US2690730A

US2690730A - Electrostatic coating apparatus

Info

Publication number: US2690730A
Application number: US249764A
Authority: US
Inventors: James C Marsh
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1951-10-04
Filing date: 1951-10-04
Publication date: 1954-10-05
Anticipated expiration: 1971-10-05

Description

Oct. 5, 1954 IN V EN TOR.

JAMES C. MARSH BY W7 ZXW Aflorney Patented Oct. 5, 1954 ELECTROSTATIC COATING APPARATUS James C. Marsh, Indianapolis, Ind., assignor to Ransburg Electro-Coating Corn, Indianapolis, Ind., a corporation of Indiana Application October 4, 1951, Serial No. 249,764

6 Claims.

This invention relates to the electrostatic coating of articles.

Articles such as automobile steering wheels have previously been coated by electrostatically depositing an atomized paint on them as they are moved in an elongated coating zone as is shown in the copending application of William A. Starkey, Serial No. 689,116, filed August 8, 1946, now abandoned. While coating such articles by the method just referred to obtained markedly improved eiiiciency over conventional mechanical and hand spray methods, some paint still passed through the electrostatic field without being deposited on the articles, and therefore spray booths were still required for surrounding the coating station to carry away the overspray.

In order to improve still further the efficiency in applying coating material to such articles, electrostatic atomizing apparatus such as that illustrated in the copending application of E. M. Ransburg, Serial No. 143,994, filed February 13, 1950, was tried. However, it was found that while the efficiency of depositing the coating material sprayed on articles being coated with such apparatus was increased such that 97 percent of the coating material sprayed was deposited onto the article, the distribution of the deposited coat-- ing material was sumciently uneven as to make the process unsatisfactory for commercial use.

Therefore, it is an object of this invention to provide novel electrostatic apparatus for applying a coating to three dimensional articles with a film thickness of commercially satisfactory uniformity.

Another object of this invention is to apply a a coating to surfaces of open-work articles electrostatically whose film thickness is of commercially acceptable uniformity.

A further object of this invention is to provide novel electrostatic apparatus for applying a coa ing of improved uniformity to round or wheelshaped articles.

Still another object of this invention is to provide novel electrostatic apparatus for applying a coating of improved uniformity to a surface of a supported article adjacent its support.

A further object of this invention is to apply a coating of commercially satisfactory uniformity to a downwardly presented surface with electrostatically atomized coating material.

In one embodiment of my invention for coating a three dimensional article, such as an automobile steering wheel, one dimension of which is materially less than the other two, there is provided an apparatus which comprises a support for holding the article to maintain its larger plane defined by the two greatest dimensions in a predetermined position. This apparatus also includes an electrostatic atomizing head, means for supplying liquid coating material to the atomizing head, means including a high voltage source for establishing a high potential diiference between the liquid coating material on the atomizing head and the article for electrostatically atomizing the coating material and electrostatically depositing the atomized coating material on the article, and means for supporting the head in spaced relation from the article. This head support is constructed to permit arranging the head so that there is an angle of approximately 30 degrees between the axis of the head and a perpendicular to the larger plane of the article which intersects the head axis at the larger plane. This angle may be a few degrees above or below thirty degrees, but I have found that if the angle is less than twenty degrees or more than forty degrees the desired results are not obtained. Also the head is so supported that its axis, when projected, passes through the article as it is moved past the head.

The invention will now be described with reference to the drawing of which:

Figure 1 is a top plan view of apparatus for coating automobile steering wheels and Figure 2 is an end elevation view taken on line 2--2 of Figure 1.

Referring more specifically to the drawing, there is shown a plurality of articles 10, illustrated as automobile steering wheels, supported on spaced spindles l2 rotatably connected to conveyor l4. Each spindle I2 is provided with a pulley I6 which is adapted to be brought into engagement with movable belt it to rotate the supported articles I0 while they are moved by the conveyor.

The conveyor Ill is arranged to move the articles In over a predetermined path in the direction of the arrow 2%? past and in spaced relation to an electrostatic atomizing device generally indicated by the numeral 22.

The atomizing device comprises base 24, a standard 26, arm 28 and atomezing head lit. The standard 26 is mounted on the base 24 to move vertically and may be fixed in any desired position by knob 32. The arm 28 is pivotally connected to the standard 26 at 3% and may be fixed in any desired position. The arm is constructed of electrically insulating material to isolate the head 3%! from ground. The head 3!) is adapted to be rotated by being geared to a rotatable shaft (not shown) in the hollow arm 28, which may be driven by any suitable means such as the motor at 34. The head 30 is arranged so that its axis is at right angles to the extent of the arm 28. The head 30 may be of any suitable construction. One such head is described in French Patent No. 982,327, published June 8, 1951. The head 30 shown comprises a shaft 3! and a flaring, recessed, conical bell 33 afiilxed to one end of the shaft. The shaft 3i is provided with an axial passage (not shown) which at one end communicates with the pipe 36 and at the other end communicates with the apex at the interior of the conical bell 33. Liquid coating material such as paint, lacquer or varnish is supplied to the conical bell 33 from a source (not shown) through pipe 36 and the passage in the shaft 3i. Rotation of the head 30 distributes the liquid fed to the bell 33 in the form of a free-surfaced film over its inner surface and flows to its outer peripheral edge 35. A high potential difference for example 90 kilovolts D. C. is maintained between the liquid coating material supplied to the atomizing bell 33 and the articles I by connecting the head to one terminal of a high voltage source 38 by means of conductor 40. The other terminal of the high voltage source is grounded as is the conveyor Id.

In operation the articles ID are supported on the spindles l2 of the conveyor 14 so that they are maintained in position so that their larger planes are in horizontal positions. These articles are moved by the conveyor I4 over a predetermined path past the atomizing device 22 for being coated thereby. In order to obtain the desired distribution of coating material on portions of the articles I B, the head 33 is arranged so that it is below and to one side of the articles H] as they move past the head, and the head is sufficiently spaced from the conveyor [4 and articles ID to avoid sparking. Also the head 30 is so arranged that the axis of the head or spray is at an angle of approximately 30 degrees to the vertical and, when projected, this axis passes within the bounds of the articles as they move past the head. While I have obtained excellent results with the axis of the head arranged at 30 degrees to the vertical, satisfactory results are also obtainable if this angle is not less than degrees or more than 40 degrees.

While I have shown and described one particular embodiment of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In apparatus for electrostatically coating a series of similar three-dimensional articles in each of which one of the three mutually perpendicular over-all dimensions is materially less than either of the other two, means for moving the articles translationally over a predetermined path in a coating zone, said article moving means including supports for holding the articles with the sides defined by the two greatest dimensions in generally horizontal positions, an electrostatic atomizing head, means for supplying liquid coating material to said head, means including a high voltage source for establishing an electrostatic field of sufificient strength between the liquid coating material on said head and the articles for electrostatically atomizing the coating material from said head and electrostatically depositing the coating material on the articles in the coating zone, means for supporting said head spaced from the path of article movement with the axis of said head lying in a plane normal to the article path and with the axis of said head being at an angle of approximately 20 to 40 degrees to the vertical and passing within the bounds of the articles as they move past said head, and means for rotating the articles during at least aportion of the translational movement in the coating zone.

2. In apparatus for electrostatically coating a series of similar three-dimensional open-work articles in each of which one of the three mutually perpendicular over-all dimensions is materially less than either of the other two, means for moving the articles over a predetermined path, said means including supports for holding the articles with the sides defined by the two greatest dimensions in generally horizontal positions, an electrostatic atomizing head, means for supplying liquid coating material to said head, means including a high voltage source for es tablishing an electrostatic field of sufficient strength between the liquid coating material on said head and the articles for electrostatically atomizing the coating material from said head and electrostatically depositing the coating material on the articles, and means for supporting said head spaced from the path of article movement below and to one side thereof and with the axis of said head being at an angle of approximately 30 degrees to the vertical and passing within the bounds of the articles as they move past said head.

3. In apparatus for electrostatically coating a three-dimensional article in which one of the three mutually perpendicular over-all dimensions is materially less than either of the other two, means for supporting the article to maintain the larger sides defined by the two greatest dimensions in predetermined positions, means for rotating the supported article, an electrostatic atomizing head, means for supplying liquid coating material to said head, means including a high voltage source for establishing an electrostatic field of suflicient strength between the liquid coating material on said head and the article for electrostatically atomizing the coating material from said head and electrostatically depositing the coating material on the article, and means for supporting said head spaced from the article and to one side of one or said larger sides, said head being so arranged that there is an angle of approximately 20 to 40 degrees between the axis of said head and a line generally perpendicular to one of said larger sides.

4. In apparatus for electrostatically coating a three-dimensional article in which one of the three mutually perpendicular over-all dimensions is materially less than either of the other two, a support for the article to maintain the sides of the article defined by its two greatest dimensions generally perpendicular to the longitudinal axis of said article support, an electrostatic atomizing head, means for supplying liquid coating material to said head, means including a high voltage source for establishing an electrostatic field of sufficient strength between the liquid coating material on said head and the article for electrostatically atomizing the coating material from said head and electrostatically depositing the atomized coating material on the article, and means for supporting said head spaced from the article and its support and on the same side of said article as is said article support, said head being so arranged that there is an angle of approximately 20 to 40 degrees between the axis of said head and the longitudinal axis of said article support.

5. Apparatus for electrostatically coating a plurality of similar three-dimensional articles in each of which one of the three mutually perpendicular overall dimensions is materially less than either of the other two, comprising a conveyor for moving the articles over a predetermined path, said articles being oriented on said conveyor so that a side of each article defined by its two greatest dimensions moves generally in the same predetermined plane, means for creating a spray of charged coating material particles at a point spaced from said conveyor, said spray creating means being spaced close enough to the article path to envelop the articles with the spray as they move past said spray creating means and being arranged so that its axis lies in a plane generally transverse to the article path and is at an angle of approximately 20 to 40 degrees to a perpendicular to said predetermined plane, and means for establishing an electrostatic field between said spray creating means and the articles, said field being substantially the sole medium for depositing the spray onto the articles.

6. Apparatus for coating a plurality of automobile steering wheels or like articles, comprising a conveyor including suitable workholders for moving said wheels along a predetermined path with their faces arranged horizontally, an atomizing head spaced from said wheels for creating a spray of coating material particles, said head being arranged with its axis lying in a plane generally transverse to the conveyor path and at an angle of 20 to degrees to the vertical, a projection of said axis passing through the bounds of the wheels moving past said head, and means including a source of high electrical potential for establishing an electrostatic field between said head and the wheels of suflicient strength to charge the coating material particles, move them from said head and deposit them onto the wheels as a coating.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,239,695 Bennett Apr. 29, 1941 2,555,519 Tolle et al June 5, 1951 2,567,781 Ransburg Sept. 11, 1951 FOREIGN PATENTS Number Country Date 982,327 France Jan. 24, 1951