Method of interconnecting two sheets of deformable material

Aug. 3, 1965

E. C. FRAZE

3,198,155

METHOD OF INTERCONNECTING TWO SHEETS OF DEFORMABLE MATERIAL

Filed March 2, 1964 4 Sheets-Sheet 1

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Aug. 3, 1965

E. C. FRAZE

3,198,155

METHOD OF INTERCONNECTING TWO SHEETS OF DEFORMABLE MATERIAL

Filed March 2. 1964

Sheets-Sheet ?.

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Aug. 3, 1965

E. C. FRAZE

3,198,155

METHOD OF INTERCONNECTING TWO SHEETS OF DEFORMABLE MATERIAL

Filed March 2, 1964

Sheets-Sheet δ

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Aug. 3, 1965

E. C. FRAZE

3,198,155

METHOD OF INTERCONNECTING TWO SHEETS OF DEFORMABLE MATERIAL

Filed March 2. 1964

Sheets-Sheet 4

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3,198,155

Patented Aug. 3, 1965

United States Patent Office

198 155

METHOD OF INTERCONNECTING TWO SHEETS OF DEFORMABLE MATERIAL

Ermal C. Fraze, 355 W. Stroop Road, Dayton, Ohio Filed Mar. 2,1964, Ser. No. 348,712

Claims. (CI. 113—121)

This invention relates to containers having tear strips adapted to be manually removed for access to the contents of the containers, and more particularly pertains to the structure of the joint between a tab and a tear strip, the joint being of sufficient strength to permit the tab to function as a lever for initiation severance of the tear strip.

It is common practice to attach a tab to a tear strip of a container by providing an aperture in the tab, forming a hollow rivet in the tear strip, inserting the hollow rivet into the aperture, and then expanding or heading the hollow rivet into overlapping engagement with the tab. It has been suggested, moreover, that instead of forming an aperture in the tab, the tab as well as the tear strip may be formed with a suitably dimensioned hollow rivet and the two hollow rivets may then be telescoped together and headed or expanded to anchor the tab to the tear strip.

This last construction is advantageous because the bond between two telescoped hollow rivets is more tenacious than the bond between an apertured tab and a hollow rivet. Another advantage is that the two telescoped hollow rivets reinforce each other.

The problem is to fabricate such a joint of telescoping rivet elements efficiently and economically without rupturing the metal wall of the container. The difficulty is that the initial distortion of the sheet metal to form the two hollow rivets strains the two metal sheets to such extent that subsequently heading the telescoped hollow rivets by the usual procedure of axial compression is too drastic and causes the metal to crack and break.

If an attempt is made to expand or head the two telescoped hollow rivets simultaneously by squeezing the double layer end wall across its thickness dimension by conventional flat faced dies, another difficulty arises in that the transverse end wall of the innermost telescoped hollow rivet is confined by the outer hollow rivet to interfere with radial expansion of the transverse end wall. Upon investigation, it is found that the squeezing action thins both of the two transverse end walls with consequent radial expansion of the two end walls by extrusion, nevertheless, the radial expansion of the outer end wall is not adequate to prevent hinderence of radial expansion of the inner end wall.

The invention meets this difficulty by using a convex outer die to exert the squeezing pressure against the outer transverse end wall of the double layer hollow rivet. It has been found that if the working face of the cooperating inner die that is inserted into the telescoped rivets to act on the inner transverse end wall is more nearly flat than the working face of the outer die, a differential radial flow occurs in which the metal of the outer transverse end wall extrudes radially further than the metal of the inner transverse end wall and, of equal importance, the radial extrusion of the outer transverse end wail is initiated in advance of the expansion of the inner transverse end wall. In the preferred practice of the invention, both the die faces are of curved convex configuration but the outer die face has the shorter radius of curvature to produce the desired effect.

The preferred practice of the invention is further characterized by first forming dimples of relatively large area in the two sheet metal parts and then transforming the dimples into the desired steep shouldered bosses or hollow rivets. The advantage of this procedure is that it crowds metal into the area of a hollow rivet and thus makes the walls of the hollow rivet thicker than would otherwise be possible. The increased thickness of the walls of the two telescoped hollow rivets provides more metal for the operation of radial extrusion of the two transverse end walls and, in addition, reduces the susceptibility of the hollow rivets to cracking.

To achieve a highly effective joint it is essential that the two hollow rivets be dimensioned for snug telescoping fit and therefore the two bosses must be of accurate dimension relative to each other. Care is necessary to avoid, on the one hand, too loose fit by the two bosses and, on the other hand, such a tight fit as to make it difficult to telescope the two bosses together in preparation for the final heading operation.

A feature of one practice of the invention is the concept of placing the two sheet metal parts together face to face and applying dies to the double layer assembly to form both bosses or hollow rivets simultaneously in nested or telescoped relation. This procedure not only assures snugger fit between the two bosses than is otherwise possible but also eliminates the step of inserting one boss into the other and thus reduces the cost of fabrication.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a plan view of the metal end wall of the can showing a dimple formed therein in preparation for forming the desired hollow rivet;

FIG. 2 is a fragmentary section along the line 2—2 of FIG. 1 showing the cross-sectional configuration of the dimple and also showing how dies may be employed to form the dimple;

FIG. 3 is a view similar to FIG. 1 showing the hollow rivet that is produced for suitably transforming the dimple;

FIG. 4 is a fragmentary cross-section along the line 4—4 of FIG. 3 and also showing how dies may be used to transform the dimple into the hollow rivet;

FIG. 5 is a fragmentary sectional view on an enlarged scale showing a steep shouldered boss or hollow rivet formed in the metal wall of the can and further showing a similar steep shouldered boss or hollow rivet formed in a tab to telescope over the first boss or hollow rivet;

FIG. 6 is a greatly enlarged sectional view showing the two hollow rivets of FIG. 5 telescoped together and further showing how a pair of dies may be positioned to head the hollow rivet by radial extrusion by the metal of the two transverse end walls of the telescoped hollow rivets;

FIG. 7 is a view similar to FIG. 6 showing the completion of the extrusion operation;

FIG. 8 is a plan view of the can top, the fabrication of which includes the steps illustrated by FIGS. 5, 6 and 7;

FIG. 9 is a sectional view along the angular line 9—9 of FIG. 8;

FIG. 10 is a greatly enlarged fragmentary cross-section showing how the scoring may be on the outer surface of the can top;

FIG. 11 is a similar view showing how the scoring may be on the inner side of the can top;

FIGS. 12 and 13 are sectional views showing how a double layer hollow rivet projection outwardly of a can top may be formed by die means;

FIG. 14 is a sectional view illustrating the step of heading or expanding the double layer rivet;

FIGS. 15 and 16 are sectional views showing how die means may be formed to employ a double layer hollow rivet that projects inwardly of the can top; and

FIG. 17 is a sectional view illustrating the operation of expanding or heading the inwardly projecting double layer rivet.

:,155 ' 4 :

placement or extrusion of the metal of the two end walls with consequent radial expansion of the two end walls to form a circumferential double layer bead 52 in the double layer hollow rivet. It is apparent that when the double . layer hollow rivet is expanded or headed in this manner, the two sheets of metal are positively interlocked to form a joint capable of withstanding high stresses.

It is to be noted that in the operation of heading the double layer hollow rivet the greater curvature of the upper die causes the radial displacement of the metal of the outer transverse end'wall 42 to occur promptly and to extend further than the radial displacement of the metal of the inner end wall 36. Thus the greater curvature of the upper die 44 keeps the outer hollow rivet 40 from interfering with the. desired radial expansion of the transverse end wall 36 of the inner hollow rivet 24.

FIGS. 8 and 9 show the completely fabricated can top. In the usual manner the can top is appropriately formed in preparation for the joining of the can top to a sheet metal cylinder that is to form the body of the can. For this purpose the can top 20 is offset to form a circumferential groove 54 and a curved peripheral flange 55. . The tab 38 is formed with an upwardly inclined flange 56 at its free end and is further formed with a central longitudinal rib 58 and two longitudinal side ribs 60, the purpose of the ribs being to make the tab sufficiently rigid for it: to function effectively as a second-class lever for initiating the severance of a tear strip 62 in which the inner hollow rivet 24. is formed. . The tear strip 62 is defined by a continuous scored line 64 and the scoring may be on the outer surf ace. of the can top as indicated in FIG. 10 or on the inner surface of the can top as indicated in FIG. 11. Usually it is desirable to score an aluminum can top from the outer side and to score a steel can top from the inner side.

It is to be noted in FIG. 8 that the tab 38 is at an acute angle relative to the tear strip 62 and it is to be further noted that the fulcrum end of the tab 38 is tapered to provide a rearwardly inclined edge 65 that is at an acute angle relative to the longitudinal axis of the tab. When the free end of the tab is lifted to carry out the lever action, the tab fulcrums on the inclined edge 65 and is thereby guided in an arcuate path which, defines a portion of a cone that is concentric to the fulcrum edge. The described arrangement is inherently conducive to a leverage operation which is natural for the user because it conforms to a natural twist or rolling of the user’s wrist.

FIGS. 12 to 14 illustrate a practice of the invention which omits the preliminary formation of dimples in preparation for the production of the hollow rivets and which is characterized by the further concept of operating on both of the sheet metal parts simultaneously to produce the two hollow rivets simultaneously with the two hollow rivets nested, or telescoped together.

FIG. 12 shows how a double layer assembly comprising a can top 2@a and a tab 38α may be positioned between an upper die 70 and a lower die 72, which two dies are of the general character of the previously described dies 30 and 34. The upper die 70 has a cavity 74 of greater depth than the height of the desired double layer hollow rivet and is further formed with a vent passage 75. The lower die 72 has a projection 76 dimensioned to fill the cavity , of the desired double layer hollow rivet.

The two dies 70 and 72 are moved close together as shown in FIG. 13 to form the desired double layer hollow rivet, generally designated 78. Here again the cavity 74 is of ample cross sectional dimension to minimize the drawing action on the side walls of the double layer hollow rivet.

FIG. 14 shows in a simplified manner how the double layer hollow rivet 78 is expanded or headed by the corporation of an upper die 80 with a lower die 82. The lower die 82 has a projection or boss 84 which fills the interior of: the double layer hollow rivet in contact with ’ the double layer transverse end wall to keep the double

3,1

In the first practice of the invention illustrated by FIGS. 1 to 7, hollow rivets are formed separately in a can top and in a tab respectively and in each instance the hollow rivet is produced by first forming a dimple of larger area than the desired hollow rivet and then transforming the dimple into the hollow rivet. Thereafter the two hollow rivets are telescoped together to form a double layer hollow rivet and the double layer hollow rivet is expanded or headed by squeezing the double layer transverse end wall of the hollow rivet to cause radial extrusion of the io metal.

FIG. 1 shows a conventional sheet metal top 20 for a can that is intended to contain a beverage, the can top being made of a suitable material such as aluminum or steel. A dimple 22 of generally conical configuration and 15 of relatively large area is formed in the can top 20 and is subsequently transformed into a hollow rivet that is generally designated 24 in.FIG, 3, the hollow rivet being of substantially smaller area than the dimple.

FIG. 2 indicates the general manner in which the dimple 29 22 is formed. The can top 20 is placed between an. upper annular die 25 and a lower male die 26, the upper die having a central cavity 28. that is of substantially greater .. axial depth than the height of the required dimple. The lower die 26 has a conical leading face of the configura- 25 tion of the desired dimple and offsets the can top into the cavity 28 with the metal of the can top free to slide radially inwardly into the die cavity. In such a die operation the dimple is formed with no significant thinning of the sheet metal. 30

After the dimple is formed, the hollow rivet 24 is formed by die means of the general character shown in FIG. 4. The upper die 30 in FIG. 4 has a cavity 32 of the overall area of the desired hollow rivet and of substantially greater depth than the height of the desired 35 hollow rivet. The lower die 34 is formed with a projection 3.5 that is of the area and depth of the interior of the desired hollow rivet. The upper cavity 32 is dimensioned with liberal tolerance in cross sectional area to minimize drawing action on the sheet metal and consequent thinning 4ft of the side walls of the hollow rivet. When the two dies 30 and 34 close the metal of the area of the dimple 22 is crowded radially inwardly with a thickening effect on the walls of the hollow rivet 24, and by virtue of the depth of the upper die cavity 32 there is minimum thinning 45 effect on the transverse end wall 36 of the hollow rivet.

A tab, generally designated 38 in FIG. 5, is processed in the same manner to form therein a hollow, rivet, generally designated 40, with a transverse end wall 42, this second hollow rivet being dimensioned to telescope snugly 50 over the first hollow rivet 24 in the can top 20. FIG. 5 shows the two hollow rivets 24 and 40 aligned to telescope together and FIG. 6 shows the two hollow rivets telescoped together.

FIG. 6 shows the two telescoped hollow rivets 24 and 55 4® positioned between an upper die 44 and a lower die 45 in preparation for the final heading operation. The lower die has a projection 46 dimensioned, to fully, occupy the interior of the inner hollow rivet 24 and thus support the double layer hollow rivet from the interior to prevent axial. 60 compression of the hollow rivet. The upper die 44 which preferably serves as an impact member has a leading face 48 of arcuate convex configuration. The leading face 50 of the lower die 45 may be flat but preferably is also of arcuate convex configuration. The radius of curvature 65 of the upper die face 48 must be appreciably less than the radius of curvature of the lower die face 5®. As heretofore explained, the shaper curvature of the leading face 48 of the upper die 44 produces a more pronounced radial displacement effect on the metal of the. upper or outer 7 transverse end wall 42 than is produced on the metal of the lower: or inner transverse end wall 36.

FIG. 7 shows how the two dies 44 and 45 are brought close together to squeeze the two transverse end walls 36 and 42 across their thickness and thus cause radial dis- ⁷

3,198,155 layer hollow rivet from being subjected to axial compression. In accord with the teaching of the invention the upper die 80 has a leading face 85 that is of sharper curvature than the leading face 8fi of the lower die.

FIGS. 15 and 17 show how the same procedure illustrated by FIGS. 12 to 14 may be employed to form a double layer rivet that projects inwardly of the can top.

FIG. 15 shows a tab 38b imposed on a can top 20Z&gt; and shows how an upper die 72 may cooperate with a lower die 70 to form the double layer hollow rivet §8 shown in FIG. 16. The upper die 72 in FIG. 15 is the same as the lower die 72 in FIG. 12 and the lower die 70 in FIG. 15 is the same as the upper die 70 in FIG. 12. FIG. 16 shows the hollow rivet completely formed and FIG. 17 shows how the hollow rivet may be headed or expanded in the previously described manner. In FIG. 17 the upper die 82 is the same as the lower die 82 in FIG. 14 and the lower die 80 in FIG. 17 is the same as the upper die 80 in FIG. 14.

My description in specific detail of the selected embodiments of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.