US3472204A

US3472204A - Electrostatic coating apparatus

Info

Publication number: US3472204A
Application number: US761357*A
Authority: US
Inventors: Norbert M Zupan; Norman S Curtis
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1968-06-14
Filing date: 1968-06-14
Publication date: 1969-10-14
Anticipated expiration: 1986-10-14

Description

Oct. 14, 1969 U A ET AL 3,472,204

ELECTROSTATIC COATING APPARATUS Filed June 14, 1968 Fig.2

/g) l J/ mvsmon NORMAN s. CURTIS Q NORBERT M. ZUPAN United States Patent 3,472,204 ELECTROSTATIC COATING APPARATUS Norbert M. Zupan, Brownsburg, and Norman S. Curtis,

Indianapolis, Ind., assignors to Ransburg Electro-Coating Corp., Indianapolis, Ind., a corporation of Indiana Continuation-impart of application Ser. No. 470,152,

July 7, 1965. This application June 14, 1968, Ser.

Int. Cl. B05!) 5/08, 13/04 U.S. Cl. 118-631 6 Claims ABSTRACT OF THE DISCLOSURE The apparatus of this invention is directed toward coating channeled articles and other articles having depressions, recesses or other irregularities and comprises a spray gun for projecting a spray of coating material particles along a predetermined axis, conveyor for moving one or more channeled articles through the spray and a supporting structure for the spray gun. The spray gun may be mounted at an acute angle with respect to the conveyor. The spray gun supporting structure includes means to intercept the channel of the article and to align it with the spray axis. It also includes means which is movable from an equilibrium position and biased to return to that position and is adapted to keep the article out of contact with stationary objects as it moves through the spray. The gun support structure may include means to permit pivotal movement so that movement of the spray gun and the intercepting means is transverse to the conveyor movement. The spray gun may be a hydrostatic-electrostatic gun of the type shown and described in U.S. Letters Patent 3,169,883.

This is a continuation-in-part of application Ser. No. 470,152, filed July 7, 1965, now abandoned.

This invention relates to an apparatus for electrostatically coating articles, particularly channeled or grooved articles.

Electrostatically spray coating articles of manufacture is a well known and widely practiced art in which charged coating material particles are deposited on an oppositely charged article. However, electrostatically coating some articles presents difiiculties because of the particular shape or configuration of the article. For example, articles of manufacture having deep grooves or deeply channeled sections, such as ceiling joists and deeply corrugated metal roof decking, are more dilficult to coat electrostatically than those which are flat or have only shallow indentations. Unless the charged coating material particles are given a strong mechanical push in the direction of the channel, such as may ocur when the coating material is atomized by hydraulic pressure, compressed air or other mechanical means, the electrostatic attraction between the charged particles and the top portion of the side walls of a deep channel will result in satisfactory deposition of coating material on the top portion, but little or no deposition of coating material near the bottom of the channel.

Electrostatic coating methods in which atomization is effected by interaction with air, such as by compressed air or hydraulic pressure, impart a substantial directional mechanical momentum to the charged coating material particles so that if properly directed they may be deposited uniformly in the depths of a channel, thus in part at least overcoming the electrostatic attraction to the upper sides of the channel. Because of the directional nature of the projected spray, however, alignment between the axis of the spray pattern and the axis of the channel is critical if satisfactory deposition in the channel is to be achieved. Misalignment of these axes will result in non-uniform g CC deposition in the channel. Long narrow articles are likely to move about considerably while being carried along on a conveyor into and through a coating zone. Although guide rails along the conveyor may somewhat confine article movement, especially movement from side to side, they cannot prevent such movement and at the same time permit longitudinal movement along the conveyor. If the channeled articles are to be coated rapidly, the guide rails must be so spaced that the articles are free to move. Where the spraying device is hand held by an operator, the operator can generally direct the spray accurately toward the article and into any channels or depressions therein, even though the article may move somewhat erratically. Where the spraying device is to be operated automatically, however, the possibility of such erratic movement of the article requires the provision of means to assure that the spray is properly directed toward the article and toward any channel therein.

One embodiment of this invention includes an electrostatic spray gun in which coating material is supplied at a very high pressure to a small elongated orifice to be projected therefrom into a thin fan-shaped film at very high velocity to be atomized by interaction with air and in which the atomized coating material is charged by a slim elongated electrode adjacent said orifice. The electrostatic spray gun is mounted on a. movable support With the spray axis oriented at an acute angle to the conveyor which carries the articles. The movable support is arranged to have an equilibrium position that will position the channeled articles intermediate guide rails of a conveyor. Upon being struck by the misaligned channel of an article, the support will transiently move laterally to intercept the channel of the article. The support will return to its equilibrium position with the article. By means connected to the support, the channel of the article and the axis of the projected spray are aligned, and alignment is maintained while the conveyor moves the channeled article through the projected spray. The alignment means is, of course, adjustable so that it may accommodate difierent sizes and various types of channeled articles.

Various features and advantages will be apparent from the description and drawings in which:

FIG. 1 is a side elevational view of one form of apparatus embodying this invention; and FIG. 2 is an end elevational view of the apparatus shown in FIG. 1.

Referring now to FIG. 1, a support 10 pivotally mounted at 11 is positioned opposite a conveyor 12 which includes a series of power-driven rollers 13. A hydraulicelectrostatic spray gun 14, which may be of a type described in U. S. Patent 3,169,883, is adjustably supported from support 10 by mounting bracket 15. Coating material is supplied to spray gun 14 by means of hydraulic pump 16 at appropriate pressures. The coating material is emitted through a small elongated orifice 17 (shown in FIG. 2), formed into an expanding fan-like spray which is directed generally along the axis of the spray gun. High voltage is brought to the spray gun from high voltage source 18 through high voltage cable 20 which passes through the insulating body of the gun to a slender elongated electrode 19 positioned closely adjacent but spaced from orifice 17 so as to charge the spray particles. Typically, such an electrostatic spray gun incorporates a resistor of several hundred megohms between the electrode and the high voltage source, and the high voltage source has an output voltage of about 60 kilovolts.

Mounting bracket 15 orients spray gun 14 so that the axis of direction of emission of the charged spray particles lies at an acute angle with respect to the plane of the conveyor. Two bars 21 are mounted on support 10 and carry centrally between them a fork-like member 22 having legs 22a and 22b. Fork-like member 22 is aligned with the axis of the spray gun and is rotatable about a shaft 23 which extends between bars 21. A series of points 22c are provided about which the fork-like member may rotate to accommodate different articles. A guiding roller 24 is journaled on a shaft 25 between legs 22a and 22b. Guiding roller 24 has a tapered periphery 29 which will fit in the channel of the articles and by bearing on the sides of the channel will align the channel and the axis of the spray emitted from the spray gun 14. At the rear end of member 22, biasing means, such as spring 26, supported from support 10, provides sufficient pressure to cause the periphery 29 of guiding roller 24 to maintain contact with the channel of the article 27.

Elements

10, 15, 21, 22, 23, 24, and 25 make up the supporting structure of the spray gun. Various sizes and shapes of rollers can be used, depending on the particular article being coated.

Pivot mounting 11 is centered above the conveyor 12 and between guide rails 28. The spray gun 14 and its supporting structure including the article guiding roller 24,

hang in an equilibrium position that is centered between L the guide rails and is free to swing transversely of the direction of article movement.

In operation a channeled article, such as a hat-section ceiling joist 27, is moved horizontally along conveyor 12 from left to right as shown in FIG. 1. Guide rails 28 guide the article 27 so that the channel may be engaged by guiding roller 24. If the channel of the article is not aligned With the guiding roller 24, pivot mounting 11 will permit the support to swing, transiently moving the guiding roller 24 and the spray gun laterally to intercept the article. The pendulum action of the spray gun and its supporting structure bias it to return to its equilibrium position and to move the article to a position out of contact with the stationary guide rails of the conveyor, permitting articles to be rapidly conveyed through the coating zone. By means of spring 2 6, sufficient pressure is exerted on fork 22 to maintain guiding roller 24 in contact with the channel 27a in article 27. As the article is moved along the conveyor and through the coating zone at the intersection of the atomized spray and the conveyor, alignment is automatically maintained between the axis of the channel 27a in article 27 and the axis of the direction of the spray emitted from the spray gun 14. Where a plurality of such articles are to be coated, they may be conveyed end to end through the coating zone so that the guiding roller will bridge the interface between the ends. Typical coating material such as red oxide primer thinned to 20 seconds, Zahn 2 with xylol is supplied at 920 pounds per square inch fluid pressure to an orifice having an area equivalent that of a circle .015 of an inch in diameter and forming an expanding fan-like spray having an included angle of The orifice is positioned approximately three inches from the top surface of the hat-shaped section and the spray was projected downwardly at an angle of with respect to horizontal. Approximately 12 to 15 inches exist between the point of guidance and the coating zone. This hat-shaped section had a channel 2%. inches wide and 1% inches deep. With the hat-shaped section carried through the coating zone at the rate of 125 feet per minute a uniform coating of /2 mil of primer was achieved on the entire surface of the channel even though the center line of the channel wobbled about 1 /2 inches.

Channeled articles of varying heights may also be coated by mounting the support 10 on a reciprocator whose vertical position is controlled by the height of the channeled article being presented to the coating zone.

Although the invention is described and shown with a source of spray in which atomization is effected by using very high fluid supply pressures and a small orifice, it is apparent that the invention is equally advantageous with a source of spray in which atomization is efiected by using compressed air.

We claim:

1. Apparatus for coating channeled articles comprising, a spray gun to project a spray of coating material particles along an axis, a conveyor to move channeled articles through said spray, and a supporting structure for said spray gun including means to intercept the channel of the article and to align it with the axis of the spray, said supporting structure being movable from an equilibrium position and biased to return to that position and to keep the article out of contact with stationary objects as it moves through the spray.

2. Apparatus for electrostatically coating an article with a channel, comprising a pivotable support, an electrostatic spray gun mounted on the support and having an elongated orifice and a charging electrode adjacent to said orifice, means for supplying coating material to said orifice at very high pressures, means for charging said electrode, a conveyor to move the article past said spray gun, a guiding roller mounted on the support aligned with the axis of the spray gun, and shaped to engage the channel of the article to maintain the alignment between the channel and the axis of the spray gun as the article moves past the spray gun, said pivotable support permitting movement of the spray gun and guiding roller transverse to the conveyor movement.

3. Apparatus as set forth in claim 2 wherein said atomizer is mounted at an acute angle with respect to the conveyor.

4. Apparatus for electrostatically coating a channeled article, comprising a pivot, a support movably carried by said pivot, an electrostatic spray gun for mechanically atomizing coating material mounted to said support, a pair of bars mounted to said support, a fork-like member rotatable about a shaft extending between said bars, a guiding roller journaled between the legs of said forklike member and having a periphery shaped to engage the channel of said article, and bias means acting on said fork-like member to maintain the engagement of the guiding roller with the channel of the article.

5. Apparatus as set forth in claim 4 wherein a conveyor supports the article and moves it horizontally past the spray gun, the pivot permits the support to swing transversely to the direction of article movement and the fork-like member includes a series of points about which it is rotatable to permit accommodation of dilferent articles.

6. Apparatus for electrostatically coating a channeled article comprising, an atomizer to atomize and mechanically impart a momentum to a spray of coating material, an electrode to charge the spray and create an electrostatic depositing field, a conveyor to move the channeled articles through the charged spray, and means aligned with the axis of the spray to maintain the alignment of the axis of the channel with the axis of the spray during deposition of the spray.

References Cited UNITED STATES PATENTS 1,419,686 6/ 1922 Nicholson 118-307 1,960,725 5/1934 Bramsen et al. 118-307 2,015,768 10/1935 Thomson 118-208 2,782,757 2/1957 Carnes 118-305 XR 2,904,894 9/ 1959 Hurst 118-8 XR 3,162,886 12/1964 Wise 118-307 XR 3,253,782 5/1966 Fischer et al. 117-934 XR 3,342,158 9/1967 Bennet et al. 118-7 PETER FELDMAN, Primary Examiner U.S. Cl. X.R. 117-93.4, 96; 118-307