US2851307A - Electrostatic deposition apparatus - Google Patents

Description

p 9, 8 J. SEDLACSIK 5 L ELECTROSTATIC DEPOSITION APPARATUS Filed Nov. 10, 1954 INVENTORQ 4 War 2g.

BY Z4412,

2,851,307 Patented Sept. 9, 1958 2,851,307 ELECTROSTATIC DEPOSITION APPARATUS John Sedlacsik, Garfield, N. J.,.assignor to Ionic Electrostatic Corporation, Garfield, N. J., a corporation of New Jersey Application November 10, 1954, SerialNo. 467,964 2.C laims. (Cl. 299-140) My invention relates to improvements inan apparatus used in applying a'liquid/gaseous 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.

Means -is provided whereby the liquid/gas may be readily and efliciently divided into minute particles by electrical force, without the assistance vof moving air streams or other means commonly employed for this purpose.

As the coating material is electrostatically charged and projected 'fromthe apparatus, the electrical charge is directed toward and e'lectrostatically deposited upon the articles to be coated. I

The invention envisions a paint spray gun mechanism wherein the forward atomizing and spray elements are isolated from the rear supportandcontrol elements and thestructure-is such as to permit the desired elimination of the possibility of'a transmittal vof an electrical charge in the forward area of the mechanism rearwardly 'to the rearward area thereof.

The rear portion of themechanism is at ground potential for the convenience and safety of the operator while, at the same time, the forward portion thereof is adapted toreceive a'high electrical potential.

In applying coating materials to articles with prior art spray guns, the :art of employing compressed air as a means for atomizing or reducing the material into a fluid of vfine comminuted particles andalso as a carrying medium-in spraying the same'upon'the surface of the articles being covered has been known. But such guns have been limited toa comparativelysmallfield of dispersion. Also, they have caused the coating material to be discharged tin non-uniform sized particles, .as Well as in variable patterns, whereby an uneven dispersion of the coating particles over the surface being coated results.

In certain prior .art devices, the projected sprayor jet is "more or less unstable. That is, the axis of the spray or jet shifts erratically from one position .to another. Expressedotherwisqthe cross-sectional shape of the spray 'or jet pattern has been observed to vary during operation. Such instability results in an obviously objectionable irregular scattering ;of the coatingmaterial upon the sur face of the articlebeing coated.

The inherent electrical effect in prior art guns causes the particles torepel each other more or less whereby lateral spreading thereofresults.

This spreading phenomena .is especially noticeable at the outer portions of the spray or'jetarea where an uneven, irregular .and indistinct edge definition to the pat- .tern of the coating material being deposited upon the article is normally observed.

By surrounding in close proximity the atomizing, projecting and depositingelectrostatic field with an envelope of .air, .whichds substantially coextensive longitudinally withthe former, .the projecting spray .jetis stabilized and '2 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 jetyis materially reduced. This results in a deposited pattern "which is more uniformly dense throughout and whichhas a desired sharp edge definition.

One object of this invention is to provide a stabilizing area adjacent the electrostatic spray atomizing field, which area is effective to stabilize thejet produced by the latter, in respect both to direction and-shape. The resulting-deposited pattern has a relatively sharper edge definition throughout its entire periphery and/or'over one-or more "portions thereof.

The .atomizing element of the apparatus consists 'essentially of a small nozzle having a sharply defined 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 theatomizing 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 attraction which pulls the spray to the grounded article, thus accounting for complete electrostatic deposition.

Optimum results are obtained where the massof the atomizing tip is as small as possible Whereas the mass of thearticle being coated is'relatively larger. Such Lfacilitates leakage of the atomized material from the high potential tip to the article. Otherwise expressed, the smaller the area at the high potential, the greater the leakage off to the mass of the article being coated.

Further, I'have determined that by isolating the atomizing head or gun tip from the remainder of the gun, as by an insulated member or members, the .des'ideratum of maintainingthe smallestportion or .area of the ,gun at ductors of:electricity, they being of rubber, glass, ceramic,

plastic, or similar non-conducting material. By .means thereof, the high voltage nozzle or headcnd of ,the gun apparatus is separated from the grounded support or control end, in such manner, that the, support and control mechanisms, as well as the operator, are safeguarded against backfiring from the nozzle orheadend.

In apparatus employed for applying a liquid coating to articles, whether or not the coating material is electrostatically deposited, it is common to :move the ,articles progressively through a coating zone in which 'the coating is applied. -I-Iere it is anticipated that the articles :to be coated may be moved past the apparatusof the invention, or the apparatus can be reciprocated along a horizontal or vertical axis, or both, past the articles.

In either event, the articles to be coated are usually .supported in spaced relation to the discharge electrode,

' between which and the articles, a potentialdiiference 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.

Broadly speaking, 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 thecorona discharge most efliciently and eifectively, 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 effect the greatest efficiency in coating a surface.

All of the above cited 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.

With the foregoing and various other and ancillary objects of my invention as will become more readily appar out as the description proceeds, my invention consists in certain features of novelty, in mode of operation, and in the combination and arrangements of parts as will be hereinafter more particularly pointed out in the claims hereunto annexed and more fully described and referred to in conjunction with the accompanying drawings wherein:

Fig. l is a side elevational view of the device of the invention with parts being shown in section;

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

Fig. 3 is an enlarged sectional view on the line 33 of Fig. 1; and

Fig. 4 is an end elevational view lOOkiIlg toward the atomizing tip of the gun as shown at the right in Fig. 1.

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

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 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 an arrangement of 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, 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 10, by means of which head the liquid coating material is electrostatically atomized.

The atomizing head may be fixedly or adjustably mounted upon a suitable support, or it may be hand manipulated by means of a handle, all as may be desired.

An elongated liquid spray material tube 20 made from glass, rubber, plastic, or similar material is provided with a longitudinal bore 21 extending therethrough. A coating material is adapted to be passed therethrough as will presently be observed.

Another elongated gas tube 22 extends parallel to the tube 20 and is spaced a distance away therefrom. Tube 22 is also provided with a longitudinal bore 23 extending therethrough. A gaseous material, such as air, is adapted tobe passed therethrough, all as will hereinafter appear.

At the opposite extremities of the tubes 20 and 22, connecting means are provided.

At the head or nozzle end of the structure, a nose piece 26 is provided and tubes 20 and 22 may be threadedly or otherwise engaged therewith. I

Interior passageways (not shown) within the nose piece 26 connect the respective tubes 20 and 22 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.

The spray gun contemplated for use in this invention consists of a conventional main body portion which 15 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 26 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 7 formed with a forwardly disposed tip 42 having a central orifice 43 therethro-ugh through which the coating material is emitted.

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 member 26.

The member 44 is connected in any suitable manner with the member 26 and is surrounded by a union nut 54 which is threadedly engageable with the forward portion 27 of the nose piece 26.

Forwardly of the member 40, an elongated connecting member 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 the union nut 54 so as to hold the member 60 in extended coaxial relation to member 40 with the tip 42 extending into the opening 62, afiording direct communication therebetween.

A hollow outer housing has a rearmost portion 72 threadedly engageable with the member 60, as shown.

An air opening 66 extends through the member 60 as shown. A plurality of such openings may be provided, if desired, permitting air to move forwardly from the area 55 within the union 54 to the area 71 between the housing 70 and the member 60.

A sleeve member is generally cup shaped in its forward area and is provided with a neck portion 81 in its rearward area. The neck portion is threadedly engageable with the forward end portion of the member 60 at 82.

A central bore or opening 83 extends longitudinally through the neck portion 81 and receives therein the shank 85 of a plug member 86, the latter having a central passage or opening 84 having its rear end in direct communication with the opening 62 in the member 60. The forward end of the opening 84 terminates in radially extending branches 87 each of which leads into the forward cup of the sleeve member 80.

An annular air space 71 is provided between the outer housing 70 and the sleeve member 60.

The plug member 86 is receivable within and spaced from the sleeve member 80 so as to provide an annular space 92 therearound between which and the sleeve member the liquid coating material passes. An annular air space 90 is provided between the housing 70 and the member 80 whereby air from the air space 71 may pass outwardly therefrom.

The forward end of the sleeve member 80 extends forwardly slightly beyond the forward end of the member 70 and the forward end of the plug member 86 extends forwardly slightly beyond the forward end of the sleeve member 80. The forward end of the member 86 is formed with a sharp edge 89 to provide a corona discharge as hereinafter made apparent. Coating material is emitted outwardly from the space 92 through the orifice 93 at the forward end of the member 80.

If desired, the forward end of the sleeve member 80 may extend inwardly of the outer end of the outer hous- 1 ing 7-0 and the forward-endof the plug member 86 .may be disposedinwafdly o'f the-outerend-ofihesleeve member 80.

"The 'nose;piece.f26 and *the other elements at the forward end'df the gun are-preferahly made from electrical conducting material, the nose piece being connected to "theungrounded terminal of a thigh "voltage source (not -shown) by means'of a connection 29.

The coating material passes through {the 'tube .and

appropriate conducting means in "the nose piece 26 to "the member-40 and-out "through 'the'opening 4? in :the

-tip 42 thereof into sthe opening 62 et the member 6! andthenceint-o and through the branches 87=of themember'86.

The atomizing air "is adapted to t be supplied through "the member 22 to :the nose; piece 2 6, then through I openings' 66 and into area T1 and through the=space around (the sleeve 80 and then outwardly through the orifice "91 "atthe 'forward end of the housingormember70.

As thestream 'o'f liquid passes outwardly through the member 40,60 and 86 'and as 'the'stream of air passes outwardly "around "the outer surface of the sleeve m-ember Stl, the "same aresubjected to the atomizingeifect of \ture, 2..(201'0113. discharge .isiormedin ,the region around the .nozzle :and .adjacent the outermost periphery thereof which issof an intensity.sufficientwto :break up orto Fatom- -ize .in'to :particledtorm .the coating material being discharged .from the .nozzle.and totproject said coating .ma- :terial in.sprayiorm..towardthesurface of the-article :being coated.

.A Ihigh electrical potential, .from :a suitable source, is

.applied to "the. nozle .orhead assembly while .thematerial Zbeing atomized and .the .gas or airzaredelivered :through the respective delivery tubes and connections 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 outwardly into the field with high turbulence.

As aforesaid, under certain conditions, the projected jet wavers erratically and continuously. This results in a scattered dispersion of the particles comprising the jet and thereby causes 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 cause 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 and around the sleeve member with which it is substantially coaxial and terminates at the surface of the article to be coated.

In this manner, an air envelope is provided adjacent the forward outer periphery of the member 80 whereby a gaseous medium of any desired intensity may be introduced around the stream being dispersed through the needle so as to surround or envelope same.

Understandably, valve means (not shown) may be provided whereby the flow of liquid and air may be better controlled.

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 .is toxbe :cioated.

6 the sprayed material as the outer edges thereof, the .air blast having the capability of directingthe-sprayed material inwardlyztoward said centralzarea.

The inner extremities ofthe tubes 20 and.22. arethreadedly engaged with.;a tailpiece 19.0 by meanszof couplings 192 and .194 respectively.

The tailpiece is connected to sources of supply of the coating material and air (not shown) bymeans of connections of'any 6f the conventionaldesigns.

In the drawing, aconnection'96 is :shown which may be connected to a source of air orgas:(not:shown;) and a connection 98 is shown whichzmay .be connected :to a source of coating material (not shown).

The liquid and gaseous materials are supplied through their respective conduits 101112 nozzle -.assembly as ,previously described.

These materialslissue from .their.-r,espective orifices at the outermost free 'end of "the :nozzle in the .form of streams where they mix with each :other. The resulting mixtureis directed outwardly withlhighitnrbulencein the form of a finely atomized stream as hereinbefore described.

In operation, an unidirectional electric potential is maintained at the high potentialnozzle zassemblyand,

:as the thus :formed :stream is directed outwardly away .from the .nozzle, fit .is subjected to .thetionizing -efiect of the .corona discharge from ithe iisolated -nozzle whereby the finely divided particles comprising tthe :spray have each imparted thereto electrical charges ;of like polarity and of substantially equal potential Twith-arespect :to the :atomizingpoint or tip.

.The positively charged particles rtend to :repel one 'another and thuszresist ICOBICSCEIICE'With the result that the electrified cloud of spray .is attracted :to surrounding grounded object desired :to :be :sprayed rand/or :coated. The particles are:attracted-rtoiandzprecipitatein a layer upon :the :nearest surface of .the grounded :article which Coating material is urged forwardly to the discharge point or tip of atomization where it is electrostatically atomized and precipitated upon the article passing the head by the action of the electrostatic field which exists between the article and the head. That is the particles are electrostaticallydispersed as they are formed or produced along the line of atomization and they are electrostatically deposited while still in the liquid state upon the article surface so as to form a finished coating.

As aforesaid, the applicator 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.

Accordingly, the space or field between the applicator head and article is electrostatically charged by reason of the article being grounded and the applicator being at the high potential.

The effect thereof is to cause an electrical force to act on the coating material causing same to be broken up into finely divided or minute particles of coating material, such as to be attracted to the grounded article for deposition thereon. Thus, the grounded article may be 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 in the field between the electrodes is such as to develop and transmit finely diyided particles of the coating material from one electrode not receive'more coating material than can be atomized from its discharge edge.

If desired, the coating material may be circulated from the source of supply through the apparatus and may be then recirculated back to the source of supply again so as to aid in the maintenance of the desired degree of control.

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

Without further analysis, the foregoing will fully reveal 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. Such adaptations therefore should and are intended to be comprehended within the meaning and range of equivalence of the claims below.

What it is desired to claim and secure by Letters Patent of the United States is:

1. An acre-electrostatic atomizing apparatus adaptedto be attached to a spray gun, a substantially cylindrical housing, spray gun attaching means adjacent an end thereof, a member in said one end having an eccentric bore through said member, said member having a reduced connecting member extending concentrically from said member and both of said members having an axial bore, a cylindrical sleeve extending from said connecting member, said sleeve being adjacent the second end of said housing and spaced therefrom, a cylindrical plug attached to said connectingmember and having a bore in register with said connecting member bore and terminating laterally of said plug, said plug being spaced from said cylindrical sleeve, whereby material entering through said 8 eccentric bore will issue between housing and said sleeve and material entering through said axial bore will issue between said sleeve and said plug.

2. An aero-electrostatic atomizing apparatus adapted to be attached to a spray gun having a high voltage instrumentality thereon, a substantially cylindrical housing, spray gun attaching means adjacent one end thereof, a member secured in said one end having an eccentric bore through said member, said member having a reduced connecting member extending concentrically from said member and both of said members having an axial bore, a cylindrical sleeve extending from said connecting member, said sleeve being adjacent and within the second end of said housing and spaced peripherally therefrom, a cylindrical plug attachd to said connecting member and having a bore in register with said connecting member bore and terminating laterally of said plug, said plug being within and spaced peripherally from said cylindrical sleeve, said plug having a peripheral knife edge at its outer end, whereby air entering through said eccentric bore will issue between said housing and said sleeve and fluent material entering through said axial bore will issue between said sleeve and said plug and be atomized at said knife edge.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,497 Popofi Sept. 29, 1942 2,302,185 Campbell Nov. 17, 1942 2,302,289 Bramston-Cook Nov. 17, 1942 2,410,532 Tessier Nov. 5, 1946 2,438,471 Ball Mar. 23, 1948 2,574,003 Wymer Nov. 6, 1951 2,577,853 Kurata Dec. 11, 1951 2,593,096 Brusdal Apr. 15, 1952 2,625,590 Peeps Jan. 13, 1953 2,658,009 Ransburg Nov. 3, 1953 2,710,773 Sedlacsik June 14, 1955

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