The rolling of titanium seamless pipes is generally carried out using a reciprocating (i.e., Peel format) cold rolling mill, and in the process, two roller (LG) and multi roller (LD) mills are generally used for multi-pass rolling. During the deformation process, titanium pipes gradually undergo wall reduction and diameter reduction as the rolling mill rotates and feeds in. Generally, pipes per unit length undergo 5-10 times of rolling and finishing in a rolling pass to obtain the pipe size specifications required by the process. The cold rolling pipe mill can perform large diameter reduction and wall reduction processing, but after rolling, the dimensional accuracy is relatively low, and the pipe ends are prone to cracking, uneven concavities, and other phenomena. For cracking, it can be mainly solved by grinding and leveling before processing the pipe blank; For the occurrence of uneven pipe ends, similar to the phenomenon of "fish mouth", it is necessary to carry out flat head treatment during the subsequent processing process, otherwise it may cause the plug to jam. Therefore, this article analyzes the causes of uneven pipe ends from the aspects of technology, tooling, equipment, etc., in order to find out the causes and take effective measures to solve them. The excessive spline clearance at the connection between the core rod and the core rod trolley and the resulting severe displacement of the core rod position are the main reasons for the uneven concavity and convexity of the pipe end after this tube blank rolling.
When pure titanium tubes are rolled through bloom rolling, they typically undergo multiple finishing operations within a single pass. After being rolled to the required titanium tube specification, the end of the tube generally exhibits a slight fluctuation of 1 to 2mm. This batch of titanium tubes has no difference in raw materials and processes from those produced before, but there are relatively serious bumps and bumps, with a length of 70 mm, accounting for 1% of the length of the tube. According to the test results of the outer diameter and wall thickness before and after processing, the sample wall thickness fluctuates greatly, with the average wall thickness measured at the convex part of 2.33 mm, and the average wall thickness measured at the concave part of 2.60 mm. The difference between the two wall thicknesses reaches 0.27 mm, After normal rolling, the wall thickness deviation at the end of titanium pipe is 0.05~0.10 mm, which inevitably leads to differences in the elongation coefficient. It can be said that uneven wall reduction during rolling of end pipes is the direct cause of uneven pipe ends. Therefore, uneven concavoconvex pipe ends may be caused by equipment or tooling.
The wall thickness caused by the tooling does not have factors such as the installation of gear and rack, mold alignment, mold opening, and so on. After measurement, the difference between the opening degrees of the upper and lower mold passes is 0.05.; The clearance between the holes measured with a feeler gauge is 0.05mm, and the clearance between the gear and rack is about 1.6mm; The rack is fixed on the rack without looseness, and the positioning block is not deformed; The hole pattern is staggered left and right by. 02mm, and the zero line is aligned. The above measured data indicate that the installation of the mold is within the design requirements. The wall thickness caused by equipment reasons is not always due to feeding amount, rotation angle, coordination of actions, and other reasons. The rolling speed and feeding amount were executed according to the process requirements. During the operation of the equipment, the rotation and feeding were performed at the rear dead center, and the rotation and feeding were performed at the front dead center. The action was coordinated, and no advance or lag of the rotation and feeding action was found; Within the scope of equipment design requirements; Continue to measure the feeding amount during rolling, and it is found that the feeding amount is uniform. However, it is found that the core rod coaxial with the tube blank moves significantly back and forth during feeding, reaching 10mm. According to the requirements, the forward and backward movement of the core rod during rolling should not be greater than 0.5mm, otherwise it will seriously affect the accuracy of the core rod position during rolling. Further inspection found that the spline clearance at the connection between the core rod and the core rod trolley is 20mm, exceeding the clearance requirement of 8mm. When titanium pipes are fed at the rear dead center, due to the excessive clearance between the splines and the core rod, it is inevitable that the core rod will also move forward when the titanium pipe blank moves forward, resulting in significant changes in the position of the core rod connected to the core rod during rolling, that is, the position of the core rod and the pass is no longer the position set by the process, but rather moves forward. In this way, when rolling to the front dead center, the pipe is actually rolled to a thinner size; However, although the core rod is moving forward with the tube blank, the spring at the front end of the spline is still under force at this time. When the pass reaches the front dead center, the inner hole of the tube and the core rod are separated. At this time, the spring pushes the core rod backward, so that the core rod also moves backward. At this time, the pass evens the parts with thicker wall thickness on the side of the titanium tube after rolling. However, due to the retreating of the core rod, the parts with thicker wall thickness that are evened are not evened, resulting in significant differences in wall thickness. Adjust the spline clearance at the connection between the core rod and the core rod trolley. After adjustment, it is found that the pipe end misalignment disappears.
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