Patent ID: 7240861

Claim:
A corona discharge apparatus for spraying powders, comprising: a) a housing having first and second opposed ends, the housing defining a chamber terminating in an outlet passageway at said first end of the housing; b) a high voltage pin electrode positioned in the chamber spaced upstream of the outlet passageway, the high voltage pin electrode having a first surface area, and including at least one charging pin connected to a conductor located in an electrically insulated tube disposed along an axis of the housing, the conductor being connectable to a power supply for applying high voltages to the at least one charging pin; c) a ground surface electrode positioned in the chamber spaced upstream from the high voltage pin electrode, the ground surface electrode having a second conducting surface area that is sufficiently larger than the first surface area of said high voltage pin electrode to give a pin-to-surface electrode configuration such that when a high voltage is applied to the high voltage pin electrode, an electrical field produced in a vicinity of the ground surface electrode is sufficiently low to prevent arc discharging occurring in the vicinity of the ground surface electrode in the chamber; d) an inlet opening into the chamber for conducting a powder-gas mixture into the chamber, said inlet opening being located at the second end of the housing; and e) means for supplying a cleaning gas toward the high voltage pin electrode to reduce powder deposits on the high voltage pin electrode, wherein the chamber defines an inner cylindrical surface and the ground surface electrode is a cylindrical electrode having an outer diameter such that the cylindrical electrode is substantially concentric with the inner cylindrical surface, the cylindrical electrode having an inner surface which has the second conducting surface area that is sufficiently larger than the first surface area of the high voltage pin electrode.