US3585120A - Novel method of electrocoating hollow bodies - Google Patents

Novel method of electrocoating hollow bodies Download PDF

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Publication number
US3585120A
US3585120A US757565A US3585120DA US3585120A US 3585120 A US3585120 A US 3585120A US 757565 A US757565 A US 757565A US 3585120D A US3585120D A US 3585120DA US 3585120 A US3585120 A US 3585120A
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water
coating
soluble
dispersible
coated
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US757565A
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English (en)
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Felix Wehrmann
Franz Aigner
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Stollack AG
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Stollack AG
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    • 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
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/04—Tubes; Rings; Hollow bodies

Definitions

  • the method of the invention for electrocoating conductive surfaces of a hollow body with a coating material comprises immersing a hollow object having at least an electrically conductive surface which acts as an electrode in an electrically conductive coating bath containing an organic coating agent to be deposited on the hollow object and provided with a counter-electrode, passing an electric current thorugh the said coating bath and removing the coated hollow object from the coating bath, the coating of the interior of the hollow object being effected by at least one bipolar auxiliary electrode with one pole inside the hollow object and one pole outside the hollow 3,585,120 Patented June 15, 1971 'ice object.
  • Bipolar electrodes are electrodes which act on one end or side as anodes and on the other end or side as cathodes and such electrodes are known such as in electrometallurgy for refining copper (Milazzo, Textbook of Electrochemistry)
  • the method of the invention has great technical advantages compared to the conventional methods for coating hollow bodies. Since the bipolar auxiliary electrodes are not in metallic conductive contact with the counterelectrodes of the hollow body to be located, there is no danger of a short-circuit in case the bipolar auxiliary electrode comes in contact with the hollow body to be coated. Destruction of the hollow body, damage to the rectifier, impulse generator or any other current source are thus impossible.
  • bipolar auxiliary electrodes are smaller than conventional auxiliary electrodes connected in the direct circuit and are made of a less expensive material than the latter, considerable savings are possible. Moreover, the complicated assembly of the auxiliary electrodes immediately before the coating is eliminated. These bipolar auxiliary electrodes can rather be mounted at the most favorable time of the manufacturing process of the hollow body to be coated. For example, it is possible, to mount the auxiliary electrodes in the wall of a car body before the wall is assembled in the car body. With the method according to the invention it is also possible to coat cavities, for example, of car bodies, which could only be unsatisfactorily coated heretofore or not at all.
  • organic and inorganic pigments such as rutile, anatase, lithopone, blanc fix, kaolin, heavy spar, zinc sulfide, carbon black, iron oxide dye, zinc chromate, lead cyanamide, heliogen blue, as well as soluble dyes, such as varnish dye, in a ratio of pigment or dye to solid resin of 0 to 5.0:1.
  • the following materials may also be organic film forming agents: water-soluble or water-dispersible synthetic resins and natural resins as well as combinations thereof, water-soluble or water-dispersible vegetable or animal oils and fats and their transformation products, such as linseed oil and sardine oil, dehydrogenated castor oil, watersoluble or water-dispersible natural resins and their transformation products, such as shellac, resins, soaps and resin esters; water-soluble or water-dispersible synthetic resins modified with natural resins, water-soluble or waterdispersible maleinate resin; water-soluble or water-dispersible saturated and unsaturated polyesters; water-soluble or water-dispersible oil-free and styrenized alkyd resins, water soluble or water dispersible alkyd resins with synthetic fatty acids; water-soluble or water-dispersible alkyd resins with vegetable and animal fatty acids; watersoluble or water-dispersible acrylic alkyd resins; watersoluble or water dispersible silicone akyd resins; water
  • the electric current used in the method of the invention may be direct current and/or alternating current and/or pulsating current of any form.
  • the use of alternating current and pulsating currents is fully described in my copending US. patent applications Ser. No. 628,390 filed Apr. 4, 1967 and Ser. No. 635,977 filed May 2, 1967, the disclosures of which are hereby incorporated by reference thereto.
  • the bipolar electrodes may take any form.
  • One embodiment is a copper wire with an iron mesh screen at one end as illustrated in FIG. 5.
  • a particularly useful bipolar anode is a plastic pipe filled with steel wool and provided with openings along its length. The length of the flexible plastic pipe may be easily adjusted to conform to the form and size of the cavity to be coated. One part of the plastic pipe will protrude into the hollow body and the other end will protrude outside the cavity and the steel wool in the outer part will be coated during the coating process.
  • the same electrode can be arranged so that the coated portion is in the cavity to be coated and uncoated portion is outside the cavity. During this coating process, the uncoated portion becomes coated and the coated portion is freed from the coating agent. This has the exceptional advantage of being able to use the bipolar electrode almost an infinite number of times.
  • the thickness of the coating on the interior of the hollow body can be regulated by varying the ratio of the surface area of the interior of the hollow body to the surface area of the coated portion of the bipolar auxiliary electrode.
  • FIG. 1 illustrates a known apparatus for electrocoating with direct current
  • FIG. 2 is an equivalent circuit diagram of the apparatus of FIG. 1.
  • FIG. 3 illustrates a known apparatus for electrocoating interiors of hollow bodies with direct current and
  • FIG. 4 is the equivalent current diagram of the apparatus of FIG. 3.
  • FIG. 5 illustrates one embodiment of the apparatus of the invention to coat the interior and exterior of a hollow object using direct current
  • FIG. 6 is the equivalent current diagram of the apparatus of FIG. 5.
  • FIG. 7 is another embodiment of the apparatus of the invention for coating hollow objects with direct current.
  • FIG. 8 is an embodiment of the apparatus of the invention for coating a hollow body with alternating current.
  • FIG. 9 illustrates an embodiment of the invention in which two car bodies are coated simultaneously using a pulsating current.
  • FIG. 10 illustrates an embodiment of the invention in which a car body is coated using direct current.
  • the coating vessel 1 acts as a cathode with respect to the electrically conductive object 2 to be coated.
  • the current supply for object 2 is derived from current-collecting rail 3.
  • the object 2 is a can which has only an opening 4 in the bottom and 5 in the top surface. After this can 2 has been introduced into the coating bath, the current is turned on and the coating of the surface beings.
  • 1a denotes the cathode
  • 2a the contact point of the coating bath with the outside of the object to be coates
  • 3a the connecting point of the current source with the object to be coated
  • 4a the resistance of the coating bath outside the object to be coated
  • 5a the resistance of the film deposited on the outer surface of the object
  • 6a the resistance of the liquid column in the opening of the object (corresponding to opening 4 or 5 in FIG. 1)
  • 7a the resistance of the coating bath inside the object
  • 8a the resistance of the film deposited on the inner surface of the object.
  • the resistance of the liquid column 6a is substantially higher due to the small cross section of the openings of the object than the resistance of the coating bath outside 4a and inside 7a of the object, and thus determines the current flowing on the inside.
  • the resistance 5a rises and with it, also according to Kirchhoff, the current flowing over the internal resistance, which is equal to the sum of the resistances 6a, 7a and 8a. Between the points 2a and 3a is thus formed a constantly increasing potential difference.
  • the higher the film resistance 5a the better is the coating on the inside. Since the film resistance cannot be increased indefinitely, however, the current density inside the hollow body to be coated is limited to such low values that no sufiicient inside coating is possible.
  • FIGS. 3 and 4 illustrate the prior are method of overcoming the deficiencies of the method of FIG. 1 by introducing an auxiliary cathode into the interior of the hollow body to be coaaed.
  • the hollow body 2 to be coated is connected by the current collecting rail 3 to the positive pole of the current source and the bath vessel 1 and auxiliary electrode 6 are connected the negative pole of the current source.
  • FIG. 4 illustrates the equivalent circuit diagram for FIG. 3.
  • FIG. 4 shows the equivalent circuit diagram of this arrangement, where 1a denotes the cathode, 9a the auxiliary cathode, 3a the connecting point of the current source with the object to be coated, 4a the resistance of the coating bath outside the object to be coated, 5a the resistance of the film deposited on the outside of the object, 7a the resistance of the coating bath inside the object and 8a the resistance of the film deposited on the inner surface of the object.
  • the inside coating is elfected here independent of the outside coating. Points 1a and 9a have permanently the same cathode potential.
  • the present invention clearly avoids the disadvantages of the prior art and is more fully illustrated in FIGS.
  • a can 2 to be coated is immersed into coating vessel 1.
  • the can 2 is provided with anopening 4 in the top surface and an opening 5 in the bottom surfaceand is electrically connected by lead wire 3 to the positive pole of-adirect current source andthe vessel 1 is connected to the negative pole thereof.
  • An auxiliary bipolar electrode consisting of copper wire 7 which passes through the side wall of can 2 at point 8 whichis insulated and outside the can the copper wire 6 is attached to an iron wire mesh 9. This auxiliary electrode is not'in galvanic contact with the current source.
  • the outer part of the bipolar auxiliary electrode 9 is arranged in the proximity of the cathode and acts therefore as 'an anode, while the part 7 in the interior of the can 2 acts as a cathode with respect to the latter.
  • the entire surface of the can 2 as well as the outer part 9 of the bipolar auxiliary electrode are coated.
  • the coated can 2 is lifted out of the bath, and rinsed with water.
  • the auxiliary electrode is removed from the can without damaging the film layer.
  • the quality 'of the stoved lacquer coat inside the can 2 is of the same quality as the layer on the outer wall of the can.
  • the coated wire mesh 9 is discarded.
  • FIG. 6 shows the equivalent circuit diagram of this arrangement where the points 1a to 8a have the same meaning as the points 1a-8a in FIG. 2.
  • 10a denotes the resistance of the bipolar auxiliary electrode, which is substantially lower than that of the liquid column 6a.
  • a can 2v to be coated is immersed in a coating vessel 1 provided with an electrode 8' connected to the negative pole of a direct current source.
  • Can 2 by lead wire 3 is connected to the positive pole of the said current source and is provided with an opening 4 in the top surface and an opening 5 in the bottom surface.
  • An auxiliary bipolar electrode 5b made of copper passes through the walls of can 2 at points 10 and 11 which are insulated. The inside and outside of the can are both then coated.
  • FIG. 8 illustrates the invention when alternating current is used for the coating process.
  • the electrocoating bath vessel 1 is made of aluminum with an interior coating of aluminum oxide and is connected to the alternating current source. Vessel 1 in combination with the coating bath acts as a rectifier.
  • the hollow body or can 2 to be coated is connected to the other pole of the alternating current source by lead wire 3 and is provided with opening 4 in the top surface and opening 5 in the bottom surface.
  • the said object 2 acts as an anode.
  • the auxiliary electrodes are comprised of a plate-shaped outer part 12 made of noncoatable material which is connected to inner part 13 which passes through the wall of object 2 at point 14 which is insulated.
  • the inner part 13 of the auxiliary electrode acts as a cathode with respect to object 2 and effects the complete coating of the interior.
  • two car bodies 12 and 13 are to be coated and are suspended one behind the other from a conveyor rail 14 in coating vessel 1.
  • the coating vessel 1 acts as a cathode and the car bodies are always in the bath at the same time and move through the bath in the direction of the arrows.
  • Car body 13 is galvanically connected by current collecting rail 15 to the current source and car body 12 is not in the direct circuit.
  • the current source is an impulse generator which generates current in the form of rectangular impulses with a maximum voltage of 400 v., an impulse duration of 30 milliseconds and an impulse interval of 30 milliseconds.
  • Car bodies 12 and 13 are provided with auxiliary electrodes 16 and 17, respectively, of copper which is conducted insulated through the wall of the car body at point 18. Between point 18 and roller mechanism 19, the auxiliary electrode is coated with an insulating mate rial.
  • the bipolar auxiliary electrode 17 is in galvanic contact with car body 12 by means of rail 20. In this position, the body 13 acts as an anode with respect to vessel 1.
  • Body 12 represents the large-surfaced part of the bipolar auxiliary electrode 17. This part of the bipolar auxiliary electrode acts therefore as an anode with respect to vessel 1, and the coating of the outer surface of body 12 which is not in the direct current flow, starts.
  • auxiliary electrode 17 The part of the auxiliary electrode 17 inside body 13 acts as a cathode with respect to body 13, so that the uniform coating of the interior is ensured. As soon as the coating of body 13 is completed, body 12 enters the direct circuit in its place. Auxiliary electrode 16 is in galvanic contact with the following body. Since body 12 is already somewhat coated, the current surge is not great when the current is turned on for this body 12. In previously known methods, however, the uncoated body had to be introduced under reduced voltage in order to avoid an excessive current surge at the start of the coating operation.
  • FIG. 10 illustrates a method of coating car bodies with direct current using bipolar auxiliary electrodes and an auxiliary cathode called a frame cathode.
  • the coating is effected by means of direct current.
  • Body 12 is introduced on the live rail 14 into the coating bath and acts as an anode.
  • Vessel 1 acts as a cathode.
  • Frame cathode 21 is inserted in body 12, insulated against the latter.
  • the frame cathode is connected to the same pole of the DC source as the vessel and acts therefore as a cathode.
  • two bipolar auxiliary electrodes 22, 23 are provided.
  • the bipolar auxiliary electrode 22 serves to coat a small cavity separated from the large cavity of the body by partition 24 and it is conducted insulated through partition 24.
  • the large-surfaced part of the bipolar auxiliary electrode 25 is arranged close to the frame electrode and acts as an anode with respect to the latter, the other part 26 protrudes into the small cavity of the body and acts as a cathode with respect to the latter.
  • the bipolar auxiliary electrode 23 protrudes partly into the coating bath outside the body in the proximity of the main cathode, partly into the interior of the body. This arrangement of the electrodes and auxiliary electrodes effects a uniform coating of the entire surface of the car body.
  • the method is also suitable for water-soluble or water-dispersible coating agents which are deposited on the cathode with the corresponding reversal of the polarity of the current sources.
  • a method for electrocoating conductive surfaces of a hollow body with a coating material which comprises immersing a hollow object having at least an electrically conductive surface which acts as an electrode in an electrically conductive coating bath containing an organic coating agent to be deposited on the hollow object and provided with a counter-electrode, passing an electric current through the said coating bath and removing the coated hollow object from the coating bath, the coating of the interior of the hollow object being effected by at least one bipolar auxiliary electrode with one pole inside the hollow object and one pole outside the hollow object, a pole of which is coated during the process.
  • At least one additional electrode is also in the cavity of the hollow body and has the same potential as the counter-electrode.
  • interior coating thickness is regulated by the ratio of the surface area of the cavity to the surface area of the coated part of the bipolar electrode.
  • An apparatus for the electrocoating of a hollow object having an electrically conductive surface at least with a coating agent comprising a hollow body adapted to act as an electrode and whose surface at least is electrically conductive, an electrically conductive coating bath adapted to an organic coating agent which is to be deposited on the hollow body, a counter-electrode adapted to be immersed in the said coating bath, an electrical source connected to the hollow body and the counter electrode and at least one bipolar auxiliary electrode adapted to extend partially into the interior of the hollow body and partially outside the hollow body and not in electrical contact with the hollow body.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Coating Apparatus (AREA)
US757565A 1967-09-08 1968-09-05 Novel method of electrocoating hollow bodies Expired - Lifetime US3585120A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT824967A AT294278B (de) 1967-09-08 1967-09-08 Verfahren zur Elektrobeschichtung von Höhlkorpern

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US (1) US3585120A (de)
AT (1) AT294278B (de)
CS (1) CS152459B2 (de)
DE (1) DE1771953C3 (de)
FR (1) FR1582692A (de)
GB (1) GB1235127A (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4432851A (en) * 1982-11-10 1984-02-21 Sumitomo Metal Industries, Ltd. Electrodeposition of lubricative coating
US4529492A (en) * 1983-07-12 1985-07-16 Herberts Gesellschaft Mit Beschraenkter Haftung Process for the coating of hollow bodies open on one side
NL1037046C2 (nl) * 2009-06-18 2010-12-21 Elsyca N V Inrichting geschikt voor het elektro-chemisch bewerken van een voorwerp, werkwijze geschikt voor het elektro-chemisch bewerken van een voorwerp alsmede simulatiemethode geschikt voor het optimaliseren van een dergelijke werkwijze voorafgaande aan het toepassen van een dergelijke werkwijze.
WO2016115258A1 (en) * 2015-01-13 2016-07-21 Raytheon Company Tailoring air cooled heat exchanger geometry to achieve environmental protection
US20170204277A1 (en) * 2016-01-20 2017-07-20 Tyco Electronics (Shanghai) Co. Ltd. Electrophoretic Coating and Preparation Method, Electrophoretic Coating Process and Selective Plating Process

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4384945A (en) * 1978-09-26 1983-05-24 Sword Wallace W Production of rotary screen printing cylinders and other fine-apertured sheet materials
DE102014210008A1 (de) 2014-05-26 2015-11-26 Muhr Und Bender Kg Verfahren und Anlage zum Herstellen eines gehärteten Formteils
DE102020113537A1 (de) 2020-05-19 2021-11-25 Hayden AG Vorrichtung und verfahren zur positionierung einer anode
DE102020128112A1 (de) 2020-10-26 2022-04-28 Audi Aktiengesellschaft Prozessanordnung zur Elektrotauchbeschichtung eines Hohlprofilteils, insbesondere einer Fahrzeugkarosserie

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4432851A (en) * 1982-11-10 1984-02-21 Sumitomo Metal Industries, Ltd. Electrodeposition of lubricative coating
US4529492A (en) * 1983-07-12 1985-07-16 Herberts Gesellschaft Mit Beschraenkter Haftung Process for the coating of hollow bodies open on one side
NL1037046C2 (nl) * 2009-06-18 2010-12-21 Elsyca N V Inrichting geschikt voor het elektro-chemisch bewerken van een voorwerp, werkwijze geschikt voor het elektro-chemisch bewerken van een voorwerp alsmede simulatiemethode geschikt voor het optimaliseren van een dergelijke werkwijze voorafgaande aan het toepassen van een dergelijke werkwijze.
WO2016115258A1 (en) * 2015-01-13 2016-07-21 Raytheon Company Tailoring air cooled heat exchanger geometry to achieve environmental protection
CN107529338A (zh) * 2015-01-13 2017-12-29 雷神公司 调整空气冷却式热量交换器几何形状以实现环境保护
US9999155B2 (en) 2015-01-13 2018-06-12 Raytheon Company Tailoring air cooled heat exchanger geometry to achieve environmental protection
CN107529338B (zh) * 2015-01-13 2019-11-19 雷神公司 调整空气冷却式热量交换器几何形状以实现环境保护
US20170204277A1 (en) * 2016-01-20 2017-07-20 Tyco Electronics (Shanghai) Co. Ltd. Electrophoretic Coating and Preparation Method, Electrophoretic Coating Process and Selective Plating Process
US11142656B2 (en) * 2016-01-20 2021-10-12 Tyco Electronics (Shanghai) Co. Ltd. Electrophoretic coating and preparation method, electrophoretic coating process and selective plating process

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Publication number Publication date
AT294278B (de) 1971-11-10
DE1771953A1 (de) 1972-03-09
CS152459B2 (de) 1973-12-19
DE1771953C3 (de) 1978-04-13
DE1771953B2 (de) 1977-07-28
FR1582692A (de) 1969-10-03
GB1235127A (en) 1971-06-09

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