Improved Method And Apparatus For Stripping Inside Seams Of Cans

Abstract

A method and apparatus for applying an impervious protective coating over the seams of cylindrical metal can bodies either before or after the seams are welded, soldered, or cemented. The apparatus is operable to intermittently apply an airless spray to the interior overlapped seams of the cans as they continuously move past an airless spray gun secured to the end of a stubhorn of a can forming line. This apparatus includes an airless spray nozzle located on one side of the seams for directing a spray onto the inside corner of the seams of the formed can bodies and an air jet located on the opposite sides of the seams from the spray nozzle for confining the atomized spray or fog to the seam area of the can.

Description

This invention relates to the application of protective coatings to the interior of metal cans and more particularly to the application of a stripe of protective coatings to the interior soldered, welded, or adhered seam of a metal can body.

One manufacturing technique employed in the manufacture of metal cans involves forming a cylindrical can body from a sheet of metal and then attaching two lids or ends to the opposite ends of the body. The invention of this application is concerned with the manufacture of these cylindrical bodies.

The procedure employed in the manufacture of can bodies is to form a cylinder from a rectangular sheet of metal which has been previously roller coated on all but the lateral edges. The roller coating is a protective coating of lacquer or other similar material. After formation into the cylindrical configuration, the lateral edges of the sheet are either butted or overlapped and secured together by either a welded seam, a soldered seam, or a cemented seam. The seam area and the previously uncoated lateral edges of the sheet are then spray coated with an epoxy or phenolic lacquer or some modification of these materials. Subsequently, the complete interior of the cylindrical body is coated with another complete protective coating which is generally of vinyl lacquer although numerous other materials, as for example, resins, lacquers, waxes and paints, are applied for this same purpose, i.e., to afford protection of the contents of the can against contamination by the metal. Particularly, beer, beverages and foods must be protected in this way against metal contamination by the application of a tasteless and odorless protective coating material to the interior of the can.

The protective material which is applied to the interior of the can must be continuous throughout the entire interior surface. Any pin holes, cracks, or imperfections in the integrity of the coating render the can unsuitable for most applications. To avoid pin holes, cracks, or imperfections in the coating, it is now common practice in the can industry to first apply a stripe of protective material over the interior seam of a can body before a second or subsequent layer is applied to the complete interior of the can. The purpose of this stripe is to provide an impervious layer of protective material over that portion of the body which is most vulnerable to imperfections and where failures most often occur.

In copending application Ser. No. 56,304 filed July 20, 1970, and assigned to the assignee of this application, there is described an airless spray technique for applying a stripe of protective material or lacquer to the interior seams of cans as the cans pass over and off the end of the stubhorn of a can manufacturing line. This invention is an improvement upon the method and apparatus described in that application.

Specifically, there is described in that application an airless spray technique for intermittently applying a stripe of lacquer to the inside seams of can bodies as the cans pass an airless spray nozzle attached to the end of the stubhorn. The spray nozzle is so positioned on the stubhorn that it is located on the interior of the can bodies as the bodies pass the striping station.

One of the problems encountered in spraying a stripe of protective material onto the seam of a can body is that of confining the spray to a stripe approximately 1/2 to 1 inch in width, depending upon the can application, without having the spray bounce up or fog onto the area or side of the can wall adjacent the stripe. This confining of the stripe to avoid its overlapping or splashing onto the side walls of can bodies is critical on all can bodies but is particularly critical in the case of soldered seam cans. Common practice is to spray the seam of the can with the protective stripe prior to soldering of the seam but after the seam has been formed and overlapped. After spraying, the seam is soldered and the area adjacent the seam is exposed during soldering to a temperature of 700.degree.-900.degree. F. during which the stripe of protective material is cured. Thereafter, the complete interior of the can body is sprayed with a coating of lacquer or protective material but one which cures at a lower temperature, as, for example, 300.degree. F. If any high curing temperature seam striping material inadvertently is sprayed onto the area adjacent the stripe, that lacquer is not subjected to the 700.degree.-900.degree. F. seam temperature and is therefore never cured, either during the soldering operation or during the subsequent curing of the low curing temperature material sprayed onto the complete interior of the can.

It has therefore been a primary objective of this invention to provide a new and improved method for applying a continuous stripe of protective material or lacquer over the interior seam of a can without splashing, spraying, or bouncing protective material off the seam area onto the sides of the can body adjacent the seam area.

Still another objective of this invention has been to provide a method and apparatus for spraying a stripe of protective material over the seam of a can with a minimum quantity of material while still obtaining a continuous uniform coating of material over the seam.

These objectives are accomplished and one aspect of this invention is predicated upon the utilization of a liquid spray nozzle for spraying the stripe of liquid protective material onto the overlapped seam of a can and the location of this nozzle on one side of the seam so that it directs its spray into the inside corner defined by the overlap of the seam. In order to confine the spray and prevent it from splashing, spraying, bouncing or fogging out of the spray area, an air nozzle is operable to create an air curtain on one side of the seam opposite from the nozzle. The air nozzle and spray nozzle are so directed that one edge of the air curtain intersects the edge of the liquid spray pattern at the can body surface and at the edge of the seam area. This positioning of the liquid and air spray nozzles has been found to minimize what has heretofore been the most troublesome aspect of inside striping of cans, the bounce or splash of the spray onto and up the side walls of the can.

In the preferred embodiment of this invention, an airless spray nozzle directs the protective liquid material onto the seam area and a spray nozzle directs the confining air curtain onto the adjacent surface of the can body. Both of these nozzles emit a spray pattern in the form of an ellipse. Another aspect of this invention is predicated upon the discovery that the elliptically shaped air curtain is most effective for confining the fan of liquid material when the liquid and air elliptical patterns are in end-to-end engagement.

Still another aspect of this invention is predicated upon the empirical determination of nozzle design and mounting positions and conditions under which an airless spray stripe may be applied to the interior seam of a can body in a uniform continuous film which meets all can industry standards in terms of continuity, uniformity, weight of material, and application of the stripe to a confined area.

These and other objects and advantages of this invention will be more readily apparent from the following description of the drawings in which:

FIG. 1 is a diagrammatic illustration of a portion of a can forming line including the invention of this application;

FIG. 2 is an enlarged view, partially in cross section, of the end of the can forming line stubhorn of FIG. 1;

FIG. 3 is an end elevational view of the end of the stubhorn including the spray gun taken on line 3--3 of FIG. 2;

FIG. 4 is a cross sectional view through the spray gun taken along line 4--4 of FIG. 3;

FIG. 5 is another cross sectional view through the spray gun taken in a plane normal to the plane of FIG. 4;

FIG. 6 is an enlarged cross sectional view through the spray nozzle taken on line 6--6 of FIG. 2; and

FIG. 7 is a top plan view of the spray pattern which emerges from the liquid spray nozzle and the air nozzle of FIG. 6.

Referring first to FIG. 1, there is illustrated diagrammatically a standard can production line used in the production of cylindrical can bodies. This line includes a stubhorn 10 which serves as a mandrel around which can bodies 11 are formed as they pass downstream. The can bodies 11 are moved longitudinally over the stubhorn from a magazine 12 by lugs on a chain conveyor which engage the rear edge 13 of the bodies and push them along the stubhorn. As bodies pass off the stubhorn, after having been formed into cylindrical configuration, they move into a network of rails 15 through which they then pass during continued formation of the cans.

In the final stages of movement of the can bodies over the stubhorn 10, the ends of the sheet metal from which the body is made are overlapped. If the bodies are to be seamed by adhesive, the adhesive is placed in the overlapping seams at the seaming station indicated by the numeral 14. Alternatively, if the bodies are to be welded, they are welded at this station 14. And if the bodies are to be soldered, they are crimped together at the seaming station 14. As the bodies pass off the stubhorn 10 and into the rails 15, they are passed through an inside striping station indicated by the numeral 16. At this station a stripe of protective material 17 (FIG. 7) is sprayed over the overlapped seam 18 (FIG. 6) of the can. Soldered can bodies then require passage through a soldering station downstream of the striping station 16 to complete formation of the seam but the adhered and welded seams are completely formed when the bodies enter the rails 15.

In order to apply the stripe 17 of protective material over the same area A (FIG. 7) of the can body, a spray gun 20 is secured to the end of the stubhorn 10. This gun is so positioned that the can bodies pass over it before passing into the rails 15.

The gun 20 is secured to the end surface 21 of the stubhorn by a generally U-shaped bracket 22 secured onto the end of the stubhorn by a plurality of bolts 23. Bolts 19 similarly secure the gun 20 to the opposite or downstream end 24 of the bracket 22. The bracket 22 may be omitted and, in fact, in one preferred embodiment is omitted, in which case the gun 20 is secured directly onto the end of the stubhorn.

The spray gun 20 is of the so-called circulating flow type; that is, there is a continuous flow of liquid or coating material to the gun through a liquid inlet line 25. There is also continuous flow of liquid or coating material from the gun via a line 26 (FIGS. 1 and 5). As a result of this continuous flow, the temperature of the liquid material may be maintained constant in the gun even when the gun is not in use and when the liquid would otherwise be stationary in the gun. Some can protective materials set up or harden at room temperature so that it is important that these materials not be permitted to stand and become hardened in the gun. The circulating flow of liquid through the gun precludes this hardening or setting of the material. In the case of other protective materials which are applied at ambient or room temperature, temperature control is not as important and a conventional noncirculating or one-fluid line gun may be used.

The gun contains a check valve, indicated generally by the numeral 30, operable to open and close a passage 31 leading to an orifice 32 of a nozzle 33 in synchronization with movement of cans past the orifice 32. The check valve is pneumatically opened by air pressure supplied to the gun via an air line 35 and is spring biased to a closed position. Air pressure at approximately 60 p.s.i. is supplied to the gun in the line 35 from an air pressure source 36 through a solenoid controlled valve. An electric photocell circuit including a photocell 38 and receiver 39 control the flow of electric current to the solenoid of the valve. The sender is operable to direct a light beam through a hole 41 in the stubhorn 10 so that cans entering the striping station 16 break the circuit and trip a solenoid, thereby causing the valve to be opened and air pressure supplied via line 35 to the gun.

In the preferred embodiment the solenoid valve comprises a 3-way solenoid operated electric valve 42 in combination with a conventional 3-way pilot operated spool valve 37. Air pressure is supplied from the source 36 at a regulated pressure of approximately 60 p.s.i. to line 35 under the control of the solenoid valve 42. When the solenoid of valve 42 is de-energized, air in line 35 to the gun is vented to atmosphere through the spool valve 37. When the electrical circuit is energized, the solenoid valve opens to connect one end of the spool of valve 37 to air at the pressure on line 43, 60 p.s.i. in the preferred embodiment. This air pressure is sufficient to overcome a spring bias acting on the spool of valve 37 and move that spool to an open position in which line 43 is open to line 35. It has been found that the solenoid valve 42 may act fast enough when used to control air flow to the gun but because of the length of the air passage to the gun and the volume therein, best performance is achieved with a second stage spool valve 37 in combination with the solenoid valve 42 to obtain the higher flow capacities necessary to keep pace with current can production speeds.

Referring again to FIGS. 4 and 5, it will be seen that the gun 20 generally comprises a two-piece cylindrical body 45 within which there is an axial or central bore 46. This bore comprises a fluid chamber 47 adjacent the front end of the body, a smaller diameter connecting chamber 48, and a large diameter piston chamber 49. The rear side of the piston chamber 49 is open to the atmosphere through a small diameter section 51 of the bore 46. An end cap 52 is secured to the body 45 by bolts 60 and closes the fluid chamber 47. The cap 52 comprises a central disc 53 from which hub sections 54, 55 extend rearwardly and forwardly, respectively. The rearward hub 54 fits within, and with an O-ring, seals the fluid chamber 47. The forwardly extending hub section 55 has an inwardly extending flange 56. An axial bore 57 extends through the cap 52 and comprises a large diameter rear section 58 and a smaller diameter front section 59.

A cylindrical metal insert 61 made from a hard material, as for example, tungsten carbide, is brazed or otherwise fixedly secured within the small diameter section 59 of the cap. This insert 61 defines the seat of the check valve 30. The insert has a stepped axial bore which comprises a large diameter rearward section 62 and the small diameter passage 31 interconnected by shoulder 63. An arcuate seat is machined into the shoulder at the point where the shoulder joins the small bore 31. This seat is configurated to cooperate with a generally semispherical end 64 of the check valve head 65 to form a seal.

The nozzle assembly 33 is bolted onto the flanged end 56 of the end cap 52. Referring to FIGS. 3 and 5, it will be seen that this assembly 33 comprises a nozzle mounting block 70, a nozzle tip support block 75, and a carbide nozzle tip 71. The block 70 is fixedly secured onto the end cap by a pair of bolts 72. This block 70 has one bore 73 which communicates with and is coaxial with the outlet passage 31 of the gun and a second passage 74 which extends through the mounting block 70 and the nozzle tip support block 75. This second passage 74 intersects and communicates with an axial flow passage 79 of the nozzle tip 71.

The construction of the nozzle tip 71 and the manner in which it is mounted in the mounting block are not illustrated or described in detail herein because these features form no part of the invention of this application. A complete description of these details may be found in copending application Ser. No. 107,632, filed Jan. 19, 1971, now U.S. Pat. No. 3,702,107 and assigned to the assignee of this application.

The outer end of the nozzle tip 71 is generally hermispherical in configuration. Orifice 32 is an elliptical shaped orifice which is machined into the tip of the dome so as to intersect at a right angle the axial orifice 79 of the tip. Conventionally, this elliptical orifice is machined into the dome by a tapered grinding wheel. Liquid emerging at a high pressure or as a high pressure stream 80 (as for example, at 200-1,000 p.s.i.) from the elliptical shaped orifice atomizes and assumes the elliptical pattern depicted by the dashed line 81 of FIG. 7.

Referring back to FIG. 6, it will be seen that as the high pressure stream 80 of liquid emerges from the nozzle orifice 32 it spreads out or fans out to form a generally fan shaped solid curtain 82 of liquid. The axis 83 of this stream is angulated to an angle .alpha. of 30.degree. relative to a diametral plane 84 of the can body which passes through the seam so that the atomized stream is directed into the corner 85 defined in part by the inside edge 86 of the overlapped seam 18. This angulation of the stream axis 83 has been found to minimize failures resulting from pin holes in the stripe 17 but at the same time it increases the problem of controlling overspray which results from the bounce, splash and fogging of the spray out of the seam area A.

To contain the finely atomized spray to the seam area A, an air curtain 89 is provided adjacent the opposite edge 90 of the elliptical shaped pattern 81 of the liquid spray. This air curtain is also elliptical in cross sectional configuration at the point where it strikes the substrate or can body adjacent the stripe 17. As indicated by the cross hatched patterns 89A in FIG. 7, this air curtain 89 has the effect of chopping off the end 81A of the fan shaped pattern 81 of atomized liquid spray so as to confine it to a width W.

We have found that if the elliptically shaped air curtain 89 is oriented so that its long axis is coincidental to or colinearly aligned with the long axis of the elliptically shaped liquid spray pattern 81, the air curtain better contains the liquid spray pattern than if the two patterns are normal to one another.

To create the air curtain 89, air is supplied to an elliptical shaped nozzle orifice 91 in a nozzle 92. This air is supplied to the nozzle in synchronization with opening and closing of the check valve 30 of the gun 20. To this end, the nozzle 92 is mounted in a block 93 which is mounted to the disc 53 of end cap 52. Suitable passages (not shown) within this block communicates with a manifold block 94 secured to the gun. The block 94 has a central passage 95 which communicates with the passage within the block 93. The passage 95 is supplied with air under regulated pressure of from 20-70 p.s.i.g. from the pneumatic line 35. It is also connected to a pneumatic line 35A of the gun. Consequently, air is supplied to the nozzle 92 in synchronization with opening and closing of the check valve 30 of the gun.

In operation, can bodies 11 are formed over the stubhorn 10 at the rate of approximately 550 plus or minus 50 cans per minute. This rate varies from one can manufacturer to another, but quite commonly today averages approximately 575 can bodies per minute per line in the production of standard beer or beverage cans. As the cans move along the stubhorn, a solder, adhesive or weld is commonly applied to the overlapping edges 18 of the sheet at the seaming station 14. This station is located immediately in front of the striping station 16 where the stripe 17 of protective material from the nozzle 33 and spray gun 20 is directed into the seam. In the case of soldered cans, the seam is subsequently completed and the striping material simultaneously cured by the application of soldering heat to the seam at a subsequent soldering station. Generally, this heat raises the temperature of the seam to above 700.degree.-900.degree. F. so as to cure the protective coating of the stripe during the soldering operation. In the case of seam welded or seam adhered cans, the striping material is either heat or air cured at a much lower temperature farther down the can production line.

The emission of liquid spray from the nozzle 33 and the emission of the air curtain from the nozzle 92 is turned on and off in synchronization with movement of the can bodies 11 over the stubhorn and through the striping station. This is accomplished by the can bodies interrupting a light beam of the photocell sender and receiver unit 38, 39. Upon interruption of the light beam and after a predetermined time delay built into a solenoid control circuit, the solenoid control circuit is operable to shift the solenoid and move a valve spool of the valve 37 so as to connect the air line 35 to the source of air pressure 36, thereby connecting a forward end chamber 92 of the check valve control piston chamber 49 to high pressure, i.e., 60 p.s.i. air. This results in movement of a piston 98 and opening of the check valve 30. Upon opening of this valve, the liquid protective material in the fluid chamber 47 is allowed to pass from the liquid chamber 47 past the head of the valve into the conduit or passage 31 and subsequently to the nozzle orifice 32 of the nozzle 33. Liquid in the chamber 47 is maintained at a pressure of approximately 250-800 p.s.i., the pressure at which it is supplied by a pump 99 from a reservoir 100.

A predetermined time after interruption of the light beam, that can which has broken the light beam passes out of alignment with the nozzle 33. After that predetermined time, a timer circuit interrupts the signal to the solenoid causing it to be de-energized and the control circuit to be reset preparatory to interruption of the light beam by the next following can. Upon de-energization of the solenoid, low air pressure, i.e., 20 p.s.i., in line 43 or spring pressure then moves the spool of the valve 37 to the position in which the air line 35 is connected to atmospheric pressure. This results in the venting of line 35A of the gun, causing the check valve 30 to be closed, which immediately cuts off the flow of liquid spray from the nozzle orifice 32 and the emission of air from the nozzle 92 until the next following can again interrupts the light beam.

In one preferred embodiment, the protective material applied to the can seam of a soldered seam beer can 2 11/16 inches and 4 11/16 inches in length is an epoxy resin coating material manufactured by the DeSoto Chemical Co. of Chicago, Ill., and designated as their No. 563-803 Epoxy Resin Can Coating. It is supplied to the nozzle at a temperature of 180.degree.-190.degree. F. at a pressure of approximately 400 p.s.i. and at a Zahn No. 2 cup viscosity of 16 seconds, 77.degree. F. The preferred nozzle is one which has a flow rate of 0.015 gallons per minute of water at 500 p.s.i. and at ambient temperature. The nozzle orifice is preferably spaced 1 1/4 inch from the can seam and lays down a protective stripe of material 9/16 inch to 11/16 inch in width W. The resulting stripe of material when subsequently cured weighs approximately 5 or 6 milligrams. Including the overspray, this stripe never exceeds 1 1/16 inch in width W, which width is adequately heated to curing temperature of approximately 750.degree. F. during the subsequent soldering operation.

Prior to this invention it has been difficult to control the application of spray to a can seam so as to avoid overspray and material being applied to the side walls of the can over so wide an area that the material remained uncured even after the subsequent soldering operation. Primarily, the problem occurred because of the atomized spray bouncing off the seam stripe area of the can and rolling up the inside walls of the can into areas adjacent the stripe area, which areas never subsequently reached the material curing temperature and which material therefore remained uncured. By the practice of this invention, though, that problem is overcome with the result that this invention enables airless spray techniques to be utilized to apply a stripe of protective material to the seam of a can. The use of airless spray techniques in turn minimizes overspray and the quantity of material required to adequately protect the overlapped seam of a can.

While we have described only a single preferred embodiment of our invention, persons skilled in the art to which this invention pertains will readily appreciate numerous changes and modifications which may be made without departing from the spirit of our invention. For example, those persons skilled in the can manufacturing art will readily appreciate that the striping appratus of this invention is equally applicable to outside can striping as to inside can striping. Therefore, we do not intend to be limited except by the scope of the appended claims.

Claims

Having described our invention, we claim:

1. The method of applying an impervious protective coating to the longitudinal seams of cylindrical can bodies, which method comprises

advancing a continuously moving line of spaced can bodies through a striping station at which an airless liquid spray nozzle is located interiorly of the cans,

emitting a high pressure airless spray fan of liquid coating material from the nozzle orifice and directing that airless spray fan angularly from one side of a diametral plane which passes through the seams of the can bodies onto the surface of the seams of the can bodies, and

emitting an air curtain from an air nozzle located on the opposite side of said diametral plane and directing that air curtain onto the surface of the can bodies on the opposite side of the seam from said diametral plane so as to contain and limit the liquid spray to the seam area of the can bodies.

2. The method of claim 1 further comprising directing said airless liquid spray at an angle of approximately 30.degree. relative to said diametral plane onto the surface of said seams of the can bodies.

3. The method of claim 1 further comprising directing both said air spray and said airless liquid spray to form an elliptically shaped pattern and directing said patterns to contact said surface of said seams of said can bodies and to intersect at said surface.

4. The method of claim 3 further comprising colinearly aligning the long axes of said elliptically shaped patterns of said airless liquid spray and said air spray.

5. The method of applying an impervious protective coating to the longitudinal seams of cylindrical can bodies, which method comprises

advancing a continuously moving line of spaced can bodies through a striping station at which an airless liquid spray nozzle is located interiorly of the cans,

emitting a high pressure airless spray fan of liquid coating material from the nozzle orifice and directing that airless spray fan angularly from one side of a diametral plane which passes through the seams of the can bodies onto the surface of the seams of the can bodies,

emitting an air curtain from an air nozzle located on the opposite side of said diametral plane and directing that air curtain onto the surface of the can bodies on the opposite side of the seam from said diametral plane so as to contain and limit the liquid spray to the seam area of the can bodies, and

starting and stopping the emission of airless liquid spray from the nozzle in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle but is turned off after that can body passes the nozzle until the seam of that next following can body moves into alignment with the nozzle.

6. Apparatus for applying an impervious protective coating to the longitudinal seams of cylindrical can bodies comprising

a striping station,

means for advancing a continuously moving line of spaced can bodies through said striping station,

an airless liquid spray nozzle located interiorly of the cans at said striping station,

means for emitting a high pressure airless spray fan of liquid coating material from the nozzle and for directing that airless spray fan angularly from one side of a diametral plane which passes through the seams of the can bodies onto the surface of the seams of the can bodies,

means for emitting an air curtain from an air nozzle located on the opposite side of said diametral plane and for directing that air curtain onto the surface of the can bodies on the opposite side of the seam from said diametral plane so as to contain and limit the liquid spray to the seam area of the can bodies,

said air spray emitting means and said airless liquid spray emitting means being operable to shape said sprays into elliptically shaped patterns and being oriented so as to direct said patterns to intersect at the surface of said seams of said can bodies and oriented so that the elliptically shaped patterns of said airless liquid spray and said air spray have long axes which are colinearly aligned, and

means for starting and stopping the emission of airless liquid spray from the nozzle in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle but is turned off after that can body passes the nozzle until the seam of the next following can body moves into alignment with the nozzle.