GB1598428A

GB1598428A - Pilfer proof closures

Info

Publication number: GB1598428A
Application number: GB13765/77A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1977-04-01
Filing date: 1977-04-01
Publication date: 1981-09-23
Also published as: IN148390B; AU3440478A; ZA781641B

Description

(54) PILFER PROOF CLOSURES (71) We, METAL Box LIMITED, of Queens House, Forbury Road, Reading RG1 3JH Berkshire, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to pilfer proof closures and more particularly to a pilfer proof closure for a bottle and a method for making such closures.

Pilfer proof closures are described in British Patents Numbered 1284640 and 1276802. The closures described consist of a cup shaped aluminium shell comprising a skirt or side wall integral with a flat top. This side wall includes an annular perforation which divides the side wall into an upper portion and a lower portion. These specifications mention that such closures can be extruded from a slug of aluminium or alternatively drawn from sheet. However, when closures having a skirt length greater than the diameter of the top are made from aluminium sheet by blanking, drawing and redrawing, care is taken to keep the side wall substantially equal in thickness to that of the top.

A cap 23 mm. diameter x 34 mm. long may require two redrawing steps and longer caps of the same diameter will require even more. In contrast the impact extrusion process will produce long caps from aluminium slugs in a single tool but the press loads required to produce such a cap from a steel slug are very large and the presses capable of imposing such loads are slow in operation.

In a first aspect, this invention provides a method of making a pilfer proof closure comprising a closure panel and a skirt, said skirt bemg greater in length than the diameter of the closure panel, said method including the steps of cutting a blank from a metallic sheet; drawing the blank into a cup having a side wall substantially equal in thickness to an end wall thereof; ironing the wall of the cup to reduce the thickness of the side wall to less than that of the closure panel and increase the length thereof; and forming a pilfer proof cap blank from the thin walled cup.

According to one method the thin walled cup is annealed or stress relieved before forming into the cap blank.

In another method a coating material or paint is applied to the thin walled cup before forming into the cap blank. The closures may be formed from metallic sheet of metals or alloys such as ferrous materials, aluminium or aluminium alloys.

In a second aspect the invention provides a pilfer proof closure made according to the method of the first aspect.

Various embodiments of the method will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 is a side elevation of a blank cut from sheet metal; Fig. 2 is a sectioned side elevation of a cup drawn in a single operation from the blank of Fig. 1; Fig. 3 is a like view of a thin walled cup formed by wall ironing the cup of Fig. 2; Fig. 4 is a like view of a cap blank formed from the thin walled cup of Fig. 3; and Fig. 5 is a sectioned side elevation of the cap blank of Fig. 4 when fitted on a bottle.

Figures 1 to 3 show the essential steps in the method according to this invention; Fig.

1 represents a circular blank 1, cut from a metallic sheet. Fig. 2 depicts a cup 2 produced in a first press tool comprising a punch, die and a blankholder. The cup 2 has a side wall 3 and a top wall or closure panel 4. The length of the sidewall is somewhat less than the diameter of the top wall. The thickness of the side wall is substantially equal to that of the top wall.

Fig. 3 shows a thin walled cup 5 produced from the cup 2 of Fig. 2, by mounting the cup upon a punch and pushing the cup 2 through a die such that the clearance between the punch and die is less than the thickness of the wall 3 of the cup 2. The side wall 3 of the cup 2 is ironed to half the thickness, and therefore doubled in length.

The thin walled cup 5 of Fig. 3 therefore consists of the top wall or closure panel 4 of virtually unchanged material and an ironed side wall 3A which has been work hardened.

The thin walled cup 5 of Fig. 3 is substantially cylindrical and smooth where Ironed and therefore suitable for decorating. with coating materials or printing inks, by known means such as roller coating or spraying.

Any stoving to dry or cure the coatings may also provide some stress relief for the worked metal.

Fig. 4 shows a long skirted pilfer proof cap blank made from the thin walled cup of Fig. 3 by known rolling operations of trimming, beading and scoring. The cap blank comprises a top wall 4'. and a side wall 3B which includes a knurled portion 7, a bead 8 to retain a wad (not shown), an upper wall portion 9, an annular interrupted perforation 10 and a lower skirt portion 11.

Fig. 5 shows the cap blank 6 of Fig. 4 after fitting on a bottle neck 12 by a known thread rolling method. The threaded portion is denoted 9A and is materially the upper skirt portion 9 of Fig. 4. The lower skirt portion 11 had been rolled to engage with a bead 13 on the bottle neck 12 so that the lower skirt portion is retained on the bottle neck when the upper portion is unscrewed and the interrupted perforation 10 is broken, as is usual with such closures.

Tests have shown that the wall ironing of a drawn tinplate cup having a wall thickness of .010" and hardness of 50 Rockwell (30T) to a wall thickness of .005" caused an increase in hardness to about 75 Rockwell (30T). This represents an increase in ultimate tensile strength from about 35 t.p.s.i.

to 65 t.p.s.i. This means that although the cup wall of Fig. 3 is thinner, it is almost as strong in tension. as that of Fig. 2. The magnesium-manganese aluminium alloys and certain iron-aluminium alloys work harden but as the hardness increases useful ductility remains, as is demonstrated by H 19 temper 3004 alloy sheet available from the Aluminium Company of America.

Therefore aluminium alloy cap blanks having an ironed side wall may be passed directly to subsequent cap making operations, provided the wall is not too hard to survive the rolling operations.

In contrast, the wort naruening of sheet steels (and steel based materials such as tinplate) is simultaneously accompanied by a loss of ductility and therefore a stress relieving or annealing operation may be necessary before the final cap making operations of trimming, knurling or scoring are performed. If a ferrous based cup 2 such as the shape shown in Fig. 2 is annealed, the mechanical properties of the side wall may be adjusted by careful choice of an appropriate wall reduction in the ironing tools followed by an appropriate heat treatment to relieve internal stress or even anneal the wall.

The following table gives examples of materials suitable for pilfer proof closures: Starting Material Ferrous Metal Aluminium/Aluminium Alloys Range of Thickness .008" to .012" .008" to .012" Temper/Hardness .46 to 56 Rockwell (30T) Soft to half hard Wall thickness of cap 004 to 008 inches 004 to 008 inches % reduction in wall 50%; 30% 50%; 30% It will be understood that if tinplate is used the tin will aid lubrication in the press tools. However, whilst the tin may survive a low temperature stress relieving operation it will be melted by a high temperature annealing operation. If annealing operations are required, because the cap skirt is severely work hardened, uncoated steels, or known chromium coated steels may be used. Various aluminium alloys may be used such as those containing from 0.5 to 1.5% of manganese and 0.6% silicon.

Aluminium caps having severely cold worked skirts may also be annealed before coating or decorating so that less roll pressure is required to form the threads on the bottles during capping.

WHAT WE CLAIMS IS: 1. A method of making a pilfer proof closure comprising a closure panel and a skirt, said skirt being greater in length than the diameter of the closure panel, said method including the steps of cutting a blank from a metallic sheet; drawing the blank into a cup having a side wall substantially equal in thickness to an end wall thereof; ironing the wall of the cup to reduce the thickness of the side wall to less than that of the closure panel and increase the length thereof; and forming a pilfer proof cap blank from the thin walled cup.

2. A method according to Claim 1 wherein the thin walled cup is annealed or stress relieved before forming the cap blank.

3. A method according to claim 2 wherein the thin walled cup is coated with a coating material or printing ink before forming the cap blank.

4. A method according to any preceding claim wherein the blank is cut from a sheet of aluminium or an alloy of aluminium.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. consists of the top wall or closure panel 4 of virtually unchanged material and an ironed side wall 3A which has been work hardened. The thin walled cup 5 of Fig. 3 is substantially cylindrical and smooth where Ironed and therefore suitable for decorating. with coating materials or printing inks, by known means such as roller coating or spraying. Any stoving to dry or cure the coatings may also provide some stress relief for the worked metal. Fig. 4 shows a long skirted pilfer proof cap blank made from the thin walled cup of Fig. 3 by known rolling operations of trimming, beading and scoring. The cap blank comprises a top wall 4'. and a side wall 3B which includes a knurled portion 7, a bead 8 to retain a wad (not shown), an upper wall portion 9, an annular interrupted perforation 10 and a lower skirt portion 11. Fig. 5 shows the cap blank 6 of Fig. 4 after fitting on a bottle neck 12 by a known thread rolling method. The threaded portion is denoted 9A and is materially the upper skirt portion 9 of Fig. 4. The lower skirt portion 11 had been rolled to engage with a bead 13 on the bottle neck 12 so that the lower skirt portion is retained on the bottle neck when the upper portion is unscrewed and the interrupted perforation 10 is broken, as is usual with such closures. Tests have shown that the wall ironing of a drawn tinplate cup having a wall thickness of .010" and hardness of 50 Rockwell (30T) to a wall thickness of .005" caused an increase in hardness to about 75 Rockwell (30T). This represents an increase in ultimate tensile strength from about 35 t.p.s.i. to 65 t.p.s.i. This means that although the cup wall of Fig. 3 is thinner, it is almost as strong in tension. as that of Fig. 2. The magnesium-manganese aluminium alloys and certain iron-aluminium alloys work harden but as the hardness increases useful ductility remains, as is demonstrated by H 19 temper 3004 alloy sheet available from the Aluminium Company of America. Therefore aluminium alloy cap blanks having an ironed side wall may be passed directly to subsequent cap making operations, provided the wall is not too hard to survive the rolling operations. In contrast, the wort naruening of sheet steels (and steel based materials such as tinplate) is simultaneously accompanied by a loss of ductility and therefore a stress relieving or annealing operation may be necessary before the final cap making operations of trimming, knurling or scoring are performed. If a ferrous based cup 2 such as the shape shown in Fig. 2 is annealed, the mechanical properties of the side wall may be adjusted by careful choice of an appropriate wall reduction in the ironing tools followed by an appropriate heat treatment to relieve internal stress or even anneal the wall. The following table gives examples of materials suitable for pilfer proof closures: Starting Material Ferrous Metal Aluminium/Aluminium Alloys Range of Thickness .008" to .012" .008" to .012" Temper/Hardness .46 to 56 Rockwell (30T) Soft to half hard Wall thickness of cap 004 to 008 inches 004 to 008 inches % reduction in wall 50%; 30% 50%; 30% It will be understood that if tinplate is used the tin will aid lubrication in the press tools. However, whilst the tin may survive a low temperature stress relieving operation it will be melted by a high temperature annealing operation. If annealing operations are required, because the cap skirt is severely work hardened, uncoated steels, or known chromium coated steels may be used. Various aluminium alloys may be used such as those containing from 0.5 to 1.5% of manganese and 0.6% silicon. Aluminium caps having severely cold worked skirts may also be annealed before coating or decorating so that less roll pressure is required to form the threads on the bottles during capping. WHAT WE CLAIMS IS:

1. A method of making a pilfer proof closure comprising a closure panel and a skirt, said skirt being greater in length than the diameter of the closure panel, said method including the steps of cutting a blank from a metallic sheet; drawing the blank into a cup having a side wall substantially equal in thickness to an end wall thereof; ironing the wall of the cup to reduce the thickness of the side wall to less than that of the closure panel and increase the length thereof; and forming a pilfer proof cap blank from the thin walled cup.

5. A method according to all or any of

Claims 1 to 3 wherein the blank is cut from a sheet of ferrous material.

6. A pilfer proof closure made according to the method of any preceding claim.

7. A method of making a pilfer proof closure, substantially as hereinbefore described with reference to the accompanying drawings.