In the production of steel rolling, this important industrial link, the roll, plays a decisive role. However, rolls often suffer various damage problems. These issues affect the rolls’ service life and impact the production efficiency of rolled steel. Understanding the damage forms and their underlying causes is crucial. Effective countermeasures are needed to ensure smooth rolling production.
Main forms and causes of rolling roller damage
Spalling is one of the main forms of roller damage or even early scrapping. During the rolling process, local overload and temperature increase can cause the strip to weld onto the rolling roller’s surface. This leads to cracks forming in the subsurface layer. These cracks extend radially toward the hardened layer and branch out in multiple directions. Under reverse rolling conditions, these cracks will cause spalling.
For the support roller, the spalling is mostly located at both ends of the roller, extending in the circumferential direction, and spalling in blocks or large pieces in the width direction. The surface of the spalling pit is relatively flat. The spalling of the working roller also has a process of crack generation and development. Most spalling of the working roller during production is caused by cracks on its surface.
Roller fracture
Rollers often break suddenly during operation. The fracture sites are mainly found in the roller body, roller neck, and the joint between the roller neck and the working roller. The proportion of each fracture site varies depending on the type, variety, and production process conditions of the rolled steel.
There are many situations in which rollers break, which can be a one-time instantaneous fracture or a fracture due to the development of fatigue cracks. Roller cracks are caused by thermal stress generated by multiple temperature cycles, which causes the rollers to gradually break. The rollers experience drastic changes in alternating hot and cold during the process. This causes severe strain on the surface, gradually leading to thermal fatigue cracks. These cracks form due to thermal cycle stress, tensile stress, and plastic strain. Among them, plastic strain promotes the appearance of cracks, and tensile stress promotes the expansion of cracks.
Roller entanglement
During the rolling process, rollers undergo drastic temperature changes. This leads to severe strain on the surface. Gradually, thermal fatigue cracks begin to form. These cracks result from the combined effects of thermal cycle stress, tensile stress, and plastic strain.
Roller adhesion
During the cold rolling process, steel strips can deviate, accumulate, and fold in waves. Coupled with high pressure and temperature, this causes the steel strip to easily adhere to the roll. This adhesion results in small area damage to the roll.
Although grinding can eliminate surface cracks and allow continued use, it significantly reduces the roll’s service life. This increase in damage risk can lead to peeling accidents in subsequent use.
Burning bearings
During the use of rolling mill rolls, dry friction between the bearings and the roll shafts often occurs due to reasons such as small gap between the roll bearings and the roll shafts, poor lubrication, asynchronous thermal expansion and deformation of the roll shafts and bearings, and poor bearing manufacturing quality. In severe cases, the roll shafts may even break.
Measures to deal with roll damage
Roll peeling:
Pay attention to controlling the load and temperature during the rolling process to avoid local overload and excessive temperature that may cause welding and cracking of the strip and the roll surface. For working rolls, it is necessary to strengthen the detection and prevention of roll surface cracks, and timely discover and deal with potential crack problems.
Roller fracture:
According to different rolling steels and process conditions, the roll structure should be reasonably designed to improve the strength and toughness of the rolls to cope with various possible stresses. At the same time, it is necessary to strengthen the monitoring of the rolls, timely discover the occurrence of fatigue cracks, and take corresponding measures, such as timely replacing rolls with crack hazards.
For roller entanglement
Engineers must fully account for pressure configuration to guide the steel straight through the hole. Technicians should secure the guard plate to ensure stability. Operators must apply uniform heating to the steel to avoid roller entanglement from the start.
For roller adhesion
During the rolling process, rollers undergo drastic temperature changes. This leads to severe strain on the surface. Gradually, thermal fatigue cracks begin to form. These cracks result from the combined effects of thermal cycle stress, tensile stress, and plastic strain.
For bearing burning
To effectively control the occurrence of bearing burning, it is necessary to strictly control the bearing quality and lubrication effect. By effectively monitoring the temperature of the roller bearing box, once an abnormal problem occurs, the roller should be stopped immediately, the bearing box should be replaced, and the bearing should be lubricated.
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