Rolling method and precautions for titanium seamless tubes and pipes

Rolling of titanium seamless tubing is generally used reciprocating (i.e., Pilger format) cold rolling mill for processing, the process is generally used two-roll (LG) and multi-roll (LD) mill for multi-pass rolling. Titanium tubing in the deformation process with the mill's rotary as well as feeding, and gradually reduce the wall, reduce the diameter of the unit length of the pipe in a rolling passes generally after 5 to 10 times rolling, finishing to obtain the process requirements of the pipe size specifications. Cold rolling mill can be large diameter reduction, wall reduction processing, but after rolling the lower dimensional accuracy, tube ends are prone to cracking, uneven and other phenomena, for the phenomenon of cracking, mainly through the billet processing before grinding, flattening and other methods can be resolved; for the emergence of the pipe end is not flush, similar to the "fish mouth" phenomenon, in the subsequent processing needs to be carried out in the flat head! Processing, otherwise it will cause plug boring accident, therefore, this paper from the process, tooling, equipment and other aspects of the analysis, aims to find out the causes of the unevenness of the tube end, take effective measures to solve. The core rod and core rod trolley connection spline clearance is too large and the resulting serious displacement of the mandrel position is the main reason for this billet rolling after the pipe end concavity and unevenness.

Pure titanium tube after open billet rolling, in a pass generally after a number of finishing, rolled into the required specifications of the titanium tube, the tube end will generally appear 1 ~ 2mm of slight undulation. The batch of titanium tubes in the raw materials and processes and the previous production of tubes, but there is a more serious concave-convex undulation phenomenon, the length of 70mm, accounting for 1% of the length of the tube, from the processing before and after the outer diameter and wall thickness test results, the specimen wall thickness fluctuations, convex part of the average wall thickness of the measurement data of 2.33mm, concave part of the measurement data of the average wall thickness of 2.60mm, the difference between the two wall thicknesses of up to 0.27mm, while the normal rolling of the titanium tube end of the wall thickness deviation of 0.05 ~ 0.10mm, wall thickness deviation will inevitably cause different extension coefficients, it can be said that the end of the rolling of the tube when the wall reduction of the amount of uneven is caused by the tube end of the direct cause of the unevenness of the tube end, therefore, resulting in the unevenness of the tube end of the unevenness of the wall thickness may be the result of the equipment or tooling.

Uneven wall thickness caused by the work mold has the installation of the rack and pinion, the alignment of the mold, mold opening degree and other factors. After measurement, the upper and lower mold hole type of the opening degree difference of 0.05.; Plug ruler to measure the hole type clearance of 0.05mm, gear and rack clearance of about 1.6mm; Rack in the rack fixed without loosening phenomenon, no deformation of the positioning block; Hole type of the left and right misalignment cut .02mm, zero line alignment. The above measurement data show that the installation of the mold are within the design requirements. Uneven wall thickness caused by the equipment have feeding volume, slewing angle, the coordination of action and other reasons. Rolling speed and feed volume in accordance with the process requirements, equipment operation, in the back of the dead center of rotation and feed, in the front of the dead center of rotation, action coordination, did not find the rotary feeding action in advance and lagging phenomenon; in the equipment within the scope of the design requirements; continue to measure the volume of rolling feed, found that the amount of uniform feed, but found that titanium tubes in the feed, coaxial mandrels and billets before and after the large fluctuation of up to 10mm! In accordance with the requirements of the core rod in rolling before and after the amount of movement should not be greater than 0.5mm, otherwise it will seriously affect the accuracy of the position of the mandrel when rolling, further inspection found that the core rod and the core rod trolley connected to the spline clearance of 20mm, exceeding the clearance of 8mm requirements. When the titanium pipe in the back dead center feed, due to the spline and core rod clearance is too large, will inevitably lead to titanium tube blanks forward when the core rod is also forward, so that the position of the mandrel connected to the core rod in rolling has undergone a large change, that is,: the position of the mandrel and the hole is no longer the position of the process settings, but the forward movement. So that when rolling to the front dead center, the pipe is actually rolled to a thinner size; but although the core rod in the billet followed by the front, the spring at the front end of the spline at this time but has been stressed, when the hole pattern to the front dead center, the pipe's inner hole and the core rod to disengage, the spring will be pushed back to the core rod so that the core rod is also backed up, this time, the hole pattern of the titanium tube rolled side of the wall thickness of the thick parts of the equalization, but due to the mandrel's backwardness. But due to the mandrel backward, the equalization of the thicker parts of the wall thickness is not equalized, resulting in a large difference in wall thickness. Adjust the spline gap between the mandrel and the mandrel trolley connection, and after adjustment, the phenomenon of pipe end unevenness was found to have disappeared.