Fluid sprinkling – spraying – and diffusing – Electrostatic type – With impeller
Reexamination Certificate
2000-01-14
2001-05-15
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Electrostatic type
With impeller
C239S703000, C239S708000
Reexamination Certificate
active
06230993
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electrostatically aided atomization and coating of articles with charged particles. It is disclosed in the context of certain types of coating material dispensers. However, it is believed to be useful in a wide range of coating dispensing applications. As used in this application, terms such as “electrically conductive” and “electrically non-insulative” refer to a broad range of conductivities electrically more conductive than materials described as “electrically non-conductive” and “electrically insulative.” Terms such as “electrically semiconductive” refer to a broad range of conductivities between electrically conductive and electrically non-conductive.
In its early years, the field of electrostatically aided coating material atomization and dispensing was dominated by the dispensing of coating materials containing organic solvents. These solvents and the coating materials they carried typically were electrically non-conductive or only very slightly conductive, but the carriers or solvents were also relatively volatile. The particles of these coating materials thus could ordinarily be charged by contact with, or at least passage within relatively short distances of, electrodes maintained at relatively high magnitude potentials with respect to the article(s) to be coated by the atomized coating material particles. However, care needed to be taken not to stimulate high energy electrical discharge across the space between the electrodes and the article(s) being coated. This need dictated considerable attention by operators of such equipment. The volatility of these solvents also raised environmental concerns about the release of so-called voc's (volatile organic compounds).
Efforts have continued to enhance solvent based coating systems, both against the hazards associated with having relatively high magnitude electrical potentials across atmospheres containing voc's, and against the inevitable close proximity of operators to the highly charged electrodes of such equipment. Standards for testing such equipment have been promulgated by a number of testing agencies in various countries. Illustrative of such standards is the Electrostatic Finishing Equipment Approval Standard, Class Number 7260, promulgated by Factory Mutual Research Corporation (the FM standard).
The FM standard includes protocols for the testing of both manual equipment (for example, hand held coating atomizing and dispensing guns—the FM standard, chapter 5) and automatic equipment (for example, atomizers mounted on robot arms—the FM standard, chapter 6). Among the tests in both cases is a test in which the equipment at operating voltage is probed using a grounded metal sphere having a diameter of one inch ( about 2.5 cm). This test takes place in an explosive atmosphere of propane in air. An explosion is a failed test. To achieve FM approval, the equipment must, inter alia, pass this test. The FM standard has caused considerable research and improvement in the safety of electrostatic coating systems. Some ways in which the protocols can be addressed are illustrated and described in co-pending U.S. Ser. No. 08/955,039 filed Oct. 21, 1997, titled SAFE CHARGING, and co-pending U.S. Ser. No. 09/046,383 filed Mar. 23, 1997, titled SAFE CHARGING WITH NON-INSULATIVE ATOMIZER, both assigned to the same assignee as this application.
In atomizers constructed generally as described in U.S. Pat. Nos. 5,622,563; 5,633,306; and, 5,662,278, illustrated in
FIGS. 1
a-b
, the atomizer
8
is constructed with a relatively well-defined atomizing edge
10
. Referring specifically now to
FIG. 1
a
, the semiconductive coating
12
applied to the rearward, or outer, surface
14
of the atomizer
8
extends all the way to edge
10
, increasing the likelihood of electrical contact between the coating
12
and the coating material
16
being atomized from edge
10
. This contact, of course, increases the likelihood that the coating material
16
being atomized from edge
10
will be electrically charged and will be attracted to the article to be coated thereby, all in accordance with known principles.
Referring now particularly to
FIG. 1
b
, however, what sometimes happens to atomizer
8
as it is used can be seen. The abrasive nature of some coating materials
16
, poor maintenance habits, and other factors can lead to a reduction in the sharpness of edge
10
, cause rounding of edge
10
, and cause the semiconductive coating
12
to wear away from edge
10
. This phenomenon is accelerated somewhat as the edge wears round, owing, it is believed, to the surface tension of the coating material causing the coating material to migrate back along the lip of the atomizer
8
toward the semiconductive coating
12
. Because the coating material remains uncharged until it contacts the semiconductive coating
12
, there is less tendency for the coating material to leave the lip. As the coating material
16
flows to edge
10
to be atomized, it becomes less likely that the coating material will contact the semiconductive coating
12
. It therefore becomes less likely that the coating material will be electrically charged as it is atomized from edge
10
. This manifests itself in a reduction in transfer efficiency, the ratio of the amount of coating material being deposited on the article to be coated to the amount of coating material dispensed by the atomizer
8
.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, an atomizer is provided for mounting on an output shaft of a motor to be rotated by the motor. The atomizer includes a first, front surface, a second, back surface, a coating material cup into which coating material to be atomized by the atomizer is dispensed, and at least one passageway from the cup to the front surface to permit the flow of coating material from the cup to the front surface as the atomizer is rotated. The front surface terminates at a discharge edge from which the coating material is discharged as the atomizer is rotated. The atomizer further comprises an electrically conductive first electrode, an electrically non-conductive portion, and a semiconductive coating provided on the back surface. The semiconductive coating terminates adjacent the edge.
Illustratively according to this aspect of the invention, the first electrode comprises the cup.
Further illustratively according to this aspect of the invention, the semiconductive coating comprises a multilayer semiconductive coating.
Additionally illustratively according to this aspect of the invention, a terminus of the semiconductive coating adjacent the edge comprises a second electrode.
According to another aspect of the invention, an atomizer is provided for mounting on an output shaft of a motor to be rotated by the motor. The atomizer includes a first, front surface, a second, back surface, a coating material cup into which coating material to be atomized by the atomizer is dispensed, and at least one passageway from the cup to the front surface to permit the flow of coating material from the cup to the front surface as the atomizer is rotated. The front surface terminates at a discharge edge from which the coating material is discharged as the atomizer is rotated. The atomizer further comprises an electrically conductive first electrode, an electrically non-conductive portion, and a semiconductive coating provided on the back surface. The semiconductive coating terminates adjacent the edge. The atomizer further comprises a third surface adjacent the edge, a second electrode provided on the third surface, and at least one electrical pathway between the second electrode and the semiconductive coating.
Illustratively according to this aspect of the invention, the second electrode comprises a groove provided in the third surface and a semiconductive material filling the groove.
Further illustratively according to this aspect of the invention, the groove extends continuously around the entire circumference of the third surface.
Additionally illustratively according to this aspect
Austin Ronald M.
Howe Varce E.
Huff David R.
Barnes & Thornburg
Ganey Steven J.
Illinois Tool Works Inc.
Scherbel David A.
LandOfFree
Method of charging using nonincendive rotary atomizer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of charging using nonincendive rotary atomizer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of charging using nonincendive rotary atomizer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2554683