Claims
- 1. In a method for depositing a particulate material upon a workpiece, wherein the workpiece is exposed, at an effectively opposite potential, to a cloud of electrostatically charged particles, the improvement comprising: disposing a cloud control grid at a level spaced above the porous plate, and impressing upon the grid a voltage having either a negative or a positive value, with respect to ground, of 1 to 20 kilovolts, whereby the spatial characteristics of the cloud of charged particles can be affected so as to control the nature of the deposit produced upon the workpiece; and passing the workpiece through said cloud at a level below and out of contact with said grid.
- 2. The method of claim 1 wherein said gird is subjected to an additional electrical effect selected from the group consisting of grounding of said grid, impressing a cyclically varying current thereupon, or both.
- 3. The method of claim 2 wherein different of said effects are impressed upon discrete portions of said grid.
- 4. The method of claim 3 wherein one of said effects is produced by electrically grounding of one of said discrete portions.
- 5. The method of claim 2 wherein one of said effects is produced by impressing upon the grid a cyclically varying current.
- 6. The method of claim 5 wherein the frequency of variation of said current is about 60 cycles to 30 megacycles per second.
- 7. The method of claim 6 wherein said current is an A.C. sine or square wave current, or a pulsating D.C. current.
- 8. In a method for depositing a particulate material upon a workpiece, wherein the workpiece is exposed, at an effectively opposite potential, to a cloud of electrostatically charged particles, the improvement comprising: disposing a cloud control grid at a level spaced above the porous plate, and impressing upon the grid a current that varies cyclically with a frequency of about 60 cycles to 30 megacycles per second, whereby the density and stability of the cloud of charged particles can be increased to improve the nature of the deposit produced upon the workpiece.
- 9. The method of claim 8 wherein said current is an A.C. sine or square wave current, or a pulsating D.C. current.
- 10. The method of claim 8, wherein discrete portions of said grid are subjected to different frequencies of said cyclical currents.
- 11. In a method for depositing a particulate material upon a workpiece, wherein ionization of a gas is effected by exposing it to electrode means maintained at a high electrical potential, the ionized gas is passed through a substantially horizontal porous plate on which is supported a bed of particles to effect fluidization and electrostatic charging, so as to thereby produce a charged cloud thereof, and wherein the workpiece is maintained at a potential effectively opposite to that of said particles and is exposed thereto, the improvement comprising: passing said ionized gas through an electrically conductive, plenum-mounted control grid before passing it through said porous plate, with said grid maintained at an electrical potential substantially different from, and between the potentials of, the workpiece and the gas ionizing electrode means; disposing a cloud control grid at a level spaced above the porous plate, and impressing an electrical effect upon said cloud control grid to affect the spatial characteristics and/or the density and stability of said cloud of charged particles, so as to afford control of the nature of the deposit produced upon the workpiece, said electrical effect being selected from the group consisting of grounding of said grid, impressing thereupon a voltage having either a negative or a positive value, with respect to ground, of 1 to 20 kilovolts, impressing thereupon a cyclically varying current, and combinations thereof.
- 12. The method of claim 11 wherein said plenum grid potential is maintained by grounding said grid through high resistance means.
- 13. The method of claim 12 wherein said high resistance means has a value on the order of magnitude of megohms.
- 14. The method of claim 13 wherein said high electrical potential of said electrode means has a value of minus 20 to 80 kilovolts, relative to ground.
- 15. The method of claim 14 wherein said high resistance means has a value of at least 100 megohms.
- 16. The method of claim 12 wherein said electrical effect is achieved by and impressing upon the cloud control grid: (a) a potential, with respect to ground, of minus 20 kilovolts to plus 20 kilovolts, inclusive, and/or (b) a current that varies cyclically with a frequency of about 60 cycles to 30 megacycles per second, whereby the spatial characteristics and the density and stability of the cloud of charged particles can be affected, to control and improve the nature of the deposit produced upon the workpiece.
- 17. The method of claim 16 wherein said high electrical potential of said electrode means has a value of minus 20 to 80 kilovolts, relative to ground.
- 18. The method of claim 16 wherein said cloud control grid is grounded.
- 19. The method of claim 16 wherein said cloud control grid is charged to a negative or positive potential, with respect to ground, of 1 to 20 kilovolts.
- 20. The method of claim 16 wherein said cloud control grid is subjected to a plurality of said effects.
- 21. The method of claim 20 wherein one of said plural effects is established by grounding of said cloud control grid.
- 22. The method of claim 20 wherein one of said plural effects is established by charging said cloud control grid to a negative or positive potential, with respect to ground, of 1 to 20 kilovolts.
- 23. The method of claim 20 wherein one of said plural effects is established by impressing said varying current upon said cloud control grid.
- 24. Electrostatic fluidized bed coating apparatus comprising, in combination: a housing having a generally planar substantially horizontal porous support member mounted therein to define within said housing a fluidization chamber thereabove and a plenum therebelow; means for introducing gas into said plenum for passage upwardly through said support member to effect fluidization of particulate coating material supplied to said chamber; means for ionizing gas passing from said plenum into said fluidization chamber, to effect electrostatic charging of such particulate material; an electrically conductive control grid mounted within and substantially across said plenum effectively interposed between said support member and said ionizing means, said grid being adapted for control of its electrical potential and for substantially unimpeded passage therethrough of the ionized gas; and an electrically conductive cloud control grid disposed within and substantially across said chamber above said support member, said cloud control grid being adapted for control of its electrical potential, and said housing being adapted for the passage of a workpiece therethrough for exposure between said support member and said cloud control grid, whereby the cooperative effects of fluidization and electrostatic charging may produce a cloud of electrostatically charged particulate material above said support member, and whereby said grids may be used to affect the deposition of powder upon a workpiece exposed to such cloud.
- 25. The apparatus of claim 24 wherein said cloud control grid is mounted for vertical adjustment within said fluidization chamber, to vary its spacing from said support member.
- 26. The apparatus of claim 24 wherein said housing is adapted for substantially horizontal movement therethrough of at least one workpiece of continuous length.
- 27. The apparatus of claim 24 wherein said cloud control grid is electrically grounded.
- 28. The apparatus of claim 27 wherein the grounding circuit of said cloud control grid includes a variable resistor, so as to enable facile adjustment of the electrical potential of said grid.
- 29. The apparatus of claim 24 wherein said cloud control grid is connected to a voltage source for control of its electrical potential.
- 30. The apparatus of claim 29 wherein said voltage source is a high voltage power supply or a low voltage frequency generator.
- 31. The apparatus of claim 24 wherein said apparatus includes a resistance having a value on the order of megohms in electrical connection with said plenum-mounted grid, through which said plenum-mounted grid may be grounded.
- 32. Electrostatic fluidized bed coating apparatus comprising, in combination: a housing having a generally planar substantially horizontal porous support member mounted therein to define within said housing a fluidization chamber thereabove and a plenum therebelow; means for introducing gas into said plenum for passage upwardly through said support member to effect fluidization of particulate coating material supplied to said chamber; means to effect electrostatic charging of such particulate material; and an electrically conductive, cloud control grid disposed within and substantially across said chamber above said support member, said housing being adapted for the passage of a continuous length workpiece longitudinally therethrough along a rectilinear path at a location between said support member and said cloud control grid, said cloud control grid having a rectilinear elongated conductor depending therefrom and extending parallel to, and substantially in the plane of, said rectilinear path of said workpiece, both said grid and said conductor being adapted for control of their electrical potential, whereby the cooperative effects of fluidization and electrostatic charging may produce a cloud of electrostatically charged particulate material above said support member, and whereby said cloud control grid and conductor may be used to affect the characteristics of such cloud.
- 33. The apparatus of claim 32 wherein said control grid is mounted for vertical adjustment within said fluidization chamber, to vary its spacing from said support member.
- 34. The apparatus of claim 32 wherein said control grid has a pair of conductors depending therefrom, said conductors being spaced from and parallel to one another, and lying substantially in said plane.
- 35. The apparatus of claim 34 wherein said housing is adapted for the passage of a plurality of continuous length workpieces substantially in said plane, said conductors of said cloud control grid being so spaced as to dispose them laterally outwardly of the workpieces.
- 36. The apparatus of claim 34 wherein said cloud control grid is substantially rectangular, and wherein said conductors depend from the opposite, laterally spaced longitudinal sides thereof.
- 37. The apparatus of claim 32 wherein said conductor is adapted for control of its electrical potential independently of that of other portions of said control grid.
- 38. A system for electrostatically coating a continuous length workpiece, comprising:
- (a) electrostatic fluidized bed coating apparatus comprising, in combination, a housing having a generally planar, substantially horizontal porous support member mounted therein to define within said housing a fluidization chamber thereabove and a plenum therebelow; means for introducing gas into said plenum for passage upwardly through said support member to effect fluidization of particulate coating material supplied to said chamber; means to effect electrostatic charging of such particulate material; and an electrically conductive, cloud control grid disposed within and substantially across said chamber above said support member, said housing being adapted for the longitudinal passage therethrough of at least one workpiece of continuous length along a rectilinear path at a location between said support member and said cloud control grid, said cloud control grid having a pair of transversely spaced, rectilinear elongated conductors depending therefrom and extending parallel to, and outwardly and substantially in the plane of, said rectilinear travel path of said workpiece, both said cloud control grid and said conductor being adapted for control of their electrical potential, whereby the cooperative effects of fluidization and electrostatic charging may produce a cloud of electrostatically charged particulate material above said support member, and whereby said cloud control grid and conductor may be used to affect the characteristics of such cloud; and
- (b) means for continuously conveying said workpiece through said housing of said apparatus along said rectilinear path.
- 39. The system of claim 38 wherein said plane is substantially horizontal, and wherein said conveying means is adapted to convey a multiplicity of such continuous length workpieces simultaneously through said housing along rectilinear paths parallel to and in the plane of said first-mentioned path, said conductors lying outwardly of all of said rectilinear paths.
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of applicant's copending application for U.S. patent Ser. No. 114,656, filed on Jan. 23, 1980 and entitled CONTROL GRID IN ELECTROSTATIC FLUIDIZED BED COATER, now issued as U.S. Pat. No. 4,297,386.
US Referenced Citations (8)
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
114656 |
Jan 1980 |
|