Causes and Prevention of Cracks and Blocks at the Bottom of Roll Groove

1. Roll material: Nickel-chromium-molybdenum infinite chilled centrifugal compound II

Roller body specification: ¢404*700mm

Types of rolled products: ¢12-25mm rebar

Use rack: K12

Description of objection form: In the second cycle of use, cracks at the bottom of the groove and small pieces fell off during the rolling process, and the surface color of the rolling groove is light blue.

Roll Groove

Cause Analysis:

1. During the rolling process, the cooling effect is not good due to the lack of water in the cooling water, the high water temperature, and the insufficient amount of water. The surface of the rolling groove is prone to cracks after thermal corrosion, thermal fatigue and thermal shock, and the infinite extension of the crack causes the block to drop.

2. The roll does not repair the hole pattern in a reasonable cycle or the repair amount does not meet the requirements, and the fatigue crack generated during the use of the previous cycle is not completely eradicated, causing the fatigue crack to extend infinitely, resulting in increased crack growth and block drop.

Preventive corrective measures:

1. Strictly control the amount of cooling water and water temperature during the rolling process to ensure that the roll has a good cooling effect during the working process and control the generation of fatigue cracks.

2. Use the rolls reasonably and repair the rolls according to the prescribed cycle. Each repair must completely eradicate the fatigue cracks and control the infinite extension of the fatigue cracks.

2. Roll material: nickel-chromium-molybdenum infinite chilled centrifugal composite III

Roller body specification: ¢380*600mm

Types of rolled products: 200mm flat steel

Use rack: K1

Objection form description: In the third cycle of use, cracks and small pieces appeared on the roller surface during use, and small cracks appeared on the entire circumference of the roller body. The partial color of the roller surface is light blue and shiny.

Cause Analysis:

1. The cooling effect during the rolling process is not good, and the roll surface is prone to cracks after thermal corrosion, thermal fatigue and thermal shock, and fatigue cracks are prone to occur.

2. During the first and second cycles of use, the maintenance and use of the rolls were not in place, the rolls were not repaired according to a reasonable use time and repair amount, and the fatigue cracks were not completely eradicated during the repair process, making the cracks infinite. Extending and deepening results in dropped blocks.

3. The hardness of the roll is high, which will increase the tendency of fatigue cracks during the rolling process.

Preventive corrective measures:

1. Improve the cooling system to ensure that the roll has a good cooling effect during the working process and control the generation of fatigue cracks.

2. Use the rolls reasonably and repair the rolls according to the prescribed cycle. Each repair must completely eradicate the fatigue cracks and control the extension of the fatigue cracks.

3. Reduce the hardness of the same material roll or replace the roll with better thermal conductivity and toughness.

3. Roller material: Nickel-chromium-molybdenum ductile ink infinite chill Ⅰ

Roller body specification: ¢520*800mm

Types of rolled products: No. 8 channel steel

Use rack: K1

Description of objection form: In the second cycle of use, cracks appear on the side of the groove during the rolling process, and small pieces appear on the side of the first groove.

Cause Analysis:

1. The cooling effect is not good during the rolling process, and cracks are prone to occur after the bottom and both sides of the rolling groove are subjected to hot corrosion, thermal fatigue and thermal shock.

2. During the first cycle of use, the use and maintenance of the rolls were not in place, the rolls were not repaired according to a reasonable use time and repair amount, and the fatigue cracks were not completely eradicated during the repair process, allowing the cracks to extend infinitely and Deepening leads to block drop.

Preventive corrective measures:

1. Improve the cooling system, improve the water quality, increase the water volume and water pressure, and reduce the water temperature to ensure that the roll has a good cooling effect during the working process and control the generation of fatigue cracks.

2. Use the rolls reasonably and repair the rolls according to the prescribed cycle. Each repair must completely eradicate the fatigue cracks and control the infinite extension of the fatigue cracks.

4. Roll material: nickel-chromium-molybdenum infinite chilled centrifugal composite III

Roller body specification: ¢295*500mm

Types of rolled products: ¢10mm rebar

Use rack: K1

Description of objection form: In the second cycle of use, cracks at the bottom of the groove and block drop occurred during the rolling process, and the surface color of the rolling groove is dark blue.

Cause Analysis:

1. The cooling effect during the rolling process is not good, and the rolling groove is prone to cracks after thermal corrosion, thermal fatigue and thermal shock.

2. During the rolling process, the roll sticks to the steel. After removing the sticking steel part with oxygen, the roll is not allowed to cool naturally, but it is put into use immediately. The roll surface is extremely cold after the roll contacts with cooling water, which affects the quality of the roll.

3. The toughness and hardness of the roll fail to meet the rolling requirements.

Preventive corrective measures:

1. Increase the amount of cooling water, reduce the water temperature and improve the water quality to ensure a good cooling effect during the rolling process.

2. Control the sticking of the roll during the rolling process. When the sticking occurs, it should be removed reasonably, and the roll should be protected so that the quality of the roll will not be affected.

3. Reduce the hardness of the same material roll or replace the roll with better thermal conductivity and toughness.

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