃ on the transmission side, average 55℃, normal. If no exception is found after disembarking, see Figure 11-Figure 14.

5.2.4 Test conclusion

The test results show that the lubrication of each bearing is good and the bearing temperature changes normally after the grease is added according to the test amount. It shows that the test scheme has practical operation in the field, and the amount and period of fat filling meet the requirements of field use.

According to the transmission capacity of the electric and pneumatic pump used in the field, the grease amount of each frame and each bearing seat can be determined.

6 Optimization of roll bearing lubrication management system

According to the test results, the lubrication management system of roll bearings is optimized, and the minimum initial loading of bearing lubrication (Table 1), the periodic replenishment amount after dismounting (Table 2), and the lubrication amount of periodic disassembly inspection are quantified. Furthermore, according to the conveying capacity of the electric and pneumatic pump used on site, the oil feed amount is controlled from the fueling amount and refueling time. Thus, the purpose of ensuring the stable operation of bearings and controlling the operating cost of bearings is achieved.

Note: Every 150h of operation, the bearing seat must be removed to check the lubrication condition, according to the minimum amount of oil lubrication.

After implementing the above optimized roller bearing lubrication system, the annual consumption of grease is shown in Table 3.

Taking into account the abnormal factors (tail dumping, pile steel, surface quality anomalies, etc.), the actual consumption should be multiplied by the coefficient 1.2 on the basis of the theoretical calculation amount to obtain the predicted actual consumption: annual consumption 171×1.2=205 barrels, which is about 155 barrels less than before optimization, and the annual operating cost is about 2.4 million yuan.

Because the roll bearing works in the environment of high speed, heavy load, high temperature, and a large amount of water erosion, the grease of the roll bearing must be selected with high temperature resistance, high extreme pressure resistance, water erosion resistance and impact load, but because of the manual grease operation, if there is no quantitative control in the amount of grease or grease time, on the one hand, it will cause a huge waste of grease consumption. On the other hand, it is not conducive to the normal operation of the bearing. After tracking the running condition of each set of roll bearings, testing the periodic replenishment amount of lubricating oil, and finally determining the relatively reasonable oil replenishment amount of each frame and each bearing seat, so as to ensure the stable operation of roll bearings and reduce the purpose of production and operation cost.