A Study On Vibration Of Oil Return Pipe Of Heavy Plate Mill Hydraulic AGC System

The plate mill hydraulic AGC system is very prevalent. Since Baosteel heavy plate mill going into production 6 years ago, pipe vibration problems with hydraulic system happen frequently, especially the edging roll AWC oil return tube vibration which incur big economic loss. It demines immediately to study the reason for the hydraulic return pipe vibration. This paper focuses on the vibration problem of hydraulic return line and research extensively on the reasons, affecting factors, detection and alleviating methods. The main work and achievements are as follow:(1)Based on the preceding work by other researchers,14 equations of hydraulic pipeline dynamics of Poisson Coupling, Bohr coupling and friction coupling are deduced. The flow-solid coupling equations are changed from time domain to frequency domain. In developing and solving the equations, no assumptions on the structure and special distribution are given and transfer matrix are used for solving the dynamic equations. Analytic solutions of several simple pipelines are obtained. Linear combination of the solutions can be used for general hydraulic pipelines. At last, according to the geometric parameters of typical tee joint pipe of Tijsseling's in Dundee University of UK, simulation is conducted by MATLAB and results compared with Tijsseling's experiment. The simulation shows little difference from Tijsseling's experiment with the natural frequency. The model describes hydraulic pipeline vibrations well and the model soundness is validated. This can lay a theoretical foundation for the research on hydraulic pipeline oscillating problems.(2)Trough test and analysis it is proved that Lance vibration test system can be used for testing vibration of hydraulic pipelines of cast steel plant in complex environment. Although Lance vibration test system is more suited for environment of cast steel plant, with the advantage of decreasing effects from oil stains and hydraulic station vibration vibration, its testing accuracy still need to be improved. With the mathematical algorithm in software replaced by Fast Fourier Transform, the accuracy can be raised.(3)This part deduces the vibration absorbing model of accumulators, the volume, the effects of previous pipe length and diameter on the vibration absorbing are analysed using MATLAB simulation. The 4-segment oscillating return oil pipeline of Baosteel 5000mm heavy plate mill hydraulic system is simulated using previous deduced model. The simulation results show a decreasing vibration of testing points if accumulator is used. At last, a novel auto-adjusting system of accumulator vibration absorbing is proposed. By adding pressure sensors and proportional valve, flow area can be adjusted regulate the natural frequency of accumulator and adapt the accumulator to the vibration variance.(4)A tee joint oil return pipeline is simulated using Fluent software. In simulation, the change of tee joint angle can effectively suppress the vibration of return pipeline. This indicates that the vibration can be relieved by changing the welding angle of return pipeline or customize nonstandard connectors of three way pipe in practice.(5)In this part is proposed a method of changing stiffness of return pipe to change return pipe natural frequency, polar moment of inertia and moment of inertia, which greatly affects the resistance to torsional and bending deformation. Through comparing the peak change of vibration acceleration and displacement by using ANSYS simulation, the feasibility of relieving return pipe vibration by changing return pipe stiffness is validated.(6) In this part, a theory relating the return pipe layout's effect on return pipe vibration is developed, based on which return pipe vibration acceleration of HGC, AWC and WRB's main return pipe and single return pipe. Simulation shows main return pipe case is vibration-less than single return pipe case. Further the author proposes HGC return pipe single oil return pipe reform project. Through on-spot testing of vibrations before and after HGC return pipe single oil return pipe reform project, it can be seen the 4 return pipes vibration is decreased dramatically after the reform. Also the effect can be seen from the comparative figure of breakdown numbers before and after changing return pipe layout, which further validate the theoretical soundness.