US3556400A

US3556400A - Appliance for the electrostatic coating of objects with coating materials in liquid or powder form

Info

Publication number: US3556400A
Application number: US729297A
Authority: US
Inventors: Otto Gebhardt; Fred Luderer
Original assignee: MESSRS ERNST MUELLER LUFT und
Current assignee: MESSRS ERNST MUELLER LUFT und
Priority date: 1967-05-17
Filing date: 1968-05-15
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: ES353953A1; DE1652390A1; FR1562746A; CH466100A; BE715226A; SE330847B; GB1198946A; DE1652390B2

Abstract

An electrostatic-painting appliance operating at high voltage to ionize paints has at least two parallel-rotating discs to disperse paint on their inner surfaces over a steplike ridge. A distributor ring between the discs permits one or more paint jets to disperse paint selectively to one or both discs to thereby permit mixing or selection of separate colors or constituent parts.

Description

United States Patent Otto Gebhardt Fellbach Wurttenberg;

Fred Luderer, Weiler Z Stein, Wurttenberg, Germany May 15, 1968 Jan. 19, 1971 Messrs. Ernst Mueller, Lufl und Farbspritztechnik Winnenden, Germany a corporation of Germany May 17, 1967 Germany No. M790 16 Inventors Appl. No. Filed Patented Assignee Priority APPLIANCE FOR THE ELECTROSTATIC COATING OF OBJECTS WITH COATING MATERIALS IN LIQUID OR POWDER FORM 9 Claims, 5 Drawing Figs.

U.S. Cl 239/15, 239/224 Int. Cl. B05b 5/00 Field of Search 239/222,

[56] References Cited UNITED STATES PATENTS 1,870,099 8/1932 Croan 239/223 2,166,772 7/ 1939 Salsas-Serra 239/224 2,220,275 1 1/1940 Preston 239/223 2,369,216 2/1945 Crisp 239/223 3,346,192 10/1967 l-lege 239/223 FOREIGN PATENTS 877,857 9/ 1942 France 239/224 884,325 7/1953 Germany.. 239/224 61,429 8/1924 Sweden 239/224 Primary ExaminerLIoyd L. King Attorney-Laurence R. Brown ABSTRACT: An electrostatic-painting appliance operating at high voltage to ionize paints has at least two parallel-rotating discs to disperse paint on their inner surfaces over a steplike ridge. A distributor ring between the discs permits one or more paint jets to disperse paint selectively to one or both discs to thereby permit mixing or selection of separate colors or constituent parts.

PATENTED JAN] 9197:

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INVENTORS 0&0 Gtbmwit FveA Lw c -c APPLIANCE FOR THE ELECTROSTATIC COATING OF OBJECTS WITH COATING MATERIALS IN LIQUID OR POWDER FORM The invention concerns an apparatus for the electrostatic coating of objects with coating materials in liquid or powder form, hereinafter referred to as paint.

In German Pat. No. 1,240,764 a process for electrostatic coating by means of a rotating sprayer-head acting as a hightension electrode with the additional application of air pressure is described, in which the paint, conducted to a sprayerhead rotating at speeds of from 4,000 to preferably 20,000 r.p.m. and higher, is whirled off and vaporized. This results by purely mechanical processes from a centrifugal discharge ridge located within a Faraday cage, and in which the mechanically produced paint mist becomes charged by a hightension field. The paint emanates from centrifugal discharge ridges or points and is diverted and transported to the object being painted by the force of the electric field as well as the air pressure in a conventional manner only after reaching a certain distance from the centrifugal discharge ridge. For the execution of this process a device with a disc mounted on a rotating shaft is suggested, in which the coatingmaterial to be vaporized is applied to the backside of this disc, which has a walled ridge functioning as a centrifugal discharge ridge, and in which the disc is surrounded by a stream of air pressure directed at the work and is connected to a high-tension generator.

With this process and this device the paint delivery per unit of time can be appreciably increased, compared to the conventional spray guns that operate with electrostatics. However, this type of arrangement also has maximum limitations of paint flow in practice, since only a certain limited amount of paint can be dispersed at a predetermined number of disc revolutions per cm. of length of the centrifugal discharge ridge, and for obvious technical reasons neither the diameter of the discs nor their r.p.m. can be increased at will.

With this invention the problem of further increasing the paint flow per unit of time while maintaining a constant diameter of the spray disc and a constant rotating speed is to be solved. According to the invention this problem is solved by installing a second rotating spray disc-of at least equal diameter closely behind the first disc and concentric to it, which has a walled ridge functioning as a centrifugal discharge ridge on its front side, to which paint to be vaporized is applied.

With this invention it is possible to double the paint flow, maintaining the same diameter and the same rotation speed compared to the device of the aforesaid patent. For, in practice, it has proved out that the two paint mists coming off the two facing discharge ridges do not interfere with one another, either mechanically or electrostatically. This is contrary to the conventional electrostatic paint guns without a Faraday cage, in which the two facing ionization ridges bring about a reduced vaporizing effect and serious voltage interreactions.

The two spray discs with their dischargeridges, can be supplied with paint through one single, common source. But it is also possible, and this is particularly advantageous, to provide the two spray discs with separate, individual paint feeder jets. In the latter case then, two different materials can be simultaneously sprayed, in which case the ionization gap between the two disc ridges provides for an intensive blending action of the two paint mists. This possibility opens the way to new areas in the field of multicomponent spraying, in which, for example, the one disc may be supplied with lacquer, the other with a setting agent, or, in the case of paintblending, for instance, of metallic lacquers, in which case then the basic material is sprayed from the one ridge, and the material producing the metallic effect from the other one. Furthermore, the design incorporating the separate paint supply method can be applied to perform a rapid color changing operation, in which each of the colors is applied to one of the centrifugal discharge ridges.

In order to achieve, even greater rates of paint flow, or an even greater variety of possible combinations, it is possible also to install several paired sets of spray discs behind one another, with the paired discharge ridges facing.

Further characteristics, advantages and particulars of the invention will be found in the description, the drawings and the claims. On the drawings, features of the invention are shown in the form of examples, in which:

FIG. 1 is an elevation view, partly in cross section, of the spray head;

FIG. 2 is a similar cross section view showing a modification of the spray head;

FIG. 3 is a fragmented view, partly in cross section, through the distributor ring of the spray head of FIG. 2 in large scale;

FIG. 4 is a further elevation view, partly in cross section of a modification of the spray head of this invention; and

FIG. 5 is a fragmental view in section of a modification of the invention.

The spray head shown in FIG. 1 consists essentially of a first spray disc I0 and a second one 11 parallel to it on the same axis and equal to it in diameter. The two spray discs 10 and II are fixed in position on the rotating shaft of a motor (not shown), for example, an air pressure motor, which is installed at the forward end of a spray gun. Disc I0 has a rounded edge 12, and is equipped on its reverse side with a steplike projection at the edge of which a centrifugal discharge ridge I3 is formed. The discharge ridge 13 is set back in a radial direction from the rounded edge 12. The second disc 11 has a rounded edge 14, and is equipped on its forward edge with a steplike projection, at the edge of which a centrifugal discharge ridge I5 is formed. The

rounded edges

12 and 14, and then the two discharge ridges l3 and 15 extend the same radial distance from the revolving axis of the spray head. Between the two spray discs 10 and 11 a distributor ring 16 is installed coaxially to them, with a diameter smaller than that of the centrifugal discharge ridges I3, 15. The distributor ring 16 has a cross section whose shape resembles roughly that of an equilateral triangle, whose apex 16a is pointed toward the revolving axis of the spray head. A supply tube 17, fixed solidly to the gun and running parallelto the axis of the spray head projects into the space between the two discs 10 and II, and points its jet opening 17a toward the apex of the ring, that is, toward the inner edge 16a of distributor ring 16.

The spray head is seated, as mentioned, on the rotating shaft of a motor, and is driven by it at a speed of from 4,000 to 40,000 r.p.m. As known, a jet stream of air pressure is directed at the spray head in such a way, that the spray head is surrounded by the air current directed at the work. Furthermore, the spray head is connected to a high-tension generator, by means of which it is kept under a tension of, for example, 50 to kv. The outer

sharp edges

12 and 14 of the spray head, therefore, act as ionizing edges.

If now paint is applied through tube 17, it reaches the inner edge 16a of the rotating distributor ring 16. The edge 16a separates the oncoming stream of paint into two equal parts, which are moved across the sloped flanks of the distributor ring 16, and over the'reverse side of disc 10 and the forward side of disc 11, out to the ridges l3 and 15, by the centrifugal forces generated, and are whirled radially outward by these ridges at a high rate of speed. The paint materials whirled off by ridges 1'3 and 15 burst immediately into minute particles as a result of impact with the air and the resulting sudden and severe braking action, so that a mist of paint is created inside the circular gap formed by the

edges

12 and 14, which flies out of the gap at reduced speed without touching

edges

12 and 14 themselves. The air

stream surrounding edges

12 and 14 seizes the paint mist coming out of the gap, directs it at the object to be painted, and forms a cone of air around the paint mist on its way to the work, preventing the escape of any of the paint particles outside the desired pattern. The electrostatic field set up by the introduction of high-tension electricity between the discharge ridges on the one hand and the work on the other ionizes the paint mist as it crosses an imaginary plane formed by the

outer edges

12 and 14 and speeds the particles of paint along the lines of the lines of the field toward the work. Since the field needs only to transport the finely atomized particles of paint and is, in addition, supported by air pressure in this transportation process, only relatively low field intensities are required.

In the spray head of this invention, then, the paint fed into the apparatus is distributed to two opposing centrifugal discharge ridges l3 and 15, which bring about a dispersion of the paint independent from one another. Compared to a spray head with but a single discharge ridge, here a discharge ridge increased to twice the length at the same disc diameter is realized. Now since the maximum paint flow is directly dependent on the length of the centrifugal discharge ridge, paint discharges increased by I per cent can be achieved with the spray head of this invention, without affecting adversely the quality of paint atomization, i.e., the fineness of the produced paint mist.

FIG. 2 represents a second embodiment of the spray head of this invention. This differs from the one described above simply with regard to the method of paint supply and the shape of the distributor ring. According to FIG. 2 two paint supply jets l8 and 19 are provided, in which the jet aperture l8a of the one tube is directed at the upper inclined surface of the distributor ring 16, and jet aperture 19a of tube 19 at the lower one. On the outer surface of the distributor ring 16, which is parallel to the rotating axis of the spray head, a guide ring 20 capable of adjustment is installed coaxially to the distributor ring in such a way that the gap for the passage of paint can be adjusted at will.

With the spray head of FIG. 2, it is possible to spray out two different substances simultaneously from the two

spray discs

10 and 11. As previously pointed out, it is possible to in troduce, for instance, lacquer through tube 18 and a drying agent through tube 19, if multicomponent materials are to be sprayed. The blending of the lacquer with the drying agent takes place only after the substances leave the discharge ridges l3, in an atomized state. It is furthermore possible with this spray head to change lacquers in extremely short sequences. In such a case, tube 18 would feed the one, for instance, the black lacquer, and tube 19 the other, for instance the white lacquer, so that rapid changes from one color of lacquer to the other are feasible without the necessity of cleaning the head between changes.

A particularly fine atomization of the painting material can be attained when the discharge ridges l3, 15 are radially straited. It is also possible, as shown in FIG. 3, to apply radial groovings 21 to the guide ring 20, in order to achieve an especially uniform distribution of paint on its way out to the discharge ridges. These riflings in the discharge ridges and/or in the guide ring eliminate air intrusion into the paint and bring about, particularly in extremely viscous lacquers, an appreciably improved surface quality in the applied layer of paint.

The spray head shown in FIG. 4 reveals the same basic structure as the one in FIG. 2; however, four discharge ridges are provided. To do this, a discharge ridge 22 is also provided on the reverse side of disc 1 l, and besides, another spray disc 23 with discharge ridge 24 is added. In the space between the reverse side of disc 11 and disc 23 another distributor ring 25 with guide ring 26 is inserted. The paint supply to the four discharge ridges l3, 15, 22 and 24 is done by the four

jet apertures

18a, 18b, 18c and 18d of paint supply tube 18 or, perhaps, as it does not show in the drawing, by four separate, individually adjustable paint tubes. The mode of operation of the spray head is obviously identical with that of FIG. 2, in which, however, it is possible to increase the paint flow even more, or, for instance, in the case of individual paint supply tubes, to spray simultaneously four different paint or lacquer components. In order to achieve a uniformly perfect blending of the paint mist coming off the four discharge ridges it is advantageous to perforate the

spray discs

10 and 23 with angular air-attracting holes 27, which pierce the disc obliquely and open to the cutback surfaces of the spray ridges l3 and 24.

Finally, in FIG. 5, a modification of the spray head ofthis invention is shown, for producing a spray pattern of a smaller diameter, in which, built on the same principle, eight

discharge ridges

28, 29, 30, 31, 32, 33, 34 and 35 are installed behind one another. In this system the arrangement is so constructed that the paired ridges facing one another 28 and 29, 30 and 31, 32 and 33, 34 and 35 always have the same diame ter, but that the diameters of the pairs increase from front to back, so that the ridge pair 28, 29 has the-smallest diameter, and the ridge pair 34, 35 the largest one. In order to achieve a uniformly perfect blending and ionization of the paint mist, the entire spray head is encircled, with spacing, by a hull-like guide funnel 36, whose leading edge 36a facing the work functions as an ionizing edge. With this arrangement the paint mist is not electrostatically charged until it leaves the guide funnel 36. With this arrangement the optimum ratio between paint supply to length of discharge ridge occurs automatically. To help this process appropriately designed and selected passages to the individual discharge ridges, combined with spillover provisions according to the cascade principle can be added.

We claim:

1. An appliance for electrostatic coating of objects with coating materials in liquid or powder form with a centrifugal discharge device operated at a high electrical potential comprising in combination, at least two parallel discs mounted on a common axis of rotation, with each disc having a steplike projection in the common passageway between the discs to serve as a centrifugal discharge ridge, the discs being mounted with ridges on the discs facing each other, means supplying said materials to the inner surface of each disc to flow separately over both respective discharge ridges and an outer ionizing gap between the outer disc edges coupled with said potential positioned to react electrostatically with the coating materials discharged from each said ridge separately without electrostatic interference.

2. An appliance as defined in claim 1, wherein the means supplying said materials to each disc comprises a rotating distributor ring coaxially located between said discs with surfaces directing the materials respectively toward the two different discs with at least one material jet directed at the ring.

3. An appliance as defined in claim 2, including separate jets each directed to a respective one of said distributor ring surfaces and each jet separately controlled, whereby different material sources may be used.

4. An appliance as defined in claim 2, including an adjustable guide ring coupled to said distributor ring adapted to control the gap for passage of materials.

5. An appliance as defined in claim 1, wherein the discharge ridges have radially disposed grooves.

6. An appliance as defined in claim 2, wherein the distributor ring has radially disposed grooves.

7. An appliance as defined in claim 1, including at least three parallel discs with said means supplying materials disposed between a central disc and each facing disc.

8. An appliance as defined in claim 7, including a guide cylinder encasing the discs and directed with a leading edge along the axis of rotation of the disc, whereby the leading edge serves as an ionizing edge.

9. An appliance as defined in claim 7, wherein at least two pairs of discs are provided with different diameters.