US3476667A - Electrode assembly used in electrocoating hollow articles - Google Patents

Description

Nov. 4, 1969 A. E. G|LHR|ST 3,416 667 ELECTRODE ASSEMBLY USED IN ELECTROCOATING HOLLOW ARTICLES Filed April 25, 1966 2 Sheets-Sheet 1 FIG.1

L I l A. H J. I

30 50 5 /5 B FIG 2 INVENTOR.

AZLAN E. G/LCHRIST A TTORNEYS Nov. 4, 1969 A. E. GILCHRIST 3,476,667

ELECTRODE ASSEMBLY USED IN ELECTROCOATING HOLLOW ARTICLES Filed April 25, 1966 2 Sheets-Sheet 2 INVENTOR. ALLAN E G/LCHRIST WWW A T TORNEYS United States Patent 3,476,667 ELECTRGDE ASSEMBLY USED IN ELECTRO- COATlN G HOLLOW ARTICLES Allan E. Gilchrist, Westlake, Ohio, assignor, by mesne assignments, to SCM Corporation, New York, N.Y.,

a corporation of New York Filed Apr. 25, 1966, Ser. No. 545,047 Int. Cl. C231! 13/00; B01k 5/02 US. Cl. 204-181 13 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an electrocoating process and apparatus, and in particular to a novel process and apparatus for electrocoating with paint articles having interior surface areas to be coated and where external access to the interior surface areas is restricted when the articles are placed in a paint bath and a current established through the paint bath between a cathode in contact with the paint bath and the article as the anode in contact with the bath.

An important object of the present invention is to provide a new and improved method and apparatus, of the character described above, for electrodepositing paint from a paint bath onto articles having interior surfaces to be coated and restricted access means for externally communicating with the interior surfaces in which electrode or cathode means projecting a short distance within the restricted access means and preferably having an overall exposed current transmitting area of to of the interior surface area to be coated are employed to increase the deposition voltage and the throwing power of the paint in the paint bath within the interiors of the articles whereby a thick paint film having a substantially uniform thickness is caused to be electrodeposited on the interior surfaces thereof.

Another object of the present invention is to provide a new and improved method and apparatus of the character described in the preceding object and which is carried out with the cathode means being detachably connected to the articles and with the exposed current transmitting areas thereof being electrically insulated from direct contact with the articles.

Yet another object of the present invention is to provide a new and improved method and apparatus of the character described in the preceding objects and which includes the establishment of an electrodeposition current in the paint bath between the articles and a primary cathode in the bath.

A further object of the present invention is to provide a new and improved method and apparatus, as defined in the preceding objects, and carried out with a paint dispersion having a composition such that a paint film having a high specific electrical resistance is electrodeposited so that the electrodeposition of the paint film is self-terminating at a predetermined thickness for a particular voltage whereby the throwing power of the paint solution is further increased to enhance the uniformity of the thickness of the paint film deposited. Upon electrodeposition I estimate that an electrodeposited wet paint film up to about 1 mil in thickness should have at least about 40 mega ohm-centimeters specific electrical resistivity to obtain good throw into interstices, and preferably even higher, e.g., to mega ohm-centimeters. Such apparent specific resistivity includes a surface resistance factor for the deposited film-bath interface and the deposited film-su'bstrate interface.

Some of the advantages of the new and improved electrocoating method and apparatus of the present invention are that a thicker and more uniform paint film is caused to be electrodeposited on the interior surface areas in the articles, a significant increase in the deposition voltage and the throwing power of the paint within the interior of the articles and in the electrical efficiency of the electrocoating process is achieved, and that relatively high system voltages are not needed. The new and improved method and apparatus of the present invention is therefore especially advantageous under electrocoating conditions where the article to be coated and other conditions, such as long electrolyte paths, or the composition of the paint solution preclude the use of a highly efficient deposition voltage or where high voltages are not available.

Another object of the present invention is to provide a new and improved cathode or electrode means for use in an electrocoating process of the character described and which can be readily inserted within a restricted access means for externally communicating with an interior surface area in an article and which is constructed and arranged such that it has a vent passage therethrough and is self-gripping with the article to enable the same to be readily attached to and detached from the article.

Other objects, novel characteristics and advantages of this invention will be apparent in the following detailed description and in the accompanying drawings forming a part of this specification, and in which:

FIG. 1 is a vertical sectional view of an electrocoating apparatus embodying the present invention and in which a box frame for an automobile is shown as being immersed therein;

FIG. 2 is a fragmentary plan view of a box frame for an automobile showing parts of the apparatus attached thereto;

FIG. 3 is a schematic wiring diagram;

FIG. 4 is an axial sectional view of an auxiliary cathode means which may be employed in the electrocoating apparatus shown in FIG. 1 and showing the same attached to a side wall of a box frame of an automobile;

FIG. 5 is a bottom plan view of the auxiliary cathode means shown in FIG. 4 looking in the direction of the arrows 55 of FIG. 4.

FIG. 6 is a perspective view of another form of auxiliary cathode means which may be employed in the electrocoating apparatus shown in FIG. 1 and showing the same attached to a sidewall of a box frame of an automobile;

FIG. 7 is an axial sectional view of yet another form of auxiliary cathode means which may be employed in the electrocoating apparatus shown in FIG. 1 and showing the same attached to a side wall of a box frame of an automobile;

FIG. 8 is a bottom plan view of the auxiliary cathode means shown in FIG. 7 looking in the direction of the arrows 88 of FIG. 7;

FIG. 9 is an axial sectional view of a further form of auxiliary cathode means which may be employed with the electrocoating apparatus shown in FIG. 1 and showing the same attached to a side wall of a box frame of automobile; and

FIG. 10 is a bottom plan view of the auxiliary cathode means shown in FIG. 9 looking in the direction of the arrows 1010 of FIG. 9.

Many articles of manufacture are coated with a paint film to prevent or substantially eliminate corrosion of the articles when the latter are subjected to environmental conditions which tend to cause corrosion. One method which has heretofore been employed for applying such a paint film is an electrocoating process in which the articles to be coated are Wired in an electrical system as an anode and then dipped or immersed in an electrically conductive paint bath in contact with a cathode or cathodes. When an electric potential is impressed on the system, an electric current is passed from the cathodes through the paint bath to the article which causes a paint film to be electrodeposited on the article.

However, when the articles to be coated have cavities therein provided with restricted access or vent means for externally communicating with the interior surface area of the cavities, difficulties have often been encountered with the use of this method in applying a paint film of sufficient thickness to the interior surface area of the cavities to insure that subsequent corrosion of the articles does not occur. These difficulties are especially acute where the geometry or configuration of the articles require the use of long electrolyte paths or where high voltages are not available or cannot be employed without causing a. breakdown in the paint bath or solution. While various techniques have been employed to improve the electro-deposited thickness of a paint film on the interior surface area of cavities in articles, they have, in many cases, not proved satisfactory.

The electrocoating process and apparatus of the present invention overcomes the difficulties heretofore encountered in obtaining a sufiicient paint film thickness on the interior surface areas in articles by employing electrode or cathode means which are inserted Within the restricted access means and preferably detachably connected with and electrically insulated from the articles. The inserted cathode means, in the preferred embodiment, are auxiliary cathode means which are electrically connected in parallel with other or primary cathodes of the apparatus and need only have an overall exposed current transmitting area from 3& to the interior surface area of the individual cavity to be coated.

It has been found that the employment of auxiliary cathode means provides a significant increase in the thickness of the paint film electrodeposited on the interior surface areas and in the uniformity of the thickness of the paint film deposited, especially when a paint film having a high specific electrical resistance is electrodeposited. The use of auxiliary cathode means significantly increases the deposition voltage within the interior of the cavities, the overall efliciency of the electrical system and the throwing power of the paint within the cavities, and significantly reduces the overall system voltage loss whereby the electrocoating process can be carried out with impressed system voltages which are substantially lower than the depressed system voltages heretofore required.

Although the novel method and apparatus of the present invention could be employed for coating the interior surface areas of cavities in articles of various shapes and configurations, it is particularly useful for coating the interior surface areas of tubular or hollow members, such as a box member of an automobile box frame, and for the purposes of illustration will herein be described with reference to coating the interior surface areas of box members of an automobile box frame.

Referring to the drawings, an automobile box frame to be electrocoated with paint is there shown as comprising a pair of laterally spaced longitudinally extending box members or panels 11 and 12 and a plurality of spaced apart laterally extending box members 13-15 having their opposite ends welded to a side wall of the longitudinally extending box members 11 and 12. Each of the box members 11-15 is here shown as being a rectangularly shaped tube with its top, side and bottom walls defining an interior cavity 20 and each is provided With a plurality of longitudinally spaced transverse openings 22 in at least one side wall 24 thereof. The openings 22 define restricted access or passage means for externally communicating with the interior surface area of the cavity 20.

When the box frame 10 is to be electrocoated with a paint film, it is first wired or electrically connected by a wire or conductor 25 to a positive terminal 26 of a DC power source means 28 so as to become a current receptive or anode member and then an auxiliary electrode or cathode means is inserted into each or most of the restricted access openings 22 in the side walls 24 of all of the box members 11-15 and detachably connected to the latter, or vice versa.

The auxiliary cathode means, in the preferred embodiment thereof shown in FIGS. 4 and 5 and generally designated by reference numeral 30, comprises a cathode or electrode element 33 and a self-gripping holder means for detachably connecting the cathode element 33 to the side wall 24 of the box member and for holding and supporting the cathode element 33 in an operative position relative to the side wall 24 of the box member. The holder means comprises an annular sleeve 34 made from a suitable electrically insulated material, preferably a yieldable or elastic plastic material, which serves to electrically insulate the cathode element 33 carried thereby from direct contact with the anode box member. The sleeve 34 at its inner or lower end, as viewed in FIG. 4, has a pair of integral, annular projecting portions or flanges 35 and 36 extending radially outwardly of sleeve 34 which defines therebetween an annular groove 37 for receiving the peripheral portion of the side wall 24 surrounding the opening 22 when the sleeve 34 is inserted therein. The projecting portion 36 is in the form of an annular bead and has a normal diameter when free of any externally imposed forces which is slightly greater than the diameter of the restricted access opening 22.

The sleeve 34 is detachably connected to the side wall 24 of the box member by axially aligning the same with the opening 22 and then forcing the projecting portion 36 and the lower end of the sleeve 34, as viewed in FIG. 4, through the opening 22. As the projecting portion 36 engages the opening 22 along its side wall 40, it and the lower end of the sleeve 34 will be deflected laterally or radially inwardly until the side wall 40 of the opening 22 is received within the groove 37 whereupon the annular projection portion 36 will snap beneath the interior side surface of the side wall 24, due to the elastic forces of the plastic material tending to return the lower end of the sleeve 34 to its normal diameter, to securely connect or attach the sleeve 34 to the side wall 24. The projecting portion 35 seats against the exterior side surface of the side wall 24 to position the sleeve 34 relative to the side wall when the latter is connected thereto.

The cathode element 33 disposed within the sleeve 34 is of a tubular shape and has an axially extending passageway or vent opening 41 therethrough to provide external access to the cavity 20 when the auxiliary cathode means 30 is detachably connected to the box member. The cathode elernent 33 comprises an annular handle portion 42 made from a suitable electrically insulated material, preferably plastic, which is bonded or otherwise secured to one end 43 of a coaxially aligned, generally cylindrically shaped metallic cathode or electrode portion 44. The cathode element 33 is axially shiftable or movable within the sleeve 34 between a retracted position, as shown by the dotted lines in FIG. 4, in which the electrode portion 44 is wholly disposed within the sleeve 34 and an extended or operating position, as shown in FIG. 4 by the solid lines, in which a major portion of the electrode portion 44 thereof projects beyond the lower end of the sleeve 34 and into the interior of the cavity 20.

The cathode element 33 when moved to its extended position is held or retained in that position by an annular, radially inwardly extending, projection portion or bead 45 on the sleeve 34 which is cooperatively received in an annular external groove 46 in the electrode portion 44. The bead 45 is located at the lower end of the sleeve 34 and directly opposite from the bead 36, as viewed in FIG. 4, and has a normal internal diameter which is slightly less than the external diameter of the electrode portion 44. When the cathode element 33 is being moved from its retracted position to its operating position, the lower end thereof engages the inwardly extending bead 45 and deflects the same and the lower end of the sleeve 34 radially outwardly until the bead 45 engages the outer peripheral surface of the electrode portion 44. As the cathode element 33 continues to be moved toward its operating position, the inwardly extending bead 45 will ride on the outer peripheral surface of the electrode portion 44 until the bead 45 and the groove 46 are radially aligned whereupon the bead 45 will snap into the groove 46 due to the elastic forces of the plastic material tending to return the bead 45 to its normal diameter to securely hold or retain the cathode element 33 in its operating position.

The cooperative engagement between the bead 45 and the groove 46 for holding the cathode element 33 is in its extended position relative to the sleeve 34 also'serves to prevent removal of the sleeve 34 from the access open: ing 22 in the side wall 24 of the box member. The c0- operative engagement therebetween prevents the bead 36 and the lower end of the sleeve 34 disposed within the cavity 20 from being deflected radially inwardly the necessary extent to permit removal of the sleeve 34 from the opening 22. To remove the sleeve 34 from the opening 22, it is necessary to first move the cathode element 33 relative to the sleeve 34 to its retracted position in which the electrode portion 44 is wholly disposed within the sleeve 34 and above the bead 45, as shown by the dotted lines in FIG. 4, so that the head 36 and the lower end of the sleeve 34 can be deflected radially inwardly when the sleeve is pulled in a direction away from the side wall 24 to detach or disconnect the same therefrom. The sleeve 34 at its upper end has a radially inwardly extending bead 49 to prevent separation of the cathode element 33 and the sleeve 34 when the former is in its retracted position.

Axial separation between the sleeve 34 and the cathode element 33 is prevented in a downward direction, as viewed in FIG. 4, by the upper end of the handle which will engage the upper end of the sleeve 34. Axial separation in an upward direction under normal conditions is prevented by the annular inwardly extending bead 49 which will engage the end 43 of the electrode portion 44. To remove the cathode element 33 from the sleeve 34, it is necessary to pull the handle portion 42 upwardly with a suflicient force to cause the end 43 of the electrode portion 44 to cam the bead 49 and the upper end of the sleeve 34 radially outwardly.

The auxiliary cathode means 30 can be individually detachably connected with the side wall 24 of the box members or elongated carrier bars 50 having a plurality of auxiliary cathode means 30 mounted thereon and spaced apart a distance equal to the distance between the centers of adjacent openings 22 in the side walls 24 of the box members can be provided to enable a plurality thereof to be simultaneously detachable connected thereto. The bars 50 have a plurality of space transverse openings 52 therethrough for receiving the sleeves 34. The sleeves 34 can be mounted or secured within the 0penings 52 in the bar in any suitable manner, such as by bonding or by screwing the same to the side walls of the openings 52.

The auxiliary cathode means 30 are, in the preferred embodiment, electrically connected in parallel with one another by a plurality of branch wires or conductors 53 each having one end thereof secured to the electrode portion 44 and the other end connected with a common line or conductor 54. The common line 54 is connected to an output terminal of a normally open switch 56, the input terminal of the switch 56 being connected by wire or conductor 57 to the negative terminal 58 of the DC power source means 28.

The electrode portions 44 of the auxiliary cathode means 30 connected to each box member have an overall or combined exposed current transmitting area which need be only from to but preferably to 4 the interior surface area of the cavity 20 in the box member. For example, if the restricted access means of the box member comprises four openings and an auxiliary cathode means 30 was inserted into each opening, the sum total of the exposed current transmitting areas thereof would be to of the total interior surface area of the cavity with the exposed current transmitting area of each auxiliary cathode means preferably being to of the adjacent one-quarter of the interior surface area of the cavity. The exposed current transmitting area is that area of the electrode portions 44 which are in contact with the paint bath when the box frame 10 is immersed therein.

After the box frame 10 is wired as an anode and the auxiliary cathode means 30 detachably connected to the individual box members, the box frame 10 is transported to a position located above an open top tank 60 containing an electrically conductive paint bath or solution 62 and then lowered and immersed or dipped within the paint bath 62. The box frame 10 can be transported to its location above the tank 10 by any suitable or conventional apparatus, not shown, such as an overhead crane or conveyor which includes a suitable power actuated hoist mechanism for then lowering and immersing the box frame 10 in the paint bath 62. The box frame 10 is here shown as being supported at its four corners by a plurality of cables 63 connected with the hoist mechanism.

The tank 60 may be of any suitable or conventional construction and is here shown as being of a generally rectangular shape. The tank 60 has a top opening 65, a bottom and opposed side and end walls. The tank 60- may be made from metal and includes a suitable insulating liner 66 for electrically insulating the bottom, side and end walls from a plurality of primary cathode elements 70 disposed therein. The primary cathode elements 70 are here shown as being generally rectangularly shaped metal plates which are supported and positioned adjacent the side and end walls in any suitable or conventional manner.

The primary cathode elements 70 are electrically connected in parallel with each other and with the auxiliary cathode means 30 by branch lines or wires 71 having one end connected to the cathode elements 73 and the other end connected to the common line or conductor 54. Alternately, the primary cathode elements 70 and the insulating liner 66 could be eliminated and the metal tank 60 itself be wired as a primary cathode.

After the box frame 10 is immersed or dipped within the paint bath 62, a voltage from the DC power source 28 is impressed on the electrical system for a predetermined length of time to establish a direct current through the paint bath to cause the latter to electrodeposit a paint film on both the exterior and interior surface areas of the box frame 10. The voltage is impressed from the DC power source 28 on the system by moving the switch 56 to its closed position to complete electric circuits from the negative terminal 58 of the DC power source 28 through normally open, but now closed switch 56, the common line 54, the parallel branch lines 71 and 53 and primary and auxiliary cathodes 70- and 30, respectively, through the paint bath solution 62 to the anode box frame 10, the electrical conductor 25 to the positive terminal 26 of the DC power source 28. The voltage impressed on the system may be from approximately 70 to 200 volts, although higher voltages could be impressed on the system if desired. It willfof course, be understood that the switch 56 could be eliminated or closed prior to immersing the box frame in the paint bath 62 so that the electric circuits would be completed immediately upon the box frame 10 coming into contact with the paint bath 62.

As previously mentioned, the employment of auxiliary cathode means 30 provides a significant increase in the thickness of the paint film deposited on the interior surface areas of the cavities 20 in the box members 11-15 over that deposited without employing any auxiliary cathode means. They also provide a significant increase in the throwing power of the paint and therefore, the paint film deposited on the interior surface areas is of a more uniform thickness than heretofore obtained, espe cially when a paint bath having a composition such that it electrodeposits a paint film having a high electrical specific resistance is used, and for reasons to be presently pointed out.

The paint bath 62 may be of any suitable or conventional composition, but is preferably of a composition like that disclosed in U.S. Patent No. 3,230,162, issued Jan. 18, 1966. The latter type of paint bath applies a paint film to an anode surface having a high specific electrical resistivity, i.e., usually from 70-140 mega ohms per centimeter, in films having a thickness up to about 1 mil. Such specific resistivity includes a surface resistance factor for the deposited film-bath interface and deposited filmsubstrate interface. The electrodeposition of such a paint film enables the thickness of the paint film electrodeposited to be controlled in accordance with the voltage impressed on the system because the electrical resistance of the deposited paint film increases with the thickness thereof. That is, the electrodeposition of the paint film practically terminates at a particular voltage when the thickness provides a system electrical resistance such that the paint film virtually completely electrically insulates the anode surface and prevents further current from passing thereto. This is commonly referred to as a shut off effect. The advantage of using such a paint bath is that the throwing power of the paint (the ability to apply a uniform coating of paint at various distances from an electrode or cathode) is significantly enhanced and, as a result, a much more uniform paint film is deposited on the interior of the cavity.

The broad term paint as used in this application is meant to include coating compositions or materials containing pigments and/or fillers in a binder or binders without pigments and/or fillers or having very little of the same, or water reducible compositions which might be analogous to enamel, varnish or lacquer bases.

After the voltage is impressed on the system for a predetermined length of time, the switch 56 is moved to its open position to de-energize the electrical circuits and the box frame 10 is withdrawn from the paint bath 62. The conductor 25 and the auxiliary cathode means 30 are then disconnected from the box frame 10 and the paint film applied to the box frame is thereafter preferably cured. The paint film can be cured in any suitable or conventional manner, such as the manner disclosed in my aforementioned U.S. patent.

FIG. 6 illustrates a different type of auxiliary electrode or cathode means, generally designated by reference numeral 85, which may be employed in place of the auxiliary cathode means 30. The auxiliary cathode means 85 comprises a cathode element 88 and a self-gripping holder means for detachably connecting the cathode element 88 to the side wall 24 and for holding and supporting the cathode element 88 in an operating position relative to the cavity 20. The holder means is generally in the form of an alligator clip and comprises a pair of members 90 and 91 which are pivotally connected together at one end thereof and which cross each other adjacent their other or free ends, To this end the member 90 has a slot opening 92 through which the member 91 extends. The members 90 and 91 at their free ends have cooperable end portions 93 and 94 which are bent and shaped so as to cooperably engage or grip the outer and inner side surfaces of the side wall 24 of the box members. The cooperable end portions 93 and 94 are biased toward one another by a compression spring 95 having one end attached and in abutting engagement with the member 90 and the other end attached and in abutting engagement with the member 91.

The auxiliary cathode means is detachably connected to the side wall 24 by grasping the members and 91 between the forefinger and thumb and applying a squeezing pressure to laterally deflect the Same and cause the spring to compress and the end portions 93 and 94 to be moved away from each other, positioning the auxiliary cathode means 85 so that the side wall 24 is disposed between the end portions 93 and 94 and then releasing the grasp on the members 90 and 91. The compression spring 95 exerts a sufiicient biasing force to cause the end portions 93 and 94 to grip or clampingly engage the opposite side surfaces of the side wall and securely retain the cathode element 88 in its operative position relative to the cavity 20.

The cathode element 88 is a metal cylindrical tube defining a vent passageway 96 therethrough for communicating paint to the interior of the cavity 20. The cathode element 88 is bonded or otherwise secured to an insulating member 97, the latter in turn being bonded or suitably secured to the member 91. The provision of the insulating member 97, which may be of any suitable material, electrically insulates the auxiliary cathode from direct contact with the box member. The cathode element 88 has an exposed current transmitting area which is the same as exposed current transmitting area of the electrode portion 44 of the cathode means 30 and has a major portion of its exposed current transmitting areas disposed within the cavity 20 of the box member when in its operating position.

FIGS, 7 and 8 show another type of auxiliary electrode or cathode means, generally designated by reference numeral 100, which may be employed in place of the auxiliary cathode means 30. The cathode means 100 is radially contractible and expandable and exerts a selfgripping force on the side wall 40 of the opening 22 in the box member when inserted therein to detachably connect the same thereto.

The auxiliary cathode means 100 comprises a onepiece metallic cathode element having a pair of oppositely disposed longitudinally extending side members 102 and 103 and an upper arcuately shaped flexible bridge portion 104 formed integral with the side members 102 and 103. The side members 102 and 103 are arcuately shaped, as viewed in transverse cross section, with their adjacent longitudinally extending side edges 105 and 106, respectively, spaced from one another so as to enable the side members 102 and 103 to be moved toward and from one another. The side members 102 and 103, as viewed in longitudinal cross section, slope radially outwardly from the bridge portion 104, as indicated by reference numeral 107, for a portion of their length and then slope radially inwardly, as indicated by reference numeral 108, for a portion of their length and terminate with their free ends spaced from one another. The cathode means 100 has a maximum diameter or transverse dimension which when free of any external imposed forced which is greater than the diameter of the opening 22 and an exposed current transmitting area which is the same as that for the auxiliary cathode means 30.

Suitably bonded or otherwise secured to each side member 102 and 103 on its exterior surface is an arcuately shaped insulating member 109 made from a suitable insulating material. The insulating members 109 include a radially outwardly extending flange 110 to prevent the cathode element 101 from being pushed completely through the opening 22 when inserted therein. The insulating members 109 serve to electrically insulate the cathode element from direct contact with the box member when the latter is detachably connected thereto.

The auxiliary cathode means 100 is detachably connected to the box member by axially aligning the same with the opening 22 and then inserting the cathode means 100 into the opening 22. As the cathode means 100 is being inserted into the opening 22, the portions 108 of the side members 102 and 103 engage the side wall 40 of the opening 22 and are deflected laterally toward each other to cause the cathode element to be contracted radially inwardly until the juncture of the portions 107 and 108 passes through the opening and into the interior of the cavity 20. When this occurs, the cathode element will expand radially outwardly toward its normal diameter and bias the insulating members 109 into gripping engagement with the side wall defining the opening 22. The space between the side members 102 and 103 provides a passageway or vent 112 for communicating paint to the interior of the cavity when the cathode element is detachably connected to the box member. It should be noted that the construction of the cathode means 100 is such that a plurality thereof could be mounted on an elongated carrier bar and simultaneously co nected with the box member.

FIGS. 9 and 10 show yet another type of auxiliary electrode or cathode means, generally designated by reference numeral 120, which may be employed in place of the auxiliary cathode means 30. The auxiliary cathode means 120 is radially contractible and expandable and exerts a self-gripping force on the side wall 40 of the opening 22 when inserted therein to detachably connect the same thereto. The cathode means 120 comprises a thin elongated metallic cathode element 121 which is bent or wound so as to form a coil or spiral spring. The distance between the adjacent winds of the spring provides an axial through passage 124 for communicating paint to the interior surface of the cavity 20 in the box member. Suitably bonded or otherwise secured to diametrically opposite locations on the exterior surf-ace of the cathode element 121 are arcuately shaped insulating members 125 made from any suitable insulating material. The insulating members 125 include a radially outwardly extending flange 126 to prevent the cathode element 121 from being pushed all the way through the opening 22 when inserted therein. The cathode means 120 has a diameter when free of any externally exposed forces which is greater than the diameter of the restricted access opening 22 and an exposed current transmitting area which is the same as that of the auxiliary cathode means 30.

To insert the auxiliary cathode means 120 within the restricted access opening 22, diametrical opposite portions of the auxiliary cathode means 120 are laterally deflected toward each other to cause the same to be radially contracted and then inserted into the access opening 22 until the flanges 126 of the insulating members 125 engage the exterior surface of the side wall 24 of the box member and then released whereupon the spiral spring thereof will expand toward its normal position and bias the insulating members 125 into gripping engagement with the side wall defining the opening 22. The insulating members 125 serve to insulate the cathode element 121 from direct contact with the box member.

The current transmitting portions of the auxiliary cathode means shown in FIGS. 4-10 of the drawings are of a short length, and preferably have a length which does not exceed one-tenth the length of the cavity to be coated if only one is employed, or exceed one-tenth the length of the adjacent portion of the total length of the cavity if more than one is employedthe length of the adjacent portion being the total length divided by the number of auxiliary cathodes employed. As examples of size, the length of the exposed current transmitting area of the cathode means 30 and 100 need be only approximately A3" and /8" long, respectively, for use in conventional size box members having /2 inch diameter holes spaced 16 inches apart.

From the foregoing, it can be seen that a novel method and apparatus for electrocoating interior surface areas of cavities in articles, such as box members, having a re stricted access means for communicating paint to the interior of the cavities has been provided. It can also be seen that the employment of auxiliary cathode means which are detachably connected to the articles with the cathode elements extending within the restricted access means provides a significant increase in the thickness and the uniformity of the thickness of the paint film deposited on the interior surface areas. Additionally, it can be seen that various novel types of auxiliary cathode means which are self-gripping with the box member when inserted into the restricted access openings to enable the same to be readily attached and detached therefrom have been provided.

Although the electrocoating process and apparatus of this invention have been illustratd and described herein to a somewhat detailed extent, it will be understood, of course, that the invention is not to be regarded as being limited correspondingly in scope, but includes all changes and modifications coming within the terms of the claims hereof.

Having described my invention, I claim:

1. Apparatus for electrocoating the inside of a hollow article having an opening leading into its interior, said apparatus comprising an electrode assembly having manually operable, detachable, article-gripping mounting means for manual attachment to and removal from the article at said opening, said mounting means being adapted to hold an electrode member in such a manner that said electrode member will be spaced from the edge of said opening and loosely extend therethrough into the interior of the article when said electrode assembly is attached to the article at said opening, said mounting means including dielectric material for insulating said electrode member from the article, said electrode assembly defining a vent passage for venting the interior of the article to the exterior when the electrode assembly is attached to the article at said opening.

2. Apparatus according to claim 1, wherein said mounting means is resiliently yieldable for releasable gripping engagement with the article at said opening.

3. Apparatus according to claim 2, wherein said mounting means comprises a sleeve of yieldable elastic dielectric material gripping said electrode member and having a radially deformable first external projection at its inner end and a second external projection spaced from said first projection by substantially the thickness of the wall of said article around said opening, said first projection being deformable radially inwardly upon insertion of the sleeves into said opening and being expandable radially outwardly after passing through said opening to grip said wall at the inside of said opening while said second projection abuts said wall at the outside of said opening, and wherein said electrode member is holl(l)w and projects inwardly beyond the inner end of said s eeve.

4. Apparatus according to claim 3 and further comprising a hollow handle of dielectric material attached to the outer end of said electrode member and extending outwardly therefrom beyond the outer end of said sleeve.

5. Apparatus according to claim 4, wherein said sleeve has radially deformable internal projections which resiliently grip said electrode member and said handle.

6. Apparatus according to claim 2, wherein said mounting means is a spring clip for attachment to the wall of the article at said opening, said clip having a portion of dielectric material connected to said electrode member, and wherein said electrode member is hollow.

7. Apparatus according to claim 1, wherein said electrode member is laterally compressible and resilient, and said mounting means comprises dielectric material on the outside of said electrode member for engagement with the edge of said opening when said electrode member is inserted therein.

8. Apparatus according to claim 7, wherein said electrode member has laterally-spaced side members and a bridging portion interconnecting the outer ends of said side members, said side members having free inner ends which are resiliently biased apart and which are displaceable toward each other to pass through said openmg.

9. Apparatus according to claim 7, wherein said electrode member is an axially elongated spiral spring which is radially compressible for insertion through said opening.

10. A process of electrodepositing paint from a paint bath onto the inside of a hollow article having an opening leading into its interior comprising the steps of: providing an electrode assembly having manually operable, detachable, article-gripping means for manual attachment to and removal from the article at said opening and having a vent passage for venting the interior of the article to the exterior when the electrode assembly is attached to the article at said opening, mounting said electrode assembly on the article at said opening with an electrode member of said assembly extending into the interior of the article and spaced from the edge of said opening and electrically insulated from the article, positioning said article and the attached electrode assembly in the paint bath, and applying a DC. voltage between said electrode member and said article to cause the eleccentimeters for a deposited coating up to substantially 1 mil thick.

13. A process according to claim 10, wherein the article to be coated has a plurality of electrode assemblies as recited in claim 10 are individually mounted at said openings, and said DC. voltage is applied between the article and the respective electrode members of said electrode assemblies simultaneously.

References Cited UNITED STATES PATENTS 2,944,953 7/1960 Borodin 204198 3,200,057 8/ 1965 Burnside et a1 204299 3,325,390 6/1967 Burnside et a1. 204300 JOHN H. MACK, Primary Examiner E. ZAGARELLA, JR., Assistant Examiner US. Cl. X. R. 204299, 300

"H050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. T Dated 1969 Inventor(s) 1*. l'fiif Fl, GILCHJTITZ'J.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the claimri, {7011mm "r2, lin 1:, fii'ior plurality 11 roll-"wing stimuU Pm insnztof:

SUGNED mu SEALED MAY 121970 Attest:

WILLIAM E. SOHUYLER, m-

Edmd member cemmise inner of Patents Attesting Officer

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