Rolls play a vital role in steel rolling production. In the case of heavy work tasks and an increase in the number of medium and thin plates, most of the work rolls have cracked edges. Generally, the cracks at the edge of the roll continue to expand after the cracks, resulting in small pieces of tissue peeling off at the edge of the roll, forming continuous or discontinuous defects. If this kind of crack persists, freely penetrating the roll body will cause large pieces of tissue to peel off, and eventually, make the roll unusable and scrapped.
The defects of the work roll edge are generally caused by the following reasons:
- The overload on the end of the work roll body is affected by the aggravated positive bending of the work roll.
- The shape and size of the chamfer at the end of the support roller body. During the steel rolling process, the pressure increases when the support roll and the work roll are in contact. In this case, if there is a stress concentration or excessive instantaneous stress at the edge of the roll, micro-cracks may appear, leading to edge defects.
- The work roll has been used for too long on the machine, resulting in excessive wear, causing partial overload at the end of the roll body, and prone to initial cracks, which continue to expand and punch out at a certain time, resulting in defects at the edge of the roll.
After the defect occurred in the work roll edge of a certain factory, various factors that may cause the defect in the rolled edge were checked one by one. Finally, it was found that the grinding of the work roll shape, the control of the crown, and the chamfering of the support roll were correct. Effective control of roll edge defects.
Work roll shape test (unit: mm)
Trapezoidal roll shape, the upper bottom is the center of the work roll 1400, the convexity is 0.0002, and the lower bottom is 4300, a sine curve with a period of 180 degrees.
As a result of the test, the center of the plate is too thin and the difference between the same plate is too large. The edge force is reduced, and the stress is in a controllable range.
On this basis, after everybody has studied together again and again experiment. Change the trapezoid to a parabola, a sine curve with a period of 180 degrees, a height of 0.0002, and a side extension of 450, similar to the “Ω”-shaped, roller shape.
The test results are good, and there is no excessive difference in the same board. The edge stress is also in the controllable range, and no edge defects are generated.
Finally, combined with the support roll chamfer (radius 30000, length 400), it is determined that the work roll shape is: a 180-degree sinusoidal curve, side length extension line is 450, height 0.0002 (convexity can increase with roll wear) Ω shape, which is Work roll shape.
The correctness of roll shape grinding, proper edge chamfering, and no roll edge defects. The micro-cracks and the early phenomena of plastic deformation did not appear, and the stress on the edges was also effectively controlled. The hardness of the roll is also within the working range. During the follow-up inspection process, problems were discovered and resolved in time.
- Appropriate chamfering of the edge of the supporting roller is very important to the service life of the supporting roller.
- For the control of work roll shape, the increase in roll wear and crown prolongs the service life of the roll.