1. Overview

It is an important tool for hot rolling mill production  hot rolling mill production that the roll directly contacts the strip steel. Reducing rolling mill roller energy consumption can effectively reduce the production cost and increase the benefit. 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 the hot-rolled strip steel, the consumption of roll is especially huge. Therefore, it is of great significance to find out the measures to reduce the consumption of roll and improve the service life of the rolling mill roll.

 

2. Optimize Roll Change Cycle

2.1 Roughing Work Roll

The original roll changing period of rough rolling is 2.5wt ~ 3.8wt. On this basis, the roll-changing period is gradually extended. The roll wear, strip shape, and surface quality of each roll are compared. At present, the roll changing period is stable at 3.8wt ~ 4.5wt. It not only does not affect the shape and surface quality of the strip steel but also prolongs the service life of the roll.  

2.2 Backup Roll for Finish Rolling

The rotation speed of F1 ~ F7 rolls is different, so the wear degree of backup rolls is not the same. The original 10wt ~ 15wt one size fits all roll change cycle is not reasonable. Since the adoption of segmented roll change, not only the rolling capacity of the rolling mill roll is increased by about 14.94%, thus prolonging the service life of the mill roll, but also the wave shape of the roll when rolling thin gauge at the end of the service life is reduced.
 

3. Correct Handling Method of Rolling Accident

Serious rolling accidents directly increase the value of rolling mill roller consumption. The key to reducing roll consumption is whether the accident roll can be handled correctly after the accident.  

3.1 Steel Jamming Accident

In case of steel jam, the cooling water shall be stopped immediately, and the upper roll shall be lifted to avoid the upper roll contacting the strip steel; after the strip steel is removed, the roller shall be changed and the roll shall be cooled slowly. If the roller can not be changed immediately and the crack is not serious, the work roll can enter the normal rolling after idling for 5-10 minutes without cooling water to make the temperature spread evenly.  

3.2 Steel Sticking Accident

First, remove the sticking steel. After that, the steel sticking area shall be inspected in detail, including hardness, crack, flaw detection, etc. the steel sticking area must be removed to ensure uniform hardness and no crack on the roll surface.

4. Innovation of Roller Defect Grinding Countermeasures

According to the statistics of unplanned roll change from August 2015 to April 2016, the accident roll accounted for 69% of the total roll change. Therefore, timely and correct treatment of mill roll after rolling accident can reduce unnecessary damage of roll to the greatest extent, prolong the service life of roll and reduce roll consumption.  

The following is a brief introduction to the treatment methods of several common accidents:

4.1 Hot Cracking

Hot cracks are mostly caused by quenching and heating of rolls after steel sticking or piling up accidents.

Treatment method: on the premise of smooth-rolling, R1 and F1-F4 rolls can be used on the line with hot crack, and the crack is closed (the closed crack does not extend, but with the extension of service time), and the crack will be gradually eliminated.  

4.2 Roll Sticking

Steel sticking, tail-flick or steel piling accident of roll cause steel sticking on the roll.  

Treatment method: when the thickness of the roll body is more than 3 mm, the sticking strip needs to be turned off first. Check the surface of the roller body after the sticking iron sheet is dropped. If there are cracks and spalling, the cutting depth shall be determined according to the damage degree to ensure that the defects are eliminated without increasing too much rolling mill roller consumption.  

4.3 Edge Spalling of Work Roll Body

The edge of the work roll is peeling off and the stress concentration of roll shoulder is caused.

Treatment method: because the shoulder of the roller does not directly contact with the steel plate, the peeling part of the crack can be removed, the chamfer can be ground, and the chamfer mode and angle of the back-up roller can be adjusted to improve the stress distribution of the roller body.  

4.4 Back up Roll Defects

The backup roll has defects, the backup roll does not directly contact the strip and the hardness is lower than the work roll, but the price is expensive, so the conventional grinding method is not suitable.

Treatment method: when the damage is at the edge of the rolling mill roll, the length of the end chamfer should be appropriately increased during grinding. The residual defects are treated with the angle grinder and the edges are smoothed to prevent the spalling defects from further spreading. When the damage is in the middle of the rolling mill roller, it should be grinded according to the conventional method, and then it should be treated by the angle grinder, and the defect should be smoothed around.

5. Adjust the Roll Profile

Combined with the actual production situation, the F1-F4 roll was changed from concave roll to HVC roll. The negative crown of the f5-f7 roll is increased to improve the stress distribution of the roll surface. It can achieve better control of plate shape and reduce roll consumption.

6. Other Ways to Reduce Roller Consumption

① Organize drills to deal with all kinds of rolling accidents, improve the speed of emergency response, and minimize the damage of accidents to rolls;

② Establish reasonable roller flaw detection standard to ensure roller quality and reduce unnecessary loss at the same time;

③ Select excellent roll manufacturers and customize high-quality rolls with materials and hardness that meet the production characteristics of Chongqing Iron and Steel Co., Ltd;

④ After stable production, high-speed steel rolls are selected as the front work rolls of the finishing mill to further reduce roll consumption.  

7. Conclusion

① The adjusted HVC roll profile and negative crown roll not only improve the stress distribution of roll surface, but also strengthen the crown control ability of strip steel, which is conducive to the guarantee of product quality.  

② Adjusting roll changing period, responding to rolling accidents and dealing with accident roll correctly can ensure product quality, increase the rolling quantity of single roll and prolong the service life of the roll.  

③ The countermeasures to deal with the accident roll reduce the unnecessary grinding of the roll, so as to reduce the labor intensity of the workers.