Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1996-05-28
1998-10-13
Lusignan, Michael
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427475, 427483, 427484, 427480, 427181, 427201, 427421, 118621, 118622, 118625, 118626, 118310, 118311, 118317, 239697, 239698, B05D 104, B05D 106, B05B 504, B05B 5047
Patent
active
058209417
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus and methods for powder spray coating a large surface area, such as the internal or external surface of a cylindrical drum or barrel, large panels, or a plurality of small objects hung in a planar array, for example.
In accordance with conventional powder coating methods and apparatus, a pressurised electrostatically charged mixture of gas and powder particles is sprayed outwardly from a gun in the direction of an object to be coated. The charged powder particles in the mixture repel one another as they travel toward the object to be coated, and the lower electrical potential of the object to be coated electrostatically attracts the particles.
When powder coating an object having a large surface area using a single spray device either the spray device or the object must be moved so as to coat the whole area, or the spray device must discharge a large volume of powder in a wide spray pattern. Moving a single spray device or an object so as to coat a large area takes a considerable time and reduces the maximum throughput of a powder coating system. Discharging a large volume of powder requires a large volume of entraining air, and, due to the large cross-sectional spray area produced by conventional high volume spray devices, the sprayed mixture produces a thick air cushion. This air cushion obstructs the flow of subsequent powder particles and causes a substantial number of these to rebound away from the surface to be coated. As a result, this method of powder coating takes additional time to ensure complete coating and significant amounts of powder are lost due to rebounding.
GB-A-2127370 discloses a dispenser of powdered electrostatic varnish in which powder in admixture with air is fed into a reservoir and thence through a gap defined between two flat parallel surfaces to be dispensed in a flat spray pattern. A number of electrodes are arranged radially adjacent the gap to charge the powder emitted therefrom electrostatically.
Conventional electrostatic powder coating methods and apparatus present further problems when coating a large surface area. When using an external electrode to establish an electrostatic field between the spray device, or gun, and the object, the strongest lines of electrostatic force are located along the direct line between the electrode and the nearest point on the object, and electrostatic lines of force directed towards the more distant portions of the surface to be coated will be significantly weaker, with the result that the object is coated unevenly, with a varying depth of powder since the charged powder follows the electrostatic field lines to the object being coated. Additionally, particles having a higher electrostatic charge retain their charge after deposition, thereby repulsing subsequent particles and resulting in uneven coating.
SUMMARY OF THE INVENTION
In accordance with a first aspect of this invention, powder spray coating apparatus comprises means for supplying electrostatically-charged powder entrained in air to a spray head having at least one nozzle from which the powder is discharged, and a deflector mounted externally of the spray head and adjacent to the or each nozzle to deflect the discharged powder into a substantially flat thin spray pattern, the spray head and the flat spray pattern being substantially symmetrical about a common longitudinal axis.
Preferably means are provided for moving the spray head and the deflector along the longitudinal axis so as to powder coat an object having a large surface area. Alternatively, the object(s) to be coated may be moved, relative to the spray body along the longitudinal axis. By providing relative movement along the longitudinal axis between the spray head and the object(s) to be coated, objects having a large surface area, such as the inside or outside surface of a drum or barrel, or the surface of a large flat object which is moved around the spray device along an omega shaped track, for example, may be coated with powder. Such an apparatus may also be used, in conjuncti
REFERENCES:
patent: 2893893 (1959-07-01), Crouse
patent: 3196826 (1965-07-01), Norris
patent: 3521815 (1970-07-01), Szasz
patent: 3667674 (1972-06-01), Parsons et al.
patent: 3746254 (1973-07-01), Duncan et al.
patent: 3767116 (1973-10-01), Clausen et al.
patent: 3873024 (1975-03-01), Probst et al.
patent: 3924810 (1975-12-01), Otterstetter
patent: 4072129 (1978-02-01), Bright et al.
patent: 4092440 (1978-05-01), Wohr et al.
patent: 4109027 (1978-08-01), Crose
patent: 4248379 (1981-02-01), Hollstein et al.
patent: 4343436 (1982-08-01), Lehmann
patent: 4380320 (1983-04-01), Hollstein et al.
patent: 4543274 (1985-09-01), Mulder
patent: 4810521 (1989-03-01), Robertson
patent: 4811898 (1989-03-01), Murphy
patent: 5102045 (1992-04-01), Diana
Felton Harry-Graham
Ruud Jan
Barr Michael
Lusignan Michael
Nordson Corporation
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