Keyword：steel mill roll
The roll is in direct contact with the strip rolled piece and is an important tool for hot rolling production. Reducing the energy consumption of the rolls can effectively reduce the production cost and increase the benefit, and at the same time, it can effectively improve the operating rate of the rolling mill and ensure the surface quality of hot-rolled products. In the production of hot-rolled strip steel, the consumption of rolls is particularly huge, so it is of great significance to find out the measures to reduce the consumption of rolls and improve the life of rolls for the production of hot-rolled strip steel.
Optimized rolling mill roll change cycle
2.1 Rough rolling work roll
The original rough rolling roll change cycle is 2.5wt~3.8wt, on this basis, the roll change cycle is gradually extended, and the wear of the rolls, strip shape and surface quality are compared each time. The current roll change cycle is stable at 3.8wt~4.5wt. It does not affect the strip shape and surface quality, and prolongs the service life of the roll.
2.2 Finishing backup roll
The rotation speeds of F1-F7 rolls are different and the difference is large, so the wear degree of the back-up rolls is also different. The original one-size-fits-all roll change cycle of 10wt-15wt is not reasonable. The current roll change cycle is detailed in Table 1:
Since adopting segmented roll change, not only the rolling capacity of the roll has been increased by about 14.94%, thereby prolonging the service life of the roll, but also according to statistics, the wave shape of the roll when rolling thin gauge at the end of use has also been reduced.
Correct rolling accident handling method
Severe rolling accidents directly increase the value of roll consumption, and whether the accidental rolls can be handled correctly after the accident occurs is the key to reducing roll consumption.
3.1 Steel jam accident
After the steel jam occurs, the cooling water needs to be stopped immediately, and the upper roll should be lifted to prevent the upper roll from contacting the strip steel; after the strip steel is removed, the roll should be changed and the roll cooled slowly. If the roll cannot be replaced immediately, and the cracks are not serious, the working rolls should be idling for 5-10 minutes without cooling water, so that the temperature can spread evenly before entering normal rolling.
3.2 Steel sticking accident
First remove the sticky steel. Finally, a detailed inspection should be carried out on the bonded steel area, including: hardness, cracks, flaw detection, etc. The affected area of the bonded steel must be removed to ensure that the roll surface has uniform hardness and no cracks.
Innovative grinding countermeasures for roll defects
From the unplanned roll change statistics from August 2015 to April 2016, it can be seen that accidental rolls accounted for 69% of the total roll change. Therefore, after a rolling accident occurs, timely and correct handling of the rolls can minimize unnecessary damage to the rolls, prolong the service life of the rolls, and reduce roll consumption.
The following is a brief introduction to the treatment methods of several common accident rolls:
4.1 Hot crack
Hot cracks are mostly caused by the sudden cooling and heating of the roll after the steel jam or stacking accident.
Treatment method: R1 and F1-F4 rolls can be used on-line with hot cracks on the premise of ensuring smooth rolling, and the cracks are closed (closed cracks will not extend, but will prolong with the use time), cracks will be gradually eliminated.
4.2 Roller bonded steel
The roll sticks to the steel, and the tail flick or stacking steel accidents cause the roll to stick to the strip.
Treatment method: The strip steel on the roll body is seriously stuck and overlapped, and the area is large. When the thickness is more than 3mm, the adhered strip steel needs to be turned off first. Check the surface of the roll body after the adhered iron sheet car falls off. If there are cracks and peeling (flesh off), determine the cutting depth according to the degree of damage to ensure that defects are eliminated without increasing excessive roll consumption.
4.3 Work roll body edge peeling
The edge of the work roll is peeled off, which is caused by the stress concentration on the shoulder of the roll.
Treatment method: Since the roll shoulder does not directly contact the steel plate, the crack peeling part can be removed, the chamfering can be ground, and the chamfering method and angle of the supporting roll in contact with it can be adjusted to improve the stress distribution of the roll body.
4.4 Back-up roll defects
Back-up roll defects, the back-up roll does not directly contact the strip steel and its hardness is lower than that of the work roll, but it is expensive, so it is not suitable to use conventional grinding methods.
Treatment method: When the damage is on the edge of the roll, properly increase the length of the end chamfer during grinding. The residual defect is treated with an angle grinder and the surrounding area is smoothed to prevent the further spread of the peeling defect. When the damage is in the middle of the roll, grind it as usual and then use the angle grinder to process it and smooth the defect around it.
Adjust mill roll profile
Combined with the actual production situation, the F1-F4 rolls were changed from concave rolls to HVC rolls. And increase the negative crown of F5-F7 rolls, so as to improve the stress distribution on the roll surface. It can achieve the purpose of better controlling the shape of the plate and reduce the consumption of rolls.
Other ways to reduce steel rolls consumption
①Organize and practice the handling methods of various rolling accidents, improve the emergency response speed, and minimize the damage to the rolls caused by accidents;
② Formulate reasonable roll flaw detection standards to ensure roll quality and reduce unnecessary losses;
③ Select excellent roll manufacturers, and customize high-quality rolls in terms of material, hardness, etc. that meet the production characteristics of heavy steel hot-rolled sheet factories;
④ After the production is stable, high-speed steel rolls are selected for the work rolls in the front section of finishing rolling to further reduce roll consumption.
in conclusion
①The adjusted HVC roll shape and negative crown roll not only improves the stress distribution on the roll surface, but also strengthens the ability to control the crown of the strip, which is conducive to the guarantee of product quality.
②Adjustment of roll changing cycle, response to rolling accidents and correct handling of accidental rolls, while ensuring product quality, increases the rolling capacity of a single roll and prolongs the service life of the rolls.
③ The measures to deal with the accidental rolls reduce the unnecessary grinding of the rolls, thereby reducing the labor intensity of the workers.
