US3325390A - Method and apparatus for electrocoating using an auxiliary electrode - Google Patents

Description

June 13, i967 G. l.. Bumxsma 15m. 3,325,399

METHOD AND APPARATUS FOR ELECTROCOATING Filed July l, 1963 USING AN AUXILIARY ELECTRODE 5 Sheets-Sheet l Rif/90%@ Mm QZ@ /Qf www,

June 139 1967 G. L, BURNSIDE ETAL METHOD AND APPARATUS FOR ELECTROCOATlNG USING AN AUXILIARY ELECTRODE Filed July l, 1963 5 Sheds-Sheet 2 June i3, i967 r3.1... BURNSIDE ETAL 3,325,390

METHOD AND APPARATUS FOR ELECTROCOATING USTNG AN AUXILIARY ELECTHODE Filed July l, 1963 5 Sheets-Sheet C' June 13, 1967 1 BURNSIDE ETAL 3,325,390 METHOD AND APPARATUS FOR ELECTROCOATING USING AN AUXILIARY ELECTRODE Filed July lv 1963 5 Sheets-Sheet 4 35's /LV a@ 5 fwm, A fromm-rs June 13, 1967 G. L.. BURNSIDE ETAL 3,325,390

METHCD AND APPARATUS FOR ELECTROCOATNG USING AN AUXILIAHY ELECTROD 5 Sheets-Sheet 5 Filed July l 1963 f .m S www@ SHSm MMMW 71 @WQ UAM @v NWN @00 fw www w03 umm@ BYQVEWM TTO/PA/EYS 3,325,390 METHGD AND APPARATUS FOR ELECTROCOAT- ING USiNG AN AUXELIARY ELECTRDE Gilbert L. Burnside, Gak Park, Raymond A. Igras, Dearborn Township, and Gordon G. Strosberg, Oak Park,

Mich., assignors to Ford Motor Company, Dearborn,

Mich., a corporation of Delaware Filed July 1, 1963, Ser. No. 291,653 9 Claims. (Cl. 2114-181) 'Ihis invention relates to electrocoating electrically conductive objects with an organic material dispersed in an aqueous bath. In particular, this invention relates to a method for controlling product quality in and improving the efficiency of a continuous process of electrically induced deposition of organic hlm-forming material wherein a substantially water insoluble coating is applied to metal objects conveyed through an aqueous bath. More parti-cularly, this invention relates to embodiments of electi'ocoating or electropainting wherein the internal surfaces of substantially hollow objects, i.e. objects having `internal compartments, cavities, recesses, etc., are coated simultaneously with the coating of the exterior surfaces of the same by the employment of electrodes both inside and outside the object being coated; to method and means within such embodiment-s for automatically measuring the electrical resistance `between a given object and the electrodes therein while such object is in movement to the coating bath; and to the utilization in such embodiments of the ow of electrical energy, if any, between an object and the electrodes therein to control movement of the object in its approach to the coating bath.

Objects to be coated are individually suspended from and transported by an overhead conveyor which, with suitable connecting devices, is constructed and arranged su-ch that the suspended workpieces successively enter the aqueous bath for coating and are withdrawn for further processing such as sanding, finish coating, etc. While being coated the object or workpiece is positively charged anda direct current iiow of electrical energy is provided between the workpiece and a negative and grounded coating tank or other electrode.

To simultaneously coat both the interior and exterior surfaces of an object it has been found advantageous to employ additional electrodes positionedeither `wholly or partially within the object. These internally positioned electrodes are provided with a polarity opposite that of the object during coating. When significant electrical connection is made between one of such electrodes and the workpiece the effectiveness of the electrode is lost and .the object often must be refinished by other methods or discarded. Such connection can result from improperly positioned or defective insulators, and the use of such electrodes in a continuous process is conducive to insulat-or failure.

In accordance with this invention the resistance to liow of electrical energy between the object to be coated and the electrodes therein is automatically measured prior to entry of the object into the coating bath. If such resistance is found to be below a predetermined value, a warning sys-tem is automatically actuated and the conveyor is `stopped for removal of the electrical connection.

. lOrganic coating materials which may be used in the bath include `but not by way of limitation alkyd resins, lacrylate resins, phenol-formaldehyde resins, and various carboxylic -acid resins or mixtures of the foregoing with each other or other hlm-forming materials including binding agents and extenders conventionally employed with water based paints. Such materials may include or be employed with other organic monomers and/or polymers including but not by way of limitation hydrocarbons and oxygen substituted hydrocarbons such as ethylene l United States Patent Patented .lune 13, 1967 ICC glycol, propylene glycol, glycerol, various monohydric alcohols and various carboxylic acids, ethers, aldehydes and ketones. The film-forming material may include or be employed with pigments, dyes, drying oils, etc., and may be dispersed as a colloid, emulsion or emulsoid with conventional dispersing agents such as ammonia, water soluble amines, polymeric amines, etc.

It is one object of this invention to provide an effective method for electrocoating internal surfaces of objects in a continuous process wherein electrodes are positioned within the object to be coated, means are provided for automatically detecting electrical connection between an object and the electrodes therein, and the entry of an object into the coating bath having such connection is automatically prevented.

With the foregoing and 4other objects in view, as will hereinafter become apparent, this invention comprises the methods, combinations, construction and arrangement of parts hereinafter set forth, disclosed, claimed and illustrated in the accompanying drawings wherein:

FIGURE l is a schematic drawing depicting electrocoating apparatus with which the feed `control systems shown in the succeeding iigures are employed;

FIGURE 2 is a schematic partial plan View of facilities larranged for continuous electrocoating of automobile bodies including a coating tank, conveyor means for moving objects through such tank and a plurality of electrode installations and resistance checking stations associated with the conveyor upstream from the coating tank;

FIGURE 3 is a schematic drawing of apparatus adapted to measure the electrical resistance between an object 4and electrodes positioned therein while such object is in movement to the coating bath, signal the detection of an electrical connection between an object andan electrode therein, and stop the conveyor for elimination of such connection;

FIGURE 4 is a schematic drawing of the resistance measuring and conveyor control device of FIGURE 2; and

FIGURES 5 and 6 are schematic `drawings of electrodes which can be used inside an object being electrocoated.

Reference is now made to FIGURE 1 which illustrates the coating process hereinafter discussed. In FIGURE 1, chemically resistant tank 11 contains a coating bath 13 and serves as a negative electrode in the coating process. Tank 11 is electrically` connected to DC. power source 17 via conductor 15..An article to be coated 19, e.g. an automobile body, is shown suspend-ed from an endless conveyor 35 by hangers 21 and 23. Conveyor 35 may be of the electrically powered, chain driven variety. Hangers 21 and 23 include insulators 25 and 27 respectively which insulate article 19 from the grounded conveyor. Contact plates or brushes 29 and 31 are attached to and in electrical connection with hangers 21 and 23 respectively. Article 19 is shown approaching bath 13 and in electrical connection with bus bar 33 which in turn is in electrical connection with D.C. power source 17 via conductor 37. Article 19 therefore serves as the positive electrode while being coated. It is to be understood that bus bar 33 may be segmented and that certain of the various segments may have no connection with the power source or be adapted for polarity reversal to provide control means over the coating process.

Referring now to FIGURE 2, there is shown a schernatic partial plan view of electrocoating apparatus and assembly equipment suitable for use in the practice of this invention including a coating tank 111, a conveyor 135, a segmented bus [bar indicated generally `at 133 and a bus bar `of unitary construction 137. Tank 111 and conveyor 135 may be the same as or different from the corresponding items in FIGURE 1. In addition, there is shown in FIGURE 2 a plurality of electrode installation stations indicated generally at 115, 117 and 119 where one or more electrodes such as those shown in FIGURES 5 and 6 are manually positioned and secured inside the article to be coated. In this embodiment such stations also serve as resistance check stations. In the alternative, resistance check stations may be positioned immediately following each electrode installation station.

To serve their intended purpose, as hereinafter and hereinbefore more fully explained, electrodes positioned within an object to be coated must be electrically insulated from the article to be coated. Such article is here represented by an automobile body 139 at station 115. Station 115 is here provided with test conductors or brush bars 121 and 123. Similar conductors are provided for each succeeding station of this type. These are represented in FIGURE 2 by conductors 125 and 127 at station 117 and conductors 129 and 131 at station 119. Means for measuring electrical resistance between body 139 and electrodes inserted therein at station 115 are indicated in FIGURE 2 by brush support member 141, conductors 143 and 145, and a control unit indicated generally at 147. It should be understood that such means are likewise available at stations 117 and 119 though not shown.

Referring now to FIGURE 3, bar conductors 121 and 123 areagain lshown in electrical connection with control unit 147 via conductors 143 and 145. This connection is indicated at terminals 217 and 249 of unit 147. Brush support member 141 is shown suspended from and supported by conveyor 135. Support member 141 is a nonconductor and supports contact plates or brushes 151 and 153. Brushes 151 and 153 are positioned so as to contact the test Vconductors at each of the aforementioned stations. Brushes 151 and 153 are here shown in electrical connection with test conductors 121 and 123 respectively. Brush 151 is in electrical connection with body 139 via insulated conductor 155. Body 139 is suspended from and supported by grounded conveyor 135 by cables or hangers which are not shown in order to more clearly show the test apparatus. Electrodes 157 and 159` are in electrical connection with brush.153 via insulated conductors 161 and 163. Electrodes 165 and 167 are in electrical connection with electrodes 157 and 159 via insulated conductors 169 and 171. Electrodes 165 and 167 are inserted into rocker panel compartments 173- and 175 respectively.

Preferably electrodes 165 and 167 are not installed until after electrodes 157 and 159 have been installed and checked.

Control unit 147 is electrically connected to an alternating current power source, not shown, via switch 179 and conductors 177, 181 and 183. A relay coil 185 is in electrical connection with conductor 183 and when actuated causes the set of contacts indicated at 187 to open. The contacts indicated at 187 are in the conveyor run circuit and are normally closed. The breaking of this electrical connection stops the conveyor. Coil 185 is also in electrical connection with signal light 189 and signal lbell 191. Signal bell 191 is in electrical connection with conductor 181 when the set of contacts indicated at 193 isV closed. These contacts are normally open.

A reset button switch 201 which is normally closed provides electrical connection between terminals 207 and 209 of control unit 147 via conductors 203 and 205 respectively. Switch 201 and its uses will be explained in relation to FIGURE4.

Referring now to FIGURE 4, conductors 181 and 183 also shown in FIGURE 3 are in electrical connection with a step-down transformer indicated generally at 311 Where the potential of the current flowing from the power source, e.g. 110 volts A.C., is decreased to provide a dif- [ference of potential of about 1 to 5 volts between conductors 3113 and 321. Conductor 313 is in electrical connection with meter coil 315, conductor 317 and terminal 217. Conductor 321 is in electrical connection with lrectifier 323 by which the alternating current is converted to a direct current, conductor 325, variable resistor 327 which provides means for gross calibration of the system, conductor 329, resistor 331, conductor 333, resistor 335, conductor 337, resistor 339, conductor 341, resistor 343, conductor 345, potentiometer 347 for ne calibration of the measuring system, conductor 349, and terminal 249.

Resistors 351 and 353 are in electrical connection with conductors 313 and 337 and, together with the aforementioned resistors, limi-t the flow of current to meter coil 315.

Condenser 355 is in electrical connection with conductors 313 and 325 and provides means for gross stabilization of voltage in the measuring system. Constant voltage is further assured by voltage regulator tube 357 which is in electrical connection with conductors 313 and 329.

In operation terminal 207 is in electrical connection with terminal 209 through conductors 203 and 205 and reset switch 201 shown in FIGURE 3.

Meter coil 315 has associated therewith a movable arm, not shown, or other suitarble device for closing the set of contacts indicated at 361. Sealing coil 359 is electrically connected to the se-t of contacts indicated at 361. This set of contacts can be preset so that a predetermined resistance to closing is assured. Upon a flow of current through coil 315 above a predetermined value, the set of contacts at i361 is forced closed electromechanically via the aforementioned movable arm associated with coil 3115. Such flow is brought into being when electrical c-onnection is established between the workpiece andan electrode positioned therein as shown in FIGURE 3. The closing of this circuit actuates relay coil 363 which is in electrical contact with terminal 207 and conduct-or 325. The actuaiton of c-oil 363 causes a set of contacts indicated a-t 1'93 t-o close .thereby 4closing the circuit shown in FIGURE 3 which includes conductor 183, coil 185, signal lamp 189, signal bell 191, and conductor 181. It is to be understood that coil y185 and its control over the conveyor may be eliminated if sufficient time and space are available for removing a defective electrode before the object reaches the coating bath. In such an embodiment warning is given as before with the aforementioned signal devices.

In FIGURES 5 and 6 there are shown two embodiments of probe electrodes which may be used in the practice of this invention. Referring to FIGURE 5, a. conductor 401 -of suitable metal is shown in electrical connection with an insulated conductor 403 which, during coating, is in electrical connection with bus bar -1'37 shown in FIGURE 2 and in testing is in electrical connection with brush 153 of FIGURE 3. Rod-401 is otherwise electrically insulated from the workpiece by a tubelike insulator 407 which is closed at one end and is prefer- .a-bly formed of a flexible material. Insulator 407 has a large number of evenly spaced openings which admit the aqueous bath to rod 401 while preventing physical and hence electrical connection between rod 401 and the workrece.

tIn FIGURE 6 there is sh-own a somewhat different embodiment wherein a conductor rod 501 is enclosed in a tube-like, perforated sheath `507 of .a suitable metal and insulated therefrom by a series, of plastic washers 503 and `an insulator end plug 505.

Referring now to FIGURES 2, 3 an-d 4, when an automobile body is brought to station by conveyor 135, electrodes 157 and 159 are installed w-ithin the body and electrical connection is established between such electrodes and test conductor 123. Electrical connection is also established between body 139 and test conductor 121. If significant electrical connection exists between one or more of the installed electr-odes and body 139 current will flow through coil 315 of FIGURE 4 causing the set of contacts at 361 to close, actuating coil 363, closing the set of contacts at 1193 and actuating the alarm and control circuit shown in FIGURE 3 including coil 185, signal light 189 and signal bell 191. As aforementioned, the actuation of coil opens the set of contacts at 187 and stops the conveyor.

If electrical connec-tion exists between the electrodes installed and the body, the electrodes and their connections are checked and the improperly insulated electrode or electrodes removed and replaced. Reset switch 20'1 of FIGURE 3, which is spring actuated, is .then depressed breaking .the electrical connection between terminals 207 and 209 shown in FIGURES 3 and 4. This break deactivates coil 363 causing the set of contacts at 193 to open which deactivates coil 185 and allows the set of contacts at 187 to close. APressure on reset switch 201 also serves to reopen the set of contacts at 361 in FIGURE 4; or, in the alternative, it may be arranged for the contacts at 361 to reopen as soon as current ceases to -liow through coil 315. The release of pressure on reset lbutton 201 reestablishes electrical connection between . terminals 207 and 209.

If no electrical connection is established between the body and the electrodes installed, the body proceeds to station 117 where other electrodes are installed, e.g. electrodes 165 and 167, and the test procedure is repeated. The foregoing procedure is repeated until all internally positioned electrodes have been installed and their insulation checked. The body 139 then proceeds through the coating bath. Upon withdrawal from the coating bath the internally positioned electrodes are removed and returned to the various installation stations.

The foregoing detailed description of the embodiments shown in the drawings is submitted solely for purposes of illustration. Those skilled in the art will be the aware .that numerous modifications canbe made in the aforedescribed system without departing from the spirit and the scope of the invention as expressed in the claims.

We claim:

1. In a method of coating an electrically conductive object which comprises moving said object through an aqueous bath having an organic `film-forming material dispersed therein and a first electrode of fixed position in contact therewith, providing a a difference of electrical potential between saidfirst electrode and said object, and maintaining the resulting direct current fiow of electrical energy .through said bath between said first electrode and said object until a coating of said coating material is deposited upon said object, the improvement which c omprises causing a movable electrode assembly comprisln-g a second electrode and an electrode cover movable therewith to move in relation to said first electrode and through said bath simultaneously with the movement of said object through 4the same, and providing a unidlrectional flow of electrical energy through said bath between said object and said second electrode while said direct current is flowing between said first electrode and said object, said cover being constructed and arranged to admit liquid into contact with said second electrode when said assembly is immersed in said ba-th and to electrically insulate said second electrode from said object.

2. In a method of coating an automobile body which comprises moving said body through an aqueous bath having an organic film-forming material dispersed therein and a first electrode of fixed position in contact therewith, providing `a difference of electric potential between said first elect-rode and said body, and maintaining the resulting direct current ow of electrical energy through said bath between said first electrode and said body until a substantially water insoluble coating of said coating material is deposited upon said body, the improvement which comprises moving said body through said bath with a second electrode at leas-t partially inside and electrically insulated from said body, providing a unidirectional flow of electrical energy between said body and said second electrode while said body moves through said bath and while said direct electric current is owing between said first electrode and said body.

3. In a method of coating an automobile body which comprises moving said body through an aqueous bath having an -organic film-forming material dispersed therein and a first electrode of fixed position in contact therewith,

providing a difference of electric potential between said firs-t electrode and said body, and maintaining the resulting direct current flow of electrical energy through said bat-h between said first electrode and said body until a substantially water insoluble coating of said coating material is deposited upon said body, the improvement which comprises moving said body through said bath with a second electrode inside and insulated from said body, and providing electrical connection between said first electrode and said second ele-ctrode while said second electrode is in movement through said bath.

4. In a method of coating an electrically conductive object hav-ing wall-s defining a chamber in iiuid communication with the exterior thereof which comprises moving said object through an aqueous bath having organic filmforming material dispersed therein and a first electrode of fixed position in contact therewith, providing inside said chamber a second electrode electrically insulated from said object, and providing a direct current of electrical energy through said bath between said object and said electrodes until a substantially water insoluble coating of said material is deposited upon said object, the improvement which comprises providing a difference of electric potential between said object and said second electrode after said second electrode is inside said chamber and prior to entry of said object into contact with said bath, measuring flow of electrical energy between said object and said second electrode resulting from said difference of potential, and utilizing said iiow when it exceeds a predetermined value to control movement of said object in its approach to said bath.

5. In a method of coating an electrically conductive object having walls defining a chamber in fluid communication with the exterior thereof which comprises passing said object through an aqueous bath having organic filmforming material dispersed therein and a first electrode of fixed position in contact therewith, providing inside said chamber a second electrode electrically insulated from said object, and providing a direct. current of electrical energy through said bath between said object and said electrodes until a substantially water insoluble coating of said material is deposited upon said object, the improvement which comprises providing a difference of electric potential between said object and said second electrode after said second electrode is inside said chamber and prior to entry of said object into contact with said bat-h, measuring flow of electrical energy between said object and said second electrode resulting from said difference of potential while said object is in movement to said bath, and utilizing said flow when it exceeds a predetermined value to stop the movement of said object to said bath.l

6. Apparatus for use in coating an electrically conductive object having walls defining a chamber in fluid communication with the exterior thereof comprising in combination a bath container adapted to retain a liquid coating bath, a fixed electrode positioned so as to Contact said bath when said container is charged therewith, a movable electrode assembly of a shape and size admitting of insertion into said chamber and comprising a movable electrode and an electrode cover movable therewith, said `cover being constructed and arranged to admit liquid into contact with said movable electrode when said assembly is in contact with said bath and to insulate said movable electrode from said object when said assembly is inside said chamber, means for conveying: said object and said electrode lassembly through said bath with at least a portion of said assembly inside said chamber, and means for providing a direct current dow of electrical energy between said object and said electrodes while said object and said electrode assembly are in movement through said bath.

7. Apparatus for use in coating an automobile -body in movement through an aqueous bath comprising in combination an electrically con-ductive coating tank serving as a first electrode and adapted to retain an aqueous coat- 7 ing bath having organic film-forming material dispersed therein, a movable electrode assembly of a shape land size admitting of insertion inside said body comprising a second electrode `and an electrode cover movable therewith, said cover being constructed and arranged to admit liquid into contact with said second electrode when said assembly is in contact with said bath and to insulate said second electrode from said body when said assembly is positioned inside said body, means for conveying said body and said electrode assembly through said bath with at least a portion of said assembly inside said body, and means for providing a direct current flow of electrical energy between said body and said electrodes while said body and said electrode assembly are in movement through said bath.

8. Apparatus for use in coating an automobile body comprising in combination a bath container adapted to retain a liquid coating bath, a first electrode positioned so as to contact said bath when said container is charged therewith, a movable electrode assembly adapted to be inserted inside said body comprising a second electrode and an electrode cover movable with said second electrode, said cover being constructed and arranged to admit liquid into contact with said second electrode when said assembly is in contact with said bath and to insulate said second electrode from said body when said assembly is positioned inside said body, means for conveying said body and said assembly through said bath with at least a portion of said -assembly inside said body, means for providing electrical connection between said first electrode and said second electrode while said second electrode is moving in relation to said iirst electrode, and means for providing -a direct current flow of electrical energy through said bath between said body and said electrodes while said body yand said assembly are in movement through said bath.

9. Apparatus for use in coating an electrically conductive object having walls dening a chamber in fluid communication with theeXterio-r thereof comprising in combination a bath container adapted to retain a liquid coating bath, a rst electrode positioned so as to contact said bat-h `when said container is charged therewith, a movable electrode assembly of a shape and size admitting of insertion into said chamber and comprisinga second electrode and an electrode cover mova'ble therewith, said cover being constructed and arranged to admit liquid into contact with said second electrode when'said assembly is in contact with said bath and to insulate said second electrode from said object when said assembly isrinside said chamber, means for conveying said object and said assembly through said bath with at least a portion of said assembly inside said chamber, means for providing a direct current ow of electrical energy -between said object and said electrodes while said object and said electrode assembly are in m-ovement through said bath, means for providing a difference of electrical potential between said object and said second electrode prior to their entry into said bath and after said second electrode is inside said chamber, means for measuring the electric-al resistance between said object and said second electrode under said difference of potential `and while said object is in movement prior to entry into said bath, and means for utilizing flow of electrical energy between said object and said second electrode resulting from said difference of potential to control movement of said object prior to entry of said object into contact with said bath.

References Cited UNITED STATES PATENTS 2,944,953 7/1960 Borodin 204-198 3,200,057 8/1965 Burnside et al 204-181 3,200,058 8/1965 Oster 204-181 JOHN H, MACK, Primary Examiner.

E. ZAGARELLA, Assistant Examiner;

Claims (1)

1. IN A METHOD OF COATING AN ELECTRICALLY CONDUCTIVE OBJECT WHICH COMPRISES MOVING SAID OBJECT THROUGH AN AQUEOUS BATH HAVING AN ORGANIC FILM-FORMING MATERIAL DISPERSED THEREIN AND A FRIST ELECTRODE OF FIXED POSITION IN CONTACT THEREWITH, PROVIDING A DIFFERENCE OF ELECTRICAL POTENTIAL BETWEEN SAID FIRST ELECTRODE AND SAID OBJECT, AND MAINTAINING THE RESULTING DIRECT CURRENT FLOW OF ELECTRICAL ENERGY THROUGH SAID BATH BETWEEN SAID FIRST ELECTRODE AND SAID OBJECT UNTIL A COATING OF SAID COATING MATERIAL IS DEPOSITED UPON SAID OBJECT, THE IMPROVEMENT WHICH COMPRISES CAUSING A MOVABLE ELECRODE ASSEMBLY COMPRISING A SECOND ELECTRODE AND AN ELECTRODE COVER MOVABLE THEREWITH TO MOVE IN RELATION TO SAID FIRST ELECTRODE AND THROUGH SAID BATH SIMULTANEOUSLY WITH THE MOVEMENT OF SAID OBJECT THROUGH THE SAME, AND PROVIDING A UNIDIRECTIONAL FLOW OF ELECTRICAL ENERGY THROUGH SAID BTH BETWEEN SAID OBJECT AND SAID SECOND ELECTRODE WHILE SAID DIRECT CURRENT IS FLOWING BETWEEN SAID FIRST ELECTRODE AND SAID OBJECT, SAID COVER BEING CONSTRUCTUED AND ARRANGED TO ADMIT LIQUID INTO CONTACT WITH SAID SECOND ELECTRODE WHEN SAID ASSEMBLY IS IMMERSED IN SAID BATH AND TO ELECTRICALLY INSULATE SAID SECOND ELECTRODE FROM SAID OBJECT.

Images