I. Introduction:
The roller table is the non-critical equipment with the largest number and the highest operating frequency in the hot rolling production equipment. It is responsible for the transportation of slabs, intermediate billets, and hot-rolled strips. The level of maintenance and management of roller table equipment is directly related to the smooth progress of production and directly affects the surface quality of products. Therefore, the management of roller table equipment must be paid attention to.
The management of roller table equipment must focus on two goals: first, to reduce failures to zero; second, to meet product quality requirements.
2. Roller table classification and maintenance points:
1. Slab warehouse transportation roller table, loading and unloading roller table:
Features:
Good working environment, low operating frequency, and low maintenance and management requirements.
Maintenance points:
1) Ensure dry oil lubrication. Check the working condition of the distributor in sections, and use the regular maintenance cycle for manual oil replenishment.
2) Strengthen the spot check and find out that the motor is powered off in time to prevent the slab from pushing back the roller drive and causing the take-over bolt to be cut off. Replace the takeover bolts in time to avoid fault expansion.
2. The working roller table before and after the roughing mill, and the E1R1 stand roller:
Features:
The working environment is harsh, the impact of the slab kowtow is large, the scale is washed by high-pressure water, frequent acceleration and deceleration, forward and reverse rotation, point inspection is difficult, and maintenance and management are very difficult.
Maintenance points:
1) Bearing selection:
Use the best quality imported bearings, SKF, FAG brands. (Double row spherical roller bearings are used in this part, with good self-aligning effect and high bearing capacity)
2) Check:
The combination of daily dynamic inspection and maintenance static inspection is adopted. In addition to visual inspection, it is also necessary to listen to the sound of the bearing with a listening stick and track the change of the sound. Track the current change of the roller motor, etc.
During maintenance, perform static inspection, step on the wheel, and check whether the rotation is flexible and whether there is any blockage. Whether the bolts of various parts are loose, whether the gaskets of various parts are falling off, etc. Periodically open the side cover of the bearing housing to check the bearing and measure the bearing clearance.
For some rolls that cannot be close to the sound of spot inspection during the rolling process, the inspection and commissioning stage can be used for inspection.
3) Lubrication:
Due to the harsh environment of the front and rear working rolls of the roughing mill, the water vapor is large, and the high-pressure water is washed. Bearing lubrication is the key point of maintenance. Except for the normal oil supply of the distributor, all are equipped with manual oil replenishment pipelines for manual oil replenishment. The 4 stand rolls of E1R1 and the 3 rolls before and after the rolling mill are manually oiled every 3 days, and the other rolls are every two weeks.
4) Bearing waterproof and sealing:
Due to the harsh environment and high-pressure water scouring, bearing waterproofing and sealing is the key. The roller water retaining ring has high installation requirements and must be concentric. After the bolts are fastened, they must be welded to prevent loosening. If it is found to be loose or fall off, it should be restored in time. Since the working roller table is in the scouring range of the descaling water, the corrosion of the iron scale causes the seal wear and the wear groove on the seal and the roller journal, as shown in the figure.
When repairing the old rollers, we must pay attention to it, and require the manufacturer to process this part to the size of the drawing, and if necessary, replace the shaft sleeve to ensure the sealing effect.
5) Fastening:
Due to the large impact, the bearing seat and the bolts are easy to loosen. They must be tightened during each maintenance, and anti-loosening measures should be taken, such as double caps to prevent loosening, welding steel bars to prevent loosening, etc. After tightening, be sure to check the cranking. If the cranking is found to be inflexible, it means that there must be a problem with the alignment on both sides of the roller, and there is a “strength” phenomenon, which needs to be adjusted by loosening the bolts.
6) Adjust:
Due to poor working conditions, it is easy for the roller bearing seat to shake in the mouth of the roller table after the bolts of the bearing seat are loosened, resulting in wear of the mouth of the roller table. The center line of the roll is perpendicular to the rolling line, and the elevations on both sides are the same. When adding pads, be careful not to blindly add pads. If the thickness of the pads is improper, it will lead to “no strength”.
Before adding pads, loosen the bolts of the bearing housings on both sides, then turn the wheel to allow the rollers to align freely, and then measure the gap between the two sides of the bearing housing and the stop of the roller table, and determine the thickness of the pads according to the size of the gap. Tighten the bolts after the padding is completed, and check by cranking again.
After confirming that the rotation is flexible, weld the gaskets firmly. There have been many cases in our factory that the rolls cannot be rotated due to improper adjustment: when the 2# roll behind the roughing mill is replaced, after tightening the bearing seat bolts, the barring cannot be rotated.
During the replacement of the 1# roller on the front roller table of the hot coil box, the height difference of the roller table frame on the operation side and the transmission side is 1.2mm, so that the barring does not rotate after the roller is replaced.
7) Cleaning:
During each maintenance, the iron scale, dry oil, and sundries on the main body of the equipment and its surroundings should be cleaned up to facilitate spot inspection and maintenance to detect abnormalities in time.
8) Replacement cycle:
Determine the economical and reasonable replacement cycle according to the roller surface condition, bearing condition, experience, etc., and carry out periodic replacement in a planned way. It is determined according to the opening inspection of the lower rolls: the three rolls before and after the rolling mill are replaced every six months, and the remaining rolls are repaired and replaced every year.
9) Drive shaft and handle bolts:
The replacement is determined according to the use condition, the roller-side cross-pack bearing is manually lubricated for each regular inspection, and the motor-side cross-pack and splines are refueled once a month. After the bolts are evenly tightened, they are welded to prevent loosening, and the keys at both ends are welded with tape for reinforcement.
10) Spare parts preparation:
Strictly control the quality of the repair of spare parts in the process, and the manufacturer makes relevant data records, including the original record before repair, the difference with the size of the drawing, the size after repair, the matching size of the bearing and the shaft diameter and the bearing seat, etc.
When repairing the old one, go to the manufacturer for a spot check. Checklists are listed for important parts, which are filled out by the manufacturer after actual measurement, so as to ensure that no items are missed during the inspection. In addition, the manufacturer is required to carry out roll inspection and eliminate cracked rolls according to the inspection results (roller breakage accidents have occurred in the past). The bearing assembly clearance, whether the inner and outer rings are fixed in place, and reliability are the keys to affecting the bearing life and should be controlled as a key point. In addition, roller surface hardness, smoothness, circular runout, etc. should also be checked during acceptance. After the roller is repaired, the bearing must be inspected when it is returned to the factory. After confirming that it is correct, add dry oil for use.
3. Intermediate conveying roller table (approaching, delaying roller table, front roller table of hot coil box, roller table before shearing):
Features:
The working environment is poor, the water vapor is large, frequent acceleration and deceleration, forward and reverse rotation, the transition plate is easily damaged by the impact of the slab kowtow, the quantity is large, and the management is difficult.
Maintenance points:
1) Lubrication:
This type of roller table is a conveying roller table and runs continuously for a long time. In addition, the working environment is poor and the cooling water is continuously sprayed, and the lubrication requirements of the bearing are high. The lubrication of this part mainly relies on the automatic oil supply of the dry oil system.
Due to a large number of rollers, the working condition of the dry oil distributor is the key point of maintenance. The parts on the working side that are easy to inspect are inspected and processed by daily inspection. For the problems that are difficult to inspect on the transmission side, the oil output of the bearing can be checked to judge the working condition of the distributor. Replace the faulty distributor in time to ensure that the bearing is lubricated. Use regular inspection to refuel the roller tooth takeover cycle, and the refueling cycle should be less than 30 days. Deal with damaged receiver seals in a timely manner to ensure that the grease can be maintained for a long time in the receiver.
2) Bearing seat fixing:
The section of the roller table near the working roller table is greatly impacted by the kowtow of the slab. After the roller table is installed and leveled, the bearing seat bolts are tightened with a hydraulic wrench and need to be loosened by welding. Tighten the loose bolts in time to prevent the wear of the roller frame mouth caused by the loose bearing seat.
3) Roller table transition plate:
The roller table transition plate is a welded profile structure with low strength and is easily damaged by slab knocking, which is the focus of spot inspection. The transition plate should be inspected and repaired for each regular inspection. At present, the forged steel welded structure is being transformed to improve the strength of the transition plate and reduce failure.
4) Replacement cycle:
According to the wear of the roller surface, the replacement cycle is carried out.
4. The characteristics of the roller table (internal cooling roller) of the hot coil box:
large impact, large transmission swing angle, poor working environment, accumulation of iron scales, and difficulty in spot inspection on the transmission side. The bearing of the inner cooling roller is easily damaged by the intrusion of cooling water, which is not easy to check, and the management is difficult.
Maintenance points:
1) Lubrication:
The roller table of the hot coil box moves frequently, is in a high-temperature environment, and is washed by cold water inside and outside. Higher requirements for lubrication. Due to the frequent movements of the equipment, the dry oil hose is seriously worn, and the working environment is harsh, which often causes the dry oil distributor to fail. Focus on maintenance of the lubrication system, mainly automatic dry oil system, supplemented by manual replenishment. Disassemble the bearing dry oil pipe every time the oil is replenished in the regular inspection cycle, check the oil supply of the distributor, deal with the failure of the dry oil system in time, and ensure that the bearing is well lubricated.
2) Sealing:
The inner cold water and the bearing are completely isolated by two lip seals. When the seal is damaged, the cooling water enters the bearing to wash out the grease and the bearing is rusted, which directly causes the bearing to be damaged. The seal must be replaced when the roller is off the machine for repair, the shaft sleeve in contact with the seal should be checked for wear, and the surface finish must reach 0.8 to ensure the service life of the seal. When the seal is installed, it should be installed with oil to avoid damage to the lip. After the roller is on the machine, dry oil should be added to the seal periodically to slow down the wear of the seal.
3) Inner cold water:
The inner cold water pressure is not easy to be too high, and the inlet pressure should be less than 1Bar. In order to reduce the possibility of intrusion into the bearing, and the backwater should be smooth, it is best to return the water directly to prevent the water pressure in the inner cooling roller from rising.
4) Fastening:
Due to the large impact during coiling and transfer of the hot coil box, the bolts of the bearing seat are easy to loosen, resulting in aggravated bearing wear and tear on the bearing seat. Therefore, the tightening of the roller bearing seat bolts at this part is the key point. If looseness is found in spot inspection, tighten it in time.
5) Spot inspection and maintenance:
The daily inspection is mainly based on listening inspection. The rolls of the hot coil box have the particularity of being difficult to replace, and it is required to ensure that the machine is foolproof. After the new roller is put on the machine, continuous listening and tracking inspection should be carried out to detect abnormal changes in sound in time and make a maintenance and replacement plan in time. Inventory inspection can be carried out during shutdown, as well as opening inspection of the non-drive side bearing of the roller, focusing on bearing clearance and seal wear.
5. Process roller table (including descaling pinch roll, coiling pinch roll, looper roll, help roll, etc.)
Features:
The biggest feature of this type of roller table is that it is closely related to the quality of the product. The requirements for the roller surface are very high. The surface finish and circular runout of the roller must reach a high standard. The passive rollers such as pinch rollers and looper rollers on the descaling box Must turn freely.
Maintenance points:
1) The most important thing for the pinch roller and the intermediate roller of the descaling box is to prevent the iron scale from entering the bearing, so the bearing seal must be reliable, and the iron scale cover should be added at the journal.
2) The pinch roller under descaling and the pinch roller under coiling must be level, and the levelness is less than 0.1mm/m. The maintenance points of other points of inspection, adjustment, lubrication, etc. are similar to those of the front and rear work rolls of the roughing mill, and will not be repeated here.
6. G roller table:
Features:
small load, high speed, smooth roll surface, no sticky matter.
Maintenance points:
1) Due to the high speed of the G roller table, the installation accuracy requirements are also quite high, and the parallelism, elevation, and alignment of the adjacent rollers must be strictly required. Dynamic balancing is required before leaving the factory.
2) The point inspection of the G roller table mainly uses the listening bar to listen to the sound to detect the deterioration and abnormal sounds in time. The transmission side is a difficult part for spot inspection, so static and dynamic spot inspections must be carried out during overhaul or roll replacement time.
3) The dry oil distributor of the G roller table is the key point of inspection and maintenance. It must be ensured that the lubrication is normal. A simple and reliable inspection method is to open the dry oil pipe at the bearing, and then start the dry oil station to check the oil output.
4) The most important thing for the cooling roller in the G roller table is to prevent the cooling water from entering the bearing, resulting in poor lubrication. There is a seal inside the inner cooling roll, and the failure of the seal will cause cooling water to enter the bearing, so the regular inspection of the seal is the key to the management of the inner cooling roll. The inspection of the seal can only be a disassembly inspection, so the replacement cycle should be shortened, and the sealing condition should be checked after disassembly.
