Study On Low-Speed Stability Of Hydraulic Cylinder In Pipe Bending Machine With Intermediate Frequency Heating

A great deal of achievements have been made by oil and gas cooperation under the framework of "The Belt and Road",and the oil and gas transportation career is at the peak of pipe network construction.Higher quality requirements are put forward for the bend in the pipelines.The intermediate frequency heating pipe bender is one of the important equipment for bending bends.Low speed and stable operation is the necessary condition for obtaining high quality elbows.As the important component of pipe bender,hydraulic cylinder is prone to creep for low speed pushing in process,which seriously affects the forming quality of elbow.The analysis and researches for the unstable factors that affect the low-speed push system are made to ensured that the stable pushing speed of the high quality elbow in the bending process.The research contents are as follow:Took the push cylinder of the intermediate frequency heating pipe bending machine as the research object.Analyzed the factors that influence the creeping phenomenon in the low speed pushing.On the basis of determining the nonlinear hydraulic spring force and the nonlinear friction force are major factors,using the nonlinear dynamics principle to have theoretical analysis and numerical experiments on the influence of nonlinear hydraulic spring force and nonlinear friction force,and studied their effect regulation on system motion characteristic.Took the main push hydraulic circuit of pipe bender as the research object,and calculated the critical creeping speed of hydraulic system.In order to reduce the influence of nonlinear hydraulic spring force and nonlinear friction force on the instability of low speed motion,had some analysis and researches on the situation that adopting the flow compensation and back pressure compensation hydraulic circuit to eliminate creeping phenomenon.The research showed that the flow compensation of the circuit to fill the oil drain can realize the low speed pushing and stabilizing system of the pipe bender,but the effects are worse under the extreme low speed condition.Back pressure compensation can increase the pressure and reduce the pressure of the circuit to realize the low speed and stable pushing of the pipe bender in time.Compared with the flow compensation mode,it made larger power loss,and the effect of circuit stability control is extremely poor under extreme low speed condition.In order to ensure the stability of the extreme low speed push system of intermediate frequency heating pipe bender,the flow compensation circuit was taken as the research object,designed the fuzzy adaptive PID control strategy to improve the adjusting ability of the flow compensation circuit.The operation results showed that the flow compensation circuit using fuzzy adaptive PID control can ensure the stability of the push speed and the very low speed operation of the intermediate frequency heating pipe bender.The results of this research guaranteed that intermediate frequency heating pipe bender produced high quality bends,and provided ideas for the low speed and stable operation of other types of hydraulic circuits.