DE1813192B2 - Use of work-hardened sheets made of an aluminum magnesium manganese alloy for easy-to-open can lids - Google Patents

Description

The invention relates to the use of work-hardened sheets made of an aluminum-magnesium-manganese alloy as a material for the production of easy-to-open can lids with riveted Tear-off tabs, whereby the reject rate in series production must not be more than 0.05%.

In recent years, aluminum alloy sheets have gained increasing acceptance, for example They are used as a can lid or the like for drinks, food and other goods. These Can ends usually have some easy-to-open part, e.g. B. a riveted pull tab, as described in U.S. Patent 3,191,797. This type of use is one of the main reasons for the increasing and widespread use of aluminum sheet for can dome, however, results in certain Problems in choosing a suitable material. First of all, the can lid must be sufficiently tight so that it securely encloses the material in the can, and this strength must be at the stoving temperatures, that arise during the hardening of the lacquer coating applied to the can lid will. Second, the material must be machinable so that it can be easily opened Can lids with riveted pull-tabs can be deformed. For example, go from the above U.S. Patent 3,191,797 immediately hot. that a can lid is quite a substantial one Deformation during the elaboration of the pull tab is subjected to the fastening of the Pull tab at the end of the barrel is used. It is true that sheets made of various aluminum alloys are available and sufficient strength after baking, but still have the desired deformability. Conversely, some have the required ductility, but they often show such poor strength that so that uneconomically high sheet metal thicknesses have to be used to achieve a sufficiently solid Manufacture can end. It is generally desirable to have a reject rate of not to be adhered to by more than 0.05%. This is quite a strict requirement for the can end material, which must also be strong enough so that it can be thin enough to allow it to work with other materials can compete economically.

The invention relates to the use of work-hardened metal sheets made from an aluminum-magnesium-manganese alloy. consisting of 4 to 5.5% magnesium and 0.2 to 0.7% manganese, with the proviso that the ratio of the manganese content to the magnesium content by the equation

% Mn = 1.700 - 0.9 (In% Mg) - 0.15%

the remainder is aluminum and admixtures of a maximum of 0.2% copper, a maximum of 0.4% iron, a maximum of 0.3% silicon, a maximum of 0.1% titanium, a maximum of 0.2% chromium and a maximum of 0.05% other admixtures in each case, which, however, together must not account for more than 0.15%, the sheets with a final thickness of 0.20 to 0.38 mm previously cold-rolled without intermediate annealing with a degree of rolling of at least 85% and, after application of a stoving varnish, a treatment known per se The lacquer coating has been baked at 204 ^° C. for 20 minutes as a material for the production of easy-to-open can lids with riveted tear-off tabs, the reject rate in series production not exceeding 0.05%.

Sheets made of an aluminum-magnesium alloy are available as AlMg 5 z. B. from the standard DIN 1725, sheet 1 (May 1961), known. This alloy, which consists of 4.3 to 5.5% Mg, 0 to 0.6% Mn, 0 to 0.30% Cr, the remainder aluminum and the usual impurities, is referred to as a non-hardenable alloy however, there is no evidence that sheets made of the AlMg 5 alloy are suitable for the series production of easy-to-open can lids with such a low reject rate. The aluminum-magnesium-manganese alloy to be used according to the invention differs from the alloy AlMg 5 in its composition in that it must contain manganese in an amount to be calculated with the aid of the specified equation (dimensioning rule).
In D. Altenpohl, "Aluminum von inside viewed", 1957, p. 108, it is described that non-hardenable aluminum alloys generally contain magnesium additions of 0.5 to 7%, with manganese atoms in the solid solution also having a strengthening effect. It says there that the naturally hard alloys have wide areas of application and that they are used instead of pure aluminum when medium strengths are required, but it cannot be deduced from this reference either

that such materials for the production of easy / u opening can lids with a reject rate of not more than 0.05% are suitable.

This is because it is used in the manufacture of easy-to-open can lids with riveted pull-tabs so. that then a reject rate in series production practically zero can be obtained if a softer metal is used. The usage such a material increases the costs, since a larger amount of metal is used for it must become. to store drinks under pressure. If you try to get around this difficulty and to use a harder metal, however, higher reject rates are obtained, so that these Solution for series production is not applicable.

This difficulty is now according to the invention by the selection of a material with special Composition and special treatment overcome.

This specific problem can also be found in the further prior art, as z. B. by "Aluminum-Taschenbuch", 12th edition, 1963. p. 393, D. Altenpohl, "Aluminum und Aluminiumiegierungen", Springer Verlag, 1965, p. 681, and the Swiss 384,873 is given, no reference.

In accordance with the invention to use aluminum-magnesium-manganese alloy is the magnesium content is preferably in the range from 4.2 to 4.8 ° / o and the manganese content is preferably in the range of 0.25 to 0.5 ° / _0th Immediately after cold rolling with a degree of rolling of at least 85%, the sheets used according to the invention have a tensile strength of 39.90 kp / mm ² , a 0.2 yield strength of 37.10 kp / mm ² , an elongation at break of 3% or more and an Olsen cupping value of 3.56 mm. After annealing for 20 minutes at a temperature of 204 ° C, the sheets have a tensile strength of 37.10 kp / mm ² and a 0.2 proof stress of 31.50 kp / mm ² as well as an elongation at break of 8% and an Olsen cupping value of 3, 81 mm.

The O'sen cupping value, the 7th B. in "Dictionary of Metallurgy «. London 1958, p. 215, gives the greatest depth of a cup that is with the. Material can be formed before the surface begins to crack. The test thus provides an indication about the permeability of the material in question.

If the manganese content exceeds the value given by the equation, then deformability drops below the value for the easy-to-open can lid with a riveted pull-tab can be produced consistently well.

The alloy to be used according to the invention can be produced as a continuously cast rolling ingot. The ingot can be homogenized by heating to a temperature of at least 426 "C but below the melting point for 24 hours. The ingot is then prepared for rolling and rolled to a certain intermediate thickness, usually about 3.8 mm., By a conventional hot rolling process then annealed by heating to about 315 ^: C for a time sufficient for recrystallization When cold rolling is carried out, it is preferred that the temperature of the sheet when it leaves the rolls ^{does not exceed 93:} C. The use of water-based lubricants is useful in meeting this temperature limit This cold rolling gives the sheet solidification, and in this state the sheet is strong due to its high strength s and also has a very good degree of deformability, so that riveted tear-off tabs can be worked out, as is indicated, for example, in US Pat. No. 3,191,797. It is also important that sufficient strength be maintained after the further treatment that is common in the manufacture of can lids when a lacquer coating is applied to the sheet and baked. A treatment at 204.degree. C. for 20 minutes corresponds to a baking treatment as it is normally used in the manufacture of can ends.

As already indicated, a combination of strength and deformability both before and after the treatment for 20 minutes at 204 ^° C. is desirable for a can lid material.

To explain the strength of the sheets to be used, these are made with sheets of similar composition compared. The compositions are given in Table I, in which A is according to the invention used sheet is. Sheet B is the product currently used by the can industry in manufacturing is used by easy-to-open can lids.

Table I.

sheet Mg Mn Fe Si Cu Cr Ti Zn A.
B. 4.54
4.45 0.37
0.01 0.21
0.19 0.10
0.08 0.01
0.02 0.02
0.00 0.02
0.01 0.01
0.01

Each alloy was continuously cast to prepare an ingot which was homogenized by for 24 hours heating at a temperature of 482 ° C, after which he brought to a temperature of about 399 ⁰ C and was then hot rolled to a plate with a thickness of approximately 3 To produce 80 mm. The plate was then annealed at 315 ° C. in order to recrystallize the structure, after which it was cold rolled into a sheet 0.33 mm thick without intermediate annealing. This cold rolling of over 90 ° / ₀ gave the sheet solidification. Samples to determine the tensile strength were taken from the sheet. In the test, the average strength values given in Table II were obtained. The table also shows the Olsen cupping value.

tensile strenght
kp / mm ² Table 11 Elongation at break
° / o Olsen cupping value
mm sheet 39.90
36.40 0.2 expansion limit
kp / mm ² 4th
4th 3.56
3.82 A.
B. 37.10
33.60

From Table II it can be seen that the invention means the operating conditions when a sheet of about 10% 10 is coated with lacquer on the sheet used according to the invention and shows higher strength in an oven than sheet B, although the latter has a higher Olsen cupping value owns. Sheet samples A and B were also ^{exposed to a temperature of 204 J} C for 20 minutes, which is an approximation

is burned in. The average values for panels A and B after treatment at 204 ^a C are given in Table III.

Table 111

sheet tensile strenght
kp / mm ² 0.2 yield strength
kp / mm ² Elongation at break
° / o Olsen cupping value
mm A.
B. 37.10
33.60 31.50
28.00 OO OO 4.06
4.57

From Table III it can be seen that the sheet A used in accordance with the invention is still by approximately 10% higher strength than sheet B shows. The Olsen cupping value for sheet A is lower than for sheet B, but has proven to be sufficient for the production of can ends Pull tabs proven.

The combination of both better strength and better ductility of sheet A goes on best from the figure in which the tensile strength against the Olsen cupping value for the sheets A and B is plotted. From the figure it is immediately apparent that for any given strength value, the Sheet A is characterized by a higher Olsen cupping value than sheet B.

In addition to the usual strength tests, another measure of the suitability of a sheet is which to serve as a can lid, the bending behavior under pressure.

This behavior is determined by the fact that a beverage can is produced, the lid of which is made of the sheet to be tested is shaped. Pressure is applied inside the can and gradually increased until the can lid bulges and plastically deforms. The pressure at which the can lid bulges is then referred to as buckling pressure. When panels A and B were compared, it was found that a 0.34 mm thick can end made from sheet A withstands the same pressure as a 0.37 mm thick one Can lids made from sheet B, which is widely used in the manufacture of easy-to-open beer can lids finds. This means a considerable saving in material.

1 sheet of drawings

Claims (2)

Patent claims: 1. Use of work-hardened sheets made of an aluminum-magnesium-manganese alloy, consisting of 4 to 5.5% magnesium and 0.2 to 0.7% manganese, with the proviso that the ratio the manganese content to the magnesium content by the equation % Mn = 1.700 - 0.9 (In% Mg) _{; r} 0.15% is determined, the remainder aluminum and admixtures of a maximum of 0.2% copper, a maximum of 0.4% iron, a maximum of 0.3% silicon, a maximum of 0.1% titanium, a maximum of 0.2% chromium and a maximum of 0.Q5 ° in each case, “others Additions, which together may not ^{amount to more than 0.15 J} / _o , whereby the sheets with a final thickness of 0.20 to 0.38 mm previously cold-rolled without intermediate annealing. ^ With a degree of rolling of at least 85% and after application of a stoving varnish have been subjected to a treatment known per se for baking the lacquer coating at 204 ^: C for 20 minutes, as a material for the production of easy-to-open can lids with riveted tear-off tabs. inclination must not be more than 0.05%. 2. Use of work-hardened sheets made of an aluminum-magnesium-M mgan alloy according to claim 1, which contains 4.2 to 4.8% magnesium and 0.25 to 0.5% manganese, for the specified Purpose.