Research on Distribution Properties of Coating Film Thickness from Air Spraying Gun-Based on Numerical Simulation

Abstract

This work aims to study the influence of the spraying parameters on the spray flow field and coating thickness distribution during the air spraying process. The shaping air pressure and the target geometry have an important influence on the distribution of coating film thickness. This paper begins with a 3-D physical model of an air spray gun, in which unstructured grids were generated for control domain. A grid independency study was also carried out to determine the optimal number of cells for the simulations. Then the Euler–Lagrange method was used to describe the two-phase spray flow by establishing a paint deposition model. The numerical simulation based on the discrete phase model (DPM) and TAB model has been carried out. A reasonable assumption was proposed based on the analysis of the spraying process, so that the droplets were injected into the airflow at the position of the paint hole. The influence of the shaping air pressure on the air flow field and the coating thickness distribution was analyzed by changing the shaping air pressure. From the numerical simulation results, it can be concluded that the smaller the shaping air pressure, the more concentrated the coating. With increasing the shaping air pressure, the length of the coating film along z-axis gradually increases, the width along x-axis gradually decreases, and the spray area gradually increases. The paper ends with a numerical simulation and experimental study on planar vertical spraying, planar tilted spraying, and cylinder spraying. Comparisons and experiment results verify the validity and practicability of the model built in this paper.

Optimal design of a pneumatic atomizer using response surface method to obtain more uniform coatings

“…In previous studies, 10,16 the initial condition of discrete phase in the spraying simulation was determined like this: the velocity and size distribution of droplets were measured by experiments that are expensive and time-consuming; then, the discrete phase was added at the inlet of paint hole to simulate the primary atomization when the liquid was assumed to be totally atomized. After that, the TAB model was used to predict the secondary breakup and the child droplets' diameters.…”

“…The Eulerian wall film (EWF) model was employed to calculate the distribution of the coating film thickness on the targe plate. 16,35 When the liquid droplets in the spray flow field impinge on the plate and deposit to form a coating film, the mass and momentum of the liquid phase are removed from the two-phase flow and added as source terms to the mass and momentum conservation equations of the liquid film, respectively. Therefore, the thickness of the coating film can be calculated through the mass and momentum conservation equations of the liquid film.…”

“…They investigated the influence of the rectangular target plate and its orientation on the paint film thickness. Further, some researchers focused on more complicated target plates, such as the inclined plane, 16 concave stepped surface, 13 and inner or outer cylindrical surface, 17 to fit in unforeseeable working situations. In terms of the operating conditions, Ye and Pulli 13 studied the effects of the atomizing and the shaping air flow rate on the droplet size distribution.…”

“…Figures 11 to16 show the response surfaces and respective contour plots that intuitively illustrate the interaction effects between two design parameters on the central pressure P c when the other parameters remain middle level.From Figure11, it can be seen that the central pressure P c rises with the increments of annular air hole diameter d and horn flare angle a. Compared with the horn flare angle a, annular air hole diameter d has a stronger effect to elevate the central pressure P c .…”

Design of a Double-Nozzle Air Spray Gun and Numerical Research in the Interference Spray Flow Field

“…In recent years, some experimental and numerical investigations [19][20][21][22][23][24][25][26][27] on the painting process have been conducted using the Euler-Lagrange method, focusing mainly on the droplet size distribution, the influences of spray gun geometry and air flow, on coating thickness distribution, as well as on droplet impingement. In the Euler-Lagrange method, the air is treated as a continuous phase and the droplets are treated as a discrete phase.…”