Research On The Development Of Equipment And Process Of Powder Electrical Explosive Spraying In Tube Inner Wall

In the project,Surface modification of the small-diameter pipes such as artillery pipes,barrels,and automobile pistons and cylinders is needed to increase their wear resistance,high temperature resistance,and corrosion resistance.The common surface modification techniques include cold spray,flame spray,arc spray,plasma spray,etc.Due to the limitations of spray gun size and spray distance,it is difficult to satisfy the preparation of the coating on the inner wall of the small-diameter tube.Electrical explosion spraying is the process which introduces a large pulse current into the spray material,and let it melts,expands,explodes,and sprays by ohmic heating of the spray material.The spraying distance is small,and it has the advantage of preparing a coating on the inner wall of the small-diameter tube.This article developed a set of continuous electrical explosion spraying equipment which is suitable for the inner wall of small-diameter tubes.The equipment is composed of three parts:the carrier rod conveying device,the tubular electric explosion gun,the substrate clamping and the motion control device.A tubular electric gun is placed in a round tube workpiece.Two electrodes are installed at the end of the electric explosion gun.The high voltage generator charges the storage capacitor.When the capacitor discharges,a high voltage electric field is established between the two electrodes through the conductor.The voltage between the electrodes is the initial value.Charging voltage;The powder material is added into a suitable amount of water to make a slurry and coated on a carrier rod,which is sequentially transported into the electric explosion spraying gun under the transmission of the conveying device;when the powder material is transferred to the two electrodes,The large pulse current is introduced into the powder material by the gas discharge.The joule heat of the powder material causes it to instantaneously melt,expand,and explode.The shock wave sprays the high-temperature particles at high speed onto the surface of the tubular work piece to form a coating.The precise control of the tubular work piece by the controller enables axial and circumferential movements to achieve the overlap of the coating.At the initial voltages of 9kV,11kV,and13kV,using the above equipment,Ni based alloy powders of 300 mesh,800 mesh,1200 mesh,and 2000 mesh were used to conduct powder electrical explosion spraying test on the surface of a stainless steel substrate to study the effect by the powder particle size and the initial voltage on coating formation.The results show that within the parameters of the test,the smaller the particle size of the powder,the higher the voltage,the more energy deposition during the electric explosion,and the higher the obtained coating's bonding strength.For example,under the 2000 mesh and 13kV process conditions,a metallurgical bonding layer with a thickness of 5 ?m can be obtained,and the bonding strength is rated as HF?1 according to the VDI3 198 standard.It is considered that the formation of the coating during the electric explosion of the powder mainly depends on the energy deposition density on it.The current and voltage waveforms during the electric explosion process were collected by Rogowski coils and high voltage probes.The reason for the formation of the above coating was related to the heating phase of the powder electric explosion process.Studies have shown that during the process of powder electric explosion,as the temperature of the powder material increases under the effect of resistance heat,a certain voltage drop begins to appear on the surface of the sprayed material,and as the temperature of the sprayed material increases,its voltage gradually increases,resulting in the material bypass discharge occurs on the surface.This current hinders the deposition of energy onto the powder.By reducing the particle size of the powder or increasing the initial charging voltage,the occurrence of the bypass current can be delayed,and the energy deposition rate on the powder can be increased.