US3759810A - Roll through method for electro coating can ends - Google Patents

Abstract

A PROCESS AND APPARATUS FOR CONVEYING ROUN, METAL PARTS HAVING RAW EDGES THROUGH AN ELECTROCATING BATH WHILE MAINTAING ROLLING, WIPING, ELECTRICAL CONTACT BETWEEN THE PARS AND A GROOVED ELECTRODE RAIL OR WHEEL.

THE PROFILE OF THE GROOVED ELECTRODE IS SHAPED TO MAINTAIN THE CONTINUOUS ROLLING, WIPING, ELECTRICAL CONTACT AGAINST THE RAW EDGE OF THE METAL PARTS.

Description

Sept. 18, 1973 LE ROY LANDAUER ET AL 3,759,810

ROLL-THROUGH METHOD FOR ELECTROCOATING CAN ENDS 3 Sheets-Sheet 1 Filed March 29, 1971 US. Cl. 204-181 6 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus for conveying round, metal parts having raw edges through an electrocoating bath while maintaining rolling, wiping, electrical contact be tween the parts and a grooved electrode rail or wheel. The profile of the grooved electrode is shaped to maintain the continuous rolling, wiping, electrical contact against the raw edge of the metal parts.

BACKGROUND OF THE INVENTION The instant invention relates to electrocoating, and more particularly to electrocoating resin-coated, metal parts such as container ends having raw (i.e., uncoated) edges. Electrocoating is the electrodeposition of resinous coating materials, such as paint materials, from water base solutions, suspensions or dispersions. In the case of anodic coating materials, the coating ions or particles carry a negative charge in the water base bath. These ions or particles migrate to and discharge onto any positively charged metal which may be immersed in the coating bath. In the case of cathodic coating materials, the coating ions or particles carry a positive charge in the water base bath, and these ions or particles migrate to and discharge onto any negatively charged metal which may be immersed in the coating bath.

Heretofore, can ends used in the packaging of beer, carbonated beverage cans and other corrosive products have been protected from attack by the product by a double coat system which includes a base coat which is applied to the metal stock while it is in the flat state, usually in a roller coating operation, and by a top coat which is applied to the fabricated end by a spraying operation to seal any discontinuities in the base coat. This top coat usually is an overall coat, since the location of the discontinuities cannot be precisely and reliably ascertained.

While the two coat system has generally been satisfactory, it does have a number of disadvantages in that the top coat is relatively difficult to apply at high speeds because of the problems which are usually associated with spraying machines. These problems include, inter alia, the contamination of machine parts because of overspray, the need for frequent cleanups and adjustments of the spray heads, and the need to bake the finished ends to drive off the solvent in the top coat. These and other problems were partially solved by the process of electrocoating, as disclosed in copending U.S. application Ser. No. 842,461, filed July 17, 1969, now abandoned by Le Roy Landauer.

In order to positively or negatively charge a metal object to be electrocoated, it is necessary to electrically contact the object. This is usually accomplished with hangers or clamps whereby one or more individual objects to be coated are hung or clipped to one or more individual hangers or clips. See said copending Landauer application. The clips or hangers are sometimes connected into groups to form racks for hanging groups of parts. These hangers or clamps can then be automated and conveyed for moving the parts into and out of the electrocoating bath. Such United States Patent "ice hanging devices have great disadvantages when a very high speed, high volume electrocoating operation is required, as in the case of manufacture of can ends.

The major problem is the size and complexity of a highspeed machine which must clamp each end individually for electrical contact and conveyance through an electrocoating bath. The problem is further complicated by the fact that any clamp, hanger, or other power transmission device which is allowed to touch the electrocoating bath will itself be electrocoated wherever bare metal is immersed. This causes insulation of the power transmission device and can result in electrical contacting problems with the parts to be processed through the electrocoating bath.

In electrocoating a resinous coating, the material being coated onto the substrate becomes an insulator for the substrate. In electroplating, the coating material is a metal, which is conductive and therefore presents no particular problems in maintaining electrical contact during a roll-through process, such as: are described in US. Pats. Nos. 1,475,198 and 1.079,427. However, a rollthrough method of electrocoating a resinous coating presents .the unique problem of continuously keeping some part of the substrate end free of coating so that said part can be utilized for electrical contact with the electrode while the substrate rolls partially immersed through the electrocoating bath.

SUMMARY OF FHE INVENTION Can ends blanked from stock whether or not covered with a base coat offer a raw, metallic edge which is electrically conductive, and capable therefore of being used to maintain wiping, electrical contact between an electrode and the rolling can end. Thus, by utilizing the raw edge of the can end produced by the blanking operation and by using a grooved electrode to wipe the raw edge essentially free of the coating material at the contact point, the problem of maintaining electrical contact inv a continuous, roll-through electrocoating process solved, whether or not the edge be somewhat cured under. The surfaces of the end may be coated, while the raw edges are used for electrical contact. The fact that the edges are not well coated is immaterial as regards the final container shape and contents therein, because the contents never see the edges, and the edges, being buried under a seam, are not visible to the observer.

The instant invention provides a roll-through method and apparatus for electrocoating round, metal parts having raw edges. The invention comprises simultaneously rolling round, metal parts having raw edges between aligned grooves of a charged electrode rail situated above an electrocoating bath containing a resinous, organic coating material and a non-conducting guide member immersed in the electrocoating bath, maintaining rolling, wiping, electrical contact between said electrode rail groove and the raw edges of said parts, and partially immersing said parts in said electrocoating bath for a time sufficient to rotate the desired surface areas of the parts through the bath. The resinous coating is deposited as D.C. current passes through the coating bath between the parts in contact wtih the non-immersed electrode rail and a second electrode immersed in the bath.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical, sectional view of a belt system used to electrocoat container ends.

FIG. 2 is a sectional view taken on the vertical plane indicated by the line 22 of FIG. 1.

FIG. 3 is an enlarged, fragmentary section of FIG. 2 showing the wiping electrical contact between the container end raw edge and the electrode rail overhead.

FIG. 4 is a sectional view taken on the vertical plane indicated by the line 44 of FIG. 1.

FIG. 5 is a vertical, sectional view of an alternative embodiment of the invention showing a wheel-rail electrocoating system.

FIG. 6 is a sectional view taken on the vertical plane indicated by the line 6-6 of FIG. 5.

FIG. 7 is an enlarged, fragmentary section of FIG. 6 showing the wiping, electrical contact between the raw edge of the container end and the electrode wheel.

FIG. 8 is a vertical, sectional view of a third embodiment of the invention.

FIG. 9 is a sectional view taken on the vertical plane indicated by the line 9-9 of FIG. 8, and shows how the end is held in contact with the electrode wheel by means of a resilient material such as black gum rubber tubing.

FIG. 10 is a fragmentary section of FIG. 9 showing the black gum rubber tubing without an end impressed therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, the round, metal part being electrocoated is a container end, generally designated 21, made from metal stock usually in the form of large, flat, rectangular sheets, or long coils or webs. The stock may be formed of any suitable metal such as aluminum, aluminum alloys or any of the various types of steel plate used in the can making industry, such as tin plate, TFS (tin free steel), black plate, etc. The sheets or coils are then fed into the bite of a pair of coating rollers which apply an organic resin material to one or both surfaces of the sheet or coil to form a base coat which functions as the primary barrier to seal and protect the metal stock from corrosion.

The base coat is composed of any suitable organic coating which will adhere strongly to the surfaces of the metal stock and will provide the desired protection thereto. There are a number of types of suitable coatings, including phenol type coatings such as are described in UJS. Pat. 2,917,481 epoxy coatings such as are described in US. Pat. 2,713,565, and vinyl polymer type coatings such as are described in US. Pat. 3,268,620. However, the invention is not limited to any specific formulation of base coat.

The sheets are then fed into an end forming press, not shown, wherein suitable gang blanking and forming punches and dies cut circular blanks from the sheets and simultaneously form each blank into a basic end 21 having a started flange 23, a countersink wall 25, a reinforcing groove 27, and a flat, central panel 29 (FIGS. 2 and 7), all of which are protected on both sides with the base coat. As a result of the blanking operation, the basic end 21 has a raw, uncoated edge 31 (FIGS. 3 and 7).

During the various operations required to produce the end, especially in the case of easy-open ends, the base coat is subject to various pressures and abuses which frequently produce small discontinuities in it with the result that the metal immediately below or adjacent the discontinuities is exposed. Unless provision is made to treat and seal all the discontinuities, the ends cannot be used in commercial production since the exposed metal may adversely affect the quality of the contents of the filled cans.

In accordance With the present invention, the discontinuities are sealed by a roll-through electrocoating operation which deposits a sealing or repair coat only on those surfaces of the end wherein the metal surface of the end is exposed because of the presence of the above described discontinuities in the base coat. Of course, this same electrocoating operation could also be used to apply a base coat to uncoated can ends.

As the first step in the repair operation, the end is often treated to remove from its surface any oil or wax which may have been deposited on it during the previously described manufacturing operations. Such materials are frequently utilized to facilitate the feeding and forming of the parts, and often form a film on the finished end.

Referring now to FIGS. 1-4 for a preferred embodiment, the ends 21 are randomly fed through a free fall chute 33 to the electrocoating equipment which generally comprises a belt system 35, and an electrocoating bath 37 contained within walls generally designated 39. A first, angled, groove 41 of a fixed charged electrode rail 43 is vertically aligned with a second groove 45 in a moving, non-conductive endless belt 47. The grooves are adapted to tightly hold the raw edge 31 of the can ends 21 so that the edges make rolling, wiping, electrical contact with electrode rail 43. The endless belt 47 is driven by wheel 49 which is rotated by conventional energizing means not shown. The path of the endless belt 47 is defined by drive wheel 49 and guide wheels 51, 53, 55, 57 and 59. Leaf springs, generally designated 61, back up the lower portion of endless belt 47 to keep it taut and thereby tightly hold the raw edge 31 of the can ends 21.

As best seen in FIG. 1, the electrode rail 43 and endless belt 47 guide the can ends 21 into the bath 37, whose height is indicated by broken line 63. The ends 21 are partially immersed in the bath 37 to a depth at least equal to /2 their diameter, for a time sutficient to rotate the entire surface area of the ends through the bath. Following partial immersion, the ends 21 are removed via takeoff belts 65.

As seen in FIG. 3, the electrode groove 41 is profiled so that the end 21 wipes its own contact edge 31 clean as it rolls through the groove 41. The electrodeposited coating which is wiped off into the groove 41 by the rolling end 21 is never baked, and thus remains uncured and soft, and is easily wiped aside by each passing end 21. Provision for periodically or continuously cleaning the groove is helpful.

The electrocoating bath 37 may be a solution, emulsion or dispersion of a suitable, organic, coating resin in deionized water. A number of different types of electrocoat resins may be used, some of which are described in US. Patent 3,230,162, granted Jan. 18, 1966, to Allan E. Gilchrist. One such coating found to be quite satisfactory is an acrylic resin of the general type disclosed in the Gilchrist patent. Preferably, a thin solution of resin, generally on the order of 2% or less resin solids to 98% or more deionized water, is used to minimize the amount of resin solid carried out by the end as it exits from the bath.

The end 21 is made the anode (FIG. 2) by being connected to the positive side of the D.C. power source 67 through the electrode rail 43. A cathode 69 is immersed in the bath 37, so that when an end 21 is immersed in the anodic coating bath 37, electrical current flows between the cathode 69 and those portions of the ends 21 which are exposed to the bath 37. Such exposed portions comprise all the discontinuities in the base coat as well as the raw edge 31.

As the current flows, the ionized resin solids in the bath 37 are deposited in the discontinuities on the ends 21, thus creating unbroken protective coatings on the ends 21. Since no electrical -fiow occurs where the cured base coat is unbroken, no resin is deposited on the cured base coat, unless said base coat is electrically conductive, which is not usually the case.

The thickness of the deposited resin is determined by the characteristics of the electrocoating bath, the voltage used, and the duration of the electrocoating operation. Preferably, the thickness of the repair resin is somewhat greater than that of the original base coat, desirably about 1 /2 times as thick. A voltage of about -500 volts, preferably about 200-400 volts, has been found satisfactory.

Using a typical carboxylic acid resin type coating with a 2% solid bath, 2 inch diameter steel, easy-open ends were electrocoated in a 100 F. bath at 400 volts D.C. drawing 2 amps of continuous current at the rate of 200 ends per minute.

Because only about /2 of the can end is immersed in the bath at any given time, about 1 second of time in the bath is required to roll the entire end through 1 revolution. However, 2 revolutions are recommended to assure sealing of all discontinuities. Usually this rate is substantially faster than that for completely electrocoating a comparable thickness where the base coat is absent, since a complete coating deposited that quickly would not have a commercially acceptable appearance. Appearance is not a factor in the repair coat, however, since the amount of resin deposited is minimal, and its surface area is so small as to be virtually unnoticeable when the electrocoating resin is selected to have the same general appearance and coloration as the base coat.

As the resin is deposited on a substantial number of ends, the supply of resin in the bath 37 must be replenished.

As each end 21 is removed from the bath 37, it drags out with it some of the bath 37 in the form of droplets on the base coat. In order to prevent spotting of the end when these droplets dry out, the end is flushed (not shown) with a clear water rinse to remove the droplets. The electrodeposited resin, which contains less than 5% water, is insoluble in water and tightly adhered to the end 21, is not washed off during this rinsing operation.

Further processing is well known to those skilled in the art of can making, and thus is not described herein.

The resultant product is a finished end which is completely protected by a continuous coating system which comprises the base coat and the repair coat. The raw edge 31 is fully protected, except possibly at the area of electrical contact between it and the electrode rail 43.

FIGS. 5-7 illustrate an alternative embodiment of the present invention. Referring now to FIG. 5, the ends 21 are randomly fed through a free fall chute 33' to the electrocoating equipment, which in this embodiment comprises a rotating inner wheel 81 driven by a power source not shown, a fixed, arc-shaped outer rail 83, and an electrocoating bath 37 contained within walls generally designated 39. In this embodiment, the ends 21 make rolling, wiping, electrical contact with the wheel 81 and are held in such contact by employing a resilient material for the outer rail 83. The end 21 functions as an anode, and a cathode 69 is immersed in the bath 37, so that current may flow from D.C. power source 67 through cathode 69, end 21, and wheel 81. As seen in FIG. 7, groove 85 is not angled, because the rail 83 has a groove comprising a resilient material to hold the can ends 21. A doctor blade 87 is employed to continuously wipe clean the wheel groove 85.

FIGS. 8-1O show a third embodiment, which is similar to that shown in FIGS. 5-7 with the exception of fixed, arc-shaped, outer rail 83', which is not resilient, and the groove 91 which is angled and accommodates a resilient material such as black gum rubber tubing 93 to hold the ends 21 in contact with the electrode wheel 81'.

The round metal part may comprise almost any design imaginable. A common example is that of car wheels, which today are frequently subject to electrocoating. Wheels, however, offer not only raw edges, but completely raw surfaces, since they are not covered with any base coats.

The depth of immersion may be /2 or more the diameter of the round part if it is desired to expose the entire surface area of the part to the bath, or it may be less than /2 of the part diameter if it is desired to expose only certain portions of the part to the bath.

The grooves of the electrode rail and guide member are preferably in vertical alignment, but any alignment desired may be used.

It is thought that the invention and may of its attendant advantages will be understood from the foregoing descirption and it will be apparent that various changes may be made in the form, construction and arrangement of the parts of the article and that changes may be made in the steps of the method described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

What is claimed is:

1. A method of electrocoating round, metal parts having raw edges with a resinous, organic coating which comprises simultaneously:

rolling said parts between aligned grooves of a charged,

electrode rail situated above an electrocoating bath containing said resinous, organic coating material and of a non-conducting guide member immersed in said electrocoating bath;

maintaining rolling, wiping, electrical contact between said electrode rail groove and the raw edges of said parts; and

partially immersing said parts in said electrocoating bath for a time sufiicient to rotate and desired surface area of the parts through the bath.

2. The method of claim 1 wherein said parts are container ends, the ends are immersed to a depth at least equal to /2 the diameter of said ends, and the desired surface area is the entire surface area.

3. The method of claim 2 wherein the grooves are vertically aligned.

4. The method of claim 3 wherein the electrode rail is a rotating, inner wheel which effects the rolling of said ends, and the non-conducting guide member is a fixed, arc-shaped, outer rail.

5. The method of claim 3 wherein the electrode rail is stationary and the non-conducting guide member is a moving endless belt effecting the rolling of said ends.

6. The method of claim 5 wherein said container ends are essentially covered with a base coat of a resinous, organic coating.

References Cited UNITED STATES PATENTS 3,476,666 11/1969 Bell et al. 204-181 3,647,675 3/1972 Fiala 204-481 HOWARD S. WILLIAMS, Primary Examiner US. Cl. X.R. 204-300

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