Research On Wall Thickness Accuracy Of Tube Rolled By Automatic Plug Mill

The seamless steel tube rolled by automatic plug mill has a wide range of product specifications and materials,flexible production and low price.It is easy to replace the specifications in rolling large diameter products,which is suitable for small batch production.Therefore,it is one of the commonly used tube making methods.Since the automatic plug mill is short plug rolling,the wall thickness accuracy and rolling length of the product have an obvious gap compared to other mills,especially retained mandrel mill,which seriously affects the product quality,yield rate and economic benefits of enterprises.Therefore,it is undoubtedly of great theoretical and practical significance to systematically study the influence of different process parameters,deformation parameters and tool parameters on the wall thickness accuracy of automatic rolling tube.This paper is based on the process and equipment conditions of automatic plug mill of a steel pipe company,combined with typical specifications and steel grades,to establish three-dimensional finite element model of automatic tube rolling process,and analyze the stress and strain distribution of rolled tube,metal flow law,tube transverse and longitudinal wall thickness accuracy.On this basis,the influence of different roll pass structure parameters,different mandrel size and lubrication state,roll pass wear and eccentricity of pierced shell on the wall thickness accuracy of automatic rolling tube is analyzed,which provides a scientific basis for the optimization of automatic rolling process and tool parameters.The main conclusions of the study are as follows:(1)In the process of automatic rolling tube,the metals at the side wall and the opening of the pass have lateral spread,and the metal at the roll gap has an additional deformation.The strain values of the inner and outer surfaces at the top of the pass have a relatively large difference.When the metal at the side wall of the pass has a lateral accumulation and the longitudinal extension is not sufficient,it is easy to produce uneven transverse wall thickness.(2)The transverse average wall thickness of the tube rolled by the existing technology is about 0.15 mm bigger than the theoretical target wall thickness,the maximum transverse wall thickness unevenness of the rolled tube is 12.66%,and the maximum longitudinal wall thickness unevenness is 14.8%.(3)When the friction coefficient of the mandrel increases from 0.08 to 0.14,the unevenness of transverse wall thickness of the rolled tube increases rapidly from 10.63%to 29.65%,and the accuracy of transverse wall thickness deteriorates obviously.Therefore,in actual production,it is necessary to strengthen the lubrication of the mandrel to reduce the loss of cutting head.(4)The hollow tube rolled by eccentric pierced tube is still eccentric,and it shows that the extension rolling has a limited ability to correct the eccentric wall thickness of the pierced tube.The unevenness of the transverse wall thickness of the tube rolled by 5%eccentricity of the pierced tube increases obviously,from 12.66% of the original process to 27.10%.(5)After the pass wear,the unevenness of the transverse wall thickness of the hollow tube increases rolled by the negative mandrel dimension repair.Therefore,in the actual production of thin-walled tubes,the negative mandrel dimension repair rolling should be avoided as far as possible,and the increase in the diameter of the mandrel should be adopted.(6)The transverse average wall thickness of the rolled tube is closer to the target wall thickness by using three-section circular arc groove,and the transverse wall thickness unevenness decreases from 12.66% of the original groove to 9.94 %,and the transverse wall thickness accuracy is obviously improved.