1. Overview
The rolls are in direct contact with the rolled steel strip and are an important tool for hot rolling production. Reducing roll energy consumption effectively reduces production costs and increases benefits. At the same time, it can effectively increase the mill operating rate and ensure the surface quality of hot-rolled products. In the production of hot-rolled strip steel, the consumption of rolls is particularly huge. Therefore, finding out measures to reduce roll consumption and increasing the life of the rolls is of great significance to the production of hot-rolled strip steel.
2. Optimize the roll change cycle
2.1 Roughing work roll
The roll change cycle of the original rough rolling is 2.5wt～3.8wt. On this basis, the roll change cycle is gradually extended, and the wear condition, strip shape and surface quality of each roll are compared. The roll change cycle is now stable at 3.8wt～4.5wt. It does not affect the strip shape and surface quality, but also prolongs the service life of the roll.
2.2 Finishing back-up roll
The F1～F7 rolls have different rotation speeds and a large difference, so the wear degree of the back-up rolls is also different. The original one-knife-cutting roll change cycle of 10wt to 15wt is not reasonable.
Since the adoption of the segmented roll change, not only has the rolling volume of the roll increased by about 14.94%, thereby prolonging the service life of the roll, but also according to statistical data, the wave shape when rolling thin gauges at the end of the roll use has also been reduced.
3. Correct handling method of rolling accident
Serious rolling accidents directly increase the value of roll consumption, and whether the accident roll can be handled correctly after the accident is the key to reducing roll consumption.
3.1 Card steel accident
After the steel jam occurs, immediately stop the cooling water and lift the upper roll to avoid the upper roll contacting the strip steel; after the strip is removed, change the roll and allow the roll to cool slowly. If the roll cannot be changed immediately, check that the crack is not serious, and the work roll can enter normal rolling without cooling water idling for 5-10 minutes to make the temperature spread evenly.
3.2 Sticking steel accident
First remove the sticky steel. Afterwards, a detailed inspection should be carried out on the steel-bonded area, including hardness, cracks, flaw detection, etc. The affected area of the steel-bonded steel must be removed to ensure that the roller surface has uniform hardness and no cracks.
4. Innovative roll defect repairing countermeasures
From August 2015 to April 2016, unplanned roll changes statistics show that accidental rolls accounted for 69% of the total roll changes. Therefore, after a rolling accident occurs, timely and correct handling of the rolls can minimize unnecessary roll damage, extend the service life of the rolls, and reduce roll consumption.
The following briefly introduces the treatment methods of several common accident rolls:
4.1 Thermal cracking
Hot cracks are mostly caused by the chilling and heating of the rolls after the stuck or piled steel accidents.
Treatment method: R1 and F1-F4 rolls can be used on-line with hot cracked rolls under the premise of ensuring smooth rolling, and the cracks are closed (closed cracks do not extend, but prolong with the use time), cracks Will gradually eliminate.
4.2 Roll sticking to steel
The roll sticks to steel, and the roll sticks to strip steel due to tail-flicking or steel pile accidents.
Treatment method: the roll body strip steel sticking is serious, the area is large, and the sticking strip steel needs to be turned off first when the thickness is more than 3mm. After the adhered iron car is dropped, check the surface of the roller body. If there are cracks and flaking (flesh), determine the depth of cut according to the degree of damage to ensure that defects are eliminated without increasing excessive roller consumption.
4.3 Peeling off the edge of the work roll body
The edge of the work roll body is peeled off, which is caused by stress concentration at the roll shoulder.
Treatment method: Since the shoulder of the roll does not directly touch the steel plate, it can remove the cracked and peeled part, grind the chamfer, and adjust the chamfering method and angle of the supporting roll in contact with it to improve the stress distribution of the roll body.
4.4 Defects of backup roll
The back-up roll is defective. 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 appropriate to use conventional grinding methods.
Treatment method: When the damage is on the edge of the roll, appropriately increase the chamfer length of the end when grinding. The remaining defects are treated with an angle grinder and the surroundings are smooth and excessive to prevent the peeling defects from spreading further. When the damage is in the middle of the roll, it should be ground as usual and then treated with an angle grinder as well, and the defect should be smooth and excessively round.
5. Adjust the roll profile
According to the actual production situation, the F1-F4 rolls are changed from concave rolls to HVC roll types. And increase the negative crown of F5-F7 rolls, thereby improving the stress distribution on the roll surface. It can achieve better control of plate shape and reduce roll consumption.
6. Other ways to reduce roll consumption
① Organize exercises to deal with various rolling accidents, increase the speed of emergency response, and minimize the damage to the rolls caused by the accident;
② Formulate reasonable roll inspection standards to ensure roll quality while reducing unnecessary losses;
③Choose excellent roll manufacturers and customize high-quality rolls with customized material and hardness that meet the production characteristics of the heavy steel hot-rolled sheet plant;
④ After the production is stable, high-speed steel rolls are selected for the front work rolls of finishing rolling to further reduce roll consumption.
7. Conclusion
① The adjusted HVC roll profile and negative crown roll not only improve the surface stress distribution of the roll, but also strengthen the crown control ability of the strip, which is beneficial to the guarantee of product quality.
②Adjust the roll change cycle, the response to the rolling accident and the correct handling of the accident roll. While ensuring the quality of the product, it increases the rolling volume of a single roll and prolongs the service life of the roll.
③The countermeasures for accident rolls reduce unnecessary grinding of rolls, thereby reducing the labor intensity of employees.
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