Study On Mechanism Of Pulling Concave Of Seamless Steel Tube Push Bench Process Of T22 Steel

As one of the mills for the production of seamless steel tubes,CPE(cross piercing and elongating)has the advantages of low cost,high production efficiency,better inner surface quality and larger extension coefficient in the production of small size thin wall and middle wall tube.Due to the little research on deformation theory of push bench process,CPE is mainly based on experience in actual production.Therefore,when producing thin-walled high steel grade seamless tubes such as T22,there are often defects such as tube pulled concave,which seriously affect product quality,yield and economic benefits of enterprises.Therefore,it is necessary to systematically study the mechanism of pulling concave in T22 steel push bench process,so as to provide theoretical basis for solving the problem of pulling concave in push bench process,which is undoubtedly of important theoretical and practical significance.This paper is based on the equipment and technological conditions of the?114mm push bench mill of a steel tube company.In view of the concave problem in the actual production of T22 seamless steel tube,the finite element analysis software Simufact is used to analyze the kinematics,mechanics and deformation parameters in the push bench process of typical T22 steel tubes,and to diagnose the formation of the concave defect in the process of push bench process.A systematic study on the influence of different push bench process parameters and pass structure parameters on the tendencies of pulling concave has been investigated.The main conclusions of the study are as follows:(1)In the process of push bench,there has a tension between stands with larger wall reduction.The greater the wall reduction of the stand is,the greater the tension between the stands and the pulled thin of the wall thickness at the roll gap is.(2)The main causes of the tube wall pulled concave are the serious inhomogeneous deformation of the workpiece along the width of the pass caused by the excessive wall reduction and the reduction rate,the larger tension between the stands and the mandrel pulling force produced by the excessive velocity difference between the mandrel and the workpiece.(3)With the decrease of the friction coefficient of the mandrel,the axial tensile stress of the workpiece in the roll gap and the tendencies of the tube wall pulled concave are increased.If the friction coefficient is too large,the steel stacking between the stands will be serious.(4)The most disadvantageous to the push bench process when the maximum speed of the mandrel is 2.4m/s.Considering the production efficiency,tool wear,energy consumption and tube wall concave,it is appropriate to select the maximum speed of 2.7m/s as the mandrel in actual production.(5)The greater the wall reduction and wall reduction rate of the stand is,the greater the additional deformation of the workpiece in the roll gap is.The increase of the stand wall reduction will aggravate the flow of metal to the side wall of the pass.Meanwhile,it will aggravate the uneven of the flow in the inner and outer surfaces of the metal at roll gap in result increasing the tendency of the tube wall pulled concave.