An effective way to reduce roll consumption
1 Overview
The roll is in direct contact with the strip rolling piece and is an important tool for hot rolling production. Reducing roll energy consumption can effectively reduce production costs and increase benefits, 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, 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.
2. Optimize the roll change cycle
2.1 Roughing work rolls
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 each roll, strip plate shape and surface quality are compared. Now the roll change cycle is stable at 3.8wt~4.5wt. It does not affect the shape and surface quality of the strip plate, but also prolongs the service life of the roll.
2.2 Finishing roll-up rolls
The speed of F1~F7 rolls is different and the difference is large, so the wear degree of the back-up rolls is not the same, and 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 the adoption of the segmented roll change, not only has the rolling volume of the roll 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 specifications at the end of 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 properly handled after the accident occurs is the key to reducing roll consumption.
3.1 Stuck Steel Accidents
After the occurrence of jamming, the cooling water should be stopped immediately, the upper roll should be lifted to avoid the upper roll touching the strip steel, and after the strip steel is removed, the roll should be changed and the roll should be cooled slowly. If the roll cannot be changed immediately, under the premise that the crack is not serious, the work roll can enter normal rolling only after idling for 5-10 minutes without boiling the cooling water to make the temperature spread evenly.
3.2 Sticking Accidents
Start by removing the sticky steel. After that, a detailed inspection should be carried out on the adhesive steel area, including: hardness, cracks, flaw detection, etc., and the affected area of the adhesive steel must be cleared to ensure that the hardness of the roller surface is uniform and there are no cracks.
4. Innovative roll defect grinding countermeasures
From August 2015 to April 2016, it can be seen that the accident rolls accounted for 69% of the total roll changes. Therefore, after the rolling accident, timely and correct treatment of the roll can minimize the unnecessary damage of the roll, prolong the service life of the roll, and reduce the roll consumption.
The following is a brief introduction to the handling of rolls with several common accidents:
4.1 Thermal cracking
Thermal cracks are mostly generated by roll cooling and heat after steel jamming or steel stacking accidents.
Treatment method: On the premise of ensuring the smooth rolling, R1 and F1-F4 rolls can be used on the upper line with hot cracks, and the cracks are closed (the closed cracks will not extend, but will be extended with the use time), and the cracks will be gradually eliminated.
4.2 Roll sticking steel
Rolls stick to steel, tail flicking or steel stacking accidents cause rolls to stick to strip steel.
Treatment method: The strip of the roll body is seriously adhered to, the area is large, and the thickness is more than 3mm, and the adhered strip needs to be turned off first. If there are cracks and peeling (falling flesh), the cutting depth is determined according to the degree of damage, so as to ensure that the defects are eliminated without increasing excessive roll consumption.
4.3 The edge of the work roll body is peeling
The edge of the work roll body is peeled off, and the stress concentration of the roll shoulder is caused.
Treatment method: Since the shoulder of the roll is not in direct contact with the steel plate, the crack spalling part can be removed, the chamfer can be grinded, and the chamfering method and angle of the back-up roll in contact with it can be adjusted to improve the stress distribution of the roll body.
4.4 Back-up roller defects
The back-up roller is defective, the back-up roller does not directly contact the strip steel and the hardness is lower than that of the work roll, but it is expensive, so the conventional grinding method is not suitable.
Treatment: When the damage is on the edge of the roll, increase the chamfer length of the end appropriately when grinding. Defect residue is treated with an angle grinder and the surrounding area is rounded to prevent further spread of spalling defects. When the damage is in the middle of the roll, it is ground as usual and then treated with an angle grinder and the defect is rounded around the perimeter.
5. Adjust the roll shape
Combined with the actual production situation, the F1-F4 rolls were changed from concave rolls to HVC rolls. And increase the negative convexity of F5-F7 rolls, so as to improve the stress distribution of the roll surface. It can achieve better control of the plate shape and reduce roll consumption.
6 Other ways to reduce roll consumption
Organize exercises on the handling methods of various rolling accidents, improve the speed of emergency response, and minimize the damage of accidents to rolls;
Formulate reasonable roll flaw detection standards to ensure roll quality and reduce unnecessary losses;
Select excellent roll manufacturers, customize high-quality rolls with materials and hardness that meet the production characteristics of heavy steel hot-rolled sheet factories;
After the production is stable, the high-speed steel rolls are selected for the work rolls in the front section of finishing rolling to further reduce the roll consumption.
7 Conclusion
The adjusted HVC roll shape and negative convexity roll not only improve the surface stress distribution of the roll, but also strengthen the convexity control ability of the strip, which is conducive to the guarantee of product quality.
Adjusting the roll change cycle, responding to rolling accidents and correctly handling accident rolls all contribute to product quality
