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EASY OPEN CAN END
BACKGROUND OF THE INVENTION
It has been known for some time in the prior art to provide can ends which can be opened without use of a can opener or other tool. For some years, the most popular can ends of this type were those in which a ring was provided for finger insertion, which when pulled io removed a section of the can end along score lines. The ring tab and the removed section of the end were then discarded. This was undersirable for a variety of reasons perhaps chiefly those of unsightly litter; and so a new type of can end was developed which could be opened 15 without the use of tools, but which did not result in any of the components of the can end becoming detached from the can.
Typically in the prior art, such can ends and tabs were both made of aluminum. However, with the well 20 known recent rise in cost of electrical power, aluminum has become a disfavored material for applications where steel can be used, inasmuch as aluminum is, in general, made by electric refining processes which con- 25 sume enormous quantities of electricity. Therefore, wherever possible, it is desired to substitute steel for aluminum.
In the can end making art, however, steel has been a disfavored material for a number of reasons, chief 30 among those being corrosion. Although steel is preferred for reasons of economy and for certain reasons of ease of manufacture which will be discussed in more detail below, steel has not been a preferred material for tab ends. The present invention involves a steel for tabs 35 coated with a metal chosen to reduce corrosion by means of sacrificial oxidation. It has been found by the applicant that if a steel tab is coated with a material having a higher electronegative potential, that material ^ will be attacked in preference to the steel and if the material is so chosen that a certain amount of oxidation only is permitted, then the tab end will rapidly form its own protective corroded layer which will prevent any further corrosive attacks upon a tab end. 45
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a method whereby a can end can be provided with a tab which is less expensive than those found in the prior art. 50
A further object of the invention to provide such a tab end which can be made readily and economically without suffering any functional disadvantages compared to those in the prior art.
Still a further object of the invention is to provide a 55 tab end of steel which is not attacked by corrosion.
SUMMARY OF THE INVENTION
In accordance with the above needs of the art and the ^ objects of the invention, a can end is provided with a steel tab as an integral part of the can end. The tab is coated with a metal chosen so as to be preferentially corroded over the steel, and which is only corroded to a certain depth below its surface, thus providing a limi- 65 tation on the total amount of corrosion suffered by the tab end. In the preferred embodiment the coating mate- • rial is zinc; another possibility would be aluminum.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of the top of a can with a can end according to the invention attached.
FIG. 2 shows a top view of such a can end.
FIG. 3 shows a cross-section at an enlarged scale of such can end.
FIG. 4 shows a detail of the anti-corrosive coating applied to the tab.
FIGS. 5A to 5F and 6A to 6F show a sequence of stages in the formation of the tab of the invention.
FIG. 7 shows a partial sequence of operations according to another embodiment of a process for making the tab of the invention.
FIGS. 8,9,10 and 11 show other embodiments of can ends which can be made according to the invention.
FIGS. 12 through 15 are photomicrographs showing the details of the coating.
DESCRIPTION OF THE PREFERRED
Understanding of the can end of the invention and the method of making it will be better understood by reference to the figures appended hereto. Referring now to FIG. 1, a can 10 is shown provided with an end 11 having attached thereto a tab 12 and having marked thereon a segment 13 of the end 11 which, upon elevation of the end of tab 12 by a consumer of the contents of the can 11, is adapted to pivot into the interior of the can 11, thus opening the can 11. Referring now to FIGS. 2 and 3, the method of operation of the can end of the invention will be described in detail. In these figures, the can end 11 is shown in FIG. 2 in an elevation, and FIG. 3 in a partial cross-section. It will be observed that the tab 12 is attached to the can end 11 by means of a rivet 14 integrally formed from the material of the can end 11. Upon the insertion of the user's finger under rounded end 15 of the tab 12, the tab 12 tends to pivot about the shortest part of its junction with a hinge member 17. As will be discussed in further detail hereinafter, the hinge member 17 is formed integrally with the tab 12, but is cut therefrom nearly entirely around its circumference, so as to provide a hinging section about which the tab 12 can pivot. When the tab 12 pivots about this hinge member 17, as shown in phantom in FIG. 3, extension portion 16 exerts a downward force on the openable section 13 of the can end 11, thus forcing this section 13 into the interior of the can 10, thus providing an opening through which the contents of the can 10 may be withdrawn. In order that the openable section 13 is not detached from the can end 11 during this operation, it is provided with a score line which runs most of the way around its circumference, but not entirely. Thus, when a force is applied to it by the extension 16 by the application of pressure by the user at 15, the openable portion 13 is detached along the scoreline 18 and pivots about the unscored section of its circumference by which it remains attached to the can end 11.
Up to this point, the description in this preferred embodiments of the invention section of this specification has been of material which is all in the prior art. However, no mention has yet been made of materials used to make can ends and tabs, which applicant has discovered to be of cardinal importance. In particular, the prior art cans and tabs have all been made of aluminum material which, while reasonably well suited to the purpose, is expensive due to the large quantities of electricity required for its refinement. Therefore, and as
suggested above, it is desirable to replace as much of the aluminum as possible with some less expensive material such as steel.
It would be desirable, of course, to make the entire can end 11 of steel; however, it turns out that it is not 5 possible to score steel, for example, around the periphery of operable portion 13 along line 18, due to the high tensile strength and ductility of the low cost steel which is sought to be used in this sort of application. The applicant has found, however, that the tab can possibly 10 be made of steel if and only if it is coated with a material which will prevent it from being corroded. It is found that steel is corroded particularly readily when in intimate contact with aluminum, as is the case here. Therefore, good corrosion prevention is particularly impor- 15 tant. Moreover, steel has other than economic advantages over aluminum in this application because the portion of the tab which connects the protrusion 16 and the handle 15 with hinge member 17 about which the tab pivots is far tougher when made of steel than it 20 would be when made of aluminum. This increased toughness eliminates breakage of this hinge section which can, when the tab is of aluminum, be a problem; that is, the tab can break off without opening portion 13 of the can, which is clearly undesirable. The constraint 25 on one seeking to make a steel tab for a beverage can is that it must be of a steel which will withstand exposure to a variety of contaminants and which, under such circumstances, will not be corroded. The applicant has found that this objective can be satisfied by manufactur- 30 ing the tab of a steel which is coated with a material which will be corroded in preference to the steel, and which has only surface corrosion properties so that once the surface is corroded by exposure to various reactant materials, corrosion will stop. By comparison, 35 it is well known that steel corrodes from the inside of a mass thereof rather than simply on the surface so that, for example, a piece of solid steel can rust through. On the contrary, a mass of, for example, aluminum is corroded only on the surface and only in a very thin layer, 40 so that once the layer has formed, no further corrosion is possible.
It will be clear to those skilled in the art that manufacturing the tab out of steel coated with a corrosion preventive material will be effective as to those surfaces of 45 the steel which are exposed when the coating is applied to the steel. However, if tabs are sheared or stamped from a sheet of steel after having been coated, it would appear that the edges of the stamped tab would not be covered with the coating, and therefore would be liable 50 to corrosion. Applicant has found, however, that if the stamping operation is properly designed and operated, the coating can be made to cover a considerable fraction of the edge of the tab, thus preventing corrosion from attacking the tab at any point. 55
Referring now to FIG. 4, a section corresponding to that identified by the box labeled "4" in FIG. 3 is shown in greater detail. There, a section of tab 12 is shown abutting against can top 13. Can top 13 is of aluminum and tab 12 is formed from sheet of steel 21, which is 60 coated all around with a layer of corrosion-reducing metal 20. In this way, it can be assured that the tab will not be attacked by corrosion and will not contaminate any beverage or any other material contained within the can. 65
FIGS. 5A through 5F and 6A through 6F show corresponding stages in the manufacture of such tabs. FIGS. 5A through 5F show elevations, and 6A through
6F show cross-sections of the tab as it is formed and as marked in FIGS. 5A through 5F. Thus, FIGS. 5A and 6A show a steel strip 30 prior to any processing leading to the manufacture of such a can tab. FIG. 6B shows a cross-section of the strip after such coating where this strip 30 has now been covered with a layer of zinc 40. FIG. 5C shows the first stamping stage which may profitably be used to form the tab. There, the tab outline 32 is shown having been formed in the strip 30 resulting in a general outline of tab 12 having a hinged section 33. In FIG. 6C, it is shown how the tab 12 coated with a layer of zinc 40 is separated from the strip 30, also coated with a layer of zinc 40, by a gap 32 which defines the periphery of the tab. It will be observed that the coating 40 is shown as having been drawn into the gap 32. It has been found by applicant that this drawing operation is effected when the dies defining the gap 32 are not too tightly fitted; that is, if, for example, the strip is stamped into tabs by a vertical process where the strip is advanced horizontally through a press and a die descends vertically upon the strip, the zinc will not be drawn into the gap thus formed as well when the die fits tightly into the die cavity as it will when the die has a certain amount of clearance with the die cavity. In FIG. 5D, the next stage in the process of manufacture of the tab is shown. There, the gap 32 has become wider and better defined, due to the curvature of the section of the periphery of the tab as shown in FIG. 6D. Furthermore, the hinged section 33 has been better defined, and a rim 34 has been formed around the inner portion of the curved section of the periphery, again referring to FIG. 6D. In FIGS. 5E and 6E, the tab 12 is shown still further defined, the edge of the tab 35 has been tucked under, and the gap 32 has been widened considably. Throughout these stages, the tab 12 remains attached to the strip 30 by a tag at its left for ease of processing. Thus, the strip 30 with its coating 40 is shown along with tabs in FIGS. 50. In FIG. 5F, the tab is shown in a finished form. There, the rim of the tab 12 has been tucked under so as to provide a smooth surface for the user's finger; consequently, the gap 32 has widened still further. The rim around the hinge section of the tab 34 has been raised, and the tab has been finally detached from strip 30 by punching at strip 36. The tab thus made can be attached to a can lid by processes well known in the art where a rivet is integrally formed out of the can top 11 through a hole 39 punched in the hinged section of the tab as shown in FIG. 3.
FIG. 7 shows another process for making such a coated steel tab. There, a strip 30, FIG. 7A, is formed into a tab, FIG. 7B, as discussed above. However, in this case, strip 30 was not coated prior to formation of tab 12. Instead, after formation the tab is dipped into a bath of molten metal 13, FIG. 7C, thus coating all surfaces, edges as well as flat surface, with essentially a uniform layer of anti-corrosive coating.
FIGS. 8,9,10 and 11 show alternative embodiments of can ends wherein the invention is also useful. In the can end of FIG. 8, a tab 201 is provided with a ring 204 and attached to a can top 200 by means of a rivet 203. Around rivet 203 is a cut line 202 which extends entirely through the tab, but which is left with an uncut area 206. When the ring 204 is picked up by the consumer of the contents of the can, the tab pivots about this area 206, thus cutting loose the can top 200 from its rim 199 along score line 207 which extends all the way around the top of the can. Again, the entire tab 201 may be made of steel coated with a protective metal in accor