Research On The Gradient Roller Remanufacturing Based On Contact Mechanics And Wear Characteristics

The roller is a key component of the rolling mill.Its surface shape and position precision directly determines the quality of steel bands.Affected by the contact and friction between rollers and steel bands,wear will emerge on the surface of rollers.The slight vibration of rollers lowers the stability of the entire rolling mill and the quality of rolling steel bands,and regular replacement of rollers is needed and waste of these rollers will be inevitable.Therefore,how to distinguish the amount of rollers’ wear and to develop the roller repairing and remanufacturing technology so that the performance of rollers can be improved,their service life prolonged and the needs of the development of modern steel rolling industry are met has become an important task in the current roller manufacturing industry.A 6-DoF nonlinear dynamic model of a six-high mill is constructed to solve problems of multi-shafting,nonlinear dynamic characteristics between rolls and variable,complicated power transfer process.Aiming at the problem that equations are difficult to solve because of multi-nonlinear stiffness and damping in the model,according to the structural size and function of the back-up roll,intermediate roll and work roll,the mass of the intermediate roll and work roll is concentrated on the back-up roll,and the equivalent two-DoF roller dynamic model of upper and lower roller systems is obtained.Thus,the 6-Dof model is changed to a 2-Dof model,which is convenient for numerical and approximate solution.A 2-Dof nonlinear dynamic model with periodic perturbation and piecewise stiffness of a roller system was established respectively to solve the issue of restricted vibration range of rolls resulting from a single dynamic model used,and the perturbation method is adopted to solve the dynamic equations,and the corresponding time-domain and frequency-domain characteristic curves are obtained.The impact of stiffness and damping changes on the vertical vibration system of a rolling mill is analyzed.The influence of different parameters on the amplitude and resonance area is studied.The range of the vibration of the roll system in the working process is determined by comparison and analysis,which provides a basis for studying the variation range of the normal contact force between a roll and a steel band under the influence of vibration of the roll system.On the issue of elastic contact and friction between rollers and steel bands,the FEM dynamic simulation model in the process of rollers,rolling of steel bands is constructed.The roller body is regarded as an isotropic elastic model,the rolled piece is seen as bilinear isotropic hardening elastic-plastic model,and the vertical vibration value of a back-up roll is treated as a displacement boundary condition.The normal contact force,tangential friction force,stress and strain characteristics of the contact area between rollers and steel bands during rollers,working process are studied using a simulation model.On this basis,the impact of rolling reduction and rolling velocity on the contact characteristics between rollers and steel bands is studied,which provides a load basis for the study of rollers,wear characteristics.On the problem of friction and wear of rollers,based on the variation law of normal contact force obtained,friction and wear experiments are conducted with the roller test specimen.The wear amount of these roller test pieces under different load and wear time conditions is obtained.Taking load and wear time as input samples and the wear amount as an output one,a RBF neural network prediction model with FOA and optimal factors is established,and accuracy of the neural network model is verified by experiments.Aiming at the issue of the post-worn roller repairing and remaking,this paper takes a high-speed-steel-similar material as a working layer,and on the basis of its composition,the transition layer is formed by lowering the content of its main elements.Then Argon arc cladding method is used to clad the material onto the#45 matrix,and the effects of different process parameters on the working layer and transition layer are studied,and the microstructure and properties of the transition layer are also studied.The results show that the contents of main elements in the working layer composition are gradually reduced and three transition layers are formed.Of the three transition layers,those with the types of hard phases fewer than ones in the working layer are mostly lath-like martensite in the microstructure.With the increasing element contents,the amount of dispersion-distributional carbides increases,and their mechanical performance is lower than that of the working layer,but better than that of the matrix.The corresponding double heat source cladding and single argon arc cladding are conducted with the basic composition of transition layers.By comparison,the microstructure and properties of double heat source cladding layer with laser cladding are better than those of single argon arc welding in terms of hardness,friction and wear,and thermal fatigue properties.Therefore,it is most suitable to choose double heat source cladding on the basis of transition layers.