the rolling of titanium seamless pipe in general is processed by reciprocating cold rolling mill (i.e., peel format). In the processing process, the two-roll (LG) and multi-roll (LD) mills are generally used for multi-pass rolling.In the process of deformation, with the rolling mill rotation and feed, gradually reduce the wall, reduce the diameter, the unit length of the pipe in a rolling path generally through 5~10 times of rolling, finishing to obtain the process requirements of the size of the pipe.Cold rolling mill can carry out large diameter reduction and wall reduction processing, but after rolling, the size accuracy is low, the pipe end is prone to cracking, uneven, and other phenomena, for cracking phenomenon, mainly through the tube processing before grinding, leveling and other methods can be solved;For the appearance of the tube end is not neat, similar to the "fish mouth" phenomenon, in the subsequent processing process needs to be flat head treatment, otherwise it will cause plug stuffy car accident, therefore, this paper from the process, mold, equipment and other aspects of analysis, in order to find out the cause of the tube end uneven reasons, take effective measures to solve.The large spline gap at the connection between the core bar and the core bar trolley and the serious displacement of the mandrel are the main reasons for the uneven end of the tube after the billet rolling.
When the pure titanium pipe is rolled in the blank, it usually needs to be finished many times in a pass. After rolling into the required titanium pipe specifications, the end of the pipe will generally have a slight fluctuation of 1~2mm.This batch of titanium tube in terms of raw materials and process before and there was no difference in the production of pipes, but more severe bump fluctuations, length is 70 mm, 1% of the pipe length, from the outer diameter and wall thickness test results before and after processing, sample thickness fluctuation is bigger, convex parts measurement data average wall thickness of 2.33 mm, concave position measurement data average wall thickness of 2.60 mm, both reached 0.27 mm wall thickness difference, the normal after rolling of titanium pipe wall thickness deviation is 0.05 ~ 0.10 mm, wall thickness deviation will cause different elongation coefficient,It can be said that the unevenness of the wall loss during the end tube rolling is the direct cause of the unevenness of the end tube.
The uneven wall thickness caused by the mold has the factors such as the installation of gear and rack, the mold alignment, the mold opening degree and so on.After the measurement, the gap between the upper and lower mold holes is 0.05.;The gap between the hole type and the gap between the gear and the rack is about 1.6mm.The rack is fixed on the rack without looseness and the positioning block is not deformed.Hole left and right dislocation cut.02mm, zero line alignment.The above measurement data shows that the installation of the mold is within the range of design requirements.The uneven wall thickness caused by the equipment has some reasons, such as feed amount, rotation Angle, coordination of movement, etc.The rolling speed and feed amount shall be executed according to the process requirements. During the operation of the equipment, the backward dead point shall be rotated and fed, and the forward dead point shall be rotated and fed. The movement shall be coordinated.Within the scope of equipment design requirements;Continue to measure the rolling amount sent to, found that sent the amount evenly, but found that titanium pipe when sent to, and core tube billet coaxial rod before and after the shot motion is bigger, to 10 mm, before and after a core rod during rolling in accordance with the requirements of the momentum should not be greater than 0.5 mm, otherwise it will seriously affect the accuracy of rolling of mandrel position, further examination found that the junction between the core and core rod car is spline clearance 20 mm, more than 8 mm clearance requirements.When the titanium pipe is sent into the back dead center, the gap between spline and core rod is too large, which inevitably leads to the core rod is also moving forward when the titanium pipe billet is moving forward. In this way, the position of the mandrel connected with the core rod during rolling changes greatly, that is, the position of the mandrel and hole is no longer the position set by the process, but the position of the mandrel is moving forward.In this way, when rolled to the front dead center, the pipe is actually rolled to a thinner size;But while core rod followed the tube billet, spline front end of the spring force, at this point has been when pass to top dead center, pipe inner hole and release of the plug, the spring push after the core rod, the mandrel is back, this time pass rolling of titanium tubes after the side wall thickness thicker parts on the whole, but due to the backward core rod, the all the wall thickness of the thicker part but not all the whole, then caused the wall thickness of the larger difference.After adjusting the spline clearance at the connection between the core rod and the core rod trolley, the unevenness of the tube end was found to disappear.