Universal machines for creating roughness on the working surface of cold-rolling mill rolls

Abstract

During recrystallization annealing in bell-type stack annealing furnaces, cold-rolled steel strip (sheet) in coil form is subjected to the combined action of pressure, temperature, and the furnace atmosphere. The pressure ensures sufficiently close contact between the surfaces of adjacent turns of the coils, while the high temperature and the reducing atmosphere create the conditions for cleaning its surface of adsorptive and oxide films. This results in even closer contact between the turns, leading in some cases to their welding. As a result, tears and fine cracks are formed on the strip as it is uncoiled prior to temper rolling. Such defects necessitate rejection of the product and a loss of metal.Among the main factors that impact the welding of turns of coiled sheet metal are: --the tension and degree of deformation of the steel strip during its uncoiling at the cold-rolling mill; --the presence of oxide fills, and the quality of the lubricant used in cold rolling; --the maximum temperature and duration of the isothermal hold during annealing; --the composition of the furnace atmosphere; --the microrelief and quality of the surface of the cold-rolled sheet. The use of one of the above factors (degree of deformation of the strip, presence or absence of oxide films) as a controlling factor is inexpedient due to their slight individual effect on welding of the turns, while the other factors (the composition of the furnace atmosphere, annealing temperature and time) cannot be used because that would disrupt the production of cold-rolled sheet metal.At the same time, a reduction in pressure between adjacent turns to 98 kPa (9.8 N/era 2) --which corresponds to a strip tension of 39.2 kN during uncoiling --almost completely eliminates welding. However, the reduction in tension also adversely affects the productivity and operating conditions of the rolling mills, makes it more difficult to transport the rolled coils, lowers the furnace utilization factor, and lengthens the annealing cycle.The effect of contact pressure on turn welding can be alleviated by using the proper lubricant. However, the service properties of the various emulsions that are available quickly deteriorate, necessitating the use of substantial amounts of lubricant.Statistical analysis of data from numerous experiments conducted in the sheet cold-rolling shop (SCRS-1) at the Nizlmaya Gora metallurgical plant "Krasnaya Etna" showed that turn welding is most heavily affected by the microrelief and quality of the surface of the cold-rolled metal. Here, the metal with the lowest tendency to weld is that metal having a rough surface with a microrelief consisting of microscopic depressions and projections of a certain height that are distributed randomly but with an equal density. Such a micro-geometry is obtained on cold-rolled metal when the working surface of the mill rolls has a corresponding microrelief. Various mechanical methods employing hydroabrasive and free abrasive particles have been used until recently to impart such a surface to the roll...