US 3483355 A
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Description (OCR text may contain errors)
Dec. 9, 1969 .R. w MURDOC'K WELDING 2 Sheets-Sheet 1 Original Filed Sept. 29, 1965 INVENTOR ROBERT W. MURDOCK Qua;
ATTORNEYS Dec. 9, 196 9 R. w. MURDOCK WELD I N6 2 Sheets-Sheet 2 Original Filed Sept. 29, 1965 INVENTOR ROBERT MURDOCK ATTORNEYS United States Patent US. Cl. 219-137 2 Claims ABSTRACT OF THE DISCLOSURE Opening tabs are welded to an end portion of a tear strip of a metal can lid by a drawn arc welding method. The opening tabs preferably are welded close to an edge of the tear strip to enable the lid to be opened more easily.
This application is a division of my application, Ser. No. 491,154, filed Sept. 29, 1965, and allowed Apr. 19, 1967, now Patent No. 3,339,790.
This invention relates to lids for containers such as tin cans and more particularly 0t such lids with opening tabs welded thereto.
Containers, particularly cans for food and drink, frequently are now made with tabs affixed thereto by means of which the cans are opened by hand without the requirement of a can opener. Heretofore, the tab has commonly been affixed to the lid by forming a hole in the tab and by forming an upwardly-extending projection on the lid. The projection was then inserted through the opening and peened over to rivet the tab to the lid, the rivet being a structurally integral part of the lid. This technique of affixing the tab has had several disadvantages. The method of attachment has been relatively slow and has been limited to the use of certain metals, particularly aluminum, for the can lid, since the metal has had to be highly ductile in order for the rivet projection to be formed therein. Furthermore, the can lids have been somewhat difiicult to open with this type of tab because, as will be more apparent later, the tab has had to be located centrally with respect to a starting end of the opening strip scored in the top of the can. This meant that a large part of the scored line separated all at once as the tab was lifted, requiring considerable extra force for the initial opening step.
The present invention provides a new lid and opening tab in which the tab is welded to the lid to enable the tab to be attached rapidly and inexpensively. The lid also can be made of other metal than aluminum since the ductility of the metal is not important. Further, with the new tab and the welding technique, the tab can be attached to the lid in an off-center position adjacent the score line thereon so that only a small portion of the score line is initially parted, requiring a minimum of force.
It is, therefore, a principal object of the invention to provide a method for attaching an opening tab to a can lid more rapidly and inexpensively than heretofore.
Another object of the invention is to provide an attachment for an opening tab and can lid which does not require that the lid be made of soft, ductile metal.
Still another object of the invention is to provide a can lid with an opening tab afiixed thereto in a position which enables the lid to be opened with much less force than heretofore required.
Numerous other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment thereof, reference being made to the accompanying drawings, in which:
3,483,355 Patented Dec. 9, 1969 lCC FIG. 1 is a plan view of a scored can lid, prior to being assembled with a can, and an opening tab afiixed to the lid in accordance with the invention;
FIG. 2 is a somewhat enlarged view in transverse cross section taken along the line 22 of FIG. 1;
FIG. 3 is a further enlarged view in vertical cross section taken along the line 33 of FIG. 2;
FIG. 4 is a greatly enlarged, fragmentary view of a portion of the lid and a portion of the opening tab, showing the position of attachment of the tab to the lid;
FIG. 5 is a fragmentary view in vertical cross section similar to FIG. 2 but showing the opening tab and lid in a partly opened position;
FIG. 6 is a fragmentary plan view of the can lid with the tab pulled farther than in FIG. 5 to open the lid further;
FIG. 7 is a partly schematic view in perspective of apparatus for aflixing the tab to the lid;
FIG. 8 is a view in vertical cross section of a welding tool of the apparatus shown in FIG. 7;
FIG. 9 is a view in perspective of a chuck of the welding tool; and
FIG. 10 is a wiring diagram of an electrical source and controls for the welding tool.
As shown in FIGS. 1-6, a can lid capable of being opened withon a can opener is indicated at 10 and includes a rim 12 by means of which the lid can be connected to a can body 14 in a conventional manner, as shown in FIG. 2. The manner in which the lid is connected to the body is not part of the invention and the rim 12 can be of the usual design, although preferably being slightly higher. The lid 10 has an opening strip 16 of spiral configuration, in this instance, which includes a terminal portion 18, a peripheral portion 20 adjacent the rim 12, and an inwardly-extending starting portion '22 terminating in a rounded initiating or leading edge 24. The opening strip 16 is defined by a score line 26 which extends partly through the thickness of the metal of the lid 10 to enable it to be more easily separated. A reinforcing rib 28 also is of spiral configuration and lies adjacent the opening strip 16, separating it from a central portion 30 of the lid. The reinforcing rib 28 stilfens the central portion 30 and reduces its tendency to bend as the strip is pulled and bent outwardly.
An opening tab 32 is afiixed to the lid 10 by being welded to the inwardly-extending portion 22 near the edge 24, as will be discussed in detail subsequently. In the specific form shown, the tab 32 is of sheet metal from 0.011 to 0.017 inch in thickness and preferably from 0.012 to 0.015 inch. It has been found that thinner stock will bend too easily when the lid is opened and possibly even burn through at the weld, whereas thicker stock is unnecessary and increases the overall cost of the lid. As shown particularly in FIG. 1, the tab 32 has a squared free end 34 and a tapered fastened end 36 terminating in a short edge 38. The length of the short edge 38 preferably is substantially no greater than the width of the inwardly-extending portion 22 of the strip 16, over which the edge 3-8 of the tab is positioned. Particularly, the end 36 is tapered to space the edge 38 from the reinforcing rib 28, eliminating the corner which might otherwise contact or almost contact the rib 28 and cause arcing therebetween rather than at the desired point of attachment.
Reinforcing ridges 40 extend longitudinally of the tab '32 near side edges 42 and should extend at least to positions transverse to a portion of an attaching dimple or projection 44 to prevent bending of the tab as it is pulled upwardly. The dimple 44 is located at the tapered end 36 of the tab 32 between the ridges 40 and near the short edge 38. The dimple 44 preferably is spaced slightly from the short edge 38 but can be tangential thereto or even intersect the edge slightly. The size of the dimple 44 is very important. As shown, the dimple or projection is generally arcuate in vertical cross section taken longitudinally of the tab and has a radius of from three-thirty-seconds inch to one-fourth inch. The dimple 44 also should extend downwardly below the plane of the main handle portion of the tab a distance of from one-thirty-second inch to one-fourth inch. The bottom of the dimple 44 can be slightly flattened if desired to provide a slightly broader base for the weld. The base should not be too large, however, since the larger size increases the area of attachment of the dimple to the lid and increases the chance for this area to incorrectly bridge the score line forming the leading edge 24. It is even more important that the dimple should not be too small in diameter or too sharp at the base since this will concentrate the Weld current excessively and cause the lid to be burned through at the point of attachment or at least destroy the protective coating on the metal at the lower surface thereof, thereby leaving the lid susceptible to attack by the contents of the can.
The dimple 44 preferably is attached to the inwardlyextending portion 22 of the strip at a small shaded area 46, as shown in FIG. 4. The area of attachment preferably is located adjacent the leading edge 24 and is outof-center or eccentric wtih respect to the geometric center of the edge 24, so as to be much closer to one portion of the edge than other portions. This is accomplished by locating the area 46 between the center of curvature designated C and the leading edge 24, with the area being preferably closed to the edge than the center C, but not so close, of course, as to overlap the edge 24 and partially contact the central portion 30 of the lid.
The leading edge of the strip 16 may be defined as any portion of the strip edge facing in a direction at least partially opposite to the direction in which the strip 16 is pulled, represented by an arrow P in FIG. 2, and extending transversely to this direction. Ideally, the area 46 should be near a portion of the edge which is perpendicular to the direction P. While, with the rounded edge 24, the preferable position of the area 46 is symmetrical with respect thereto, the area can be located to one side or the other of this position, as indicated by the dotted areas designated 46'. Whether the edge 24 is arcuate, triangular, square, or whatever, the area 46 will be satisfactorily positioned if the portion of the edge to which it is the closest is a leading edge as defined above. As noted in FIG. 4, even the extreme two dotted areas 46' from the direction P and transversely to this direction.
With this positioning, whenever the tab 32 is raised, a relatively concentrated force will be applied to that part of the score line representing the edge 24 adjacent the area 46 or 46' and thus initiate separation of the score line at a very small portion thereof. In contrast, with the integral rivet type of tab connection heretofore employed, the rivet had to be located at the center of the edge 24 in order not to rupture or separate the score line as the rivet projection was being formed. Consequently, when the tab was subsequently lifted, substantially the entire leading edge 24 around the periphery separated at once with a definite popping sound and with considerable force being required. The large initial force also was needed because the parting was accomplished under tension rather than shear. By separating only a small portion of the score line at a time by shearing, the force required to initiate the opening of the lidis a fraction of the force heretofore required.
Apparatus for welding the tabs to the lids is shown in FIGS. 7 and 8. In this instance, the lids 10 are supported and aligned by a guide 48 beneath a welding tool 50 which is moved toward and away from the lids 10 by a hydraulic cylinder 52. The cylinder 52 is of the double-acting type, moving the tool 50 toward the lid 10 when fluid is supplied under pressure to an upper line 54, and moving the tool away from the lid when fluid under pressure is supplied to a lower line 56. As schematically shown in FIG. 7, the fluid can be supplied from a reservoir 58 through a pump 60 to one of the lines 54 and 56 by an electrically controlled four-way valve 62. When fluid is supplied through one of the lines, it is returned through the other of the lines to the reservoir 58. In this instance, when the valve 62 is not energized, the fluid under pressure supplied to the line 56 so as to position the tool 50' above the lid to be welded.
The tool 50 includes a magnetic chuck 64 consisting of a plurality of concentric rings 66 and 68 as shown in FIG. 9 with the lower surface of the chuck having a recess 70 of a contour to receive the tab 32. The tab can be quickly assembled with the chuck 64 by being slipped into the recess 70 With the tapered end forward. In this manner, the tabs can be welded at a relatively high rate of speed because of the quick loading made possible by the magnetic chuck. After the tab is welded to the lid, and the tool 50 is raised, the tab is automatically separated from the chuck 64, the lid and affixed tab being held down by a suitable electrical contact 65.
The chuck 64 is atfixed to a connecting leg 72 which is electrically connected to a cable clamp 74 to which a welding cable 76 is affixed. The cable clamp 74 is connected to a movable core 78 which extends into a lifting coil 80. When the coil 80 is energized, it pulls in the core 78 against a stop 82, and when the coil is de-energized, a plunge spring 84 moves the clamp 74 downwardly until the tab 32 engages the lid 10, with the Welding are preferably applied between the tab and the lid durin the plunge stroke. The welding current establishes a molten pool of metal at the extremity of the dimple 44 and at the closest portion of the lid 10 with the molten metal joining the two pieces when they are placed in contact under pressure at the end of the plunge stroke.
The operation of the tool 50 and the ram 52 can be controlled with a circuitry shown in FIG. 10. Accordingly, a source of direct current is established between leads 86 and 88. When a manually-controlled operating trigger 90 is closed, power is supplied to a coil 92 of the four-way valve 62 to cause the cylinder 52 to move the tool 50 downwardly until the tab carried by the chuck 64 moves into contact with the lid 10; specifically, the dimple 44 engages the inwardly-extending portion 22 of the strip. When this occurs, a circuit is established through a control relay 94. This causes normally-open contacts 941 to close and complete a circuit through the lifting coil 80, thereby retracting the tab from the lid. The relay 94 can be held in during the welding cycle by a capacitor 95, positioned thereacross. At the same time, a pilot arc is established between the tab dimple and the lid by the closing of normally-open contacts 94-2 which establishes a circuit through a resistance 96 across a main capacitor 98.
The control relay 94 has a third set of normally-open contacts 94-3 located in series with a contactor 100 which is energized when the contacts 94-3 are closed. The contactor 100 then closes heavy contacts 100-1 thereby to establish a main welding are through an impedance 102 and across the tab and lid to form the molten pools of metal thereon. This arc is established by the capacitor 98, which arc is of short duration and effects a weld without destroying any protective coating on the underside of the lid. At approximately the time the main welding arc is established, contacts 100-2 in series with the coil 80 open to de-energize the coil 80 and enable the plunge spring 84 to move the tab toward the lid and complete the weld. The relay 94 is subequently de-ener gized, when the trigger 90 -is released and the capacitor is discharged, to open its corresponding contacts, deenergize the contactor 100, and return the welding circuitry to its original condition. At this time, the capacitor 98 is recharged to a predetermined voltage by a voltage regulation circuit designated VR, as discussed more fully in Glorioso Patent 3,136,880, for example.
When the trigger 90 is released, the tool 50 is raised and the tab separates from the magnetic chuck 64, remaining with the lid 10. A new tab can then be inserted quickly into the recess 70 of the chuck 64 and a new lid positioned therebelow. An extremely rapid attaching operation is thereby effected which can be made even faster by the use of suitable automated feeding devices.
From the above, it will be appreciated that a fast and inexpensive method has been achieved by the use of the invention for attaching opening tabs to can lids. The particular attachment of the tab requires no special metals and also enables the lid to be opened much more easily than heretofore.
Various modifications of the above described embodiment of the invention will be apparent to those skilled in the art, and it is to be understood that such modifications can be made without departing from the scope of the appended claims.
1. A method for attaching an opening tab having a projection thereon to a can lid having an opening strip provided with an opening end, said method comprising holding the tab in a predetermined position spaced from said lid and parallel thereto with the tab projection facing said lid and positioned opposite said opening end, moving said tab toward said lid until said projection contacts said opening end, retracting said tab from said pilot are between said projection and said opening end, moving said tab toward said lid after a predetermined period, initiating a main welding are between said projection and said lid, and subsequently contacting a portion of said opening end to complete a weld therebetween, said portion of said opening end being positioned closer to one edge portion of said opening end than the remainder of the edge, whereby when said tab is raised to shear said end portion from the remainder of the lid, the shearing force will be initially concentrated at one small part of said edge and then progress over the remainder of the edge.
2. A method according to claim 1 wherein said opening end has a rounded leading edge and said tab is engaged with a portion of said opening end closer to said edge than to the center of curvature of said rounded leading edge.
References Cited UNITED STATES PATENTS 2,779,859 1/1957 Shoup et al. 219-98 3,136,880 6/1964 Glorioso 21998 3,319,039 5/1967 Glorioso 21998 JOSEPH V. TRUHE, Primary Examiner C. L. ALBRITTON, Assistant Examiner U.S. Cl. X.R.
lid a predetermined distance, simultaneously drawing a 2Z054