1. Overview
Mill Roll is an important part that is in direct contact with strip steel rolled piece for hot rolling production. Reducing mill roll energy consumption can effectively reduce production costs and increase efficiency. At the same time, it can effectively increase the operation rate of rolling mills and ensure the surface quality of hot-rolled products. In the production of hot-rolled strip, the consumption of rollers is enormous. Therefore, to find out measures to reduce roller consumption and improve roller life are of great significance to hot strip production.
2. Correct rolling accident treatment method
Severe rolling accidents lead to more mill roll consumption. The key to reduce roll consumption is whether the accidental roll can be properly handled after an accident.
2.1 Jamming Accident
After Jamming Accident, it is necessary to stop the cooling water immediately and lift the upper roll to prevent the upper roll from contacting the strip. When the strip is removed, change the roll and cool it slowly. If it is not possible to change the roll immediately and the crack is not serious, the work roll can run for 5-10 minutes without cooling water. Before normal rolling, the temperature needs to be diffused evenly.
2.2 Strip Welding Accident
First remove the sticking steel. Then inspect the bonded steel area, including: hardness, cracks, flaw detection, etc. The sticking steel area must be removed to ensure that the uniform roller surface, no cracks.
3. Innovative Mill Roll Defect Repair Measures
The following is the brief description of several common accident roll handling methods:
3.1 Hot Crack
Hot cracks, mostly appear when the rolls are chilled and heated in the case of jamming or piling-up of steel.
Treatment method: R1 and F1-F4 rolls can be used on the roll with hot cracks under the premise of smooth rolling, and cracks are closed (closed cracks won’t extend), cracks will gradually eliminate.
3.2 The Roll Sticking of Strip
The roll sticking of strip, tail-drag or steel stack accidents cause roll sticking of strip.
Treatment method: Roller roll body steel strips are sticky and overlapped, and the area is large. When the thickness is more than 3mm, the attached strip steel needs to be turned off first. Check the surface of the roll body after the attached iron sheet has fallen. If cracks and peeling occur, determine the depth of cut depending on the degree of damage. Make sure that the defect is eliminated without increasing the excessive roll wear.
3.3 Work Roll Body Edge Peeling off
The edge of the work roll body is peeled off and stress concentration occurs on the roll shoulder.
Treatment method: Since the shoulders of the rollers do not directly contact the steel plate, the crack spalling part can be removed, the grinding chamfering can be performed, and the contact roller chamfering method and angle can be adjusted to improve the stress distribution of the roller body.
3.4 Support Roller Defects
Support roller defects, the backup roller does not directly contact the strip and the hardness is lower than the work roll, but the price is expensive, so it is not suitable to adopt a conventional grinding method.
Treatment method: When the damage is at the edge of the roll, increase the length of the chamfer at the end when grinding. Residues of defects are treated with an angle grinder and the surrounding area is over-smoothed to prevent further spreading of the spalling defects. When the damage is in the middle of the roll, it is conventionally ground and then also treated with an angle grinder and the defect is rounded all around.
4. Adjust Mill Roll Type
In accordance with the actual production situation, the F1-F4 rolls can be changed from concave rollers to HVC roller types. And increase F5-F7 roller negative crown, thereby improving the roll surface stress distribution. Can achieve a better control of the purpose of the plate, and reduce roll consumption.
5. Other Ways to Reduce Mill Roll Consumption
5.1. Organize various treatment methods for rolling accidents, increase the speed of emergency response, and minimize the damage of the accident to the rollers;
5.2. To establish a reasonable roll inspection standards to ensure the quality of the roll while reducing unnecessary losses;
5.3. Select excellent roll manufacturers, and customize high quality rolls such as material and hardness that meet the production characteristics of heavy steel hot-rolled sheet mills;
5.4. After the production is stable, the high-speed steel rolls are selected in the front end of the finishing roll to further reduce the roll wear.
6. Conclusion
6.1 The adjusted HVC roll and negative crown roll not only improve the stress distribution on the roll surface, but also strengthen the control of the crown of the strip, which is beneficial to the product quality assurance.
6.2 Adjust the roll change cycle, response to rolling accidents and proper handling of the accident roll, all while ensuring product quality, increase the rolling volume of a single roll and prolong the service life of the roll.
6.3 The treatment measures for the accidental rolls have reduced unnecessary grinding of the rolls and reduced the labor intensity of the employees.
