US3392043A

US3392043A - Electrostatic coating apparatus and method for applying a hammer tone finish to an article

Info

Publication number: US3392043A
Application number: US398554A
Authority: US
Inventors: James R Maugans
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1964-09-23
Filing date: 1964-09-23
Publication date: 1968-07-09
Anticipated expiration: 1985-07-09

Description

July 9, 1968 .1. R. MAUGANS ELECTROSTATIC COATING APPARATUS AND METHOD FOR APPLYING A HAMMER TONE FINISH TO AN ARTICLE 2 Sheets-Sheet 1 Filed Sept. 23, 1964 IN VENTOR.

A TT'ORNEYS.

y 9, 1968 J. R. MAUGANS 3,392,043

ELECTROSTATIC COATING APPARATUS AND METHOD FOR APPLYING A HAMMER TONE FINISH TO AN ARTICLE 2 Sheets-Sheet 2 Filed Sept. 23, 1964 INVE/V TOR heggwdym y l m] A TTORNEYS ywm I Mi

United States Patent 0 3,392,043 ELECTROSTATEC COATING APPARATUS AND METHOD FOR APPLYING A HAMMER TONE FINISH TO AN ARTICLE James R. Maugans, Peru, Ind., assigns: to Ranshurg Electra-Coating Corp., a corporation of Indiana Filed Sept. 23, 1964, Ser. No. 398,554 11 Claims. (Cl. 117-37) ABSTRACT OF THE DISCLOSURE An electrostatic coating apparatus and method for applying a hammertone finish to an article. The article is carried on a loop conveyor through a coating zone around a rotating disc atomizer. An auxiliary electrode adjacent a portion of the periphery of the disc alters the electrostatic field conditions so that the paint discharged into the final portion of the coating zone has a larger particle size than that discharged into the initial portion of the coating zone.

This invention is concerned with an apparatus and method for applying a hammer finish to articles, utilizing electrostatic coating techniques.

The hammer finish is one in which the coating, as a paint, is patterned, having the appearance similar to that of a surface tapped with a rounded head of a ballpeen hammer. A finish of this type aids in hiding surface defects of the article, yet is smooth and may be readily cleaned by wiping, in contrast with the wrinkle finish which traps dirt in small cracks.

In the past, hammer finishes have been applied by either of two methods. In the first, utilizing a two-coat application, the article is sprayed with the desired paint in which there has been dispersed a small percentage of leafing or non-leafing metallic pigment. Then when the paint is partially set, it is sprayed with droplets of paint thinner which produce localized Wet areas in which metallic pigments can orient to produce the desired pattern. The second method produces a hammer pattern with a one-coat hammer material. The two-coat method has the obvious disadvantage, compared to a one-coat operation, of requiring a duplication of equipment and labor. A one-coat hammer coating material includes a component which has an incompatibility with other components of the coating so that areas will be formed on the film where this incompatibility shows itself as the film dries to form the hammer pattern. Great care is required in adjusting the solvent content of one-coat paints to insure that the deposited film has the correct degree of wetness to produce a large hammer pattern while achieving a satisfactory film thickness without sagging of the film. This solvent adjustment has made the application of one-coat hammer tone finishes somewhat difiicult to control. To aid in overcoming this difiiculty, one-coat hammer finishes normally are applied with air spray devices where the degree of atomization and the rate of film buildup can readily be controlled.

In the electrostatic application of hammer finishes, the hammer characteristics have been more difficult to overcome. Because of the fine atomization which is obtained with electrostatic spraying apparatus under normal operating conditions, the paint arrives at the article to be coated in a relatively dry condition so that the areas of incompatibility cannot develop within the coating material and the pigment orientation in these areas is not sufficient to 3,392,043 Patented July 9, 1968 produce a marked hammer pattern. The addition of high boiling point solvents does not completely solve the problem because of the difficulty of obtaining a satisfactory film thickness without the film sagging. Attempting to spray electrostatically under conditions of poor atomization results in poor transfer efiiciencies, poor wrap around deposition, and a poor over-all quality of finish.

This invention is concerned with the utilization of electrostatic coating apparatus and method in the application of a hammer finish. An improvement in the uniformity of the hammer design is achieved in addition to the high quality finish and the coating material savings associated with electrostatic coating operations.

One feature of the invention is the provision of an apparauts for applying a hammer finish to an article, including a source of coating material connected with an atomizing device, a source of high voltage which establishes an electrostatic field between the atomizing device and the articles being coated, and a means for varying the size of coating material particles. More particularly, a rotating disc atomizer is utilized and in a preferred embodiment of the invention an auxiliary electrode is located adjacent at least a portion of the periphery of the disc atomizer, affecting the electrostatic field gradient over that portion of the periphery of the disc atomizer to cause variation in the coating characteristics of the apparatus and thus vary the size of the coating material particles. The degree of hammer effect may be varied by adjusting one or more of the configurations of the auxiliary electrode, its location with respect to the periphery of atomizing disc, or the voltage to which the auxiliary electrode is charged.

Another feature of the invention is that the article being coated passes through an extended coating zone and the disc distributes coating material in such a manner that several applications of the material are made to the article during its passage through the zone. The coating characteristics of the atomizer are atfected so that the size of the coating material particles is larger over a portion of the extended coating zone which portion is also extended enough that the entire article surface is exposed to at least one complete application of a full range of particle sizes.

A further feature of the invention is that the electrostatic field gradient over a portion of an electrostatic disc atomizer is reduced sufiiciently that poor atomization occurs over this portion of the periphery of the disc.

Still another feature of the invention is that the auxiliary electrode extending over a portion of the periphery of the rotating disc atomizer affects the uniform flow of coating material to atomizing edge in such a manner that large paint particles are formed over a portion of the periphery of the disc atomizing device.

A further feature of the invention is the method of applying a hammer tone coating to an article including the steps of atomizing coating material, establishing an electrostatic field which etfects the transfer of atomized particles of coating material to the article being coated, and affecting an operating condition of the atomizing step to vary the size of the particle of coating material produced over at least a portion of the coating zone through which the article passes.

Further features and advantages of the invention will be readily apparent from the following specification and drawings, in which:

FIGURE 1 is a diagrammatic plan view of an apparatus employing the invention:

FIGURE 2 is an elevation view of the apparatus of FIGURE 1;

FIGURE 3 is a plan view of a disc-type atomizer, embodying the invention; and

FIGURE 4 is an edge view of the disc of FIGURE 3.

The advantages of electrostatic coating in terms of quality of the finish and efliciency of the coating material deposition are well known and will not be discussed here. It is s-ufiicient to note that the present invention provides an apparatus and method for achieving a uniform improved hammer finish While at the same time enjoying many of the other benefits of electrostatic procedures.

Turning now to the drawings, FIGURES 1 and 2 illustrate an electrostatic coating system utilizing a rotating disc atomizer of the type illustrated in Simmons Re. 24,602, which may be utilized in the practice of the present invention. In FIGURE 1 a rotating disc is shown diagrammatically, with the articles to be coated, as panels 11, carried by a conveyor in a generally annular path 13 around the disc. Coating material is discharged from the rotating disc 10 around the periphery thereof providing an extended coating zone through which-the panels 11 move. As will appear, the disc 10 is maintained at a high DC. potential with respect to the articles which are grounded, establishing an electrostatic field therebetween. The particles atomized on the edge of the rotating disc are charged and deposited on the articles to be coated through action of the field. The DC. potential which establishes the electrostatic field may be, but is not necessarily, well filtered. The specific potential figures given represent the average value of unidirectional potential without regard to the peak value of an alternating component which may be present.

In order to coat completely a large article, it may be necessary to provide a relative movement between the disc and article, as by vertically reciprocating the disc while the articles pass through the coating zone. FIG- URE 2 illustrates an apparatus in which the disc is reciprocated. The articles 11 are supported by hangers 14 from a conveyor 15 and move in a generally circular path around atomizing disc 10. Disc 10 is carried on a shaft 17 which extends from disc drive motor 18. Drive shaft 17 extends through a metal tube 20 which depends from an insulating support 21, passing through a metal sleeve 22 carried by a fixed insulating support 23. A high voltage DC. power supply 24 is mounted on insulating member 23 and has one terminal connected to a high voltage cable 25 which in turn is connected with sleeve 22. The other terminal is connected to a conductive frame member 26, providing a reference or ground for the high voltage.

Coating material is supplied to the upper surface of disc 10 by a pump 28, from a paint supply 29, through a fiexi'ble tube 30, which discharges the paint at a point near the center of the disc. The coating material used is selected for the one-coat hammer tone quality.

The entire motor and disc assembly is mounted for vertical reciprocation, the tube 20 sliding in the sleeve 22..An arm 32, pivoted at 33, has a pin 34 at the free end thereof which extends into slot 35 of bracket 36, which is a part of the movable disc and motor assembly. Pneumatic piston cylinder device 38 is pivotally mounted on frame member 39 and the piston rod 40 thereof is connected at an intermediate point of arm 32. Compressed air, from a source 42 is connected through

conduits

43 and 44, with the piston and cylinder device 38 to effect reciprocation of the arm 32 and atomizing disc assembly 10. A suitable valve and control are shown in the aforementioned Simmons Patent Re. 24,602, to which reference may be had for further details of the mechanism and controls.

The relative speeds of the articles 11 along conveyor 15 and of the reciprocation of atomizing disc 10 are such that the disc will undergo several complete cycles of reciprocation during the time required for articles to pass along the circular path 13 through the coating zone.

In accordance with the invention, it is desired to aifect a characteristic of the coating apparatus during the period of coating, so as to cause a variation in the size of the particles of coating material discharged from the disc over a portion of the periphery of the disc, resulting in a hammer finish. By spraying with fine particles under normal operating conditions during the first portion of the coating cycle, a uniform film is obtained with the proper dryness to allow a satisfactory film thickness, and a high quality finish with no sagging. Furthermore, substantially all the paint particles are deposited upon the articles being coated. Alteration of the operating conditions of the atomizer over a portion of its atomizing zone to increase the paint particle size being discharged through this portion of the atomizing zone results in a splattering etfect upon the uniform coating because of the increased size of the particles and their increased wetness. The portion of the atomizing zone in which operation is affected is preferably selected so that the splattering effect takes place as the article leaves the extended coating zone. This provides the advantages of the two-coat method of applying a hammer finish with one coat hammer finish materials and without the duplication of coating equipment. The increased wetness of the larger paint particles as they are deposited is due to the reduced evaporation of solvents because of the increased volume to surface ratio of the particles. This invention renders the character of the resulting hammer pattern subject to control by selecting the size to which the paint particles are increased.

In the embodiment of the invention illustrated herein, the decrease in atomization quality over the selected portion of the periphery of the atomizing device is effected by charged auxiliary electrode located closely adjacent the edge of the atomizing device. The auxiliary electrode decreases the electrostatic field gradient at the portion of the periphery of the atomizing device and interferes with the uniform flow of paint to the atomizing edge. This results in larger paint particles over that portion of the atomizing device.

The coating material used may be a commercially available one-coat hammer finish. Satisfactory results have also been obtained with metallic paints.

In the specific embodiment of the invention illustrated in the drawings, an auxiliary electrode, identified generally as 77, is located immediately above and adjacent the edge of a portion of rotating disc atomizer 10. Electrode 77 is supported by a conductive arm 78 from the tube 20 and is charged to the same high voltage as the disc. Electrode 77 comprises a plate member 79 which extends throughout approximately a 90 portion of the periphery of the disc. The outer edge 79a of the plate is located outwardly of the edge of the atomizing disc and between the disc edge .and the grounded articles 11. The presence of the charged plate 79 with its edge between the edge of the disc and the grounded articles substantial- 'ly reduces the electrostatic field gradient at the edge of the disc. This reduction of the field at the edge of the disc prevents the coating material from being atomized from the disc at the same rate at which it is atomized when subjected to the full field strength. The paint which builds up on the surface of the disc during its passage under the auxiliary electrode is discharged in a narrow pattern of coating material particles larger than the particles discharged from the unshielded portion of the disc periphery, as the disc passes from the auxiliary e1ectrode. These particles are discharged in a generally tangential direction at the intersection of the periphery of the disc and the trailing edge 79b of the auxiliary electrode. An elongated probe 80 is secured to the surface of the auxiliary electrode and extends outwardly generally parallel with the plane of the disc, in the direction of discharge of the coating material particles. The end portion 81 of the probe extends downwardly at right angles to the disc into the discharge path of the large particles. The physical interference of the probe end with the coating material tends to widen the spray pattern.

In the specific embodiment of the invention illustrated in the drawings, the auxiliary electrode covers approximately one-fourth of the periphery 'of the disc. The auxiliary electrode is located over the lower right hand quadrant of the disc and as viewed in FIGURE 1. Articles to be coated pass from the right upwardly and around the disc, traveling in a counterclockwise direction while the disc itself rotates in a clockwise direction. Thus, the position of the auxiliary electrode corresponds generally with the first portion of the loop through which the articles pass, and its terminal edge 79b is located in a portion of the coating zone from which the particles ar discharged to the articles as they leave the coating zone. Thus, during the first portion of the travel of the articles through the coating zone, they receive a coating of finely atomized particles which provide an adequate covering of the surface. As the articles pass through the last portion of the coating zone, they pass through a pattern of larger, poorly atomized particles, which provide a mottled or hammer effect. The reciprocation of the disc atomizer is so coordinated with the travel of the articles along the conveyor that the entire surface of each of the articles is thoroughly exposed both to the finely atomized spray during the first portion of the travel through the coating zone and the poorly atomized coating material in the last portion of the coating zone.

The size of the poorly atomized particles, and thus the resulting pattern, may be controlled by varying the length or annular extent of the auxiliary electrode. The longer the electrode, the more opportunity the coating material has to build up on the surface of the disc and the larger the particles, producing a rough hammer pattern. As the angular extent of the auxiliary electrode is reduced, there is less buildup of coating material, the particles are smaller and the hammer pattern is finer. The size and location of the probe may be varied to vary the pattern of discharge of the large poorly atomized particles.

I claim:

1. Apparatus for applying to an article a coating with a hammer finish, comprising: a source of coating material; an atomizing means connected with said source for discharging finely divided particles of coating material therefrom; means for transporting articles through an extended coating zone adjacent said atomizing device, from a first portion to a second portion; circuit means connected with a source of DC. high voltage establishing an electrostatic field between said atomizing device and articles to 'be coated, for moving coating material particles toward said articles; and means for varying the size of coating material particles atomized into said extended coating zone, the particles being larger in the second portion than in the first portion.

2. Apparatus for applying to an article a coating with a hammer finish, comprising: a source of coating material; a rotating disc atomizing device connected with said source for discharging finely divided coating material particles therefrom; means for transporting articles to be coated through an extended coating zone, in a generally horizontal plane, and a generally circular path around said disc irom an initial portion to a terminal portion of the zone; circuit means connected with a source of DC. high voltage establishing an electrostatic field between said atomizing device and articles to be coated, for moving coating material particles toward said article; and an auxiliary electrode means adjacent the disc portion which discharges coating material into the terminal portion of said zone, for increasing the size of the paint particles being discharged into said terminal portion of said coating zone.

3. Apparatus for applying to an article a coating with a hammer finish, comprising: a source of coating material; a rotating disc atomizing device connected with said source for discharging finely divided coating material particles therefirom; means for transporting articles to be coated through an extended coating zone, in a generally horizontal plane, and a generally circular path around said disc from an initial portion to a terminal portion of the zone; circuit means connected with a source of DC. high voltage establishing an electrostatic field between said atomizing device and articles to be coated, for moving coating material particles toward said article; and an auxiliary electrode means comprised of a flat electrode parallel to the atomizing edge of said rotating disc atomizer and extending beyond said atomizing edge, said electrode shielding a portion of the disc periphery for varying the size of the paint particles being discharged over another portion of the periphery adjacent the shielded portion.

4. The apparatus of claim 3, wherein said auxiliary electrode means also includes a rod extending from said flat electrode parallel to the disc atomizer in the direction of rotation and terminating in a point which intersects the spray of paint particles from said atomizing edge.

5. The method of applying a hammer finish to an article, which comprises: directing a flow of coating material to an atomizing means having an extended atomizing zone; atomizing coating material from said means; establishing an electrostatic field between said atomizing means and said article; transporting articles through an extended coating zone adjacent said atomizing means from a first portion to a second portion; and varying the field gradient over a portion of the atomizing zone to vary the particle size, the gradient in the portion 'of the atomizing zone from which particles are discharged into the second coating zone portion being less than the gradient in the atomizing zone portion from which particles are discharged into said first coating zone portion.

6. A method of claim '5 wherein the particle size is varied over a portion of said extended coating zone by an auxiliary electrode means.

7. A method of claim 6, wherein said coating material is atomized from a rotating disc, and said extended coating zone describes an annular path around said disc, said auxiliary electrode means being located to vary the paint particle size of the coating material applied to the article over the terminal portion of said extended coating zone.

8. The method of applying a hammer finish to an article, which comprises: directing a flow of coating material to a rotating disc atomizer; atomizing coating material from said rotating disc; effective relative movement between said atomizing disc and articles to be coated, the articles passing through an extended coating zone describing an annular path around said disc from an initial portion to a terminal portion; effecting reciprocation of said disc in a direction generally at right angles to the plane of movement of said article; establishing an electrostatic field between said atomizing device and said article; and varying the electrostatic voltage gradient of said field over a portion of the atomizing edge of said rotating disc atomizer to vary the size of paint particles being discharged, the gradient being higher for the portion of the disc from which coating material is discharged into the initial portion of the coating zone than for the disc portion from which coating material is discharged into the terminal portion of the coating zone.

9. The method of claim 8 wherein said variation of the voltage gradient is accomplished by any auxiliary electrode means.

10. The method of applying a hammer finish to an article which comprises: establishing an electrostatic field in a coating zone; moving said articles through said zone from a first to a terminal portion thereof; atomizing coating material with a fine particle size into said first portion of said coating zone for deposition of the coating 7 8 material particles, affected by said field, on said article to References Cited form atnnifornz c ozlitinghtherleong and tthereafter aitomiz UNITED STATES PATENTS mg coa mg ma ena W1 a arger par rc-e size 1n 0 sax terminal portion of said coating zone for deposition of 2754226 7/1956 Juvinau 117*93 I I 5 2,780,565 2/1957 Juvrna-ll 11793.42 the coating material particles, aifected by said field, 0n

3,147,145 9/1964 Simmons 118624 the article to form a nonuniform coating thereon, overlying the uniform coating. FOREIGN PATENTS 11. The method of claim 10 in which said electrostatic 747,543 4/1956 Great Brita-in field' affects the particle size and the field gradient is greater for producing the fine particle size than for pro- 10 M sistant xamin r.

ducing the larger particle siz ALFRED L. LEAVITT, Primary Examiner.