Abstract
The paper aims to investigate the airflow dynamics of electric-arc spraying (EAS) with airflow pulsation. The study is focused on the dynamic structure of the airflow with an obstacle in the form of crossed electrodes at the steady and the pulsating air supply (with a frequency up to 120 Hz). The work was fulfilled using a computer simulation, the airflow “shadow” photo visualization, and the microstructure characterization of the coatings formed. It was found that when air flows along the crossed electrodes with a gap of 2 mm, a depression zone appears in the flow with a pressure drop from 0.56 MPa to 0.01 MPa. The air pulsation resulted in a change in a flow’s dynamic structure towards an increase in the length of the depression zone, which covers most of the arc, affecting the liquid metal oxidation. It is established that the frequency of a droplet formation should match the frequency of the airflow pulsation to minimize the metal oxidation. With the air pulsating at about 65 Hz, the oxide volume fraction in the aluminum coating was reduced by 3.6 times compared to the steady airflow. EAS with airflow pulsation has the potential for technological cost reduction.
Highlights
Surface modification and protective coating deposition are widely spread technologies used to improve the exploitation durability of machine parts and tools [1,2,3]
The high pulsation frequency has almost no influence on the flow gas dynamics. This can be explained by the effect of the pulsation frequency on the curvature radius of molten metallic droplets forming at the electrode butt
The characteristics of the gas dynamics of the airflow under the electric-arc spraying with airflow pulsations and its effect on aluminum coating oxidation behavior were evaluated
Summary
Surface modification and protective coating deposition are widely spread technologies used to improve the exploitation durability of machine parts and tools [1,2,3]. Particular attention was paid to spraying distance as a key EAS parameter, determining atomizing gas dynamics. Much attention has been paid to the investigation of the influence of nozzle geometry and dynamics of atomizing gas flows on the properties of steel coatings [18,19,20]. The numerical hydro-dynamic analysis performed in [24,25] with the application of equations of continuity and momentums for different inclination angles of the front spraying nozzle revealed a high-velocity area inside the airflow. Experimental determination of the molten particle velocity and the porosity of the deposited coating showed that the density and the temperature of the flow grow with an increase in the electrode inclination angle
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