Steel mill rolls directly contact the steel strip and are an important tool for hot rolling production. Reducing roll consumption can effectively reduce production costs and increase benefits. At the same time, it can effectively improve the mill operation rate and ensure the surface quality of hot rolled products. In the production of hot rolled steel strip, the consumption of rolls is particularly huge. Therefore, finding measures to reduce roll consumption and increase roll life is of great significance to the production of hot rolled steel strip.
Optimizing roll changing cycle
Roughing Roller
The original roughing roll changing cycle was 2.5wt～3.8wt. On this basis, the roll changing cycle was gradually extended, and the wear of the rolls, the strip shape and the surface quality of each roll were compared. The current roll changing 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 rolls.
Finishing Roller
The speeds of the F1～F7 rolls are different and vary greatly, so the wear degree of the support rolls is also different. The original one-size-fits-all roll changing cycle of 10wt～15wt is not reasonable. The current roll changing cycle is detailed in Table 1:
Since the adoption of segmented roll changing, not only has the rolling volume of the rolls increased by about 14.94%, thereby prolonging the service life of the rolls, but also according to statistical data, the wave shape of the rolls when rolling thin specifications at the end of their use has also been reduced.
Correct method of handling rolling accidents
Severe rolling accidents directly increase the value of roll consumption, and whether the accident roll can be properly handled after the accident is the key to reducing roll consumption.
Steel jamming accident
After the steel jam occurs, the cooling water must be stopped immediately, the upper roll must be lifted to prevent the upper roll from contacting the strip; after the strip is removed, the roll must be changed and the roll must be cooled slowly. If the roll cannot be changed immediately, the working roll must be idle for 5-10 minutes without cooling water on the premise that the crack is not serious, so that the temperature can be evenly diffused before normal rolling can be started.
Steel sticking accident
First, remove the steel sticking. After that, a detailed inspection of the steel sticking area should be carried out, including: hardness, cracks, flaw detection, etc. The steel sticking affected area must be removed to ensure that the roll surface hardness is uniform and crack-free.
Innovative countermeasures for grinding roll defects
After a rolling accident occurs, timely and correct handling of the rolls can minimize unnecessary damage to the rolls, extend the roll service life, and reduce roll consumption.
The following briefly introduces several common methods for handling roll accidents:
Hot cracks
Hot cracks are mostly caused by the rollers being cooled and heated after steel jams or steel piles.
Treatment method: R1 and F1-F4 rollers can be used on-line with hot cracks on the premise of ensuring smooth rolling, and the cracks are closed (closed cracks do not extend, but extend with the use time), and the cracks will gradually disappear.
Roller sticking steel
Roller sticking steel, tail swinging or steel piling accidents cause the roll to stick to the strip steel.
Treatment method: If the roll body strip steel is seriously adhered and overlapped, the area is large, and the thickness is above 3mm, the adhered strip steel needs to be turned off first. After the adhered iron sheet is turned off, check the surface of the roll body. If there are cracks and peeling (flesh loss), determine the cutting depth according to the degree of damage to ensure that the defects are eliminated without increasing excessive roll consumption.
Peeling of the working roll body edge
Peeling of the working roll body edge is caused by stress concentration on the roll shoulder.
Treatment method: Since the roll shoulder does not directly contact the steel plate, the crack peeling part can be removed, the chamfer 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.
Support Roller Defects
Support roll defects. Support rolls do not directly contact the strip and have a lower hardness than working rolls, but are expensive, so conventional grinding methods are not suitable.
Treatment method: When the damage is on the edge of the roll, increase the end chamfer length appropriately during grinding. If the defect remains, use an angle grinder to process it and smooth it around to prevent further spread of the peeling defect. When the damage is in the middle of the roll, grind it according to the conventional method and then use an angle grinder to process it and smooth it around the defect.
Adjusting the roll profile
In combination with the actual production situation, the F1-F4 rolls are changed from concave rolls to HVC rolls. And the negative crown of the F5-F7 rolls is increased to improve the stress distribution on the roll surface. This can achieve the purpose of better controlling the plate shape and reduce roll consumption.
Other ways to reduce roller wear
Organize exercises on the handling methods of various rolling accidents, improve the speed of emergency response, and minimize the damage to the rollers caused by accidents;
Formulate reasonable roller flaw detection standards to ensure the quality of rollers while reducing unnecessary losses;
Select excellent roller manufacturers and customize high-quality rollers with materials and hardness that meet the production characteristics of Chongqing Steel Hot Rolled Thin Plate Plant;
After production stabilizes, high-speed steel rollers are selected for the working rollers in the front section of finishing rolling to further reduce roller consumption.
in conclusion
The adjusted HVC roll profile and negative crown roll not only improve the stress distribution on the roll surface, but also strengthen the ability to control the crown of the strip, which is conducive to ensuring product quality.
Adjusting the roll replacement cycle, responding to rolling accidents and correctly handling the accident rolls all increase the rolling volume of a single roll and extend the service life of the roll while ensuring product quality.
The handling measures for the accident rolls reduce unnecessary grinding of the rolls, thereby reducing the labor intensity of employees.
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