Fluid sprinkling – spraying – and diffusing – Electrostatic type
Patent
1992-01-31
1994-07-26
Merritt, Karen B.
Fluid sprinkling, spraying, and diffusing
Electrostatic type
239700, 118629, 118630, 118DIG7, B05B 508
Patent
active
053321626
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrostatic spray apparatus and, more particularly, to a spray hood for electrostatic spray apparatus.
It is well known in the art to discharge solids in particle, fibre and the like divided solids forms, and liquids in droplet form, all hereinafter called "spray particles," from a spray head and to apply a high voltage electrostatic charge to said spray particles to form a cloud falling onto a target at a lower potential than the spray particles. The spray apparatus may be static, whereupon the target to be sprayed may be static or traversed beneath the spray head, or the apparatus may be mobile, whereupon the apparatus is traversed over the target.
The falling charged particles are very susceptible to displacement by air currents and uncontrollable air currents can adversely affect the deposition pattern of the spray particles on the target.
When the spray head and the target are static it is the practice to carry out the spray operation in a closed spray booth. In all other applications it is necessary to shield at least the upper regions of the spray cloud against uncontrollable air currents and the practise is to mount the spray head in the upper regions of a hood, the lower regions of which are open to the target.
In more recent times it has been proposed that the electrostatic spray particles be focussed by passing through an electrical field, generated by an electrode between the spray head and the target.
Such an arrangement, intended to apply electrostatically charged spray particles to crops on a conveyor passing beneath the spray head, is disclosed in, for example, British Patent Application No. 8727184 (Publication No. 2197601) and wherein electrostatically charged spray particles are released within a hood and an electrode, wound around the inside of the hood and supported by internal ribs of the hood, establishes a focussing electrical field through which the charged particles fall.
The present invention seeks to provide a hood for an electrostatic spray apparatus, which is more efficacious than spray hoods proposed by the prior art, and an electrostatic spray apparatus including such a hood.
According to the present invention there is provided a a spray hood, for an electrostatic spray apparatus, comprising a first hood element defining a top region with a downwardly depending skirt and an electrode supported within said first hood element, characterized in that the hood includes a second hood element within the first element, the electrode is sandwiched between said first and said second hood elements and extends across the top region and down the greater part of said skirt, and the composite hood does not have any junction of its planar surfaces, other than at the lowermost regions of the said skirt, having a radius of less than one hundred and fifty millimeters throughout its construction.
Spray hoods proposed in the past have included junctions between plane surfaces defining sharp comers, or minimally radiused junctions, and the present invention recognises that such sharp junctions create adverse conditions in the electrode-generated electrical field at and adjacent such junctions.
In one preferred embodiment the spray hood is characterised in that the electrode is in the form of a metallic film.
In another embodiment the electrode is in the form of a mesh.
In a preferred embodiment said first hood element is defined by a moulded shell, the electrode is applied to the internal surface of said moulded shell and the second hood element comprises a lining applied to cover, support and maintain the electrode within the moulded shell.
With such an arrangement the second hood lining element is conveniently applied to the first hood element by a spray process.
In another embodiment the second hood element comprises a moulded shell and said second hood element shell is a neat fit within the said first hood element.
Preferably the first and second hood elements are bonded together along the lower edge regions of the skirt defined by the composite hood structure.
Pre
REFERENCES:
patent: 2980338 (1961-04-01), Kozinski
patent: 4836137 (1989-06-01), Heine et al.
patent: 4901666 (1990-02-01), Nagasaka et al.
Peck, deceased Arthur G. E.
Peck, legal representative by Margaret
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