Effective ways to reduce roll consumption in hot-rolled strip production

1. Overview

 

The roller is in direct contact with the strip and is an important tool in hot rolling production. Reducing roller energy consumption can effectively reduce production costs and increase efficiency. It can also effectively improve rolling mill operation rates 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 measures to reduce roll consumption and improve roll life is of great significance to the production of hot-rolled strip steel.

 

reduce roll consumption, hot rolled strip

 

2. Optimize the roll replacement cycle

 

2.1 Roughing work rolls

 

The original rough rolling roll change cycle was 2.5wt~3.8wt. On this basis, the roll change cycle was gradually extended, and the roll wear, strip shape and surface quality of each roll were compared. The current roll replacement cycle is stable at 3.8wt~4.5wt. It does not only affect the strip shape and surface quality but also extends the service life of the roll.

 

2.2 Finish rolling backup roll

 

The rotation speeds of rollers F1 to F7 are different and the difference is large, so the degree of wear of the backup rollers is also different. The original one-size-fits-all roll replacement cycle of 10wt to 15wt is not reasonable.

Since the adoption of segmented roll replacement, not only has the rolling capacity of the roll been increased by about 14.94%, thereby extending the service life of the roll, but statistics show that the wave shape of the roll when rolling thin specifications at the end of its use has also been reduced.

 

3. Correct method of handling rolling accidents

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 Steel stuck accident

 

After the steel jam occurs, the cooling water must be stopped immediately and the upper roller must be raised to prevent the upper roller 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 and the cracks are not serious, the work roll should be idle for 5-10 minutes without cooling water to allow the temperature to spread evenly before normal rolling can begin.

 

3.2 Steel sticking accident

 

First, remove the sticky steel. Afterwards, a detailed inspection of the steel-sticking area should be carried out, including hardness, cracks, flaw detection, etc. This steel-sticking affected area must be cleared to ensure uniform hardness and no cracks on the roll surface.

 

4. Innovative grinding strategies for roll defects

 

From the statistics of unplanned roll replacements from August 2015 to April 2016, it can be seen that the accident roll accounted for 69% of the total roll replacements. Therefore, after a rolling accident occurs, handling the rolls promptly and correctly can minimize unnecessary damage to the rolls, extend the service life of the rolls, and reduce roll consumption.

The following is a brief introduction to the handling methods of several common accident rolls:

 

4.1 Hot cracks

 

Hot cracks are mostly caused by the cold and heat of the roll after the steel jamming or steel stacking accident.

Treatment method: Under the premise of ensuring smooth rolling, R1 and F1-F4 rolls can be used online with rolls with thermal cracks, and the cracks are closed (closed cracks will not extend, but will extend with use time), cracks will be gradually eliminated.

 

4.2 Roller steel sticking

 

The roll sticks to the steel, and tail flicking or steel stacking accidents cause the roll to stick to the strip.

Treatment method: The strip steel on the roll body is seriously overlapped and the area is large. When the thickness is more than 3mm, the adhered strip steel needs to be turned away first. After the adhered iron sheet is removed, check the surface of the roller body. If there are cracks and peeling (meat loss), determine the cutting depth based on the degree of damage to ensure that the defects are eliminated without increasing excessive roller consumption.

 

4.3 The edge of the work roll body peels off

 

The edge of the work roll body is peeled off and the stress on the roll shoulder is concentrated.

Treatment method: Since the roll shoulder does not directly contact the steel plate, the cracked and peeled part can be removed, ground and chamfered, 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 Defects of back-up roll

 

The backup roll does not directly contact the strip steel and has a lower hardness than the work roller. However, it is expensive, so conventional grinding methods are not suitable.

Treatment method: When the damage is on the edge of the roll, appropriately increase the end chamfer length during grinding. The remaining defects are treated with an angle grinder and smoothed around to prevent the further spread of peeling defects. When the damage is in the middle of the roll, grind it as usual and then use an angle grinder to smooth around the defect.

 

5. Adjust the roll shape

 

Based on the actual production conditions, the F1-F4 rolls were changed from concave rolls to HVC roll types. The negative crown of F5-F7 rolls is increased to improve the stress distribution on the roll surface. It can achieve better control of plate shape and reduce roll consumption.

 

6. Other ways to reduce roller consumption

 

Organize exercises to deal with various rolling accidents, improve emergency response speed, and minimize the damage to the rolls caused by accidents;

Develop reasonable roll flaw detection standards to ensure roll quality while reducing unnecessary losses;

Select excellent roll manufacturers and customize high-quality rolls with materials, hardness, etc. that are in line with the production characteristics of Chongqing Steel Hot Rolled Sheet Plate Factory;

After production stabilizes, high-speed steel rolls are selected for the work rolls in the front section of finishing rolling to further reduce roll consumption.

 

7. Conclusion

 

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

Adjusting the roll replacement cycle, responding to rolling accidents and correctly handling accident rolls all ensure product quality while increasing the rolling volume of a single roll and extending the service life of the rolls.

The countermeasures for dealing with accidental rolls reduce unnecessary grinding of rolls, thus reducing the labour intensity of employees.

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