US3418233A - Apparatus for electrocoating using an auxiliary electrode - Google Patents

Description

APPARATUS FOR ELECTROCOATING USING AN AUXILIARY ELECTRODE Filed July 1. 1963 Dec. 24, 1968 R. A. IGRAS ETAL 2' Sheets-Sheet 1.

GORDON 6 57190386796 mmvrom United States Patent 3,418,233 APPARATUS FOR ELECTROCOATING USING AN AUXILIARY ELECTRODE Raymond A. Igras, Dearborn Township, Wayne County, and Gordon G. Strosberg, Oak Park, Mich., assiguors to The Ford Motor Company, Dearhorn, Mich, a corporation of Delaware Filed July 1, 1963, Ser. No. 291,741 1 Claim. (Cl. 20430(l) This invention relates to method and means for electro-coating a conductor with an organic material dispersed in an aqueous bath. In particular, this invention relates to method and means for controlling anodic deposition of an organic coating material upon a metal object in an aqueous bath by providing a difference of potential between the object and an electrode of opposite polarity suflicient to cause the dispersed coating material to form on the object a coating that is essentially irreversible under the conditions of coating. More particularly, this invention relates to method and means for electropainting metal objects in a continuous or intermittently continuous painting process wherein the object is passed through an aqueous dispersion of an organic resin or other filmforming organic polymer or monomer.

Organic coating materials which may be used in the bath include but not by way of limitation alkyd resins, acrylate resins, phenol-formaldehyde resins and various carboxylic acid resins or mixtures of the foregoing with each other or other film-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 glycol, propylene glycol, glycerol, Carbitol, methanol 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.

The organic coating material is dispersed in the bath with the aid of a conventional dispersing agent such as ammonium and basic amine salts, polymeric amines, etc. Such materials are described at length in US. Patent 2,530,366 to A. G. Gray and elsewhere in the literature.

It has been discovered that the upper surface layers of an electropainting bath often receive and retain certain soluble and insoluble materials which can have a deleterious effect upon the quality of the coating if coating is initiated or terminated with the workpiece within such area. These may include low molecular weight deterioration products of the coating materials and foreign matter which floats upon the bath or otherwise becomes entrapped on or near the surface. It also has been found that water line marks appear on the coating if the line is interrupted for more than a few minutes with a workpiece only partially immersed.

One object of this invention is to provide a more uniform coating in an electrocoating process by initiating and/ or terminating the coating period while the surface to be coated is completely submerged in the coating bath.

Another object of this invention is to correlate the duration of the period of coating with the speed at which the article to be coated moves through the coating bath so as to maintain a predetermined constant coating time through fluctuations in conveyor speed.

Another object of this invention is to reduce or eliminate irregular coatings resulting from a temporary cessation of coating while a portion of the article being coated extends out of the bath.

Still another object of this invention is to provide effective means for electrocoating in accordance with the foregoing objects.

With the foregoing and other 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 1 is a schematic drawing depicting a side view of one embodiment of apparatus used in performing the instant process.

FIGURE 2 is a schematic drawing depicting a partial end View of the apparatus shown in FIGURE 1 taken along line 2-2 with a workpiece immersed in the coating bath.

Referring now to 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 59 via conductor 56. The articles to be coated 15 and 17 are placed upon conductor hangers 19 and 21 respectively which in turn are suspended from and transported through bath 13 by a conveyor 23 which may be of the conventional chain driven variety. Hangers 19 and 21 include insulators 25 and 27 respectively which isolate articles 15 and 17 from the grounded conveyor 23. Contact plates or brushes 29 and 31 for establishing electrical connection between the workpieces 15 and 17 and segmented bus bar 33 are attached to and in electrical connection with hangers 19 and 21 respectively. In this view brushes 29 and 31 are shown in electrical contact with approach segment 35 of segmented bus bar 33 with the articles to be coated in their approach to the bath. In addition to segment 35 bus bar 33 includes a withdrawal segment 45 and a plurality of intermediate segments 37, 39, 41 and 43 here shown separated by insulators 36, 38, 42 and 44 respectively.

Segment 35 is negative or of opposite polarity to the coating polarity of the workpiece and is here shown in electrical connection with DC power source 59 through conductor 54.

As article 15 approaches the bath a set of contacts inldicated at 47 is closed and segment 37 is of the same polarity as approach segment 35. As article 15 moves from right to left with respect to the drawing, brush 29, which is of sufiicient length to extend across insulator 36, passes over insulator 36 and contacts segment 37 while still in contact with segment 35. Article 15 is then in electrical connection with segment 37 via hanger 19 and brush 29. By this time article 15 has passed beneath the surface of bath 13 and brush 29 trips limit switch 49. This tripping of switch 49 opens the set of contacts indicated at 47 and closes the set of contacts indicated at 51 by electromechanical means, not shown, thereby breaking the electrical connection between segments 35 and 37 and establishing an electrical connection between segments 37 and 39 allowing brush 29 to complete the change of polarity without arcing damage to brush or bus bar.

The connecting mechanisms between limit switch 49 and contacts 47 and 51 are not shown in the drawing but it will be understood by those skilled in the art that this action can be carried out in a variety of ways with conventional switching devices. For example, switch 49 may be arranged such that upon being mechanically tripped by the movement of brush 29 it will energize a conventional relay which will energize contactors which will force open the set of contacts indicated at 47 and close the set of contacts indicated at 51.

Segment 39 is positively charged being connected to conductor 53, a positive lead from DC power source 59. The closing of the set of contacts indicated at 51 imparts positive polarity to article 15 initiating the coating period or cycle when the set of contacts indicated at 61 on conductor 53 is closed. Segment 39 when in electrical connection with DC power source 59 is provided with direct 3 current at a potential in the range of about 50 to 1000, preferably 100 to 500, volts.

When the set of contacts indicated at 6.1 is open, as here shown, initiation of the coating period is delayed until the closing of the same imparts positive polarity to segment 39 or until brush 29 comes into electrical connection with a succeeding segment of bus bar 33 that is so charged. This provision for delay in coating initiation is one of many that may be employed to maintain a constant coating time in the event that the speed of the conveyor line is reduced in accordance with reduced production schedules. Provision is made for actuating segment 39, i.e., establishing electrical connection with power source 59, through limit switch 55. In this embodiment the tripping of limit switch 55 actuates a conventional timing device, not shown, through which the closing of the set contacts indicated at 61 is effected after a predetermined time by conventional switching devices. In one preferred embodiment, delay and acceleration means are in electrical connection with such timing device and with the conveyor run circuit whereby the initiation and termination of the coating period is automatically delayed or accelerated through conventional switching devices to provide constant coating time for each article passing through the tank thus promoting coating uniformity.

It is thus within the scope of this invention to provide in the system a current sensing device adapted to determine changes in current flow within the conveyor run circuit and provide electrical or electromechanical connection between such device and the electrical circuit providing electrical energy to the workpiece so as to provide automatic control of coating time through changes in conveyor speed.

In this embodiment segment 41 is shown connected to DC power source 59 by conductor 57 which is equipped with a set of movable contacts indicated at 63. It is to be understood that segment 41 may be supplemented by any desired number .of similar segments which in turn may be connected to power source 59 by leads equipped with contacts similar to those shown at 61 and 63. These contacts and the set of contacts indicated at 63 may be connected with limit switches, timing devices and/ or similar equipment as aforedescribed in relation to the set of contacts indicated at 61 and through such means participate in the automatic control of coating time to eliminate differences which would otherwise occur with changes in conveyor speed.

The tripping of limit switch 55 also serves to open the set of contacts indicated at 51 and close the set of contacts at 47 through mechanisms, not shown, which are actuated in a manner either identical or similar to that described in connection with limit switch 49. This returns the approach mechanism to original electrical conditions and article 17 can then be brought into bath 13 in the same manner as heretofore described for article 15.

As article 15 proceeds through bath 13 brush 29 eventually contacts limit switch 65 which opens the set of contacts indicated at 67 and closes the set of contacts indicated at 69 through mechanisms, not shown, which are actuated in a manner identical or similar to those aforedescribed in connection with limit switch 49. Section 43 is thus placed into electrical connection with withdrawal segment 45. Conductor 58, a negative lead from DC power source 59, provides electrical connection between segment 45 and source 59. Limit switch 65 is positioned such that its actuation and the resulting opening of the set of contacts indicated at 67 will terminate the coating cycle while article 15 is still immersed to the desired depth in bath .13. In the continuation of the withdrawal movement brush 29 trips limit switch 71 which opens the contacts at 69 and closes the contacts at 67 as aforedescribed in relation to limit switch 49. This action leaves the withdrawal system in the same electrical condition it assumed prior to the tripping of limit switch 65 by brush 29. Article 17 may then be brought through the withdrawal system in an identical manner.

Tank 11 is equipped with one or more agitation means here represented by propeller 73 and means for rotating such propeller indicated by electric motor 75. Motor 75 is electrically connected by suitable conductors, not shown, to a power source. This power source may be DC power source 59 if a direct current motor is used, or a suitable independent power source may be employed.

L1 this embodiment two fixed, auxiliary electrodes 77 and 79 are employed to facilitate the coating of the center portion of the top surface of a wide workpiece, e.g., the top of an automobile body. Electrode 77 is shown in FIGURE 1 with conductors 76 and 78 which establish electrical connection between such electrode and tank 11.

Referring now to FIGURE 2, electrodes 77 and 79 are shown positioned to either side of hanger 19, beneath the surface of bath 13 and above article 15 as it passes through the bath. It will be understood that electrodes 77 and 79 and their respective electrical connections with tank 11 are positioned so as not to interfere with either the entry or exit of the workpiece from the tank. This may be effected in a number of ways. This may be effected by using irregularly shaped electrodes providing a suitable separation at the point of entry and exit, by positioning such electrodes in the central portion of the tank and establishing electrical connection with the sides of the tank which are parallel to the electrodes or to an independent source of current, or by raising and lowering such electrodes for each workpiece.

The foregoing detailed description of this embodiment of apparatus for carrying out the process of this invention is submitted solely for purposes of illustration. Those skilled in the art will be aware that numerous modifications can be made in the aforedescribed system without departing from the spirit and the scope of the invention as expressed in the claims.

What is claimed is:

.1. Apparatus for coating electrically conductive objects comprising in combination an electrically conductive coating tank adapted to retain an aqueous coating bath in which organic film-forming materials are dispersed, said tank comprising a first electrode, a second electrode of the same polarity as said first electrode extending longitudinally of said tank so as to be positioned beneath the surface of said bath when said tank is charged with said bath, transfer means for transporting said objects through said bath and under said second electrode, electrical means for providing a unidirectional fiow of electrical energy between each object and said electrodes when said bath is in said tank and said object is in contact with said bath, said electrical means including a conductor in electrical connection with said object and means for imparting an electrical charge to said object through said conductor of opposite polarity with respect to said electrodes, and means associated with said conductor and adapted to be actuated by movement of said object with respect to said bath whereby said flow of electrical energy is initiated.

References Cited UNITED STATES PATENTS 2,503,812 4/1950 Fath 198--232 2,709,010 5/1955 Todd 204203 2,709,512 5/1955 Curtis 204--203 2,924,564 2/ 1960 Jackson 204-204 3,163,592 12/1964 Dolan et al 204-481 3,200,057 8/1965 Burnside et al. 204l8l 3,200,058 8/1965 Oster 204181 FOREIGN PATENTS 452,298 11/1948 Canada.

E. ZAGARELLA, Assistant Examiner.

JOHN H. MACK, Primary Examiner.

Claims (1)

1. APPARATUS FOR COATING ELECTRICALLY CONDUCTIVE OBJECTS COMPRISING IN COMBINATION AN ELECTRICALLY CONDUCTIVE COATING TANK ADAPTED TO RETAIN AN AQUEOUS COATING BATH IN WHICH ORGANIC FILM-FORMING MATERIALS ARE DISPERSED, SAID TANK COMPRISING A FIRST ELECTRODE, A SECOND ELECTRODE OF THE SAME POLARITY AS SAID FIRST ELECTRODE EXTENDING LONGITUDINALLY OF SAID TANK SO AS TO BE POSITIONED BENEATH THE SURFACE OF SAID BATH WHEN SAID TANK IS CHARGED WITH SAID BATH, TRANSFER MEANS FOR TRANSPORTING SAID OBJECTS THROUGH SAID BATH AND UNDER SAID SECOND ELECTRODE, ELECTRICAL MEANS FOR PROVIDING A UNIDIRECTIONAL FLOW OF ELECTRICAL ENERGY BETWEEN EACH OBJECT AND SAID ELECTRODES WHEN SAID BATH IS IN SAID TANK AND SAID OBJECT IS IN CONTACT WITH SAID BATH, SAID ELECTRICAL MEANS INCLUDING A CONDUCTOR IN ELECTRICAL CONNECTION WITH SAID OBJECT AND MEANS FOR IMPARTING AN ELECTRICAL CHARGE TO SAID OBJECT THROUGH SAID CONDUCTOR OF OPPOSTIE POLARITY WITH RESPECT TO SAID ELECTRODES, AND MEANS ASSOCIATED WITH SAID CONDUCTOR AND ADAPTED TO BE ACTUATED BY MOVEMENT OF SAID OBJECT WITH RESPECT TO SAID BATH WHEREBY SAID FLOW OF ELECTRICAL ENERGY IS INITIATED.

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