US3195819A

US3195819A - Spray nozzle for coating articles

Info

Publication number: US3195819A
Application number: US261373A
Authority: US
Inventors: Watanabe Tamotsu
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-03-14
Filing date: 1963-02-27
Publication date: 1965-07-20
Anticipated expiration: 1982-07-20
Also published as: NL290138A; LU43257A1; BE629589A; ES285532A1; GB1010618A; FR1350407A; DE1571086A1; CH412655A

Description

July 20, 1965 TAMOTSU WATANABE 3,

SPRAY NOZZLE FOR COATING ARTICLES Filed Feb. 27, 1963 6 Sheets-Sheet l A 27 28 B 5 3O 21 E,

. I L 26 31 I I 5 24 A ,,L\ Y\ July 20, 1965 TAMOTSU WATANABE 3,

SPRAY NOZZLE FOR COATING ARTICLES Filed Feb. 27, 1963 s Sheets-Sheet 2 July 20, 1965 TAMOTSU WATANABE 3,

I SPRAY NOZZLE FOR COATING ARTICLES Filed Feb. 27. 1963 e Sheets-Sheet s July 20, 1965 TAMOT'SU WATANABE 3,

- SPRAY NOZZLE FOR COATING ARTICLES Filed Feb. 27, 1963 6 sheets-sheet 4 y 5 TAMO'TSU WATANABE 3,195,819

SPRAY NOZZLE FOR COATING ARTICLES Filed Feb. 27, 1963 6 Sheets-Sheet 5 July 20, 1965 TAMOTSU WATANABE 3,1 5,8

SPRAY NOZZLE FOR COATING ARTICLES 6 Sheets-Sheet 6 Filed Feb. 27, 1963 edges and potential gradients thereof are different.

United States Patent 3,195,819 SPRAY NOZZLE FOR COATING ARTECLES Tamotsu Watanabe, 28 Yasukata-cho Ghta-ku, Tokyo, Japan Filed Feb. 27, 1963, Ser. No. 261,373 Claims priority, application Japan, Mar. 14, 1962, 37/9,798 1 Claim. (Cl. 239-601) by causing a considerable amount of coating material to rebound and scatter instead of being deposited on the article being coated. Not only does this cause a substantial loss of coating materials, but also an unsanitary condition for the operator in the spray booth is created.

With conventional air spray nozzles, in addition to the air supply means for spraying and atomizing the coating material, another specific air supply means is required to control the spray pattern and zone of discharge of the coating material particles. This tends to increase air currents and reduce, where electrostatic deposition is being used, the effect of electrostatic force.

Consequently, in electrostatic coating in which compressed air is employed as a means for atomizing the coating material, it is desirable that the air pressure should be made as low as possible in order to obtain high coating efiiciency.

' Also, one type of spray nozzle used for electrostatic coating has a coating material discharge outlet in the center thereof surrounded by a slit-shaped compressed air discharge outlet. However, in this type of nozzle, the electrostatic charge given to the atomized coating material particles is uneven between the particles in the central portion and those in the peripheral portion. Conse quently, this causes an uneven deposition of coating materials on articles to be coated, especially when the article to be coated has many uneven surfaces and sharp Furthermore, it is diflicult to impart sufiicient electrostatic charges to the atomized coating material particles because of the limited charging ability of this type of spray nozzle due to the nature of its construction, thereby requiring additional touch-up Work to even out the deposition layer.

For the purpose of lowering the air pressure, another type of nozzle is designed to have a plurality of subdivided coating material discharge outlets with respective compressed air discha-rge outlets arranged in parallel. With such spray nozzles, it is true that the velocity of the discharged coating material particles can be decreased to a certain extent and the electrostatic charges which are imparted to said particles are increased, but such a nozzle is still unable to obtain a uniform deposition of said particles on articles to be coated due to the reasons mentioned above.

Therefore, in order to avoid such uneven electrostatic charges on the particles and obtain a uniform coating layer of desired thickness on the entire surface of the arti cles to be coated, it is desirous to have an atomizing means so designed as to effect uniform corona discharges on its entire surface, and, at the same time, be able to reduce the air pressure employed for atomization to as low a pressure as possible so that the electrostatic attraction force will not be interrupted.

While spray nozzles designed to meet the above requirements may be deemed satisfactory, it will still be impossible to obtain an absolutely uniform coating layer of desired thickness on the entire surface of the article to be coated where a high potential gradient exists between the atomizing means to which high voltage is applied and the article to be coated the article being the opposite electrode. This is especially true when the article to be coated has many uneven surfaces, sharp edges, corners and the like. This tendency becomes conspicuous and is disadvantageous for practical applications, especially when the potential gradient is so great as to result in electrostatic atomization.

The purpose of my invention is to satisfy all the necessary requirements herein referred to above and to offer such an air spray nozzle which can atomize coating materials efiiciently with the lowest possible air pressure and obtain the widest possible spray pattern in the'required zone.

The principal object of this invention is to provide an improved spray nozzle with an atomizing means for coating materials.

Another object of this invention is to provide an improved spray nozzle usable for electrostatic coating under application of high voltage, for mounting to electrostatic hand spray guns or automatic electrostatic coating devices.

A further object of this invention is to provide a spray nozzle as described above having atomizing means of preselected configurations with sharp edges so that the corona discharges can be formed over the entire surface to enable it to impart uniform electrostatic charges to the atomized coating material particles.

Still another object of this invention is to provide a spray nozzle with one elect-rode or a plurality of additional corona discharge electrodes on the surface of the atomizing head for the purpose of controlling the formation of corona discharges at the atomizing means and for having electrostatic charges imparted to the atomized coating material particles mainly by said electrode or electrodes.

An additional object of this invention is to provide such spray nozzle as described above with one electrode or a plurality of said corona discharge electrodes on the surface of the atomizing head for the purpose of maintaining a potential difference between said atomizing head and the corona discharge electrode or electrodes by applying different potentials of high voltage respectively in order toimpart more uniform electrostatic charges to the atomized coating material particles.

Another object of this invention is to provide such spray nozzle as described above with the outlets of said atomizing means being so shaped as to enable it to control the spray pattern or spray zone of the atomized particles flowing towards the article to be coated.

A further object of this invention is to provide such spray nozzle as described above with a valve plate exactly fitting the inside of the coating material outlet for controlling the spray pattern and zone of coating materials by adjusting the opening degree of said outlet by means of said valve plate.

Still another object of this invention is to provide a spray nozzle as described above that can be rotated about an axis in order to obtain a circular spray pattern of coating materials.

An additional object of this invention is to provide a spraying device usable for coating work having one or a plurality of nozzles being arranged on the periphery of a rotary body, the body being rotated in a direction opposite to the direction of discharge of coating materials, and at the velocity substantially equal to the dis charge velocity of coating materials to provide substanmaterial particles around the rotary body.

will'in part be obvious and the specification. t T

The invention is illustrated in the following description and the accompanying drawings: V

FIG. 1 is a schematicview of a spray gun system; FIG. 2 is .a schematicview or aspray gun syste-rnus'ed for electrostatic coating;

FIG:.3 is. a partial "sectional view taken in a vertical plane taken along vline 3-3 ofFIG, 4, illustrating the internal structural details of a spray gun andnozzleconstructed in accordancewith the invention; f 1

FIG; 4 is 'a partial sectional elevational view taken alonglineH -of FIG,- 5 illustrating astructural section otrthe spray nozzle constructed in'accordance with'the nt Qn; i

will in part be apparent from FIG. 5 is a frontview of the spray nozzle looking in the direction indicated by line 5-3-5 of FIG. 3; 1 FIG. 6 is at partial sectional view taken in a vertical plan al ng ,n. --6 f-F G.-- 7 s owi ganalternate embodiment of the invention and illustrating a valve plate which controls the supply-and spray anglejof coating materials, and alsoillustrating the corona-discharge tially zero or near zero :velocity of atomized coating 7 direction opposite to the direction of discharge of coating materials, and at a velocitysubstantially equal to the V I Spray nozzle A shown in FIG. 1 is mounted generally on the front-endtof a spray gun Br The spray gun B is connected to a coating material supply tanlcC, and a compressed air supply source E- by a supply pipe D.

When this type of pneumatic spray gun is used for electro static coating, the spray nozzle Ais generally connected to a high voltage power pack F by 'ineans ofa high ring to FIGURES 3 to 8,.zwhere vbasic forms of the spray nozzles are'illujstrated; the body 21. of; said spray gun B has a coating material intake 23 at the front portion along its axis for receiving the coating material to electrodes which impart-the major electrostatic charges 7 to the atomized coating material particles; i 7

FIG. 7' is a partial sectional view taken along'line 7-7 of FIG. 8'showing structural section of the spray nozzle I shapes for along line 10-10 @51 FIG.;11' illustrates the spray patterns'or spray zones created by three different shaped atomizing meansrespec:

tivelyselected from amongthose illustrated in FIG, 9b,

and the planar. shapes of the atomizing means which create such patterns are illustratedrespectively in con- 7 A i c o with hc spr ypa terns 7 FIG. 12 illustrates configurations of corona discharges produced by three different shaped;;aton1izing means respectively selected from among; those 7 illustratedin FIG; 9b-under application of high voltage to said atomiz ing means; s g FIG 13 illustrates the configuration of'corona dis charges produced by straight; edge atomizing means;

FIG. l4 illustrates;the action of electrostatic; charges view of the spray nozzle looking 7 FIG. 10 is an enlarged partialsectional'view taken V sage25 through an air pool 36.

be fed toa coating material passage '23 and a valve rod inserted into .a coating material discharge orifice 24 in the'front endof said passage for controlling the flow of 'coating materials, therethrough'and an vair passage 26 alongand'inside the body 21; 'an'atomizing head 29 is removably fixed to 'the body '21 fat its front end'by .means of a set ring 28, with a packing 27. A

As shO n in FIG; '3 of ,theplane, view, the tip of said atomizing head .29 has a semi-circulararcuate outline outwardly 'swollenfrom a base 30, and as shown in FIG. 4 p P of the side view, the-tip of said atomizing head 29 has an angularly protruding'surface '31 having a slit shaped coating material-outlet 32 along the ridge-like end of the surface, communicating with the coating material passage 23 through a coating material'pool enclosedsby partition walls 33; in parallel with said outlet 32,'slitshaped comp'ressed airj discharge outlets "34'are provided;

on both sides thereof, communicating:with said air'pasw by this atomizing means 37 having said coating material outlet 32 and compressed air discharg'e outlets 34, asthe air -pressure employed for atomization is low, it is pos sible to obtain'finely atomized coating material particles pattern in the required zone. without requiring any addi-. .50

produced by said additionalcorona' discharge electrodes which impartthe major electrostatic charges to :the atomized coating material particles; FIG. 15 illustrates several'forms of the valve plates connected to valve rods to control the supply and spray angle of coating materials;

'FIG. 16 illustrates aystate of atomization of] coating materials. by one forrnof a spray nozzle and the vegtor chart explaining the attendantphenomenom', I r FIG. 17a are front. and. side views ofthe'atomizing' means showing a locus of rotation and a spray pattern produced by the atomizing means when the atomizingf head-is rotated about a fixed axiswiththelength of said coating material outlet as a radius" 7 FIG.- 17b are front-and side views v I means'showinga locus of rotation and a spray pattern produced by the atomizing head rotated about a med of the atomi'zingl with minimum :velocity and the widest possible spray tiona l aircurrentfor. controlling the original spray pattern. When high voltage-is applied to the atomizing head 29 of said spray nozzle,A, the atomizing means 37 being "designedto produce uniforrn'corona discharges along its entire sharp arcuate edges impartsmniform" electrostatic charges tothe atomized coating material particles, resulting in a uniform layer of depositionon the article to be coatedr In addition, since the air pressure employed for the purpose of atomization is low, theloss of coat- ;ing materials by oversprayingis minimized.

. By the sprayin'gimethod mentioned above and as shown diagrammatically ii -FIG.v 16, the pressure in the central port on isaerodynamically lower resulting in the inflow of air current thereto from the oppositedirection, thereby axis with the lengthof said coating material-outlet as a diameter;

FIG. 18 is a front view of a rotary" body equipped with a plurality of said atomizing nozzles onthe periphery thereof, in which; said rotary body is rotated in the rapidly diminishing the velocity of the discharged particles; as compared tothe velocity of, the particles on the outer per phery; to zero or nearly, zero at the area very close tothe center of jthe atomizin'g means. This phenomenon renders more effective the actioniof electrostatic attraction. p

However,' in this embodimennif appropriate means are not provided; it often happens" that the'deposited layer of'coating materials on thearticle. to be coated is uneven when the potential g'radientisi made toogreat between said atornizing means-37 and the articletobe coated H, or when the article to be coated has uneven surfaces,

When the atomization of coating materials is effected sharp edges or corners, or in case the atomizing means is placed excessively near the article to be coated.

To overcome this, as best shown in FIGS. 7, l and 14, additional corona discharge electrodes 40 are provided on a base ring 39 secured firmly to the base 30 of said atomizing head 29. It is necessary for said corona discharge electrodes ttl to be positioned slightly ahead of the front tip of the atomizing means 37 and each of these electrodes 4% should have a front end with a suitably sharp edge in order to control the corona formation along the surface of said atomizing means 37. At the same time, said corona discharge electrodes should be placed in such position that high voltage applied to the atomizing head 29 can also be applied to said corona discharge electrodes.

With such an arrangement, uniform and suitable electrostatic charges are imparted to the atomized coating material particles, that is, the central portion of the spray is charged by the atomizing means 37 and the outer portion of said spray is charged by said corona discharge electrodes 40 as illustrated in FIG. 14.

In the foregoing embodiment, the high voltage applied to the atomizing means 37 is also applied to the corona discharge electrode 49. However, a similar eifect may be :obtained when a pro-scribed potential ditference is given to the atomizing means 37 and these electrodes 40.

The providing of said corona discharge electrodes 40 as described hereinbefore, is effective not only to increase the coating efiiciency by controlling the electrostatic charges to be given to the atomized particles, but also protect the spray nozzle from possible damage caused by dropping or giving shock to said gun by impact with other objects, and further, avoids the possible danger of sparking caused by accidental contact of the gun with the article to be coated.

In the embodiments illustrated in FIGURES 6 to 8, a slidable valve plate 41 is provided within the coating material outlet 32 for the purpose of changing the angular aperture of the opening of said outlet 32 in order to con trol the discharge angle of coating materials. The installation of the valve plate 41 can be made by any of several desired means, but in the illustrated embodiments, the valve plate 41 is fixed to the front end of a support rod 42, which is an elongated part of a valve rod 25 controlling the flow of coating materials from the discharge orifice 24. Therefore, a simultaneous control of the supply and spray angle of coating materials is accomplished.

By sliding the valve plate 41 forward, the crescent shaped clearance shown in FIG. 6 will be gradually narrowed. In the illustrated embodiment, the valve plate is capable of controlling the spray angle in the ranges from zero to 180 degrees.

By sliding the valve plate 41 completely forward, the coating material discharge outlet 32 is tightly closed, and the spray of atomized coating material is stopped nearly instantly. This means that the spray of coating materials is perfectly controlled by said valve plate 41 and that the spray nozzle equipped with this valve plate 41 can be effectively used for an automatic coating operation as it can be easily controlled to spray only when the articl to be coated is passing in front of said nozzle by means of conveyor. For example, in an automatic coating operation for automobile bodies, it is possible to coat effectively the specific or desired portion of automobile bodies being successively transported in front of said nozzle by means of a conveyor, with the aid of a photoelectric tube interlocked with said valve plate 41.

The shape of said valve plate is not limited to be a semicircular plate, but it can be designed in any shape according to the requirement. As illustrated in FIG. 15 a semi-circular wire or strip or a plurality of said wire or strip can be used. It can also be used in the form of a semi-circular plate being cut partially in the central portion thereof so that the spray angle can be controlled at the near zero degree at the coating material discharge outlet. It is also possible to change the shape so as to meet the shape of said coating material discharge outlet employed.

The shape of the atomizing means is semi-circular in the plane view of FIG. 3, but it can be made in a polygonal or pseudoarcuate or semi-circular shape in a broad sense, or if desired, a plurality of such shapes of atomizing means can be used, also. While the atomizing means has a narrow slit-like shape in the front view of FIG. 5, it does not need to be exactly such a narrow slit-shape, but any modified shapes as illustrated in FIG. 9b can be used, also. For example, an atomizing means with a discontinuous narrow slit can be used.

However, when this spray nozzle A is used for electrostatic coating applications, the atomizing means should be provided with sharp edges so that the corona discharges can be formed over the entire surface thereof. Thus, the required spray pattern and zone of coating materials can be obtained by using the proper shape of said atomizing means 37 and valve plate 41.

FIGURES 12 and 13 illustrate the states of corona discharges formed by different shapes of the atomizing means.

All the spray nozzles as herein described either as a basic or modified embodiment of this invention can be rotated by means of a motor 44 about an axis 43, positioning the atomizing head 29 thereon, with the full length of the atomizing means 37 as the radius or the diameter as illustrated respectively in FIGURES 17a and 17b in order to obtain a circular spray pattern.

Furthermore, one or a plurality of said atomizing heads 29 having atomizing means 37, may be secured on the periphery of a rotary body 45 with the discharge direction of coating materials being tangential to the circle 46 as a locus of rotation of the atomizing head 29 as shown in FIGURES 18 and 19. Body 45 can be rotated by means of a motor 44 about an axis 43 in a direction opposite to the discharge direction of coating materials at a velocity substantially equal to the discharge velocity of coating materials and thereby zero or nearly zero velocity of atomized coating material particles can be obtained in the vicinity around the rotary body 45, and the atomized coating material can be easily and efiectively deposited on the article to be coated by the electrostatic attraction force.

As described above, this spray nozzle can be used as an atomizing means for conventional air spray guns as well as electrostatic spray guns of electrostatic coating devices and obtains a high coating efiiciency because of its specific featur of atomizing coating materials with low air pressure irrespective of the nature of coating materials whether it may be oil-based or water-based or any other coating materials.

While I have disclosed some embodiments of the present invention, it is to be understood that these embodiments are given as examples only and not in a limiting sense, the scope of the present invention being determined by the objects and the claim.

What I claim is:

A spray nozzle for atomizing liquid coating materials comprising a substantially bell-shaped housing having a long and narrow aperture therethrough, said aperture scribing an areuate path on a plane passing through the longitudinal axis of said aperture, a first plate extending into said aperture from within said bell-shaped housing on one side of said plane, said first plate having an end substantially following said areuate path and terminating at a sharp edge within said aperture, and a second plate extending into said aperture from within said bell-shaped housing on the other side of said plane, said second plate having an end substantially following said areuate path and terminating at a sharp edge within said aperture, said first and second plates forming therebetween a first narrow arcuately shaped outlet through which the liquid coating material passes, said first plate cooperating with said bell-shaped housing to define a second narrow arcuately shaped outlet, said second plate cooperating with opposite Side of and substantially parallel to said first outlet, said, second and third outlets fconimunicating with a supply source of compressed air.

References Cited by-the Examiner UNITED STATES PATENTS 2 i V ,7 I 81 1 0 De Vllblss 239 117 10 M. HENSON W001),- 1R, Primary Examiner. V

EVERETT W. KIRBY, Examiner;

4/14 Stone et al. 239'-418 3/28 Sharp 239-117 V V 8. V Parker 239-601 Tracy j 239290 ,Niebur'g 239 300 Holub etal; 239 422 Thomas et a1. 239-422 Hupp 239-422 Schweitzer et al 239-15 Point 23915