| Electrical explosion spraying has certain advantages in material surface sprayingfields as a new, efficient and low cost surface modification method. Existing sprayingmaterial used in electrical explosion method are mostly wire or foil and the majorityof spraying material exist in the form of power, so it’s a certain advantage in powderelectrical-thermal explosion spraying. Based on gas discharging in current mechanism,put forward a electrical explosion spraying method of continue feeding powder inconstraining tube. Powder is sent to the conveyor belt by feeding powder device, andinto the constraining tube with conveyor belt. When reached a certain position,current is imported in powder by gas charging and it occurs explosion. The productsof explosion emit from the constraining tube on substrate forming coating.This paper developed continuously feeding powder electrical explosion sprayingdevice in constraining tube. This device included high voltage generating device,capacitor, electrode, feeding powder device, conveyor belt and constraining tube. Theamount of powder could be effectively controlled by feeding powder device. Throughconveyor belt, power could be continuously, uniformly, accurately sent to the placebetween two electrodes. Electrode which had a tip could import high current intopowder by tip discharging, thus it made sure to breakdown the air gap betweenpowder and electrode under low voltage and occur explosion. Under the action ofconstraint of constraining tube, products of explosion emit out with stable jet toachieve directional spraying.This paper developed powder electrical explosion spraying device inconstraining tube, put WC powder as spraying material to conduct tests. The changelaw of coating area in different process parameters was analyzed by observing surfacemorphology of coating. Coating was consisted with the center of spraying layer andexternal spraying layer. Coating area was large at a small distance. With the sprayingdistance increased, area deceased. When spraying distance increased to a certainextent, area reached minimum. Thereafter as the spraying distance continuouslyincreased, coating area continuously increased. As the spraying distance increased,area of the center of coating remained unchanged and its size was similar toconstraining tube diameter. The thickness of coating was analyzed by SEM indifferent process parameters. When the spraying distance was small, due to theformation of jet instability, the average thickness of coating was thin and thickness ofcoating was not uniform. As spraying distance increased, jet of explosion productstent to stability, the average thickness of coating increased, thickness tent to uniform. When spraying distance increased to a certain extent, coating thickness reached amaximum. Thereafter, with spraying distance continuously increased, coatingthickness continuously deceased.To study coating character in different process parameters, surface coating andmorphology of cross section were observed, combined with EDS, and bonding ofcoating and substrate was analyzed. The results show that in a certain distance ofspraying range, the liquid spraying coating is formed which high melting point WCparticles are all in melted condition in the method of continuous feeding powderelectrical explosion spraying in constraining tube. This kind of coating is dense andhas a high bonding strength with substrate. When spraying distance is small, coatinghas vapor deposition characteristics. With the spraying distance increased, the partialmelted particles of explosion products begin to solidify into solid phase particles. Thedensity of this kind of coating deceases, and the bonding strength deceases withsubstrate. When the number of solid phase particles reach to a certain extent, theeffective spraying coating is unable to be formed. In the high initial voltage, the rangeof spraying distance increases where liquid spraying coating and solid sprayingcoating are obtained. |
PDF Full Text Request