TAB MANUFACTURE

Abstract: A method and apparatus for making a tab for an easy open can end in which the tab comprises a handle (30), a fixing hole (40) for a rivet and a nose for breaking a score on the end. The method includes a curling step, the curling tool (50) for this step is modified to provide not only a peripheral curl around the tab but also a pair of lugs either side of the apex of the nose. These lugs have been found to give greatly improved abuse resistance and significantly to reduce initial opening force.

Description: TAB MANUFACTURE This invention relates to tab manufacture. In ■ particular, it relates a process and apparatus for manufacturing a metal tab for a full aperture easy open can end. Such tabs typically comprise a handle in the form of a ring, a pair of arms, a central hole for a rivet connection and a nose. The arms often each include a bead for strengthening the tab. Further strengthening of the tab is achieved by means of an inturned curl around the periphery of the tab. This curl is interrupted at the apex of the nose by a beak for puncturing a score on the easy open end. A food can end of the "easy opening" type comprises a seaming panel, a chuck wall and a countersink joining the chuck wall to a central panel. A circumferential score is provided adjacent the countersink and a metal tab is riveted to the central panel so that its beak is positioned above the score. In some instances, the score may have a variable depth, measured in terms of the remaining metal thickness, or "residual". In an easy open food can end having such a circumferential score, the beak of the tab pierces the score directly when the handle is lifted. Breaking the score takes place in three stages. Firstly, by lifting the handle, the score tears or "pops" as the tab is lifted to the position where the tab is perpendicular to the end. By pushing the tab over in a second action until it meets the peripheral chuck wall of the end, the initial score tear is propagated. In the third stage, the tab and end panel are pulled out away from the can body so that the end peels away from the can body. The force required for initial rupture of the score is therefore RECTIFIED SHEET (RULE 91) known as the "pop force" and the force required for the " third stage when the whole panel is removed is known as the "tear force". In designing easy open tabs, there is often a compromise to be made in reducing the pop or tear forces in that reducing one may adversely affect the other. Easy open ends must also satisfy certain abuse criteria since the provision of a score may, whilst rendering the end easier to open, also lead to premature failure of the end by score. One common situation when failures arise is when filled cans are on conveyors since the base of one can may enter into the top of another. If this leads to the upper can pushing the tab nose of the lower end into its score, fracture of the score often occurs. The present invention seeks to provide a method of manufacturing a tab which, when fixed to a full aperture can end, overcomes the above problems. According to the present invention, there is provided a method of manufacturing a tab, the method comprising: providing a strip of sheet metal; forming a tab blank in the strip, the blank having a handle portion at one end and a nose at its opposite end and being connected to the strip by one or more carriers; curling the perimeter of the blank; and detaching the blank from the strip by severing the or each carrier; in which the curling step comprises forming a continuous curl around the handle portion, and forming a curl around the nose including a pair of lugs either side of the nose by providing a pair of recesses in a curling tool whereby the lugs comprise uncurled or incompletely curled portions of the tab perimeter. RECTIFIED SHEET (RULE 91) The method may further comprise stamping one or more beads along arms of the tab blank which link the handle to the nose. Usually, the handle may be annular and the curling step further comprises forming a continuous curl around the internal circumference of the handle. This curl acts as a safety device for preventing a user's finger from coming into contact with a sharp edge of metal . In a preferred embodiment of the invention, the method further comprises forming a beak at an apex of the nose. Generally, the beak may be formed by cutting the blank either side of the apex and partially curling the cut region, whereby the curl around the nose terminates either side of the beak. According to a further aspect of the present invention, there is provided an apparatus for manufacturing a tab, the apparatus comprising: at least one punch for forming a tab blank in the strip, the blank having a handle portion at one end and a nose at its other end and being connected to the strip by one or more carriers; a curling tool for curling the perimeter of the blank; and a cutter for detaching the blank from the strip by severing the or each carrier; in which the curling tool includes a pair of recesses for forming a pair of lugs either side of the nose, whereby the lugs comprise uncurled or incompletely curled portions of the tab perimeter. Preferably, the recesses are positioned so that the lugs will be between the score and the leading edge of the rivet when the tab is fixed to a can end. In one embodiment, for making a tab for a can end having a diameter of 99 mm, the recesses are at ±45° to the RECTIFIED SHEET (RULE 91) longitudinal axis of the curling tool. The recesses in -this embodiment may be at least 0.5 mm deep and ideally no more than 0.55 mm deep. This depth is measured relative to a face of the tool adjacent the recess. The width of the recess may be between 1.5 and 1.55 mm. In another embodiment, for making a tab for a can end having a diameter of 100 mm, the recesses are preferably between 2 and 2.1 mm wide and between 0.7 and 0.8 mm deep. The present applicant has found that tabs manufactured in accordance with the method and apparatus of the present invention reduce the pop force requirements by about 10% without adversely affecting tear force. A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a schematic showing the progression of tab formation; Figure 2 is a plan view of a curling tool; and Figure 3 is an underside view of a tab formed using the tool of figure 2. Figure 1 shows a method of tab manufacture in which a strip of metal 10 passes through a conversion press in order progressively to form tabs in two lanes 12, 14. The progression can be clearly seen by viewing from left to right in the drawings in the direction of the arrow. A tab blank is retained on the strip 10 by a pair of tab carriers 16. Firstly, a nose 20 is stamped, then a ring pull handle 30 at the rear of the blank. Further passage through the conversion press adds a fixing hole 40 for a rivet and a pair of reinforcing beads 18. RECTIFIED SHEET (RULE 91) Final stages of the tab formation include curling stations to form curls around the periphery 22 of the blank and within the handle ring 32. The finished tab is detached from the strip by cutting tab carriers 16. In the present invention, the tool 50 used to form the curls on a 99 mm diameter end has been modified as shown in figure 2. The tool 50 comprises a handle region 52 and a nose region 54 and has longitudinal axis 55 which passes through the apex 56 of the nose region. A pair of recesses 58 are provided either side of the apex 56, at ±45° to the longitudinal axis 55. This ensures that when the tab is fixed to an easy open end, the lugs will be positioned between the score and the leading edge of the rivet. In the example shown, each recess 58 has a width w of 1.5 mm and a depth of 0.5 mm. These values are allowed a tolerance of up to +0.05 mm but should not be less than the given values for satisfactory formation of lugs. The angle of the recesses to the longitudinal axis should, however, ideally not be varied and must not be such that the lugs will lie directly over the score, since they might accidentally rupture the score, or behind the rivet, since they would not serve any useful function in this position. A tab formed using the tool of figure 2 is shown m figure 3. The tab comprises a handle 30 and nose 20, linked by a pair of arms along which reinforcing beads 18 are provided. A hole 40 is provided for fixing the tab to an end, for example by means of a rivet. Around hole 40, a horseshoe shaped cut 42 enables the tab to be pivoted about a line 43 linking the ends at the front of the cut when the handle is raised, thereby pressing the nose onto the can end. RECTIFIED SHEET (RULE 91) The handle 30 includes an inner 32 and an outer 22 ■ curl which protect the user from cut edges on the tab. The outer curl 22 extends around entire periphery of the tab except for breaks at the tab carriers 16, where the tab was attached to the strip during its formation (see figure 1) . A further interruption is apparent at the apex 24 of the nose 20, where the curl is replaced by a beak 26. In accordance with the present invention, the tab is formed with a pair of lugs 28 either side of the beak 26, positioned at 45° to the longitudinal axis of the tab. The provision of these lugs leads to not only an increased abuse resistance when used with easy open ends but also a reduction in the initial force required to rupture or "pop" a score on such an end. As described above, a tab for a full aperture easy open end is fixed by means of a rivet with the beak of the tab directly above a line of weakening, or score, around the end. Abuse resistance is measured by applying pressure directly to the tab nose and noting the applied load when the score is broken by the beak. Further tests for easy open ends include measurements of pop force, tear force, burst pressure (i.e. internal overpressure) and score residual at the nose apex and either side of the apex. A "Ziglo" test comprises a drop test after which penetrant die is used to identify score failures. Example 1 Standard measurements as described above were taken for 99 mm diameter can ends having tabs both with and without lugs. The results are given in table 1. It is apparent that the presence- of lugs reduces the pop force RECTIFIED SHEET (RULE 91) and improves abuse resistance by up to 20%. There is no " adverse effect on burst pressure and tear force is within the specification of 6 ± 2 dN. Example 2 Three sets of 99 mm diameter ends were tested in particular for score residuals at the nose of the tab (position "0") and either side of the nose (positions "1" and "2"). Further tests were as in example 1, with the addition of a Ziglo test. Again there was a significant reduction in pop force with the provision of lugs, tear force was within specification and abuse resistance tests by applying direct pressure to the nose were improved by about 10% in each case. The Ziglo tests demonstrated excellent performance improvement for ends using tabs with lugs, all of the samples in two of the sets showed no sign of score fracture and 70% in the third set. RECTIFIED SHEET (RULE 91) Table 1 RECTIFIED SHEET (RULE 91) Table 2 30 rπ m σ >» m m 70 C i— m o

Claims: CLAIMS : 1. A method of manufacturing a tab, the method comprising: providing a strip of sheet metal; forming a tab blank in the strip, the blank having a handle portion at one end and a nose at its opposite end and being connected to the strip by one or more carriers; curling the perimeter of the blank; and detaching the completed tab from the strip by severing the or each carrier; in which the curling step comprises: forming a continuous curl around the handle portion, and forming a curl around the nose; and providing a pair of recesses in a curling tool to form a pair of lugs either side of the nose, each lug comprising uncurled or incompletely curled portions of the tab perimeter which extend away from adjacent uncurled blank on the same side as the curl and the curl around the nose extending along the tab perimeter on both sides of each lug, whereby each lug interrupts an otherwise continuous curl. 2. A method according to claim 1, in which the position of the lugs is such that, when the tab is fixed by a rivet to a can end having a circumferential score, the lugs extend towards the can end between the score and the edge of the rivet nearest to the score. 3. A method according to claim 1 or claim 2, in which the lugs are positioned at ±45° to the longitudinal axis of the tab. RECTIFIED SHEET (RULE 91) 4. A method according to further comprising stamping one or more beads along arms of the tab blank which link the handle to the nose. 5. A method according to any one of claims 1 to 4, in which the handle is annular and the curling step further comprises forming a continuous curl around the internal circumference of the handle. 6. A method according to any one of claims 1 to 5, further comprising forming a beak at an apex of the nose. 7. An apparatus for manufacturing a tab, the apparatus comprising: at least one punch for forming a tab blank in the strip, the blank having a handle portion at one end and a nose at its other end and being connected to the strip by one or more carriers; a curling tool for curling the perimeter of the blank; and a cutter for detaching the blank from the strip by severing the or each carrier; in which the curling tool includes a pair of recesses for forming a pair of lugs either side of the nose, each lug comprising uncurled or incompletely curled portions of the tab perimeter which extend away from adjacent uncurled blank on the same side as the curl and RECTIFIED SHEET (RULE 91) the curl around the nose extending along the tab perimeter on both sides of each lug, whereby each lug interrupts an otherwise continuous curl. 8. An apparatus according to claim 7, in which the recesses are at ±45° to the longitudinal axis of the tool. RECTIFIED SHEET (RULE 91)

Inventors: LAMBIN CLAUDE, LAMBIN, CLAUDE
Applicants: CROWN CORK & SEAL TECH CORP, LAMBIN CLAUDE, METAL BOX PLC, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, LAMBIN, CLAUDE
Application year: 1998
Main classification: B21D51
IPC codes: B21D51