Abstract The problems existing in the use of the four-row tapered roller bearings installed on the work rolls and the intermediate rolls, the reason analysis and the effect after installation and adjustment are discussed.
The work rolls and intermediate rolls of the six-high cold rolling mill of Anshan Iron and Steel Cold Rolling Plant are respectively installed with FAG four-row 802045-H122AA and 802137-H122AA tapered roller bearings as radial bearings, and the backup rolls use four-row cylindrical roller bearings as radial bearings. The radial bearings of the work rolls and intermediate rolls are lubricated with oil and gas, and the radial bearings of the backup rolls are lubricated with circulating oil. During the use of the cold rolling mill from November 2007 to June 2008, dents were found on the raceway of the four-row tapered roller bearing, and the inner ring raceway of the four-row cylindrical roller bearing was severely peeled off. The 802137-H122AA outer ring raceway has dents, and the 802045-H122AA outer ring raceway has dents in the areas III to IV, and some of the dents are deep. The inner ring raceway of the four-row cylindrical roller bearing is peeled off, the rolling elements of the bearing are corroded, there are axial indentations on the rolling surface, and the roller neck surface matched with the four-row tapered roller bearing is worn.
2. Failure cause analysis
For the on-site observation and analysis of FAG four-row tapered roller bearings, the dents on the raceway are caused by foreign impurities, and a large number of metal particles are found in the bearing seat, which are hard in texture and large in size. The impurities should be left inside the bearing seat during machining, and these hard particles will cause deep dents on the raceway when the bearing is running. More fine particles are found in the oil-air lubricated filter, which may be brought by the lubrication equipment pipeline or lubricating oil, and these particles leave shallow fine indentations on the raceway.
3. Improvement measures
Before the bearing is reinstalled, it is recommended that the bearing, housing and lubrication system be thoroughly cleaned to remove impurities. According to the number and depth of dents, the four-row tapered roller bearing can continue to be used, and its performance is basically unaffected. It should be noted that the outer ring of the FAG four-row tapered roller bearing is marked with four load-bearing areas. It is recommended to use the I area as the load-bearing area, and adjust the load-bearing area after running for 1000-1200 hours. Judging from the dents in the 802045-H122AA outer ring raceway III to IV areas, the III to IV areas are placed in the load-bearing area during initial installation. In view of the deep dent in the existing part of this area, it is recommended to adjust this area relatively when installing again, that is, the I and II areas are placed in the bearing area.
In addition, there is wear on the mating surfaces of the four-row tapered roller bearing of the roll neck. Due to the limitation of the structural characteristics of the four-row tapered roller bearing itself, and in order to facilitate the roll change, there is a clearance fit between the bearing and the roll neck, so there is relative rotation between the inner ring of the bearing and the roll neck. In order to reduce roll neck wear, it is necessary to ensure proper fit and good lubrication between the inner ring and the roll neck. According to the wear of the roll neck, it is recommended to check the size of the roll neck to verify whether it is within the recommended dimensional tolerance. At the same time, it is necessary to ensure that the oil supply of oil and gas lubrication and the oil level in the bearing seat are located at the position where half of the bottom roller of the bearing is submerged. For four-row cylindrical roller bearings, the severe spalling of the inner ring raceway material may be caused by pre-damage. Judging from the serious peeling of the raceway at the distance between the rolling elements and the axial indentation on the rolling elements, there may be friction between the rolling elements and the inner ring raceway during the bearing installation. Pre-damage may also be caused by local burns or defects in bearing materials and heat treatment caused by grinding the inner ring raceway. If you want to obtain the exact cause of early damage, metal material analysis should be carried out on the damaged raceway and roller, including the depth of the carburized layer of the inner ring raceway, grinding burns, and the indentation stress distribution of the damaged rollers.
In addition, large-scale corrosion occurs on the bearing rollers, and the moisture content in the lubricating oil should be controlled. The moisture content significantly affects the service life of the bearing.
4. Four-row tapered roller bearing installation
The basic requirements for installation are: specially trained installers, check the shape and position tolerance of the bearing mating surface, keep the installation site clean, open the bearing package after the installation is ready, and do not wash off the anti-rust oil of the bearing.
(1) Configuration of bearing assembly. Open the bearing package, do not wash off the anti-rust oil, check the bearing assembly to ensure that the bearing assembly is complete, the production year is the same, and the production serial number and installation order are indicated by letters. The bearing mating surface is marked with 4 load-bearing areas separated by 90° from I to IV, and the load-bearing areas are marked on the outer diameter of the outer ring of the axial etched line.
(2) The mating surface of the bearing. In order to prevent the friction corrosion of the roller neck and the bearing seat mating surface, it must be coated with a thin layer of installation paste (such as FAG ARCA. The opening is placed on a flat support upwards.
(3) Open bearing. First, with the E end facing down, lift the outer ring D-E and the outer spacer D and put them into the bearing housing, then lift up the parts in the given order and put them into the bearing housing. Pay attention to the alignment of the load area, the rear mounted components must be in full contact with the front components and must not be tilted or skewed.
(4) Installation of open bearings with stamping cages. For bearings with stamped cages, lay the inner ring E-Ce flat on the support (E end facing down), then place the components one by one in the correct order, and use the lifting device to install the complete bearing assembly into the bearing housing to ensure load Zone I is properly aligned. For pin-type cage bearings, put the inner ring E-Ce (E end down), inner spacer C (positioning rib down), double-row outer ring B-D and outer spacer B into the housing pin-type For cage bearings, install the inner ring A-Ca and the single-row outer ring A-B into the bearing housing to ensure the correct alignment of the load zone I. The pin-type cage bearing can be installed using the same lifting device as the bearing with stamping cage.
(5) Installation of sealed bearings. Sealed tapered roller bearings are mounted with the aid of a special lifting device. Completely assemble the bearing assembly on the lifting device in the order given. Install seal ring E first. When installing grease lubricated bearings, the roller and cage combination must be lubricated manually. Make sure that load zone I is properly aligned, and fit the complete assembled bearing into the housing.
(6) Rotary bearing. Lightly install the second end cap on the bearing housing with 4 bolts symmetrically on the circumference (do not tighten the bolts), rotate the bearing housing to the horizontal position, use the tie rod to fix the clamp on the inner ring end face, start When it is lighter, the clamp can only touch the end face of the inner ring. For sealed bearings, the lifting device also acts as a clamp. Gradually tighten the tie rod and end cap bolts, and rotate the inner ring slowly and evenly until the inner ring is fully engaged with the inner spacer C without any gaps. Use a feeler gauge to measure the clearance S between the end cap and the bearing housing to determine the seal thickness B. Rigid seal B=S-(0.05～0.1)mm; elastic seal B=1.2Smm.
(7) Install the seal. Loosen the end cap bolts and remove the end cap, seal the desired thickness
Insert the cover into the end cap, apply grease to the inner ring hole, and complete the installation.
(8) Heat the labyrinth seal ring in an oil bath, push the labyrinth seal ring together with the O-ring onto the roll neck, and press it tightly on the end face of the roll during the cooling process of the labyrinth seal ring .
(9) Push the assembled bearing seat onto the roll neck, regularly check the effectiveness of the bearing seat seal and the bearing temperature, and change the bearing area of the bearing after the bearing works for 1000-1200 hours. Record all maintenance and inspection work of the bearing on the rolling bearing inspection card. Change the bearing area of the bearing, disassemble the bearing in the reverse order of installation, carefully clean the bearing parts, then immediately apply oil, visually inspect the raceways and rollers for damage, check the axial clearance, pack the bearing with new grease, and follow the installation instructions Install the bearing and go to the next load zone. When changing the load zone for the first time, rotate the outer ring 180° to load zone III; the second time to rotate 90° to load zone IV; the third time to rotate 180° to II. For the sealed tapered roller bearing, after the bearing has been operated for 300h, 600h and 900h respectively, follow the steps below to perform supplementary inspection: remove the bearing seat and remove the end cover, and check the amount and state of grease in the bearing and labyrinth seal. If the grease is discoloured or contaminated, fill the bearing and labyrinth with new grease. Carefully check the bearing seals, replace the seals even if there is slight damage, and record all maintenance and inspection work on the bearings on the rolling bearing inspection card.
The four-row tapered roller bearings 802045-H122AA and 802137-H122AA of work rolls and intermediate rolls of the six-high cold rolling mill were re-installed and adjusted, and no abnormality was found after operation, the axial and radial runout were not out of tolerance, and the bearing temperature was normal. One year later, the four-row tapered roller bearing was disassembled and inspected again, and the raceway and roller wear were within the normal range. By re-cleaning the equipment and adjusting the bearings, the average service life of the bearings has been extended from 8,000h to more than 12,000h, and the average annual production cost has been saved (3-5 million yuan).