CA1288641C - Method for forming a metal cylindrical container - Google Patents

Abstract

ABSTRACT OF THE INVENTION

An improved method of forming a cylindrical metal can body is disclosed. The improvement includes forming special ears for the bale and orientating the ears in a specific direction so that the ears can be resistance welded to flat rectilinear sheet stock which can subsequently be accurately rolled into a cylindrical form with a closely controlled overlap.

Description

P~Tt~GI~ FOR FGRIRIIdG A ~ET#1L CYLId~tDRIG~S,I. GG~~PAIi~
This application is related to prior Canadian application Serial No. 580,73 filed on October 20, x.988 and entitled "RINGLESS PAINT CONTAINER".
This application relates generally to metal containers and more particularly to an improvement in the manufacture of cylindrical paint containers which use a wire bale or handle for carrying purposes and will be described with par ticular reference thereto.
~AGDCGR~tJND
In the related application 580,713, a metal container is described which is of a ringless type. The container described in the related application had several unique features, one of which included the use of bale ears or lugs into which the ends of a wire handle or bale were snapped for carrying the container. The ears are resistance welded to the container. This application relates to the manufacturing technique used in welding the lugs to any cylindrical container, whether of the ringless or ring type design.
Heretofore, the conventional method of manufacturing cylindrical metal paint containers, particularly of the gal lon size, was to stamp the ear into a cup shape form, the cup having a base with an opening therethrough and a rim from which extended a circular flange. The metal, tin plat ed stock was stamped into a plurality of rectilinear sheets and each sheet was subjected to movement through several die forming stages which progressively indented the sheet to provide a recess for receiving the ears with the sheet stock _1-VAC-'7586-1 then bent over the flanges of the ears to hold the ears in place. After the sheet was thus formed and clinched about the ears flange, the sheet was then formed into a cylindxi-cal form and the width edge of the sheet crimped back onto itself for a soldered side seam or overlapped for a resi~-tance welded side seam. The bottom of the container was then double seamed to one end of the cylinder and a ring double seamed to the other end of the cylinder in accordance with conventional practices.
Applying the sate to the container by clinching the container about the ears, while occurring at a fast rate is nevertheless a limiting factor in the capacity of a can man-ufacturing line resulting in a lesser production rate than that which is otherwise possible to achieve or alternatively requiring more than one ear applying station to maintain a high throughput capacity. Importantly, it has been deter-mined that as the metal is stretched while it passes through the dies and is clinched about the flanges of the ears, the straightness of the width edges of the sheet is distorted.
The straight edge distortion does not occur in a repeatable, consistent manner, but is irregular and when the longitudi-nal side seam is to be resistance welded, the overlap must be increased to compensate for the irregularity. In a ringless can design, the resistance welded side seam becomes pronounced and can adversely affect the seal o~ the lid. In a conventional can design, the overlap becomes of concern when the container is used to store water based paints. For water based paint applications the seam is coated to prevent rust by a spray striped system. When the overlap becomes significant, the coating cannot penetrate the space between the overlapped metal. An overlap of about 0.4 to 0.5 mm can be effectively penetrated with a spray striped system. Un-fortunately, the distortion of the straight edge from clinching the ears typically can equal 1 mm. This fact gen-erally dictates that resistance welding of the side seam is .i~ ~~~'~~.
V~7C-7586-1 not possible for water based, metal paint containers which clinch the ears in the method described above and necessi-tates the more expensive, crimped soldered seam method.
The prior art has attempted to overcome such limita Lions and has applied the ears to the can bodies by pr~~ec tion welding. However, the ears have been applied after the body has been formed into a cylindrical shape and the longi tudinal side seam welded. when the ears are applied to the cylindrical bodies, the fixture required to spot weld the ears to the rounded body limit the tame required for the operation to about 20 or so can bodies per minute. This in turn limits the throughput of the line or alternatively re-quires a plurality of expensive ear welding stations. At-tempts to pro3ection weld the ears prior to forming the rec-tilinear sheet into a cylinder resulted in a flattening of the cylinder where the ears were applied or the ears "pop-ping off" if they were not adequately welded.
It is also noted that the present state-of-the art within the metal can industry does not permit butt-welding of the container's longitudinal side seam but that efforts are being made to utilize laser technology to effect butt-welding. When such developments occur, it is quite likely that the straightness of the flat plate°s width edges will have to be carefully controlled and the distortion of the edge's straightness by the ear clinching process will not be possible.
~lfif~IARSL ~OF 'I111~ IPd9lL~'tiTION
It is thus a principal object of the present invention to provide a method for manufacturing a Cylindrical metal container which permits the ears to be applied by resistance welding to the container in a fast and efficient manner.
This object along with other features of the invention is achieved in a method for forming the metal cylindrical container for paint cans and the like from a stock of tin _3_ ~_~~~~9~
~IDC-7586-1 coated sheet metal cut into a plurality of rectilinear sheets with each sheet having a pair of length edges approx-imately equal to the diameter of the container and a pair of width edges approximately equal to the height of the con tainer. The improvement includes the steps of providing two bale lugs or ears for each sheet, each ear having a cup shaped body with the body having a circular base portion with an opening therethrough for receiving a wire bale and a circular rim portion and each ear further having a pair of diametrically opposed generally rectilinear tabs extending from the rim. ~1 pair of ears are positioned at discrete points on a flat sheet with each ear orientated so that its tabs are generally perpendicular to the length edges and generally parallel to the width edges and the tabs are then resistance welded to the sheet while the sheet is in a flat position. The sheet is then accurately rolled about its length edges into a smooth cylindrical form with one width edge overlapping the other width edge whereat the width edg-es can be longitudinally seamed and the container svbse-quently formed in a conventional manner.
In accordance with another feature of the invention, the resistance welding of the tabs to the sheet stvek does not distort the straightness of the width edges thus permit-ting the overlapping step to occur so that one lateral edge does not overlap the other lateral edge more than about 0.04 millimeter, thus permitting a fast, side seam resistance welding step to occur while minimizing the metal used to manufacture the container and reducing the cost thereof.
In accordance with still another feature of the inven tion, the tabs are preferably welded to the flat sheet stuck by resistance welding thus permitting the welding thereof at a rate of approximately 250 sheets per minute, a significant increase when compared to the methods used in projection welding the ears in the prior art.

wnc-~58s-1 Accordingly, it is another object of the invention to provide a method for applying the ears to the sheet metal stock of a metal container which permits the overlap of the width edges to be accurately controlled.
It is another object of the aub~ect inv~ntion to pxa-vide an improved method of manufacturing cylindrical metal container which minimizes the amount of metal stock other-c~ise utilizec9 in the process.
Yet another object of the invention is to securely and permanently fasten the ears to a ~lat metal rectangular sheet which can be accurately and smoothly rolled into a cylindrical can body.
These objects and other features of the present inven tion will become apparent from the following description of species thereof taken together with the accompanying draw ings.
~RILF DES~IPTIO~ OF T~: TlR~idINGS
The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompa-nying drawings which form a part hereof and whexeinc FIGURE 1 is a perspective view of the ear of the present invention which is to be applied to the can body;
FIGURE 2 is a top plan view of the ears applied to the flat can sheet;
FIGURES 3a, 3b and 3c are schematic views illustrating conventional process steps used in forming the can body; and FIGURE ~E is an exaggerated view illustrating the defor mation of the sheet stock edge which occurred is~ the prior art.

DET.a~,ILED DESG'9'tIP1'ION DF TDE PEE~°EItItED I~ODI~' Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only and not for the purpose of limiting the same, the invention will be described with reference to forming a conventional, metal, cylindrical one gallon paint container. Such containers are formed from tin plated, sheet metal stock with the gauge of the stack typically specified in pounds. For one gallon paint containers, the gauge is usually between 75 lbs. and 90 lbs. with a tin coating of .25 lbs. The actual thickness of the stock is between .0083 and .0099 inches. Good results have been ob-tained with a gauge thickness of .0094 and a tin costing of .25 lbs. although it is contemplated that the invention will work within the range of stock specified for the one gallon container sizes.
Referring now to FIGLtRE 1, there is shown a cup-shaped ear 10 for holding the ends of a bale or wire handle for carrying the container. Cup-shaped ear 10 has a base 12 and a circular rim 13. Within base 12 is a central opening 15 extending therethrough which receives the ends of the bale and extending from diametrically opposite sides of rim 13 is a pair of mounting tabs 16. Cup-shaped ear 10 is formed by conventional die-pressing operation from a stock which is 95 lbs. (0.0105") tin plate.
Referring now to FIGURES 1 and 2, a diameter D of base 12 is about 0.750 inches and the width W of mounting tabs 16 is about 40 percent of diameter D and the length L of tabs 16 is about 25 percent of diameter D.
In the conventional can manufacturing process, the first step is to form a cylindrical body from a flat piece of sheet metal stock which has been sheered into a rectilin-ear plate 20 having parallel longitudinally extending length ~_~~~~~j~ ADC-7556-1 edges 21 approximately equal to the diameter of the cylin-drical cantainer and parallel width edges 22 appro~cimately equal to the height of the paint container. Positioned on rectilinear plate 20 are a pair of ears and they are ~paced apart from one another a distance equal to the diamettsr of the paint container. For a standard one gallon paint con-tainer, the diameter would be 6.500" and the dimensions aeae~
and "b" shown in FIGURE 2 would equal 5.110°° and 1.745" re-spectively.
Because sheet 20 is flat, ears 10 can be accurately positioned thereon and easily clamped or otherwise posi-tioned for welding tabs 16 to rectilinear sheet 20. For purposes of explanation, a conventional Larson pro3ection welding machine could be used to weld tabs 16 to rectilinear sheet 20. Such machine has the capacity to weld 0.9 ears per second which, when used with conventional feed mecha-nisms customarily used in can lines, would produee 20 con-tainer bodies per minute. It is specifically contemplated that tabs 16 will be resistance welded to rectilinear sheet 20 by a resistance welding machine 30 as shown diagrammati-cally in FIGURE 3A. Such resistance welding machines could be of the type used to effect continuous side seam welding identified hereafter) and which would be modified to resis tance weld the tabs as the sheet passes by. Specially mod ified projection welders could significantly reduce the welding time and it is anticipated that as many as 250 rec-tilinear sheets per minute could be fed through such spe-cially adapted pro,~ection welder. When the ears are welded to rectilinear shape 20, the thickness of the sheet plus mounting tabs 16 would be about twice the thickness of rec-tilinear sheet 20 and the welded connections would occur at only 2 points which are spaced vertically or parallel to width edge 22 and perpendicular to length edge 21 which, importantly, permits rectilinear sheet 20 to be rolled into a true cylinder using conventional cylinder forming rolls 40 'VDC-7586-1 ~_~~~'~.
schematically illustrated in FIGURE 3b. A conventional cy-lindrical roll forming machine such as Model No. EWL-250 supplied by Soudronic A.G. or Model No. F8W-22-420-S sup-plied by Fael A.G. used in prior art devices can be em-ployed. It should be hated that the machines described axe roll forming machines in distinction to other conventional cylindrical forming machines which in theory cauld also be used. In the sense that the welded connectian of the tabs 16 to rectilinear plate 20 must hat laosen during railing while at the same time permit accurate rolling without denting the side of the can, the dimensional relationships set forth above are critical. In the roll forming operation of F%GUltE
3b, the overlap between width edges 22 can be carefully con trolled and in point of fact is carefully controlled to be no more than 0.5 mm.
With rectilinear sheet 20 thus rolled into a cylinder, the overlap width edges 22 are continuously welded by a con-ventional side welder such as diagrammatically illustrated as 50 in FIGURE 3c. 'Typical, continuous side seam welders which could be employed to effect longitudinal welding of the side seam could be Model Na. EWL-250 supplied by Soudronic A.G. ar Model Dlo. FIiW-22-420-S supplied by Fael A.G.. Once the side seam is welded a cylindrical can body 60 is formed and the can body is then subjected to the nox-mal steps in the can manufacturing proeess which include seaming a bottom to one end of the can body 61 and a zing to the other end of the can body 62 ar, if the can body is of the ringless type as described in the parent application, end 62 is appropriately profiled. Such steps are canven-tional in the can manufacturing art and do hat, per se, form a part of the invention and will hat be described in detail herein.
As noted in the background portion of the specifica tion, rectilinear sheet 20 was heretofore subjected to a series of dies which would stamp indentations in the _g_ rectilinear sheet at the position where ears 10 are welded.
~:ars 10 having an annular flange instead of tabs 1G would then be placed in the indentations and the metal clinched over the flange to maintain the ears in place. Since the metal will simply stretch, there was no problem in forming the cylinder. however, during the die forming operation, the straightness of width edge 22 would distort and the dis-tortion, which was irregular in occurrence and is shown by dimension X in FIGURE 4, would be in excess of 0.5 mm and sometimes as high as 1.0 mm which is more than twice the distance permissible for water based paint containers using conventional stripe spray systems noted above. This in turn would require a larger overlap of the width edges in the side seam welding station of FIGURE 3c (if soldered side seams were not employed) and to cause the seam to fuse even-ly, notwithstanding the distortion, would result in a higher capacity side seam welder 50 or a slower operating welder 50 than that which would otherwise be employed. In accordance with the present invention, distortion X is removed and the side seam overlap can be carefully controlled to the dimen-sion noted and, theoretically even peranit butt welding of width edges 22. However, butt welding, as a practical mat-ter, is not feasible at the present time for the thicknesses described and for the tolerances which can be maintained on the straightness of width edges 22. Importantly, by dimen-sionin~, mounting tabs 16 and orientating them in a straight line direction para11e7. to width edge 22 and not parallel to longitudinal edge 21, a true cylinder can be rolled as shown in the conventional cylinder forming step of FIGURE 3b.
It is thus the essence of my invention to provide an improvement in manufacturing cylindrical metal containers which permits the permanent application of ears to the rec tilinear sheet in a flat state in a manner which permits the cylinder of the can body to be subsequently formed in an -g_ v~~-~5~s-.~.
~_~~~~~&'~.
accurate manner and without distorting the straightness o~
the width edges of the rectilinear sheet.
_~0_

Claims (5)

1. An improved method for forming a metal cylindrical container for paint and the lake from a stock of tin coated sheet metal cut into a plurality of flat rectilinear sheets, each sheet having a pair of length edges approximately equal to the diameter of said container and a pair of width edges approximately equal to the height of said container. The improvement comprising the steps of:
a) providing two bale ears for each sheet, each ear having a cup shaped body, said body having a base portion with an opening therein for receiving a ware bale and a cir-cular rim portion, each ear having a pair of diametrically opposed generally rectilinear tabs extending from said rim;
b) positioning a pair of ears at discrete points on a flat sheet, each ear orientated so that its tabs are gener-ally perpendicular to said length edges and generally paral-lel to said width edges;
c) resistance welding said tabs to said sheet at said position;
d) rolling said sheet about said length edges into a cylinder with one of said width edges overlapping the other width edge; and e) seaming said width edges.

2. The method of claim 1 wherein said one width edge does not overlap more than about 0.5 mm the other width edge in said rolling step and said seaming step comprises contin-uously resistance welding said overlapped width edge to the rolled cylindrical body.

3. The method of claim 2 wherein said tabs are resis-tance welded to said flat stock at a rate of 250 pairs of tabs/minute.

4. The method of claim 3 wherein the width of said rectilinear tabs equal 25% of the diameter of said rim and the centerline of said tabs of one ear relative to the other ear equals the diametrical distance of the rolled can body.

5. The method of claim 4 wherein said container is a one gallon paint container, and the gauge of said stock is between 75% and 90%.