US2782074A - Electrostatic spraying apparatus - Google Patents

Description

Feb. 19, 1957 J. SEDLACSIK ELECTROSTATIC SPRAYING APPARATUS Filed Nov. 15, 1954 IN V EN TOR.

United States Patent ELECTROSTATIC SPRAYING APPARATUS John Sedlacsik, Ga1-field, N. 3. Application November 15, 1954, Serial No. 468,670

2 Claims. (Cl. 299-140) My invention relates to improvements in apparatus for applying a liquid coating to an article by electrostatically charging and depositing the comminuted coating material upon the article within an electrostatic field created between the article to be coated and the issuing source of the coating material. That is, it relates to means for imparting an electrical charge to coatingmaterials, said electrical charge being such that when the material is atomized, precipitated, and dispersed, the spraying charge is smoothly deposited upon the object toward which the atomized material is directed.

The invention relates to the formation of a paint spray or similar spray from a liquid material capable of relatively rapid atomization by expelling same from the reservoir in which the'material is held in the liquid form. This is accomplished through the use of air, in conjunction with an electrostatic attraction toward the distant article or target.

As is well known, small particles when electrified by charges of like sign repel one another, whereas particles or masses of opposite sign are attracted.

This invention is directed to means for improving this dispersion and deposition of the atomized particles from a charged gun mechanism upon an oppositely charged article, such means providing greater stability to the projected spray or jet and imparting a sharper edge definition to the issuing pattern. b

The invention contemplates a paint spray gun mechanism wherein the forward atomizing and spray elements are isolated from the rearward support and control elements thereby preventing the possibility of a transmittal of an electrical charge from the forward area of the mechanism rearwardly to the rearward area thereof, the rearward portion of the mechanism being at ground potential and the forward portion thereof being connected to the high electrical potential.

The inherent electrical effect in prior art guns causes the particles to repel each other more or less whereby objectionable lateral spreading thereof 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 often 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 jet is stabliaed, and is made more definite in its shape and more constant in its direction. The scattered spreading effect upon the particles, particularly at the outer portions of the jet, is materially reduced resulting in a deposited pattern which is more uniformly dense throughout its area and which has a desired sharp edge definition.

The sprays of atomized material may be directed forwardly in a straight manner toward the article to be coated or they may be made irregular so as to have. a kinked contour by subjecting them during their expulsion from the liquid mass and before their complete atomization, to an intermittent force acting in line with their direction of travel. This is accomplished in one way by arranging at one or the other or both of the sides of the path of travel of the spray a stream or streams of air. It is accomplished in another way by turning one or the other of the lips of the device of the invention in a predetermined direction. It is accomplishedin still another way by rotating the device of the invention itself.

The atomizing element of my apparatus consists essentially of a reservoir which has a feed means connected therewith and leading thereinto. There is also a small head or nozzle having a sharply defined distributing or atomizing point or tip from which the coating material is metered at a predetermined rate in the form of atomized particles.

The device is provided with a spout or lips so that, as

material is supplied to it, said material tends to flow out over the lips.

A source of electrostatic high potential, having one terminal grounded and its opposite terminal 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 transforms the coating material into a spray of fine, charged particles and creates an at; traction which pulls the spray to the grounded article.

In this invention, the coating material is normally supplied to the discharge spout and its region of corona discharge at a rate at which it can be electrically atomized by the corona discharge most efliciently and effectively, after which the charged particles are projected in spray form toward and deposited upon the oppositely charged article. 1

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 particles so as to effect the greatest efficiency in coating a surface.

These objects, I accomplish by means of such structure as will fully appear by a perusal of the description which follows and by various specific features which will be hereinafter set forth in connection with the drawings wherein: Y

Fig. l is a top plan view of the device of the invention;

Fig. 2 is an enlarged sectional view of the device shown in Fig. 1; and

Fig. 3 is an enlarged sectional view of a modified forward or head end of the device shown in Fig. 2.

In this drawing, I have illustrated a complete example of one physical embodiment of the invention. It will however be understood that changes and alterations are contemplated and may be made within the scope of the claims, without departing from the basic principles of the invention.

Referring now to the drawing more in detail, in which similar characters of reference indicate corresponding parts in the several figures, and referring more particularly to the preferred form of my invention selected for illustrative purposes, I have shown a horizontally positioned atomizing. head, generally designated by the numeral 10, by means of which head the liquid coating material may be electrostatically atomized.

The liquid spray material is lead from a source (not shown) through a conduit (not shown) to the nozzle or head end of the structure which incorporates the features of this invention. Likewise air is led from its source (not shown) through a different conduit (not shown) to the nozzle or head end of the structure.

At the head or nozzle end of the structure, a 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 forwardly disposed members, shortly to be described.

7 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 U. S. Letters Patent #2,070,696, dated February 16, 1937.

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 atomizing spray guns using air for the atomizing medium.

The spray head comprises an inner liquid or fluid nozzle 40 formed with a forwardly disposed tip 42 having a central orifice therethrough through which the coating material is emitted. The nozzle 46 abuts the outer surface of a washer 43 which is receivable in an appropriate opening in the member 60 and the tip 42 extends through a centrally disposed opening in the washer 43.

The inner fluid nozzle 40 is threadedly receivable in a sleeve 44 which is receivable in an appropriate opening in the forward face of the nose piece.

Forwardly of the member 40, an elongated connecting member 60 is provided having a central orifice 62 extending therethrough throughout the longitudinal length thereof.

The member 60 has an outwardly extending annular skirt portion 64 which is adapted to be engaged at its outer peripheral edge by a union nut 54 so as to hold the member 60 in extended coaxial relation with member 40 with the tip 42 of member 40 extending into the opening 62 and affording direct communication therebetween.

One or more openings 66 extend through the member 60 in a direction parallel to the plane of the central orifice 62.

A sleeve-like outer shell member 70 may be made of metal and may be provided with a central opening 72 extending longitudinally through the rearward area thereof, as shown.

The rearmost portion of the inside wall of the member 70 is threadedly engaged with the member 60 at 73, as shown.

At the forward end of the member 70, and in a manner so as to be separated from the opening 72, by means of a wall 74, a spherical container 76 is provided having a hollow interior 78 serving as a reservoir.

A connection 80 is coupled at its rearward end to the member 60 by means of a coupling 82 which is in threaded engagement with the member 60 as shown. The connection 80 extends through an appropriate centrally disposed opening through the wall 74 so that the outer free end 84 thereof is disposed within the reservoir 78.

A bushing or Washer member 85 is nested in the opening in the wall 74 and supports the member 80.

The reservoir is adapted to contain a suppiy of the liquid coating material which may be supplied thereto by the feeding means comprising the members 60 and 80 inasmuch as the connection 80 is hollow throughout its length as shown and is disposed in alignment with the opening 62 through the member 60 so that direct communication therebetween is afforded and the coating material is led from the rear end of the gun forwardly to the reservoir.

An annular plunger member 86 is provided upon the connection 80 and is adapted to be fitted tightly against the member 85 whereby the washer member 85 is held snugly within the opening so as to insure against leakage of coating material therethrough from the reservoir or the leakage of air therethrough from the compartment or area 72.

On the forward side of the spherical member 76, a spout or mouth is provided by extending, from a slit or opening in the member 76, a pair of spaced lip members comprising an upper lip member 92 and a lower lip member 94, from between which the liquid coating material in the reservoir may be withdrawn toward the article to be coated.

If desired, one lip may be extended slightly forwardly beyond the other lip member, as best shown in Fig. 2, wherefor the coating material issuing therepast is defiected in an upwardly direction away from the longitudinal axis of the device.

One or more air conducting tubes 100 may be disposed through appropriate openings in the wall 74 having free inner ends 102 within the openings 72 and extending outwardly through the chamber 78 and through appropriate openings in the wall of the member 76 to the outer side thereof where a free outer end 104 of the tubes may be disposed in close adjacency to one of the lips 92 or 94.

By this means, air is enabled to pass through the member 70, past the chamber 78, and forwardly to the head end of the gun.

If desired, the lips may be equidistant in their extended relation away from the spout or mouth as shown in the modified view of Fig. 3 wherein an upper lip member 92 and a lower lip member 94 extend outwardly so as to form an extended mouth or spout 93. In such case, air conducting tubes having free outer ends 104 are provided with outer openings which discharge air therethrough toward the outer surface of the adjacent lip from which it flows toward the outer open end of the mouth 93'.

The device may be rotated so that the opening between the lips may be disposed in horizontal or vertical position or in angular positions therebetween. The reservoir being spherical in its configuration the particular disposition of the device is of no import insofar as the material contained therewithin is concerned. That is to say, no matter what the position to which the device is rotated, the reservoir still functions as such.

If desired, means may be provided whereby the air passing through the member 100 may be pulsated so as to distinguish it from the normal situation where it passes through all openings 100 evenly. By passing the air first through one member 100 and thence through another member 100, 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 effect.

Or if desired, the device may be operated without air at all, the coating material being drawn through away from the reservoir by means of the electrical force itself.

The union nut 54 and the other elements at the forward end of the gun are preferably made from electrical conducting material, the union nut being connected to the ungrounded terminal of a high voltage source (not shown) by means of a connection 55.

The coating material passes from the source thereof to the member 40 and out through the opening thereof into the opening 62 of the member 60 and thence into and through the opening through the member 80.

The atomizing air is adapted to be supplied to the nose piece, then through an opening 48 around the member 44 and thence through openings in member 60 and into and through the opening 72 in the sleeve around the member 80.

As the stream of liquid passes outwardly through the lips 92 and 94 and as the stream of air passes outwardly around the lips, the same are subjected to the atomizing effect of the corona discharge from the electrode whereby the finely divided particles comprising the spray are each imparted electrical charges of like polarity. A halo efiect is attained thereby. With voltage applied directly 1 to the spray head structure, a corona discharge is formed i in the region around the lips and. adjacent the outermost periphery thereof which. is of. an intensity sufficient to atomiz e into. particled form 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.

That is to, say, in actual operation, 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 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 and are atomized and electrically charged passing outwardly into the field with high turbulence.

As aforesaid under certain conditions, the projected jet wavers erratically resulting in a scattered dispersion of the particles comprising the jet and causing the deposited pattern upon the article to have irregularly disposed lakes. In addition, the mutual electrical repulsion of the particles due to their being charged to the same sign causes them to spread and scatter laterally, particularly at the outer portions of the jet. This makes a less sharply defined edge at the boundary of the deposited pattern.

To overcome these objectionable characteristics, I provide a gaseous field surrounding in close proximity the electrostatic atomizing field and coextensive in length with the latter. That is, it extends along the lips 92 and 94 with which it is substantially coaxial and terminates at the surface of the article to be coated.

In this manner, an air chamber is provided adjacent the outer periphery of the lips whereby a gaseous medium of any desired intensity may be introduced around the stream being dispersed through the lips so as to surround or envelope the same.

By the use of this gaseous envelope outside of and surrounding the liquid, the paint or other material being sprayed with the apparatus may be better concentrated or dispersed over a given area of an article being coated.

By means of this concentration of air around the liquid, the center of the area being sprayed receives as much of the sprayed material as the outer edges thereof, the air blast having the capability of directing the sprayed material inwardly toward the central area if desired.

The lips 92 and 94 present toward the articles to be coated a reduced or relatively sharp tip or discharge point from which the coating material may be withdrawn in the form of particles, thereby accounting for the electrostatic deposition.

The liquid and gaseous materials are supplied through their respective conduits to the nozzle assembly as previously described. These materials issue from their respective orifices at the outermost free end of the nozzle in the form of streams where they mix with each other. The resulting mixture is directed outwardly with high turbulence in the form of a finely atomized stream.

In operation, an unidirectional electric potential is maintained at the high potential nozzle assembly and, as the formed stream is directed outwardly through and away from the nozzle, it is subjected to the ionizing effect of the corona discharge from the isolated nozzle whereby the finely divided particles comprising the spray are each imparted electrical charges of like polarity and of substantially equal potential with respect to the atomizing lips.

The positively charged particles tend to repel one another and thus resist coalescence with the result that the electrified cloud of spray is attracted to surrounding grounded article desired to be sprayed and/or coated. The particles are attracted to and precipitate in a layer upon the nearest surface of the grounded article which is to be coated.

Coating material is urged forwardly to the discharge lips where it is electrostatically atomized and precipitated upon the article passing the head the action of the electrostatic field which exists betw en; the article and the head. The particles are electrostatrcally dispersed as they are formed or produced along theline of atomization and they are electrostatically deposited while still in the liquid state upon the article surface so as tofforrn a finished coating.

As aforesaid, the spray head is connected to a source of high voltage (not shown) through one terminal thereof. The other terminal of the source is grounded and through ground is connected with the article to be coated and/ or the conveyor therefor all to the end that the space or field between the spray head and article is electrostatically charged.

The electrical force acting on the coating material causes same to be broken up into finely divided or minute particles of coating material, so as to be attracted to the grounded article for deposition thereon.

he grounded article is referred to as a collecting electrode of one potential with the applicator head serving as a discharge electrode of a different potential.

The electrostatic force set up on the field between the electrodes transmits the finely divided particles of the coating material from one electrode-to the other.

The same action will take place when the spray head is grounded and the article is directly connected with the Source of high voltage and is charged at a high potential.

With voltage applied directly to the spray head structure, a corona discharge is formed in the region therearound and adjacent the outermost periphery thereof and is of. an intensity suflicient to break up or to atomize into particled form the coating material and toproject the coating material in a spray form toward the surface of the article being coated.

The foregoing reveals the gist of my 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 it is desired to claim and secure by Letters Patent of the United States is:

1. In an aero-electrostatic atomizing apparatus of the class described for attachment to a spray gun for use in discharging an electrically-charged air-supported stream of coating material, the improvement in a fluid spray nozzle comprising an outer main casing disposedforwardly of the spray gun and in axial alignment therewith, the rearward extremity of said casing being fixed to the forward extremity of the spray gun, a fluent coating material supply chamber within said casing, a longitudinally extending discharge orifice in the forward extremity of said casing terminating in an outer forwardly-facing discharge lip and communicating with said chamber facilitating discharge of the coating material therefrom, means coaxial with and extending longitudinally through said casing facilitating feeding of a supply of coating material to said chamber, a motive agent conduit coaxial with said casing and extending longitudinally thereof from a point Within said casing to a point outside of said cas ing and having an outer inwardly directed discharge opening converging on the adjacent discharge lip of said discharge orifice for discharging the motive agent in impinging relation upon the main discharge of coating material at a multiplicity of points lengthwise and transversely thereof.

2. The structure of claim 1, including, a plurality of said motive agent conduits having outer discharge openings converging on the adjacent discharge lip of said discharge orifice.

(References on following page) "Re fe'rences Cited in the file of this patent UNITED STATES PATENTS Murphy Aug. 2, 1887 Gidino June 30, 1925 Murray Aug. 10, 1926 Barnes Feb. 24 1931 Norton July 21, 1936 Campbell Nov. Bramston-Cook Nov. Ransburg et a1 Nov Ball Mar. Peeps Ian. Ransburg Nov Sedlacsik June

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