US2960273A - Electrostatic spray painting apparatus - Google Patents

Description

Nov. 15, 1960 Filed June 24, 1958 F. A. CROSKEY ET AL ELECTROSTATIC SPRAY PAINTING APPARATUS 2 Sheets-Sheet l INVENTORS 55022 @(Imsgg, e

B Y 65.474225 Q ZZZ??? Nov. 15, 1960 F. A. CROSKEY ETAL 2,960,273

ELECTROSTATIC SPRAY PAINTING APPARATUS Filed June 24, 1958 2 Sheets-Sheet 2 if {HE ELECTROSTATIC SPRAY PAINTING APPARATUS Frank A. Croskey, New Baltimore, and Charles D. Tuttle,

Wyandotte, Mich, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed June 24, 1958, Ser. No. 744,189

4 Claims. (Cl. 239-15) This invention relates to electrostatic spray'painting apparatus, and more particularly to electrostatic spray painting apparatus wherein spray emitting means, as a spray gun, emits a spray of atomized particles along a path directed through an electrostatic field.

One feature of the invention is that it provides improved electrostatic spray painting apparatus; another feature of the invention is that it provides electrostatic spray painting apparatus including spray emitting means for directing a spray of atomized particles along a path and discharge electrode means and collector electrode means, both located on the same side of the path of atomized particles emitted by spray emitting means; yet a further feature of the invention is that the collector electrode comprises a conductive cylinder located in spaced relation to the discharge electrode means and to the spray emitting means on the same side of the path of spray as the discharge electrode means; still another feature of the invention is that it provides discharge electrode means located in spaced relation to the spray emitting means in the direction in which spray is emitted therefrom and on one side of the path of the spray and a collector electrode located in spaced relation to the discharge electrode means and to the spray emitting means generally opposite the spray emitting portion thereof and on the same side of the path of spray as the discharge electrode means.

It is well known in the prior art to use a spray painting apparatus in which a pneumatic spray gun emits a spray of atomized particles through an electrostatic field created between a discharge electrode having a plurality of pointed members and a broad flattened collector electrode. The discharge electrode and the collector electrode are located on opposite sides of the path of spray so that the atomized particles pass through the field in a direction generally transverse to the direction of extent of the lines of force therein.

When using such prior art apparatus, the high intensity field existing between the discharge electrode and the collector electrode creates an electric wind which tends to force the atomized particles back toward the spray gun with the result that higher pneumatic pressures are required than would otherwise be necessary to atomize the paint and blow it through the field. Additionally, the paint tends to collect on the broad flattened collector electrode. This is due in part to the relatively large surface expanse of the collector electrode and in part to the location of the collector electrode with reference to the discharge electrode and the gun. When a quantity of paint has been deposited on the collector electrode, it is necessary to clean the apparatus in order to prevent the formation of paint stringers extending from the collector electrode toward the discharge electrode. Such stringers would shorten the air gap of the field and increase the field intensity with the resultant danger of arcing. In the use of electrostatic apparatus of this general type, it has been determined that a field intensity of the order of 13 kv. per inch provides the States Patent ice greatest efliciency; for example, when utilizing a voltage of the order of 40 kv., it is preferable to space the discharge electrode and the collector electrode a distance of about three inches from each other. The build-up of paint stringers on the collector electrode efiectively changes this spacing and may result in danger of arcing.

The invention disclosed and claimed herein provides improvements over such prior art apparatus by locating both the discharge electrode and the collector electrode on the same side of the path of spray emitted from the spray gun. This modifies the efiect of the electric wind created by the field, whereby the area of greatest intensity of the electric wind is not directed against the atomized particles but is out of the path of movement of the atomized particles. Furthermore, since the particles are not moved transversely through the field, i.e., are not moved between the two electrodes-the collector electrode does not accumulate an excessive amount of paint so that it is not necessary to clean the apparatus frequently, nor is there the likelihood that enough paint will build up on the collector electrode to form paint stringers feeding out into the field.

These and other features of the invention will be apparent from the following description and from the drawings, in which:

Fig. 1 is a plan view of an electrostatic spray painting installation including the new apparatus;

Fig. 2 is an enlarged view of a portion of the apparatus of Fig. 1;

Fig. 3 is a side elevation taken along the line 3-3 of Fig. 2;

Fig. 4 is a detail section taken along the line 44 of Fig. 3 and showing the discharge electrode arrangement; and

Fig. 5 is a detail section through the discharge electrode taken along the line 5-5 of Fig. 3.

Referring now more particularly to the drawings, a conventional conveyor 10 mounts a plurality of hangers 12 which carry a succession of workpieces 14 which, for example, may be automobile window garnish moldings. These workpieces are moved in succession past the electrostatic spray apparatus described below. A mounting stand 16 carries a yoke 18, the height of which may be adjusted by a clamping device controlled by a hand wheel 20. From the yoke 18 a mounting rod 22 projects angularly upwardly, and at its top end is secured to a metallic housing bracket 24. A clamping device controlled by turn handle 26 is provided for adjustment of the angular relationship between the mounting rod 2 2 and the housing bracket 24. A conventional pneumatic spray gun 28 is mounted on the housing bracket 24 and terminates at its forward end in a conventional atomizing spray nozzle 30 which is directed toward the workpieces which pass on the conveyor. The gun 28 is connected by a tube 32 to a source of paint and is connected by a tube 34 to a source of compressed air so that during operation paint is atomized and emitted from the spray gun 28 as shown at 36 along a path directed toward a workpiece 14 on the conveyor. The atomized paint is dispersed in an expanding fan-shaped pattern.

At one end the housing bracket 24 is formed with an integral generally cylindrical support sleeve 24a having a longitudinal bore in which is mounted an insulating tube 40 which may be of nylon. This tube extends forwardly a distance about four inches beyond the end of the housing sleeve 24a and at its free end it carries a discharge electrode assembly. The assembly comprises a plurality of elongated pointed needle-like conductor members 42 which may be No. 1/0 steel darning needle. In the illustrated embodiment of the invention there are seven of these needles arranged in a fan-shaped array and all connected, as by soldering to a base member 44 which may be formed of brass wire. The bulk of the body portion of the pointed discharge electrode members and the entire base 44 upon which they are mounted are molded as a unit into an insulating casing 45 which may be formed of epoxy resin and the pointed end of each electrode member projects out of the casing.

As shown in Fig. 5, the base member 44 is attached to a connector 46 which extends into the bore of the nylon tube 40 and in turn is connected to a lead wire 48 which at its other end is connected to a source of high voltage in a power supply 50. Although the power supply 50 is not shown in detail, it is of conventional construction, including a high voltage developing means and a low voltage return arrangement, and preferably, is arranged to deliver a voltage output of the order of 40 kv.

On the same side of the gun 28 as the discharge electrode means there are formed upper and lower bosses 24b and 24c which respectively mount metallic holding rods 52 and 54 upon which is clipped a conductive collector electrode comprising an elongated metallic cylinder 56. In a preferred construction of the invention, the collector electrode 56 comprises a brass tube having an overall length of about seven inches, an inner diameter of 3 inch, and an outer diameter of 1 inches. The tube is formed with spaced key slots for the reception of buttons formed on the ends of the rods 52 and 54 so that the tube is removably mounted on these rods.

It may be seen from an examination of Figs. 2 and 3 that the discharge electrode means, which are electrically insulated from the spray gun by the tube 40, are located in spaced relation thereto in the general direction in which spray is emitted and on one side of the path of the spray. Furthermore, the pointed needle-like members 42 are arranged in a fan-shaped array lying in a plane perpendicular to the plane of the fan-shaped spray pattern emitted by the spray gun. The needle-like discharge electrode members are arranged perpendicular to the direction of movement of the spray particles and point toward the plane of the fan-shaped spray pattern. The collector electrode 56 is located in spaced relation to the discharge electrode means and to the spray gun. Preferably the distance between the discharge electrodes and the collector electrode is about three inches, and preferably a voltage of the order of 40 kv. is used so that the field intensity be tween the discharge electrode and the collector electrode is of the order of 13 kv. per inch. The collector electrode is also spaced from the nozzle or paint emitting end portion 30 of the spray gun and is generally opposite the nozzle on the same side of the path of spray as the discharge electrodes. The axis of the cylindrical collector electrode is transverse to the axis of the spray gun 28 and is generally transverse to the axis of the center one of the pointed discharge electrode members as shown best in Fig. 3. Furthermore, the axis of the collector electrode preferably is parallel to the plane of the fan-shaped spray pattern. The collector electrode is electrically connected to the spray gun through the rods 52, 54 and the support bracket 24, and these elements are connected to the ground return portion of the power supply through a wire 60. If desired, the spray gun 28 and the collector electrode 56 may be grounded or these elements may be a relatively few volts (as 80 or 90 volts) above ground if the ground return circuit includes a low voltage developing means.

In operation, paint is atomized and sprayed from the nozzle 30 of the spray gun 28 under a relatively low pressure of a few pounds per inch to form an expanding fan-shaped spray directed in a path toward workpiece 14 as it passes on the conveyor 10. A high voltage electrostatic field is developed between the discharge electrodes 42 and the collector electrode 56. This field is defined by a plurality of lines of force of elliptical shape extending between the two electrodes so that the path of paint spray is through the field, whereby the paint particles are charged as they pass through the field and are attracted to workpieces on the conveyor, which workpieces preferably are grounded. Normally the discharge electrodes are maintained at a negative potential. Since the discharge electrode and the collector electrode are both located on the same side of the spray gun, the greatest intensity of electric wind created by the electrostatic field between these electrodes is not in opposition to the moving atomized particles, and in fact the path of movement of these particles does not bring them into contact with the electric wind of greatest intensity. In fact, the electric wind which exists in that part of the field intersecting the path of movement of the particles, when combined with the direction of particle movement in said path, results in a force vector which will carry the particles awayfrom the electrodes. Furthermore, by virtue of the cylindrical shape of the collector electrode and by virtue of its location generally opposite the nozzle 30 from which the atomized particles are emitted, the collector electrode does not receive any substantial amount of paint. Con sequently, it is not necessary to shut down the apparatus frequently for cleaning, nor is the arrangement conducive to the collection of enough paint on the collector electrode to develop paint stringers extending from the collector electrode towards the discharge electrodes to change the field strength and increase the possibility of arcing. The intense field between the two electrodes insures charging paint particles moving in a path through this field to provide an effic-ient electrostatic painting arrangement.

While we have shown and described one embodiment of our invention, 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 set forth in the appended claims.

What is claimed is:

1. An electrostatic spray painting apparatus, comprising, in combination, a support, spray emitting means mounted on said support for emitting a spray in a path, discharge electrode means mounted on said support and electrically insulated from said spray emitting means, said discharge electrode means being located in spaced relation to said spray emitting means in the direction in which the spray is emitted therefrom and on one side of and adjacent to the path of the spray, a collector electrode mounted on said support in spaced relation to said discharge electrode means and adjacent to said spray emitting means, said collector electrode being located on the same side of and adjacent to the path of the spray as the discharge electrode means, and means providing a high voltage field between said discharge electrode means and said collector electrode. 2. An electrostatic spray painting apparatus, comprismg, in combination, a support, spray emitting means mounted on said support for emitting a spray in a path, discharge electrode means mounted on said support and electrically insulated from said spray emitting means, said discharge electrode means being located in spaced relation to said spray emitting means in the direction in which the spray is emitted therefrom and on one side of and adjacent to the path of the spray, a collector electrode mounted on said support in spaced relation to said discharge electrode means and adjacent to said spray emitting means, said collector electrode being located on the same side of and adjacent to the path of the spray as the discharge electrode means, means providing a source of high voltage and a low voltage return, means connecting said discharge electrode means to said source of high voltage, and means connecting said collector electrode to said low voltage return.

3. An electrostatic spray painting apparatus claimed in claim 1, wherein the collector electrode comprises an elongated metallic cylinder, the longitudinal axis of which is transverse to the path of the spray.

4. An electrostatic spray painting apparatus claimed in claim 1, wherein the discharge electrode means comprises a plurality of pointed members arranged in an array pointing perpendicular to and toward the path of the spray, and wherein the collector electrode comprises an elongated metallic cylinder, the longitudinal axis of which is transverse to the path of the spray and to the axis of the center one of the pointed members of the discharge electrode means.

References Cited in the file of this patent UNITED STATES PATENTS Ransburg Dec. 21, 1954 Tuttle et a1. Nov. 8, 1955 Juvinall July 10, 1956 Larsen et a1. Oct. 16, 1956 FOREIGN PATENTS Great Britain May 29, 1957

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