Forming Mechanism And Virtual Simulation System On Three-roll Retained Mandrel Pipe Mill (PQF)

As a kind of important economical section steels, seamless tube is one of theimportant raw materials in the national economy construction. Continuous rolling is animportant procedure in the industry hot rolling process for seamless steel pipes whichdirectly affect the final product size precision and subsequent processing. Currently, threerolls mandrel pipe mills has been the mainstream mill type of the large seamless steel pipeproduction in the last ten years. With internationalization and increasing competition inproduct market, the steel pipe production enterprises continuously improve its productquality, expand product specifications, reduce production cost and develop new productsto improve their market competitiveness. Therefore, it is of great significance and practicalvalue for further optimizing the process parameters, establishing quality pre-controlsystem, realizing energy saving and consumption reducing to carry out the study on basictheory and simulation of three roll mandrel pipe mill rolling process, master the forminglaw, forecast the product precision and performance.The rolling process of three roll mandrel pipe mill is a very complex multi-stand passrolling procedure with characteristics of typical three-dimensional nonlinear,thermal-mechanical coupling and parameter time-varying. In order to improve thesimulation speed and formulate the rolling schedule rapidly, metal flow and geometricdeformation are analyzed firstly and the thermo-mechanical coupling analytical model isbuilt in this paper. Based on the heat transfer mechanism analysis, the mathematical modelof heat transfer in the rolling process of three roll mandrel pipe mill is established with thefinite difference method which can deal with the complex deformation field, as well asvarious thermodynamic boundary conditions. Also, the rolling power and torque of eachstand are obtained by the upper bound method. The simulation results show a goodagreement with the measured values.In order to study the plastic deformation mechanism of the metal intensively andcalculation the rolling technological parameters, a3d finite element model for the rollingprocess is established in this paper according to the roll pass and processing characteristics of the three roll mandrel pipe mill. The effect of the spread regularity on the product sizeprecision and the tube cross-sectional area is also analyzed using this model. Throughseries of simulations for different roll pass and various specification products, theinfluence factors of the spread rule are researched, such as the influence of the elongationcoefficient and the void ratio on the circumference coefficient, the influence of theelongation coefficient and the diameter reducing rate on the wall thickness ratio, as well asthe influence of tension effect on the spread rule. Spread model is obtained using multiplelinear regression analysis method, the BP neural network and GA-BP neural network.Simulation results are in good agreement with the actual plant data. Fast and exactprediction of the steel pipe’s dimensional accuracy is realized which can provide atheoretical guidance for the roll pass designing and the process parameters setting.The seamless steel pipe is influenced by the roll pass, the roll speed, the mandrelspeed and other factors. Therefore, the metal flow law and the influence factors of theforward-backward slip in the deformation zone during the rolling progress of three rollmandrel pipe mill are studied in the paper. Moreover forward slip model is obtained whichcan provide the speed schedule setting model for rolling technology. Moreover the effectsof the mandrel retaining speed and the tension on the speed schedule are analyzed.A virtual simulation system for the rolling process of three roll mandrel pipe mill isdeveloped by introducing the CAE parametric technology and combining with thesecondary development technology of MARC in the Visual Basic programming platform,which can carry on deeply analysis of the process design, the pipe dimensional accuracy,the temperature distribution and the mechanics parameters. The system can establish themodel, transfer the related data, predict the pipes dimensional accuracy and analyze thestress field, the strain field, the temperature field distribution and transformation. Thesystem has the very good actual using value which can effectively shorten the new productdevelopment cycle, improve the pass design reliability, reduce the rolling energyconsumption and the production cost.