Fluid sprinkling – spraying – and diffusing – Electrostatic type – With impeller
Reexamination Certificate
2001-06-05
2003-06-17
Hwu, Davis (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Electrostatic type
With impeller
C239S703000, C239S706000, C239S690000, C239S690100
Reexamination Certificate
active
06578779
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rotary atomizer including a bell element for application of powder paint in mass production applications.
BACKGROUND OF THE INVENTION
Powder paint, including primer or basecoat and color coats have been used or proposed in mass production applications, including automotive applications, to reduce volatile organic compounds, such as solvents used in or in connection with liquid paint. Such powder paint is typically applied in mass production applications by a rotary atomizer having a rotary bell element, generally referred to in the industry as a “bell cup.” A conventional bell element includes a paint tube, which receives the liquid or powder paint and which may be threadably attached to the bearing of the atomizer, a deflector or diverter element having a distribution surface opposed to the outlet of the paint tube which directs the paint radially and axially to an overflow surface. The bell element is rotated by the atomizer at a relatively high velocity, typically about 5,000 to 15,000 RPM, which “atomizes” the stream of paint by centrifugal force and directs the paint to the workpiece, such as an automotive body. Shaping air may also be used to improve the deposition efficiency of the paint on the workpiece.
To further improve the deposition efficiency of a rotary atomizer, the paint is electrostatically charged by the rotary atomizer and the workpiece is grounded which reduces paint overspray. One method of electrostatically charging paint, typically used for liquid paint, is the use of a charge ring or “halo” surrounding the bell element having a plurality of axially extending electrodes. Another method is to electrostatically charge a component or components of the bell element which contact the paint and which thereby imparts an electrostatic charge to the atomized paint. For example, U.S. Pat. No. 5,358,182 which discloses an electrostatic sprayer device for liquid coating which includes an elongated central counter-electrode at ground potential which “deforms” the electrostatic field near the atomizer edge or overflow surface to increase the time the liquid coating product droplets pass through a high electric field. Another example is disclosed in a PCT published application WO 99/49982, wherein the bell is electrically connected to a plurality of Corona discharge elements and a generator capable of detecting variations in the current passing through the discharge elements.
Although the use of powder paint reduces or eliminates volatile organic compound emissions as compared to liquid paint, collection and recycle systems for powder paint are complex and expensive. Therefore, it would be very desirable to reduce overspray of powder paint or increase deposition efficiency. It is a primary object of the present invention to improve the deposition efficiency of rotary atomizers for powder paint.
SUMMARY OF THE INVENTION
The atomizer for powder paint of this invention includes a rotary bell element comprising a generally axial paint tube, a deflector or diverter having a distribution surface opposed to the outlet of the paint tube directing the paint radially and axially toward an overflow surface through an annular channel, an annular electrostatically charged surface adjacent an end surface of the bell element generating an annular electrostatic field electrostatically charging the paint, and an axially extending electrostatically charged electrode having a distal end preferably in the plane of the annular electrostatically charged surface generating an axial electrostatic field of generally the same charge as the annular electrostatic field. It has been found by the applicant that a central axial electrostatic field of substantially the same charge as the annular electrostatic field extending from adjacent the edge of the bell element results in an improvement in deposition efficiency of about eight percent, which thus significantly reduces overspray. This improvement is of particular importance for the color coats which presently cannot be recycled except as a basecoat.
In the most preferred embodiment, the bell element includes a nonconductive end face preferably formed of a polymer having a low coefficient of friction, such as polytetraflouroethylene or Teflon®. The end face includes a depression surrounding the center electrode and a planar surface surrounding the central depression having a circular outer edge adjacent the paint overflow surface. The annular electrostatically charged surface which generates the annular electric field is preferably adjacent to and surrounds the circular outer edge of the nonconductive end face and most preferably the end face is integrally formed with the deflector or diverter. In the preferred embodiment, the distribution surface of the deflector includes a generally cone-shaped deflector tip having a concave exterior surface which directs the paint into a cone-shaped annular channel or passage defined by opposed conical surfaces, wherein a distal end of one of the conical surfaces defines the annular electrostatically charged surface generating the annular electrostatic field. In the disclosed embodiment, one of the conical surfaces which define the annular conical channel is continuous with the generally conical surface of the deflector and this surface extends to and supports the circular outer edge of the end face. In this embodiment, the distal annular edge provides the annular electrostatically charged surface which is coplanar with the planar surface of the nonconductive end face. Alternatively, the opposed conical surface may extend to the plane of the end face, wherein the distal outer edge provides the annular electrostatically charged surface.
In the most preferred embodiment, the paint tube is connected to the bearing of the atomizer and electrostatically charged. In this embodiment, the paint tube is electrically connected to both the annular electrostatically charged surface and the center electrode, such that the central electrode and the annular electrostatically charged surface are at the same electrical potential and generate electrostatic fields having substantially the same charge. In the disclosed embodiment, the paint tube is connected to a source of electric current and the center electrode is electrically connected to the paint tube by a tubular ring which surrounds the deflector.
As set forth above, the atomizer having a rotary bell element of this invention results in an improved deposition efficiency of about eight percent as compared to a bell element of essentially the same design without a center electrode as described above. Other advantages and meritorious features of the present invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.
REFERENCES:
patent: 4576827 (1986-03-01), Hastings et al.
patent: 5011086 (1991-04-01), Sonnleitner et al.
patent: 5346139 (1994-09-01), Davis et al.
patent: 5358182 (1994-10-01), Cappeau et al.
patent: 5707009 (1998-01-01), Schneider
patent: 6056215 (2000-05-01), Hansinger et al.
patent: 6189804 (2001-02-01), Vetter et al.
patent: 3241504 (1984-04-01), None
patent: 1038587 (2000-09-01), None
Publication No. WO 99/49982; International Publication Date Oct. 7, 1999; PCT/FR99/00752; Search Report Jun. 14, 1999.
Behr Systems, Inc.
Howard & Howard
Hwu Davis
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