DRAWN AND IRONED CAN MADE OF RESIN-COATED ALUMINUM ALLOY

A drawn and ironed can made of resin-coated aluminum alloy includes a can body having a bottomed cylindrical shape. The can body includes a can bottom and a can barrel having a cylindrical shape. A height of the can body from a grounded part of the can bottom to an upper end of the can barrel is 151 mm to 160 mm. An outer diameter of the can barrel is 45 mm to 59 mm. The can barrel includes a tapered part formed in at least part of an area between 80 mm to 140 mm from the grounded part of the can bottom to the upper end of the can barrel. A plate thickness of the can barrel gradually increases inside the can barrel in the tapered part. An angle of the tapered part with respect to the can axis is 50 seconds to 1 minute and 30 seconds.

BACKGROUND

1. Technical Field

The present invention relates to a drawn and ironed can made of resin-coated aluminum alloy.

2. Related Art

There has been known a drawn and ironed can made of resin-coated aluminum alloy (two-piece can) as a container filled with contents such as beverage. The drawn and ironed can made of resin-coated aluminum alloy is obtained by integrally molding the can barrel and the can bottom by, for example, the DI (drawing and ironing) process.

In the DI process, first, a cupping and pressing step is performed to punch a circular plate out of a metal plate and draw the circular plate, and therefore to mold a shallow cup material. Next, a body making step is performed to redraw the shallow cup material by moving a punch while the can material is pressed onto a redrawing die, and therefore to mold a deeper cup. After that, the punch is further moved, and the cup is passed through a molding die and ironed to gradually reduce the thickness of the side wall of the cup to form a bottomed cylindrical can. Next, the can is stripped from the punch by fingers and pulled out. See, for example, Japanese Examined Patent Application Publication No. S60-133. The entire contents of this disclosure are hereby incorporated by reference.

In the above-described molding process, a drawn and ironed can made of aluminum alloy which is not coated with resin is molded while the can or die is directly sprayed with a lubricant. On the other hand, the drawn and ironed can made of resin-coated aluminum alloy is molded without using a lubricant (coolant), because the resin coating serves as a lubricant. See, for example, Japanese Patent No. 2010-75932. The entire contents of this disclosure are hereby incorporated by reference.

SUMMARY

An aspect of the present invention provides a drawn and ironed can made of resin-coated aluminum alloy including a can body having a bottomed cylindrical shape. The can body includes: a can bottom; and a can barrel having a cylindrical shape around a can axis and extending from an outer circumference of the can bottom along the can axis. A height of the can body from a grounded part of the can bottom to an upper end of the can barrel is 151 mm to 160 mm. An outer diameter of the can barrel is 45 mm to 59 mm. The can barrel includes a tapered part formed in at least part of an area between 80 mm to 140 mm from the grounded part of the can bottom to the upper end of the can barrel. A plate thickness of the can barrel gradually increases inside the can barrel in the tapered part. An angle of the tapered part with respect to the can axis is 50 seconds to 1 minute and 30 seconds.

DETAILED DESCRIPTION

As described above, the molding process of the drawn and ironed can made of resin coated aluminum alloy does not use a lubricant, and therefore a large force may be required to pull a can out of the punch depending on conditions such as the temperature of the punch.

Incidentally, in recent years, a slim two-piece can having a smaller diameter (for example, 204 diameter) has been increasingly popular because of its stylish design, instead of a general two-piece can (211 diameter) containing beer and so forth. Moreover, the plate thickness of the can barrel has been reducing because of a request for resource saving.

In the case of the slim can having a small diameter, the degree of elongation is large in the height direction of the can. Therefore, the length of the can adhering to the punch is long relative to the unit length for which the fingers of the stripper hang on the opening end of the can, during the stripping in the body making step. As a result, while the molding is performed at a high speed (for example, 300 cans per minute), the opening end of the can cannot bear the force of the stripping, and consequently the can barrel may crack. The smaller the plate thickness of the can barrel is, the easier it is to crack the can barrel.

The present invention has been achieved considering the above-described circumstances to address the above-described problems. It is therefore an object of the invention to prevent the can barrel from cracking during the stripping.

Hereinafter, an embodiment of the invention will be described with reference to the drawings. In the description below, the same reference numbers indicate the same functional sections, and therefore repeated description for each of the drawings is omitted.

FIG.1is a vertical cross-sectional view along a can axis O of a drawn and ironed can made of resin-coated aluminum alloy according to an embodiment of the invention, which schematically illustrates the drawn and ironed can made of resin-coated aluminum alloy. Here,FIG.1is a diagram illustrating the shape of the cross section without the plate thickness of the can body. As illustrated inFIG.1, a drawn and ironed can made of resin-coated aluminum alloy1includes a can body10having a bottomed cylindrical shape.

The can body10is made of resin-coated aluminum alloy. The resin-coated aluminum alloy includes, for example, outer coating resin which forms the outer surface of the can body10, inner coating resin which forms the inner surface of the can body10, and aluminum alloy provided between the outer coating resin and the inner coating resin.

The can body10includes a can bottom11, and a can barrel12having a cylindrical shape around a can axis O and extending from the outer circumference of the can bottom11along the can axis O. The bottomed cylindrical shape of the can body10is formed by the can bottom11and the can barrel12. The can bottom11and the can body12have the same shape along the entire circumference around the can axis O. The can body10is obtained by: punching a circular plate out of a plate material made of resin-coated aluminum alloy; drawing the circular plate to mold a bottomed cylindrical cup member; redrawing and ironing the cup member to integrally mold the can bottom11and the can barrel12; and trimming, necking and flanging the opening end of the can barrel12.

The height of the can body10from the grounded part (described later) of the can bottom11to the upper end of the can barrel12is 151 mm to 160 mm. With the example illustrated inFIG.1, the height is 155.0 mm. The outer diameter of the can barrel12is 45 mm to 59 mm. With the example illustrated inFIG.1, the outer diameter is 57.2 mm.

The can bottom11includes a dome part111and an annular convex part112. The dome part111is provided in the center of the can bottom11, and has a concave curved surface like a dome which is concave into the inside of the can barrel12along the direction of the can axis O. With the example illustrated inFIG.1, the dome part111includes a first curved surface111A located in the center and having a radius of curvature R1, and a second curved surface111B located around the first curved surface and having a radius of curvature R2different from the radius of curvature R1. The dome part111may include a plurality of curved surfaces having different radius of curvatures as the example illustrated inFIG.1, or may include one curved surface having a radius of curvature. Otherwise, a well-known dome shape may be applicable.

In a predetermined region of the dome part111including a point on the can axis O, it is preferred that the thickness of the outer surface coating resin is 0.008 mm to 0.015 mm, the thickness of the aluminum alloy is 0.18 mm to 0.24 mm, and the thickness of the inner surface coating resin is 0.010 mm to 0.020 mm.

The annular convex part112is formed on the outer circumference of the dome part111to annularly protrude to the outside of the can barrel12along the can axis direction, and includes a grounded part112A. When the can body10is placed on a horizontal surface, the grounded part112A contacts the horizontal surface to support the can body10. In the vertical cross-sectional view ofFIG.1, the tip of the annular convex part112may bend to the inside of the can barrel12in the radial direction. That is, bottom reforming as the example illustrated inFIG.1is applied, and therefore it is possible to improve the strength of the can bottom11.

The can barrel12has a cylindrical shape around the can axis O and extends from the outer circumference of the can bottom11along the can axis O. The can barrel12includes a neck121provided in the upper end, and a tapered part122provided between the upper end and the lower end.

The neck121is formed such that the outer diameter of the can barrel12is gradually decreased toward the top of the can barrel along the can axis O. A can lid (not illustrated) having a diameter smaller than that of the can barrel12is provided in the neck121. Here, with the example illustrated inFIG.1, the minimum outer diameter of the neck121is 52.4 mm.

The neck121includes a concave curved surface121A formed on the upper end to be concave toward the outside in the radial direction and having a radius of curvature r1, a convex curved surface121B formed on the lower end to be convex toward the outside in the radial direction and having a radius of curvature r2, and a concave curved surface121C formed between the upper end and the lower end to be concave toward the outside in the radial direction and having a radius of curvature r3.

With the example illustrated inFIG.1, the radius of curvature r1is 1.5 mm, the radius of curvature r2is 5.0 mm, and the radius of curvature r3is 10.0 mm. However, the values of the radius of curvatures are merely an example, and are by no means limiting. In addition, it is preferred that an angle θ1formed between a straight line L1connecting the convex curved surface121B to the concave curved surface121C and the straight line parallel to the can axis O is smaller than 27 degrees. With the example illustrated inFIG.1, the angle is 24 degrees.

A flange123is formed on the opening end of the can body10, that is, on the upper end of the neck121. With the example illustrated inFIG.1, the distance from the upper end of the flange123to the lower end of the neck121along the direction of the can axis O is 11 mm.

FIG.2andFIG.3are enlarged views illustrating the tapered part122.FIG.2is an enlarged view illustrating area A ofFIG.1, andFIG.3is an enlarged view illustrating area B ofFIG.1. Here, the magnification ofFIG.3is higher than that ofFIG.2.

To be more specific, the tapered part122is provided at a position between 80 mm and 140 mm from the grounded part112A (area A ofFIG.1) of the can bottom11to the upper end of the can barrel12. As illustrated inFIG.2andFIG.3, in at least part of the area A of the tapered part122of theFIG.1, the plate thickness of the can barrel12is gradually increased inside the can barrel12toward the top of the can barrel along the can axis O. The tapered part122is formed such that the inner surface of the can barrel12is inclined to the inside while the plate thickness of the can barrel is increased upward.

With the example illustrated inFIG.2andFIG.3, the can barrel12is formed to have a plate thickness which gradually increases around a position of 90 mm from the grounded part112A of the can bottom11toward the upper end of the can barrel12, and further increases around a position of 135 mm to the neck121.FIG.4illustrates the plate thickness distribution of the can body10.

As illustrated inFIG.2andFIG.3, the angle of inclination of the tapered part122on the inner surface of the can barrel12, that is, an angle θ2formed between the tapered part122and the straight line parallel to the can axis O is 50 seconds to 1 minute and 30 seconds. In this way, even though the plate thickness of the can body10is decreased, the angle of the tapered part122is optimized to slow the change in the plate thickness. By this means, it is possible to improve the release property during the stripping, and prevent the can barrel from cracking during the stripping.

FIG.5illustrates a result when a can body including a can barrel having an outer diameter of 57.2 mm is molded from a circular plate material having a blank diameter (B.D.) of 143.0 mm, while the angle of the tapered part122is changed from 30 seconds to 1 minute and 50 seconds by 10 seconds for each time. In addition,FIG.6illustrates a result when a can body including a can barrel having an outer diameter of 57.4 mm is molded from a circular plate material having a blank diameter (B.D.) of 143.0 mm, while the angle of the tapered part122is changed from 30 seconds to 1 minute and 50 seconds by 10 seconds for each time.

The tables illustrated inFIG.5andFIG.6indicate the results when the molding speed is 300 cans per minute, and the original plate thicknesses are 0.22 mm and 0.23 mm for each of the angles of the tapered part122. In addition, Yes means that the can barrel cracks, and No means that the can barrel does not crack. Here, the numeric values of the original plate thicknesses illustrated inFIG.5andFIG.6indicate the plate thickness of the aluminum alloy, but does not include the thickness of the outer surface coating resin and the thickness of the inner surface coating resin.

Whether or not the can barrel cracked was evaluated using the ERV (enamel rate value) method. That is, by using an enamel rater, a part to which the metal was exposed was formed in the inner surface of the molded can and an anode is connected to the part; a cathode is immersed in salt solution filled in the can, and a DC voltage of 6V was applied for 4 seconds at a temperature equal to or lower than the room temperature (23 degrees Celsius); and then the current value was evaluated. As to the evaluation criteria, it was evaluated that the can barrel did not crack when the current value was equal to or lower than 60 mA, and that the can barrel cracked when the current value is higher than 60 mA.

Based on the tables illustrated inFIG.5andFIG.6, it is understood that the can barrel cracks during the drawing or during the redrawing when the angle of the tapered part122is 40 seconds or less (comparative examples 1-1, 1-2, 2-1, and 2-2), or 1 minute and 40 seconds or more (comparative examples 1-8, 1-9, 2-8, and 2-9). On the other hand, it is understood that the can barrel does not crack during the drawing and during the redrawing when the angle of the tapered part122is 50 seconds to 1 minute and 30 seconds (comparative examples 1-3 to 1-7, and 2-3 to 2-7).

As described above, according to the present embodiment, even though the fingers of the stripper apply the load to the opening end of the can barrel12during the stripping in the body making step, the tapered part122is provided to have the optimum angle with respect to the can axis, and therefore to slow the change in the plate thickness. By this means, it is possible to improve the release property during the stripping, and to prevent the can barrel from cracking even though the plate thickness of the can barrel is decreased.

According to the invention, it is possible to prevent the can barrel from cracking during the stripping.