US2966310A - Electrostatic deposition spray means - Google Patents

Description

Dec. 27, 1960 J. SEDLACSIK ELECTROSTATIC DEPOSITION SPRAY MEANS Filed June 30, 1959 \w xww INVENTOR. Lib/7w JEDLAca/K j Z ,h

United States Patent ELECTROSTATIC DEPOSITION SPRAY MEANS John Sedlacsik, Garfield, N.J., assignor to Interplanetary Research & Development Corp., Garfield, N.J., a corporation of New Jersey Filed June 30, 1959, Ser. No. 823,953

5 Claims. (Cl. 239-15) This invention relates to improvements in an apparatus for applying coating material to an article by electrostatically charging and depositing the comminuted coating material upon the article within an electrostatic field created between the article and the issuing source of the coating material. This application is a continuation-inpart application of copending application Serial Number 481,532, filed January 13, 1955 for Electrostatic Deposition, and now abandoned.

Means is provided whereby the coating material may be efiiciently divided into minute particles by electrical force, without the assistance of moving air streams. or other means commonly employed for this purpose. As :the coating material is electrostatically charged and pro- 'jected from the apparatus, the electrical charge is directed toward and electrostatically deposited upon the article to be coated.

This invention contemplates a paint spray system and gun mechanism wherein the forward atomizing spray elements are isolated from the rear support control elements.

The structure is such as to permit the desired elimination of the possibility of a transmittal of an electrical charge in the forward area rearwardly to the rearward area of the mechanism.

The rear area of the mechanism is at ground potential for the convenience and safety of the operator. At the same time, the forward area thereof is adapted to receive a high electrical potential.

In prior art devices for applying coating materials to articles, the use of compressed air as a means for atomizing or reducing the material into comminuted particles and as a carrying medium in spraying the same upon the surface of the article being covered has long been known. Such guns have been limited to a comparatively small field of dispersion, however, and they have caused the coating material to be discharged in non-uniform sized particles, and in variable patterns, all to the end that uneven dispersion of the coating particles over the surface being coated frequently results. Also, the projected spray or jet is sometimes unstable in that the axis of the spray or jet shifts erratically from one position to another. Expressed otherwise, the cross-sectional shape of the spray or jet pattern has been observed to very during operation. Such instability results in an objectionable irregular scattering of the coating material upon the surface of the article being coated.

Additionally, the inherent electrical effect in prior art guns causes the particles more or less to repel each other so that lateral spreading results. This spreading phenomenon is especially noticeable at the outer portions of the spray or jet area where an uneven, irregular and indistinct edge definition to the pattern of the coating material being deposited upon the article is observed.

By surrounding the atomizing, projecting and depositing electrostatic field with an envelope of air, which is substantially coextensive longitudinally with the former, the projecting spray is stabilized and is made more definite in its shape and more constant in its direction.

2,966,310 Patented Dec. 27, 1960 The scattered spreading effect upon the particles, particiilarly at the outer portions of the jet, is materially reduced resulting in a deposited pattern which is more uniformly dense throughout and which has the desired sharp edge definition.

The mechanism of this invention provides a stabilizing area immediately adjacent the electrostatic spray atomizing field, whereby the jet produced is stabilized in respect to its direction and to its shape and the deposited pattern has a sharper edge definition throughout its entire periphery.

The atomizing element of the apparatus consists essentially of a small nozzle having an annular shaped distributing or atomizing tip from which the coating material is metered at a predetermined rate in the form of atomized particles.

A source of electrostatic high potential, having one terminal grounded and its opposite terminal connected to the atomizing head is capable of creating a strong electrostatic field between the head and the article to be coated, which article also is grounded. The force of the field transforms the coating material into a spray of charged particles and creates an attraction which pulls the spray to the grounded article, thereby accounting for the electrostatic deposition. That is, a potential difference of suflicient magnitude is maintained so as to create an electrostatic field with an atomizing corona discharge in the region adjacent the discharge end of the discharge electrode.

The coating material is normally supplied to the discharge end and its region of corona discharge at a rate at which it can be electrically atomized by the corona discharge most efiiciently and effectively, after which the charged particles are projected in spray form toward and deposited upon the oppositely charged article. Depending upon the viscosity and other characteristics of the material, the control of the supply is such as to permit the discharge of precisely the correct quantity and size of the particles so as to attain the greatest efiiciency in coating a surface.

Optimum results are obtained where the mass of the atomizing tip of the mechanism is as small as possible and where the mass of the article being coated is relatively larger. This relationship facilitates leakage of the atomized material from the high potential tip of the mechanism to the article. That is to say, the smaller the area at the high potential, the greater the rate of leakage of atomized material to the mass of the article being coated.

Furthermore, by isolating the atomizing head or gun tip from the support or control elements of the gun by an insulated member, the desideratum of maintaining the smallest portion or area of the gun at a high potential is attained. In order to separate or isolate the atomizing head from the remainder of the gun mechanism, I employ connections between the gun tip and the support or control elements of the gun which comprise non-conductors of electricity, they being of rubber, glass, ceramic, plastic, or similar non-conducting material. Thus, the high voltage nozzle or head end of the gun apparatus is separated from the grounded support or control end so that the support and control mechanisms, as Well as the operator, are safeguarded against dangerous backfiring from the nozzle or head end.

With the above and other other objects of this invention as will become more readily apparent as the description proceeds, this invention consists in certain features of novelty, and in the combination and arrangements of parts, as will be hereinafter more particularly pointed out in the claims hereunto annexed and more full described and referred to in conjunction with the accompanying drawings wherein: it

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

Fig. 2 is an enlarged sectional view of the line 2-2 of Fig. 1;

- Fig. 3 is an enlarged sectional view on the line 3-3 of Fig. 1',

Fig. 4 is an enlarged sectional elevational view of the atomizing tip of the gun as shown at the right in Fig. 1; and

'Fig. 5 is a schematic representation of an electrostatic spray system.

In the accompanying drawing, there is illustrated an example of a physical embodiment of the invention in which the components are combined and arranged in accordance with one mode which has been devised for the practical application of the principles of the invention.

Various changes and alterations are contemplated and may be made in these exemplifying drawings and mechanical structures, within the scope of the claims, without departing from the basic principles of the invention.

In the following description and claims, various details will be identified by specific names for convenience. These names however are intended to be as generic in their application as the art will permit.

Referring now to the drawing in detail, and referring more particularly to the preferred form of the invention selected for illustrative purposes, there is shown the head end of an apparatus which is suitable for coating articles (not shown) which are preferably moved along a path of article-movement through a coating zone which the device of the invention projects.

The gun mechanism contemplated by this invention, and not shownherein, is disposed at one side of the path of article-movement. By means of such mechanism, the atomizing head of this invention is held so that the liquid coating material passing therethrough may be electrostatically atomized.

A liquid coating material and a gaseous material, such as air, are passed through the gun mechanism.

The spray gun contemplated for use in this invention consists of a conventional main body portion whichis 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 U.S. Letters Patent #2,070,696, dated February 16, 1937.

The gun mechanism 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 atomizing spray guns using air for the atomizing medium.

The spray head comprises an inner fluid nozzle 40 formed with a forwardly disposed tip 42 having a central orifice 43 extending therethrough and through which the coating material is emitted.

The inner fluid nozzle 40 is threadedly receivable in a sleeve 44 which is connected in any suitable manner within the cap 46 which is attached to the nose piece element 112. Tubular element 108 for the paint communicates with the inner fluid nozzle 40, while the air from the tubular element 109 communicates with the air passage in the interior of the cap and the air opening 6d through the member 60 retained by the cap. The nose piece element 112 is in turn connected to the grounded support and operators control elements of the gun by connections of suitable electrically non-conductive material, for example, rubber, glass, ceramic, plastic or the like, whereby to insulate the high potential nozzle from gun support and control end as heretofore disclosed.

Forwardly of the member 40, an enlongated connecting member 60 is provided having a central longitudinally extending bore 62 extending therethrough throughout the length thereof.

'An annular bearing and sealing member 63 is receivable in an opening 64 in the inner end of themember- 60 against which the member is adapted to abut and through a central opening of which the member 42 extends, as shown.

The member 60 has an outwardly extending annular skirt portion 65 which is adapted to be engaged at-its outer peripheral edge by the union 46 so as to hold member 60 in extended coaxial relation to member 40 with the tip 42 of member 40 extending into the opening 62, affording direct communication therebetween.

A hollow outer housing 7% has a rearmost portion 72 which is threadedly engageable with the member '60, as shown, so as to be held relative thereto.

An air opening .66 extends longitudinally through the member 60 in a direction .more or less parallel to the orifice 62, as shown. A plurality of such openings may be provided, if desired, permitting air to move forwardly from the area 47 within the union 46 and the area 71 within the housing 70 and surrounding the outermost portion of the member 60.

The member 70 is provided with a tapered forward sleeve portion 74 providing a restricted throat or opening 76 with which the area 71 is in direct communication, the member 70 providing a motive agent conduit.

A stem member 80 having a longitudinally extending opening 82 extending inwardly from the :inner end thereof is receivable within the throat 76 of the sleeve portion 7.4.

The'inner end of the stem member 80 is threadedly engageable at 84 with the free end of the member 60 so that the opening 82 is in communication and in coaxial alignment with the opening 62, as shown, the members 60 and 80 providing a liquid coating conduit.

A boss 86 is provided on the outer side of the member 80 by means of which the member 80 is retained in position centrally of the sleeve 74.

At the outer end of the member 30 an annular cup shaped head or nozzle 90 is provided which may be integral-with the member'80 and may serve as a plug at the outer end of the passageway 82. Around the shoulder of the member 90, openings 92 afiording communication between the passageway 82 and the outside are provided. It is through these openings that the coating material passes. The head 9b is provided with a sharp edge to effect a corona discharge in connection with the electrostatic field. Therefore, when liquid is atomized, it will be electrically charged. This construtcion permits the liquid to be atomized without the use of any air whatsoever. However, air under pressure may be used and its pressure may be decreased anywhere from a high point to zero to vary the shape of the spray pattern.

The sleeve 46 and the other elements at the forward end of the gun are preferably made from electrical conducting material, the member 46 being connected to the underground terminal of a high voltage source (not shown) by means of a high voltage instrumentality 46'.

The coating material passes through the appropriate conducting means in the gun mechanism to the member 40 and out through the opening 43 thereof into the opening 62 of the member 60 and, thence into and through the opening 82 of the member 80 and out through the openings 92.

The atomizing air is adapted to be supplied through the gun mechanism to the area 47 around the member 44, then through openings 66 and into area 71 and through the space 76 around the member 80.

As the stream of liquid passes outwardly through the openings 92 and as the stream of air passes outwardly therearound, the same are subjected to the atomizing effect ofthe corona discharge from the rod electrode whereby the finely divided particles comprising the spray have each imparted thereto electrical charges of like polarity.

With voltage supplied directly to the spray head structure, a-eorona=discharge is formed in the region around the outermost openings and adjacent the outermost periphery thereof which is of an intensity sufiicient to break up or to atomize into particlcd form the coating material being discharged and to project said coating material in spray form toward the surface of the article being coated.

The electrical energy is maintained at the high potential nozzle or spray assembly. The material being atomized and the gas are delivered through the respective conduits within the gun mechanism to the nozzle or head assembly. This material, and the gas, issue from their respective orifices in the nozzle in the form of high velocity streams where they meet and mix with each other under pressure and are atomized and electrically charged passing out wardly into the field with high turbulence.

Fig. 5 is a schematic representation of a conveyor system indicating a multiplicity of articles 100 carried in a conventional manner on a conveyor track 101, so that the articles 100 may be sprayed by coating material 102 emitted from the representation gun 103 as the conveyor moves the articles past the spray-end of the gun and within effective spraying distance thereof for electrostatic wrap-around action of the particles of coating material onto the articles due to the atomizer or gun being at one polarity, such as plus, and the conveyor and articles being of a minus polarity in the well known electrostatic attraction of the particles by the article which is grounded.

A conventional power supply 104 for unidirectional voltage is coupled between the gun 103 and the ground shown by conventional symbol.

It will be noted that the conveyor and articles are both grounded, so that when the trigger rod 107 of the gun is actuated, the fluid coating material is emitted through opening 43 into the opening 62 of the member 60 and emitted from the free end of the nozzle.

Tubular elements 108 and 109 represent communicating passages for the paint and air respectively from the rear end 110 of the gun to the head end of the gun, Threads 111 are shown dotted in the rear end of the nozzle portion and are connected to complemental thread means on the element 112 through which the tubular elements 107 and 108 are connected. The rear end portion of the gun may be similar to either of the Patents Nos. 2,710,773 or 2,739,838 for operation of the system.

While several embodiments of the invention have been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

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

1. For use in an electrostatic spraying system of the class described for attachment to a spray gun control end for feeding fluent coating material and air to a spray nozzle, a fluent material spray nozzle for discharging an electrically charged stream of coating material, said fluent coating spray nozzle comprising a housing portion coupled to the spray gun control end and terminating in an annular edge, a longitudinally extending stem means having a fluent coating material passageway formed therein disposed within said housing portion and spaced therefrom adjacent said housing portion annular edge to provide an annular air curtain passageway about said stem means, an atomizing head on the outer end of said stem means having an outer material receiving surface means communicating with said fluent coating material passageway formed in said stern means for receiving fluent coating material and forming a thin film of said fluent coating material thereon and an inner cavity forming an external surface substantially merging with said outer material receiving surface means to provide an annular material discharge edge for atomizing said thin film of coating material from said discharge edge in the form of a spray, and means carried by said spray nozzle to be electrically charged for electrostatically atomizing said thin film of coating material from said annular material discharge edge within the air curtain about said stem means.

2. Apparatus as set forth in claim 1, wherein said fluent material spray nozzle includes adjustment means for adjustably positioning said housing portion relative to said longitudinally extending stem means for altering the air current about the stem means for controlling the pattern of the spray.

3. Apparatus as set forth in claim 1, wherein said fluent material spray nozzle includes control means positionable for controlling said air curtain for controllably directing said air current against the surface of the fluent coating material on the outside of the atomizing head for influencing said expanding spray.

4. A spray attachment for use in an electrostatic coating system for connection to the material outlet end of a spray gun for use in spraying fluent coating material onto a surface having a definite contour spaced from the gun, comprising a nozzle assembly adapted to be fixed to said spray gun outlet end and provided with independent fluent coating material and air passageways for receiving said fluent coating material and air from said spray gun outlet end, said assembly having a stationary atomizing spray head with an outer material receiving surface means for receiving said fluent coating material and forming a thin film of said fluent coating material thereon and an inner cavity forming a surface substantially merging with said outer material receiving surface means to provide an annular material discharge edge for atomizing and projecting said thin film of coating material from said discharge edge in the form of a spray towards said surface for deposition thereon, said air passageway having an air discharge outlet terminating adjacent said head for discharging a stream of air toward said head for restricting dispersal laterally of mutually repelling particles of the charged spray of said material into a controllable pattern.

5. Apparatus as set forth in claim 4, wherein said nozzle assembly includes control means adjustably positionable for influencing the expanding pattern of the spray.

Pontius Aug. 17, 1937 Sedlacsik Sept. 9, 1958

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