US 3279421 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Oct. 18, 1966 TILNEY ETAL 3,279,421
ELECTROSTATIC SPRAY COATING SYSTEMS Filed April 1, 1963 4 Sheets-Sheet l uuuuununnunnn INVENTORS. RICHARD TIL/VEY, YJOHN Geo/2G5 Cam ew G0FFEY JA 5 Lmpus Oct. 18, 1966 R. TILNEY ETAL ELECTROSTATIC SPRAY COATING SYSTEMS 4 Sheets-Sheet 5 Filed April 1, 1965 5 S M l Y O Y P I F am 0 WNRS f VM W 7 N 50 I GJ W m y H N F l K H W W w Oct. 18, 1966 R. TlLNEY ETAL ELECTROSTATIC SPRAY COATING SYSTEMS 4 sheets-sheet 4 Filed April 1, 1965 .YIM Z T R mmc v 5 m e e 00 m W United States Patent 3,279,421 ELECTROSTATIC SPRAY COATING SYSTEMS Richard Tilney and John George Campbell, London, and
Geoffrey James Liddle, Christchurch, England, assignors, by mesne assignments, to Ransburg Electro-Coating Crp., Indianapolis, Ind., a corporation of Indiana Filed Apr. 1, 1963, Ser. No. 269,442 Claims priority, application Great Britain, Apr. 3, 1962, 12,704/ 62 7 Claims. (Cl. 1182) This invention relates to electrostatic spray-coating systems of the type in which deposition of the spray upon the article being coated is promoted by means of a high volt-age electrostatic field maintained between the article and a charging electrode for the spray. The invention is especially, but not exclusively, applicable to an apparatus in which each spray is produced by a rotating, electrically charged atomizing head of the general type set forth, for example, in U. S. Letters Patent No. 2,893,894 granted on the application of E. M. Ransburg.
In commercial electrostatic spray coating systems, it is common to mount the articles on a conveyor which moves them past the atomizers to receive the spray there from. When atomizers of the general type described in the aforesaid Rams-burg patent are employed, it is essential for best results that the distance between each atomizer and the surface receiving its spray be maintained within apropriate limits. Relatively small articles present no problem in this regard, and the same is true of some relatively large objects, such as refrigerator cabinets, which possess a comparatively regular shape. However, when the objects are both relatively large and irregular in shape, it is frequently neccesary, in order to maintain appropriate distances between each atomizer and the surface receiving its spray, to move the atomizers transversely of the article path as the article passes through the coating zone. Articles of irregular shape frequently present an additional problem in regard to the aspect of the atomizing head relative to the spray-receiving surface; for if the plane of the edge of the rotating atomizing head departs too far from parallelism with the surface receiving the spray, undesirable disuniformity may exist in the finish produced. Automobile bodies are examples of articles presenting problems of the type noted, and this invention will be described below as embodied in a system for painting automobile bodies, although it is to be understood that the invention may find use in the coating of other articles.
On form of apparatus suitable for use in the painting of automobile bodies comprises a lower pair of atomizing head-s disposed on opposite sides of the conveyor path at an elevation which adapts them for spraying the lower side portions of automobile bodies moving through the coating zone. These lower heads are mounted, conveniently with their axes approximately horizontal and perpendicular to the path of the article movement, on trolleys arranged to be moved toward and away from each other in order to maintain the atomizers appropriately positioned relative to the body surface receiving the respective sprays. An upper pair of atomizers, .adapted primarily to spray the upper side portions and outer top portions of the body, are likewise mounted on trolleys located on opposite sides of the body path and movable toward and away from each other to maintain proper distances between the atomizers and the body portions receiving their spray. For the purpose of coating the middle portion of the automobile body, it is preferred to employ an atomizer supported from overhead on a recprocator which will operate, like the previously mentioned trolleys, to maintain a proper distance betwen the atomizer and the body-surface receiving its spray.
Any of the atomizers mentioned may be carried by a swiveled suport which can be anuglarly adjusted during a spraying operation to maintain the proper aspect of the atomzer relative to the spary-receiving surface. It has been found that in apparatus for coating automobile bodies it will usually be necessary to provide such a swiveled support only for the central, or overheadmounted atomizer.
Power operated means of any appropriate type are operatively associated with each of the trolleys, 'with the overhead reciprocator, and with each swiveled support for the purpose of changing the positions of the atomizers as a body passes through the coating zone. These several power-operated means are automatically controlled by mechanism operating in timed relation with movement of the conveyor. Triggering mechanism responsive to approach of a body to the coating zone automatically initiates operation of the control mechanism which functions, as the body proceeds through the coating zone, to control the several power-operated means in a manner that will maintain each of the atomizers in proper position at all times during the coating operation.
Further featuers of the invention will become apparent from the following more detailed description and from the accompanying drawings in which:
FIG. 1 is a diagrammatic side elevation of a conveyor line and an associated set of atomizers;
FIG. 2 is a diagrammatic plan view of the same apparatus;
FIG. 3 is a vertical cross-section transversely of the conveyor showing an automobile body, the atomizer, and the respective supports in elevation;
FIG. 4 is a diagram indicating the functional control arrangement of .a system suitable for use with the apparatus shown in FIGS. 1-3;
FIG. 5 is a vertical section through a head-driving and head-positioning mechanism especially suited for use in connection with an overhead atomizer; and
FIG. 6 is a side elevation of the mechanism shown in FIG. 5.
In the apparatus shown in FIGS. 1-3, automobile bodies 10 to be painted are mounted on wheeled carriers 11 moved along tracks 12 by a conveyor chain 13. The conveyor moves in the direction indicated by arrow 14, and each body is first subjected to the spray from two heads 15, 16 disposed on opposite sides of the conveyor line, and both facing towards that line. The heads are mounted upon suitable trolleys 17, 18, which run on guide rail structures 20, 21, so as to move to and from the conveyor line along the rail structures. The function of the heads 15 and 16 is primarily to coat the lower portions of the side surfaces of the car body and to a lesser extent other surface portions, as will be brought out hereinafter.
The spray painting station includes also a further pair of heads 26, 27. These heads are mounted in a fashion similar to heads 15, 16 upon trolleys 28, 29 which are likewise given the facility of movement towards and away from the conveyor line along rails 31, 32. As will be seen from FIGS. 1-3, the heads 26 and 27 are desirably mounted so that they can spray the upper portions of the body-sides and the edge portions of the body-roof.
The middle portion of each body is coated with spray from a head 34 supported from overhead by mechanism 35 operable to control the vertical position of the head. In the particular embodiment illustrated, the head 34 is mounted on the mechanism 35 through a swiveling device 36 by which the position of the head can be angularly varied, in the direction indicated by arrow 39.
It will be understood that each head will have associated with it a head-rotating motor, as well as means for feeding paint to the head near the center thereof, the
paint so fed being delivered in the form of a film to the edge of the head by centrifugal force.
The trolleys such as 17 18 and 28, 29 can be reciprocated to and from the conveyor line by any suitable means, but a simple and effective method of achieving this is shown in FIGURE 3. In this arrangement a reversi-ble electric motor 41 drives a pinion 42, engaged at opposite points by two racks 43, 44, attached to the ends of a drive cable 45. The cable 45 passes round a series of guide pulleys 46, so as to provide .two spans of cable extending across the line of the conveyor, and the trolleys, such as 17 and 18, are attached to the spans at oppositely moving points.
It is arranged that the paint spraying means is operated by the arrival of a body to be painted, and for this purpose there is provided a triggering device comprising a light source 47 and a photo-electric cell or other detecting device 48. These two parts are so disposed that the light falling upon the cell is interrupted when a body arrives, and this is used to initiate the operation. If desired, the system can be arranged to paint automatically different shapes of body. One way of accomplishing that result is through the use of one or more additional triggering devices each including a light source and photoelectric cell, one such additional device being indicated at 50, 51. The disposition of the several triggering devices is such that bodies of difierent shapes will interrupt difierent sets of light beams; and, through an appropriate discriminating apparatus, the particular set of light beams interrupted will condition the control mechanism to perform the head-positioning and spray-timing.
operations. If, as will frequently be the case, the differences between two body shapes includes a difference in over-all length it will be sufiicient to provide two triggering devices so spaced along the conveyor line that the longer body will simultaneously interrupt both light beams while the shorter body will interrupt the beams one at a time.
The general functional arrangement of means for automatically controlling an apparatus such as that shown in FIGURES l-3 is indicated in FIGURE 4. Conveniently, the automatic control means comprises one or more drum cams each actuating a series of switches through which operation of the several head-positioning mechanisms, as well as initiation and termination of each spraying operation, are controlled. Each cam is driven at a speed coordinated with that of the conveyor 13 and is so arranged that its rotation, when once initiated, will continue for one full revolution to carry the cam from, and return it to, a home position. The number of cams employed will vary, depending upon the number of different body shapes .the system will be called on to coat and upon whether or not the cycle of operations necessary to coat one body will be completed before initiation of the cycle involved in coating the next body. In general, one cam or set of two cams will be provided for each body-shape to be coated, and whether there are two cams or only one for each body-shape will depend upon whether one cycle of operation is initiated before the preceding cycle ends or whether there is a time interval between successive cycles.
In the case of the apparatus shown in FIG. 4, it is contemplated that there will be an overlapping (in time) of successive cycles and that the apparatus will be called upon to paint bodies of two different shapes. Accordingly, there is provided one set of two earns 55 and 56 for one body shape and a second set, 55a and 56a, for the other body-shape. Which set of cams 55-56 or 55a- 56a, will operate to control the cycle of operation initiated by approach of a body to the coating zone will be determined by a discriminator 57 responsive to signals from the several cells 48 and 51.
As previously mentioned, each of the heads has associated with it a motor for rotating it. Two of such head-rotating motors are indicated at 60, 61 in FIG. 4.
Ordinarily, the rotation of the heads will not be interrupted during operation of the complete coating apparatus, and the same is true of the supply of high voltage to the heads. Accordingly, FIG. 4 shows a manually operated device 62 which controls operation of all the head-rotating motors and also activation of a high-voltage source 63 from which high voltage is applied to the heads over a conductor 64. Preferably the high voltage circuit includes or has associated with it a spark guard 65 which may be of a type commonly used in electrostatic spray-painting systems to deactivate the highvoltage source or otherwise interrupt the supply of high voltage to an electrode when any grounded object approaches the electrode and thereby creates danger of a disruptive dischar e.
Paint is supplied to the atomizing heads from a paintsupply line 67 through conduits 68 containing valves 69 which are selectively controlled by the control cams. If desired, the apparatus may be adapted for the application of paints of different colors by providing a plurality of paint lines 67 and a set of valves 69 for each paint line. If that is done, it is desirable to include in the apparatus means for flushing the atomizing heads and the conduits leading to them with an appropriate solvent before paint of the new color is supplied. Means of this type are known, one such being shown in the copending application of James W. Juvinall, Ser. No. 775,316, filed November 20, 1958, now abandoned.
In addition to controlling operation of the paint-supply valves 69, the control cams also control the mechanisms by which the positions of the atomizing heads are changed as each spraying cycle passes. Each of such head-positioning mechanisms includes a reversible motor, two of which are shown in FIG. 4 at 71 and 72. When it is desired to control not only the direction of rotation, but also the speed of operation, of the motor embodied in a head-positioning mechanism, it is convenient to use a reversible motor of the hydraulic type. The motor 72 in FIG. 4 is of that type. As shown, it is arranged in a hydraulic circuit 73, which includes a flow-control valve 74, across the outlet ports of a reversing valve 75 supplied with fluid under pressure from a pump 76. The control cams control both the flow-control valve 74 and the reversing valve 75, and the latter is of the known type which can be selectively positioned to cause flow in either direction in the circuit 73 or to interrupt flow in that circuit.
While specific forms of head-positioning mechanisms are described below, this invention, in its broader aspects, is not concerned with details of such mechanisms or with the precise form of other devices controlled by the control cams. As previously mentioned, the lateral positions of the trolleys 17, 18, 28 and 29 relative to the conveyor line can be controlled by reversible electric motors, such as indicated at 41 in FIG. 3. The mechanism 35, which controls the height of the overhead atomizer 34, is conveniently a hydraulic motor of the cylinder and piston type, and may have an associated speed control like that provided for the motor 72 of FIG. 4. Valves, such as the valves 69 and 75 of FIG. 4, can be controlled by solenoids activated and deactivated by the control cams. A valve, like the flow-control valve 74 of FIG. 4, which may have more than three positions, can be operated by an appropriate form of servo mechanism controlled by the control cams.
The apparatus as so far described is conditioned for operation by operating the manual control 62 to initiate rotation of all the atomizing heads and to activate the high voltage source 63. The conveyor 13 is then started to move the bodies 10 successively through the coating zone. The bodies are grounded through the carriers 11 and tracks 12 and hence will attract the charged paint particles discharged from the atomizing heads as those heads are successively supplied with paint by operation of the valves 69.
Until the first body reaches the coating zone, the
several atomizing heads will normally be in the positions desired for them when spraying is to start, such positions being determined by the control cams, all of which will be in their home positions. For most bodies this means that the heads 15 and 16 will be at their innermost limits of movement, usually in the path of an approaching body, and that the head 34 will be at the lower limit of its movement and also in the path of an approaching body. The head 34 will be swiveled to an inclined position adapted to cause discharge of its spray toward the lower portion of the front end of the approaching body. Vertically the heads 15, 16 and 34 will be so disposed that their sprays will reach the lowermost point of the front end of the approaching body, and the two heads 15 and 16 will be so positioned laterally of the conveyor that the margins of their deposited sprays will overlap the margin of the spray deposited from the head 34. In the particular apparatus illustrated, which has been used inthe coating of the bodies for small automobiles, the bells 15 and 16 can be so positioned vertically that their sprays will both reach the lowermost points at the front and rear ends of the body and also the side portions of upwardly presented surfaces, such as the tops of the fenders, the trunk, and the hood, if the hood is in place. Accordingly, it is unnecessary to provide any mechanisms for adjusting the heads 15 and 16 vertically on the trolleys; but such mechanisms could be provided if necessary.
As a body approaches the coating zone, one or more of the triggering devices will be actuated and will operate, through the discriminator 57, to initiate rotation of one of the control cams. Hereafter it will be assumed that the cam so thrown into rotation is the cam 55. As that cam rotates, it will cause operation of valves 69 (FIG. 4) to initiate spraying from the heads at the proper times. After spraying from the heads 15 and 16 has started, the cam 55 will cause the trolleys 17 and 18 to move gradually outward to positions in which the heads 15 and 16 will clear the approaching body and thereafter to maintain an appropriate distance between each of those heads and the sides of the body passing it. As the body moves beyond the heads 15 and 16, the carriages 17 and 18, will be moved inwardly to cause the sprays from the heads 15 and 16 to coat rear end surfaces of the body. As the body passes through the coating zone, the head 34 will be moved vertically to maintain the appropriate distance between it and the body surface receiving its spray. Additionally, the head 34 will swivel as necessary to maintain it as nearly as possible in proper aspect relative to the spray-receiving surfaces. In its final position, approximating that shown in FIG. 1, the head 34 will be positioned to discharge its spray toward the extreme rear of the body where the spray it deposits will overlap that from the heads 15 and 16.
The heads 26 and 27, and the supply of paint thereto, will be controled by the cam 55 in a manner generally similar to that followed in respect to the heads 15, 16 and 34. As shown, the only positonal adjustment provided for the heads 26 and 27 is that afforded by in and out.
movement of the trolleys 31 and 32, but if desired those heads could be provided with positioning mechanisms which function under control of the control cams to vary the elevation of the heads as a body passes through the coating zone. Any of the heads 15, 16, 26, and 27 can if desired be provided with svvivelling supports operable under control of the control cams to vary the aspect to the head relative to the spray-receiving surface.
Reference has been made above to the possibility of providing for any head-positioning mechanism a variable speed control such as that provided for the motor 72 in FIG. 4. In the case of heads whose change of position can be effected at rates that do not vary too widely a sufficiently close approximation to the optimum rate of position-change can be obtained with constant-speed head-positioning motors by appropriate regulation of the frequency and duration of the intervals during which the head is moved. Variable speed control is indicated, however, in the case of swivelling of the head 34; for, while the swivelling of that head may proceed at a relatively low rate as its spray follows the contours of hood and trunk, a relatively rapid swivelling movement of the head is desirable when the head is in the angle between the hood and the front corner posts of the body or the angle between the rear corner posts of the body and the trunk. Relatively rapid swivelling movement of the head 34 may also be necessary to reverse its position after it has completed the sprayping of one body and before it begins spraying the next. In the particular apparatus illustrated in FIGS. 13, it has not been found necessary or desirable to provide variable speed control except in the case of the mechanism which swivels the head 34.
The positioning of the various a'tomizing heads relative to each other along the conveyor line may vary c0nsiderab-ly; but it is desirable that heads which deposit spray in overlapping patterns should not be spaced so far apart along the conveyor line that the paint deposited by one head will have dried unduly before the overlapping spray is deposited. The relative spacing of the various heads along the conveyor line will affect the possibility of beginning the coating of one body before the coating of the preceding body is completed. For example, if the spraying from all heads is terminated approximately simultaneously, it will be impossible for the spraying of one body to start before that of the other body is completed; but if those heads which are initially thown into operation at the institution of a spraying cycle complete their function of coating one body while other heads are still spraying that same body, a second cycle may be instituted before the first is completed. In the assumed case, where the spraying of the one body is being carried out under control of the cam 55, as a second body of the same shape approaches the coating zone and actuates the triggering device, the cam 56 will be thrown into rotation and will control the coating of the second body, the cam 55 continuing to rotate until the coating of the first body is completed and the cam reaches its home position ready for operation to control coating of a third body.
The problem of designing mechanisms suitable for rotating the atomizing heads, and also for changing their angular disposition, is one which is susceptible of a variety of solutions but FIGS. 5 and 6 show a form of device which is especially suitable for use with the overhead supported head 34. That device comprises a housing 82, which is intended to be mounted upon the moving part of the head-positioning mechanism 35. Mounted within the housing 82 are two drive motors 83 and 84, of which the former is reversible and used to cause angular movement of the atomizing head 34, whilst motor 84 is used for rotating the head about its axis. Depending from the lower side of housing 82 are two flanged, hollow brackets 85 and 86 of highly insulating material, the lower ends of which are respectively received in and secured to two similar connectors, 87, 88. A horizontal support sleeve 90 has its ends rotatably received in the connectors 87 and 88, desirably through roller bearings 91, 92. A hollow head-drive shaft 93 is mounted transversely in sleeve 90' by means of bearings 95, 96 and between these bearings the sleeve carries a bevel drive gear 97. A drive shaft 100 mounted in the connector 88, by means of bearings 101, 102, carries at its inner end a further bevel gear which meshes with the bevel gear 97. At its outer end the shaft 100 carries another bevel gear 104, in turn meshing with a bevel gear 105' on the end of a vertical shaft 106, which extends upwardly through the connector 88 and bracket 86 to be driven from motor 84 through a resilient coupling means 107. By this means, the drive motor 84 will drive shaft 106, and through gears 105, 104 the shaft 100. In turn shaft 100 drives the head drive shaft 93 through gears 105 and 97. In use, a paint supply tube can be located down the center of the drive shaft 93, to supply paint to the bell 34, which will be secured to the lower end of such shaft.
To adjust the angular positon of sleeve 90, motor 83 is coupled through a belt drive 110 to a speed reduction gear box 111. The output shaft 112 of the gear box is connected through a flexible coupling 113, to a shaft 114, carrying at its lower end within the connector 87 a bevel gear 115, meshing with a similar gear 116 on a transverse shaft 117. Shaft 117 is carried at its outer end in a bearing 118 in the connector 87, but its inner end is fast to the sleeve 90. In this way, when the motor 83 drives, it will rotate shaft 114, and thus shaft 117, causing angular move-ment, about a horizontal axis, of the sleeve W and the atomizing head supported therefrom on the end of shaft 93. The speed reduction gear 111 carries a cam 120, which operates limit switches 121, 122 in order to protect the apparatus against excessive movement of the connecting sleeve 96.
The insulating brackets 85 and 86 electrically isolate the sleeve 90 and the parts, including the head, it carries from the housing 82 and the support therefor, thus making it possible to maintain high voltage on the head. It will be understood that all heads and head-mountings will be supported through insulating material for the same purpose.
The apparatus described can be set up to give a very high quality and uniform finish on an article such as a car body, eliminating or reducing to a minimum the necessity for hand touch-up. The facility of moving the heads to and from the surface of the body being coated enables the appropriate quantity of paint to be uniformly deposited upon the body from spray heads which do not approach so closely to the surface being coated as to create danger of a disruptive discharge from any head, nor recede too far from the body, which might produce a deleterious eifect on the finish, due to an excessive loss of solvent from the paint spray, thus causing the deposit of dry paint upon the surface being coated, with consequent loss of finish quality. Further, the change of attitude of a spray atomizing head with respect to the surface being coated also may have an important effect upon the quality of the finish. As will be obvious, the attitude of the head can be such that spray particles leaving one segment of the head-edge may travel farther and become drier before being deposited than particles leaving another segment of the head-edge. If the farthertravelling particles become dry enough and are the last particles deposited on any given area they will not blend with the previously deposited paint, and a deterioration in quality of finish will result. It is therefore desirable to control the attitude of the head in such a way that spray particles travelling far enough to become unduly dry before being deposited will be the first to reach any point on the surface, so that the later-deposited, wetter particles will produce blending and a smooth finish. To minimize the likelihood that the particles last deposited will be unduly dry it is desirable that, when possible, the head be maintained at all times in an attitude such that the distance between the plane of the head-edge and any passing point on the body surface will be greater when that point first receives paint than it is when that point last receives paint.
It has been mentioned above that it is desirable that the heads in operation should not approach too closely to the grounded surface upon which paint is being deposited, for the reason that it may then occur that the potential gradient across the gap between the two parts will be such as to give rise to a disruptive discharge. This will not occur normally once the apparatus has been set up, and protection against disruptive discharge will be afforded by the spark guard circuit. However, if a fault should develop in the apparatus damage might be caused by the body being painted, or some part of the conveyor system, colliding with one or the other of the heads or their positioning means. The spark guard 65 can in these circumstances be arranged to give protection against any such collision. If the spark guard responds to the proximity of the car body, it can be arranged that the spark guard, acting through the control drums, will cause the withdrawal of one or more of the atomizing heads from the path of the approaching body portion. In one practical form of the invention, it has been found advantageous to arrange that the spark guard causes an initial withdrawal of the heads in this way; should the spark guard continue to respond, indicating that the Withdrawal is insufiicient, a second stage of withdrawal can take place. If again the spark guard continues to respond, then the apparatus can be shut down, so that the faulty condition can be investigated and remedied. In general, with a highly mechanized sytsem such as is normally adopted for car assembly, it is very undesirable that a conveyor should be stopped, and the system described is a compromise which reduces the likelihood of conveyor stoppage.
1. Electrostatic spray-coating apparatus, comprising a conveyor for conveying through a coating zone a succession of articles to be coated, a plurality of atomizing devices for spraying liquid coating material on to each article as it passes through the coating zone, means including a high-voltage source for creating an electrical charge differential between the spray particles and an article in the coating zone, at least one of said atomizing devices being mounted on a swivelled support the axis of which is transverse to the direction in. which spray is projected from such atomizing device and also transverse to the conveyor, whereby the atomizing device can be directed alternatively toward either an approaching article or a receding article, power-operated means for swivelling said support, and automatic control means operating in timed relation to the conveyor for controlling said power-operated means and the supply of coating material to each atomizing device.
2. Electrostatic coating apparatus as set forth in claim 1 with the addition of a carrier arranged for movement transversely to the path of article movement under control of said automatic means, said swiveiled support being mounted on said carrier.
3. Electrostatic coating apparatus according to claim 1 characterized in that each of said atomizing devices comprises a rotating atomizing head electrically connected to said high-voltage source and from the periphery of which atomization of the coating material takes place, said power-operated means being controlled to maintain said atomizing head in such an attitude that the plane of its periphery will be approximately parallel to the article surface opposite the head.
4. Electrostatic coating apparatus according to claim 1 with the addition of means controlled by said automatic means for regulating the operational speed of said poweroperated means.
5. Electrostatic spray-coating apparatus, comprising a conveyor for conveying through a coating zone a succession of articles to be coated, a plurality of atomizing devices for spraying liquid coating material on to each article as it passes through the coating zone, means including a high-voltage source for creating an electrical charge differential between the spray particles and an article in the coating zone, at least one of said atomizing devices being mounted on a carrier arranged for movement transversely of the path of article movement, poweroperated means for cyclically moving said carrier, means for regulating the operational speed of said carrier-moving means, and automatic means operating in timed relation to the conveyor for controlling the supply of'coating material to each atomizing device, said automatic means also operating to control said speed-regulating means to vary the speed of the carrier in predetermined manner as the carrier proceeds through its cycle of movement.
6. Electrostatic spray-coating apparatus, comprising a conveyor for conveying through a coating zone a succession of articles to be coated, a plurality of atomizing devices for spraying liquid coating material on to each article as it passes through the coating zone, means including a high-voltage source for creating an electrical charge differential between the spray particles and an article in the coating zone, at least one of said atomizing devices being mounted on a swivelled support and comprising a rotating atomizing head from the periphery of which atomization of the coating material takes place, said head being maintained at high voltage by connection to said high-voltage source, said swivelled support having rigid with it a sleeve the axis of which is transverse to that of said head, means including a shaft extending axially within said sleeve for rotating said head, power operated means for rotating said sleeve about its axis, and automatic means operating in timed relation with the conveyor for controlling said power-operated means.
7. Electrostatic spray-coating apparatus, comprising a conveyor for conveying through a coating zone a suc cession of articles to be coated, a plurality of atomizing devices for spraying liquid coating material on to each article as it passes through the coating zone, means including a high-voltage source for creating an electrical charge diiferential between the spray particles and an article in the coating zone, at least one of said atomizing devices comprising a rotatable head from the periphery of which atomization of the coating material takes place,
said head being maintained at high voltage by said highvoltage source, a driven shaft to which said head is fixed, a sleeve on which said shaft is rotatably mounted with its axis transverse to that of the sleeve, a housing, a pair of spaced hollow brackets of insulating material projecting in generally parallel relation from said housing, bearing means at the outer ends of said brackets rotatably receiving the ends of said sleeve, means including a first motor in said housing and a first drive shaft extending through one of said brackets for rotating said sleeve about its axis, an intermediate shaft rotatably mounted within and extending axially of said sleeve, gearing providing a driving connection from said intermediate shaft to said driven shaft, and means including a second motor in said housing and a second drive shaft extending through the other of said brackets for driving said intermediate shaft.
References Cited by the Examiner UNITED STATES PATENTS 2,729,189 1/1956 Schweitzer et al. 118-323 X 2,736,671 2/1956 Ransburg et a1. 118631 X 2,785,088 3/1957 Ransburg 11793.42 2,894,485 7/1959 Sedlacsik ll8323 X 2,900,950 8/1959 Peeps 1182 2,955,568 10/1960 Blenman et a1 1182 X 2,996,042 8/1961 Juvinall 11793.42 X 3,001,504 9/1961 Gengenbach et al. 118-2 CHARLES A. WILLMUTH, Primary Examiner. PETER FELDMAN, Assistant Examiner.