Study On The Influence Mechanism Of Ambient Pressure On Plasma Cutting Arc

The high-pressure environment refers to an environment where the atmospheric pressure is higher than 1 atm,that is,atmospheric pressure.The pressure level is determined by the specific project.If the water depth increases by 10 m,the pressure increases by 1 atm.The operation of highpressure environment involves inspection,cleaning and many other contents.Among them,welding and cutting are the most technically difficult.Welding research under pressure environment is more,but cutting research under pressure environment has not been reported in the literature.The number of high-pressure maintenance of cutter head cutters of shield machines far exceeds that of ocean and nuclear power.Currently,carbon arc gouging is usually used for cutting.Carbon arc gouging requires replacement of carbon rods,and the cutting process is not continuous.This paper proposes the use of plasma arc cutting in the high-pressure maintenance of the shield cutter of the shield machine.Compared with carbon arc gouging,it has the advantages of high cutting efficiency and less smoke and so on.Plasma arcs are complex magnetic fluids with high temperatures,high speeds,large gradients,drastic changes,and physical properties that strongly depend on temperature.The plasma theory is described,the magnetohydrodynamics is used to describe the plasma behavior,and the influence of environmental pressure and temperature on physical properties parameters are considered in the simulation control equation.The k-? model with low Reynolds number was used to describe the turbulent flow,and the computational fluid dynamics software Fluent was used to simulate the plasma arc temperature field under normal pressure and high pressure.The simulation results of the temperature field show that the maximum temperature of the plasma cutting arc decreases with increasing pressure.Plasma arc is essentially a gas discharge phenomenon,and its characteristics must be affected by the gas medium,of which pressure is the primary factor.The existing plasma arc cutting power supply cannot ignite the arc in a high-pressure environment.Starting with the highpressure gas ionization process,a plasma arc ignition system was developed.By adding external electrical energy,a reliable arc ignition under 0.4MPa pressure was achieved.Based on the 2MPa high-pressure welding test cabin,a high-pressure plasma arc cutting test system was established.The system is mainly composed of high-pressure plasma arc cutting power supply,automatic cutting trolley,and arc monitoring device.Atmospheric and high-pressure plasma arc cutting experiments were carried out to study the effect of pressure on the shape of the plasma arc and the effect of pressure on the cutting process parameters.The cutting test shows that the arc image taken by the arc monitoring device basically conforms to the shape of the simulated arc,and both are cylindrical.As the pressure increases,the arc absorbs heat and shrinks.The cutting process parameter test shows that as the pressure increases,the width of the cut increases significantly due to the contraction of the arc and the concentration of energy.In this paper,the ionization process,arc ignition system,temperature field distribution,arc shape and cutting process parameters of plasma arc in high-pressure environment are studied.The research conclusion has a guiding role in the application of plasma arc cutting.