The present invention relates generally to the application of powder coatings. More particularly, this invention relates to the controlled delivery of powder paint to a spray applicator.
Currently powder paint is supplied to the applicator by a venture pump that first pulls powder from a fluidizing hopper via negative pressure generated by compressed air flowing through a venturi, then transports the powder pneumatically in a dilute phase condition to the spray applicator through a relatively large hose (typically 9–11 mm diameter), at relatively high velocity (typically 15 m/sec). Significant variation in powder flow is inherent to venturi based systems due to their sensitivity to changing conditions (hose length, back pressure, feed hopper pressure etc.) The current venturi based powder pump technology is being pushed to the edge of its operating envelope as a result of increasingly stringent control and output and requirements.
There are also a number of disadvantages associated with venturi based systems. For example, they are limited in maximum flow rate by practical hose size and supply pressure to the venturi. Additionally, significant variation in powder flow is inherent to venturi based systems due to their sensitivity to changing conditions (hose length, back pressure, feed hopper pressure etc.) and wear of the venturi due to erosion. Variations in powder flow over time causes unacceptable variation in the thickness of the applied powder coating or resulting paint film. Venturi pump systems also use significant quantities of costly conditioned compressed air. They require frequent preventative maintenance both in the form of venturi replacement due to wear, and hose cleaning due to the deposition of powder on the hose walls typical of dilute phase powder transport. Finally, venturi pumps impart enough energy into the powder paint to cause measurable degradation in the mechanical characteristics of the powder.
It would therefore be advantageous to have a powder paint delivery method and apparatus that provides a very consistent supply of powder paint to the applicator without the inconvenience and cost of frequent maintenance and venturi replacement, that uses minimal compressed air, and imparts only low forces on the powder to minimize or eliminate damage caused by the transporting process.