Maintenance of Roll Bearings

Roller bearings must be regularly removed from the mill for testing and maintenance, thus maximizing the service life of the roller bearings. The frequency of bearing maintenance and repair 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 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. Abroad, the U.S. ESSO company produces aluminum mill roll bearings without stains lubricant WYTOLB220, not only has good anti-wear properties, oxidation stabilization properties, etc., but also has a very good clean annealing performance, no pollution of aluminum rolling oil.
Recommended amount of lubricating grease: the amount of grease filling, to fill the bearings and bearing shell space of 2/3 or 1/3 is appropriate, not excessive lubrication. Recommended grease dosage after each grinding roll is 1/5 of the initial dosage.The replenishment period of grease is related to the structure of the bearing, rotational speed, temperature and environment, etc. Users can adjust it according to the actual operating environment, so that the bearings always have clean lubricating grease in a reasonable way.

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