The nature and destruction characteristics of the back-up rolls of the mill 2300/1700

Abstract

An analysis of the operational durability of the working back-up rolls of sheet hot-strip mill was given. It was shown that their function - in the runout conditions, satisfies 61% back-up rolls. The failures of the rolls on the chips, delaminations, chipped ends and the destruction of the barrel lead to crashes which causes a decrease in the performance of the mills. It was noted that the definition of patterns and the mechanism of the destruction of the back-up rolls will allow, depending on the initial profiling, to develop recommendations that will increase their production and productivity of the rolling mills. The mechanism of runout and destruction of the working surface of the back-up rolls was determined by the standard method using plastic replicas and electronic fractography. The research was carried out on the back-up rolls of the quarto cage with different hardness of the working surface, which were used in combination with work rolls with concave and cylindrical profiling of the working surface. The temperature of the rolled metal was in the range of 1050 ± 50 ° С, the rolling speed was 2.0-3.0 m / s, the maximum rolling force was 18.46 mN. Studies were carried out on the most characteristic rolls of the considered totality according to the degree of damage. As a result of the research performed, it was found that the working surface of the back-up rolls wears out unevenly during operation. Significant impact on the character of destruction of the surface layer of the back-up rollers exerts profiling working rolls with which they operate in the stand. Regularities of microrelief formation and factors affecting the damageability of the surface layer depending on the distribution of contact pressures along the length of the barrel of steel back-up rolls have been established. The results of electron-diffraction studies of working surfaces were presented depending on the nature of roll profiling. In the middle of the back-up rolls, which worked complete with workers with concave barrel profiling, traces of oxidative and abrasive wear in the mechanochemical form were revealed. In the same zones of the rolls, in an insignificant amount, the detachment of secondary protective structures of the oxide type takes place with exposure of the subsurface carbide phases. On the section of the working surface near the edge of the barrel, the mechanochemical form of abrasive wear prevails. This indicates that the contact pressure along the length of the roll barrel increases from the middle to its edge, i.e. the middle is underloaded, the edge is overloaded. Studies have shown that by changing the sign and the radius of curvature of the profile of the roll barrel, it is possible to reduce their wear and increase the service life.