Theoretical analysis of formation of automobile sheet roughness during temper rolling in shot-blasted rolls

The methods of microgeometry formation for the surface of temper mills rolls are presented providing the required roughness of the cold rolled strip. It was established that with the electroerosion processing a more uniform structure is formed on the roll surface with a smoothly changing microrelief, compared with the mechanical action of the abrasive. The most effective abrasive for the microrelief formation on the rolls surface is cast and split steel shot. The process of interaction predominantly occurs with round-shaped shot, since the sharp edges of the split shot also become blunt during it. In the present work, the microdepression of the roll is approximated by a spherical shape. A model of roll roughness transfer to the strip was developed taking into account the type of roll processing and tempering conditions, which makes it possible to evaluate the degree of filling of a single microdepression relief at known pressures at contact of the strip with the roller, friction coefficient, roll roughness parameters and tempering modes. A quantitative estimation of reproduction of the roll roughness on the trained strip was obtained, characterized by the roughness ratio, which is the ratio of the depth of the metal flow into the strip microdepression to the depth of the roll spherical microdepression. Determination of the dimensionless pressure required for flowing a deformable metal into it was performed using the superposition method for meridian sections in two mutually perpendicular planes. The reproduction dependencies of the micro-geometry of a temper mill roll on a rolled strip on the shot size, tension, and the height parameter of roughness are presented during the tempering of stripes with various thickness, which can be used to simulate the transfer of the roll micro-relief to the rolled strip.

Effects of Lubrication in Ferrite Rolling of Interstitial Free Steel

Ferrite rolling of interstitial free steel strip in the temperature range 650-850°C can effectively reduce furnace costs and scale formation as a result of lower strip reheating temperatures. Different lubrication conditions of lubricating oil, solid lubricant and dry condition were used during ferrite rolling tests of thin interstitial free steel strip on a 2-high Hille 100 experimental rolling mill. Different rolling speed, rolling temperature and reductions were applied to the rolling process. The rolling force and roll roughness were affected by the lubrication conditions and rolling parameters. Solid lubricant indicated an improved performance in terms of the roll roughness, as well as the oxidation property of the strip surface during ferrite rolling.