Method and apparatus for electrostatic spray powder coating
First Claim
1. A method for electrostatic powder coating by spraying powder particles entrained in a carrying gas stream upon a surface to be coated, said method comprising dispensing an ionized powder by a carrying gas in an axial direction, introducing a control air into the carrying gas powder mixture in a substantially radial direction for retarding the axial velocity of the carrying gas powder mixture, characterized in that a gas stream is fed through a passage separate from those of the carrying gas powder mixture and from the control air and is ionized before being discharged, said gas stream being introduced in a substantial radial direction in an area of reduced flow velocity of the carrying gas powder mixture.
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Abstract
The invention relates to a method and apparatus for electrostatic spraying of powder particles on a surface to be coated. The carrying gas powder mixture axially discharged from a nozzle is expanded by a radially discharged control air stream to thereby form the desired spray mist. The electrostatic charging of the powder is achieved by an ionized gas stream which is fed into the carrying gas powder mixture separately from the control air stream. Some of the advantages achieved by the invention are an improved spray pattern and a more uniform coating.
18 Citations
13 Claims
- 1. A method for electrostatic powder coating by spraying powder particles entrained in a carrying gas stream upon a surface to be coated, said method comprising dispensing an ionized powder by a carrying gas in an axial direction, introducing a control air into the carrying gas powder mixture in a substantially radial direction for retarding the axial velocity of the carrying gas powder mixture, characterized in that a gas stream is fed through a passage separate from those of the carrying gas powder mixture and from the control air and is ionized before being discharged, said gas stream being introduced in a substantial radial direction in an area of reduced flow velocity of the carrying gas powder mixture.
- 3. An apparatus for electrostatic spray powder coating comprising a tube extending forwards beyond an outlet nozzle for discharging a carrying gas powder mixture, said tube including an annular passage for feeding control air, a radial gap between the forward end of the tube and an insert member closing said end of the tube, said radial gap communicating with said annular passage for expanding the carrying gas powder mixture discharged from said outlet nozzle through the action of said control air, and in electrode for ionizing the carrying gas powder mixture, characterized in means for introducing an ionized separately fed gas stream into the gas powder mixture downstream of said radial gap.
Specification