US2703549A

US2703549A - Apparatus for the electrostatic spray coating of articles

Info

Publication number: US2703549A
Application number: US278852A
Authority: US
Inventors: Edwin M Ransburg
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1952-03-27
Filing date: 1952-03-27
Publication date: 1955-03-08
Anticipated expiration: 1972-03-08

Description

March 8, 1955 E. M. RANSBURG 2,703,549

APPARATUS FOR THE ELECTROSTATIC SPRAY comma 0F mucus Filed March 27, 1952 s Sheets-heet 1 Hr unseat March 8, 1955 E. M. RANSBURG APPARATUS FOR THE ELECTROSTATIC SPRAY COATING 0F ARTICLES 3 Shets-Sheet 2 Fill d larch 27, 1952 vw M Altar/lays March 8, 1955 E. M. RANSBURG 2,703,549

APPARATUS FOR THE ELECTROSTATIC SPRAY comma 0F ARTICLES Filed March 27, 1952 3 Sheets-Sheet 3 mmvroa.

EDWIN M. RANSBURG A Harneys 4 United States Patent APPARATUS FOR THE ELECTROSTATIC SPRAY COATING 0F ARTICLES Edwin Ransburg, Indianapolis, Ind., assignor to Ransburg Eleetro-Coating Corp., a corporation of Indiana Application March 27, 1952, Serial No. 278,852

3 Claims. (Cl. 118-51) This invention relates to electrostatic coating and more particularly tocoating apparatus and coating methods to be used in electrostatic coating systems.

In a majority of electrostatic coating systems a field of electrostatic force is set up which includes the article being coated and the atomized coating material particles in movement toward such article. In normal commercial practice it is desirable to mount the article on a grounded conveyor and thus to make the articles themselves (if they are of conducting material)"or electrodes within or immediately behind the articles, an electrode at ground potential. Another electrode at high electrical potential is provided, with this electrode sometimes being the spraying device and sometimes being a separate electrode near or past which the spray passes in its movement toward the article.

When articles are moved along a conveyor in spaced relationship and are successively exposed to the spray issuing from a spraying device in an electrostatic coating system where deposition of the atomized particles is primarily the result of electrostatic forces and where the particles are given an electric charge at the time they leave the spraying device or shortly thereafter, difiiculty has-sometimes been encountered in some installations where the articles must be sufiiciently widely spaced on the conveyor to permit their being carried around corners and up and down elevations, inasmuch as coating material atomized during the time that no article is within coating range is lost, resulting in inefiiciency in the spraying operation.

One of the features of the present invention is that the atomizing device is reciprocated in a path paralleling the conveyor with the apparatus being so arranged as to supply coating material to the atomizing means only while such means are moving along with, and hence is coating, an article. A further feature of the invention is the provision of means for synchronizing the movement of the atomizing means with movement of an articlealong the conveyor so that the atomizing means is given two motions, one forwardly along with the article moving on the conveyor and the other in a direction substantially normal to the movement of the article so as to cause the atomizing means to sweep the article.

In most commercial installations it is preferable that the articles on the conveyor travel horizontally, and thus where such an installation is encountered, the atomizing means is movable both horizontally and vertically. As it is preferred to move the atomizing means horizontally at the same speed as the movement of the article, the relative movement between the atomizing means and the article is vertical only.

A further feature embodied in the preferred form of the invention hereafter to be described is that the atomizing means is so mounted as to move in one vertical direction while coating one article and in the other vertical direction while coating a succeeding article. Thus, the system may be arranged so that as the atomizing means moves horizontally along with a horizontally moving article, it is also moved vertically downwardly so as to sweep the article from top to bottom. When the atomizing means has reached the lowest position of its movement, supply of coating material is interrupted; and the atomizing means is returned, while in such lower position, horizontally to its starting point; and then when moved along with a succeeding'article, is moved upwardly to sweep such succeeding article from bottom to top.

The apparatus of the invention may, if desired, be

employed to apply a double coating of the material. Thus, the mechanism utilized to achieve movement of the atomizing means may be adjusted so as to move the atomizing means both upwardly and downwardly while moving along with a single article so as to sweep such article twice.

The mechanism may be adjusted so as to coat each article on the conveyor or to coat alternate articles and when employed in the latter manner, a similarly constructed atomizing means may be used to coat the intermediate articles on the conveyor. To prevent loss of coating material during return movement of the atomizing means, means are provided for interrupting the flow of coating material to the atomizing means during the return movement so that no loss or over-spray results.

Other and further objects and features of the invention will be readily apparent from the following description and drawings, in which: I

Fig. 1 is an end elevation of an electrostatic coating system embodying the invention;

Fig. 2 is a side elevation of the apparatus shown in Fig. 1; and

Fig. 3-is a diagrammatic view illustrating the various motions which can be achieved with the apparatus of the invention.

While one form of apparatus is illustrated in the accompanying. drawings, and will be described hereafter as providing means for practicing the present invention, it will be understood that this is a representative embodiment only. It will also be understood that forms of spray ing devices other than the particular electrostatic atomizing device shown may be utilized and that other apparatus may be employed for accomplishing the purposes and for practicing the methods of the invention and it is to be understood that other embodiments may be utilized without departing from the contemplated scope of the present invention and that no limitations are to be implied from the specific description now provided.

Referring now to Figs. 1 and 2, the apparatus comprises a conveyor mechanism 10 for moving a plurality of articles, such as the article 11, along a predetermined path, an atomizing means 12 for atomizing into discrete particles coating material and means generally indicated at 13 for moving the atomizing means along the path with an article and for simultaneously moving the atomizing means in a direction substantially normal to the direction of movement of an article on the conveyor For convenience, and in conformance with normal commercial practice, the conveying means 10 is shown as being arranged to convey the articles horizontally during their passage through the coating'zone, the zone where coating is applied.

Mounted upon suitable posts 15 is a top support plate 16 which carries at one end an I-beam 17, the lower flange 18 of which serves as a track for rollers 20. A yoke-type bracket 21 is suspended from the rollers and carries a drive chain 22, movement of which serves to move the yoke along the track. A pendant 23 is suspended from the yoke and may be provided with a hook or other means at its lower end for carrying the articles 11.

Suspended from an intermediate portion of the top plate 16 is a pair of spaced parallel bracket plates 25 which carry at their lower ends-a pair of parallel T- beams 26, the flange 27 of each of which forms a track. Mounted for movement along the track on wheels 28 is carriage 29 provided with a suitable bearing 30 whic rotatably carries a threaded shaft 31. A second carriage 29 is similarly provided with wheels 28' for movement along the track 27.

Carriages

29 and 29 are tied together as a mobile unit by means of angle iron members 24 which are rigidly attached to each carriage. Mounted on the carriage 29' is a second bearing 30' rotatably carrying a second threaded shaft 31, with each shaft being provided with

sprockets

32 and 32 encircled by a chain drive 33 so that the shafts may rotate together. Nuts 34 and 34' engage the threads on the shafts 31 and 31' respectively and carry a support column 35 made of insulating material which in turn carries the atomizing means 12. Rotation-of the shaft 31 causes rotation of the shaft 31' by means of the chain drive 33 and such rotation of the shafts causes the nuts 34 and' 34', and hence the atomizing means, to move vertically. Rotation of the shaft 31 is achieved through a motor 40 secured to the underside of the carriage 29 and connected by a drive shaft 41 to a suitable reduction gearing mechanism 42 in turn driving a drive gear 43 meshing with a driven gear 44 fixed to the shaft 31.

Means are provided for energizing the motor 40 at appropriate times to cause rotation of the motor in either direction to move the atomizing means 12 vertically upwardly or downwardly during the coating operation.

Means are also provided for moving the carriages 29 and 29' along the track 27 in spaced parallel relationship to an article moving along the conveyor 10. The latter means include a sprocket wheel 50 engaging and rotated by the chain 22 with the sprocket wheel being secured to a drive shaft 51 journaled at 52 in the top plate 16 and carrying at its upper end a-sprocket 53. Another shaft 54 is journaled at 55 tn the plate 16 and carries an upper sprocket 56 engaging a chain 57 which passes therearound and also around the sprocket 53 to rotate the shaft. The lower end of the shaft 54 carries another sprocket 58 around which passes a chain 59 which extends parallel to the conveyor. The other end of the chain passes around an idler sprocket 60 rotatab ly mounted upon a shaft 61 mounted in a bearing 62 in the top late. p The carria 29 is provided with a cross rod 70 adapted to be engag by a pendant 71 fixed to the chain 59. When the sprocket 58 is rotated, the pendant 71 engages the cross rod 70 to move both carriages on the track 27 along with an article 11 so as to carry the atomizing means 12 therewith. When the pendant 71 reaches the idler sprocket 60 and passes therearound, return movement of the pendant serves to return the carriage to its rmttal starting position. Thus, the chain drive just described serves to move the carriage in a reciprocal motion back and forth parallel to the movement of an article along the conveyor. While the reciprocal motion of the carnage rs under the direct control of the conveyor, it is of course possible to vary the extent of the motion of the carnage by varying the distance between the

sprockets

58 and 60.

The motor 40 is energized by means of an electrical switch 80 provided on one of the brackets 25 with the switch being positioned to be contacted by an operating finger 81 extending downwardly from the carriage 29. the carriage 29 starts to move from the initial starting position shown in Fig. 2 along with an article, the finger 81 contacts the switch 80 to start the motor 40. Operation 'of the motor causes rotation of the shafts 31 and 31' to move the atomizing means 12 vertically. If the atomizing means is in the top position shown, the shafts 31 and 31' are rotated in a direction to move the atomizing means vertically downwardly. When the carriage ap proaches the end of its stroke, the finger 81 contacts a second switch 82 to stop the motor 40 and the motor is maintained stopped until the carriage returns to its starting position. Subsequent contact of the switch 80 by the finger 81 during the next succeeding movement of the carriage along with an article causes the motor 40 to operate in the reverse direction, thus raising the atomizing means from its lowermost position to the upper position illustrated.

By varying the operation of the gear reduction device 42 and by the employment of suitable clutch mechanism in the sprocket 58, various motions of the atomizing means relative to an article may be achieved.

Referring now to Fig. 3, the diagrams A, B, C and D illustrate some of the various motions possible with the apparatus. In A, the movement of the atomizing means along with the article and downwardly is illustrated by the solid line 90. Return movement of the carriage with out vertical movement of the atomizing means is illustrated by the dashed line 91. On the succeeding movement of the carriage the atomizing means is moved upwardly, and thus follows the line 92 indicated by the circles. Return movement of the carriage after this stroke is again without rotation of the shaft 31, and hence the head follows the line 93 indicated by the crosses.

With the motion just described the atomizing means misses eve other article on the conveyor and thus must be duplicated farther along the conveying system so as to coat the intermediate articles.

Preferably the switch 82 not only de-energizes the motor 40 but also serves to interrupt the flow of coating material to the atomizing means such as by shutting oti the supply pump so that no material is atomized during the return movement of the carriage, or substantially none. In this manner over-spray or waste of coating material can be avoided.

If it is desired to spray the article twice, the motor 40 can be arranged so as to carry the atomizing means along the path indicated by the solid line 94 in B. Thus the motor serves first to rotate the shaft 31 in one direction relatively ra idly to lower the atomizing means from top to bottom 0 the article, and then is reversed as the atomizing means reaches the lower end of its stroke to bring the atomizing means upwardly. Return movement of the atomizing means is along the line 95 indicated by crosses.

The motions illustrated in A and B provide a system which, as noted, coats every other article on the conveyor. If it is desired to coat every article, the timing of the two movements can be arranged in the manner shown in C. In this modification the reduction gearing 42 is arranged to move the atomizing means 12 downwardly across the surface of the article along the solid line 96 as the conveyor moves the article a distance correspondrng to half the distance between the article centers and then to return it to its original position along the dashed line 97 as the conveyor moves the parts a corresponding distance. When this occurs the atomizing means is now in a position to coat the next following article by starting at its lower point, and following the line 98 indrcated by circles, moving upwardly across the face of the article.

In the last modified movement illustrated in D the forward motion of the carriage 29 parallel to the conveyor takes place at a different rate than its return. This change of rate may be accomplished by a clutch mechanism associated with the sprocket 58 whichshifts the rate of rotation of this sprocket from one speed to another. Mechanisms for accomplishing this purpose are well known. With such a device coating on the forward stroke can be accomplished as the atomizing means moves down relatively rapidly across the surface of the article along the solid line 99 and then the carriage is returned to its starting position to move the atomizing means along the dashed line 100 at an increased speed so as to be in a position to travel upwardly along the line 10!. indicated by circles, as the next article comes in the coating zone.

The particular atomizing means 12 illustrated is of the type described in the copending application of E. M. Ransburg and W. A. Starkey filed September 29, 1944 as Serial No. 556,390 wherein atomization occurs electrostatically from the particular device there illustrated. The atomizing head shown is of the wedge type and is supplied with coating material through a plastic or rubber hose connected to a suitable pump 106 and supply tank 107, with the atomizing head being so arranged as to spread the coating material into a thin film'which flows to an atomizing edge 108. The atomizing head is connected by means of the lead 109 to the hot terminal of a power pack 110 whose other terminal is grounded as indicated at 111. Thus, in the particular embodiment illustrated the atomizing means is also one electrode of the electrostatic field. Obviously other forms of atomizers may be used and in such cases the electrode may also be a part of the atomizing unit or may be an independent element. In any case the atomizing means is given the motion described, and if an electrode separate from the atomizing means is provided, such electrode is R either moved along with the atomizing means or a plurality of such electrodes may be provided spaced along the path of movement of the atomizing means. in either case the atomized particles are deposited by the electrostatic field existing between the article and the particles regardless of whether the particles are charged at or shortly after they leave the atomizing means; and the described motion of the atomizing means causes the depositing field, that is the field including the atomized particles, to sweep the article being coated during movement of the atomizing means.

While I have shown and described a particular embodiment of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. Electrostatic coating apparatus comprisng a conveyor for conveying a plurality of articles in spaced relationship along a predetermined horizontal path, a track paralleling the conveyor, a carriage movably carried by the track, an atomizing means mounted on the carriage for reciprocating movement in a vertical plane, means for supplying coating material to the atomizing means for atomization therefrom, means including an electrode mounted on the carriage for reciprocating movement in a vertical plane for creating an electrostatic field electrostatically to deposit atomized particles on an article in a pattern whose vertical dimension is less than the vertical dimension of said article, a motor for moving the atomizing means and the electrode vertically on the carriage, drive means for the conveyor, means connecting the drive means to the carriage to move thecarriage on the track from a first position along with an article on the conveyor and then to return the carriage to said first position, means operating during movement of the carriage along with an article moving on the conveyor to energize the motor to move the atomizing means and the electrode only in one vertical direction to cause the depositing field to sweep the article, and means operated during return movement of the carriage to de-energize the motor to maintain the atomizing means in the position attained relative to the carriage by movement in said direction during such reverse movement of the carriage.

2. Electrostatic coating. apparatus comprising a conveyor for conveying a plurality of articles in spaced relationship along a predetermined horizontal path, a track paralleling the conveyor, a carriage movably carried by the track, an atomizing means mounted on the carriage for reciprocating movement in a vertical plane, means for supplying coating material to the atomizing means for atomization therefrom, means including an electrode mounted on the carriage for reciprocating movement in a vertical plane for creating an electrostatic field electrostatically to deposit atomized particles on an article in a pattern whose vertical dimension is less than the vertical dimension of said article, a motor for reciprocating the atomizing means and the electrode vertically on the carriage, drive means for the conveyor, means connecting the drive means to the carriage to move the carriage on the track from a first position along with an article on the conveyor and then to return the carriage to said position, means operating during movement of the carriage along with an article moving on the conveyor to energize the motor to move the atomizing means and the electrode only in one vertical direction to cause the depositing field to sweep-the article interrupt the supply of coating material to the atomizing means, and means operating during the succeeding movement of the carriage along with another article to resume the supply of coating material to the atomizing means and to re-energize the motor to move the atomizing means and the electrode only in the other vertical direction to cause the depositing field to sweep said other article vertically during coating deposition.

3. Electrostatic coating apparatus comprisng a conveyor forecollyqing articles having a surface to be coated along a predetermined first path, a carriage mounted for movement in a second path paralleling an article moving along the first path, an atomizing means, means for supplying coating material to the atomizing means for atomization therefrom, means including an electrode adjacent the atomizing means for creating an electrostatic field for causing the deposition of atomized particles on the article in a pattern having its maximum dimension normal to the direction of article movement smaller than the corresponding dimension of said surface, means for mounting the atomizing means and the electrode on the carriage to laterally space the atomizing means and the electrode from said first path including means for moving the atomizing means and the electrode in two opposite directions angularly related to said first path, means for moving the carriage along said second path, means operated in timed relationship to movement of an article along said first path to operate both of said moving means to move the carriage from a starting position along with and at substantially the same speed as the article and to move the atomizing means and the electrode in at least one of said angularly related directions while atomization of the coating material is being effected to cause the depositing field to sweep the article to deposit coating on said surface over an area having a dimension normal to the direction of article movement along the first path substantially greater than the corresponding dimension-of the spray pattern, and means for reversing said carriage moving means to return the carriage to its starting position.

References Cited in the file of this patent UNITED STATES PATENTS