Вплив температурно-контактних умов теплої прокатки на формування якості поверхні тонкого листового металопрокату

The surface quality of thin flat-rolled products is formed under the combined influence of the temperatures of the metal and work rolls, contact stresses, external friction, rolling speed, reduction, and heat transfer within the deformation zone. Based on the results of mathematical modelling and experimental studies, this paper analyses the effects of different heat-supply schemes on the thermal and contact conditions of warm rolling. The rolling of strips made of L68 brass, 08kp steel, M1 copper, and beryllium was considered under conditions involving preheating of the metal, preheating of the work rolls, or simultaneous heating of both. It was established that heating the work rolls reduces the cooling of the near-surface metal layers, limits oxidation of the workpiece before it enters the deformation zone, and creates favourable conditions for the use of process lubricants. Simultaneous heating of the strip and rolls to 300 °C produced the greatest reduction in rolling force, amounting to approximately 22–30% for L68 brass depending on the reduction ratio. It was shown that a mismatch between the roll temperature and the workpiece temperature may produce a temperature difference exceeding 100 °C between the surface and the central region of the metal. For thin beryllium strips, increasing the rolling speed and initial thickness intensifies temperature non-uniformity, with the temperature difference between the contact surface and the strip centre exceeding 200 C. The stability of the contact-surface temperature, the level of contact stresses, and the through-thickness temperature gradient are proposed as interrelated technological criteria governing surface quality formation. Recommendations are formulated for selecting heating schemes, rolling speeds, and conditions for the application of process lubricants.