In the process of hot strip continuous rolling, due to the influence of process parameters such as the temperature of the rolling stock, the speed of the roll, the coefficient of friction, and the difference in roll diameter, asymmetrical rolling phenomena in which the extension of the upper and lower surfaces of the rolling stock are inconsistent often occur, resulting in different heads The degree of warpage (referred to as buckling head) directly affects the rolling stability. When the head of the strip is too large, it will have a strong impact on the roller table. When the head of the strip is too up, it will hit the roller or the guide device, thereby reducing the service life of the equipment and seriously affecting the output, quality and product of the product. Rate, increasing the time for maintenance and repairs and maintenance costs, especially when rolling hard-to-roll varieties such as thin and wide specifications, it is easy to cause threading failure and form rolling waste. Therefore, effective control of the buckling head has always been one of the technical difficulties in hot strip production.
When a plant uses a hot continuous rolling unit to produce pure titanium coils, due to the differences in thermal conductivity, specific heat, deformation behavior and other aspects of pure titanium and carbon steel, the effect of process parameters on finishing rolling warping is more complicated. The head warpage control technology of carbon steel is no longer suitable for pure titanium rolling, and the problem of warping heads in finishing rolling has not been well solved. To this end, the researchers used the elastoplastic finite element method to establish the thermo-mechanical coupled asymmetric rolling model for the problem of hot rolling of pure titanium coils in hot continuous rolling. The rolling head put forward effective measures and scientific basis.
The root cause of the warpage of the rolling head is due to the asymmetry in the rolling process. According to the actual situation on the industrial site and the experience of solving the problem of warpage during the actual rolling of the steel strip, the main factors that affect the warpage are summarized These are: the difference in diameter between the upper and lower work rolls, the temperature difference between the upper and lower surfaces of the rolled part, the pass reduction rate, the wear of the rolls and the friction caused by the changes in the surface of the rolled part. Law of influence.
Curved head warping of pure titanium coil is a typical thermal-mechanical coupling problem. Considering the small amount of lateral deformation of the rolled piece, it can be regarded as a plane strain problem. An asymmetric finite element model was established using the finite element software MSC.Marc. The test results are as follows:
- (1) Aiming at the problem of hot rolling of pure titanium coils in hot rolling, a thermo-mechanical coupled asymmetric rolling model was established. The process simulation showed that the flow of metal in the deformation zone during pure titanium rolling was slightly “w” type, which was similar to ordinary carbon The metal flow in the deformation zone “C” of steel rolling is different.
- (2) Through calculation and analysis, it is found that the difference in surface temperature difference and friction coefficient of the rolled product has the most obvious influence on the finishing rolling warp, and the influence of the thickness of the oxide layer and the roll diameter difference on the finishing rolling warp is not significant.
- (3) The specific measures to control the finishing rolling warp are to add a water cooling device at the entrance of finishing rolling. By controlling the water flow rate, the temperature difference between the lower surface temperature and the upper surface of the rolled product is appropriately adjusted. The decrease in the temperature of the lower surface of the rolled product increases the coefficient of friction of the lower surface, so that the sum of the frictional forces of the upper and lower work rolls with the pressure difference is closer to balance. In order to effectively suppress the serious head warping phenomenon of pure titanium coil finish rolling, the head of the rolled product exit is in a micro-buckle state.
- (4) After adopting effective control measures for the finishing roll of titanium coil, the process yield index has been greatly increased from 91.85% to 96.8%, with significant economic benefits.