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Analysis of defects in cold rolled bars of pure titanium strip

Jun 12, 2014

At present, the production of pure titanium plate and strip mainly adopts six rolls, ten rolls and twenty rolls. In the most advanced production technology of titanium plate belt in Japan, twenty high rolling mills are used for rolling. The thickness is 0.3 ~ 3mm, the production efficiency is high, the size accuracy, the shape and the surface quality are very good. But in the actual production process, especially large wide strip production process, there is still a rib, wave shape and other quality problems.

The cold rolled titanium strip is a local bulge in the circumferential direction of the roll surface after coiling. For pure titanium thin strip, the reinforcement is mostly produced under the thickness <0.8mm, and the specifications are mostly single tendon. The direct consequence caused by the rib is to make the strip produce additional wave shape, the shape and surface quality are affected, causing the product degradation, even to shear, shear processing. Not only reduce the quality of the product, but also cause waste of raw materials, reducing production efficiency.

The rolling test found that different batches of the same specifications of cold rolled steel and hot rolled coil after the bar shows different probability of cold hot rolled material itself, rib has a great influence. In hot rolling materials, there are some defects such as scratching, sickle bending and crack, which have some influence on the various defects in the subsequent cold rolling. Effect of hot strip local high points on cold rolled strip while confined in a small area near the highs and, but for the super thin strip, the strip is sufficient to cause the local uplift "rib" and even the formation of serious quality defects of local wave and heave intersect.

Through the test of different rolling tension of the same tension on different shape curve with the same shape of the curve, under the same tension of different shape curve under the set conditions, when the shape curve of reference stainless steel strip set, rib probability is high, the plate shaped curve setting adjustment after rolling test, rib probability with the muscle volume dropped significantly. In the same shape curve of different tension setting conditions, high tension rolling small tension rolling bar with high probability, but the size of tension rolling rib probability and rib size difference is not obvious, so that the traditional rolling stainless steel strip tension rolling is not suitable for pure titanium strip. Through the analysis of test results of rolling over, up to the bar this week uplift, is a common effect of various shape control, tension control and other factors, from the perspective of mechanics, rib is a result of axial force.

Although the rolling speed of titanium strip is very slow in cold rolling, if the lubrication fluid saponification value is poor or the nozzle is blocked, it will lead to uneven lubrication, resulting in uneven stress distribution in the deformation zone, resulting in axial component force. In the rolling deformation zone, the axial component produced by the offset of the neutral surface may be very small, but it has a certain influence on the tightening of the plate to the center. In the process of rolling deformation, the local high or local hardness causes the uneven stress distribution in the deformation zone to produce axial component.

The equipment vibration tension and uneven interaction will produce axial force, rolling when the superposition effect of central small offset, uneven thickness and pore deviation between layers and so on will produce axial force.

Based on field test and theoretical analysis on the mathematical model of rib critical condition is established according to the characteristics of the actual production, the buckling critical stress of four times and the strip thickness is proportional to the square of the width is inversely proportional to. At the same time, the axial stress before tension, friction coefficient and thickness ratio of the three most important factors, in width to thickness ratio is unchanged, by decreasing the tension, change the lubrication oil in the winding end or pad paper to increase friction etc. can effectively suppress the occurrence of tendon defects.

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