Study On The Control And Process Analysis Of The Stainless Steel Pipe Tube Inner Wall Spraying With Porous Coating

The demand for increasing the pore area and roughness of the inner wall of stainless steel pipe and improving the heat exchange efficiency of the inner wall of the pipe is increasing day by day.Aiming at the problem that the traditional surface processing method is difficult to deal with the inner wall of small-diameter stainless steel pipe,the key technology of spraying porous coating on the inner wall of smalldiameter stainless steel pipe by wire electrical explosion spraying method was proposed.Based on the application of the phenomenon of conductor wire electrical explosion spraying,the wire electrical explosion spraying is a new coating preparation method.It has the advantages of environmental protection,high energy utilization rate,little influence on the sprayed substrate,high coating bonding strength,convenient adjustment of process parameters and so on.Based on the understanding of the wire electrical explosion spraying,this thesis designs and assembles a set of automatic equipment which can carry out continuous electro explosive spray on the inner wall of small-diameter stainless steel pipe.The equipment mainly includes high-voltage rectifier power supply,energy storage capacitor bank,telescopic mobile electrode,disconnector,high-voltage and lowvoltage coaxial guide rod,wire electrical explosion spraying spray gun,base tube movement and clamping mechanism,wire transmission mechanism and wire position detection based on eddy current sensor,servo motor drive and control,energy storage capacitor charging circuit and wire electrical explosion spraying discharge control circuit.Aiming at the problems of complex wiring and difficult function modification of the traditional relay contactor control system,a spray deposition control system for the inner wall of wire electrical explosion spraying pipe based on programmable controller(PLC)was designed,so that the spraying device can continuously spray porous coating on the inner wall of the whole small diameter stainless steel pipe.In the process of wire electrical explosion spraying,the electrical parameters have an important impact on the quality of wire electrical explosion spraying spray coating.The wire electrical explosion spraying circuit of small diameter wire electrical explosion spraying spray deposition equipment was modeled.The nonlinear metal wire impedance in the process of electrical explosion spraying was described according to the resistivity specific action model,and the wire electrical explosion spraying circuit was equivalent to RLC series circuit for analysis.The wire electrical explosion spraying model of metal wire was established by PSpice software.On this basis,the wire electrical explosion spraying discharge waveform of metal wire under different diameter,different initial voltage and different line parameters was simulated.Through induction and analysis,the effects of initial charging voltage,wire diameter,line resistance and inductance on the energy deposition of wire electrical explosion spraying are studied,and then a control system which can improve the quality of wire electrical explosion spraying coating was designed.The copper and aluminum porous coatings were prepared by wire electrical explosion spraying spray deposition equipment.The changes of resistive voltage,loop current and deposition energy on copper wire and aluminum wire during wire electrical explosion spraying were studied under different wire diameter and different initial voltage.Under the same initial voltage,with the increase of wire diameter and the backward movement of phase explosion point,the lower the resistive voltage peak and current rise rate,the higher the deposition energy and the lower the vaporization degree of the whole wire;Under the condition of the same wire diameter,with the increase of the initial voltage,the voltage peak and current peak on the wire increase greatly,the phase explosion point time moves forward,and the voltage breakdown phenomenon occurs faster.By adjusting the initial voltage,the deposition energy on the wire can be controlled and the relative energy deposition density in the vaporization stage can be changed,so as to change the surface morphology of the porous coating.The macro and micro morphology of the porous coating surface were analyzed to obtain the copper and aluminum porous coating with the best application performance.The porosity,bonding strength and wettability of the copper and aluminum porous coating were measured and analyzed experimentally.The experimental results show that the copper and aluminum porous coatings have high bonding strength with the inner wall of small-diameter stainless steel base pipe,the porosity reaches 60%,and their surfaces reach superhydrophobic state and hydrophilic state respectively,which can effectively improve the heat exchange efficiency.