Research On The Wall-thickness Shrinkage Of The Shell Elongated By Mandrel Mill

In the production of hot rolled seamless steel tubes, continuous rolling technology is one of the most important methods. Although mandrel pipe mill has the capacity of high production and high efficiency, but in the process of continuous rolling thin-walled tubes for certain kinds of steel and steel grade is easy to course wall-thickness shrinkage(pull concave, pull leakage) greatly reduce the rate of qualified products, serious enterprise production. For now, fewer literature research on the previous issues, and most limited to qualitative analysis. Some conclusions is only reasoning or hypothesis, lack of experimental support, lack of proper experimental support. In this paper, it is necessary to further research the wall-thickness shrinkage defects.The single, double-stand and multi-stand continuous rolling process with Φ152.5 mm main pass system of Φ140 mm mandrel mill in Bao Steel has been simulated with the aid of the FE code MSC.SuperForm. This paper mainly studies the influence of deformation distribution, roll speed configuration, interface friction, and mandrel velocity on metal flow; analyze the tendency of generating wall-thickness shrinkage defects.From the study mentioned above, the main conclusions of this paper are as follows:(1) When the reduction of wall thickness remained unchanged, wall thickness at the opening of the pass changed from “wall increase” to “wall decrease” as the D/S ratio of the reduced hollow billet increased, and there is a critical D/S ratio; the D/S ratio within the range of “wall decrease”, the extent of wall thickness shrinkage increases with the the D/S ratio of the reduced hollow billet increased, it means that when rolling thin-walled tube the wall thickness is prone to shrinkage.(2) When the D/S ratio remained unchanged, wall thickness at the opening of the pass changed from “wall increase” to “wall decrease” as the reduction of wall thickness increased, and there is also a critical reduction value. So, we can control the shrinkage of the wall-thickness through changing(improving) the distribtion of the thickness ereduction.of the tube rolled.(3) The drastic wall thickness shrinkage of the steel tube happened in even-stand, such as the second and the fourth stand.(4) The wall thickness at the opening of the pass with mandrel velocity has the characteristics of “first increase and then decrease”. It means that when mandrel velocity reaches a certain value, the higher the speed of the mandrel, the wall thickness shrinkage at the opening of the pass more severe. And the smaller the friction coefficient of mandrel, the wall thickness shrinkage more severe.