US3281076A - Method and apparatus for atomizing liquids - Google Patents

Description

OCL 25, 1966 BURNSlDE ET AL 3,281,076

METHOD AND APPARATUS FOR ATOMIZING LIQUIDS Original Filed June 11, 1964 2 Sheets-Sheet 1 lAl .ON

GILBERT L.BURN$|DE JOHN W. MISTELE mvmroas BY I, B, F 0 6 ATTORNEYS Eo mwwum Oct. 25, 1966 G. L. BURNSIDE ET AL 3,281,076

METHOD AND AFPARATUS FOR ATOMIZING LIQUIDS Original Filed. June 11, 1964 2 Sheets-Sheet 2 FIG. 2

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GILBERT L. BURNSIDE JOHN W. MISTELE TNVENTORJ ATTORNEYS United States Patent 3,281,076 METHOD AND APPARATUS FOR ATOMIZING LIQUIDS Gilbert L. Burnside, Oak Park, and John W. Mistele, Detroit, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Original application June 11, 1964, Ser. No. 375,425, now Patent No. 3,224,680, dated Dec. 21, 1965. Divided and this application June 4, 1965, Ser. No. 461,259

11 Claims. (Cl. 2397) This application is a division of our application Serial No. 375,425, filed June 11, 1964, now Patent No. 3,224,680.

This invention relates to a method and apparatus for comminuting liquid coating materials and for the electrostatic transportation of the comminuted particles for deposition on an article. It is particularly directed to the repetitious electrostatic painting of similar articles in which the paint is first atomized by centrifugal force and then, after receiving an electrical charge, transported to and deposited on the surface of an article to be painted.

The painting art has resorted to the use of rotating atomizing heads such as metallic cups or discs for the production of a charged mist or spray of paint. These metallic atomizing heads are rotated about their own axis, and paint is fed to the central portion of the head from whence is flows to the periphery of the head under the influence of centrifugal force. At the periphery, the paint may also be atomized electrostatically and, therefore, departs from the atomizing head in a direction which amounts to the vector sum of the centrifugal and electrostatic forces.

'P-resent practices of delivering liquid coating materials such as paint to the center portion of an atomizing head require a conduit means extending through the inner shaft which supports the head as illustrated in US. Patent 2,759,763. Another type of atomizing head in the prior art is center fed through a non-rotating nozzle located in the center of a cup which .is connected to a paint supply tube as depicted in US. Patent 2,922,584.

The method for center feeding paints to the atomizing surfaces or edges of atomizing devices used for electrostatic p-ainting in the present state of the art has been found to be unsatisfactory as it is difficult to obtain uniform wetting of the atomizing surfaces or edge, especially at high speeds of rotation. Incomplete or uneven wetting results in spitting or nonuniform atomization of the paint. Also, liquid coating materials and cleaning solvents have a tendency to penetrate the bearings supporting the rotating atomizing head through the inherent clearances between rotating and nonrotating members. Seepage of coating materials such as red oxide primer, which is highly abrasive, results in extensive wear of bearing surfaces. Further, low viscosity solvents used for flushing liquid coating materials from the atomizing devices penetrate the bearings and seals due to the vibrations and centrifugal forces present in the operation of these atomizing devices. Seals such as 0 rings and gaskets are chemically attached by the solvents that also dissolve and destroy the effectiveness of lubricants applied to moving parts.

The method and apparatus of this invention overcome the deficiency of the center feed atomizing devices by feeding the liquid coating material first to a cavity machined into the hub portion of the atomizing head where complete distribution of the coating material is effected. Then the coating material flows uniformly from the cavity through a plurality of passages to the feeding zone of the atomizing head from whence it continues to be distributed to the periphery of the head so as to Wet the entire edge under the influence of the centrifugal and inertial forces. Actually, the cavity acts as a storage reservoir for the liquid coating material before it is forced out through the passages at a uniform rate and pressure to the feeding zone.

An object of this invention is to provide an atomizing device to be used for the commercial application of electrostatic paint coatings involving centrifugal atomization.

A further object of this invention is to providean atomizing device in Which the liquid coating material is fed from a cavity located in one surface of the atomizing head through passages to the periphery of the head where it is atomized.

A still further object is to provide a spraying device for electrostatic coating which is relatively free from breakdown and requires little or no maintenance.

Other objects and advantages of this apparatus will become more apparent as this description proceeds, particularly when considered in conjunction with the drawings in which:

FIGURE 1 is a side elevational view, partially in sec- ,tion, of the spraying apparatus of this invention; and,

FIGURE 2 is a front view of the atomizing head of the spraying apparatus of this invention.

In FIGURE 1 can be seen a spraying device 11 comprising an atomizing head 12 which may be in the form of a bell, cup, disc, or plate. The atomizing head 12, in this instance, has a tubular hub portion 13 on one end which is integrally formed with a cup-shaped body portion 14 on the other end. The cup-shaped body portion 14 is concentric and coaxial with the tubular hub portion 13.

The atomizing head 12 is rotated 'by a driving means, such as an air motor 15, which is supplied by compressed air through coupling 16. Spent air is exhausted from the air motor 15 through a second coupling 17. The air motor '15 is contained in a housing 18 by screws 19. The housing 18, the air motor 15, and its associated atomizing head 12, which are preferably constructed out of metal, are charged to a high potential by a voltage source 20 by means of conduit 21.

The housing 18 is attached to a support plate 22 by studs 23. Each stud 23 is locked to a handle 24 bya dowel pin 25. Manual rotation of the handle 24 adjusts the housing 18 audits contained spraying device 11 to assure that the atomizing head 12 is properly aligned with the surfaces of an article (not shown) to be coated. The support plate 22 is attached to a clamp 26 which permits the mounting of the spraying device 11 on a post 27. The post 27, which is usually manufactured from a dielectric material, may be installed in a spray booth or other enclosure.

The atomizing head 12 is provided with a bore 28 which is concentric with the axis of rotation of the atomizing head 12 and the air motor 15. A bushing 29 in the bore 28 receives shaft 30 of the air motor 15. The atomizing head 12 is driven by the shaft 30 through a pin 31 held in a vdrive plate 32. The drive plate 32 is secured to the atomizing head 12 by screws 33. To retain the atomizing head 12 on the shaft 30, a stop plate 34 is screwed onto the threaded end portion of the shaft 30. A set screw 35 looks the stop plate 34 to the drive plate 32 in order to retain the rotating atomizing head 12 on the shaft 30 during the operation of the spraying device 11. t

The hub portion 13 of the atomizing head 12 has a con centric annular cavity 36 machined into its back surface 37. The internal peripheral and bottom surfaces of the cavity 36 are sloped to form a recessed continuous outer corner 38 at their junction. A continuous radius 39. is formed in the corner 38. The cup-shaped body portion 14 of the atomizing head 12 has an internal, concaveshaped feeding zone 40 terminating in a circular atomizing edge 41.

cavity 36 in a counterclockwise direction. same angular direction in which the atomizing head 12 is rotated (as designated by arrow).

- air motor 15.

cavity'36 in communication with the feeding zone 40 of the body portion 14 of the atomizing head 12. The passages 42 are sloped outwardly from the recessed outer corner 38 of the cavity 36. The cavity 36, as it is annular shaped, also has a continuous recessed inner corner 54.

An axially mounted liquid coating material delivery tube 43 is held in the housing 18 by a screw 44. The delivery tube 43 is supplied with a liquid coating material through a hose 45 connected to a coupling 46. A valve 47 installed in the hose 45 regulates the flow of the liquid coating material that may be fed from a reservoir 48 by a pump or by any other suitable means. A nozzle 49, which is attached to the front end of the delivery tube 43, feeds the liquid coating material to the inner corner 54 of the' cavity 36 of the atomizing head 12.

As seen in FIGURE 2, the nozzle 49 is angled in order to feed the liquid coating material to the corner 54 of the This is the The passages 42, as best seen in FIGURE 2, are equally spaced to permit the uniform distribution of the liquid coating material from the feed tube 43 to the feeding zone 40 of the atomizing head 12. Experimentally, it has been determined that, for liquid coating materials such as automotive paints, the

, angular spacing of the passages 42 should not exceed 6.

In the utilization of this apparatus for priming of sheet metal parts, eighty tubular passages, each of .062 inch diameter and placed 4% apart, were found to be satisfactory.

In the application of the method and apparatus of this invention, liquid coating materials are fed to the cavity 36 while the atomizing head 12 is being rotated by the It is essential that the atomizing head 12 rotates rapidly to enable the paint to be atomized by centrifugal action. Rotating speeds of 1,200 to 5,000 rpm. have been found very satisfactory for a six-inch atomizing head 12 with a conventional liquid prime coating material. The rotational speed may be varied to accommodate such variables as paint viscosity, paint composition, and temperature. The high potential impressed on the atomizing head 12 and the steep electrostatic gradient immediately adjacent to the edge 41 of the atomizing 'head 12 charge the atomized particles of paint and permit their acceleration, transportation, and deposition by the electrostatic field existing between the atomizing head 12 and the article to be painted.

The liquid coating material flows from the reservoir 48 to fill the cavity 36 of the atomizing device 11 when valve 47 is opened. Then the coating material is forced outwardly from the cavity 36 through the passages 42 at a uniform rate and pressure to the feeding zone 40 by virtue of the centrifugal and inertial forces acting on it. The liquid coating material continues to flow to the peripheral edge 41, wetting the entire feeding zone 40 of the atomizing head 12 during its rotation. contact with the shaft 30 or the bushing 29 to cause seep- No liquids come into age between the rotating and stationary members of the atomizing device 11. a

It has been found that the provision for a large number of tubular passages 42 results in a more uniform distributionof liquid coating material on the entire surface of the feeding zone. This avoids what is commonly referred to as .a stripping effect or incomplete wetting of 'the surface of the cup. To assure that the flow of liquid coating material is eifectedthrough all passages at one time 'and at a uniform rate and pressure, it is essential that the liquid coating material has to be accumulated within the cavity to a certain depth prior to being distributed therefrom to the feeding zone. This is achieved by feeding the coating material to the inner corner 54 and by sizing the tubular passages'42 so that they initially impede the flow, thereby causing a backup of liquid coating material in the 4 cavity 36 to establish a reservoir therein. The steady accumulation of liquid coating material in the cavity 36 will provide a sutficient pressure head due to the centrifugal and inertial forces acting thereon to force the liquid coating material through the passages 42 at a uniform pressure and rate to the feeding zone 40 to establish a flow balance between the nozzle 49 and the peripheral edge 41 at the speed of rotation of the atomizing head 12. The angling of the nozzle 49 further assures uniform distribution of the liquid coating material in the cavity 36, especially at high speeds of rotation.

The design of the atomizing device 11 of this invention permits the utilization of more than one delivery tube 43 to feed paint to the liquid receiving cavity 36 of the atomizing head 12. As can be seen in FIGURE 1, a second delivery tube 50 with its nozzle 51 (as shown in phantom lines), may be mounted around the periphery of the atomizing head 12. This second feed tube 50 may be connected to a second reservoir 52 and regulated by a valve 53 installed between the reservoir 52 and the atomizing device 11. Delivery tube 50 and other delivery tubes, if desired, may be installed in housing 18 similar to delivery tube 43. V

The use of a plurality of delivery tubes 43 and 50 permits the mixing of liquid coating materials of different colors or compositions by opening valves 47 and 53 simultaneously. Also, it is possible to switch from one color to a second color without requiring the flushing out of the various delivery tubes 43 and 50. An alternate arrangement can be eifected to permit the instantaneous cleaning of the atomizing head 12 by connecting delivery tube 50 to the reservoir 52 filled with a solvent. Then, by opening valve 53, the atomizing head 12 is cleaned while paint may be retained in delivery tube 43, ready for painting, by keeping valve 47 closed.

We claim:

1. A method for atomizing at least one liquid with a rotatable atomizing head, said atomizing head having a recessed liquid receiving cavity located thereon and a feeding zone terminating in a peripheral edge which defines unrestricted circular exit means from said feeding zone and is located on the side of the atomizing head remote from but in communication with said liquid receiving cavity, said method comprising the steps of rotating said atomizing head, feeding liquid to said cavity, and restricting the flow of liquid from said cavity to said feeding zone to cause the accumulation of liquid in said cavity until a flow balance is established therebetween resulting in a uniform continuous flow of liquid to said feeding zone from said cavity at a given rate of liquid feed and speed of rotation for said atomizing head.

2. A method for atomizing liquid with a rotatable atomizing head, said atomizing head having a recessed liquid receiving cavity located thereon and a feeding zone terminating in a peripheral edge which defines unrestricted circular exit means from said feeding zone and is located on the sideof the atomizing head remote from but in communication with said liquid receiving cavity, said method comprising the steps of rotating said atomizing head, feeding liquid to said cavity, .and restricting the flow of liquid from said cavity to said feeding zone to cause the accumulation of liquid in said cavity to a certain depth until the head of said liquid accumulate d therein will result in the distribution of liquid therefrom to said feeding zone at a uniform pressure and rate and from said feeding zone to said peripheral edge to place the flow in balance under the influence of centrifugal and inertial forces.

3. A method for atomizing liquids with a rotatable atomizing head, said atomizing head having a recessed liquid receiving cavity located thereon, a feeding zone terminating in a peripheral edge which defines unrestricted circular exit means from said feeding zone and is located on the side of the atomizing head remote'from said liquid receiving cavity, and a plurality of passages placing the feeding zone in communication with said liquid receiving cavity, said method comprising the steps of rotating said atomizing head, introducing liquids to said cavity, sizing said passages so as to impede the flow of liquids from said cavity to said feeding zone through said passages to cause the accumulation of liquids in said cavity until the head of said accumulated liquids therein brings about the distribution of liquids through said passages at a uniform pressure and rate to said feeding zone and from said feeding zone to said peripheral edge to place the flow in balance under the influence of centrifugal and inertial forces for an established rate of liquid feed and speed of rotation of said atomizing head.

4. A method for atomizing liquids with a rotatable atomizing head, said atomizing head having a recessed liquid receiving cavity located thereon, a feeding zone terminating in a peripheral edge which defines unrestricted circular exit means from said feeding zone and is located on the side of the atomizing head remote from said liquid receiving cavity, and a plurality of passages placing said feeding zone in communication with said liquid receiving cavity, said method comprising the steps of rotating said atomizing head, introducing liquids to said cavity at a point remote from said passages and restricting the flow of liquids by sizing of said passages so as to cause the accumulation of liquids in said cavity to a substantially uniform depth until the head of said accumulated liquids therein under the influence of centrifugal and inertial forces acting thereon will effect a flow of a uniform pressure and rate through said passages to said feeding zone to place the flow of liquids from said cavity to said peripheral edge in balance.

5. A method for atomizing a plurality of liquid coating materials with a rotatable atomizing head comprising the steps of rotating said atomizing head, actuating a means for sequentially introducing a first liquid coating material through a first conduit means and a second liquid coating material through a second conduit means to an annular recessed liquid receiving cavity located on one surface of said atomizing head, said atomizing head having a plurality of tubular passages to place a second surface remote from said one surface in communication with said liquid receiving cavity, said second surface terminating in a continuous peripheral edge which defines unrestricted circular exit means from said atomizing head for liquid introduced to said second surface from said liquid receiving cavity, and restricting the flow of each of said liquid coating materials by sizing said tubular passages so as to cause the accumulation of liquid coating material in said cavity until the head of said accumulated liquid coating material therein under the influence of centrifugal and inertial forces acting thereon will effect a flow at a uniform pressure and rate through said tubular passages to said second surface to place the flow of liquid coating material from said receiving cavity to said continuous peripheral edge in balance.

6. A method for atomizing at least one liquid with a rotatable atomizing head having a feeding zone on one side thereof, said feeding zone being essentially defined by a concave surface terminating in a peripheral edge which in turn defines unrestricted circular exit means from said feeding zone, an annular recessed liquid receiving cavity in a side opposite said feeding zone, a plurality of passageways interconnecting said annular cavity and said feeding zone, and providing means for fluid communication between a peripheral portion of said annular cavity and a plurality of sites on said concave surface substantially evenly spaced from each other and from said peripheral edge, and drive-and-support means positioned on said side opposite and concentric with the axis of rotation of said head, said method comprising the steps of introducing liquid into said cavity and rotating said atomizing head at a rate sufficient to generate centrifugal forces and distribute said liquid about said peripheral portion of said annular cavity and provide a uniform continuous flow of said liquid through said plurality of passage-ways to said plurality of sites and thence along said concave surface to said peripheral edge.

7. The method of claim 6 wherein said passages are sized so as to impede the flow of said liquid from said cavity to said feeding zone through said passages to cause accumulation of liquids in said cavity sufficient to provide a uniform liquid pressure within the several passages of said plurality of passages and a uniform rate of liquid flow at said sites into said feeding zone.

8. The method of claim 6 wherein the flow of liquid to said plurality of sites from said cavity proceeds substantially tangentially of said peripheral portion of said cavity.

9. The method of claim 6 wherein said liquid enters said feeding zone at a plurality of sites positioned intermediate the axis of rotation of said head and said peripheral edge.

10. The method of claim 9 wherein said liquid enters said feeding zone at sites positioned a distance from said axis of rotation substantially less than the distance between said sites and said peripheral edge.

11. The method of claim 9 wherein said liquid is introduced into said annular cavity in the angular direction of head rotation.

References Cited by the Examiner UNITED STATES PATENTS 3,121,024 2/1964 Wampler et al. 239-223 FOREIGN PATENTS 101,440 4/ 1941 Sweden.

M. HENSON WOOD, JR., Primary Examiner.

ROBERT B. REEVES, Examiner.

R. S. STROBEL, Assistant Examiner,

Claims (1)

1. A METHOD FOR ATOMIZING AT LEAST ONE LIQUID WITH A ROTATABLE ATOMIZING HEAD, SAID ATOMIZING HEAD HAVING A RECESSED LIQUID RECEIVING CAVITY LOCATED THEREON AND A FEEDING ZONE TERMINATING IN A PERIPHERAL EDGE WHICH DEFINES UNRESTRICTED CIRCULAR EXIT MEANS FROM SAID FEEDING ZONE AND IS LOCATED ON THE SIDE OF THE ATOMIZING HEAD REMOTE FROM BUT IN COMMUNICATION WITH SAID LIQUID RECEIVING CAVITY, SAID METHOD COMPRISING THE STEPS OF ROTATING SAID ATOMIZING HEAD, FEEDING LIQUID TO SAID CAVITY, AND RESTRICTING THE FLOW OF LIQUID FROM SAID CAVITY TO SAID FEEDING ZONE TO CAUSE THE ACCUMULATION OF LIQUID IN SAID CAVITY UNTIL A FLOW BALANCE IS ESTABLISHED THEREBETWEEN RESULTING IN A UNIFORM CONTINUOUS FLOW OF LIQUID TO SAID FEEDING ZONE FROM SAID CAVITY AT A GIVEN RATE OF LIQUID FEED AND SPEED OF ROTATION FOR SAID ATOMIZING HEAD.

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