The Study of the Grit-blasting Parameters and Their Effects on the Adhesive Strength of the Plasma Sprayed Coatings

Surface Preparation is very important in adhesive b on ding of spray coatings to the surface of a work piece. The common practice is gr it-blasting of the surface before subjecting it to the spray coating process. In this study, grit-blasting of an AISI 4130 steel (of different heat treatmen ts) with Al 2O 3 particles was studied. Various grit-blasting parameters such as blasting particle size, the distance between blasting nozzle and the work pi ece (25, 30 and 40 cm.), blasting pressure (3,4,5,6 and 7 bars), blasting time ( 3, 6 and 10 seconds), and the blasting angle (45° and 90°) were examined in or der to find the optimum roughness. The mean roughness (Ra) of the grit-blasted surfaces were measured and the vari ations of the roughness with respect to the above mentioned variables were studi ed. The results show that by increasing blasting time, surface roughness increas es up to a maximum and then slightly decreases it with further duration of t he process. On the other hand a lengthy blasting causes some undesirable results such as an increase in residual particles between surface irregularities. There fore an optimum blasting time is of great importance. Increasing the blasting pr essure also provides a rougher surface, but in grit blasting of harder specimens the surface roughness decreases when the pressure reaches a certain limit. About the blasting angle, it was noticed that an angle of 45° results in less r esidual particles between the surface irregularities, in comparison to the angle of 90°. After grit-blasting, the specimens were plasma spray coated with 80% ZrO 2-20 % Y 2O 3 powder. The adhesive strength of the coating to the substrate was the n measured according to the DIN 50160 standard. The results show that for a certain base metal, the adhesive strength is directl y related to the surface roughness of the base material. Residual particles afte r grit-blasting the surface of the specimens can also have a strong deteriorati ng effect on adhesive strength. Finally, it was shown that the hardness of the b ase material had a direct effect on the adhesive strength of the sprayed coating s.

CALCULATION AND EXPERIMENTAL INVESTIGATION OF ELECTRIC FIELDS INDUCED BY ELECTRODES IN ELECTROSTATIC CHARGED POWDER SPRAYING TECHNIQUE

Electric fields induced by ring and pin electrodes in electrostatic charged powder sprayingtechnique are analysed. The fundamental formulae to deseribe these fields have been built up. Theseformulae could be used to design electrostatic charged podwer spraying system. The chargingeffectiveness of ring and pin electrode is experimentally investigated and compared each other. Theperformance of ring electrode is better than that of pin electrode.

Downwash distribution of single-rotor unmanned agricultural helicopter on hovering state

The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect.The downwash of the unmanned agricultural helicopter(UAH)N-3 was discussed in the paper.The computational fluid dynamics(CFD)methods were used to simulate and analyze the distribution of the downwash,and a wind field measurement device had been designed to test the downwash of UAH N-3.In the tests,the UAH N-3 was raised up to 5.0 m,6.0 m and 7.0 m from the ground,“annular-radial-distribution-point”method was introduced,8 directions separated by an angle of 45°(the radial direction)with the intersection point of the main rotor shaft and the ground plane as the center,0.5 m as the step length for the longitudinal(to 2.5 m)and radial(to 4.0 m)direction to set the sample points,considering the range of the rotor rotating circular area mainly.The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased.The standard deviations of five test altitudes for eight directions were comparatively analyzed,the results showed that the total standard deviation was not greater than 0.6 m/s.The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7,which verified the credibility of the simulation data.High-order polynomials were used to fitting the simulation and measurement data,the fitting results showed that the polynomial coefficient of determination R^(2) met or exceeded 0.75 when the altitudes were more than 1 m,indicating the fit equation having the reference values.When the altitudes equal or less than 0.5 m,the polynomial coefficient of determination R^(2) was smaller,ranging during 0.3 to 0.7.The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH,which would promote China aviation plant protection.