Electrostatic spray apparatus

• US 3,964,683 A
• Filed: 09/02/1975
• Issued: 06/22/1976
• Est. Priority Date: 09/02/1975
• Status: Expired due to Term

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Champion Spark Plug Company
• Inventors: Gimple, James J.
• Primary Examiner(s): Ward, Jr., Robert S.
• Application Number:
  US05/609,669
• Time in Patent Office: 294 Days
• Field of Search: 239/3, 239/15, 239/63, 239/64, 239/105
• US Class Current: 239/691
• CPC Class Codes: B05B 5/032 for spraying particulate materials

Abstract

An improved electrostatic spray gun for the deposition of powdered coating material on a workpiece is disclosed. The spray gun includes a housing having a barrel to which a nozzle is attached for directing the powdered material to the workpiece. A charging electrode, which is connected to a high voltage power supply, is mounted on a diffuser assembly which is clamped between the nozzle and the housing, on which the nozzle is threaded. A regulated gas flow supplied through the housing and the diffuser assembly provides a gas shield around the charging electrode to prevent a buildup of the coating material on the electrode. A novel pneumatic safety interlock continuously monitors the pressure of the gas supplied to the diffuser assembly. The interlock turns off the high voltage power supply and a pump for the coating material in response to a drop in such pressure resulting from a loose nozzle.

Claims

1. An improved electrostatic spray gun for the deposition of a coating material on a workpiece comprising, in combination, a nozzle having a passage for emitting a flow of the coating material toward the workpiece, a housing, means releasably attaching said nozzle to said housing, means for supplying a flow of the coating material through said housing to said nozzle passage, means for electrostatically charging the material emitted from said nozzle passage, means for supplying gas at a predetermined high pressure to a passage having an end closed by said nozzle when said nozzle is attached to said housing, the pressure of such gas in said passage decreasing when said nozzle is loosened on said attaching means, means for sensing a drop in the pressure of such gas in said passage to below a predetermined low pressure lower than said predetermined high pressure, and means responsive to said pressure sensing means sensing a pressure drop to below said predetermined low pressure for interrupting said charging means from charging the coating material.

2. An improved electrostatic spray gun, as set forth in claim 1, and further including means responsive to said pressure sensing means sensing a pressure drop to below said predetermined low pressure for interrupting said material supplying means from supplying a flow of the coating material to said nozzle passage.

3. An improved electrostatic spray gun, as set forth in claim 2, and further including valve means for normally maintaining the gas pressure sensed by said pressure sensing means below said predetermined low pressure, and trigger means for manually actuating said valve means to cause said pressure sensing means to sense the gas pressure in said passage.

4. An improved electrostatic spray gun, as set forth in claim 1, and further including valve means for normally maintaining the gas pressure sensed by said pressure sensing means below said predetermined low pressure, and trigger means for manually actuating said valve means to cause said pressure sensing means to sense the gas pressure in said passage.

5. An improved electrostatic spray gun for the deposition of powdered coating material on a workpiece comprising, in combination, a nozzle having a passage for directing a fluidized flow of the powdered coating material toward the workpiece to be coated with the material, a housing, means releasably attaching said nozzle to said housing, means for supplying a fluidized flow of such powdered material through said housing to said nozzle passage, a diffuser assembly having a charging electrode projecting therefrom, said diffuser assembly having support means clamped between said nozzle and said housing for holding said charging electrode centered in the path of the fluidized powdered material passing through said nozzle passage, said support means having a passage extending between said housing and said nozzle, means for applying compressed gas through said housing to said support means passage, said diffuser assembly including means for forming a gas shield around said charging electrode from a limited flow of the compressed gas from said support means passage to prevent a buildup of the powdered coating material on said charging electrode, the compressed gas in said support means passage normally having a predetermined high pressure, means for applying a high voltage to said charging electrode for imparting an electrostatic charge to the powdered material flowing through said nozzle passage, and means responsive to a drop in the predetermined high gas pressure in said support means passage for interrupting said high voltage applying means, whereby the high voltage on said charging electrode is interrupted when said nozzle loosens from said housing.

6. An improved electrostatic spray gun, as set forth in claim 5, and further including means responsive to a drop in the predetermined high gas pressure in said support means passage for interrupting said material supplying means.

7. An improved electrostatic spray gun, as set forth in claim 6, and further including a trigger attached to said housing, and trigger actuated valve means located within said housing between said support means and said pressure responsive means for manually controlling said high voltage applying means and said material supplying means.