Research On Controlling Method Of Mandrel Instability Of Rotary Piercing For Tube Of Thick Wall

In the cross piercing process,the force that rolls on the tube billet will pass on to the plug and mandrel along the direction of the rolling line.When the axial force is too large,which will cause the mandrel instability bent,so as to make the rolling of steel tube bending deformation.In order to prevent this phenomenon happening,it is necessary to install the centralizer to ensure that the hollow billet axis and the rolling centerline are consistent to ensure that the mandrel has a high stability during the rolling process,reduce the consumption of the mandrel and plug and improve the production rate.However,the position of the centering roller of the existing skew roll piercing mill is uniformly arranged,and the installation position of the centering roller is not coincident with the unstable position of the actual mandrel,thus making instability of prevention and control capacity low and increasing the unnecessary equipment investment and maintenance costs.Regarding the issue above,in this paper,the theoretical analysis and finite element simulation method are used to analyze the installation position and instability control effect of mandrel centering roller.The main contents and analysis are as follows:According to the instability analysis of the compression bar,the models of uandω are established.The buckling position and the bending deflection value of themandrel are analyzed and calculated,so that the unstable position of the mandrel and the arrangement of the centering device can be determined.The calculation shows that the risk of instability of the mandrel is asymmetrical.Generally,long mandrel of10~12m the arrangement from the end to the top is :The ABAQUS finite element simulation software was used to establish the simulation model of mandrel bending.Influence of different factors on unstable bending process was simulated by ABAQUS elastoplastic finite element software.The simulation results show that the bending point at the end of the mandrel is fixed at 2/3L from the fixed end.Under the conditions of 1600 KN four-column hydraulic press,the bending process of the mandrel was simulated.The finite element model was established combined with the actual mandrel bending and the ABAQUS software,the influence of different factors on the critical buckling force,maximum deflection value and equivalent stress of the mandrel was simulated.The simulation results show that with the increasing of the length of the mandrel,the critical force of instability decreases,and the maximum deflection value increases,equivalent stress decreases;with the increasing of the diameter of the mandrel,the critical force of instability increases,and the maximum deflection value decreases,equivalent stress decreases.The bending process of the mandrel was tested under the conditions of 1600 KN four-column hydraulic press.The experimental results show that the unstable positions of the mandrels are bent at 2/3 from the fixed end of the mandrel,and the axial force at the time of bending also exceeds the critical force of instability and the change of the deflection value consistent with theoretical calculation and simulation results.However,due to the limited testing conditions,the test is not carried out in the ideal state,so there is a certain deviation between the deflection value,the theoretical calculation and simulation results.