US3049092A - Apparatus for the electrostatic coating of articles - Google Patents

Description

Aug. 14, 1962 J. SEDLACSIK ETAL APPARATUS FOR THE ELECTROSTATIC COATING OF ARTICLES 2 Sheets-Sheet 1 Filed July 24, 1959 1 INVENTOR. J'OHU JvLAcJ/K bfYof/A/ JEOLAC6/K J.

g- 1962 J. SEDLACSIK ETAL 3,049,092

APPARATUS FOR THE ELECTROSTATIC COATING OF ARTICLES Filed July 24, 1959 2 Sheets-Sheet 2 LIQUID COATING MATERIAL 2o4 mil-1 2 224 \LIQUID COATING MATERIAL 212 2|4 2l6\ 2l5 Pg 6 INVENTOR w 208 HV 4mm SEDLACSIK d I, JOHN SEDLAGSIK JR.

Qmmmm ilnited States Patent @fice 3,049,992 Patented Aug. 14, 1962 3,049,092 APPARATUS FOR THE ELECTROSTATIC COATING (PF ARTICLES John Sedlacsilr and John Sedlacsik, Jr., Garfield, N.J., assignors to interplanetary Research & Development Corp, Garfield, N.J., a corporation of New Jersey Filed July 24, 1959, Ser. No. 829,373 5 Claims. (Cl. 118-629) Our invention relates to electrostatic coating and more particularly to coating apparatus and coating methods to be used in electrostatic coating systems. This application is a continuation-in-part application of copending application Serial Number 533,691, filed September 12, 1955, now abandoned, for Apparatus for the Electrostatic Coating of Articles.

Generally speaking, in electrostatic coating systems of the present known types, a field of electrostatic force is created which includes the article being coated and the atomized coating material particles in movement toward such article. In normal commercial practice, it is desirable to mount the article on a grounded conveyor and thus to make the article itself (if it is of conducting material) or an electrode adjacent the same, an electrode at ground potential. Another electrode at high electrical potential is provided, with this electrode normally being the spraying device. Sometimes a separate electrode near or past which the spray passes in its movement toward the article is employed.

The present invention contemplates the formation of a paint or similar spray from a liquid material capable of relatively rapid atomization by expelling same from the device to which the material is introduced in the liquid form. This is preferably done through the use of coating material and air in a spray gun, in conjunction with an electrostatic attraction of the atomized particles produced therewith toward an oppositely charged article or target, as Well as by the repulsion between the charged surface portions of the liquid and other adjacent parts of the mass.

That is to say, the invention relates to improvements in an apparatus for applying a liquid coating to an article by electrostatically charging and depositing the comminuted coated material upon the article within an electrostatic field created between the article to be coated and the issuing source of the coating material. The coating material is issued from a spray gun or similar suitable atomizing device preferably utilizing air under pressure as a vehicle to convey the finely divided or atomized particles onto the surface of the article to be coated.

In the use of spray guns or the like of the known prior art types, many disadvantages develop in that the gun is usually limited to a comparatively small field of dispersion. It carries the coating material to be discharged in non-uniform sized particles and in variable patterns. Thus, there is an uneven dispersion of the coating particles over the surface to be coated due to the inertia generated in the discharge, causing the larger particles to travel further in the field than the more finely divided particles. Sometimes a variable pattern of spray is created and re produced on the surface to be coated, the heavier coating particles being caused to impinge over one area and the more finely divided particles over another area. By reason of such variance, it has been found necessary in prac tice under certain conditions of coating to arrange a sizeable battery of spray guns with particular regard to their variable patterns of coating application so that the several guns complement each other to even out the pattern as a battery.

One object of the invention is to provide means for controlling the deposit of the sprayed material on the surface to be coated, thereby reducing and minimizing the waste material due to loss by dispersion into the atmosphere, and

eflfecting substantial savings in labor and equipment while simultaneously increasing the coverage of the coating material issuing from the spray device.

In prior art spraying devices utilizing air pressure to atomize the coating material, the spray mixture issuing from the spray nozzle spreads outwardly or expands uniformly taking the form of a generally conical mist-like stream. The sides of this stream travel outwardly in diverging paths in the general direction of the surface to be coated. Upon impact therewith, considerable of the coating material, entrained with the air, is deflected in a swirling action away from this surface and is dispersed into the atmosphere. A great deal of the coating material discharged from the nozzle is thereby lost and, therefore, more material than actually needed is usually used to produce the desired coating.

To avoid some of this waste of material and also to eliminate attendant fire hazards, where inflammable coating materials are used, it has been the practice in some industries to provide special spray booths or chambers in which to conduct the spray operations. These booths are often equipped with high powered suction or blower systems to remove the waste material from the atmosphere. In some cases, special equipment is installed for salvaging the material thus conveyed away as well as reclaiming wasted material deposited on the walls of the spray booths.

This invention has, for its primary purpose, the provision of an improved spray coating device which is capable of reducing this loss and waste of coating materials, increasing the amount of effective coverage which may be obtained from a given quantity of coating material, reducing the fire hazards and generally improving the character of the coating produced by the spray device by offering uniform dispersion without objectionable ripples and concentrations.

Another object of the invention is to provide means for controlling the diverging column or stream of atomized coating material after issuance from the spray nozzle so that lateral deflection and dispersion of the mixture along the margin of impact of the stream with the coated surface is appreciably reduced and so that much of the material which would otherwise be dispersed into the atmosphere is now directed on the article surface.

Under the influence of the electrostatic charging, in combination with the air, a spray of uniform dispersion of particles can be attained. Further, the spray may be directed forwardly in a straight manner toward the article to be coated or it may be made irregular so as to have more or less conical contour by subjecting it during its expulsion from the liquid mass and before its complete atomization, to an intermittent or pulsating force acting in lines concomitant with its direction of travel.

The atomizing element of my apparatus consists essentially of a small head or nozzle having a sharply defined distributing or atomizing point or tip from which the coating material is directed at a predetermined rate in the form of atomized particles.

In this invention, a source of electrostatic high potential, having one terminal grounded and its opposite termi' nal connected to the atomizing head, creates a strong electrostatic field between the head and the article to be coated, which article is also grounded. The force of this field transmits the pre-atomized coating material as a fine spray of charged particles and creates an attraction which pulls the spray to the grounded article. The coating material is normally supplied to the discharge edge or lip and its region of corona discharge at a rate at which it can be pneumatically atomized most efliciently and effectively,

after which the charged particles are projected in spray form and deposited upon the oppositely charged article. Other objects of this invention will appear in the follow ing description and appended claims, reference being had to the accompanying drawings wherein:

FIG. 1 is a sectional elevational view of the device of the invention;

FIG. 2 is a sectional view on the line 22 of FIG. 1;

FIG. 3 is a partial sectional view of the plug member or cap of the invention;

FIG. 4 is a partial vertical view showing the nozzle employed for spraying articles carried on opposed sides of a conveyor;

FIG. 5 is a top view of the 360 nozzle of the invention used in the center of an arcuate conveyor; and

FIG. 6 is a further modification showing the nozzle having its axis disposed at right angles to the path of the conveyor.

Before explaining the present invention, in detail, it is to be understood that same is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments. It is also to be understood that the phraseology or terminology employed herein is for the purpose of description only and not of limitation. It is further to be understood that forms of spraying devices other than the particular ato-mizing device shown may be utilized and that other apparatus may be employed for accomplishing the purposes and practicing the methods of the invention without departing from the contemplated scope of the present invention. No limitations are to be implied from the specific description now provided.

In the practice of this invention, there is provided a discharge member or atomizing head, a spray gun mechanism with which said discharge member is associated, a source of liquid supply, a source of air supply, and distributing means for transferring the liquid and air from their respective sources of supply to the spray gun and thence to the discharge member for atomization and dispersion.

For purposes of simplification, all of these members are not shown, they being more or less conventional in paint spraying apparatus and not forming a part of this specific invention.

Referring to the drawing more in detail, and more particularly to the preferred form of my invention selected for illustrative purposes, I have shown an arrangement of apparatus which is suitable for coating articles which are preferably moved along a path of article movement through a coating zone in which the device of the invention, normally fixed in location, projects.

Disposed at one side of the path of article-movement is a horizontally positioned atomizing head, generally designated by the numeral 16, by means of which head the liquid coating material is atomized.

The liquid spray material is led from a source (not shown) to a spray gun (not shown) and thence to the nozzle or head end of the structure which incorporates the features of this specific invention. Likewise air is led from its source (not shown) to the spray gun and thence to the nozzle or head end of the structure.

The spray gun contemplated for use in this invention consists of a conventional main body portion which is disposed rearwardly of the apparatus of this invention. Same does not form a part of this invention and accordingly is not shown. It also includes a spray head similar to the type disclosed in US. Letters Patent #2,070,696, dated February 16, 1937.

At the head or nozzle end of the spray gun structure, a nose piece is provided and the liquid and gas conducting members may be connected thereto. Interior passageways within the nose piece (not shown) connect the respective tubes with appropriate means at the forward face of the nose piece whereby the liquid and air may pass therethrough to the forwardly disposed elements of the nozzle, about to be described.

The nose piece is of such configuration as to be adapted to receive, in threaded engagement therewith, the spray head of the above patent or of any other of the well known commercial types of atornizing spray guns using air for the atomizing medium.

The conventional spray gun includes an inner liquid or fluid transmitting member 20, formed with a forwardly and horizontally disposed tip having a central orifice therethrough which the coating material is emitted into the nozzle of this invention.

The member 20 abuts against the outer surface of a washer 2.2 and the tip extends into, if not through, a centrally disposed opening in the washer, which member is seated Within the nozzle as will presently be appreciated.

Forwardly of the member 20, an elongated connecting member 30 is provided having a central bore or orifice 32 extending therethrough throughout the longitudinal length thereof. The bore 32 communicates with the opening in the tip of the member 20.

Member 30 has an enlarged end portion 31 which is externally threaded for purposes shortly to be observed. The member 30 also has an outwardly extending annular skirt portion 34 which is adapted to be engaged along its outer peripheral edge by a union nut 36 so as to hold member 30 in extended coaxial relation with member 20 with the top thereof extending into the opening 32 and affording the direct communication therebetween as aforesaid.

One or more air openings 38 extend through the outer end portion 31 in a direction parallel to the plane of the bore 32, at a distance away therefrom, as shown.

A sleeve or barrel-like outer shell member 40 is provided having a central opening 42 extending therethrough.

The rearmost portion of the inside wall of the member 40 is threadedly engaged with the member 31, as shown, whereby member 40 may be held so as to surround and enclose member 30'.

An insert member 50 is insertable into the member 40 at the open forward end thereof, as shown.

A rearmost stem-like portion 52 of the member 50 has an enlarged outer end portion 53 which may be threadedly engaged at 54 with the forward free end of the member 30. A centrally-located longitudinally-disposed opening 56 is provided through the insert member 50, which opening is in communication with the opening 32 of the member 30.

A T-sha-ped annular plug member or cap 69 has a stem portion 62 which extends rearwardly into the outer end of the opening 56 so as to seal the same, the stem portion 62 being press-fitted into the opening. A shoulder on the stem 62 serves to prevent the plug from being positioned relative to the member 50 beyond a certain predetermined limit.

An annular ring of openings 64 lead obliquely from the opening 56 to the outer wall of the member 50 and terminate at their outer ends adjacent an annular shoulder 66 of the member 50.

An offset Wall portion 68 of the member 50 extends outwardly away from the shoulder 66 whereby the coating material passing through the bores 32 and 56 and the openings 64 passes outwardly between the wall portion 68 and the outer end portion of the member 40.

Air passes through openings 38 in member 31 and thence into the area 42 within the barrel 40. A plurality of openings 70 extend from the area 42 through the member 50. Air may thus be conducted forwardly from the chamber 42 to the head end of the device.

The air passes outwardly through the openings 70 into the area 72 at the head end of the structure beneath or to the rear of the plug member 60 which is spaced away from the forward edge portion of the member 50 so as to permit the escape of air around the peripheral edge thereof.

An 0 ring is seated in an annular groove around the body of the member 50 and functions to seal the connection between members 50 and 40 whereby the escape of air therepast is obviated.

The shell 40 and insert member 50 terminate at their outer ends in thin edges. The ratio of discharge area to the area of the article being coated is reduced to a minimum; the leakage of electrical charges from the forward end of the high potential nozzle electrode is increased, thereby more etficiently charging the liquid spray particles.

By judicious experimentation, We have determined that the size of the formed cone of coating material and thus the pattern may be variably controlled by increasing or decreasing the amount of air discharged through the apparatus. Compressed air issues from the air chamber 42 through the recess 72, and expands radially outwardly within the column of coating issuing from the narrow radially outward orifice at the forward end of the nozzle.

That is, where the amount of air employed is increased, the sheath of particles of coating material is caused to expand outwardly in more or less an umbrella-shaped pattern whereas when the amount of air employed is decreased, the sheath of particles of coating material is caused to be directed forwardly in more or less of a bullet-shaped pattern.

If desired the inner peripheral edge or skirt of the plug member 60 may be chamfered as shown at 61 in FIG. 3 so as to facilitate the passage of air therepast.

Also if desired plugs of varying diameters may be employed so as to aid in the dispersal of air therepast.

If desired, means may be provided whereby the air passing through the device may be pulsated so as to distinguish it from the normal situation where it passes through all openings evenly. By passing the air intermittently through the device, the air issuing therefrom has a pulsating action causing the air to deflect the liquid material first in one direction and then in another. This resultant effect is known as a pulsating eifect.

The nose piece and the other elements at the forward end of the gun are preferably made from electrical conducting material, the nose piece being connected to the ungrounded terminal of a high voltage source (not shown).

As the streams of liquid and gas pass outwardly through the member 10, the same are subjected to the charging effect of the corona discharge from the electrode whereby the finely divided particles comprising the spray have each imparted thereto electrical charges of like polarity. A halo effect is attained thereby.

With voltage applied directly to the spray head structure, as shown at 23, a corona discharge is formed in the region around the edge or lip of the cap 60 adjacent the outermost periphery which is of an intensity sufiicient to transmit the coating material being discharged from the nozzle and to project the coating material in spray form toward the surface of the article being coated,

In actual operation, the electrical energy is maintained at the high potential nozzle assembly. The material being atomized and the gas are delivered through the respective delivery tubes and connections to the head assembly. The material and gas are released in the form of high velocity streams where they meet and mix with each other under pressure, are atomized and electrically charged and pass outwardly with high turbulence.

FIGS. 4, 5 and 6 show the system employing a nozzle 10 of the invention connected to a spray gun 200 which is a representative form shown in United States Patent No. 2,710,773.

I FIG. 4, the nozzle 10 is connected to the gun 200 which is mounted on a reciprocator 202. The conveyor 204 is of conventional type used for carrying the articles 206 to be coated on opposite sides of the conveyor, which conveyor may be of any desired configuration.

The conveyor 204 shown, may be of the circular type as shown in FIG. 5 and wherein the cross-sectional portion 207 of the nozzle 10 is a view taken along lines 5A-5A of FIG. 4.

In FIGS. 4, 5 and 6, it will be noted that the spray nozzle 10 is connected to a high voltage source 208 and to ground shown by symbol, while the conveyor and the 6 articles are also shown connected to ground. The high voltage, which normally is of direct current type, may be any suitable voltage in a range from 40,000 to 300,000 volts D.C. and creates or establishes an electrostatic field between the nozzle, or the area of a nozzle, and the articles to be coated 206. While the spray gun is shown electrically charged by having a metallic outer shell connected to a voltage source, an electrode 210 which may be of the annular type, having needles 211 equally spaced thereabout, may be connected with the high voltage source as shown, if this is desired, so that the spray may be charged directly by contact with the charged nozzle as shown by connecting the nozzle 10 directly to the high voltage source, or by employing the annular discharge ring 210 which is connected to the high voltage source by conductor such as 212 and wherein the conductor such as 214 connected from the terminal 215 to the atomizer 10 may be disconnected, thus indirectly charging the paint by spraying same into the electrostatic field. The dash lines 216 show representative confines of a spray which may be obtained by adjusting the nozzle shell for creating a penetrating spray under the influence of the air pressure.

The confines of the spray pattern defined by the dotted lines 218 show another spray pattern which may be obtained by moving the shell of the nozzle outwardly in a direction away from the gun, so that the air pressure may throw the paint particles radially into a spray of 360' which may be substantially transversely or at right angles to the axis of the nozzle 10 as shown in FIG. 4 and defined by the dash lines 220. The upper and lower dash lines 220 show a general height of a spray pattern which increases by electrostatic particle repulsion as the spray gets further from the source of the nozzle though the spray emitted is substantially radially from the nozzle.

In FIG. 5, it will be seen that the nozzle is positioned like that shown in FIG. 4 between opposed sides of a conveyor, which conveyor may embrace a portion defining a circular configuration. The atomizer 10 of FIG. 4 would, therefore, spray all of the articles within the general area defined by the arcuate configuration of the conveyor. The nozzle may be of any suitable size and have dimensions anywhere from one-half inch in diameter to approximately ten or more inches in diameter depending upon the particular operation to be performed. Consequently, the nozzle set forth in the system is shown in FIG. 5 and an an nular spray pattern may be utilized under the influence of air pressure to project the particles in an annular pattern. The articles carried by the conveyor may be rotated not only about the axis of the nozzle but also on their respective axes in a conventional manner such as by a conventional roller 226 engaging a rub-board 223.

In normal operation, the nozzle may be adjusted to spray generally forwardly as shown in FIG. 6, or transversely as shown in FIG. 4. When the coating material is charged either directly as by paint being emitted from the metallic nozzle connected to the voltage source, or indirectly as by the annular discharge electrode or its equivalent, the coating material is electrostatically charged and deposited at least in part by electrostatic means in a wrap around action while the atomization from the nozzles is by pressure. While air pressure is referred to herein, it will be understood that the nozzle is such that hydraulic pressure may be used on the paint, or with the source of coating material, for spraying the material outwardly from the nozzle to be electrostatically charged for ultimate deposition upon the articles to be coated.

With this arrangement shown in FIG. 4, instead of spraying the liquid coating material transversely from the axis of the vertical nozzle, the nozzle may be angled so that the spray will be generally directed in a plane inclined to the general surfaces of the work pieces to be coated. In this way, instead of having a very narrow horizontal pattern, the effective spray, which is in a 360 spray from the nozzle, will have the upper portion coating the upper part of the work pieces and with the lower portion of the aoaaoez spray for coating the lower portion of the work pieces. Since the spray is projected completely around the nozzle or at 360 degrees, the effective height of the annular spray will depend, in large part, on the angle of the nozzle 10 in relation to the axes of the spray gun 200. With this arrangement, the nozzle may have a greater vertical height of coverage in a stationary condition, and will, in effect, cause the spray to be projected higher and lower than would normally be the case if the nozzle were mounted aligned as shown in FIG. 4. Accordingly, even when the nozzle is employed with a reciprocator, the angular displacement of the spray nozzle will permit a vertical coverage of the pain greater than the vertical range of the reciprocator movement since the spray paints on one side of the conveyor higher than the opposite side, which is sprayed lower on the articles on the opposite side of the conveyor.

With the arrangement shown in FIGS. 4, 5, and 6, inclusive, a nozzle may be made to spray 360 or annular spray pattern internally or within the confines of a loop type conveyor of any particular configuration.

The foregoing reveals the gist of our invention whereby others can, by applying current knowledge, readily adapt it for various applications without omitting features which, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An electrostatic spraying system employing a conveyor for carrying articles to be coated along a predetermined path having at least a portion thereof defining an arcuate configuration, a pressure operated atomizer having a peripheral discharge edge and disposed relative to said conveyor adjacent the arcuate configuration path for projecting a 360 spray pattern radially from said atomizer by pneumatic force, means for adjustably positioning the atomizer so that the plane of the atomizing edge may be set adjustably at different relative angles for establishing the vertical height of the spray pattern on the article carried along the arcuate configuration of the predetermined path, and means for establishing an electrostatic field between the atomizer and the articles to be coated to electrostatically charge particles of coating material to be sprayed from the pressure operated atomizer .1

onto said articles.

2. An electrostatic spraying system employing a conveyor for carrying articles to be coated along a predetermined path as set forth in claim 1, and wherein said path of the conveyor is normal to the axis of the peripheral discharge edge of the atomizer.

3. An electrostatic spraying system employing a conveyor for carrying articles to be coated along a predetermined path, a stationary atomizer disposed relative to said conveyor and having a peripheral discharge edge positioned for projecting a spray substantially radially of the axis of said discharge edge, said stationary atomizer having surfaces defining means for controlled movement of a curtain of liquid coating material axially of the stationary atomizer, surfaces carried by said atomizer defining a 360 baflie about the axis of said atomizer, and surfaces carried by said atomizer to provide control of a curtain of air under pressure within the confines of said curtain of liquid coating material and with said curtain of air directed to impinge said battle for directing said curtain of air substantially radially from said bathe to facilitate atomization of said curtain of liquid coating material to provide an enlarged controlled area of the atomized coating material spray pattern, and electrostatic means for altering the path of the particles radially projected by said air under pressure.

4. An electrostatic spraying system employing a con veyor for carrying articles to be coated along a predetermined path, a stationary atomizer disposed relative to said conveyor and having a peripheral discharge edge positioned for projecting a spray substantially radially of the axis of said discharge edge, said stationary atomizer having surfaces defining means for controlling movement of a curtain of liquid coating material axially of the stationary atomizer, surfaces carried by said atomizer defining a 360 baiiie about the axis of said atomizer, and surfaces carried by said atomizer to provide controi of a curtain of air under pressure within the confines of said curtain of liquid coating material and with said curtain of air directed to impinge said baffle for directing said curtain of air substantially radially from said bafiie to facilitate atomization of said curtain of liquid coating material to provide an enlarged controlled area of the atomized coating material spray pattern, electrostatic means for altering the path of the particles radially projected by said air under pressure, and means for altering the axial position of the pressure operated stationary nozzle to vary the vertical extent of the spray coverage as the articles to be coated move along said predetermined path.

5. As electrostatic spraying system employing a conveyor for carrying articles to be coated along a predetermined path, a stationary atomizer disposed relative to said conveyor and having a peripherai discharge edge portioned for projecting a spray substantially radially of the axis of said discharge edge, said stationary atomizer having an internal element and a cap being spaced from one another in part and having surfaces defining means for controlled movement of a curtain of liquid coating material axially of the stationary atomizer, said cap having surfaces defining a 360 bafiie about the axis of said atomizer, and an outer shell of said atomizer and said internal element being spaced from one another in part and each having surfaces to provide control of a curtain of air under pressure within the confines of said curtain of liquid coating material and with said curtain of air directed to impinge said bathe for directing said curtain of air substantialiy radially from said baffle to facilitate atomization of said curtain of liquid coating material to provide an enlarged controlled area of the atomized coating material spray pattern, and electrostatic means for altering the path of the particles radially projected by said air under pressure.

References Qited in the file of this patent UNITED STATES PATENTS 1,855,869 Pugh Apr. 26, 1932 2,090,150 Pontius Aug. 17, 1937 2,275,691 Simanton Mar. 10, 1942 2,442,986 Ransburg June 8, 1948 2,710,773 Sedlacsik a- June 14, 1955 2,884,204 Feis Apr. 28, 1959 2,894,691 Sedlacsik July 14, 1959 FOREIGN PATENTS 1,040,961 France May 27, 1953 1,094,132 France Dec. 1, 1954

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