US 2754226 A
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y 10, 6 J. w. JUVINALL ATOMIZING AND COATING SYSTEM AND METHOD Filed July 24, 1953 INVENTOR. JAMES W. JUVl/VALL A lorneys United States Patent 2,754,226 ATOMIZING AND COATINGSYSTEM AND METHOD James W. Juvinall, Indianapolis, Ind, assignor to Ransburg- Electra-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application u y 19 .3, Serial No- 3 0,168 13 Claims. (Cl. 117-93) The invention relates to atomization and .deposition of a spray of liquid coating materialparticles in an electr static field and more particularly the. invention relates to. methods and apparatus for electrostatically controlling the deposition of charged, atomized liquid spray particles.
Electrostatic deposition of a charged spray of enamel, paint, lacquer, and the like on articlesv in a coating zone having a quiescent atmosphere has marked advantages in paint savings, coating uniformity, and ready adaptation to conveyorized production methods. Coating in a quiescent atmosphere and the elimination of the turbulent air blasts of conventional com ressed air atomizing guns result in the deposition of the coating material being effected mainly if not entirely by electrostatic forces exerted on the charged spray particles projected into the electrostatic field. The term quiescent atmosphere as used herein does not mean an absolute stillness for freem f om ll ir o men s nc s ch fact rs as rotation of a member of the atomizing device or the electric wind may cause air movement in the coating zone. However, the coating zone is free of the turbulentair blasts of the order of those used with conventional compressed air spray guns which would prevent the deposition of a substantial portion of the spray particles onto the articles being coated.
To eliminate the objectionable compressed air atomizing guns and effect the desired quiescent atmosphere in the coating zone certain atomizing devices have been suggested which produce expanding annular or ring-like sprays of finely divided liquid coating material particles. Annular-edged atomizing devices which produce annular sprays, that is, expanding circular sprays havinga central area substantially devoid of spray particles, are described in the previously filed application of W. W. Crouse, Serial No. 13,174, filed March 5, 1948.
My invention includes an electrostatic spray coating apparatus which comprises an atomizing device of a type capable of forming and projecting into a quiescent a tmosphere a charged spray of finely divided liquid coating material particles having a substantially annular pattern. Such apparatus includes a shielding member for intercepting a substantial segment of said spray and apparatus associated therewith for collecting and recovering the liquid material so intercepted. The apparatus further includes a conveyor for moving articles along a path on the generally opposite side of the atomizing device from the shielding member and a source of high electrical potential which is used to create an electrical potential difference between the spray particles or atomizing device and the articles to be coated so as to electrostatically move and deposit charged spray particles. The shielding member is preferably maintained at the same electrical potential as the articles or at an electrical potential intermediate between that of the atomizing device and the articles being coated.
The invention further encompasses deflecting electrodes for dividing an annular spray into two segments, one segment being deposited on articles of manufacture and Th b t om of th h ud ice the other being collected in a shroud. These deflectors, normally maintained at or near the potential of the charged atomizer, provide the further feature of repelling spray particles from the edges of the shroud to keep the edges free'from liquid which might interfere with the satisac o y opera ion of the sy I have discovered an efificient process for the coating of articles of manufacture by which an annular spray of charged liquid coating material particles is projected from annular atomizing zone into an electrostatic fiel he part les from a substanti l ar of s d spr y are intercepted by a shielding member, the liquid material so intercepted is reclaimed, and the balance of said spray is electrostatically deposited on the articles.
A feature of the present invention is directed to. the
"more .efi'icient use of a rotating annular-edged atomizing device or other atomizer capable of producing an annular spray in an electrostatic coating system. A further feature is that of improved coating uniformity, that is, more uniform thickness of the deposited material. Other featuresand objects of this invention will now be described n detail n c n ec ion. with the ac o pa y ng drawing in which:
11 is a plan view, somewhat diagrammatic, showing an a omizing devi ut l zing the n ention in an electrdstati'c sys em for ng cy n ica arti l s;
Fig. 2 is an .elevatiopal view of the system shown in Fig. 1;
3 i a t p pl n. v ew, somewha di gr ma c, showng'the invention used in another coating system;
Fig, 4 is an elevational view of a portion of the system shown in Fig. 3; and
Fig. 5 is an isometric view showing details .of the pair of oppositely rotating discs used in the system illustrated in Figs. 3 and 4.
e nve i n may e ut z d n nume u o ms- There are shown in the drawings and will be fully described two specific embodiments which it is understood are merely illustrative .of the principles of the invention without limiting the invention to the embodiments shown and described. The full scope of the invention is set forth in the appended claims.
Referring to Figs. 1 and 2, a spindle conveyor 10 uses plurality of spaced supports 11 to move a seriesof articles, shown as cylindrical ammunition containers 1 2, in succession along a predetermined rectilinear path whose center line is indicated in Fig. 1 by broken line 13. The articles may be rotated about their centers by friction contact between rotators 14 rigidly mounted on each support 11 and a rotator bar 15.
Spaced from the article path 13 to form therebetween a coating zone is an atomizing device 16. The atomizer includes an annular-edged flat horizontal disc 17 fired for rotation on a hollow shaft .18 of a motor. The motor 19 is mounted on a column 2.9 of insulating material. Liquid coating material is fed from a source of supply (not shown) through a conduit 21 to the interior of the hollow motor shaft, then through a hole in the center of disc 17 to the upper surface of the disc. A troughlike shielding member or shroud 24 surrounds one side of s Shr ud 24 may be ma e o ei he ucting or insulating material but in the embodiment shown it is of a conductor, sheet steel. The shroud shown encloses an arc of about of the edge 17a of the disc and its open face lies generally parallel to article path 13. The close c ve rear si e f shroud 24. has a radius f cu va ur b tan lly gr t r han hat of disc 17 so that its terminal edges. 24!) and 2,46 lie further f om dis e ge 17 than does the r of the s rou i l p d. oward a rain encuing 2 i r o lecting and ec v r ng qu d m terial- The shroud is supported in fixed relation to atomizer 16 .trical connection of atomizer by a supporting column 26 of insulating material and a bracket 27 preferably with the shroud substantially closer to disc edge 17a than are articles 12. Thus spray particles intercepted by the shroud, as hereinafter described, will retain a substantial portion of their volatile solvents thereby making recovery and reuse of the liquid material easier and more economical. Two substantially identical deflecting electrodes 23 and 29 of suitable conducting material may be mounted on opposite sides of motor 19 extending outwardly somewhat beyond disc edge 17a and terminating in vertical portions passing through the plane of the disc.
Disc 17 and electrodes 28 and 29 may be maintained at substantially the same high electrical potential by elec- 16 to the high voltage side of a voltage source 38. A particle-depositing electrostatic field is thereby established throughout the coating zone between disc edge 17a and adjacent articles 12 which are grounded through conveyor 10. The particle-depositing field may alternatively be established by maintaining the articles at high voltage and grounding the atomizer and deflectors. It is noted that the shroud 24 is electrically isolated from both disc 17 and articles 12 and preferably the shroud is maintained at such voltage that the potential gradient along the entire circumference of disc edge 17a is approximately uniform. subjecting a rotating disc edge portion alternately to widely varying potential gradients as it revolves through the field may adversely V aifect the spray particle size and the volume of atomization from such edge portion. A reasonably uniform potential gradient extending around disc edge 17a is therefore desirable to insure relatively uniform conditions for the atomization of the liquid material. This may be accomplished by allowing the shroud to float and thus seek a potential determined by its position in the electrostatic system or by connecting the shroud to a source of voltage intermediate that of the disc and articles of such value that the field around the disc edge is generally uniform even though the shroud may be somewhat closer to the disc edge 17a than are articles 12.
In the operation of the system, power supplied to the motor of atomizer 16 causes rotation of shaft 18 and disc 17 while the desired liquid coating material is fed at a controlled rate through conduit 21 and hollow shaft 18 to the upper surface of the rotating disc. Liquid coating material thus fed to the surface of the rotating disc will flow as a thin film over the surface to disc edge 17a. At or adjacent the disc edge the liquid material Will be atomized into the electrostatic field existing about the edge as a spray of finely divided particles in a substantially annular pattern.
The deflectors 28 and 29, due to the potential at which they are maintained as above set forth, tend to form zones of particle-repelling electrostatic force which serve to split or divide the annular spray into two semi-annular portions, one portion being directed into shroud 24 and the other being directed into the coating zone for deposition on articles 12. The deflectors are preferably located intermediate terminal edges 24b and 240 of the shroud and disc edge 17a and serve to keep spray particles from depositing on shroud edges 24b and 24c where an accumulation of liquid material may be most undesirable because of dripping and electrostatic atomization from such edges. Since the presence of electrostatic repelling zones closely adjacent disc edge 17a may unduly deteriorate the atomization of the coating material from the disc edge, deflectors 28 and 29 should be spaced a sufficient'distance from edge 17a. Other types of deflectors V veyor system (not shown) may, of course, be used to create the desired particlerepelling zones and to divide the annular spray,
Where the system is to be used to coat articles whose dimensions parallel to the disc axis are materially greater than the width of the spray, the disc may be somewhat tilted from horizontal (or otherwise maintained at an angle in relation to the article path) in order to increase the efiective width of the spray band, or the atomizer 16 may be reciprocated along the axis of rotation of the disc. Fig. 2 shows apparatus for reciprocating the atomizer 16 integrally with shroud 24. Insulating columns 20 and 26 and bracket 27 are mounted for vertical reciprocation on shaft 31 of a reciprocator 32. By suitable means the reciprocation of shaft 31 may be varied in order to provide a stroke substantially equalto the 10 inches. 900 rev. per minute. 90,000 volts (negative).
G rounded. 4 /2' inches.
73,000 volts (negative). Red synthetic enamel,
modified urea formaldehyde, 20 sec. on Zahn #2 Cup at 68 F. Rate of feed of coating matecc. per minute.
rial. I Referring now to Figs. 3, 4, and 5, there is illustrated a further embodiment of the invention for electrostatically coating sides of generally cubical boxes 40. This system with the narrow elongated band form of its deposited spray pattern is especially adapted to the triggering or automatic turning on and off of the spray of coating material from the atomizing devices in response to the presence or absence of an article in the coating zone. Articles 40 to be coated are moved on an overhead conalong a generally rectilinear line 4-1. The articles moving path indicated by broken along path 41 are successively presented in coating rela- 7 tion to first one and then the other of two substantially coaxial atomizing devices shown generally as 42 and 43..
Atomizer 43 only is shown in detail in Fig. 4 but atomizer 42 is generally of similar construction.
Atomizer 43 comprises a motor 44 mounted on an in- V sulated support 44a adapted to cause the rotation of a disc 45 lying in a substantially vertical plane. Openfaced shielding member 46 encloses one side of disc 45 and the members open face lies generally parallel to article path 41. A. vertical dam 47 (shown only in Fig. 5) closes off the bottom portion of the open face of shielding member 46 in order to collect liquid material intercepted by the shielding member and a conduit 48 is provided in the bottom of the shielding member to drain off accumulated liquid material. Member'46 is supported in fixed relation to disc 45 and motor housing 44 and in electricalisolation therefrom by an insulating column 49 and a bracket 50. A pair of deflecting electrodes 51 and 52 are mounted on motor 44 and extend generally'horizontally respectively above and below the vertical edge 45a of disc 45.
Disc 45 and electrodes 51 and 52 are maintained at a high electrical potential in relation to the grounded articles 40 by their connection through motor 44 to 'a source of a high voltage 53 in' order to establish a particle-depositing iacent article 40. Shielding member 46, electrically isolated from disc 45 and articles 40, is also connected to source 53 but is maintained at a potential intermediate between the discs and the particles by means of suitable resistors 54a and 54b between the members and the voltage source so as to permit disc edge 45a to have a substantially uniform potential gradient along its entire ex tent.
Liquid coating material stored in reservoir 55 is fed through a pair of pumps 56 and 57 adjusted to deliver substantially equal amounts of the liquid coating material through feed lines 58 and 59 to atomizers 42 and 43 respectively. Each of pumps 56 and 57 is independently operated by a triggering mechanism comprising microswitches 60 and 61 respectively which are activated by the passing of an article 40 into contact with an arm of the micro-switch. Micro-switches 69 and 61 are so located in relation to atomizing devices 42 and 43 respectively that liquid coating material will be pumped to the associated atomizing device only when an article is moved into coating relation, i. e., directly opposite from, the atomizing device as is shown in Fig. 3-. It may be noted that the relatively narrow or thin spray band projected radially from an atomizer such as device 42 lends itself especially well to incorporation in an arrangement where the spray is triggered. With both the atomizer axis and the least dimension of the spray pattern extending parallel to the path of article movement, it is a comparatively simple matter to trigger the supply of coating material in a way which, while avoiding excessive loss of coating material, will still provide an adequate coating at the leading and trailing edges of the articles.
The detailed construction of atomizer 42 is not described since it is generally similar with the foregoing description of atomizer 43. One important difference, however, exists. While the atomizers are coaxial and revolve around their substantially common axis, their directions of revolution are opposed as is shown in Fig. 5. The reason for the opposed revolution of the discs of atomizing devices 42 and 43 lies in the fact that the rotation of a single disc results in a somewhat heavier deposition of coating material at one end of the elongated spray pattern. For example, considering one of atomizers 42 or 43 alone, the device deposits spray particles on an article to form a narrow vertically extended or elongated band which, apparently due to the rotation of disc 45, tends to have one end of the band with a somewhat heavier or thicker deposit of material than the opposite end of the spray band. In order to balance out this non-uniformity where articles are being passed generally parallel to the axis of the atomizing device, two discs rotating in opposite directions are used.
Except for the feature of opposite rotation of their discs, atomizing devices 42 and 43 each operate substantially as atomizing device 16 previously described insofar as feed, atomization, separating the spray into two portions, electrostatic deposition of spray particles and intercepting and collecting that portion of the spray not deposited on articles. Each of atomizers 42 and 43, however, is triggered individually through pumps 56 and 57 and micro-switches 6t and 61 to deliver a substantial amount of spray into the coating zones only when articles 49 are passing through these zones.
A further feature of the invention lies in the ease with which undeposited liquid spray is collected and made ready for reuse. In most older systems requiring collection and reclamation of a portion of the spray of liquid coating material elaborate baflies and/ or other expensive collecting apparatus are employed. Moreover, since the coating material was recovered at a relatively great distance from the spray guns and almost invariably at a distance greater than that between the spray guns and the articles being coated, most of the solvents and other volatile ingredients of the coating material would have vaporized, leaving only a disagreeable gummy residue of pigments and slow drying .oils to be collected. Such residue was not only difiicult and expensive to recapture, but required a complete reformulation in order to obtain a product suitable for reuse.
By providing an intercepting shield and collecting device relatively close to the atomizer as described above the spray is collected in .a liquid state with most of its solvents intact. Deposition of coating material on file shield is favored by the electrostatic field between the disc edge and the shield. Thus, the collected material is both easily recovered and requires. only the addition of a small amount of solvent, rather than factory reformulation, to obtain a reusable coating material.
1. An electrostatic coating apparatus comprising a rotatable disc, means for rotating said disc about its axis, means for flowing liquid coating material onto the surface of said disc for movement to and atomization from the outer edge thereof, a conveyor for moving articles to be coated along a substantially rectilinear path spaced from, said disc, a shroud surrounding that portion of said disc most remote from said article path, a pair of deflecting electrodes each spaced from said disc and article path and located adjacent the generally opposite edge portions of said disc emerging from said shroud, and means including a high voltage source for establishing between said disc and the conveyed articles an electrostatic field of suflicient force to cause atomized liquid coating material particles to move toward and be deposited on the articles, said last mentioned means also maintaining said deflecting electrodes at substantially the same potential as said disc edge to electrostatically repel spray particles from the regions adjacent said electrodes.
2. Apparatus as set- -forth in claim 1 with the addition of means for reciprocating said disc and shroud together along the axis of said disc.
3. An electrostatic apparatus for coating articles comprising a conveyor for moving the articles along a predetermined path, an atomizing device with a rotating annular-edged atomizing member spaced from the article path with one portion of said annular edge lying substantially more remote from said predetermined path than the other portion thereof, means for supplying liquid coating material to said member for atomization from the annular edge thereof, a shroud partially surrounding said atomizing member and disposed in opposed spaced relation to that portion of said annular edge which lies more remote from such article path, the distance between the annular edge of the atomizing member and the shield being less than the distance between such edge and the article-path, a high voltage source having a terminal connected to said annular-edged member to, establish a particle-depositing electrostatic field between the articles to be coated and that portion of said annular edge not surrounded by said shroud, and means for maintaining said shroud at an electrical potential intermediate between said member and the articles whereby it will attract atomized particles discharged from said member.
4, Apparatus as set fQ th in claim 3 with the addition of means for reciprocating said atomizing member along its axis of rotation.
5 An electrostatic spray coating system comprising an annular-edged atomizer capable of forming an outwardly moving annular spray of coating material particles; a curved shield spaced from said atomizer for receiving a substantial segment of said spray; a deflector lying at least in part in the plane of the edge of said atomizer and adjacent to an edge of said shield; means for reciprocating said atomizer, shield and deflector as an integral unit along the axis of rotation of said atomizer; a grounded conveyor for'moving an article to be, coated in a path passing through a second segment of said spray; a source of high electrical potential; means for connecting said source to the rotating atomizer to create a high electrical of articles into and through potential difference between said atomized particles and the article electrostatically to move particles toward and deposit them on the article; means connecting the deflector to said source of high potential; and means for electrically isolating said shield from said atomizer, deflector, and article.
6. An electrostatic spray coating system comprising an atomizer for creating and projecting into a quiescent atmosphere a charged spray of liquid coating material particles radiating from the atomizer outwardly across and throughout substantially the entire circumference of an annular region surrounding the atomizer, a spraycollecting shielding member spaced from said atomizer and occupying a first substantial segment but less than all of the circumference of said region and located in the paths of the spray particles within such segment to intercept spray particles within such segment, means for supporting an article to be coated within a second segment of said region, means including a sourceof high voltage for maintaining an electrical potential difference between said atomizer and the article to' electrostatically deposit charged spray particles on the article, and means for maintaining said shielding member at a potential such that it attracts said spray particles in said first segment.
7. An electrostatic spray coating system comprising an atomizer including an annular-edged member mounted for rotation about an axis, means for feeding liquid coating material to the surface of the member, means for rotating said member to flow coating material on said surface to the edge thereof for atomization therefrom as a spray in a generally annular pattern, a shield spaced about a portion of the edge of said member for receiving a limited segment of said'spray, means operatively associated with said shield for collecting the liquid coating material received by said shield from said spray segment,
deflecting electrodes positioned in the plane of the annular edge of said member, circumferentially beyond the respective ends of the shield, and radially intermediate the shield-ends and the annular edge of said member, said member and a grounded conveyor for moving a plurality a coating zone adjacent to a second portion of the edge of said member, a source of high electrical potential, means for connecting said source to the atomizer to create an electrical potential difference between the atomized particles and articles in said coating zone to move a substantial portion of the particles toward and deposit them on the articles in said coating zone, and means for maintaining said deflecting electrodes at a particle-repelling potential.
8. An electrostatic coating apparatus comprising a pair of similar coaxial discs, means for rotating said discs in opposite directions, pump means for feeding liquid coating material at an equal rate to each of said discs for atomization therefrom as an annular spray, a pair of curved shielding members each spaced from a disc and positioned to receive a substantial segment of the spray from said disc, means operatively associated with each of said shielding members for collecting the liquid coating material received by said shielding members, a conveyor for moving a series of articles successively past said discs along a path generally on the opposite side of said discs from said shielding members and parallel to the axis of said discs, four similar deflecting electrodes each spaced from a disc and lying adjacent to an edge portion of said disc emerging from a shielding member, means including a source of high voltage for creating a spray particle depositing electrostatic field between the unshielded portion of each disc and the articles, and means for creating a spray particle repelling zone about each of said deflectingelectrodes and the adjacent edges of said shielding members.
9. An electrostatic coating apparatus comprising a pair of similar coaxial discs, means for rotating said discs about their axis in opposite directions, pump means'for feeding liquid coating material at an equal rate to each of said discs for atomization therefrom as an annular spray of finely divided particles, a pair of shielding members each spaced from a disc and positioned to receive a substantial segment of the spray from said disc, means for collecting and recovering the liquid coating material received by said shielding members, a conveyor for moving a series of articles successively past said discs along a path generally on the opposite side of said discs from said shielding members and parallel to the axis of said discs, means including a source of high voltage for creata particle depositing electrostatic'field between the unshielded portion of each disc and the articles, and means for creating a particle-attracting electrostatic field between the shielded portion of each disc and its adjacent shielding member.
l0. An electrostatic spray coating system comprising an atomizer including an annular-edged member mounted for rotation about an axis, means for feeding liquid coating material to the surface of the member, means for rotating said member to flow coating material on said surface to the edge thereof for atomization therefrom as a spray in a generally annular pattern, a shield spaced about a portion of the edge of said member for receiving a limited segment of said spray, means operatively associated with said shield for collecting the liquid coating material received by said shield from said spray segment, deflecting electrodes positioned in the plane of the annular edge of said member, circumferentially beyond one end of the shield, and radially intermediate such shieldend and the annular edge of said member, a grounded conveyor for moving a plurality of articles into and through a second segment of said spray, a source of high electrical potential, means for connecting said source to the atomizer to create an electrical potential difference between the atomized particles and articles within said second spray-segment to urge the particles of such segment toward deposition on such articles, and means for maintaining said deflecting electrode at a particle-repelling potential.
11. An electrostatic spray coating system comprising an atomizer including an annular-edged member mounted for rotation about an axis, means for feeding liquid coating material to the surface of said member, means for rotating said member to cause such coating material to flow to the annular edge of the member for atomization therefrom as a spray of substantially annular pattern, a shield for intercepting a substantial segment but less than all of the projected spray, said shield having a first wall extending in and transversely to the plane of the annular edge of said member in opposed radially spaced relation to such edge and at least one side wall'joining said first Wall and located in axially spaced, overlapping relation to said member, a peripheral portion of said member projecting radially outward beyond said side wall, means associated with said shield for collecting and recovering the liquid material intercepted by said shield;
from said substantial segment, a support to position an article in a coating zone in opposed spaced relation to said projecting peripheral portion of said member, a source of high electrical potential, and means for connecting said source to the shield and atomizer to create an electrical potential difference between the spray particles and the article in the coating zone to electrostatically move charged spray'particles toward and deposit them on the article in said coating zone and to maintain the shield at a potential such that it attracts said spray particles.
12. in a method of electrostaticallycoating articles wherein electrically charged particles ofliquid coating material are atomized from an annular atomizing zone and projected therefrom generally in the plane thereof with a substantial radial velocity component, the steps of maintaining in the plane of the atomizing zone two elec trically charged zones of particle-repelling potential spaced from said atomizing zoneand from each other within the limits of said spray to divide the spray into two segmental spray portions, intercepting one of said spray portions, collecting and reclaiming the liquid material so intercepted, and electrostatically depositing the second portion of said spray on the articles to be coated.
13. An electrostatic spray coating system comprising a rotating atomizer for creating and projecting into a quiescent atmosphere a spray of liquid coating material particles radiating from the atomizer outwardly across and throughout substantially the entire circumference of an annular region surrounding the atomizer, a spraycollecting shielding member spaced from said atomizer and occupying a first substantial segment but less than all of the circumference of said region and located in the paths of the spray particles within such segment to intercept spray particles within such segment, means for supporting an article to be coated Within a second segment of said region, and means for electrically charging the spray particles and for electrostatically urging charged particles in said second segment toward deposition on said supported article, said last named means including an electrode spaced from said article and shielding mem- References Cited in the file of this patent UNITED STATES PATENTS 1,022,956 Lengerke Apr. 9, 1912 2,559,225 Ransburg July 3, 1951 2,658,009 Ransburg Nov. 3, 1953 2,651,287 Turner Sept. 8, 1953 2,438,561 Kearsley Mar. 30, 1948 2,456,853 Arbrom Dec. 21, 1948 2,221,338 Wintermute Nov. 12, 1940 2,191,827 Benner Feb. 27, 1940 2,097,233 Meston Oct. 26, 1937 2,070,972 Lindenblad Feb. 16, 1937 OTHER REFERENCES No. 2 Electrostatic Process, Ransburg Electro-Coating Corp., Indianapolis, Ind., 195.