US3017114A

US3017114A - Electrostatic paint spray

Info

Publication number: US3017114A
Application number: US757263A
Authority: US
Inventors: John T Marvin
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1958-08-26
Filing date: 1958-08-26
Publication date: 1962-01-16
Anticipated expiration: 1979-01-16

Description

Jan. 16, 1962 J. T. MARVIN ELECTROSTATIC PAINT SPRAY Filed Aug. 26, 1958 Hi HIHHHHHHIHHIHH Fig. 6

btates This invention relates to electrostatic coating operations and is particularly concerned with a method and apparatus for electrostatically dispersing coating material in a predetermined pattern.

It is an object of the invention to provide a stationary coating material dispersing unit which will disperse coating material such as paint in a predetermined pattern therearound.

In carrying out this object, it is a further object to provide a stationary container of a predetermined shape and having a substantially continuous lip therearound wherein all portions of the lip lie in the same horizontal plane whereby paint supplied to said container in quantities sufiicient to overflow the lip portion thereof is electrostatically dispersed simultaneously from all lip portions and is deposited upon articles spaced therefrom when opposite electrostatic charges are impressed on the container and the articles.

Another object of the invention is to provide a method for electrostatically dispersing coating material such as paint from a stationary container whereby a predetermined paint pattern may be established without moving parts.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a plan view of one type of electrostatic paint spray apparatus as used in connection with the present invention.

FIGURE 2 is a view in section on line 22 of FIG- URE 1 and showing an article being painted.

FIGURE 3 is a fragmentary view of one of the lip portions of the device shown in FIGURE 4.

FIGURE 4 is a view taken on line 44 of FIGURE 3.

FIGURE 5 is a plan view of another type of apparatus shown in connection with a conveyor which is diagram matically depicted.

FIGURE 6 is a plan view of still another type of apparatus.

FIGURE 7 is a view of the device shown in FIGURE 6 taken in the direction of the arrow marked 7 thereon.

Electrostatic coating apparatus as heretofore described generally comprises a moving element, such as a centrifugal distributor, for distributing the coating material in an expanding circular pattern. This distributor is charged electrostatically and the coating material, such as paint, when it is thrown from the distributor, is simultaneously charged, atomized and dispersed electrostatically. The charged particles thereof are attracted to the article to be painted which carries an opposite charge to the charge on the particles. One of such distributors is clearly described in copending application S.N. 687,107, now Patent No. 2,975,755 and assigned to the assignee of the present invention. The distributor used in connection with the present invention will likewise provide an expanding circular pattern of paint, as desired, but, due to the peculiar nature thereof, involves no moving parts. Further, by changing the shape of the distributor, it is possible to provide patterns of varying shape as desired.

Referring specifically to the drawings, FIGURE 2 shows a section of a distributor as shown in plan view in FIG- URE 1. This distributor is essentially a circular con- Jatent U T 3,017,114 Patented Jan. 16, 1962 tainer or cup 20 supported upon a dielectric base 22 and including a paint supply tube 24 extending preferably centrally therein. Around the edge of the container 20 is a lip 26 which is substantially horizontal in extent wherein all portions of the lip 26 lie in the same horizontal plane. The container 20 may be made from metal, or nonconducting material, and is connected to one side of an electrostatic power source 30, the other side of which is connected to a hanger 32 which supports and is electrically connected to an article 34 to be painted. Thus, the container 20 and the article 34 have impressed thereon opposite electrostatic charges.

In operation of the device, paint or other suitable coating material is supplied through the tube 24 to the container 20 as by pump or gravity feed and the tube 24 in this instance is preferably formed from a material having high dielectric strength such as polytetrafiuoroethylene (Teflon), polyethylene, polymonochlorotrifluoroethyl (Kel-F), etc. When the paint fills the container 20, it will overflow substantially simultaneously from all portions of the lip 26. The quantity of overflow may be controlled by controlling the quantity of incoming paint and is preferably maintained in a thin film to provide the most desirable dispersion of paint therefrom. As the paint overflows the lip, it is distributed, atomized and electrostatically charged. That is to say, the paint, as it overflows the lip 26, is electrostatically dispersed in a fine mist wherein each particle bears an electrostatic charge opposite to the charge carried by the article 34 so that the charged particles of paint are attracted to the surface of the article 34 which bears the opposite charge. Obviously, since the container 20 is circular, it provides an expanding circular pattern of paint whereby articles spaced or conveyed therearound will be coated.

A modification of this structure is shown in FIGURE 3 wherein a plurality of depressed lip portions 36 are provided around the periphery of the container 20. These lips take the form shown in section in FIGURE 4 and may be closely spaced around the cup to provide a plurality of separated jets of paint spray. Obviously, these jets, due to the normal pattern of the atomized paint, will join into a continuous expanding pattern at some distance from the distributor whereby the same results are ob tained in connection with the device shown in FIGURE 2. The present modification provides a substantially continuous discharge edge since the spacing of the several lips 36 is preferably about equal to the width of the lips. It is apparent, however, that fewer lips may be used if desired although, for most purposes, a rather complete atomization around the edge is most desirable. This modification simplifies flow control to a degree. I

Modifications of the present invention permit unique distribution of paint in that paint can be projected outwardly of the container in a plurality of separated fields if desired. For example, in connection with FIGURE 5, a square container 50 is shown wherein the corner portions 52 are preferably built up slightly higher than the straight side portions 54 thereof. In this connection, therefore, the paint is distributed or projected in four directions to provide four fields of spray, each oriented from the adjacent fields. This permits the use, for example, of a square conveyor as shown at 56 wherein the articles 58 to be painted pass around the four sides of the distributor or container 50 and are equally painted at each of the four sides. It is apparent too that, should it be desired to blank out the entry side of the conveyor as noted at 60, the side 62 may be higher than the other three sides whereby no spray is provided at this side only of the device.

In FIGURE 6, the triangular paint distributor 70 is shown wherein paint is distributed in three disconnected fields as noted by the dot-dash lines. Here again, the

3 corner portions 72 are preferably slightly higher than the main side portions as shown in FIGURE 7 which is a view taken in the direction of the arrow 7 in FIG- URE 6. Of course, it is understood that these higher corner portions are not necessarily required in order for the device to function although it is generally desirable to separate the distribution into uniform fields as shown.

From the foregoing, it is apparent that many modifications of the present invention may be made without departing from the spirit thereof. In other words, any shape distributor or container may be used such as a hexagonal container, a generally clover-leaf-shaped container, etc., whereby the density of paint distributed on articles that are being transported therearound on a conveyor may be fully controlled by the shape of the distributor and the shape of the conveyor used therewith which permits very flexible operation. Furthermore, a single device may be utilized which includes adjustable side walls whereby portions only of the device may be used as desired. For example, in the circular container, it is possible to have an adjustable side wall that will block out any desired portion of the lip whereby a semicircle of active lip only is used or a quarter of a circle is used. In this manner, considerable flexibility of the device may be realized while not adding appreciably to the cost thereof. Furthermore, the cost of the device, since no moving parts are involved, is extremely low and the function thereof is extremely economical and effic'ient.

I In practice, a circular container 12 inches in diameter and one and one-half inches deep at the lip portion has been used to coat articles with a solvent-containing paint maintained eighteen inches from the lip thereof. In this instance, an electrostatic power unit with an output of from 90,000 and 100,000 volts was utilized.

It is also apparent that suppressor electrodes may be used to more closely direct the path of the distributed paint. Such suppressor electrodes are clearly shown in copending application S.N. 726,450 assigned to the assignee of the present invention.

While the embodiments of the present invention as herein disclosed constitutepreferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a method for spraying a coating material in a plurality of separated patterns simultaneously from a common source, the steps of; supplying coating material to a stationary container, providing separated lips on said container extending upwardly and in different directions from a central point all having the same height and being of substantial extent wherein the longitudinal extent of all of the lips is in the same horizontal plane, overflowing simultaneously coating material from said container over all of said lips, and simultaneously impressing an electrostatic charge on the container lips whereby the coating material as it passes over the lips is dispersed, atomized and charged solely by electrostatic forces into separated spray patterns expanding outwardly around said central-point.

2. In a method for electrostatically distributing a liquid coating material in a plurality of fields oriented in diiierent vertical planes around the central point wherein the coating material for all operations is contained in a single container, the steps of; providing a stationary central container having separated upwardly extending contiguous lip portions disposed in the same horizontal plane and oriented from one another, supplying liquid coating material to the container, simultaneously overflowing the coatingmaterialfromthe container and over all of said lips while preventing fluid flow at the junctions between said lip portions and simultaneously charging the container with an electrostatic charge whereby particles of coating material are electrostatically atomized from said lips into separated fields of coating material sprays and around said container.

References Cited in the file of this patent UNITED STATES PATENTS 2,049,940 Barthel Aug. 4, 1936 2,808,343 Simmons Oct. 1, 1957 2,899,136 Reindl Aug. 11, 1959 V FOREIGN PATENTS 521,794 Belgium Aug. 14, 1953 1,004,084 Germany Mar. 7, 1957