US3921574A

US3921574A - Coating method with cleaning and apparatus therefor

Info

Publication number: US3921574A
Application number: US546547A
Authority: US
Inventors: William P English
Original assignee: ELECTROSTATIC EQUIPMENT CORP
Current assignee: BARRACK COMBUSTION PTY Ltd; E T TECH ACQUISITION CORP; ELECTROSTATIC EQUIPMENT CORP
Priority date: 1972-05-24
Filing date: 1975-02-03
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

An apparatus and method are provided for producing a coating of resinous material upon only a portion of a workpiece, the resinous material preferably being deposited upon the workpiece as electrostatically charged solid particles. One zone of the workpiece is contacted, in the substantial absence of relative movement therebetween, with the cellular, resiliently deformable contact surface of a particle removal member to pick up particles of the resinous material therefrom without wiping or brushing the surface. Preferably, the resinous material is of such a nature that it can be fused to a unified coating, and the apparatus and method are particularly adapted for producing thermoplastic coatings upon armature rotors for electric motors.

Description

C United States Patent 11 1 [111 3,921,574 English Nov. 25, 1975 [54] COATING METHOD WITH CLEANING AND 3,355,309 11/1967 Bender et a1. 1. 427/104 PP T THEREFOR 3,355,310 11/1967 De Jean et al.. 427/104 3,781,107 12/1973 Ruhland 118/104 [75} Inventor: William P. English, Bridgeport,

Conn' Primary Examiner-Mervin Stein [73] Assignee: Electrostatic Equipment Assistant ExaminerSteven Hawkins Corporation, New Haven, Conn.

[22] Filed: Feb. 3, 1975 [57] ABSTRACT [21] Appl. No.: 546,547 An apparatus and method are provided for producing Related US Application Data a coat ng of resinous material upon only a portion of a workpiece, the resinous material preferably being de- [62] of 256294, May 1972' posited upon the workpiece as electrostatically charged solid particles. One zone of the workpiece is [52] "8/106; 1 18/104; 1 18/107; contacted, in the substantial absence of relative move- 2 118/109; 427/27; 427/104; 427/185 ment therebetween, with the cellular, resiliently de- [51] Int. Cl. 805C ll/02 formable Contact Surface of a particle removal [58] held of Search 1 18/100 bet to pick up particles of the resinous material there- 118/109, 309, 603; 427/27, 28, 104, from without wiping or brushing the surface. Prefera- 359 bly, the resinous material is of such a nature that it can be fused to a unified coating, and the apparatus [56] References (Med and method are particularly adapted for producing UNITED STATES PATENTS thermoplastic coatings upon armature rotors for elecl,860,132 5/1932 Broadston 118/106 motors- 3,083,683 4/1963 Fischer et al.... 118/106 3,136,650 6/1964 Avila 427/185 16 Clam, 17 D'awmg F'gures POWDER RECOVERY AND FEED POWDER REPLEN1SH O ELECTRIC INTEHFACE /ACCESS CHANNEL Hcoxxrmc PROCESS UNIT OVEN COLRJITII'NG MAIN i A; CONTROL OVEN CONTROL U.S. Patent Nov. 25, 1975 Sheet 1 of7 3,921,574

Sheet 2 of 7 3,921,574

' U.S. Patent Nov. 25, 1975 US. Patent N0v.25, 1975 Sheet30f7 3,921,574

Sheet 4 of7 3,921,574

. Patent Nov. 25, 1975 9B IEIQ U.S. Patent Nov. 25, 1975 Sheet5of7 3,921,574

U.S Patent Nov. 25, 1975 Sheet60f7 3,921,574

U.S. Patent Nov. 25, 1975 Sheet 7 of7 3,921,574

FIG. 12 m M 13 COATING METHOD WITH CLEANING AND APPARATUS THEREFOR This is a division of application Ser. No. 256,294, filed May 24, 1972.

BACKGROUND OF THE INVENTION Of the various ways in which coatings of fusible resinous materials are produced upon various workpieces, those in which the material is applied in particulate or powdered form are often found to be the most effective and satisfactory. Such techniques are used to produce coatings upon a wide variety of workpieces, including continuous lengths of wire and strip stock as well as individual objects which are often of a complex configuration, as would make coating by other techniques difficult or impossible. For example, attempts have been made to insulate the slots of rotors and stators for electric motors by depositing the resin in powdered form, which has proven particularly difficult due to the presence of reentrant surfaces which must be covered.

A common method of producing coatings of thermoplastic particulate materials is to utilize heat from the workpiece to cause softening and fusion of the particles upon contact. Thus, it has long been the practice to heat the article and to then submerge it in a bed (desir ably fluidized) of the particulate material so as to produce a coating upon all exposed surfaces, and as far as is known prior attempts to produce coatings from powdered resins upon electric motor components have employed this technique. However, the inherent drawbacks are quite apparent, and include the need for masking of portions of the workpiece which are to remain free from the coating material and/or the need to handle or direct the resin in such a manner that contact will be avoided. Not only are such precautions timeconsuming, but frequently they are difficult if not impossible to achieve in practice. Moreover, since the amount of material deposited using such a method is dependent upon the intensity of heat available from the workpiece and/or the duration of exposure, uniform thicknesses are oftentimes most difficult to obtain.

It is also well known that electrostatic forces may be utilized to cause attraction and adhesion of particles of resinous materials to a wide range of workpieces, which may thereafter be heated or otherwise treated to fuse the resin and produce the final unified coating. This approach has many advantages including uniformity of coverage, ease of access to undercut or reentrant surfaces, coating thickness control, etc. Nevertheless, the production of preferential deposits upon selected areas of the object has typically relied upon the use of mechanical or air masking techniques which are not entirely satisfactory under certain circumstances, such as when it is necessary to obtain a virtually clean surface closely adjacent to one that is to be relatively thickly covered.

Accordingly, it is an object of the present invention to provide a novel method and apparatus for the production of a coating of a solid, particulate resin upon a limited portion of a workpiece.

A more specific object of the invention is to provide such a method and apparatus for electrostatically coating the workpiece and for effecting the removal of the resinous material from selected portions thereof which are to be uncoated.

An even more specific object is to provide such a method and apparatus whereby a generally cylindrical article having reentrant surface portions may be coated with an adherent deposit upon the reentrant surface portions thereof.

Another object of the invention is to provide such a method and apparatus whereby such coatings may be produced quickly, easily and economically, which method and apparatus may be automatic and continuous.

A further object is to provide a novel contact belt unit which is adapted to remove the particulate resin from one zone of a workpiece without causing undue thinning or thickening of the deposit on an adjacent zone thereof.

SUMMARY OF THE DISCLOSURE It has now been found that certain of the foregoing and related objects are readily attained in apparatus comprising, in combination, a. chassis, particle removing means thereon, means for carrying a workpiece along a travel path, and drive means for the particle removing means and carrying means. The particle remov ing means includes a member movably mounted over the travel path and having a relatively resiliently deformable contact surface thereon of small open-cell construction, which is disposed for direct contact upon a portion of the workpiece as it is carried along the travel path. The carrying means and particle removing means are adapted for coaction to move the contact surface and the contacted portion of the workpiece at the same linear speed during contact to substantially prevent wiping of the workpiece by the contact surface.

Preferably, the portion of the travel path over which the particle removing means is mounted is generally rectilinear, with the member of the particle removing means being positioned to move in a circuitous path in a plane parallel to the axis of the travel path portion. The particle removing means may comprise a set of spaced pulleys about which extends an endless flexible belt having the contact surface disposed on its outer surface. Most desirably, the contact surface is comprised of an open-cell foam elastomer having a cell size of about 1 to 20 mils, and polyurethane is advantageously utilized as the elastomer.

The particle removing means may include a plurality of contact elements spaced along the travel path to sequentially contact substantially the same portion of the workpiece. Alternatively, or additionally, the particle removing means may include a plurality of elements which are spaced across the travel path to contact different portions of the workpiece.

In the preferred embodiments of the invention, the apparatus is adapted for the coating of a generally cylindrical article, and the carrying means thereof is a conveyor adapted to support the article with its axis extending transversely across the travel path. In such an embodiment, the conveyor desirably supports the article for free rotation thereon with contact of the article by the contact surface of the particle removing means causing rotation thereof as the: conveyor carries the article along the travel path. The apparatus is especially suited for the coating of an armature rotor having a cylindrical core portion with a shaft portion extending axially from each end thereof. In such a case, the conveyor is adapted to engage the shaft portions of the rotor, and the contact surface of the particle removing means is disposed for contact with the circumferential surface of the core portion so as to effect the removal of particles therefrom.

The apparatus may include vacuum means disposed adjacent the contact surface to effect the removal of particles of the resinous material therefrom. In instances in which the apparatus is adapted for the production of a coating of a thermoplastic resinous material, it will additionally include heating means on the chassis along the travel path downstream of the particle cleaning means. Such heating means will be adapted to heat at least a first zone of the workpiece to produce at least partial fusion and coherence of the particles thereon. Moreover, the apparatus may include means on the chassis upstream of the particle removing means for producing a cloud of electrostatically charged solid particles of resinous material.

In especially preferred embodiments of the invention the cloud producing means employed in the apparatus includes an electrostatic cloud chamber. Such a chamber may comprise a receptacle having means for pro ducing a fluidized bed of charged particles including a gas-permeable plate extending thereacross in a generally horizontal intermediate plane and spaced above the bottom wall of the receptacle to define a plenum chamber therebelow. The receptacle also has electrode means extending thereacross to electrostatically charge particles of solid resinous material passing proximate thereto. Most desirably, the apparatus will include a particulate material reservoir having feed means communicating with the cloud chamber. In such a case, the electrode means may span a lesser area than the gaspermeable plate to provide an electrode-free vertical corridor within the receptacle through which particles of the resinous material may pass without acquiring a significant charge. A device for sensing the level of the bed of particles within the receptacle, in response to which the feed means conveys resinous material from the reservoir to the chamber when the bed level falls below a preselected height, may also be provided. The sensing device is positioned within the vertical corridor over the horizontal porous plate, to thereby minimize the effect of electrostatic charging upon the sensed level of the bed. The electrode employed may be a generally planar, grid-like structure disposed adjacent the upper surface of the gas-permeable plate, and electrode and plate may be substantially coextensive except at one area of the plate over which the electrode does not extend, thereby providing the electrode-free vertical corridor.

Certain objects of the invention are attained in accordance with the method hereof, whereby a cloud of electrostatically charged solid particles of resinous material is produced and the workpiece is exposed to the charged particles with a charge effectively opposite thereto, so as to cause a layer of particles to deposit thereon. Thereafter, a portion of the workpiece is contacted with a relatively resiliently deformable contact surface having a small open-cell construction. Such contact is effected under conditions avoiding relative movement between elements of the workpiece portion and of the contact surface while in such contact, to avoid wiping action from occurring therebetween. The contact surface and workpiece are thereafter separated with the particles lodged within the cells of the contact surface to thereby effect the removal of particles from the contacted portion.

Preferably, the workpiece moves along a travel path during contact with the contact surface, which simultaneously moves adjacent thereto. The workpiece may be a generally cylindrical article supported for free rotation about its axis transversely across the travel path. Contact by the contact surface on a circumferential surface of the article causes rotation thereof with the circumferential surface moving at the same linear speed as that at which the contact surface moves. It is especially preferred that the article be an armature rotor for an electric motor having reentrant surface portions in the cylindrical core portion thereof defining winding slots therein. In such an instance, the contact element removes particles from the circumferential surface of the core portion without causing undue thinning or thickening of the layer of particles along the edges of the slots. Most desirably, the contact surface is comprised of an open-cell foamed elastomer having a cell size of about 1 to 20 mils, and the resinous material is a powder consisting essentially of particles smaller than about mesh. The resinous material may be thermoplastic, in which event the method will include the additional step of heating the particles of resinous material remaining on the workpiece subsequent to the particle removal step, so as to cause at least partial fusion and coherence thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of apparatus embodying the present invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a side elevational view of the coating pro cess unit of the apparatus of FIGS. 1 and 2, drawn to an enlarged scale and with housing portions removed to expose internal features thereof;

FIG. 4 is a perspective view of an armature rotor for which the illustrated apparatus is particularly adapted;

FIG. 5 is a fragmentary perspective view of the forward end of the coating process unit including the load zone and a portion of the electrostatic coating station, drawn to a scale enlarged from that of FIG. 3;

FIG. 6 is an enlarged sectional view along line 66 of FIG. 3 illustrating the support and positional control structure provided at the load zone and showing an armature rotor carried on the forward conveyor for movement therethrough;

FIG. 7 is an end view of the electrostatic coating station along line 77 in FIG. 3 with portions of the housings broken away to illustrate the internal features thereof and drawn to a greatly enlarged scale;

FIG. 8 is a side elevational view of the sensing device employed in the cloud-coating unit of the electrostatic coating station;

FIG. 9 is a fragmentary end view along line 99 in FIG. 3 showing the powder removal zone of the apparatus with the contact belt unit thereof in its normal operating position, drawn to a greatly enlarged scale and having portions in vertical section to illustrate the construction thereof;

FIG. 10 is a front view of the powder removal zone at an acute angle to the upper surface of the deck, drawn to a slightly diminished scale from that of FIG. 9 and showing the contact belt unit in its raised position;

FIG. 11 is a fragmentary end view of the powder removal zone along line 11-11 of FIG. 3, drawn to the scale of FIG. 9;

FIG. 12 is a fragmentary plan view of the shaft cleaning units provided within the powder removal zone, drawn to a scale enlarged from that of FIG. 10 and with the hold-down brackets removed to expose the vacuum slots thereof;

FIG. 13 is a side elevational view of the vacuum nozzle and associated parts employed with each of the units of FIG. 12;

FIG. 14 is an enlarged sectional view along line 14-14 in FIG. 3 showing the precuring unit of the apparatus with an armature rotor passing therethrough, and in phantom line showing the raised position of the cover assembly;

FIG. is a perspective view of the air knife assembly at the powder recovery zone of FIG. 3, drawn to a greatly enlarged scale;

FIG. 16 is a fragmentary perspective view to a greatly enlarged scale of the intermediate conveyor employed in the apparatus; and

FIG. 17 is a fragmentary perspective view of one band of the endmost conveyor of the apparatus, drawn to the scale of FIG. 16.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detail to the appended drawings, therein illustrated is an armature slot-coating system embodying the present invention and details of the various units and zones thereof. FIGS. 1 and 2 illustrate the overall layout of the system, the heart of which is the coating process, so designated on the drawing. Auxiliary to the coating process unit is an oven and a cooling unit, and main control and oven control facilities are furnished. Also included in the system to enable a desirable mode of operation is a power recovery and feed unit and a powder replenishment unit. As will be appreciated from FIG. 2, the workpieces are loaded at an infeed zone at the left-hand end of the coating process unit from which they pass serially through an electrostatic coating zone, a powder removal zone, a precure zone, and a powder recovery zone; they then pass into the oven and finally through the cooling unit. Excess powder from the electrostatic coating zone is recovered in the powder recovery and feed unit and is returned through an appropriate conduit to the coating unit on a substantially continuous basis, and additional powder is furnished from the powder replenishing unit .as needed. An electric interface access channel runs along the rear of the coating process unit to provide power at the various zones thereof.

With specific reference now to FIG.- 3, the coating process unit of the system is depicted in greater detail. It includes a frame 10 on which are rotatably supported three conveyor drive sprockets, generally designated by the numerals l1, l2 and 13 respectively from left to right in the F IG., and idler wheels 14 are positioned between adjacent sprockets. A forward endless conveyor, generally designated by the numeral 16, runs about

sprockets

11 and 12 and the idler wheel 14 therebetween; a center endless conveyor, which is generally designated 18, runs about sprockets l2 and 13 and about the idler wheel 14 positioned between them, and a rearward endless conveyor, which is generally designated and is fragmentarily illustrated, runs about the right-hand sprocket l3 and a cooperating sprocket which is not illustrated and is positioned adjacent the end of the cooling unit shown in FIGS. 1 and 2. A drive pulley 22 operates the powder removal unit and is driven by the electric motor 24 which is supported within the frame 10. A second motor 25 is connected to sprocket 13, thereby synchronously driving all

conveyors

16, 18, 20 since they are coupled by the sprockets l2, 13.

Although the invention is not to be construed as limited to coating of any particular workpiece, and may be feasible for coating selected portions of objects which are elongated or of continuous" length, the system illustrated is especially suited for the coating of armature rotors of the type generally designated by the numeral 26 in FIG. 4, and is intended principally for that purpose. The rotor 26 is of conventional configuration and includes a cylindrical core portion 28 having spaced about its circumference four axially extending, reentrant winding slots 30. Extending from opposite ends of the core portion 28 are simple and crank-

type shafts

32, 34 respectively, and the shaft 34 has a spring clip 35 engaged upon it adjacent the end of the core portion 28.

As will be appreciated, the slots 30 of the rotor 26 are designed to receive wire windings, making it necessary to provide the slots 30 and the opposite end faces 37 of the core portion 28 with a layer of insulating material to enable magnetic poles to be defined thereon. It is also important that the outer circumferential surface of the core portion 28 and the

shafts

32, 34 be free from insulating material; the present system is unique in enabling the rapid and facile production of coated rotors having deposits of insulating material which are present only at selected locations and are of substantially uniform thickness, particularly along the edges of the slots 30.

FIG. 5 illustrates in greater detail the loading zone of the coating process unit, whereat a narrow rectangular opening 38 is provided through the deck 36 of the frame 10 to accommodate the edge of drive sprocket 11. As can be seen, the forward conveyor 16 is comprised of two independent flexible and continuous parallel bands, generally designated by the

numerals

44 and 45, and the drive sprocket 11 consists of a pair of parallel sprocket wheels 40 mounted on a common shaft for concurrent rotation. Each of the sprocket wheels 40 has about its circumferential edge a multiplicity of small rectangular teeth 42; the belt portion 46 of each of the

bands

44, 45 is provided with a multiplicity of rectangular apertures 48 which are spaced along the length thereof, the apertures 48 meshing with the rectangular teeth 42 of the respective sprocket wheels 40 as the bands pass thereover along their travel path. Extending at a right angle from the inner edge of the belt portion 46 of each of the

bands

44, 45 are a multiplicity of

carrier tabs

50, 50 respectively, and each tab 50, 50' has bevelled shoulders 51 leading into the shaft slots 52, 52' therebetween. As will be appreciated, the

slots

52, 52 are dimensioned to receive the shafts of the armature rotor 26, and the tabs 50' are slightly narrower than the tabs 50 to render the slots 52 somewhat wider than the slots 52, thereby enabling close-fitting engagement of

shafts

32, 34, notwithstanding their different diameters. It will be evident that the bevelled shoulders 51 facilitate insertion and removal of the shafts of the armature rotors 26 into and from the slots 52.

As can most readily be seen by additional reference to FIG. 6, one of a pair of elongated rectangular curb blocks 54 extends along each side of the upper flight of the conveyor 16, with the curb blocks 54 being secured to the deck 36 by bolts 56 (fastened in an appropriate manner, not illustrated). Coextensive with each of the curb blocks 54 is a guide rail 58 which is secured upon the upper surface of the associated curb block 54 by a number of bolts 60 spaced along the length thereof. A

shallow recess 61 is provided along the upper surface adjacent the inner edge of each of the curb blocks 54 enabling the belt portion 46 of the

conveyor bands

44, 45 to pass between the curb blocks 54 and the bottom surface of the guide rails 58. The guide rails 58 have inner surfaces which extend downwardly and then at an angle inwardly to provide guide surfaces 62 sloping downwardly toward the travel path. The guide surfaces 62 define therebetween a trough which is dimensioned so that armature rotors 26 carried by the conveyor 16 extend thereacross with little free space adjacent the ends, thus ensuring that the rotors 26 remain accurately positioned across the conveyor 16 and centrally positioned on the axis of the travel path of the unit.

Extending forwardly from adjacent the ends of the curb blocks 54 is a support extension 64 which underlies the conveyor 16 and provides support therefor as the

bands

44, 45 disengage from the sprocket wheels 40. Supported above the extension 64 is a loading platform portion 66 from which extend rearwardly a pair of thin support rails 68 which are secured in a parallel relationship against the inner faces of the curb blocks 54. The loading platform 66 is provided to facilitate loading and seating of the rotors 26 in the slots 52 of the conveyor 16, and the support rails 68 provide underlying support for the

shafts

32, 34 as the rotors 26 proceed along the travel path, it being appreciated that the shafts ride upon the upper edges of the support rails 68 rather than resting at the bottom of the slots 52. As a result, the conveyor 16 serves only to drive the rotors 26 forwardly through the system, with contact upon the rails 68 causing them to rotate as they are conveyed.

From the load zone, the armature rotors 26 are conveyed to the electrostatic coating station illustrated in detail in FIG. 7, which is comprised of a hood, a powder feed stack, and an electrostatic coating chamber, generally designated by the

numerals

72, 74 and 76 respectively. The electrostatic coating chamber 76 consists of an upwardly opening enclosure 78 secured against the bottom surface of the deck 36 and having a bottom wall opening through which air is charged from a pressurized source 79 thereof. A horizontal, porous ceramic partition 80 divides the enclosure 78 into a lower air plenum chamber 82 and an upper cloud chamber 84. The partition 80 supports an overlying grid-type electrode 86 connected to a diagrammatically illustrated high voltage source 88 and extending partially across the enclosure 78 to provide an electrodefree area 85 between its inner edge 87 and the sidewall 89, through which extends an imaginary vertical corridor.

Within the corridor, supported upon the depending bracket 92, is a pneumatically operated fluidic sensing device comprised (as seen in FIG. 8) of a body 90 with a wire actuating finger 94 extending therefrom; one appropriate device is sold by Norgren Fluidics of Littleton, Colorado under the name FEATHERFLEX FS- 010-000. On the outer end of the wire finger 94 is a float sphere 96 which may be fabricated of a foamed polystyrene or comparable lightweight material, and pneumatic control lines 98 extend from the body 90 and are connected to control means (not illustrated).

The feed stack 74 consists of a sifter box 100 having a screen 102 horizontally positioned across the central portion thereof and having a recycle feed conduit 104 and a replenish conduit 106 leading thereinto. As will be appreciated, the conduit 104 extends from the powder recovery and feed unit and the conduit 106 extends from the powder replenishment unit, both shown in FIGS. 1 and 2. The

conduits

104, 106 deliver thermoplastic resin powder 103 into the upper portion of the sifter box 100 from which it passes through the screen 102 and the opening 108 in the deck 36 with lumps and foreign matter being removed by the screen 102. The powder 103 then falls upon the porous partition where it becomes fluidized by air passing upwardly from the plenum chamber 82 in a conventional manner. The fluidized powder 103 exerts an upward force upon the float sphere 96 of the fluidic sensing device; when the quantity of powder 103 above the partition 80 is insufficient to urge the sphere 96 (and hence the actuating finger 94) upwardly to the necessary extent, a signal from the sensor causes the control means (not illustrated) to deliver an additional quantity of powder 103 through the conduit 106 from the powder replenish unit, thereby correcting the deficiency.

The hood 72 is positioned over an elongated slot 1 10 in the deck 36 along which the parallel guide rails 68 extend. It is secured to the deck by bolts 112 and has a tunnel portion 1 14 with an end wall 1 16 forming a partial closure therefor and defining a tunnel opening 1 15 at each end thereof. A stack portion 118 extends upwardly from the tunnel portion 114 of the hood 72, and has a takeoff conduit 120 which is attached to a suitable vacuum source and enables excess powder to be removed from the coating station. Such powder is returned to the recovery and feed unit for ultimate recycle through the conduit 104 leading to the feed stack 74. An elongated baffle plate 122 is inclined downwardly from each sidewall of the tunnel portion 114 toward the travel path of the unit, and the plates 122 cooperate with the carrier tabs 50, 50' to confine powder 103 which passes upwardly through the slot 110 to the central portion of the rotors 26 passing thereover.

As will be appreciated, the powder 103 employed for the coating operation is of such a nature that it is capable of acquiring an electrostatic charge as the particles pass through the grid electrode 86. The rotors 26 are maintained at ground potential (such as by grounding the conveyor 17 with which they are in contact) during passage over the slot 1 10, thus causing attraction and adherence of charged powder particles to the surface 8 of the rotors 26, with the electrostatic effect ensuring that all exposed surfaces, including winding slots 30, are coated. Due to the charge on the powder particles, it is important that the fluidic sensing device be positioned over the electrode-free area of the horizontal partition 80. In this region charging of particles is minimized, as a result of which the attractive force from the grounded rotors 26 is quite insignificant and particles thereat are elevated only by the buoyant effect of the pressurized air. Otherwise, the electrostatic force on the particles would lead to an inaccurate indication of the quantity of powder present in the system, rendering control of the automatic replenishment system virtually ineffective.

Since the armature rotors 26 must be substantially free of insulating material on the circumferential surface of the core portion 28 and along the

shafts

32, 34, and since in the coating step powder deposits upon all exposed surfaces, the method and apparatus of the invention require that means be provided for removing powder from selected surfaces of the rotor 26 where it is unwanted. To that end, the illustrated apparatus is provided with a powder removal station which includes the contact belt unit, generally designated by the numeral 124, and shown in FIGS. 3, 9 and 10. The contact belt unit 124 includes an elongated forward frame member 126 from which extend rearwardly triangular mounting brackets 128 which are pivotally supported upon posts 130 projecting upwardly from the deck 36. In this manner, the unit 124 is hingedly supported for ready displacement from the position over the deck 36 shown in FIG. 9 to its open position in FIG. 10. Affixed in a central location behindthe forward frame member 126 is a pinion block 131 which, in turn, has a gear train block 132 mounted behind it. A short central shaft 134 is journaled at its ends by appropriate means to extend transversely through the forward frame member 126, the pinion block 131, and the gear train block 132, and it has a drive gear 136 affixed on it within the gear train block 132. The shaft 134 also has a drive pinion 138 affixed to it in front of the gear 136, with the pinion 138 residing generally within the pinion block 131. A lower shaft 140 is journaled at its ends and extends transverselybetwe'en the pinion block 131 and the gear train block 132; on it is affixed, in meshing engagement with the drive gear 136, an upper transfer gear142. The transfer gear 142 communicates through a deck opening 143 with a lower transfer gear 144 which is supported upon a shaft l46 positioned and appropriately journaled (by means not shown) below the deck 36; As can be seen in FIG. 3,'the lower transfer gear 144 meshingly engages a gear 148 which is affixed to the shaft on which the drive pulley 22 is supported. In this manner, power is delivered from the motor 24 through the drive pulley 22 and the train of

gears

148, 144, 142 ultimately to the drive gear 136 for the contact belt unit 124. As can be seen, pivoting the unit 124 upwardly about the posts 130 simply disengages the

gears

142 and 144, discontinuing operation of the unit 124"andfpermittingaccess to the normally covered portion thereunder. 1

A belt pulley shaft 150 is journaled in the forward frame member 126 and pinion block 131 on either side of the central shaft 134, andapulley pinion (not exposed .but' identical to pulley pinions 152 to be discussed hereinafter) is affixed to'the inner end of each of the shafts 150 anclis in meshing engagement with the drive pinion 138. (It will be. understood that the pulley pinion onshaft 150 to the left of shaft 134m FIG. 10

lies behind pinion 138, as viewed in FIG. 9, and that the pulleys and belt assembly at the left side of FIG. 9 are shown along a section line somewhat forward of line 9-9.) To the opposite ends of the pulley shafts 150 are affixed belt pulleys 154. Spaced to either si'deof the central pinion block 131 is an auxiliary pinion block 156 in which is contained a pair of belt pulley'shafts 150 and atransfer pinion shaft-134 therebetween. The inner ends of the pulley shafts 150 have affixed to them pulley pinions 152 (as can be seen in the left-hand auxiliary pinion block 156 in FIG. 10) and the transfer pinion shaft 134 has affixed to its inner end a transfer pinion 158 in meshing engagement with each of the pulley pinions 152 on either side thereof. Adjacent each end of the forward frame member 126 is a rectangular bearing block 162 in which is journaled, by appropriate means, a belt' pulley shaft 150. A belt pulley 154 of the type previously referred to is secured on the outer end of each belt pulley shaft supported in either the auxiliary pinion blocks 156 o'rrthe bearing blocks 162.

The eight pulleys 154 function as four sets with adjacent pairs of pulleys supporting a belt assembly consisting of an underlying support element 164 and an outwardly exposed contact element 166, .backup blocks 165 being affixedto the frame member 126 within the confines-of each assembly. Thecontact element is preferably of afoamed elastomer-Oracomparable material providing an open-cell outer surface. Such a structure enables the contact element 166 to pick up powder from the surface of the core portion 28 simply by contact therewith, with no wiping or brushing action being necessary or desirable. More particularly, it is believed that by simple contact of the element 166 upon the rotor 26 the powderpresent onthe surface contacted becomes lodged in the cellsor small openings present over the surface of the element .166, such engagement overcoming the electrostatic attraction and permitting pick-upof particles by the element 166. Typical ofthe materials that are suitable as the contact element 166 are polyurethane (preferably) and silicone resins, -polybutadine,.butyl and neoprene "rubbers, etc.- The material should provide open cells of about 1 to 20 mils at the surface of the element 166, and accordingly the elastomer foams are very conveniently used; however, other materials might be substituted, andit is not believed that the internal structure is of basic significance. The support element 164 may be a timing belt (i.e., having transversely extending ridges about its inner surface) with the pulleys 154 being provided with corresponding ridges and grooves, or square teeth, to cooperate therewith. Drive power is transferred from the motor 24, through the

gears

148, 144, 142, 136, to the pinion 138 within the central pinion block 131, and to the innermost belt pulleys 154. Due to the interconnection through the pulley pinions 152 and ,transfer pinion 158 within each of the auxiliary pinion blocks 156, the belt assemblies on the outer sets of pulleys 154 are simultaneously driven,.-with all belt assemblies rotating at precisely the same rate and, in the same direction. 7

As is seen in FIG. 9,-a central sprocket wheel 40' having' rectangular circumferential teeth. 42 is supported on a common shaft (not shown) with two outside wider than the slots between the tabs 178 to snugly receive the

shafts

34, 32 of the rotor 26, respectively. The following edges of each of the tabs 178,-178 have bevelled shoulders 51 to facilitate entry of the

shafts

32, 34 thereinto; however, it will be noted that the forward edges of the tabs 178, 178' are not bevelled, and the reason therefor will be explained directly.

- As can be seen in FIG.- 10 a transfer of the rotors 26 occurs within the powder removal zone with the rotors 26 shifting from-the forward conveyor 16 to the intermediate conveyor 18. Engagement of both conveyors -l6, 18 on different sprocket-wheels 40, 40' of the common -.drive sprocket "12 and the construction employed permits conveyor 18 to pass between the

bands

44, 45 of the conveyor 16. At the point of common tangency of the

conveyors

16, 18 to sprocket 12 of the

respective slots

52, 180 thereof are substantially aligned, causing the

shafts

32,34 of the rotors 26 to momentarily reside in slots of both conveyors simultaneously. As the

bands

44, 45 of the forward conveyor 16 pass downwardly about the sprocket 12, the upper corners of the tabs 180, 180' of the intermediate conveyor 18 engage behind the

shafts

32, 34 to smoothly and effectively carry them out of the slots 52 with the bevelled shoulders 51 at the following edges of the

tabs

50, 50 facilitating withdrawal. Thereafter, the rotors 26 are propelled through the system by the center conveyor 18.

Assuming movement to be in a left to right direction, contact of the ends of the

shafts

32, 34 upon the support rails 68 causes rotation of the rotors 26 in a clockwise direction. If the motor also drives the belt assemblies of the contact belt unit 124 in a clockwise direction, the direction of rotation of the rotors 26 will reverse upon encountering the lower flight of element 166 at the entrance of the unit 124 (the relationship at contact being as depicted in FIG. 9). Such contact causes a significant proportion of the powder on the outer circumferential surface of the cylindrical core portion 28 of the rotors 26 to be displaced therefrom and to fall into the powder recovery hopper 184, which is positioned at an appropriate location beneath the deck 36 (as may be seen in FIG. 3); most, if not all powder entering the slots 30 as a result of such contact will simply fall out during subsequent rotation of the rotor 26. The hopper 184 is connected to the powder recovery and feed unit through a vacuum system (not illustrated) by a conduit 186. Most of the remaining powder on the surface of the core portion 28 is picked up by the contact element 166 of the belt assembly, as previously described, with any additional powder being removed by the successive belt cleaning effects in the same manner. As will be appreciated, since the rotors 26 are supported for free rotation, after contact with the contact element 166 they turn at precisely the same speed under the influence thereof. This prevents relative wiping or brushing action between the element 166 and the rotors 26, such as would tend to cause uneven deposits to be produced, particularly at the edges of the slots 30 where complete coverage is most important. Notwithstanding the backup blocks 165, pressure from the belt assemblies will generally be attributable only to the weight thereof. Nevertheless, the contact element 166 would tend to enter the slots 30 as a result of relative movement, wiping and removing powder from the edges thereof. Accordingly, the substantial absence of such movement constitutes a primary benefit of the present invention. The nozzles 170 and associated vacuum conduits 172 are adjustably supported in the bifurcated end portions of the nozzle support arms 168 with the nozzles 170 lying closely adjacent the contact elements 166. In this way, the powder picked up by the elements 166 is withdrawn from the cells thereof and is conveyed to the recovery portions of the system for recycle.

Positioned within the powder removal zone near the forward end of the second belt assembly of the unit 124 is a pair of vacuum blocks 188, which are secured to the deck 36 along the sides of the travel path. As can best be seen in FIG. 12, each of these blocks has a

face plate

190, 190 secured upon its upper surface and of an elongated vacuum channel 192 extending lengthwise therein. As can be seen with additional reference to FIGS. 3 and 13, a vacuum nozzle 194 of generally oval cross section is secured against the lower surface of each of the vacuum blocks 188, each nozzle 194 12 having a circular throat portion 196 about which is positioned an annular mounting collar 200 by which it is secured against the associated vacuum block 188Jby means not shown). Secured over the throat portion 196 of each nozzle 194 is a vacuum hose 198 which is connected to a vacuum source (not shown) and ultimately to the powder recovery and feed unit illustrated in FIGS. 1 and 2.

The

face plates

190, 190 on the vacuum blocks 188 are provided with elongated slots 202, 202', each of which extends in a generally angular relationship outwardly from the travel path. These

slots

202, 202 register over the channels 192 in the blocks 188 and serve to define a flow passage for air under the influence of vacuum drawn through the conduits 198. As the armature rotors 26 travel between the vacuum blocks 188 with the

shafts

32, 34 thereof in rolling contact upon the

face plates

190, 190 respectively, the vacuum effect from below thoroughly cleans the

shafts

32, 34 of any powder which may have become deposited thereon. Normally, powder will be present in the

shafts

32, 34 as a result of the initial electrostatic coating operation and/or due to displacement from the circumference of the cylindrical core portion 28 during powder removal by the first belt assembly in the contact belt unit 124. The divergent disposition of the slots 202, 202' will cause particles of powder to be removed first from the portions of the

shafts

32, 34 adjacent the core portion 28 and progressively outwardly therealong. It will be appreciated that the nonlinear and nonuniform configuration of the slot 202 is necessitated by the configuration of the crank shaft 34 which passes thereover. As can be seen in FIGS. 9 and 10, a hold-down bracket 201 is secured to each of the vacuum blocks 188. Each bracket 201 includes a pressure plate element 203 which overlies the

slot

202, 202 of the associated block 188 and serves to engage the tops of the

shafts

32, 34 as they are conveyed thereunder, thereby forcing the shafts against the

face plates

190, 190 to ensure efficient powder removal therefrom.

After travelling past the vacuum blocks 188, the armature cores 26 are conveyed beneath the third of the series of belt-cleaning assemblies while being supported upon parallel side rails 182. The fourth contact belt effect is similar in design to the first three, with the exception that it is provided with contact belt assemblies for the

shafts

32, 34 as well as for the cylindrical core portion 28 of the rotors 26. The construction of this portion of the contact belt unit 124 is most clearly illustrated in FIG. 11, wherein it can be seen that a set of three belt pulleys 154 are mounted on a common shaft for simultaneous rotation. Each of the pulleys has a belt assembly consisting of a support belt 164 and a contact belt 166 constructed as hereinbefore described, and it will be appreciated that the belts extend between two of such sets of three belt pulleys 154 (as can be seen in FIG. 10). The outer belt assemblies are cleaned by passage under nozzles of the vacuum assembly 171, shown only in FIG. 3. It should be appreciated the location of the belt assemblies for the shafts may be altered from that illustrated; for example, relocating them to the second of the four belt effects may facilitate operation of the vacuum blocks 188 thereat and render shaft cleaning more effective.

From the contact belt unit 124, the armature rotors 26 pass into a precuring unit, generally designated by the numeral 204 and shown in FIGS. 3 and 14. With specific reference to the latter figure, it can be seen that the precuring unit 204 consists of a cover assembly, generally designated by the numeral 206, which has affixed thereto a pair of angle brackets 208, only one of which is visible in FIG. 14. The brackets 208 are secured at one end to the cover assembly 206 by appropriate bolts 210, and the opposite ends thereof are pivotally supported upon posts 212 which are mounted upon the deck 36 of the machine. Also secured to the cover assembly 206 is a right angle contact arm 214 which has an element extending over the end of a spring-loaded plunger assembly 216. In normal operation the cover assembly 206 will be maintained in the position illustrated in full line in FIG. 14 by fluid pressure means acting against the upward force of the plunger assembly 216. If the machine'stops or if some emergency situation occurs, the fluid pressure force is disrupted, permitting the plunger assembly 216 to immediately raise the cover assembly 206 to the position shown in phantom line.

The cover 218 of the cover assembly 206 is elongated (as can be seen in FIG. 3) and is of inverted, generally U-shaped configuration (as is shown in FIG. 14). It has a number of layers 220 of insulating material lining the top wall thereof, which are secured, along with a metal sheet reflector 222 and a pair of elongated angular baffle plates 224, to the cover 218 by appropriate bolts 226. Heating elements 228, which may be CALROD units, extend longitudinally within the cover 218 and are supported therein by a number of inserts 230, which are spaced along the length of the cover 218 and have pairs of apertures 231 to receive and support the heating elements 228. The baffle plates 224 are constructed with inclined walls 232 which slope downwardly and inwardly toward one another and toward the travel path; the walls serve to support the inserts 230 as well as their primary function of reflecting and concentrating heat from the elements 228 upon the central portion of the travel path.

Supported along each side of the cover 218 at the lower edges thereof is one of a pair of configured cool ing blocks 234, which may be constructed of aluminum or another suitable material having a high heat transfer coefficient. It will be appreciated that these cooling blocks are elongated and extend along substantially the entire length of the cover 218. The cooling blocks 234 have inner upstanding elements 235 which are configured to define behind them circular recesses 236, in which are supported cooling tube portions 238. Small, downwardly opening U-shaped channels 240 are defined along the lower inner edges of the upstanding elements 235, and a depending ridge 242 is provided on each of the cooling blocks 234 adjacent the lower outer edge thereof.

The ridges 242 of the cooling blocks 234 are received in narrow, upwardly opening U-shaped channels 244 defined in the upper surface of the base of the precuring unit 204, the base being generally designated by the numeral 246. A relatively large, upwardly opening U- shaped channel 250 extends axially in the base 246 along its entire length to define the travel path there through. The underside of the base 246 has a U-shaped channel 248 of a similar size running along its length, with the opposed relationship of the channels creating a relatively thin floor portion 252 therebetween. A rectangular base block 254 is seated in the downwardly opening channel 248 and is welded in place with its upper surface spaced a short distance downwardly from the lower surface of the floor portion 252 to define a shallow water channel 256 therebetween. Upwardly opening U-shaped slots 258 are formed in the upper surface of the block and along the entire length thereof between the central channel 250 and each of the relatively narrow channels 244, and each of the slots 258 has a cover strip 260 engaged over its open end to thereby define closed conduits therewithin.

At each end (only one end being shown) the base 246 is provided with a transverse bore 262 which communicates with the opposite ends of the shallow water channel 256. To facilitate manufacture, the bores 262 are simply drilled inwardly from the side of the base 246, with plugs 264 being inserted afterward to close the ends. Extending upwardly and inwardly from the opposite ends of the bores 262 are short connecting channels 266 (only two of the four of which are seen because only one end of the base 246 is illustrated), one of which communicates with each of the U-shaped slots 258 at one end thereof. Finally, an inlet port 268 communicates from the lower surface of the base 246 with the transverse bore 262, and it will be appreciated that the other end of the base 246 has a similar port 268 communicating with the associated bore 262 provided thereat.

In operation, the precure unit 204 heats the cylindrical core portion 28 of each of the armature rotors 26 while simultaneously cooling the

shafts

32, 34 thereof. Heat is generated by the elements 228, with the reflector 222 and the baffle plates 224 effectively directing the heat inwardly toward the core portion 28 and concentrating it thereat. The simultaneous cooling effect is provided by passing water through the base 246 and the configured cooling blocks 234. With respect to the base 246, water passes inwardly through the illustrated port 268, transversely across the block in the bore 262, and thence along the length of the base 246 within the shallow water channel 256 and the U-shaped slots 258 to pass outwardly through the transverse bore and port not illustrated. In this manner, a cooling effect is transmitted through the thin floor portion 252 to cool the central band 176 of the conveyor 18 and the surrounding area. Water passing through the slots 258 serves not only to cool the sides of the conveyor 18, but has the primary function of producing a cooling effect through the cover strips 260. The

shafts

32, 34 of the armature rotors 26 contact these strips 260 directly, so that the cooling water passing therebeneath very effectively lowers the temperature of those portions. The configured blocks 234 are cooled by water passing into one of the cooling tube portions 28 and out of the other, the portions 238'being parts of a continuous conduit. As a result, the horizontal part 237 of each of the blocks 234 is cooled and cooperates with the base 246 to effectively maintain the

shafts

32, 34 at a relatively low temperature. The upper ends of the

carrier tabs

178, 178 of the conveyor 18 extend into the downwardly opening U-shaped channels 240 adjacent the lower inner edges of the blocks 234, and are cooled thereby. In addition, the engagement of the depending ridges 242 in the upwardly opening channels 244 increases the effectiveness of cooling by unifying the cover 218 and base 246 of the precure unit 204. A low temperature shell is thereby defined about the travel path through the precuring unit 204, except in the limited area thereabove at which the heating effect is concentrated. Accordingly, the unit 204 very effectively cools parts of the ro tors 26 which lie outwardly of the cylindrical core por tion 28, while the portion 28 is heated to a relatively elevated temperature. As a result, only resin on the core portion 28 is melted and fused, with any powder remaining on the

shafts

32, 34 being maintained in a solid particulate state. This permits removal of unwanted powder from the

shafts

32, 34 while simultaneously producing a relatively adherent coating in the slots of the core portion 28, the circumferential surface of the core portion 28 having been free from powder by the action of the belt assemblies in the contact belt unit 124.

Turning now in detail to FIG. 15, therein illustrated is an air knife assembly, generally designated by the numeral 270, which is positioned immediately downstream from the precure unit 204, as can be seen in FIG. 3. The air knife assembly 270 consists of a pair of spaced, inverted U-shape bridge members 272 which have mounted thereon a pair of spaced air manifold bars 274. The manifold bars 274 are adjustable (by means not shown) to vary their spacing and angular attitude relative to one another, and each of them has a number of flattened nozzles or air knives 276 extending downwardly therefrom toward the deck 36 of the machine. In general alignment under each of the manifold bars 274 is an upwardly opening elongated trough 278 which is connected to a vacuum source (not shown) through vacuum conduits 280 attached to the lower ends thereof. As will be readily appreciated, armature rotors 26 pass from the precuring unit 204 beneath the bridge members 272 of the air knife assembly 270 with their

shafts

32, 34 extending outwardly over the troughs 278. Air is charged under pressure into the manifold bars 274 through the air conduits 282 and is blown at high velocity upon the

shafts

32, 34 through the air knives 276 as the rotors 26 travel through the assembly 270. Due to the discrete form in which the particles are maintained as a result from the cooling effects of the precuring unit 204, the air from the knives 276 effectively dislodges any particles present on the

shafts

32, 34 and propels them into the troughs 278. In this manner, the shafts are thoroughly cleaned prior to entry of the rotor 26 into the oven, with the excess powder being returned to the system through the conduits 280.

As will now be appreciated, uncoated armature rotors 26 are loaded in successive pairs of slots 52, 52' of the

conveyor bands

44, 45 at the infeed station of the apparatus, and enter the oven with at least partially fused and cohered coatings of resin in the slots 30 and on the end faces 37 thereof. The circumferential surfaces of the cylindrical core portions 28 of the rotors 26 are virtually devoid of any powder particles. This is accomplished by the contact belt elements 166, which effectively remove all powder deposited thereon without causing significant amounts of the resin to be removed or built up at the edges of the slots 30, which is achieved due to the absence of any significant wiping or brushing effect.

The

shafts

32, 34 are preliminarily cleaned in the belt contact unit 124 by passage over the slotted face plates 190, 190' of the vacuum blocks 188, and by the contact elements 166 of the fourth set of belt assemblies, as illustrated in FIG. 11. Thereafter, the rotors 26 pass to the precuring unit 204 at which the powder remaining on selected portions may be partially fused and cohered (when a thermoplastic resin is used) so as to permit other portions to be finally cleaned without disturbing the desired deposits. While it should be appreciated that the precuring unit 204 might be eliminated if so 16 desired, and might be inappropriate under certain circumstances, preferred practice utilizes a thermoplastic resin and both the contact belt unit 124 and the precuring unit 204, as illustrated. From the precuring unit 204 the rotors 26 are carried to the air knife assembly 270 for a final cleaning, through the oven for complete fusion, and finally to the cooling unit for solidification of the resin.

Subsequent to the air knife assembly 270 and ahead of the oven is a second transfer point which occurs over the rearmost drive sprocket 13. Since the transfer is quite comparable to that which occurs over the sprocket 12, a detailed explanation is not believed to be necessary. However, as illustrated in FIG. 16, the construction of the conveyor 20 to which the cores are transferred at this point is somewhat different from any described previously. More particularly, the conveyor 20 consists of a pair of spaced chain assemblies, generally described by the numeral 283 (only one being shown in FIG. 16) which, at the point of transfer, lie to either side of the conveyor 18. Each of the chain assemblies 283 includes an endless sprocket chain 292 on which is mounted a multiplicity of U-shaped cradles 284. Each of the cradles 284 has in its inner wall 288 an upwardly opening U-shaped socket 286 in which the shafts of the rotors are received. The cradles 284 have a depending flange element 290 secured thereto, and the flange elements constitute part of the sprocket chain 292 while affording the means of attachment thereto. As will also be appreciated, drive sprocket 13 will consist of a pair of sprocket wheels similar to those employed for the drive sprocket 12, one wheel being used to support and drive each of the chain assemblies 283.

Of the numerous types of materials which are suitable for use as the particulate resin, thermoplastics, and particularly synthetic thermoplastic resins, are preferred. Exemplary of such thermoplastic resins are the vinylidenes and vinyls (e.g., polystyrene and polyvinyl chloride), the olefins (e.g., polyethylene, polypropylene and copolymers thereof), the cellulosics, polyamides (e.g., nylons), etc. Generally, the resin will be a powder smaller than mesh (i.e., substantially all of the particles will pass through an 80 mesh (U.S.) sieve. Preferably, the powder will be less than mesh, and most desirably it will be mesh or finer.

As will be appreciated by those skilled in the art, many changes may be made in the illustrated apparatus without departing from the concept of the invention hereof. For example, heating (when used) may be by any appropriate means, and may employ convection, conduction, infrared, induction, or like effects. Similarly, cooling may be accomplished in any appropriate manner, such as by the use of cooled air of other fluid, conventional refrigeration, etc. The proper electrical circuitry will also be readily apparent and of the type conventionally employed in the electrostatic coating and electromechanical arts. It should be appreciated that, although good practice and safe operating procedures will normally dictate electrical grounding of the apparatus and of the workpiece by contact therewith, no special provision need normally be made for grounding of the workpiece to ensure adequate electrostatic attraction and adhesion. The high voltage charging of the particles will usually suffice to establish an adequate potential relative to the workpiece, regardless of the measures taken with respect to the latter; however, independent connections may be made to the workpiece if so desired. v

Although the term fusion" as used herein will most generally relate to the effect induced at elevated temperatures, as is consistent with its most literal definition, a somewhat broader interpretation is intended to be applied to its present use. Thus, for example, treat ment with solvent vapors and electron irradiation can be used to induce flow in certain materials, and in instances in which materials of those types are employed theterm fusion is intended to encompass such techniques. Moreover, ultrasonic vibrations may be utilized to produce fusion of certain types of particles. As will be apparent, in such cases suitable equipment will be used instead of the oven depicted in the drawing; it will also be apparent that such techniques will permit other materials to be employed for the coating, for example materials which are not well-suited to use at elevated temperatures. The terms partial fusion and coherence are intended to connote a state in which the individual particles of the resin have been affected by the fusion treatment sufficiently to at least loosely join them together, so as to resist separation. In such a condition individual particles may be discernible, whereas upon complete fusion or melting the particles are no longer identifiable as such. Due to the variety of resinous materials that may be employed in the practice of the invention, it is not possible to place specific values upon the temperatures or other conditions involved for fusion or melting without unduly limiting the scope hereof. Moreover, the conditions of operation that are appropriate in such instance will be readily apparent to those skilled-in the art in view of the foregoing detailed information.

Thus it can be seen that the present invention provides a novel method and apparatus for the production of a coating of a solid, particulate resin upon a limited portion of a workpiece. More specifically, it provides such a method and apparatus for electrostatically coating the workpiece and for effecting the removal of the resinous material from selected portions thereof which are to be uncoated, and the method and apparatus are particularly adapted for coating reentrant surface portions of generally cylindrical articles. the coatings are produced quickly, easily and economically, and on an automatic and continuous basis if so desired. A novel contact belt unit is also provided which is adapted to remove the particulate resin from one portion or zone of a workpiece without causing undue thinning br thickening of the deposit on an adjacent portion thereof.

Having thus described the invention 1 claim: I 1. In apparatus for producing a coating of resinous material upon only a portion of a workpiece, the combination comprising:

a. a chassis;

b. means on said chassis for removing particles of the resinous material, including a member movably mounted over a path for the workpiece and having a relatively resiliently deformable contact surface thereon of small open-cell construction;

c. means for carrying the workpiece along said travel path; and

d. drive means for said particle removing means and for said carrying means,

said contact surface being disposed for direct contact upon a portion of the workpiece as it is carried along said travel path, and said carrying means and said particle removing means being adapted for coaction to 18 move said contact surface and the contacted portion of the workpiece at the same linear speed during such contact to substantially prevent wiping of the workpiece by said contact surface.

2. The apparatus of claim 1 ,wherein the portion of said travel path over which said particle removing means is mounted is generally rectilinear, and wherein said member of said powder removing means moves in a circuitous path in a plane parallel to the axis of said travel path portion. p

I 3. The apparatus of claim 2 wherein said particle removing means comprises a set of spaced pulleys about which extends an endless flexible belt, said belt having said contact surface disposed on the outer surface thereof.

4. The apparatus of claim 3 wherein said contact surface of said movably supported member of said particle removing means is comprised of an open-cell foam elastomer having a cell size of about 1 to 20 mils.

5. The apparatus of claim 4 wherein said elastomer is polyurethane.

6. The apparatus of claim 1 wherein said particle removing means includes a plurality of contact elements spaced along said travel path to sequentially contact substantially the same portion of the workpiece.

7. The apparatus of claim 1 wherein said particle removing means includes a plurality of said contact elements, said contact elements being spaced across said travel path to contact different portions of the workpiece.

8. The apparatus of claim 1 additionally including vacuum means disposed adjacent said contact surface to effect the removal of particles of the resinous material therefrom.

9. The apparatus off claim 1 wherein said apparatus is adapted for use with a generally cylindrical article, and wherein said carrying means is a conveyor adapted to support the article with its axis extending transversely across said travel path.

10. The apparatus of claim 9 wherein said conveyor supports the article for free axial rotation thereon, contact of the article with said contact surface of sadi particle removing means causing rotation thereof as said conveyor carries the article along said travel path.

11. The apparatus of claim 10 wherein the article is an armature rotor having a cylindrical core portion with a shaft portion extending axially from each end thereof, wherein said conveyor is adapted to engage the shaft portions of the rotor, and wherein said contact surface of said particle removing means is disposed for contact with the circumferential surface of the core portion to effect the removal of particles therefrom.

12. The apparatus of claim 1 wherein said apparatus is adapted to coatings of thermoplastic resinous materials, and wherein said apparatus additionally includes heating means on said chassis along said travel path downstream of said particle cleaning means, said heating means being adapted to heat at least a first zone of the workpiece to produce at least partial fusion and coherence of the particles thereon.

13. The apparatus of claim 1 wherein said apparatus is adapted for the initial production of a coating and additionally includes means on said chassis upstream of said particle removing means for producing a cloud of electrostatically charged solid particles of resinous material.

14. The apparatus of claim 13 wherein said cloudproducing means includes an electrostatic cloud chamher, said chamber comprising a receptacle having means for producing a fluidized bed of charged particles including a gas-permeable plate extending thereacross in a generally horizontal intermediate plane spaced above the bottom wall thereof to define a plenum chamber therebelow and having electrode means extending thereacross for electrostatically charging particles of solid resinous material passing proximate thereto.

15. The apparatus of claim 14 additionally including a particulate material reservoir having feed means communicating with said cloud chamber, wherein said electrode means spans a lesser area than said plate to provide an electrode-free vertical corridor within said receptacle through which particles of the resinous material may pass without acquiring a significant charge,

said receptacle also including a device for sensing the level of the bed of particles therewithin to which said feed means is responsive to convey resinous material from said reservoir to said chamber when said bed level falls below a preselected height, said sensing device being positioned within said vertical corridor over said permeable plate to minimize the effect of electrostatic charging upon the sensed level of the bed.

16. The apparatus of claim 15 wherein said electrode is a generally planar, grid-like structure and is disposed adjacent the upper surface of said gas-permeable plate, said electrode and plate being substantially coextensive except at one area of said plate over which said electrode does not extend to thereby provide said electrode-free vertical corridor.

Claims

1. In apparatus for producing a coating of resinous material upon only a portion of a workpiece, the combination comprising: a. a chassis; b. means on said chassis for removing particles of the resinous material, including a member movably mounted over a path for the workpiece and having a relatively resiliently deformable contact surface thereon of small open-cell construction; c. means for carrying the workpiece along said travel path; and d. drive means for said particle removing means and for said carrying means, said contact surface being disposed for direct contact upon a portion of the workpiece as it is carried along said travel path, and said carrying means and said particle removing means being adapted for coaction to move said contact surface and the contacted portion of the workpiece at the same linear speed during such contact to substantially prevent wiping of the workpiece by said contact surface.

2. The apparatus of claim 1 wherein the portion of said travel path over which said particle removing means is mounted is generally rectilinear, and wherein said member of said powder removing means moves in a circuitous path in a plane parallel to the axis of said travel path portion.

3. The apparatus of claim 2 wherein said particle removing means comprises a set of spaced pulleys about which extends an endless flexible belt, said belt having said contact surface disposed on the outer surface thereof.

5. The apparatus of claim 4 wherein said elastomer is polyurethane.

14. The apparatus of claim 13 wherein said cloud-producing means includes an electrostatic cloud chamber, said chamber comprising a receptacle having means for producing a fluidized bed of charged particles including a gas-permeable plate extending thereacross in a generally horizontal intermediate plane spaced above the bottom wall thereof to define a plenum chamber therebelow and having electrode means extending thereacross for electrostatically charging particles of solid resinous material passing proximate thereto.

15. The apparatus of claim 14 additionally including a particulate material reservoir having feed means communicating with said cloud chamber, wherein said electrode means spans a lesser area than said plate to provide an electrode-free vertical corridor within said receptacle through which particles of the resinous material may pass without acquiring a significant charge, said receptacle also including a device for sensing the level of the bed of particles therewithin to which said feed means is responsive to convey resinous material from said reservoir to said chamber when said bed level falls below a preselected height, said sensing device being positioned within said vertical corridor over said permeable plate to minimize the effect of electrostatic charging upon the sensed level of the bed.