Cause Analysis and Preventive Measures for Roll Neck Fracture and Roll Surface Explosion

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

Roller body specification: ¢282*600mm

Types of rolled products: ¢10mm rebar

Use rack: K10

Objection form description: In the first cycle of use, the roll neck fracture and the roll surface burst during the rolling process. The macroscopic structure of the fracture is fine, and there are serious burn marks and cracks in the burst section.

Cause Analysis:

1. There is insufficient water supply during the rolling process, and when the surface temperature of the roll rises, it is not allowed to cool naturally. The method of flushing and cooling is adopted, resulting in the explosion of the high-temperature roll immediately after contact with the water. Impact force or jamming in the roll gap causes the roll neck to break.

2. During the rolling process, the machine jam or foreign matter falls into the rolling groove, which increases the instantaneous reduction between the roll gaps, and the excessive force on the working face causes the burst block and the roll neck to break.

Preventive corrective measures:

1. Increase the amount of cooling water, reduce the water temperature, and fix the water supply position of the water pipe to ensure that the cooling effect and the heating temperature of the rolls remain stable during the rolling process, prevent the rolls from continuing to operate in the absence of water, effectively protect the rolls and improve the quality of the rolls. service life.

2. Seriously supervise the rolling process, and strictly control the bad phenomena such as jamming, supercooled steel or foreign matter falling into the rolling groove during the rolling process.

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

Roller body specification: ¢405*700mm

Types of rolled products: ¢6.5-8mm wire rod

Use rack: K16

Description of objection form: In the first cycle of use, the roll surface exploded in large blocks during the rolling process, delamination occurred at the position where the outer layer and the core were fused, and the surface of the rolling groove was blue.

Cause Analysis:

During the rolling process, the cooling effect is not good (the surface color of the rolling groove is blue), which causes the surface temperature of the roll to rise. The thermal conductivity of the roll of this material is not good, and the bonding strength of the molten iron between the outer layer and the core cannot be satisfied. Due to the rolling conditions and other reasons, the roll surface burst into large blocks during the rolling process.

Preventive corrective measures:

1. Reduce the cooling water temperature and increase the water volume to ensure a good cooling effect during the rolling process.

2. It is necessary to control the low-temperature rolling of the rolled products and the shearing of the head of the rolled products to reduce the instantaneous impact force on the rolls.

3. Regularly repair the roll pass, control the infinite extension of the fatigue layer crack, and use the roll reasonably.

4. Replace the roll material and use a roll with higher strength.

 

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

Roller body specification: ¢305*500mm

Types of rolled products: ¢10mm rebar

Use rack: K1

Object form description: In the first cycle of use, the edge of the roll body dropped blocks during the rolling process, the macroscopic structure of the bottom surface of the dropped blocks was normal, and there were no bad phenomena such as slag inclusion and sand inclusion.

Cause Analysis:

The occurrence of similar falling blocks is mainly due to the explosion of the rollers under the action of strong external force. The position of the roll edge drop is wider, which is not caused by the pressure and impact force of the rolled product when the roll is working. The main reasons for similar dropped blocks are:

1. The rollers are not well protected during transportation, so that the surface of the rollers is impacted and the interior of the rollers is injured, resulting in the rolls falling off when running at high speed.

2. During the rolling process, bumping rolls or other sundries fall into the roll gap, causing the pressure between the roll gaps to be too large to cause explosion blocks.

Preventive corrective measures:

1. The rolls need to be packaged during transportation or moving to prevent the rolls from being injured internally due to collisions.

2. When the roll is used on the machine, the parallelism between the two rolls should be corrected in time to prevent the two roll surfaces from colliding with each other. During the rolling process, it is forbidden for foreign matter to fall into the roll gap or enter the pass along with the rolled product.

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

Roller body specification: ¢297*600mm

Types of rolled products: ¢12mm rebar

Use rack: K6

Description of objection form: During the second cycle of use, the edge of the roller body has dropped blocks. The macroscopic structure of the bottom surface of the dropped block is good, and there is no abnormal phenomenon. The dropped part has local burns.

Cause Analysis:

The main reason for the occurrence of block drop on the roll surface is that there is a jam during the rolling process, and the rolled product is stuck in the roll gap when the rolling mill fails. After the surface temperature rises, it is not allowed to cool naturally, but it is put into use immediately. Because the cooling water rushes to the roll surface, the temperature of the roll surface drops sharply, causing the roll body to be injured.

Preventive corrective measures:

During the use of the roll, when the rolling mill needs to be stopped for inspection due to failure or other reasons, the roll should be effectively protected, and the roll should not be damaged. The surface temperature should not be cooled in place or it should not be cooled immediately after being raised by external influences. The roll should be allowed to cool naturally before it can be put into use.

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