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Analysis of Rib Defects in Cold Rolling of Pure Titanium Coil and Strip

At present, the production of pure titanium plate and strip is mainly rolled by other multi-roll mills such as six-high, ten-high and twenty-high. In Japan, where the production technology of titanium strips is the most advanced, a twenty-high rolling mill is used for rolling, with a thickness of 0.3-3mm, high production efficiency, and excellent dimensional accuracy, shape and surface quality. However, in the actual production process, especially in the production process of large-volume, heavy-width and thin strips, there are still quality problems such as ribs and waves. Among them, tendons are the most serious, which have a negative impact on the quality of products and the benefits of enterprises, and are product quality problems that need to be solved urgently.
After the cold-rolled titanium strip is coiled into a coil, the circumferential local bulge on the surface of the coil is called a rib. For pure titanium thin strips, the rib mostly occurs in the thickness < 0.8mm, and the manifestation is mostly single rib. The direct consequence of the rib is to produce additional waves of the strip, which will affect the shape and surface quality of the strip, resulting in product degradation. It 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 rib and the probability of rib after cold rolling of different batches of hot-rolled coils of the same specification were different, indicating that the hot-rolled raw material itself has a greater impact on the cold-rolled rib. In hot-rolled incoming materials, there are common defects such as scratches, cambers, and cracks, which have a certain impact on the generation of various defects in the subsequent cold-rolling process. Although the influence of the local high point of the hot-rolled incoming material on the cold-rolled strip is only limited to the high point and a small range nearby, for the extremely thin strip, it is enough to cause the local bulge of the strip to "rib" or even to form local waves and bulges. Serious quality defects intertwined.
Through the test rolling of the same tension of different shape curves and different tensions of the same shape curve, it is found that under the conditions of the same tension and different shape curve settings, when the shape curve is set with reference to the stainless steel strip, the ribs will rise. The probability is high, and the plate shape curve is set for trial rolling after adjustment, and the probability of rib formation and the amount of rib formation are greatly reduced. Under the conditions of the same shape curve and different tension settings, the probability of rib formation in high tension rolling and small tension rolling is high, but the difference between the rib formation probability and rib amount in large and small tension rolling is not obvious. High tension rolling is not suitable for the rolling of pure titanium strip. Through the analysis of the above test rolling results, the circumferential uplift of the rib is the result of a combination of factors such as plate shape control and tension control. From the mechanical point of view, the rib
is the result of an axial force.
Although the rolling speed of titanium strip is very slow during cold rolling, if the saponification value of the lubricating fluid is not good or the nozzle is blocked, it will lead to uneven lubrication and uneven stress distribution in the deformation zone, resulting in axial component force. 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 influence on the tightening of the plate facing the center. In the process of rolling deformation, local high points or local hardness will cause uneven stress distribution in the deformation zone and generate axial component forces.
Axial component force will be generated after the interaction of equipment vibration and uneven tension, and the superimposed effect of slight center deviation, uneven thickness and gap deviation between layers during winding will generate 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-thickness ratio. On the premise that the width-thickness ratio remains unchanged, by appropriately reducing the front tension, changing the rolling lubricating oil or padding paper at the winding end By means of increasing friction, it can effectively suppress
The occurrence of rib defects.

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