Numerical Investigation of Electrostatic Spray Deposition Process for Powder Towpregging Line
Topic(s) : Manufacturing
Co-authors :
Hanisa HASRIN (UNITED KINGDOM), Amer SYED (UNITED KINGDOM), Conchúr M Ó BRÁDAIGH (UNITED KINGDOM), Colin ROBERT (UNITED KINGDOM)Abstract :
The electrostatic spray powder coating method demonstrates substantial economic viability due to its exceptional transfer efficiency. This deposition method has been strategically employed for a powder-epoxy towpregging line for the production of low-cost towpreg. The electrostatic spray on the line allows for efficient coating of dry carbon fibre on both the upper and underside of the tow following the ‘wraparound effect’. Subsequently, the coated tow undergoes a sintering and consolidation process under infrared heating.
In the electrostatic deposition process, powdered epoxy is mixed with compressed air within a compact pump and then conveyed to the spray gun. At the tip of the spray gun, an electrode creates a charged corona field which applies a strong negative charge to each particle passing through it. As the charged powder particles approach the carbon fibre tow, the electrostatic attraction between the powder and the tow cause adhesion, ensuring a uniform coating. An extraction unit is attached to the underside of the spray chamber to keep the chamber constantly under negative pressure to ensure the powder stays inside the chamber. The overspray powder, extracted from the chamber, is collected for potential reuse, enhancing the economic appeal of the process. This feature not only underlines its operational efficiency but also aligns with sustainable practices by minimizing material wastage.
Assuming complete consolidation of the adhered powder onto the fibre tow, the quantity of powder deposited on the fibre tow has a direct impact on the towpreg Fibre Volume Fraction (FVF) when maintaining a constant line speed. Therefore, understanding the coupled interaction between continuous airflow and the charged powder particle in the spray chamber allows prediction over the powder particle trajectories and at once the towpreg FVF which directly influences composite part mechanical behaviour. In this study, a numerical investigation of the powder and airflow with commercial computational fluid dynamics coupled with discrete particle modelling (CFD-DEM) on Siemens STAR-CCM+ is used to simulate the multiphase electrostatic spray process in the powder chamber of the towpregging line.
The internal dynamics of the powder chamber are conceptualized as a three-dimensional turbulent continuous gas flow, where solid powder particles are treated as a discrete phase. The continuous gas flow is predicted through the solving of the Navier–Stokes equations, employing a standard K–ε turbulence model featuring non-equilibrium wall functions. Simultaneously, the discrete phase is modelled based on the Lagrangian approach. The electrostatic field, including the impact of space charge attributed to free ions, is calculated to determine the electrostatic potential and charge density. This approach allows for a comprehensive analysis of the interaction between the continuous gas flow, discrete powder particles, and the electrostatic field within the powder chamber.
In the electrostatic deposition process, powdered epoxy is mixed with compressed air within a compact pump and then conveyed to the spray gun. At the tip of the spray gun, an electrode creates a charged corona field which applies a strong negative charge to each particle passing through it. As the charged powder particles approach the carbon fibre tow, the electrostatic attraction between the powder and the tow cause adhesion, ensuring a uniform coating. An extraction unit is attached to the underside of the spray chamber to keep the chamber constantly under negative pressure to ensure the powder stays inside the chamber. The overspray powder, extracted from the chamber, is collected for potential reuse, enhancing the economic appeal of the process. This feature not only underlines its operational efficiency but also aligns with sustainable practices by minimizing material wastage.
Assuming complete consolidation of the adhered powder onto the fibre tow, the quantity of powder deposited on the fibre tow has a direct impact on the towpreg Fibre Volume Fraction (FVF) when maintaining a constant line speed. Therefore, understanding the coupled interaction between continuous airflow and the charged powder particle in the spray chamber allows prediction over the powder particle trajectories and at once the towpreg FVF which directly influences composite part mechanical behaviour. In this study, a numerical investigation of the powder and airflow with commercial computational fluid dynamics coupled with discrete particle modelling (CFD-DEM) on Siemens STAR-CCM+ is used to simulate the multiphase electrostatic spray process in the powder chamber of the towpregging line.
The internal dynamics of the powder chamber are conceptualized as a three-dimensional turbulent continuous gas flow, where solid powder particles are treated as a discrete phase. The continuous gas flow is predicted through the solving of the Navier–Stokes equations, employing a standard K–ε turbulence model featuring non-equilibrium wall functions. Simultaneously, the discrete phase is modelled based on the Lagrangian approach. The electrostatic field, including the impact of space charge attributed to free ions, is calculated to determine the electrostatic potential and charge density. This approach allows for a comprehensive analysis of the interaction between the continuous gas flow, discrete powder particles, and the electrostatic field within the powder chamber.