At present, the production of pure titanium sheet and strip mainly adopts other multi-roll mills such as six-roll, ten-roll and twenty-roll. In Japan, which has the most advanced production technology of titanium strip, a 20-roll mill is used for rolling, with a thickness of 0.3 to 3 mm, high production efficiency, and excellent dimensional accuracy, plate shape, and surface quality. However, in the actual production process, especially in the production process of large coils, heavy and wide strips, there are still quality problems such as ribs and waves. Among them, buckling is the most serious, which has an adverse effect on the quality of products and the benefits of enterprises. It is a product quality problem that needs to be solved urgently.
After the cold-rolled titanium strip is wound into a coil, the local bulge in the circumferential direction of the coil surface is called ribbing. For pure titanium thin strips, the ribs mostly occur in thicknesses below 0.8mm, and the main manifestations are mainly single ribs. The direct consequence of ribbing is to produce additional wave shape of the strip, which will affect the shape and surface quality of the strip, which will lead to product degradation. In serious cases, shearing and rewinding will be required. Not only reduces the quality of products, but also causes waste of raw materials and reduces production efficiency.
The rolling test found that the amount of ribming and the probability of ribbing after cold rolling of different batches of hot rolled coils of the same specifications are different, indicating that the hot rolled raw material itself has a greater influence on cold rolling ribs. In the hot rolling incoming materials, there are generally defects such as scratches, sickle bends, cracks, etc., which have a certain impact on the occurrence of various defects that occur in the subsequent cold rolling process. Although the influence of local high point of hot-rolled incoming material on cold-rolled strip is limited to the high point and a small range nearby, for very thin strip, it is enough to cause local bulge "ribbing" or even local wave shape and bulge Severe quality defects intertwined.
Through the trial rolling of the same tension of different plate shape curves and different tensions of the same plate shape curve, it was found that under the setting conditions of the same tension and different plate shape curves, when the plate shape curve is set with reference to the stainless steel strip, the ribs The probability is high. After setting the shape curve for adjustment and trial rolling, the probability of ribbing and the amount of ribbing are greatly reduced. Under the same shape curve and different tension setting conditions, the high-rolling and low-tension rolling have a high probability of rolling, but the difference between the large-tensile rolling and the rolling amount is not obvious, which shows that the traditional stainless steel strip High tension rolling is not suitable for rolling pure titanium strip. Through the analysis of the results of the above trial rolling, the circumferential bulge is a result of a variety of factors such as shape control and tension control. From a mechanical point of view, the rib
It is the result of an axial force.
Although the rolling speed of the titanium belt is very slow during cold rolling, if the saponification value of the lubricating fluid is not good or the nozzle is blocked, it will cause uneven lubrication and uneven stress distribution in the deformation zone, resulting in axial component forces. In the rolling deformation zone, the axial component force generated by the offset of the neutral plane may be small, but it has a certain effect on the tightening of the plate facing the center. In the process of rolling deformation, the local high point or local hardness will cause uneven stress distribution in the deformation zone and produce axial component forces.
The interaction of equipment vibration and uneven tension will produce an axial component force, and the mutual stacking effect of small center deviation, uneven thickness and layer-to-layer gap deviation during winding will produce axial component force.
On the basis of field test and theoretical analysis, a mathematical model of critical conditions for stiffening is established according to the characteristics of actual production. The critical stress of buckling instability is proportional to the fourth power of the strip thickness and inversely proportional to the square of the width. At the same time, the axial stress is most affected by the three factors of front tension, friction coefficient and width-to-thickness ratio. Under the premise that the width-to-thickness ratio is unchanged, by appropriately reducing the front tension, the rolling lubricating oil is changed or the liner is lined at the winding end It can be effectively suppressed by means such as increasing friction
Occurrence of ribbing defects.