CA1054558A - Method and apparatus for electrophoretic coating - Google Patents
Method and apparatus for electrophoretic coatingInfo
- Publication number
- CA1054558A CA1054558A CA257,381A CA257381A CA1054558A CA 1054558 A CA1054558 A CA 1054558A CA 257381 A CA257381 A CA 257381A CA 1054558 A CA1054558 A CA 1054558A
- Authority
- CA
- Canada
- Prior art keywords
- work piece
- coating
- linear
- electrophoretic coating
- nozzle
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D13/00—Electrophoretic coating characterised by the process
- C25D13/12—Electrophoretic coating characterised by the process characterised by the article coated
- C25D13/14—Tubes; Rings; Hollow bodies
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D13/00—Electrophoretic coating characterised by the process
- C25D13/22—Servicing or operating apparatus or multistep processes
Abstract
ABSTRACT
Method and apparatus for electrophoretically coating a surface of an electrically conductive work piece having a selected linear dimension including the steps of: establishing the work piece at one electrical potential, flowing an electro-phoretic coating in a linear stream corresponding to the linear dimension and in close proximity to the work piece surface, imparting an electrical charge to the electrophoretic coating, impinging the charged linear stream of electrophoretic coating onto the work piece surface and moving the work piece and charged linear stream relative to one another and in a direction lateral to the selected linear dimension, to electrophoretically coat the entirety of such work piece surface.
Method and apparatus for electrophoretically coating a surface of an electrically conductive work piece having a selected linear dimension including the steps of: establishing the work piece at one electrical potential, flowing an electro-phoretic coating in a linear stream corresponding to the linear dimension and in close proximity to the work piece surface, imparting an electrical charge to the electrophoretic coating, impinging the charged linear stream of electrophoretic coating onto the work piece surface and moving the work piece and charged linear stream relative to one another and in a direction lateral to the selected linear dimension, to electrophoretically coat the entirety of such work piece surface.
Description
1~5~S58 The present invention relates generally to the coat-ing of a work piece with an electrophoretic coating material.
The preeent invention has particular applicatlon in the coat-ing of lnternal and external sur~aces of containers, such as cans, and other ob~ects, such as heat exchangers, radiators, drums, automobile wheels, automobile oil filter caps and the like.
Electrophoresis generally concerns the movement of ionic particles within an aqueous system in response to elec-trical charges imparted to such system. Negatively chargedparticles or ions in such an aqueous solution (i.e., an anodic coating) migrate in response to such electrical potential to any positively charged conductor which may be immersed in the solution for deposit thereon. Positively charged particles or ions (i.e., cathodic coating materials) likewise migrate and are deposited upon a negatively charged conductor within the coating bath.
Typically, an electrical potential in the range of approximately 100 to 500 volts has been used for electropho-retlc coating. The thickness, and hence durability, of suchelectrophoretically deposited coating layer is dependent upon a number of factors, including, inter alia, the voltage used, the separation between the anode and cathode, the length Or tlme coating is permitted to continue, the pH of the coating solution, the characteristics of the coating polymer used and the conductivity of the particular material then belng coated~ -During coating, after some coating particles havè been depos-ited upon the C~nductive surface being coated, there is a gradual reduction in the conductivity thereof and the work piece belng coated becomeæ increasingly insulated. When the thicknes~ of the electrophoretic~lly deposited coating layer lCI SasS5~
becomes su~flciently thick for a given system, the previously conductive surface becomes insulated to the extent that no further substantlal electrodeposition wlll occurO Slmilarly, if some portion of the surface of the work piece to be coated has been previously coated with an insulating coating, further electrodeposition on that coated surface will occur only with hlgher voltages, clo~er proximity of electrodes, more conduc-tive coating materials, longer coating times or other changes to the system.
Various of the above techniques of electrophoretic coating have been used heretofore in the art. Those tech-niques have had a number of disadvantages associated there-with. In many such prior art electrophoretic coating tech-niques, it has been necessary to immerse the work piece into a coating bath, which has neces~itated large capital outlays for the often spacious tanks required to accommodate the w~rk piece therein. Also, such immersion techniques have been found to require an excessive amount of time and extra:mechan-ical equipment to accomplish such dipping or immersion.
A further serious disa~vantage of such pri~r art immersion techniques is the necessary result that both the internal and external surfaces of the work piece to be coated must be done simultaneously. This is especially undesirable when, as is often the case, either the exterior surface or the interior surface thereof should not or does not need to be coated, or when different types of coating are required for the interior and exterior surfaces. The waste involved and lack of product flexibility constitute in many cases debilitatlng disadvantages so severe that other, e~en more expensive, tech-nique~ may become necessary.
Another technique used heretofore has been the elec-105455~ ~
trodeposition of coating materials on sheet metal prior to lts being fabricated into a particular coated bOdy. Such tech-nique~ have resulted in exposed and/or uncoated breaks in the coating, which have occurred during the various fabrication steps, such as stamping, welding, heating, etc. Such unpro-tected areas may be especially undes~rable in the container industry, or in other industries where bare metal will con-stitute a safety hazar or economic loss.
Yet another prior art technique, that of electro-static spraying, has been used for various commercial coating operations. A number of further disadvantage~ have also re-sulted from the use of those techniques. Such spray techniques have required difficult ad~ustments and excessive maintenance problems. Further, in electrostatic spraying techniques a relatively thick coating has been required to insure complete coverage of the surface to be coated. Yet iurther, spraying techniques have been espècially difficult to utilize where the coating of an iriegular and/or interior surface has been re-quired.
Inversion flooding has been suggested as a technique for electrocoating of the interior surface of wide mouthed containers. That process is suitable for columnar containers and contemplates inverting the can and inserting upwardly and into the can opening a mating prod with a diameter which closely matc~es the internal diameter of the can. Electro- ;
deposition coating material is then force-pumped into the can from the top of the prod so aæ to flood the constricted space between the prod and the can from the top, down ~long the sides, and out the bottom, thereby to coat the sur~ace. Such a system is limited inherently to coating the interior of con-tainers and, because of the force flooding in the constricted '1054558 space unless the constrictions are uniform and continu~us thecoating thickness will vary and may be striped.
Accordingly, in view of the shortcomings of the prior art, it is an ob~ect of the present invention to provide method and apparatus for electrocoating wherein the problems and disadvantages associated with the prior art may be materi-ally reduced or avoided~
Accordingly, the present invention provides a method for electrophoretically coating a surface of an electrically conductive work piece having a selected linear dimension, com-prising the steps of establishing said work piece at one elec-trical potential, flowing an electrophoretlc coating ln a linear stream corresponding to said selected linear dimension and in close proximity to said surface of said work piece, im-parting an electrical charge to sald linear stream, impinging said charged linear stream`of electrophoretic coating onto said surface o~ said work piece, and moving said work piece and said charged linear stream of electrophoretic coatlng rela-~ive to one another in a direction lateral to said linear di-mehsion, thereby to electrophoretically deposit coating overthe entirety of said surface of said work piece.
The present invention al8o provides an apparatus for electrophoretically coating a surface of an electri¢ally con-ductive work piece having a selected linear dimension, said apparatus comprising a reservoir for containing the electro-phoretic coating material, means for mounting the work piece to display the linear dimension thereof, nozzle mean~ for pro- :
viding a 11near stream of electrophoretic coating material onto said linear dimension o~ said work piece, means for 8Up-plying electrophoretic coating material from the reservoir to the nozzle means, means for charging the linear stream of --4- : .
1~5~55~3 electrophoretic coating material relative to the work piece, and means for moving said mounting means and said nozzle means relative to one another in a direction later~l to said linear stream, whereby an entire surface of the work piece on said mounting means may be coatedO
In accordance with the invention a work piece may be coated selectively and uniformly on the interior or exterior surfaces thereo~.
The invention will now be described with re~erence to accompanying drawings, in which Figure 1 is a schematic plan view of apparatus used in coating the exterior surface of a work piece, showing an epdless conveyor strand reeved about sprockets and.carrying work pieces in the form of can bodies thereon through coating, rinsing and curing stations;
Figure 2 is a slighly enlarged portion of the plan view of Figure 1 with the can body and work piece holder re-moved and shQwing rack and pinion and chain means for rotating work pieces during coating, rinsing and curing of the exterior surface the.reof;
Figure 3 is a slightly enlarged elevational-view of the structure for moving the work piece holder means along the endless conveyor strand and for rotation thereof, as shown in Figure 2;
Figure 4 is an enlarged elevational view of the coating Or the exterior surface of a work piece, showing means for disposing the structure into an electrical circul~t rela- ~ .
tionship, including alsD an application nozzle~electrodeg an auxiliary ele~trode, and means for rotating during coating;
Fi~ure 5 is ~ plan view of the structure.shown in ~igure 4, :~
-5- : :
~ . .
~:
. - . . , . - , .. . .. . .. . . . . .. ... . .
. . . ; . . ' , . . ' . ' ' " , ' . ', . ' ` ' . ' ' " " ' ' '; .; ' ' .
105455~
Figure 6 is a schematic elevational view showing ap-paratus for coating the interior of a work piece including an insulated application nozzle/electrode means ~or disposing such work piece lnto electrical circuit relationship with the nozzle/electrodej means for rotating either the container or the nozzle during coating, and a coating reservoir with asso-ciated chilling means, filtering means, and pumping means;
Figure 7 is an enlarged transverse cross-sectional view o~ a work piece, such ~s a containër9 as shown in Figure 6, and taken along line 7-7 o~ Figure 8, with an electrically charged coating nozzle disposed therein, ~urther showing the expansion portion of a nozzle embodiment and an insulating ring for preventing electrical short circuiting of said charged application nozzle;
Figure 8 is an enlarged longitudinal cross-sectional view of a work piece with an electrically charged coating de-livery nozzle disposed in the interior thereof, the particular nozzle having an expansion at the distal end thereof to insure more complete bottom surface coverage, slots or per~orations therein for more uniform coating delivery, insulating rings to prevent accidental electrieal shDrt circ~lting, and insulator means between such nozzle and the reservoir, with arrows indi-cating the direction of flow of such electrophoretic coating material;
Figure 9 is an enlarged longitudinal cross-sectional -~
view pf another form of nozzle for coating the interior of a work piece, such as an extruded beer can with beaded bottom portion, illustrating a wedge-shaped nozzle for assuring uni-form application of coating material to sueh beadR o~ the con- :
30 tainer bottom and showing a non-eonductive mesh covering for ~
the application nozzle openings to promote laminar flow and to :
, ~ -, - .. ~ ,... . .. , : .. :
- ..... . .. ~ . . . -1~545S8 prevent bubbling;
Figure 10 is an enlarged longitudinal cross-sectional view showing coating of the exterior surface of a rotating work piece by use of a stationary non-charged nozzle having a wedge-shaped top portion and having a separate electrode in the form of a conductive grid or mesh and also showing inside the work piece a schematic view of a vacuum operated work piece holder;
Figure 11 is an end view taken along line 11~11 of Figure 10;
... . ..
Figure 12 is an enlarged longitudinal cross-section-al view showing coating of the exterior surface of a station-ary work piece by means of a rotating application nozzle;
Figure 13 is a transverse cross-sectional view taken along line 13-13 of Figure 12;
Figure 14 is an enlarged longitudinal cross-section-al view showing coating of the~interior surface of a station-ary work piece by a rotating application nozzle and also show-ing a vacuum operated work piece holder for gripping an ex-terior surface;
Figure 15 is a transverse cross-sectional view taken along line 15-15 of Figure 14; and Figure 16 is an enlarged achematic elevational view showing coating of the exterior surface of a contoured work piece, such as an automobile wheel, by means of a stationary application nozzle and/or electrode having a surface matching the contours of the work piece, and means for rotating such work piece, whereby uniform application of coating material :
may be achieved.
In its preferred form the method of electrophoretic coat1n~ of the present lnvention is carried out by me~ns o~
' ' :
,.
- . . .
1~4558 the coating structure set forth generally in Figure 1 hereofO
With specific reference to Figure 1, the coating apparatus lO
cQmprises a coating chamber 11 feedlng serially into a pair of side-by-side rinsing chambers 12, 13 and a drying chamber 14, such chambers being separated by walls 17 each having openings 16 therein for movement therethrough of a can body CB for coating, rinsing, and curing thereof respectively in such chambers.
The path of movement of can body CB is along a gen-erally circular path beginning at entrance opening 18 to coat-ing chamber 11 and exiting at opening 20 of drying chamber 14.
Such circular movement during processing is provided by means of an endless conveyor strand 21 being reeved preferably about spaced sprockets 22 and a pair of smaller intermediate sprock-ets 22 disposed respectively near entrance 18 and exit 20.
Endless strand 21 may preferably be in the form of a link chain having mandrels 19 disposed in spaced relationship there-along for support and rotation of the can body CB to be coated.
An a~xillary electrode as shown in Figure 4 may be disposed in said coating chamber 11 adjacent such can bodies CB~
Although the conveyor system of Figure 1 is shown in a horizontal configuration it is understood that other con-figurations, such as for example a vertical configuration, may be utilized and such modifications are intended to be included with the scope of the present invention.
Referring now to Figures 2 and 3, the mandrels 19 are supported upon a rotating shaft 24 having fixed thereon a pinion 26 meshing with a curved rack 27 for providing rotation to such shaft 24 of mandrel 19 and, consequently, to can body CB. Such rotation of can bodies CB occurs by reason of the fact that prlor to entering the coating chamber 11, the can : ~ --8- :
1(~54558 bodies CB are placed upoh and supported by mandrels 19 about an axial axis of such can bodies. A wear plate 28 may be pro- :
vided ad~acent said endless strand 21 for urging pinion gear 26 into engagement with rack 27. By reason of the movement of endle~s strand 21 along rack 27 and the meshing of pinion 26 therewith, the can bodies CB supportéd by such mandrels 19 are caused to rotate and move through the coatin~ chamber 11 and rinsing chambers 12 and 13 while rotatingO Although the man-drel rotational speed may be ad~usted depending on the physical characteristics o~ the particular coating material used and the voltage applied, suitable rotational speeds have been found to be in the range of approximately 60-400 R~PoMo This speed of rotation has been found to permit the can body CB to make at least one.complete revolution, and possibly to make two such revolutions, during coating application. Such can bodies CB may be placed on mandrels 19 manually or by other apparatus means (not shown). Likewise, apparatus (not ~h~wn) may be provided for removing such can bodies CB from mandrels 19 after theIr exit at opening 20.
AIternatively, a star drive conveyor mechanism of a type well-known in the art may be used for transmitting such work pieces through the coating, rinsing and curing stations.
Referring now particularly to Figures 4 and 5, which ~. :
show one embodiment of the coating of an exterior surface by rotating the work piece while moving through coating chamber 11, as set forth hereinabove. ~ can body CB is rotated by .
means of mandrel 19 during coating. Liquid elec~rophoretic coating material is supplied t~ the exterior surface 40 of : :
such can body CB through application nozzle 29, disposed equi~
30 distant said can body CB and is connected to a supply pipe 31 .
drawing such coating material from a reservoir disposed there-_g_ ....
.. . . . . ..
1~54558 beneath. Such reservoir (not shown) also serves to collect excess coating material flowing from such exterior surface 40 of can body CB to prevent waste thereof.
The supply nozzle 29 may include a supply arm 32 ex-tending over the bottom of exterior surface 40 of inverted can body CB. Where the coating material used is anodic, shaft 24 for turning mandrel 19 is provided with concentric electrical-ly conductive anode means 35 with the nozzle 29 belng connect-ed to the cathod side of the anodic-cath~dic circuit. (For a cathodic coating material, not shown, the application nozzle would become the anode and the ob~ect to be coated would be the cathode.) An auxiliary cathode 33 may be provided oppo-site said supply nozzle 29 to improve the uniformity of the flow and distribution of the electrophoretic coating material.
The nozzles 29 are provided with a ~ultiplicity of small open-ings 30 to improve uniformity of flow distribution of such coating material. The distance between such openings 30 and the exterior'surface 40 of such body are preferably in the range of approx'imately 2 to 15 millimeters.
Rinsing of excess electrophoret~c material is pro-vided in ri~sing chambers 12 and 13, each of which is supplied from supply pipe 37 connected to nozzle 36J as set ~orth in Figure 1.- Such excess material ~ay thus be returned to the reservoir. Deionized water is used for such rinsing. In a preferred embodiment, rinse water is supplied as permeate ~rom an ultrafiltration system. The rinse water may be recycled to provide a closed, non~polluting system. Such coated and rinsed can body CB then moves through curing or drying chamber 14 in a path past heater elements 39 provided for curing such rinsed coating. No rotational movement need be provided during cur-ing. When cured, such coated containers may be removed from ~054558 mandrel 19 by automated means (not shown).
Figures 6-9 illustrate method and apparatus for coating the interior surface 50 of a can body or container CB.
Such apparatus generally designated as apparatus 49 includes a coating nozzle 51, serving as the electrophoretic coating ma-terial delivery tube and also as the cathode in an anodic-cathodic relationship with the container, where anodic coating material is used. Such can body or container CB is supported by and rotationally driven about the axial axis thereof by mandrel means 52 connected to a rotational drive unit (not shown). Alternatlvely rotational movement may be applied to nozzle 51, with can body CB remaining stationary. Such man-drel means 52 may be connected to the container CB by means of a collar 53 fitting over the bottom exkerior surface 54 of -such container CB. Alternatively, a vacuum operated work piece holder may be used, as shown in Flgure 14. The power supply 69 utilized typically delivers between approximately 50 and 350 volts. The coating nozzle 51 is insulated from the coating reservoir 56 by means of an insulator 57. Coating material 58 i8 delivered to the coating nozzle 51 by means of a pump means 59 from coating res~rvoir 56 into which snorkel means 61 is disposed. After flowing over lnterior surface 50 of the con-tainer CB, excess coating material flows back into reservoir ;
56. Arrows in Figures 6-9 illustrate the path of movement of such coating material 58 from the coating reservoir 56, through snorkel 61, through pre-pump conduit means 62 to pump 59, through post-pump conduit means 63 to nozzle 51, onto the charged interior surface 50 of container CB, with the excess returning to reservoir 56. In a preferred embodiment a chiller 64 and a filter means 65 may be connected to such reservolr 56 for chilling and filtering such coating material.
~054558 Figures 7, 8 and 9 show in greater detail the shape, disposition, and component parts of coating application nozzle 51. In Figure 8 for example, such nozzle 51 at a distal end 51a thereof has an expansion portion 66 to insure more complete coverage of the interior bottom surface 50A of such container CB. Insulating rings 67 are provided spaced along such nozzle 51 to prevent accidental electrical short circulting of the cathodic nozzle 51 with the anodic container CB. In general, the application nozzle 51 is ad~ustably disposed at a distance of approximately two to fifteen millimeters from the container interior surface 50. Disposed at intervals along such applica-tion nozzle are slots or perforations 68 for supplemental coating delivery, which slots 68 aid in producing unlformity of the coating.
The embodiment shown in Figure 9 differs from that of Figure 8 in the shape of nozzle 51, which is wedge-shaped to provide u~i~orm application of coating material 58-into beads 60 at the bottom of can body CB, which may be for ex-ample an extrude~ beer can. Also provided is a non-cond~ctive mesh 67a covering openings 68 of nozzle 51 to insulate nozzle 51 from can body CB, to promote laminar flow, and to prevent bubbling of the coating material. Preferably, the application nozzle 51 i8 ad~ustably disposed at a distance of approximate-ly two tb fifteen millimeters from the container interior sur-face 50. Apparatus in accordance with the present invention should preferably have the open end thereof tilted slightly downwardly from the horizontal to permit excess coating mater-ial to flow back into the bath as illustrated by arrow A in Figure 9.
The apparatus set forth ln Figures ~-9 ~or coating the interior surface 50 of a rotating container CB by a ætationary ~' .. . - .. . - - . . .. . , ,, . . . ,. ~ .
- . .. :, ... : : , , .
1~545S8 nozzle 51 may be utilized with an endless chain driving means in con~unction with the rack and pinion drive for coating an e~terior surface as set forth in Figure 1, and the principles set forth therein are equally applicable to such apparatus for coating interior surfaces.
Referring now to Figures 10 and 11, the coating of the exterior surface 70 of a rotating work piece CB by means of a stationary nozzle 71 similar in principle to that shown in Figures 4 and 5 is shownO The stationary and uncharged nozzle 71 has a wedge-shaped top portion 72 which is contoured to correspond to the contours of exterior surface 70 of the work piece CB, which may be a beer can as shown. The nozzle 71 contains coating openings 73 ad~acent work plece CB for flowing a uniform coating over such work piece CB as shown by arrows. A similarly shaped electrode grid 74 is disposed inter-mediate said nozzle 71 and the work piece CB to provide elec-trical current to the electrocoating material as it flows from nozzle 71 onto work piece CB. A non-conductive mesh 75 covers grid 74 for preventing accidental short circuiting between work piece CB and grid 74 and also to promote laminar flow and to reduce bubbling. Grid 74 has a wedge-shaped portion dis-posed proximate to the exterior surface of the closed end of the container C~ being coated and serves to insure the same dwell coating time for any polnt on the closed end of exterior surface 76 of work piece CB for a given rotation, to permit uniform electrocoating thereof. Figure 10 also schematically shows can holder means generally designated as 78. A vacuum cup 80 engages the interior bottom surface 81 of the work piece CB and is supplied with vacuum by means of a vacuum line 82. The can holder means 78 also holds the work piece CB in ; place by means of spring 83 abutting against interior side ' 1~54558 surface 84 and is supported on either side by spring supports 85, 85 connected to and projecting from vacuum line 82.
Power supply 69 is shown connected to grid 74`and to work piece CB through its conductive connection~with a slip ring 86 having brushes 87 abutting on vacuum line 82 to provide electrical current thereto through electrically conductive spring supports 85, 85 and spring 83. Electrical current is then applied to work piece CB through its contact'with spring 83. As indicated by arrow R, can holder 78 provides rotation to the work piece CB by rotation means (not shown).
Figures 12 and 13 illustrate apparatus for coating the exterior surface 90 of a stationary work piece CB by rotat-ing an electrically charged application nozzle/electrode 91.
Nozzle 91 may completely enclose the portion of work piece CB ~-to be coatedg such that, during rotation, the coating material ~ -~lowed over surface 90 will be centrifugally urged against 6uch exterior surface 90 and not be wasted. After coating, the excess coating drains back into the bath as illustrated by arrow A.
Flow openings 93 are provided in nozzle 91 from coating channels 94 therein. Although openings 93 only need be provided over one side and one-half of the bottom of nozzle 72, a symmetrical arrangement such as shown in Figure 13 is preferred for balance during rotation.
Coupling 95, which transmits coatlng material to nozzle 91, is rotat~onallg disposed on electrically charged coating supply tube 96. Rotational means (not shown) are co~-nected to coupling 95 and provide rotation thereto and t~
nozzle 91 thereby as illustrated by arrow R. Power supply in the form of a rectifier 69 provides~electrical curre'nt to nozzle 91 and also to work piece CB through vacuum line 82 of -14- ~ ' . . .
lOS4~58 can holder 78. The details of can holder 78 and the electric-al connection provided thereby are similar to those described hereinabove in connection with Figure 10.
As also disclosed hereinabove, the particular direc-tion of the current applied depends upon whether anodic or cathodic coating is to be used. A~ter rotational coating, nozzle 91 and work piece CB may be separated by removal of either, such as for example by reciprocating movement.
Figures 14 and 15 illustrate embodiments of the present invention for coating the interior surface 50 o~ a stationary work piece CB by means of a rotating application nozzle/electrode. Rotating application nozzle/electrode, gen-erally designated as 101, comprises an interior coating tube 102 opening into one or more coating channels 103, 103. As shown by arrows, coating material flows through grid 104, which is connected to power supply 69 to also serve as an electrode. Pre~erably, a non-conductive mesh 105 covers grid 104 to prevent accidental contact between nozzle 101 and work piece CB. As with the embodiment shoNn in Figure 9, nozzle 101 may have wedge-shaped terminal pqrtions 106, 106 to match more closely the contours of a beaded bottom can, such as a beer can, for uniformity of electrocoating deposition.
Figures 14 and 15 also depict schematically the structure of an eIectrically conductive can holder generally designated as 107. A vacuum cup 108, ~upplied by a vacuum -line 109 eng~ges a portion of the bottom exterior surface 110 of work piece CB to hold it securely. A non-conductive collar 111 concentrically disposed with respect to the vacuum line 109 engages a portion of the exterior wall surface 112 of the work piece CB to supplement the support provided py vacuum cup 108. An electrically conductive bottom plate 100 is disposed ~' ~
1~5455B
within holder 107 to provide electrical current to the work piece CB.
Figure 16 shows the electrophoretic coating of a work piece WP having a surface 113 having an axis of symmetry, such as for example an automobile wheelO Electrical current is applied in one polarity from power supply rec~ifier 69 to application nozzle and/or electrode 114 and in the opposite polarity to a conductive work piece holder 115 and thereby to work piece WP. Nozzle 114 is disposed to be co-extensive with the longitudinal linear dimension of surface 113 and is shaped to conform to any contours in surface 113 of work piece WP, such that each nozzle opening 116 is proximate to and substan-tial}y equidistant from surface 113 for uniformitylof applica-tion of coating material.
Nozzle 114 may alternatively be made of a flexible conductive material to be ad~ustable for various different contoured surraces and can preferably be readily ad~usted for a different such contoured surface merely by first pressing it firmly against the surface to be coated and then disposing the matching nozzle a selectedJ proximate dis*ance from the sur-face.
A linear stream 117 of electrophoretic coating is ~ :
applied to surface 113 co-extensive wlth the longitudinal linear dimension thereof and relative movement is provided be~
tween the linear stream 117 and the ~ork piece surface. Such relative motion i8 lateral to the linear dimension and circum-ferential to and about the axis Or symmetry of the work piece : .
surface 113. Although such relative movement may be accom~
plished by moving either the work piece WP or the linear stream 117, in the example shown in Figure 16 work piece WP is ro-tated by means o~ a holder 115, which may also serve as a -16- :
~54SS8 reciprocator connecting means f~r separating the work piece from the application nozzle after coa~ing. Alternatively, nozzle 114 may be mounted for reciprocating movement by means not shown.
Although the selected linear dlmension of the work piece is illustrated as being rectilinear in Figures 1-9 and 11-15 and partially rectilinear in other embodiments illus-trated herein, it is within the contemplation of the present invention that such selected linear dimension may also be par-tially or totally curvilinear For example, where the select-ed linear dimension of the work piece is curvilinear such as for example in cylindrical tubing, the nozzle for flowing the coating could be disposed annularly or semi-annularly with respect to the surface to be coated and either the noZzle or the work piece moved axially (laterally) with respect to the circumferential (linear) dimension for coating the entirety of the surface.
In the above described prefçrred embodiments the distance between the anode and cathode can vary between 2 and 15 millimeters with a preferred separation of 4 to 5`~milli-meters. The speed of rotatlon of the work piece or the elec-trode may range from 60 R.P.M. to 400 R.P.M.; however, the preferred range is 120 to 240 R.P M.
The flow o~ coating can vary from one quart to 5 gallons per minute per application nozzle. There is no ab-so~ute optimum as the flow rate must be determined for each ~pecific work piece to be coated and will vary with the size and shape thereof.
The coating voltage can range from 50 to 350 volts.
However, the preferred voltage will va~y with the size and shape of the work piece and the formulation of the coating.
. ~ . .. . ..
. .
1~54558 However, 150 to 180 volts is generally satisfactory.
Coating temperature can range from 60 to 140F., butthe most practical range is 70 to 90F. The vlscosity of the coating is not critical, but is most usually close to that of water. The percent solids of the coating can be varied be-tween 7 and 15~, but the preferred operating range is approx-imately 12~.
~ oating time will vary considerably depending upon voltage, paint temperature, type of substrate, and film thick-ness desired; however, it is desirable to keep the coatingtime as low as possible. Practical operating ranges will vary from 0.1 second to 10 seconds, with coating times of between 0.3 second and 3 seconds, usually being the most practical.
A typical example of apparatus ln accordance with the present invention for coating the interior of aluminum containers, as shown in Figures 6-9, would be designed to coat 300 cans per minute using a coating time of 0.5 seconds and a voltage of 180 volts. The paint temperature would be 80F. - ~-90F. and the percent solids of the paint would be 12~ to 14%.
The speed of rotation of the can would be 240 R.P.M. and the flow rate of the paint would be 3/4ths of a gallon per minute ;
per application nozzle. Distance from the elect~ode to the container would be 4 millimeters. Following the coating pro-cess, the can would be rinsed to remove exceæs coating material and baked in an oven at any desired temperature to e~fect sat-isfactory cure o~ the coating.
The preeent invention has particular applicatlon in the coat-ing of lnternal and external sur~aces of containers, such as cans, and other ob~ects, such as heat exchangers, radiators, drums, automobile wheels, automobile oil filter caps and the like.
Electrophoresis generally concerns the movement of ionic particles within an aqueous system in response to elec-trical charges imparted to such system. Negatively chargedparticles or ions in such an aqueous solution (i.e., an anodic coating) migrate in response to such electrical potential to any positively charged conductor which may be immersed in the solution for deposit thereon. Positively charged particles or ions (i.e., cathodic coating materials) likewise migrate and are deposited upon a negatively charged conductor within the coating bath.
Typically, an electrical potential in the range of approximately 100 to 500 volts has been used for electropho-retlc coating. The thickness, and hence durability, of suchelectrophoretically deposited coating layer is dependent upon a number of factors, including, inter alia, the voltage used, the separation between the anode and cathode, the length Or tlme coating is permitted to continue, the pH of the coating solution, the characteristics of the coating polymer used and the conductivity of the particular material then belng coated~ -During coating, after some coating particles havè been depos-ited upon the C~nductive surface being coated, there is a gradual reduction in the conductivity thereof and the work piece belng coated becomeæ increasingly insulated. When the thicknes~ of the electrophoretic~lly deposited coating layer lCI SasS5~
becomes su~flciently thick for a given system, the previously conductive surface becomes insulated to the extent that no further substantlal electrodeposition wlll occurO Slmilarly, if some portion of the surface of the work piece to be coated has been previously coated with an insulating coating, further electrodeposition on that coated surface will occur only with hlgher voltages, clo~er proximity of electrodes, more conduc-tive coating materials, longer coating times or other changes to the system.
Various of the above techniques of electrophoretic coating have been used heretofore in the art. Those tech-niques have had a number of disadvantages associated there-with. In many such prior art electrophoretic coating tech-niques, it has been necessary to immerse the work piece into a coating bath, which has neces~itated large capital outlays for the often spacious tanks required to accommodate the w~rk piece therein. Also, such immersion techniques have been found to require an excessive amount of time and extra:mechan-ical equipment to accomplish such dipping or immersion.
A further serious disa~vantage of such pri~r art immersion techniques is the necessary result that both the internal and external surfaces of the work piece to be coated must be done simultaneously. This is especially undesirable when, as is often the case, either the exterior surface or the interior surface thereof should not or does not need to be coated, or when different types of coating are required for the interior and exterior surfaces. The waste involved and lack of product flexibility constitute in many cases debilitatlng disadvantages so severe that other, e~en more expensive, tech-nique~ may become necessary.
Another technique used heretofore has been the elec-105455~ ~
trodeposition of coating materials on sheet metal prior to lts being fabricated into a particular coated bOdy. Such tech-nique~ have resulted in exposed and/or uncoated breaks in the coating, which have occurred during the various fabrication steps, such as stamping, welding, heating, etc. Such unpro-tected areas may be especially undes~rable in the container industry, or in other industries where bare metal will con-stitute a safety hazar or economic loss.
Yet another prior art technique, that of electro-static spraying, has been used for various commercial coating operations. A number of further disadvantage~ have also re-sulted from the use of those techniques. Such spray techniques have required difficult ad~ustments and excessive maintenance problems. Further, in electrostatic spraying techniques a relatively thick coating has been required to insure complete coverage of the surface to be coated. Yet iurther, spraying techniques have been espècially difficult to utilize where the coating of an iriegular and/or interior surface has been re-quired.
Inversion flooding has been suggested as a technique for electrocoating of the interior surface of wide mouthed containers. That process is suitable for columnar containers and contemplates inverting the can and inserting upwardly and into the can opening a mating prod with a diameter which closely matc~es the internal diameter of the can. Electro- ;
deposition coating material is then force-pumped into the can from the top of the prod so aæ to flood the constricted space between the prod and the can from the top, down ~long the sides, and out the bottom, thereby to coat the sur~ace. Such a system is limited inherently to coating the interior of con-tainers and, because of the force flooding in the constricted '1054558 space unless the constrictions are uniform and continu~us thecoating thickness will vary and may be striped.
Accordingly, in view of the shortcomings of the prior art, it is an ob~ect of the present invention to provide method and apparatus for electrocoating wherein the problems and disadvantages associated with the prior art may be materi-ally reduced or avoided~
Accordingly, the present invention provides a method for electrophoretically coating a surface of an electrically conductive work piece having a selected linear dimension, com-prising the steps of establishing said work piece at one elec-trical potential, flowing an electrophoretlc coating ln a linear stream corresponding to said selected linear dimension and in close proximity to said surface of said work piece, im-parting an electrical charge to sald linear stream, impinging said charged linear stream`of electrophoretic coating onto said surface o~ said work piece, and moving said work piece and said charged linear stream of electrophoretic coatlng rela-~ive to one another in a direction lateral to said linear di-mehsion, thereby to electrophoretically deposit coating overthe entirety of said surface of said work piece.
The present invention al8o provides an apparatus for electrophoretically coating a surface of an electri¢ally con-ductive work piece having a selected linear dimension, said apparatus comprising a reservoir for containing the electro-phoretic coating material, means for mounting the work piece to display the linear dimension thereof, nozzle mean~ for pro- :
viding a 11near stream of electrophoretic coating material onto said linear dimension o~ said work piece, means for 8Up-plying electrophoretic coating material from the reservoir to the nozzle means, means for charging the linear stream of --4- : .
1~5~55~3 electrophoretic coating material relative to the work piece, and means for moving said mounting means and said nozzle means relative to one another in a direction later~l to said linear stream, whereby an entire surface of the work piece on said mounting means may be coatedO
In accordance with the invention a work piece may be coated selectively and uniformly on the interior or exterior surfaces thereo~.
The invention will now be described with re~erence to accompanying drawings, in which Figure 1 is a schematic plan view of apparatus used in coating the exterior surface of a work piece, showing an epdless conveyor strand reeved about sprockets and.carrying work pieces in the form of can bodies thereon through coating, rinsing and curing stations;
Figure 2 is a slighly enlarged portion of the plan view of Figure 1 with the can body and work piece holder re-moved and shQwing rack and pinion and chain means for rotating work pieces during coating, rinsing and curing of the exterior surface the.reof;
Figure 3 is a slightly enlarged elevational-view of the structure for moving the work piece holder means along the endless conveyor strand and for rotation thereof, as shown in Figure 2;
Figure 4 is an enlarged elevational view of the coating Or the exterior surface of a work piece, showing means for disposing the structure into an electrical circul~t rela- ~ .
tionship, including alsD an application nozzle~electrodeg an auxiliary ele~trode, and means for rotating during coating;
Fi~ure 5 is ~ plan view of the structure.shown in ~igure 4, :~
-5- : :
~ . .
~:
. - . . , . - , .. . .. . .. . . . . .. ... . .
. . . ; . . ' , . . ' . ' ' " , ' . ', . ' ` ' . ' ' " " ' ' '; .; ' ' .
105455~
Figure 6 is a schematic elevational view showing ap-paratus for coating the interior of a work piece including an insulated application nozzle/electrode means ~or disposing such work piece lnto electrical circuit relationship with the nozzle/electrodej means for rotating either the container or the nozzle during coating, and a coating reservoir with asso-ciated chilling means, filtering means, and pumping means;
Figure 7 is an enlarged transverse cross-sectional view o~ a work piece, such ~s a containër9 as shown in Figure 6, and taken along line 7-7 o~ Figure 8, with an electrically charged coating nozzle disposed therein, ~urther showing the expansion portion of a nozzle embodiment and an insulating ring for preventing electrical short circuiting of said charged application nozzle;
Figure 8 is an enlarged longitudinal cross-sectional view of a work piece with an electrically charged coating de-livery nozzle disposed in the interior thereof, the particular nozzle having an expansion at the distal end thereof to insure more complete bottom surface coverage, slots or per~orations therein for more uniform coating delivery, insulating rings to prevent accidental electrieal shDrt circ~lting, and insulator means between such nozzle and the reservoir, with arrows indi-cating the direction of flow of such electrophoretic coating material;
Figure 9 is an enlarged longitudinal cross-sectional -~
view pf another form of nozzle for coating the interior of a work piece, such as an extruded beer can with beaded bottom portion, illustrating a wedge-shaped nozzle for assuring uni-form application of coating material to sueh beadR o~ the con- :
30 tainer bottom and showing a non-eonductive mesh covering for ~
the application nozzle openings to promote laminar flow and to :
, ~ -, - .. ~ ,... . .. , : .. :
- ..... . .. ~ . . . -1~545S8 prevent bubbling;
Figure 10 is an enlarged longitudinal cross-sectional view showing coating of the exterior surface of a rotating work piece by use of a stationary non-charged nozzle having a wedge-shaped top portion and having a separate electrode in the form of a conductive grid or mesh and also showing inside the work piece a schematic view of a vacuum operated work piece holder;
Figure 11 is an end view taken along line 11~11 of Figure 10;
... . ..
Figure 12 is an enlarged longitudinal cross-section-al view showing coating of the exterior surface of a station-ary work piece by means of a rotating application nozzle;
Figure 13 is a transverse cross-sectional view taken along line 13-13 of Figure 12;
Figure 14 is an enlarged longitudinal cross-section-al view showing coating of the~interior surface of a station-ary work piece by a rotating application nozzle and also show-ing a vacuum operated work piece holder for gripping an ex-terior surface;
Figure 15 is a transverse cross-sectional view taken along line 15-15 of Figure 14; and Figure 16 is an enlarged achematic elevational view showing coating of the exterior surface of a contoured work piece, such as an automobile wheel, by means of a stationary application nozzle and/or electrode having a surface matching the contours of the work piece, and means for rotating such work piece, whereby uniform application of coating material :
may be achieved.
In its preferred form the method of electrophoretic coat1n~ of the present lnvention is carried out by me~ns o~
' ' :
,.
- . . .
1~4558 the coating structure set forth generally in Figure 1 hereofO
With specific reference to Figure 1, the coating apparatus lO
cQmprises a coating chamber 11 feedlng serially into a pair of side-by-side rinsing chambers 12, 13 and a drying chamber 14, such chambers being separated by walls 17 each having openings 16 therein for movement therethrough of a can body CB for coating, rinsing, and curing thereof respectively in such chambers.
The path of movement of can body CB is along a gen-erally circular path beginning at entrance opening 18 to coat-ing chamber 11 and exiting at opening 20 of drying chamber 14.
Such circular movement during processing is provided by means of an endless conveyor strand 21 being reeved preferably about spaced sprockets 22 and a pair of smaller intermediate sprock-ets 22 disposed respectively near entrance 18 and exit 20.
Endless strand 21 may preferably be in the form of a link chain having mandrels 19 disposed in spaced relationship there-along for support and rotation of the can body CB to be coated.
An a~xillary electrode as shown in Figure 4 may be disposed in said coating chamber 11 adjacent such can bodies CB~
Although the conveyor system of Figure 1 is shown in a horizontal configuration it is understood that other con-figurations, such as for example a vertical configuration, may be utilized and such modifications are intended to be included with the scope of the present invention.
Referring now to Figures 2 and 3, the mandrels 19 are supported upon a rotating shaft 24 having fixed thereon a pinion 26 meshing with a curved rack 27 for providing rotation to such shaft 24 of mandrel 19 and, consequently, to can body CB. Such rotation of can bodies CB occurs by reason of the fact that prlor to entering the coating chamber 11, the can : ~ --8- :
1(~54558 bodies CB are placed upoh and supported by mandrels 19 about an axial axis of such can bodies. A wear plate 28 may be pro- :
vided ad~acent said endless strand 21 for urging pinion gear 26 into engagement with rack 27. By reason of the movement of endle~s strand 21 along rack 27 and the meshing of pinion 26 therewith, the can bodies CB supportéd by such mandrels 19 are caused to rotate and move through the coatin~ chamber 11 and rinsing chambers 12 and 13 while rotatingO Although the man-drel rotational speed may be ad~usted depending on the physical characteristics o~ the particular coating material used and the voltage applied, suitable rotational speeds have been found to be in the range of approximately 60-400 R~PoMo This speed of rotation has been found to permit the can body CB to make at least one.complete revolution, and possibly to make two such revolutions, during coating application. Such can bodies CB may be placed on mandrels 19 manually or by other apparatus means (not shown). Likewise, apparatus (not ~h~wn) may be provided for removing such can bodies CB from mandrels 19 after theIr exit at opening 20.
AIternatively, a star drive conveyor mechanism of a type well-known in the art may be used for transmitting such work pieces through the coating, rinsing and curing stations.
Referring now particularly to Figures 4 and 5, which ~. :
show one embodiment of the coating of an exterior surface by rotating the work piece while moving through coating chamber 11, as set forth hereinabove. ~ can body CB is rotated by .
means of mandrel 19 during coating. Liquid elec~rophoretic coating material is supplied t~ the exterior surface 40 of : :
such can body CB through application nozzle 29, disposed equi~
30 distant said can body CB and is connected to a supply pipe 31 .
drawing such coating material from a reservoir disposed there-_g_ ....
.. . . . . ..
1~54558 beneath. Such reservoir (not shown) also serves to collect excess coating material flowing from such exterior surface 40 of can body CB to prevent waste thereof.
The supply nozzle 29 may include a supply arm 32 ex-tending over the bottom of exterior surface 40 of inverted can body CB. Where the coating material used is anodic, shaft 24 for turning mandrel 19 is provided with concentric electrical-ly conductive anode means 35 with the nozzle 29 belng connect-ed to the cathod side of the anodic-cath~dic circuit. (For a cathodic coating material, not shown, the application nozzle would become the anode and the ob~ect to be coated would be the cathode.) An auxiliary cathode 33 may be provided oppo-site said supply nozzle 29 to improve the uniformity of the flow and distribution of the electrophoretic coating material.
The nozzles 29 are provided with a ~ultiplicity of small open-ings 30 to improve uniformity of flow distribution of such coating material. The distance between such openings 30 and the exterior'surface 40 of such body are preferably in the range of approx'imately 2 to 15 millimeters.
Rinsing of excess electrophoret~c material is pro-vided in ri~sing chambers 12 and 13, each of which is supplied from supply pipe 37 connected to nozzle 36J as set ~orth in Figure 1.- Such excess material ~ay thus be returned to the reservoir. Deionized water is used for such rinsing. In a preferred embodiment, rinse water is supplied as permeate ~rom an ultrafiltration system. The rinse water may be recycled to provide a closed, non~polluting system. Such coated and rinsed can body CB then moves through curing or drying chamber 14 in a path past heater elements 39 provided for curing such rinsed coating. No rotational movement need be provided during cur-ing. When cured, such coated containers may be removed from ~054558 mandrel 19 by automated means (not shown).
Figures 6-9 illustrate method and apparatus for coating the interior surface 50 of a can body or container CB.
Such apparatus generally designated as apparatus 49 includes a coating nozzle 51, serving as the electrophoretic coating ma-terial delivery tube and also as the cathode in an anodic-cathodic relationship with the container, where anodic coating material is used. Such can body or container CB is supported by and rotationally driven about the axial axis thereof by mandrel means 52 connected to a rotational drive unit (not shown). Alternatlvely rotational movement may be applied to nozzle 51, with can body CB remaining stationary. Such man-drel means 52 may be connected to the container CB by means of a collar 53 fitting over the bottom exkerior surface 54 of -such container CB. Alternatively, a vacuum operated work piece holder may be used, as shown in Flgure 14. The power supply 69 utilized typically delivers between approximately 50 and 350 volts. The coating nozzle 51 is insulated from the coating reservoir 56 by means of an insulator 57. Coating material 58 i8 delivered to the coating nozzle 51 by means of a pump means 59 from coating res~rvoir 56 into which snorkel means 61 is disposed. After flowing over lnterior surface 50 of the con-tainer CB, excess coating material flows back into reservoir ;
56. Arrows in Figures 6-9 illustrate the path of movement of such coating material 58 from the coating reservoir 56, through snorkel 61, through pre-pump conduit means 62 to pump 59, through post-pump conduit means 63 to nozzle 51, onto the charged interior surface 50 of container CB, with the excess returning to reservoir 56. In a preferred embodiment a chiller 64 and a filter means 65 may be connected to such reservolr 56 for chilling and filtering such coating material.
~054558 Figures 7, 8 and 9 show in greater detail the shape, disposition, and component parts of coating application nozzle 51. In Figure 8 for example, such nozzle 51 at a distal end 51a thereof has an expansion portion 66 to insure more complete coverage of the interior bottom surface 50A of such container CB. Insulating rings 67 are provided spaced along such nozzle 51 to prevent accidental electrical short circulting of the cathodic nozzle 51 with the anodic container CB. In general, the application nozzle 51 is ad~ustably disposed at a distance of approximately two to fifteen millimeters from the container interior surface 50. Disposed at intervals along such applica-tion nozzle are slots or perforations 68 for supplemental coating delivery, which slots 68 aid in producing unlformity of the coating.
The embodiment shown in Figure 9 differs from that of Figure 8 in the shape of nozzle 51, which is wedge-shaped to provide u~i~orm application of coating material 58-into beads 60 at the bottom of can body CB, which may be for ex-ample an extrude~ beer can. Also provided is a non-cond~ctive mesh 67a covering openings 68 of nozzle 51 to insulate nozzle 51 from can body CB, to promote laminar flow, and to prevent bubbling of the coating material. Preferably, the application nozzle 51 i8 ad~ustably disposed at a distance of approximate-ly two tb fifteen millimeters from the container interior sur-face 50. Apparatus in accordance with the present invention should preferably have the open end thereof tilted slightly downwardly from the horizontal to permit excess coating mater-ial to flow back into the bath as illustrated by arrow A in Figure 9.
The apparatus set forth ln Figures ~-9 ~or coating the interior surface 50 of a rotating container CB by a ætationary ~' .. . - .. . - - . . .. . , ,, . . . ,. ~ .
- . .. :, ... : : , , .
1~545S8 nozzle 51 may be utilized with an endless chain driving means in con~unction with the rack and pinion drive for coating an e~terior surface as set forth in Figure 1, and the principles set forth therein are equally applicable to such apparatus for coating interior surfaces.
Referring now to Figures 10 and 11, the coating of the exterior surface 70 of a rotating work piece CB by means of a stationary nozzle 71 similar in principle to that shown in Figures 4 and 5 is shownO The stationary and uncharged nozzle 71 has a wedge-shaped top portion 72 which is contoured to correspond to the contours of exterior surface 70 of the work piece CB, which may be a beer can as shown. The nozzle 71 contains coating openings 73 ad~acent work plece CB for flowing a uniform coating over such work piece CB as shown by arrows. A similarly shaped electrode grid 74 is disposed inter-mediate said nozzle 71 and the work piece CB to provide elec-trical current to the electrocoating material as it flows from nozzle 71 onto work piece CB. A non-conductive mesh 75 covers grid 74 for preventing accidental short circuiting between work piece CB and grid 74 and also to promote laminar flow and to reduce bubbling. Grid 74 has a wedge-shaped portion dis-posed proximate to the exterior surface of the closed end of the container C~ being coated and serves to insure the same dwell coating time for any polnt on the closed end of exterior surface 76 of work piece CB for a given rotation, to permit uniform electrocoating thereof. Figure 10 also schematically shows can holder means generally designated as 78. A vacuum cup 80 engages the interior bottom surface 81 of the work piece CB and is supplied with vacuum by means of a vacuum line 82. The can holder means 78 also holds the work piece CB in ; place by means of spring 83 abutting against interior side ' 1~54558 surface 84 and is supported on either side by spring supports 85, 85 connected to and projecting from vacuum line 82.
Power supply 69 is shown connected to grid 74`and to work piece CB through its conductive connection~with a slip ring 86 having brushes 87 abutting on vacuum line 82 to provide electrical current thereto through electrically conductive spring supports 85, 85 and spring 83. Electrical current is then applied to work piece CB through its contact'with spring 83. As indicated by arrow R, can holder 78 provides rotation to the work piece CB by rotation means (not shown).
Figures 12 and 13 illustrate apparatus for coating the exterior surface 90 of a stationary work piece CB by rotat-ing an electrically charged application nozzle/electrode 91.
Nozzle 91 may completely enclose the portion of work piece CB ~-to be coatedg such that, during rotation, the coating material ~ -~lowed over surface 90 will be centrifugally urged against 6uch exterior surface 90 and not be wasted. After coating, the excess coating drains back into the bath as illustrated by arrow A.
Flow openings 93 are provided in nozzle 91 from coating channels 94 therein. Although openings 93 only need be provided over one side and one-half of the bottom of nozzle 72, a symmetrical arrangement such as shown in Figure 13 is preferred for balance during rotation.
Coupling 95, which transmits coatlng material to nozzle 91, is rotat~onallg disposed on electrically charged coating supply tube 96. Rotational means (not shown) are co~-nected to coupling 95 and provide rotation thereto and t~
nozzle 91 thereby as illustrated by arrow R. Power supply in the form of a rectifier 69 provides~electrical curre'nt to nozzle 91 and also to work piece CB through vacuum line 82 of -14- ~ ' . . .
lOS4~58 can holder 78. The details of can holder 78 and the electric-al connection provided thereby are similar to those described hereinabove in connection with Figure 10.
As also disclosed hereinabove, the particular direc-tion of the current applied depends upon whether anodic or cathodic coating is to be used. A~ter rotational coating, nozzle 91 and work piece CB may be separated by removal of either, such as for example by reciprocating movement.
Figures 14 and 15 illustrate embodiments of the present invention for coating the interior surface 50 o~ a stationary work piece CB by means of a rotating application nozzle/electrode. Rotating application nozzle/electrode, gen-erally designated as 101, comprises an interior coating tube 102 opening into one or more coating channels 103, 103. As shown by arrows, coating material flows through grid 104, which is connected to power supply 69 to also serve as an electrode. Pre~erably, a non-conductive mesh 105 covers grid 104 to prevent accidental contact between nozzle 101 and work piece CB. As with the embodiment shoNn in Figure 9, nozzle 101 may have wedge-shaped terminal pqrtions 106, 106 to match more closely the contours of a beaded bottom can, such as a beer can, for uniformity of electrocoating deposition.
Figures 14 and 15 also depict schematically the structure of an eIectrically conductive can holder generally designated as 107. A vacuum cup 108, ~upplied by a vacuum -line 109 eng~ges a portion of the bottom exterior surface 110 of work piece CB to hold it securely. A non-conductive collar 111 concentrically disposed with respect to the vacuum line 109 engages a portion of the exterior wall surface 112 of the work piece CB to supplement the support provided py vacuum cup 108. An electrically conductive bottom plate 100 is disposed ~' ~
1~5455B
within holder 107 to provide electrical current to the work piece CB.
Figure 16 shows the electrophoretic coating of a work piece WP having a surface 113 having an axis of symmetry, such as for example an automobile wheelO Electrical current is applied in one polarity from power supply rec~ifier 69 to application nozzle and/or electrode 114 and in the opposite polarity to a conductive work piece holder 115 and thereby to work piece WP. Nozzle 114 is disposed to be co-extensive with the longitudinal linear dimension of surface 113 and is shaped to conform to any contours in surface 113 of work piece WP, such that each nozzle opening 116 is proximate to and substan-tial}y equidistant from surface 113 for uniformitylof applica-tion of coating material.
Nozzle 114 may alternatively be made of a flexible conductive material to be ad~ustable for various different contoured surraces and can preferably be readily ad~usted for a different such contoured surface merely by first pressing it firmly against the surface to be coated and then disposing the matching nozzle a selectedJ proximate dis*ance from the sur-face.
A linear stream 117 of electrophoretic coating is ~ :
applied to surface 113 co-extensive wlth the longitudinal linear dimension thereof and relative movement is provided be~
tween the linear stream 117 and the ~ork piece surface. Such relative motion i8 lateral to the linear dimension and circum-ferential to and about the axis Or symmetry of the work piece : .
surface 113. Although such relative movement may be accom~
plished by moving either the work piece WP or the linear stream 117, in the example shown in Figure 16 work piece WP is ro-tated by means o~ a holder 115, which may also serve as a -16- :
~54SS8 reciprocator connecting means f~r separating the work piece from the application nozzle after coa~ing. Alternatively, nozzle 114 may be mounted for reciprocating movement by means not shown.
Although the selected linear dlmension of the work piece is illustrated as being rectilinear in Figures 1-9 and 11-15 and partially rectilinear in other embodiments illus-trated herein, it is within the contemplation of the present invention that such selected linear dimension may also be par-tially or totally curvilinear For example, where the select-ed linear dimension of the work piece is curvilinear such as for example in cylindrical tubing, the nozzle for flowing the coating could be disposed annularly or semi-annularly with respect to the surface to be coated and either the noZzle or the work piece moved axially (laterally) with respect to the circumferential (linear) dimension for coating the entirety of the surface.
In the above described prefçrred embodiments the distance between the anode and cathode can vary between 2 and 15 millimeters with a preferred separation of 4 to 5`~milli-meters. The speed of rotatlon of the work piece or the elec-trode may range from 60 R.P.M. to 400 R.P.M.; however, the preferred range is 120 to 240 R.P M.
The flow o~ coating can vary from one quart to 5 gallons per minute per application nozzle. There is no ab-so~ute optimum as the flow rate must be determined for each ~pecific work piece to be coated and will vary with the size and shape thereof.
The coating voltage can range from 50 to 350 volts.
However, the preferred voltage will va~y with the size and shape of the work piece and the formulation of the coating.
. ~ . .. . ..
. .
1~54558 However, 150 to 180 volts is generally satisfactory.
Coating temperature can range from 60 to 140F., butthe most practical range is 70 to 90F. The vlscosity of the coating is not critical, but is most usually close to that of water. The percent solids of the coating can be varied be-tween 7 and 15~, but the preferred operating range is approx-imately 12~.
~ oating time will vary considerably depending upon voltage, paint temperature, type of substrate, and film thick-ness desired; however, it is desirable to keep the coatingtime as low as possible. Practical operating ranges will vary from 0.1 second to 10 seconds, with coating times of between 0.3 second and 3 seconds, usually being the most practical.
A typical example of apparatus ln accordance with the present invention for coating the interior of aluminum containers, as shown in Figures 6-9, would be designed to coat 300 cans per minute using a coating time of 0.5 seconds and a voltage of 180 volts. The paint temperature would be 80F. - ~-90F. and the percent solids of the paint would be 12~ to 14%.
The speed of rotation of the can would be 240 R.P.M. and the flow rate of the paint would be 3/4ths of a gallon per minute ;
per application nozzle. Distance from the elect~ode to the container would be 4 millimeters. Following the coating pro-cess, the can would be rinsed to remove exceæs coating material and baked in an oven at any desired temperature to e~fect sat-isfactory cure o~ the coating.
Claims (20)
1. A method for electrophoretically coating a sur-face of an electrically conductive work piece having a selec-ted linear dimension, comprising the steps of establishing said work piece at one electrical potential, flowing an electrophore-tic coating in a linear stream corresponding to said selected linear dimension and in close proximity to said surface of said work piece, imparting an electrical charge to said linear stream, impinging said charged linear stream of electrophoretic coating onto said surface of said work piece, and moving said work piece and said charged linear stream of electrophoretic coating rela-tive to one another in a direction lateral to said linear di-mension, thereby to electrophoretically deposit coating over the entirety of said surface of said work piece.
2. The method according to claim 1 including the additional steps of rinsing excess electrophoretic coating from said coated work piece, and curing the remaining electrophoretic coating on said coated work piece.
3. The method according to claim 1 or 2, wherein said work piece is moved relative to said linear stream of electro-phoretic coating.
4. The method according to claim 1 or 2, wherein said linear stream of electrophoretic coating is moved relative to said work piece.
5. The method according to claim 1, wherein said work piece has an axis of symmetry, said linear stream of electro-phoretic coating is coextensive with a longitudinal linear dimension of a surface of said work piece, and said relative movement lateral to said linear dimension is circumferential to and about said axis of symmetry of said work piece.
6. The method according to claim 5, wherein said symmetrical work piece is a cylindrical body, said cylindrical body is closed at one end, and said linear stream of electro-phoretic coating also extends along the radius of said closed end to the longitudinal axis of said cylindrical body.
7. The method according to claim 1 or 2, wherein said linear stream of electrophoretic coating is flowed in close proximity to the exterior surface of said work piece, whereby electrophoretic coating is deposited over the entire exterior surface of said work piece to provide a work piece electrophoretically coated on said exterior surface.
8. The method according to claim 1 or 2, wherein said linear stream of electrophoretic coating is flowed in close proximity to the interior surface of said work piece, whereby, electrophoretic coating is deposited over the entire interior surface of said work piece to provide a work piece electrophoretically coated on said interior surface.
9. An apparatus for electrophoretically coating a surface of an electrically conductive work piece having a se-lected linear dimension, said apparatus comprising a reservoir for containing the electrophoretic coating material, means for mounting the work piece to display the linear dimension thereof, nozzle means for providing a linear stream of electrophoretic coating material onto said linear dimension of said work piece, means for supplying electrophoretic coating material to the nozzle means, means for charging the linear stream of electro-phoretic coating material relative to the work piece, and means for moving said mounting means and said nozzle means relative to one another in a direction lateral to said linear stream, whereby an entire surface of the work piece on said mounting means may be coated.
10. Apparatus according to claim 9, further compri-sing means for rinsing excess said electrophoretic coating material from said work piece.
11. Apparatus according to claim 9, further compri-s ing means for curing said electrophoretic coating material on said work piece.
12. Apparatus according to claim 9, further compri-sing conveyor means connected to said mounting means for con-veying the mounted work piece.
13. Apparatus according to claim 9, wherein said mounting means includes vacuum means for contacting a surface of said work piece and for holding said work piece firmly during said electrophoretic coating.
14. Apparatus according to claim 13, wherein said vacuum means is disposed external to said work piece and further includes collar means for supplementarily supporting said work piece during said coating thereof.
15. Apparatus according to claim 9, wherein said nozzle means is charged oppositely to the work piece and has a plurali-ty of coating flow openings therein corresponding to said se-lected linear dimension of said work piece surface.
16. Apparatus according to claim 15, further compri-sing non-conducting means for insulating said charged nozzle means, said non-conducting means being disposed between said nozzle means and said charged work piece surface, whereby elec-trical short circuiting therebetween is prevented.
17. Apparatus according to claim 16, wherein said non-conducting means comprises an insulating mesh means for promoting laminar flow and for reducing bubbling.
18. Apparatus according to claim 9, wherein said nozzle means includes an electrically conductive grid disposed on said nozzle means proximate to said work piece surface, where-by said coating is electrically charged as it flows from said nozzle means onto said work piece surface.
19. Apparatus according to claim 9, further comprising means associated with said reservoir for controlling the tempera-ture of the electrophoretic coating material.
20. Apparatus according to claim 9, further compri-sing means associated with said reservoir for filtering the electrophoretic coating material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59731475A | 1975-07-21 | 1975-07-21 | |
| US68611076A | 1976-06-07 | 1976-06-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054558A true CA1054558A (en) | 1979-05-15 |
Family
ID=27082793
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA257,381A Expired CA1054558A (en) | 1975-07-21 | 1976-07-20 | Method and apparatus for electrophoretic coating |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5241655A (en) |
| CA (1) | CA1054558A (en) |
| CH (1) | CH612697A5 (en) |
| ES (1) | ES450009A1 (en) |
| FR (1) | FR2318948A1 (en) |
| GB (1) | GB1535077A (en) |
| IT (1) | IT1075015B (en) |
| MX (1) | MX143585A (en) |
| SE (1) | SE7608242L (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2014611B (en) * | 1978-02-17 | 1982-06-16 | Standard T Chemical Co Inc | Method and apparatus for removing excess electrophoretic material from coated interior workpiece surface |
| US4210507A (en) * | 1978-09-18 | 1980-07-01 | Aluminum Company Of America | Electrocoating flow control electrode and method |
| GB2085922B (en) * | 1980-10-15 | 1984-01-25 | Metal Box Co Ltd | Electrocoating apparatus |
| DE3304940A1 (en) * | 1983-02-12 | 1984-08-16 | Herberts Gmbh, 5600 Wuppertal | METHOD FOR COATING SINGLE-SIDED OPEN HOLLOW BODIES |
| JPS59185879A (en) * | 1983-04-07 | 1984-10-22 | Kotaro Inoue | Generating set utilizing wind force produced in time of train running |
| DK0431711T3 (en) * | 1989-11-16 | 1993-12-13 | Plm Berlin Dosenwerk Gmbh | Method and apparatus for anodic or cathodic electro-coating of hollow portions, especially of cans |
| CA2056037A1 (en) * | 1990-11-28 | 1992-05-29 | Mitsuhiro Seki | Electrodeposition process and device |
| JPH04321774A (en) * | 1991-04-20 | 1992-11-11 | Taimei Kinzoku Kogyo Kk | Wind power generator utilizing railway |
| DE4136237A1 (en) * | 1991-11-02 | 1993-05-06 | Basf Lacke + Farben Ag, 4400 Muenster, De | METHOD FOR PAINTING RADIATORS |
| US5409585A (en) * | 1993-04-05 | 1995-04-25 | Ppg Industries, Inc. | Nozzle arrangement for electrocoating container interiors |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL127473C (en) * | 1963-04-10 | |||
| DE1646168B2 (en) * | 1966-01-27 | 1970-10-15 | ||
| AT279002B (en) * | 1966-05-12 | 1970-02-25 | Reichhold Chemie Ag | Process for electrophoretic coating and devices for carrying out the same |
| JPS5250407B2 (en) * | 1974-05-24 | 1977-12-24 |
-
1976
- 1976-07-20 SE SE7608242A patent/SE7608242L/en unknown
- 1976-07-20 GB GB3019676A patent/GB1535077A/en not_active Expired
- 1976-07-20 IT IT2552276A patent/IT1075015B/en active
- 1976-07-20 CA CA257,381A patent/CA1054558A/en not_active Expired
- 1976-07-21 CH CH934676A patent/CH612697A5/en not_active IP Right Cessation
- 1976-07-21 JP JP8710176A patent/JPS5241655A/en active Granted
- 1976-07-21 FR FR7622272A patent/FR2318948A1/en active Granted
- 1976-07-21 ES ES450009A patent/ES450009A1/en not_active Expired
- 1976-07-21 MX MX16560876A patent/MX143585A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FR2318948B1 (en) | 1979-07-13 |
| JPS5241655A (en) | 1977-03-31 |
| FR2318948A1 (en) | 1977-02-18 |
| ES450009A1 (en) | 1977-11-16 |
| JPS572280B2 (en) | 1982-01-14 |
| CH612697A5 (en) | 1979-08-15 |
| GB1535077A (en) | 1978-12-06 |
| MX143585A (en) | 1981-06-05 |
| IT1075015B (en) | 1985-04-22 |
| SE7608242L (en) | 1977-01-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4107016A (en) | Method and apparatus for electro-phorectic coating | |
| CA1054558A (en) | Method and apparatus for electrophoretic coating | |
| US5810987A (en) | Process for efficiently electrophoretically coating small items | |
| US4377603A (en) | Method and apparatus for electrostatic powder coating | |
| US4094760A (en) | Method and apparatus for differentially and simultaneously electrocoating the interior and exterior of a metal container | |
| EP0276234A1 (en) | Electro-coating apparatus and method | |
| US3849284A (en) | Apparatus method and valve for electrodepositing a coating on interior surfaces of container bodies | |
| CN101535156A (en) | Workpiece carrier for conveying a workpiece to be painted | |
| CN1116122C (en) | Workpiece treating apparatus | |
| CA1322346C (en) | Method for electrodeposition coating | |
| US20170216879A1 (en) | System and method of coating products | |
| US4659445A (en) | Process for coating hollow bodies, which are open on one end | |
| HU216495B (en) | Device for the electrolytic coating of the electrically conductive products | |
| CA1294917C (en) | Method for electrodeposition coating | |
| US3476666A (en) | Centrifugally operating electrodeposition apparatus and method of use | |
| US4119522A (en) | Nozzle apparatus for electrophoretic coating of interior surfaces | |
| WO2006061659A1 (en) | Process and apparatus for multiple surface treatments of battery cans | |
| US3945901A (en) | Method for electrocoating conductive articles | |
| US20060011479A1 (en) | Method and apparatus for the bulk coating of components | |
| EP0050045B1 (en) | A method of, and apparatus for, electrocoating | |
| US3759810A (en) | Roll through method for electro coating can ends | |
| US3694336A (en) | Method for can electrodeposition | |
| US3898151A (en) | Apparatus for electrocoating conductive articles including magnet means to convey the articles | |
| US3801485A (en) | Apparatus and method for electrodepositing a coating on interior surfaces of container bodies | |
| CA2687313C (en) | Work electrodeposition coating method and work electrodeposition coating device |