Electrostatic powder coating for deep cavities and right-angled workpieces: Matching logic of AFC, low current and high voltage, spray distance and fine-tuning airflow.
When it is difficult to powder deep cavities and right-angle workpieces, "low current and high voltage" cannot be understood as a fixed set of parameters, let alone increase the voltage, powder volume and air flow all at the same time.A more plausible matching logic is: The current concentration at the inlet edges and sharp corners is first suppressed with a lower current upper limit, so that the powder is not preferentially stacked on the notches, folded edges and outer edges. Sufficient voltage settings are retained to provide starting conditions for long-distance live and powder cloud charging; however, when the gun is close to the workpiece and the actual current touches the upper limit, the AFC class control usually reduces the actual output voltage, so it is necessary to look at the actual voltage and actual current, rather than just the set value. Use the spraying distance to control the electric field load and the degree of current limiting intervention: the distance is too close to quickly trigger the current limiting, the actual voltage drops and aggravates the edge capture; the distance may be too far and the powder cloud may lack effective transportation into the deep cavity. Control aerodynamics with softer, stable powder clouds: The airflow is only responsible for steady delivery of the powder into the target area and should not be so strong as to create an impact, gyration, bounce or push the powder towards the edge of the inlet. Spray the dead angle first, and then spray the plane; spray thinly from both sides or obliquely, and use the geometric path to solve the problem that a single front spray cannot solve. Therefore, what really needs to be matched is "upper current limit — actual voltage — spray distance — powder cloud momentum — spray angle — spray sequence", rather than looking for a so-called universal AFC parameter in isolation.