The Dynamic Research Of Unsteady Lubrication System Based On The Interface Of Rolling

The self-excited vertical vibration of high speed rolling mill is chosen as the case for analysis in this thesis. On the basis of rolling theory, hydromechanics theory, lubrication and friction theory, mechanic vibration theory, the basic theory of dynamics of rolling mill system based on the rolling gap at unsteady lubrication process has been presented. The original work of this thesis is as follows:1. Based on the theory of unsteady hydrodynamic lubrication and relevant mathematic and physical methods, the basic theory of unsteady lubrication in full film lubrication regime in strip rolling is developed. The inlet film thickness is defined by the analysis of the inlet zone, and the influence of unsteady variables such as strip tension stress, rolling speed and inlet angle variation on inlet film thickness are investigated, and an analysis of linear solutions and frequency response of inlet film thickness is made. The analysis of the unsteady work zone is based on the known inlet film thickness by which the distribution information of pressure stress and friction stress in the work zone can be obtained. The influence of such parameters as back tension stress, surface average speed, inlet angle and angle frequency on the distribution of film thickness, pressure stress and friction stress has been analyzed by calculation.2. According to Tsao and Sargent's model, the basic theory of unsteady lubrication in mixed film lubrication regime in strip rolling is presented on the basis of the calculation results of inlet film thickness and the work zone film thickness distribution during unsteady lubrication process in full film lubrication regime. A systematic analysis of the corresponding distribution of friction stress and pressure stress at different surface roughness and different time during the impact of sinusoidal back tension stress is made. At a certain reduction the influence of the surface roughness at different time on the distribution of friction stress and pressure stress is also analyzed. A diagraph is made to show how the rolling force changes with time, reduction and surface roughness.3. A dynamic model based on the unsteady work interface is developed, in which the coupling interactions based on the metal plastic fluid process, the mixed friction process of the co-existent fractional fluid lubrication and dry friction, and the process of work roll movement etc. are taken into account. In the analysis of plastic fluid process, the dynamical changes of the interface friction regime is considered, and the dynamical coupling of work roll movement is taken into account in the interface friction analysis, therefore the rolling force model,interface friction model and work roll movement model constitute the interface coupling model of thin film binding.4. The self-excited vertical vibration mechanism of work roll is analyzed, the negative damping character is discussed and vertical self-excited vibration of the work roll is explained.5. The vertical vibration feedback mechanism of rolling mill based on the unsteady lubrication process and the causes of the vibration are presented. The negative damping of the rolling interface is the cause of self-excited vibration and the negative damping results from combined effect of the glutinous and sliding rolling interface, fractional fluid lubrication and back tension stress fluctuation. The combined effect of the interface negative damping and positive damping resulting from roll gap friction determine the occurrence of self-excited vibration. The interface damping plays an important role in systematic dynamics. Negative damping is related to such interface parameters as surface roughness, strip tension stress, lubricant viscosity, rolling speed and reduction. An increase in surface roughness and a decrease in lubricant viscosity is conducive to reduce negative damping.6. A numerical simulation of vertical self-excited vibration of 2800 rolling mill is made on the basis of the basic theory of roll gap dynamics together with the theory of unsteady lubrication. The corresponding simulation software has been developed and it is found that the parameters that have a great impact on critical speed of vertical vibration include : lubricant viscosity, the inlet and outlet thickness of strip, material of strip, surface roughness of roll and strip, roll radius. Those parameters that have a great impact on vibration amplitude are as follows: rolling speed and positive damping of vertical system of the rolling mill. Rolling speed is in a directly proportion to vibration amplitude while the positive damping of the system is in inverse proportion to vibration amplitude.7. 2800 rolling mill in Southwestern Aluminum corporation is chosen as the subject for study. Meanwhile the experiment research on the lubricant condition based on the rolling interface in Southwest Aluminum corporation is carried out. Multi-physical process information collected from the rolling mill in operation provide facts and datum for research and prove definitely that the theory of this thesis and simulation analysis are true. The cause and character for the vibration is defined. The main impact of the parameters on vibration is compared and analyzed.