What is claimed is
1. A closure cap for application to a bottle or the like, said cap comprising: a top panel with a generally cylindrical skirt depending therefrom and terminating downwardly in a circular lowermost edge, at least that portion of said skirt which extends from a first plane below said panel to said edge being formed of sheet material of substantially uniform single thickness, said skirt portion being corrugated so as to define a circumferential series of straight outward ridges and straight flutes therebetween extending from said first plane to a second plane spaced from said edge, the crests of said ridges and the outer surface of said skirt from said second plane to said edge lying on a common substantially cylindrical surface.
2. The invention as defined in claim 1, said corrugated skirt portion being sized for constriction about external thread formations on the finish of a bottle so as to deform inward portions of said material along the lines of said flutes over and about portions of the thread formations and thereupon to form female thread elements in said skirt conforming to the external thread formations.
3. The invention as defined in claim 2, the depth of said flutes being approximately the same as the depth of the external thread formations, whereby, subsequent to said constriction, the outside diameter of said skirt across the major diameter of said thread elements will be substantially the same as the diameter of said cylinder.
4. The invention as defined in claim 3, the depth of said flutes being greater than the thickness of said material, whereby upon generally uniform said constriction of the entire said skirt below said first plane, the inside diameter of said skirt between said second plane and said edge will be not less than the major diameter of the external thread formations.
5. The invention as defined in claim 1, said skirt being weakened around a circle in a plane between said second plane and said edge.
6. The invention as defined in claim 5, said cap being adapted for application to a bottle having a downwardly facing external shoulder below the thread formations on the finish, said skirt being of such length that a lip portion thereof below said circle of weakening will extend below the shoulder when said cap is applied to the bottle, whereby said lip portion can be formed into engagement with the shoulder so as to form a tamper-proof closure for the bottle.
7. A twistably removable closure cap for engaging external thread formations on the finish of a bottle or the like, said cap comprising: a top panel and a generally cylindrical skirt depending therefrom and terminating downwardly in an edge, at least that portion of said skirt which extends from a first plane below said panel to said edge being formed of sheet material of substantially uniform single thickness, said skirt being corrugated so as to define straight outward ridges extending from said first plane to a second plane spaced from said edge, there being flutes between said ridges, portions of said skirt along the lines of said flutes being conformed to elements of the external thread formations so as to define female thread elements between said ridges, the crests of said ridges and a circumferential band of said skirt immediately downward of said second plane being elements of a hollow cylinder having an inside diameter not substantially less than the major diameter of the external thread formations, the other portions of said skirt below said first plane lying substantially within the outside diameter of said cylinder.
8. The invention as defined in claim 7, said ridge crests and the crests of said female thread elements being rounded, the outside diameter of said skirt across the major diameter of said female thread elements being substantially equal to the outside diameter of said cylinder, said ridges, said thread elements and said band thereby defining a grid around said skirt adapted to shield said edge and to afford a sure and comfortable finger grip for twisting said cap off and on said finish.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bottle cap of the press-on, twist-off type. More particularly, the cap of this invention is of the type adapted for formation of thread elements in the skirt upon application of the cap to the threaded finish of a bottle so as to secure the cap thereto.
2. The Prior Art
Crown caps have been generally used for beverage bottle closures. A crown cap has a corrugated skirt which is normally crimped under a collar or bead on the bottle neck. It has been proposed to apply a crown cap to a finish having external threads or thread formations to form a twist-off closure. However, the short, flared skirt of a typical crown cap does not afford sufficient thread engagement upon crimping to assure a secure closure with dependable twist characteristics. The sharp corrugation ridges and the undulated, projecting sharp edge do not afford a satisfactory grip for twisting the cap. The cap is often hard to turn and the user may cut his fingers on the edge. Reclosure is usually difficult and impractical.
It has also been proposed to provide a cap of the crown type with a protected edge. The lip of the cap may be curled, bent inwardly or otherwise formed to shield the edge when the cap is on the bottle. Such caps usually involve additional operations, additional material, or both, as compared with crown caps heretofore in more general use. Even the relatively small cost increases are a considerable disadvantage in a highly competitive market. Furthermore, there remains the difficulty of forming adequate threads in the corrugated skirt typical of crown caps.
Caps suitable for roll-on thread formation have been marketed. For this purpose, the cap is usually made of aluminum and is provided with a cylindrical skirt which slips over the bottle threads when the cap is pushed on. While the cap is held in sealing position against the bottle lip, threads are rolled in the skirt, the threaded finish constituting a die.
The material costs for the aluminum roll-on cap are generally rather high. It is not ordinarily feasible to use commercial tin plate or the like, because low cost varieties of such material do not have satisfactory thread-rolling characteristics. The thread rolling operation involves extra equipment and is generally slow, as compared to the usual crown crimping operation. Furthermore, thread rolling requires that most of the skirt be free of corrugations or other such reenforcement, so that the skirt tends to warp due to irregular stresses, fatigue and the like. Hence, the twist-torque and reclosure characteristics of the roll-on cap are often unsatisfactory. Reinforcing the skirt by means of beads, curls, pockets or similar formations involves special tooling, extra operations, or both, still further increasing the cost of manufacture.
SUMMARY OF THE INVENTION
The cap according to this invention is designed to overcome the several above-noted disadvantages of previously proposed caps, affording a dependable press-on, twist-off cap for beverage bottles and the like at a cost which compares favorably with that of regular crown caps.
The cap has a generally cylindrical skirt depending from a top panel. The skirt terminates downwardly in a circular edge. The skirt is formed from single-thickness sheet material and includes a corrugated portion whose length is about equal to the overall length of the threads on the finish. The circumferential series of corrugations define straight flutes and ridges, the crest elements of which constitute elements of a common cylinder. The ridges extend downward from a plane just below the top panel to a plane spaced from the edge. The lower skirt or lip, extending from the lower termini of the ridges to the edge, is a cylinder of substantially the same diameter as that of the ridge crest elements.
The root elements of the flutes lie on a cylinder sized for close telescopic fit over the external threads on the finish to which the cap is to be applied. The depth of the flutes is greater than the thickness of the skirt material and about equal to the depth of the finish threads. When the skirt is uniformly constricted about the thread formations, female thread elements are formed in the skirt by bending of material along the lines of the flutes, but otherwise the skirt maintains its generally cylindrical configuration. The flute depth being not less than the effective thread depth, the constricted lip will clear the crests of the finish threads when the cap is twisted off.
The cap according to this invention can be readily formed from sheet material in a single stroke of a double-acting punch press, using a simple blank-and-form die set. The cap configuration lends itself to use of light-gauge tin-free steel, minimizing stress cracking and spoliation of coating and decoration. The corrugations are more numerous than is usually feasible on crown caps. The closely spaced ridges provide a high degree of radial stiffness, minimizing buckling upon constriction, so that the skirt thread elements can be well-conformed to the finish thread formations, providing secure retention and minimal tendency to warping of the skirt. A greater lineage of thread engagement with given skirt length is obtainable than with the corrugations usually provided in standard crown caps.
After constriction, the outside diameter of the skirt across the major diameter of the thread elements is about the same as the diameter of the ridge crests and the subjacent smooth lip. The resultant surface constitutes a knurl grid which affords a sure and comfortable finger-grip for twisting the cap off and on the bottle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of a bottle cap according to this invention;
FIG. 2 is an enlarged, fragmentary elevational view similarly to FIG. 1, a portion of the cap being shown in vertical section taken through one of the corrugation ridges;
FIG. 3 is a fragmentary vertical sectional view similar to the sectional portion of FIG. 2, but taken through the root of one of the corrugation flutes;
FIG. 4 is a fragmentary horizontal sectional view taken on line 4--4 of FIG. 2, showing the corrugation contour;
FIG. 5 is a view similar to FIG. 4, showing a variant of the corrugation contour;
FIGS. 6 and 7 are views similar to the sectional views of FIGS. 2 and 3 respectively, but showing the cap applied to a bottle, preparatory to constriction of the skirt;
FIG. 8 is an elevational view of the cap applied to a bottle, after constriction of the skirt about the finish;
FIG. 9 is an enlarged fragmentary view similar to FIG. 8, partially in section, showing details of the skirt thread elements;
FIGS. 10, 11 and 12 are views similar to FIGS. 2, 3 and 9 respectively, showing a modified form of the cap.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, cap 10 is proportioned for application to thread formations on the finish of a bottle such as is used for carbonated beverages. Skirt 11 is generally cylindrical, terminating downwardly in a circular edge 12. The skirt 11 is sized to telescope closely over the finish and to be secured thereto by substantially uniform constriction of the skirt.
As seen in FIG. 2, cap 10 has a domed top panel 13, which is connected to skirt 11 by a radiused portion 14, which defines a seal recess, as subsequently seen. Skirt 11 is formed with a circumferential series of corrugations 15 defining outwardly projecting axial ridges 16 and flutes 17, extending from the bottom of portion 14 to lowermost termini 18 in a horizontal plane spaced from circular edge 12. The surface of lip 19, extending between the plane of flute termini 18 and edge 12, lies on a cylinder of substantially the same diameter as the cylinder on which lie the crest elements of ridges 16. As best seen in FIG. 3, the depth of flutes 17 is somewhat greater than the thickness of the material of skirt 11, the depth being about that of thread elements to be formed in the material along the lines of the flutes.
Referring to FIG. 4, the preferred corrugation pattern is characterized by ridges 16 somewhat narrower than flute width W. The cap may be made of 55 No. steel sheet. A cap of that material for a standard beverage bottle opening, preferably has about 40 corrugations. This corrugation pattern provides the radial stiffness and circumferential contractibility requisite to retention of the generally cylindrical configuration upon application of radially inward pressure uniformly around and along the skirt. The material indicated is substantially less costly than the 75-90No. tin plate in general use for conventional crown caps intended for the same service conditions as the cap here shown. The root material is conformed to the inner circle, providing a substantial lineage of material lying thereon. The material defining the flutes 17 being thus preformed, fairly high temper characteristic of double-reduced, light gauge material is feasible, requiring only moderate constrictive force to form thread elements therein. Less severe deformation is involved in forming thread elements along the lines of the flutes than is the case with typical crown cap corrugations.
FIG. 5 shows another corrugation pattern for the same size cap as that of FIG. 4. In the pattern of FIG. 5 the corrugations are generally sinusoidal, the flutes 217 having substantially the same radii as the ridges 216. This corrugation pattern provides generous radii at crests and roots which minimize malformation and tearing in the forming operation.
FIGS. 6 and 7 show cap 10 in position upon a bottle 20, preparatory to constriction of skirt 11 about the thread formations 21 on finish 23. A gasket or liner 24 extends along panel 13 and radius 14, so as to seal on top and around the side of lip 25, when cap 10 is pressed down. Flutes 17 are substantially coextensive with the axial extent of threads 21, the material of the skirt along the lines of the flutes closely opposing the crests of the threads. The ridges 16 and lip 19 are radially spaced from threads 21, the clearance corresponding to the depth of the flutes.
Cap 10 can be applied in a crowning machine of the type generally used for applying crown caps. Suitable tooling is indicated fragmentarily in phantom lines, comprising sealing punch 40, sleeve punch 50, squeeze die 60 and back-up ring 70. Die 60 is made of an elastomeric material, rubber for example. While cap 10 is held in the sealing position shown, by means of punch 40, punch 50 descends, compressing die 60 against ring 70. Die 60 deforms and exerts uniform inward radial pressure around and along skirt 11, constricting it about finish 23.
FIGS. 8 and 9 show the cap 10 after constriction of skirt 11, with female thread elements 22 formed therein upon constriction. As here shown, threads 21 comprise half-turn elements of a compound thread. The pitch is somewhat greater than the thread width at the pitch circle. This is a preferred form of threading, providing ample thread engagement, yet with wide roots to accommodate thread elements 27 formed by radially inward displacement of material along the lines of flutes 17 between threads 21. The coarse thread pitch will establish rather high localized bending stresses in the skirt material bearing along the crests of threads 21. This assures close conformation of the skirt material along the lines of flutes 17, across and about the threads 21, thereby creating a number of female thread elements 22 engaging elements of finish threads 21. The total pitch-line lineage of engagement is about equal to WxNxT, wherein W is the flute width (FIGS. 4, 5), N the number of flutes and T the number of thread turns of the finish threads. This structure provides excellent retention characteristics under high thrust, even with a large thread helix angle. Compounding the threads 21, as shown, enhances ease of removal and replacement of the cap. A short twist frees the cap for removal and develops a tight seal on reclosure, at moderate torque.
When uniform constrictive forces are applied, the material of the skirt along the lines of flutes 17 bears on the crests of the threads 21. The material bends over and around the threads due to the high localized bending stresses developed. The material defining the ridges 16 does not bear on the threads. Hence, substantial bending stresses do not develop in the ridge material. Furthermore, the ridges 16 are sufficiently stiff to obviate buckling under shear stresses imposed by bending of the material along the flutes. The ridges 16 remain straight, while providing the accordion effect to evenly accommodate reduction of the skirt diameter. This accordion effect obviates irregular buckling or wrinkling. Upon completion of the constrictive deformation, the diameter across the crest elements of ridges 16 is less than the original diameter by an amount about equal to the double depth of the threads 21. Also, the outside diameter of the skirt across the major diameter of the female thread elements 22 is about the same as the diameter across the crests of the ridges 16.
The cylindrical contour of lip 19 is substantially unaffected by constriction stresses, the lip being restrained against scalloping or curling by the stiffening effect of the ridges 16. Upon constriction, lip 19 has an inside diameter slightly greater than the major diameter of thread formations 21. Then, upon unscrewing cap 10, lip 19 clears thread formations 21.
The length of flutes 17 is substantially the same as the total axial thread length of the threads 21, thus assuring ample thread engagement. The depth of the flutes is about equal to the depth of the threads 21, this dimensioning being conducive to forming well-defined thread elements 22, closely conformed about the threads. Because of the stiffening effect of the ridges 16, the constricted cap has good shape-retention characteristics, conducive to true-running thread engagement, for low-torque twist-off and good reclosure characteristics. The general stiffness of the skirt is such as will afford good resistance to warping, which might otherwise result from irregularities or locked-in stresses developed either in originally forming the cap or in forming the closure.
As previously observed, lip 19 is cylindrical. The crests of ridges 16 and thread elements 22 are of the same diameter, being elements of a common cylinder, and are rounded. The generally cylindrical grid thus formed constitutes a fine knurl with smoothly contoured outermost surfaces, affording a comfortable, sure finger grip. The skirt can be gripped firmly without cutting or abrading one's fingers. With moderate grip pressure required there is little risk of a finger being cut by curling over the edge. Easy twisting of the cap is facilitated by the well-formed threads in the skirt and minimal tendency to ovality, warping, or cocking, which assures a low ratio of torque to sealing pressure, yet with relatively coarse threading, as preferred for quick release and reclosure. These easy-opening features are particularly advantageous in soft-drink bottles which are commonly opened by children.
The configuration of FIG. 4 is particularly conducive to good thread formation and retention characteristics. Root elements 217 are initially inwardly concave. Less severe deformation is involved in conforming the material upon and about the threads 21. The necessary constriction of the skirt can be generally achieved with somewhat less radial pressure than will be the case of the inwardly convex root configurations of the corrugations shown in FIG. 5. However, the choice as to number and form of corrugations requires giving due consideration to the properties of the cap material, cap size, thread form, bottle finish quality and related factors.
FIGS. 10 and 11 illustrate a tamper-proof form of the cap, parts corresponding to those in FIGS. 1-9 being given the same reference numbers with the addition of 100. Cap 110 is similar to cap 10, except for greater skirt length beyond the corrugations, corrugation length being the same in both caps, for the same threading. Skirt 111 depends from panel 113 along radius portion 114, with ridges 116 and flutes 117 having termini 118 in a plane spaced from the edge 112. However, there is a longer cylindrical portion 119 between the plane of corrugation termini 118 and edge 112 than the corresponding marginal portion or lip 19 of the regular cap.
Portion 119 is lanced intermediate the corrugation termini 118 and edge 112, so as to cut a circumferential series of narrow slots 130. Then a series of short, frangible bridges 131 connect the upper and lower bands of marginal portion 119. The orientation and spacing of bridges 131 are so selected that each bridge is aligned with a ridge 116. Except for minor adaptation of the tools to accommodate the longer skirt and for the lancing operation, cap 110 can be made in the same manner as cap 10.
Aluminum is a preferred material for the cap 110. Aluminum is usually more satisfactory and economical than steel for caps of the tamper-proof type. Aluminum generally provides the most desirable combination of ductility for forming and requisite frangibility of the bridges.
Referring to FIG. 12, cap 110 is applied to the finish 120 in the same general manner as above described with respect to the regular cap of FIG. 1. Lip 132 is crimped under shoulder 133, below threads 121. This crimping operation can be performed simultaneously with the general constriction of the skirt, by means of a compressible die similar to die 60 (FIG. 6). Lip 132 being remote from ridges 116, and aluminum being highly ductile, a generally uniform radial constrictive pressure sufficient to conform skirt 116 to the thread formations 121 will usually suffice to crimp the lip 132 against shoulder 133. Alternatively, lip 132 can be crimped, rolled or spun under with an auxiliary die or tool. Collar 135 prevents excessive constriction of skirt portion 134 and bridges 131. Cap 10 can also be applied to this style of finish, if desired.
After completion of the closure as described, the tamper-proofing means of cap 110 operates in the same manner as with other caps having similar frangible bridge structure. The engagement of inturned lip 132 under shoulder 133 inhibits rise of the cap upon initial application of twist-off torque. Thereafter the twist torque and camming action of the threads impose sufficient stress on bridges 131 to fracture them. The lip portion 132 then drops down, visually signalizing attempted opening, even though the body of the cap be not actually twisted off. After the bridges are broken, the body of the cap can be twisted off to open the bottle. The body of cap 110 is substantially the same as cap 10, as to form, thread formation, grip, easy twist-off and reclosure. The inside diameter of the constricted skirt portion 134 and the bridge circle are slightly larger than the major diameter of threads 121. Hence, the body lip and remnants of the bridges will clear the threads when the body of the cap is unscrewed.
Referring again to FIGS. 2, 3, 9 and 10, it will be seen that the cap shell of either type can be readily formed from sheet material in a punch press with simple blank-and-form tooling. The equipment and set-up used can be substantially that used for manufacturing conventional crown caps, with comparable production rates and overall economy. Dies for the regular and tamper-proof types may be of similar design, differing essentially only in blank size and depth.
The regular cap of FIG. 1 has a skirt 11 of about the same length as that of a conventional crown cap for a similar bottle. Hence, the blank size for the plain cap of the invention is about the same as the blank for the crown cap; correspondingly, the same quantity of caps in each case can be made from about the same square footage of material. Since the regular cap here described can be produced from low-cost tin plate or tin-free steel of lighter gauge than has been found feasible with crown caps, for reasons above noted, the total material and cost thereof for the cap of this invention is generally less than for conventional crown caps.
The tamper-proof cap of FIGS. 10-12 has the same length and form above bridges 131 as the complete regular cap, for the same bottle size and finish. Only so much additional material is required as corresponds to the width of the tamper proofing band 132. Either regular or tamper-proof type may be made shorter than the nearest equivalent practical roll-on type of cap.
The caps according to this invention are adaptable to relatively fine threads, because of their suitability to thread formation by means of a compressible die. In contrast, a cap designed for roll-on thread formation is generally suitable for application only to fairly wide, coarse-pitch threads. The localized high tool pressure involved with thread rolling necessitates liberal tool bearing spun to obviate tearing of the cap skirt and to minimize tool or bottle breakage consequent upon jamming of the solid rolling tool between threads or excessive side pressure on the tool. Correspondingly, a roll-on cap generally requires a substantially longer skirt than that of an equivalent cap of this invention for comparable thread engagement. Thus, the caps here described afford greater economy of material as compared with roll-on types, with respect to both blank size and gauge. Lighter gauge is feasible due to lesser risk of tearing or warping when applying uniform overall pressure, as compared with the highly concentrated pressure of the thread-rolling operation.
It will be seen from the foregoing that the closure cap according to this invention affords improved performance and economy, as compared to prior caps employed in similar applications. The caps above described are designed for application to the threaded bottle finish shown by way of example. It will be understood that the cap of this invention is adaptable to thread forms other than that here shown, or to thread equivalents such as cam lugs, or the like.