Physicochemical Characteristics And Concentration Distribution Of Dust In Thermal Spraying

Thermal spraying is one of the important processes of surface treatment techniques,widely used in aerospace,metallurgy,defense industry,petrochemical equipment and machinery manufacturing.At the same time,lots of dust particles will be generated in the thermal spraying process,which will not only endanger the health of workers,but also cause serious environmental problems.Therefore,this paper studied the regularity of dust diffusion and analyzed the influence of environmental factors on the distribution of dust concentration in thermal spraying workshop which is of great significance to control dust pollution and reduce dust hazards.The dust generation mechanism in thermal spray process was analyzed in this paper.Dust particles generated in high velocity oxy-fuel spraying were characterized in terms of mass concentrations,particle size distribution,micro morphologies and composition.Results showed that the concentration of dust was much higher than the occupational exposure limits.Some toxic metal elements were detected and a large number ultrafine particles were found in the workshop.Potential occupational hazards of the dust particles were further analyzed based on their characteristics.Based on the computational fluid dynamics theory,the numerical simulation method was used to analyze the characteristics of flow field and temperature field of thermal spraying workshop.Relevant experimental studies have been performed to verify the accuracy of the simulation results.Results showed that the distribution of airflow in the workshop was complex and many air vortexes were found near the wall and wind columns under the existing ventilation mode.The temperature distribution of the workshop was uniform.The temperature decreased rapidly along the radial direction from the heat source and high temperature area was relatively small in in the workshop.According to the physicochemical characteristics of the dust and distribution characteristics of the flow field,the force and motion equation of dust were analyzed.Based on the gas-solid two-phase flow theory,the diffusion process of dust in the workshop was simulated using the discrete phase model(DPM)in Fluent and the diffusion regularity of dust and the effect of air velocity on dust concentration distribution were analyzed.Results showed that the dust particles generated in thermal spray process diffused along radial direction and then moved following the airflow under the action of the air drag force.The dust concentration in the workshop decreased with the increase of airflow velocity.Finally,the distribution of dust mass concentration along the route was analyzed by field measurement and the feasibility of the numerical simulation method was verified by comparing with the simulation results.