US2945472A - Apparatus for electrostatically spraying paint - Google Patents

Description

July 19, 1960 o. GENGENBACH ET AL 2,945,472

APPARATUS FOR ELECTROSTATICALLY SPRAYING PAINT Filed Jan. 23, 1956 PRESSURE-ADJUSTA BLE INVENTORS OTTO, GENGEN BACH HORST SCHENE ATTORNEYS APPARATUS FOR ELECTROSTATICALLY SPRAYING PAINT btto Gengenbach and Horst Schene, Sindelfingen, Kreis Bohlingen, Germany, assignors to Daimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany Filed Jan. 23, 1956, Ser. No. 560,825

Claims priority, application Germany Feb. 9, 1955 Claims. (Cl. 118-626) The present invention relates to a process and apparatus for coating objects with a liquid, and more particularly to a process and apparatus for electrostatically spraying paint.

The known processes exhibit the disadvantage that the paint to be sprayed can be applied to large surfaces only in a relatively uneven manner. This may be attributed to the fact that the spray-paint in the prior art devices leaves a nozzle or similar device under pressure out of a plurality of small bores from which it is usually discharged in the form of a cone or fan.

'With other known processes this disadvantage is sought to be avoided in that the paint to be sprayed is sucked or drawn off electrostatically from a stationary liquid surface. However, with this process the spray-paint can be applied or sprayed only in a horizontal direction so that objects with large surfaces to be sprayed have to be guided or moved past the stream of paint spray in a vertical direction. However, such a flow or movement of the material and goods is inappropriate in connection with modern production methods which are based on horizontal assembly lines.

Accordingly, it is an object of the present invention to provide a process and apparatus for carrying out the process which obviates all these disadvantages of the prior art.

It is another object of the present invention to provide a process and apparatus enabling the spraying of paint onto large surfaces in a very even manner.

A still further object of the present invention resides in an arrangement which permits the undercoating of large surfaces in a very even manner by electrostatically spraying the coating onto these large surfaces.

Another object of the present invention lies in the realization of a coating process, such as a paint-spraying process, which is suitable for assembly lines moving in essentially horizontal planes.

It is a still further object of the present invention to provide an installation for carrying out an improved electrostatic spraying process in which the coating material such as paint, is circulated under pressure and to provide a nozzle particularly appropriate for use in such installations.

Another object of the present invention lies in the use of an electrostatic field for drawing off the fluid to be sprayed which is subjected to a capillary action at the place where its electrostatic discharge occurs and to return to the circulatory system any excess fluid not drawn off electrostatically during the spraying action.

Still another object of the present invention resides in providing an electrostatic spraying system in which a narrow longitudinal gap exerting a capillary action on the fluid is used as a nozzle and in which the fluid is circulated under such a pressure that in the absence of and electrostatic field of predetermined strength the fluid merely flows over out of the gap but is not subjected to any discharge action.

" The present invention avoids the disadvantages of the prior art in that the liquid such as paint to be sprayed which, for example, is continuously circulated by means of a pump, leaves through a narrow longitudinal gap out of which the electrostatic suction takes place. More paint is ordinarily supplied through the gap by appropriate adjustment than is drawn oif electrostatically and the excess portion of the paint which is not drawn ofl? electrostatically for purposes of spray-painting passes over into a collecting container.

The present invention further relates to an installation and apparatus for carrying out the process.

The apparatus consists of two concentrically arranged pipe or tube sections open only on one side thereof, of which the inner pipe section serves as supply line for the spray-paint and the open gap of which serves as spray nozzle while the outer pipe section forms thereturn line for the excess paint which has flown over out of the gap.

Further objects, features and advantages of the pres ent invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein Figure 1 illustrates schematically a spraying installation in accordance'with the present invention;

Figure 2 is a perspective view through a section of the spray nozzle drawn approximately in its actual size, showing that end portion of the nozzle as seen at the left of the section line IIII of Figure 3; and

Figure 3 is a longitudinal section of the spray nozzle with the arrows indicating the path of non-sprayed liquid over-flow.

Referring now more particularly to the drawings wherein like reference numerals are used throughout the various views to designate like parts, reference numeral 6 designates a container for the paint. The paint is continuously supplied from the container 6 by means of a pump 5 through the feed or supply line 5a to the inner line or tube section 4 of the spray nozzle 3. ject 8 which may be supported from a transporting device 7, which at the same time serves as conductor, passes past or over the spray nozzle 3, the particles of the paint are subjected to the influence of an electric high voltage field which is maintained between the supply nozzle 3 connected through line 13, for example, to the positive terminal of an appropriate power supply or high voltage source and the goods or objects 8 which are connected with the negative terminal of the power supply through the conductor formed by the transporting device 7 and which serve as opposite pole of the electrostatic field. If so desired, the negative terminal of the high voltage generator HV may be connected to ground so that each object or article 8 passing the nozzle 3 constitutes a grounded mass as regards the electrostatic field. e

The actual mode of operation in the spray nozzle 3 will now be explained with reference to Figure 2. The

paint to be sprayed flows under the pressure caused by the pump 5 through the cross section 9 of the pipe 4 and leaves the same through the gap 10; The width However, the overall cross section of the gap formedbetween wall portions 4 and 4" and the pressure caused by the circulation pump 5 are so selected and adjusted with respect to each other that the paint to be sprayed would not be subjected to any spraying action out of If an obgap without the presence of an electric field of predetermined strength but would merely flow over. -'Ihe thus over-flowing paint is caught in the gaps 10a which are formed by the essentially straight, parallel wall portions 11', 11" extending parallel to and on the outside of both wall portions 4' and 4" and is thereupon returned through the annular channel 12 formed between the con centric Walls of the pipe section 4 and of the pipe section 11 into the circulatory system in any suitable manner, illustrated schematically only in Figure 1 in which the excess paint is permitted to flow back into the container 6.

During the spraying operation which occurs with the passage of the object 8 the paint is drawn 01f under the effect of the electric high voltage field to thereby prQ hre a Sp y ng r atc ing t on om he edges of the gap 10 to the objects or goods filwhich are to be coated with the paint.

The process and the described installation in accordance with the present invention ofier the advantage. with respect to those of the prior art that a surface like spray discharge of very great evenness is produced thereby.

The illustrated arrangement is particularly appropriate if objects with large surfaces are to be sprayed from the undersides thereof. However, with an inclined arrangement of the, spray nozzle vertical surfaces may also be sprayed.

The liquid used in connection with the present invention may be any suitable paint or other liquid coating material the even application of which to surfaces, particularly large surfaces, is desired.

It is understood that one end of the cross section 9 of nozzle 3, for example, the one not visible in Figure 2,

is closed in any suitable manner, while the other end is connected with the supply line 5a.

While we have shown and described one specific embodiment of our invention it is understood that the same is susceptible of many changes and modifications without departing from the spirit and scope of our invention, and we intend to cover all such changes and modifications except as defined by the appended claims.

We claim:

1. An apparatus for electrostatically spraying objects comprising supply means ofpaint, paint spray means con nected to said supply means including a nozzle, means for continuously circulating said paint under pressure from said supply to said paint spray means and back to. said supply means, said nozzle. being formed by two rela tively fixed elongated concentric members of which the inner member has a laterally exposed liquid discharge gap and forms the discharge nozzle and the outer memher an over-flow channel, said circulating means including a liquid supply line connected to one end of said inner member, said inner member being so constructed that substantially all of the liquid supplied thereto discharged through said gap, said inner member having closely spaced Walls defining said discharge gap with at least one of the walls having an electrically conducting edge, and means for establishing an electrostatic fieldin,

the region of said nozzle between said edge and an object to be coated to produce a spray discharge of said paint from the edge of the Walls of said inner member forms aid p- 2. The apparatus according to claim 1, wherein said liquid, through said spray means. to saidnozzle, said nozzle,

comprising an elongated liquid carrying line having a narrownpwardly directed longitudinal liquiddispha rge.

therein, and a channel structure at least partiallysurrounding said line to receive liquid overflow from said gap, said liquid carrying line being so constructed as to discharge liquid therefrom primarily only through said gap, and means electrically connected to an electrically conducting portion of said nozzle extending along the edge of said gap for establishing an electrostatic high voltage field within the area of said nozzle to produce a spray discharge of liquid therefrom to an object being sprayed.

4. An apparatus for electrostatically spraying objects with a liquid, comprising spray means including a nozzle, means for continuously circulating liquid through said spray means to said nozzle, said nozzle comprising a line with an upwardly directed elongated liquid discharge gap and a channel structure fixed relative said line to receive liquid overflow from the gap, means for returning said liquid overflow from said channel to said circulating means, and means electrically connected to a portion of said nozzle defining an edge of said gap for establishing an electrostatic high voltage field within the rea of said nozzle to produce a spray discharge of liquid from said gap to an object being sprayed.

5,. An apparatus for electrostatically spraying objects with a liquid comprising a source for supplying said liquid, spray means including an elongated nozzle, said nozzle comprising a tube-like structure connected to said liquid supply source for receiving liquid therefrom under slight presusre, said tube-like structure having an elongated upwardly directed gap for discharging liquid therefrom, said structure being so constructed that substantially all of the liquid passing therethrough is discharged from said gap, said gap being defined by closely spaced walls at least one of which is provided with an electrically conducting edge extending longitudinally of said gap, said nozzle further comprising a channel structure at least partially surrounding said tube-like structure and extending at least the length of the latter to receive liquid overflow from the gap, and means for establishing an electrostatic high voltage field within the area of said nozzle between said edge and an object to be sprayed to produce a spray discharge of liquid upon the latter.

6. An apparatus for electrostatically spraying objects with a liquid comprising a source for supplying said liquid, spray means including an elongated nozzle, said nozzle comprising a tube-like structure connected to said liquid supply source for receiving liquid therefrom under slight pressure, said tube-like structure having an elongated upwardly directed gap for discharging liquid therefrom, said structure being so constructed that substantially'all of the liquid passing therethrough is discharged from said gap, said gap being defined by closely spaced walls at least one of which is provided with an electrically conducting edge extending longitudinally of said gap, said nozzle further comprising a channel structure at least partially surrounding said tube-like structure and extending at least the length of the latter to receive liquid overflow from the gap, and means for establishing an electrostatic high voltage field within the area of said nozzle between said edge and an object to be sprayed to produce a spray discharge of liquid upon the latter, said liquid source including means for adjustingthe pres sure of said liquid supply with respect to the rate of liquid flow through said gap and the strength of said electrostatic field so thatin theabsence, of said. field said liquid will only flow over the edge ofv said, gap into said channel structure without being discharged as, a, spray from said nozzle.

7. An apparatus. for. electrostatically spraying objects.

with a, liquid, comprising a source for supplying. said liquid,, Spray means, including an elongated, nozzle, said.

tially all of the liquid passing therethrough is discharged from said gap, said gap being defined by closely spaced walls at least one of which is provided with an electrically conducting edge extending longitudinally of said gap, said nozzle further comprising a channel structure at least partially surrounding said tube-like structure and extending at least the length of the latter to receive liquid overflow from the gap, means for establishing an electrostatic high volatge field within the area of said nozzle between said edge and an object to be sprayed to produce a spray discharge of liquid upon the latter, and means for continuously circulating said liquid from said supply source through said nozzle and back to said source producing only overflow of said liquid from said gap in the absence of said electrostatic field.

8. An electrostatic spray apparatus comprising two telescoped tube-like members each having a longitudinally extending gap defined by spaced wall portions, the wall portions of the inner of said structures being closely spaced and extending outwardly between the wall portions defining the gap of said outer tube, said inner structure being closed to prevent discharge of said liquid therefrom except at said gap, means connected with said inner structure to supply liquid thereto, at least the portion of said inner structure extending longitudinally of said gap at the edge thereof being electrically conducting, and means for establishing an electrostatic high voltage field between the electrically conducting portion of said nozzle and an object disposed in front of said dis- 6 charge gap for producing a spray discharge of liquid upon said object, the walls of said outer tube-like structube being so positioned relative said inner structure as to receive overflow liquid from said gap and conduct said overflow liquid longitudinally of said nozzle.

9. An electrostatic spray apparatus according to claim 8, wherein the walls of said inner tube defining the discharge gap are closely spaced so that the liquid is distributed therebetween at least partially by capillary action.

10. An electrostatic spray apparatus according to claim 8, including means for receiving the overflow liquid from said outer structure and recirculating the overflow liquid to said liquid supply means.

References Cited in the file of this patent UNITED STATES PATENTS 1,416,929 Bailey May 23, 1922 1,641,403 Van Derhoef Sept. 6, 1927 1,968,687 Johnson July 31, 1934 2,111,761 Eckert Mar. 22, 1938 2,309,981 Randall Feb. 2, 1943 2,394,656 Beregh Feb. 12, 1946 2,658,009 Rausburg Nov. 3, 1953 2,685,536 Starkey et al Aug. 3, 1954 2,781,279 Miller Feb. 12, 1957 2,784,114 Miller Mar. 5, 1957 FOREIGN PATENTS 518,820 Canada Nov. 22, 1955

Images