DE3104079A1 - Process for preparing rolled strips from an aluminium alloy for manufacturing two-part cans - Google Patents

Abstract

The invention relates to a process for preparing rolled strips from an aluminium alloy for manufacturing drinks cans or the like. With a view to simplifying the manufacture and facilitating the repeated use (recycling) of the material of used drinks cans, considerable efforts have been made for years to provide an aluminium alloy which is equally suitable for manufacturing the can bodies and the can covers. Because of the very different requirements regarding the rolled strips for manufacturing can covers on the one hand, and for manufacturing one-part can bodies by deep-drawing and ironing, on the other hand, it had not been possible hitherto to solve this problem. According to the invention, an aluminium alloy is proposed which has as its main constituents from 1.15 to 2.0 % of Mn, from 0.85 to 2.0 % of Si, from 0.25 to 0.75 % of Mg, from 0.2 to 1.0 % of Fe, the remainder being aluminium, and which, employing known process steps, is rolled down to a suitable intermediate thickness, is then subjected to recrystallisation annealing at from 450 to 580 DEG C and can then be processed, while certain conditions for the cool-down rate and the rolling-down degree as a function of the required final strength are adhered to, to give a strip of the required final thickness. Figure 4 shows for a number of final strength factors (Rm) the associated values for the minimum cool-down rate (V) and the minimum rolling-down degree ( phi ) for treating the intermediate strip recrystallisation -annealed at from 450 to 580 DEG C. <IMAGE>

Description

Process for the production of rolled strips

made of an aluminum alloy for the production of two-piece cans The invention relates to a method for producing rolled strips from an aluminum alloy for the production of beverage cans or the like.

Such cans have been used increasingly as single-use containers for years for beverages, in particular for beer and carbonated soft drinks used.

They consist of one produced by deep drawing and ironing one-piece can bodies and a lid that is flared after filling Pull tab.

The starting material for the manufacture of the can body and lid are rolled strips made of differing aluminum alloys.

An AlMg L 4.5 Mn alloy (US designation 5182) used in a highly work-hardened state (H 19), which after the partial Softening during stoving has a tensile strength of at least 350 N / mm2 and has an elongation of at least 6%. These values must be adhered to thus the lid, weakened by impressions along the tear line, on the one hand withstand the required bursting pressure for cans filled with beverages containing CO2 can and on the other hand a crack-free flanging is possible.

The alloy mentioned is - as many years of tests have shown - Not even with less work hardening for the manufacture of the can body suitable. Because the desired ratio of height to diameter by deep drawing is not achievable, the cans are made by deep drawing and ironing. It has been found that alloys with a Mg content of more than 1% tend to wear and stick to the tool during ironing, which is undesirable Drawing marks and frequent downtimes. An economical production the can body is not possible with such alloys. For the production For this reason, an AlMn1 Mg 3004) is predominantly used for the can body. she has the required tensile strength of at least 270 after stove enamelling N / mm2 and an elongation of 1% and can be ironed perfectly.

The one that has been common up to now with regard to the different requirements Use of two different aluminum alloys for the production of beverage cans, not only requires a consistently two-pronged manufacturing process with careful Separation of what occurs to a greater extent, in particular when punching out the round blanks Waste material, it also makes the loading aspirations to save material and energy by recycling the empty cans. At the When recirculated cans are melted down, an alloy is obtained depending on the scrap content with about 1 5 'Mn and more than 1 but less than 4.5% Mg, without alloying Measures neither for the production of lids nor for the production of can bodies suitable is. In order to come up with one of the two usable alloys, expensive ones have to be Raw metals are added, which makes recycling for the individual manufacturer economically loses interest and therefore the economically necessary The recycling of old materials is not encouraged to the extent that is desirable.

To overcome the difficulties mentioned is in US-PS 37 87 248 proposed a method for the production of tapes for the manufacture of lids which is assumed to be an alloy which is essentially the same Composition such as that to be used for the can body.

The alloy should be 0.5 to 2 96 Mn and 0.4 to 2 5 'Mg, the remainder essentially Al1 included. After a homogenization annealing of 2 to 24 hours at approx 455 to 6550C (850 to 11500F) is adhered to the material in several steps certain starting temperatures and degrees of rolling hot and cold rolled and then subjected to a heat treatment to stabilize the structural condition. In the cheapest In this case, a tensile strength of 316 N / mm2 (45 psi) is achieved at an elongation of 496. It can be seen that despite a comparatively complex manufacturing process, the Requirements mentioned at the beginning are not met. These could be achieved if the upper part of the specified Mg range, i.e. over 1 to 2% would be exploited. Then the alloy for making can bodies but certainly not suitable due to ironing.

The proposed in the US-PS method can therefore not be used as a be considered a satisfactory compromise.

According to another proposal (DE-OS 29 01 020) is from an alloy started with 0.4 to 1% Mn and 1.3 to 2.5% Mg, which was made by means of a belt caster is to be potted continuously to form a tape. The cast tape should be warm between preferably 490 and 280 0C at least 7Q 96 are rolled and reeled, then cool in still air and finally cold-rolled to the final thickness. The tensile strength values achieved in the work-hardened state are below 350 N / mm2 and fall depending on the annealing temperature used to simulate the paint baking process from 330 to 310 N / mm2. The desired elongation of at least 696 is only achieved if when the annealing temperature is at least 2000C, but the tensile strength is only about 325 N / mm2. For this proposal, too, it is true that the intended Values for the lid material could not be achieved.

With regard to the difficulties in ironing is only mentions that the alloy used has a lower tendency to stick to the tool shows than conventional can strip alloys. Overall, the The subject of DE-OS 29 01 020 does not provide a satisfactory solution to the problem described.

There is therefore still the task of developing a method of the initially specified type, in which the problem of the return of used material through use a uniform alloy for lid and can body is solved without disadvantages in terms of strength properties, especially in the case of the lid material and in terms of the Processing, especially when it comes to the material for the can bodies.

To solve this problem it is proposed that an alloy of the following composition: 1.15 to 2.0 5 'Mn 0.85 to 2.0% Si 0.25 to 0.75 5' Mg 0.2 to 1.0% Fe at most 0.2% Cu at most 0.2% Zn at most 0.1% Zr at most 0.1% Ti remainder aluminum, including a maximum of 0.2% impurities in total, cast in a known manner to form a cast block and, if necessary, homogenized or is cast into a cast strip and then rolled warm and / or cold to an intermediate thickness Dz, that then the intermediate strip is subjected to a recrystallization annealing at 450 to 5800 c and that finally the intermediate strip is cooled and cooled at a minimum speed V (° K / s) is rolled with a minimum degree of rolling ç (%) to the final thickness De, whereby the following condition must be observed depending on the required etld strength Rm (N / mm2) The method according to the invention has the advantage that the required strength properties for the lid material can be achieved with an alloy which contains significantly less magnesium than the previously used and which therefore brings better preconditions from the outset for the production of the can body by ironing. The method also has the advantage that it is also suitable for starting material that is not produced on tape casting machines and that it is very flexible with regard to cooling speed and degree of final rolling, so that existing systems can be used for this without further ado. The low magnesium content of the alloy has the further advantage that this expensive additional material is less important in terms of cost, which is particularly important because when the old material is remelted, the higher the magnesium content of the, the greater the loss of magnesium due to combustion Is scrap.

In a further embodiment of the invention it is provided that in a The required final strength in the range of 220 to 275 N / mm2, the intermediate strip at 450 Annealed to 5800C, cooled in still air and finished with a final rolling degree of + = f (Rm) is rolled cold to the final thickness according to the diagram in FIG.

The method can also be carried out in such a way that at a required final strength in the range 220 to 275 N / mm2 in the usual way directly rolled to final thickness, then the strip annealed to recrystallize at 450 to 5800C and at a speed V = f (Rm) according to the diagram in FIG. 3 to below 2500C is cooled.

Furthermore, it is also possible with the specified alloy, from one starting with at least 10 0K / s cooled cast strip and without recrystallization annealing to be rolled directly warm and / or cold to the final thickness, possibly with a non-recrystallizing Intermediate heating can be made.

The intermediate strip is expediently to a thickness Dz of 1 to 4 mm rolled, while the final thickness De is in the range from 0.20 to 0.50 mm.

Finally, tapes made by the process are in quenched Condition also suitable for the production of extrusion parts.

With the method according to the invention, it is possible to use a single Aluminum alloy is used for the manufacture of the can body and can end. This eliminates all the difficulties that resulted from the usual use from two different alloys.

The recycling of the can material is therefore economically important has become more interesting and for everyone involved, i.e. the can manufacturers, the beverage fillers and the end user, there is a greater incentive to use the material of the empty beverage cans to be recycled.

There is a very important advantage of the method according to the invention that the magnesium content compared to that previously used for beverage cans Aluminum alloys can be reduced significantly. In 1978 approx. 1 million tons of rolled strip used for beverage cans. At a high Recycling rate of 40% there is a need for new metal of 600,000 t.

Suppose that for this amount 1% magnesium by 1% silicon can be replaced, there is a price difference for these metals of about 3 DM / kg and a requirement for alloy metal of 6000 t, a saving of 6000 t x 3000 DM / t = 18 million DX using the method according to the invention to provide the annual requirement for strip material.

For the processing of the assumed 40 5 'recycled can scraps 400,000 t of can strip (of which 320,000 t for can bodies and 80,000 t for can lids), about 2000 t of magnesium are used for alloying the lid material and about 78,000 t Primary aluminum is required to dilute the can body material. Would the can scrap consist of uniform material according to the invention, the material would be practical be reusable without the use of new metal, resulting in further savings in the order of 6 million DM alone from the elimination of the costs for the magnesium new metal result. The above savings are, of course, first Line depending on the metal prices. It is foreseeable, however, that in the future it will be more likely Even higher savings can be achieved because of the production of the pure metals is associated with high energy consumption and with further energy costs an increasing tendency is to be expected.

For a further explanation of the inventive concept, reference is made to the figures referenced.

Figure 1 shows the tensile strength values achieved as a function of Magnesium content of the alloy for different cooling speeds and degrees of rolling after a recrystallization annealing at 5200C. At the rehearsals 1 and 2 according to Table 1, the magnesium content is below 0.25 96 and there are only comparatively low tensile strength values under all cooling and rolling conditions achieved. In the case of samples 3 to 7, however, practically independent of the magnesium content, which was varied between 0.26 and 0.66 96, significantly higher tensile strength values achieved. A tensile strength of over 370 N / mm2 results when cooling with 900K / s and a degree of rolling of 75 96 (upper curve). With the same cooling rate, but only 45% degree of rolling, the tensile strength values are around 325 N / mm2 (lower curve). In the middle curve, the samples cooled down at only 20K / s, but with a degree of rolling of 82% rolled to final thickness; the tensile strength values are around 335 N / mm2. These test results show that the magnesium content above 0.25 96 does not Has an influence on the final strength and that it is therefore arbitrary in the area investigated on possibly

other conditions of the manufacture of beverage cans is adjustable. It can also be seen that with an appropriate choice of the process parameters The tensile strength of 350 N / mm2 required for can lids is reached and clearly exceeded can be so that the material even after a partial softening at Burn-in paint meets the requirements. On the other hand, the two below show Curves that the same thing with a high cooling rate and a low degree of rolling can be achieved, such as with a low cooling rate and a high degree of rolling. Unless there is a continuous, annealing and quenching system for the production of the strips is available, so the same can be achieved by a higher degree of rolling will. Conversely, the final rolling with a smaller degree of rolling and can therefore be carried out more economically if correspondingly high cooling speeds are realizable.

This relationship is formulated as an inequality in the condition mentioned in claim 1, including the required final strength, and is shown graphically again in FIG. 4 for various tensile strength values. Since applies to the degree of rolling the inequality can also be written as follows: For practical operation, with a given final strength and depending on the achievable cooling rate, the required intermediate thickness can easily be calculated if the final thickness is given.

It should also be pointed out that the inequality for tenur for Values Rm 275 N / mm2 applies. At Rm = 275 N / mm2, the value for T is> 0, i.e. no further rolling would be required regardless of the cooling rate.

When applying the inventive concept, it is mainly based on the strength range above 275 N / mm2 arrive, but also for the area below this can be used for the alloy process conditions which lead to a given final strength.

Figure 2 shows the required degree of rolling depending on the required strength for a strip annealed at 5200C, which in still air with about 20K / s was cooled. Such a tape has a strength of approx. 220 N / mm2, which can be increased to around 290 N / mm2 with a degree of rolling of 60%.

Figure 3 shows the required cooling rate as a function a given final strength for one rolled to final gauge and then at 5200C annealed tape.

Based on the alloy specified in claim 1, accordingly specified a process with which tapes for the manufacture of beverage cans are made that have any final strength required in this area of application can. The tape material made available in this way can be used for production of can lids with a strength of at least ski50 N / mm2 is required; but it can also be used to manufacture the can body by deep and ironing are used because of the low magnesium content offers no difficulties in these forming operations. So that is for the manufacture a way has been found for beverage cans that significantly simplifies production, recycling of the old material makes it economically more interesting and quite significant Brings savings.

TABLE 1 Chemical Composition (5 ') Sample No. Mg Cu Fe Si Mn other - Al 1 <0.01 0.06 0.52 1.51 1.40 <0.1 remainder 2 0.12 0.06 0.49 1.32 1.38 <0.1 remainder 3 0.26 0.06 0.50 1.40 1.38 <0.1 remainder 4 0.35 0.07 0.51 1.38 1.37 <0.1 remainder 5 0.41 0.13 0.52 1.52 1.37 <0.1 remainder 6 0.51 0.13 0.53 1.57 1.39 <0.1 remainder 7 0.66 0.13 0.55 1.52 1.39 C0.1 remainder claims

Claims (1)

PATENT CLAIMS 1. Process for the production of rolled strips from an aluminum alloy for the production of beverage cans or the like, characterized in that an alloy of the composition: 1.15 - 2.0% Mn 0.85 - 2.0% Si 0, 25 - 0.75% Mg 0.2 - 1.0% Fe at most 0.2 5 'Cu at most 0.2% Zn at most 0.1 O / G Zr at most 0.1% Ti remainder aluminum, including a maximum of 0 in total , 2% impurities are cast in a known manner to form a cast block and, if necessary, homogenized or cast to form a cast strip and then rolled warm and / or cold to an intermediate thickness Dz, so that the intermediate strip is then subjected to a recrystallization annealing at 450 to 5800C and that finally the intermediate strip is cooled at a minimum speed V (OK / s) and rolled with a minimum degree of rolling t (5 ') to the final thickness De, the following condition having to be met depending on the required final strength Rm (N / mm2) 2. The method according to claim 1, characterized in that with a required final strength in the range 220 to 275 N / mm2, the intermediate strip is annealed at 450 to 580 0C, cooled in still air and with a final rolling degree Q = f () according to the diagram in Figure 2 3. The method according to claim 1, characterized in that with a required final strength in the range from 220 to 275 N / mm2, rolled directly to the final thickness in the usual manner, then the strip is annealed in a recrystallizing manner at 450 to 5800C and at a speed V = f (Rm> according to the diagram in Figure 3 is cooled to below 2500C. 4. The method according to claim 1, characterized in that of one with at least 10 ° K / s cooled cast strip is assumed and that without recrystallization annealing is rolled directly warm and / or cold to the final thickness. 5. The method according to claim 4, characterized in that if necessary. A non-recrystallizing intermediate heating is carried out. 6. The method according to claim 1 or 2, characterized in that on an intermediate thickness Dz of 1 to 4 mm is rolled off. 7. The method according to any one of claims 1 to 6, characterized in that that is rolled to a final thickness De of 0.20 to 0.50 mm. 8. Use of one prepared according to one of claims 1 to 7 Belt in the quenched state for the production of extrusion parts.