Roll bearing maintenance skills analysis

Aluminum rolling mill rolls and roll bearings are important parts of the mill. In rolling production, the rolls should be rolled with the metal in direct contact, so that the metal produces plastic deformation, therefore, the rolls are the main deformation tool of the mill, the rolls are supported by various types of bearings, rolls and roll bearings of the quality and service life is directly related to the quality of the products of the mill, production efficiency and production costs. Therefore, the maintenance and management of roll bearings is particularly important.


First, the working characteristics of the roll bearings
Roll bearings are used to support the rolls, and compared with the general purpose bearings, roll bearings have the following characteristics:
(1) to withstand high unit pressure. Due to the limitations of the external dimensions of the bearing seat, can not be greater than the minimum diameter of the roll body, and the length of the roll neck is shorter, so the unit load on the bearing is large. Usually roll bearings unit pressure is as high as 2000-4800Mpa, for ordinary bearings 2-5 times, and pv value (the product of unit pressure and linear velocity) is 3-20 times the ordinary bearings.
(2) running speed difference. Different rolling mill running speeds vary greatly, for example, the modern six-stand cold rolling mill exit speed has reached 42m/s, high-speed wire rod mill exit speed of 100m/s, while some low-speed mill speed is only 0.2m/s. Obviously, different speeds of the mill should be used in different types of bearings.
(3) poor working environment. Hot rolling rolls should be cooled with water, and sewage, iron oxide and other easy to fall into the bearing. Cold rolling mill using process lubricants (emulsions, etc.) to lubricate and cool the rolls and rolled parts, they can not be mixed with the bearing lubricant. Therefore, the sealing of the bearings puts forward high requirements.
Therefore, the requirements of the roll bearings is a large bearing capacity, small coefficient of friction, impact resistance, can work at different speeds, in the structure, the radial size should be as small as possible (in order to use a larger roll neck diameter), there are good lubrication and cooling conditions.

Second, the maintenance of roll bearings
Roller bearings must be regularly removed from the mill for testing and maintenance, so as to maximize the service life of the roller bearings. Bearing maintenance and maintenance frequency should be adjusted according to the operation of the mill, mainly based on experience. The usual maintenance frequency for full load operation every three months, most mills every six months, light operation of the mill every December. Roller bearings should be disassembled and inspected after the first 1000h of operation. The bearings need to be thoroughly cleaned in operation while the oil seals are checked, and the seals should be completely replaced if necessary. If no abnormality is found, the second inspection interval can be extended, e.g., after every 2,000h of operation or longer. Each time after removing the bearings and housing assembly from the mill, the location of the bearings in the mill and the bearing area should be recorded.
(1) General steps for roll bearing maintenance. Track the location of the bearings in the mill and record it. The use of special roll bearing maintenance service record card, can be used to record the bearing seat number, roll number, rack number, bearing position in the mill, outer ring bearing area and rolled product tonnage and bearing working hours and other data. Record card should be updated at any time and easy for maintenance personnel to check the use of the bottom of the blank space can be recorded bearing measurement data and other inspection details. Remove the bearing housing from the roll and the bearing from the housing. Special lifting methods and tools are required both for removing the bearings from the housing and for bearing inspection.


(2) Cleaning the bearings. All spalling, water, residual lubricant, and any other dirt that would cause severe wear on the bearings should be removed during the cleaning of the bearings. Cleaning bearings used by the cleaning method and cleaning agent according to the size of the bearing to be cleaned or the number of bearings to decide, small bearings or a small number of bearings available kerosene, mineral oil or other commercial solvents. For large bearings or a large number of bearings, can be used 40% when the viscosity of 22cSt (or 100% for 100SUS) of neutral oil in the cleaning tank cleaning.
(3) Inspection of bearings, including visual inspection and minor repairs. If small spalls or skin cracks are found on the raceways or roller surfaces of the inner ring where the rollers can be removed, a grinder is usually used to grind away the metal spalls and polish the edges of the spalled surfaces. Bearings should be inspected periodically for wear, which can be assessed by measuring the bearing clearance. As needed, inspect and repair the bearing housing and put the bearings back into the housing. As required, inspect and service the roll necks and install the housings with bearings into the rolls.
(4) Lubricate bearings. Due to the rapid development of aluminum processing industry, China has a large number of domestic and imported modern four-roll or six-roll mill, these mills have a large rolling force, high rolling speed characteristics, which gives the roll bearings and their supporting auxiliary equipment lubrication puts forward harsh requirements, the requirements of the lubricant has excellent viscous temperature, oxidation stability, rust resistance, anti-friction and so on. At present, most of the bearing lubricant of domestic aluminum rolling mill adopts No. 220 medium load closed gear oil. The lubricant has the function of reducing wear, taking away the heat generated by friction, anti-corrosion and rust prevention, etc. However, its viscosity is high, flash point is high, sulfur content is large, and annealing cleaning performance is poor. In the mill operation process, inevitably due to equipment sealing and other issues occurring lubricant leakage, this gear lubricant once leaked to the rolling process lubricant, will make the rolling oil serious pollution, resulting in a decline in the performance of its annealing cleanliness, aluminum strip foil surface formation of oil spots, affecting the quality of the product, and shorten the process of lubricating oil use cycle.

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