Research On Large Cylindrical Shell Rolling Deformation And Roundness Control

Large cylindrical shell is a basic key part in heavy pressure vessel and powerequipment, including large nuclear power cylindrical shell, large hydrogenationreactor cylindrical shell and coal liquefaction cylindrical shell. Large cylindrical shellis widely used in nuclear power, petrochemical industry, coal liquefaction industry andother national economy important fields. As environmental issues become increasinglyserious, energy structure has begun a transition toward clean energy, thus the demandfor large cylindrical shell in nuclear power becomes more and more in our country.Besides, with the industry development, the demand for large cylindrical shell inpetrochemical industry, coal liquefaction industry becomes increasingly urgent.Compared with the traditional forging process, the advantages of large cylindricalshell rolling include high effciency, considerable cost-saving in energy and material,good quality.As the radii and speeds of upper and lower rolls are unequal, large cylindricalshell rolling is a special asymmetrical rolling. Based on the theory of statics, thebitting condition and forging condition of large cylindrical shell rolling are deduced,and the effect of rolling process on the bitting condition and forging condition isanalyzed. Based on the finite element simulation, plasticity zone distribution inforging process is studied. The satisfaction of bitting condition and forging conditionwill keep rolling smoothly.The mechanical models of large cylindrical shell rolling are established by theslab method. This mehod has considered the uneven normal stress, shear stress andtemperature. Combining the boundary condition and yield equation, the forcedifferential equations of the backward-slip zone, the cross shear zone and theforward-slip zone are developed to predict therolling force and torque, the netrualpoints. And the influence of process parameters on the force parameters is analyzed.The common problems in large cylindrical shell rolling are:(1) Width spread isdifficult to control, and the end surface appears fishtail;(2) Cylindrical shell appears elliptical, irregular circle, and the roundness could not meet requirement. To solve theabove problems, this paper carries on research from two aspects: the control of endface flateness and roundness, in order to get a better forming quality.For large blank and asymmetrical rolling, a new strip layer method is developedto simulate the three-dimensional deformations of large cylindrical shell rolling. Thismethod has considered the asymmetry of the upper and lower rolls, unevendeformation and stress. The deformation zone is divided into a number of strips andlayers along the width and thickness respectively. The metal transverse displacementmodel is constructed by polynomial function, so the unknown optimizing parametersdecrease, leading to the computation speed increased greatly. Based on the plasticmechanics principles, the three-dimensional stresses and deformations are formulated.The strain and stress fields, flow speed field and the spread distribution in thedeformation zone can be predicted. The effect of process parameters on the spread canbe analyzed. By optimizing the rolling process parameters, the flatness of the end faceis improved.Roundness is an important index of circumferential dimension precision. Basedon theoretical models and FEM, the roundness is controlled by guide rolls and processparameters. The roundness error is got by controlling guide roll trajectory and constantguide force, as well as the effect of feed rate and roll speed on the roundeness error.Finally, the industrial experiment of large cylindrical shell rolling is carried out.The correctness of the analytical and numerical models established is verified. Thenumerical simulation, theoretical and experimental studies of large cylindrical shellrolling provide theoretical basis and technical support for rolling equipment andprocess design, optimization.