Patent Grant
11738382
The principles of the present invention relate to a method for making a shaped metal container, and to a microstructure thereof.
Metal containers are generally used for packing food, paint, ink, gas, liquid spray, particulate material, and beverages, such as soft drinks. The metal containers generally have a cylindrical shape. Such metal containers can be easily produced with known methods in the art, such as by (deep) Drawing and Wall Ironing (DWI).
The metal containers have generally no substantial impact on the quality and taste of the content. Handling is very convenient because the metal container generally does not break when dropped unwantedly. The strength of the metal container is usually provided by the combination of the container and its content. After emptying the metal container the metal container can easily be reduced in volume without the risk of injuries. Finally, the metal container may be recycled.
However, there is a tendency not only to produce the traditional cylindrical metal containers, but also to produce metal containers having the form of glass or plastic (PET) bottle as are presently in the market for beverages. Glass and plastic, used for making such beverage bottles, however, have properties that are very different from metal properties. Differences in properties relate to ductility and handling after heating. For instance, a glass or plastic preform may be blown directly into the required bottle shape. Such shapes are characterized in that over the axial height, the bottle may have (gradually changing) different diameters. The top section may have a smaller diameter (Dt). Towards the bottom, the diameter increases gradually in the middle section to a largest diameter (Dm). Thereafter, the diameter may decrease to a minimum, thereby forming a tailored shape. Subsequently, the diameter increases gradually towards the bottom diameter Db, which is equal to or less than the largest diameter Dm.
Another type of glass bottles are perfume bottles which vials in silhouette having attractive aesthetic shapes. Such silhouettes may be similar to a female silhouette, a football silhouette, an hour glass silhouette, and the like. As understood in the art, such shapes cannot be produced using metal as the container or vial material.
Because of the tailored shape and/or bulging shapes, such bottles containers or vials made of glass or plastic, having properties very different from metal, such as aluminum and steel, it is generally accepted that such shapes cannot be made as such from metal.
It is known to make containers, such as aerosol containers, by blow forming metal, but such method is not suitable for making shaped metal containers similar to the described shaped metal containers. There is a way to improve the cost efficiency is to make a two-piece container, with bottom and sidewall made of two-piece metals and joined together. However, for many applications, one-piece metal beverage containers having an integral bottom are preferred.
Generally, one-piece metal beverage containers are made by (deep) drawing and wall ironing (DWT) or by a Draw and Re-Draw process (DRD). These processes use a combination of ironing and deep drawing, or drawing and redrawing, to produce a pre-determined wall thickness with a smaller diameter and an increase wall height. Starting from a flat blank (in general a disk to achieve a round can), the first drawing operation create a “cup” defined by a diameter and a height. In order to respect the material formability, it is only possible to achieve the final diameter with a sequence of re-draw. All the (re)-drawing operations transform a shape (like a cup) from one diameter to another smaller diameter. The height is given by the volume of material of the original blank. The thickness of the body is about the original thickness. For a tall can, this process creates progressive thickening toward the top of the can. In such conditions, to achieve a tall can with a great ratio height/diameter, a lot of metal shaping steps are required. For DRD containers, a deep drawn container means a container made in general by a large number of re-draw steps to achieve the height/diameter ratio.
A more recent technology, used for decades in beverage industry, introduces the possibility to manage the thickness of the body. The start of the process is same as DRD, namely one draw operation (to make the cup) and at least one re-draw operation to reduce the shape diameter to the final diameter of the can. The next steps of the process only change the body wall thickness, not the diameter. These steps are defined by the motion of a punch (inside the shape) through calibrated rings. The sequence of rings allows reducing progressively the thickness of the body. This part of the process is called wall ironing. The entire process is called Draw and Wall Ironing (DWI). On top of that, the profile of the punch makes possible to get different thicknesses on the body. In general, a thin wall and a thick upper part dedicated to form a neck and seam. This DWI process has a major action on the material especially during wall ironing phase, and is an example of massive work hardening. The DRD process with the re-draw steps has a similar effect on the wall, but to a lesser extent. The drawback, however, is the work hardening. Due to the work hardening phenomenon, the hardness of the body increases significantly. For example, for some types of steel, the hardness can increase to 650 MPa or more. For aluminum, the hardness can increase up to 300-350 MPa dependent on the alloys used. This increase of hardness is accompanied by a corresponding fall in the available elongation, therefore reduced forming capability.
Ultimately, a container preform having a cylindrical body with a cylinder diameter Dc is formed. The DWI and DRD technology are generally used for manufacturing, but the drawing, redrawing and/or ironing generate work hardening of the body of the preform. The drawing and/or ironing generate(s) tensile stress in the material. The tensile stress results in a crack when a particular elongation percentage is surpassed. This work hardening results in a reduction of the elongation percentage of the preform available for further shaping, such as but not exclusively by blow forming or mechanical expansion.
Such metal container preforms may be shaped by outwardly shaping, such as by using blow forming. Thereto, the container preform is positioned in a mold dictating the desired ultimate outer shape of the container. High pressure is applied to the container preform which will be blown outwardly and in contact with the inner surface of the mold. The blow forming of the preform also results in a reduction of the height of the preform.
Metal container preforms may be subjected to necking for reducing the diameter of the top section of the preform. Necking generates compression stress in the material, which results in wrinkles when a particular compression stress threshold is surpassed. A hard material is more sensitive to wrinkles because the compression stress to achieve is higher to move to the plastic domain. During necking, the free end of the preform is subjected to a number of small reductions of the diameter.
It is evident that the working of the preform increases the strength or hardness of the worked preform part. Such increase in hardness or strength is not desired because it is counter acting other types of shaping that require softer metal. This applies even more for products that have a non-circular body.
An option for having better performance in either a DWI process or a necking process could be the selection of adapted aluminum or steel alloys. However, such alloys may have other or less suitable properties and/or alloys are not generally used, which has a result on the material costs.
The principles of the present invention provides both a shaped metal container and its preforms that exhibit a rounded grain structure characteristic created by an annealing process and a method for making a shaped metal container. The process of making the metal container results in a quicker process time and uses less metal (at least 10% metal weight savings) thus allowing for a decrease in the costs of making such shaped metal containers. Additionally, the current process results in a surprising and unexpected way of identifying a metal shaped container. The shaped metal container exhibits a rounded grain structure characteristic created by an annealing process. The rounded grain structure, which is defined by an aspect ratio at least in part, constitutes the basis for the improvement of the properties and represents a “fingerprint” for determining whether the shaped metal container (or its preforms) was subjected to annealing after work hardening. In one embodiment, the annealing process may be performed at a higher temperature than typical heating of work hardened metal, such as work hardened rolled metal (e.g., 3000 series aluminum, and in particular, 3104 series aluminum alloy), which metal in non-annealed form is used for forming metal containers (e.g., beverage containers). In an alternative embodiment, the annealing process may be performed at an annealing temperature at or slightly higher (e.g., within 5° C.) than a recrystallization threshold temperature or solid-state solution threshold temperature.
In one embodiment, a method for making a shaped metal container, may include a container middle section having at least one middle section diameter Dm, which container middle section is connected at one end to a container bottom section having at least one bottom section diameter Db, and at the other end connected to a container top section having a container opening, and having at least one top section diameter Dt by: (i) providing a container preform having a cylindrical body with a diameter Dc, (ii) inwardly shaping by necking at least a section of the cylindrical body, and (iii) outwardly shaping at least a section of the cylindrical body, where at least a section to be inwardly or outwardly shaped is annealed such that at least one of the middle section diameter Dm, the bottom section diameter Db, and the top section diameter Dt is greater than, and at least one of the middle section diameter Dm, the bottom section diameter Db and the top section diameter Dt, is smaller than the cylinder diameter Dc of the container preform.
The principles of the present invention is based on the insight, which by making use of an annealing step carried out on a container preform, the yield strength is reduced, and ductility increased, whereby the metal of the container preform becomes softer, and allows for more elongation before failure. In the annealing step, the metal of the preform may be subjected to an elevated temperature generally in the range of 150-450° C., such as 200-400° C. and 200-350° C. (preferred range 200° C. to 450° C., more preferred range 250° C. to about 400° C., most preferable range 315° C. to about 385° C.) that alters the material property yield strength, ductility and elongation at break, whereby the material becomes more workable. The annealing is carried out at a suitable temperature during a suitable period of time for acquiring the desired reduction in yield strength and improvement in ductility and elongation at break or failure. The time is dependent on the technology for imparting the product with the annealing temperature. The faster the annealing temperature is reached, the shorter the annealing period of time, which may be useful in high volume production rate processes.
Generally, for aluminum, the temperature is in the range of 200° C.-400° C., for so-called high temperature annealing, the annealing temperature is higher, such as 350° C.-454° C. for a period of time of 1 μsec to 1 hour, such as 0.1 sec to 30 min, 1 sec to 5 minutes, or 10 sec to 1 minute. For steel, the annealing temperature range is normally much higher and may be for instance 500° C.-950° C. and the period of time may be for instance of 1 μsec to 1 hour, such as 0.1 sec to 30 min, 1 sec to 5 minutes, or 10 sec to 1 minute. It is evident that dependent on the work hardened aluminum alloy used and the thickness of the material, the temperature and period of elevated annealing may be adjusted. Such adjustments, however, are within the skills of the person skilled in the art. The annealing may be carried out in an oven in which the container preform is present for a sufficient period of time in order to acquire the desired reduction in yield strength or increase in ductility and elongation.
The annealing treatment results in a reduction of the hardness, a reduction of the yield strength, and an increase of ductility. Moreover, as a microstructure of a cylindrical metal preform changes during an annealing process that heats the metal preform to temperatures higher than typical heating processes as described herein below, grains of the annealed sections of the metal container are changed from having high average aspect ratios (e.g., greater than about 5) from rolled work hardened sheet-metal to having short average aspect ratios of less than about 4 to 1, and preferably less than 3.5 to 1, more preferably less than about 3 to 1, most preferably less than about 2.5 to 1, or most preferred less than about 2.0 to 1, because of recovery, recrystallization and possible grain growth.
In the oven, and in one embodiment, the entire container preform is annealed so that the yield strength of the container preform is decreased, the ductility increased, and the percent elongation-to-break increased over the entire height. Such a change in properties is not always desired when in a subsequent making step for the shaped metal container, a shaping step is carried out at a axial force, with an axial load that cannot be withstood by other sections of the container preform that are less strong, and, therefore, would collapse or irregularities, such as wrinkles, buckles and/or pleats, are formed.
Accordingly, the principles of the present invention provide as an option that at least one sub-section is annealed, whereas other sections arc not annealed and maintain the original material properties. Such sectional annealing is possible by induction annealing or other localized heating techniques.
In an induction annealing treatment, the relevant section of the container preform is subjected to electromagnetic induction generating within the metal so called Joule heat of the metal. For such electromagnetic induction heating, an induction heater is used that includes an electro magnet through which a high-frequency alternating current is passed. Obviously, the conditions for the induction heating are dependent on the size of the container preform, on contact and distance to the induction heater, and/or the penetration depth. In the case of using induction heating on work hardened rolled sheet metal (e.g., aluminum and its alloys), such as 3000 series aluminum, such as 3104 series aluminum, time for heating the work hardened rolled sheet metal to above a recrystallization threshold temperature to cause the aspect ratio of the grains of metal to be reduced to less than about 4, less than about 3.5, less than about 3, less than about 2.5, or less than about 2, may be less than 5 seconds. In contrast to induction heating, a box oven or other air heating technique may take five minutes or less to raise the temperature of the metal so as to cause the aspect ratio of the grains of metal to be reduced to less than about 4, less than about 3.5, less than about 3, less than about 2.5, or less than about 2. Time of maintaining the temperature above the recrystallization threshold level for either of the heating processes may vary based on the thickness of the metal and specific composition of the metal, but is easily ascertainable by one skilled in the art. A temperature to be reached to cause the aspect ratios in a shorter period of time that may be used for mass production of metal containers formed by work hardened rolled aluminum and its alloys may be higher, such as between about 315° C. and 450° C., and between about 325° C. and 350° C., and at or about 350° C. for a time duration between about 0.1 second to about 1 minute, for example. Cooling of the annealed metal preform may be performed in ambient temperature, such as room temperature.
In the subsequent shaping step, the shaping is the result of a plastic (permanent) deformation and not of an elastic deformation. Due to the annealing treatment, the material may be elongated to an extent of about 10% to 20%, dependent on the type of material and material alloy, such as 3000 series, like 3104H19. Since the annealing treatment results in an increase of elongation, it is evident that the annealing treatment has a beneficial effect on outwardly shaping, which is generally based on a material elongation. The beneficial effects of the annealing treatment is based on the conversion of the flat, “pancake” work hardened grain structure having an elongated average aspect ratio (e.g., greater than about 5) into a rounded grain structure having a shortened average aspect ratio (e.g., less than about 4 to 1, and preferably less than 3.5 to 1, more preferably less than about 3 to 1, most preferably less than about 2.5 to 1, or ideally less than about 2.0 to 1), which is more symmetrical and multidirectional in properties, and has less stresses and with significantly enhanced formability.
In relation to the sections of the container preform that could be subjected to an annealing treatment, it is evident that when the container middle section is to acquire a larger diameter than the container preform by outwardly shaping, such as by blow forming, then the middle section is subjected to the annealing treatment. The container bottom section may not be subjected to an annealing treatment because the bottom is the thickest section of the container preform, which thickness is substantially equal to the thickness of the disk shaped blank. The transition from the bottom to the cylindrical body is generally less strong due to the change in thickness, the curved shape, and its location, so annealing of this transitional area is generally not required. In relation to the container top section, which is generally to be subjected to a necking, or inward shaping, annealing is not required or only to a limited extent. When annealed, the subsequent necking operation can be performed on hard material. The use of annealing to reduce yield strength can help to reduce a number of die necking steps in the multi-die necking, which reduces complexity and cost of forming metal containers. Although blow forming and die necking are presented herein to shape a metal container from an annealed metal preform, it should be understood that any other metal shaping technologies, such as pressure forming, hydro forming, mechanical, and/or non-mechanical metal shaping technologies, may be utilized in accordance with the principles of the present invention. Because of the rounded grains of the metal, the metal preform formed of work hardened aluminum and its alloys may be reshaped at room temperature to expansion level than previously considered possible. However, when the necked container top section is to be provided with a thread and/or a circumferential bead, then annealing is generally utilized as a thread and/or circumferential bend is more easily formed on metal with reduced stress. Since the extent of annealing may be different between the container middle section and the container top section, induction annealing may be utilized so that each of the sections is annealed to a different extent, as desired.
When the container preform is to be provided with a lacquer and/or a printing, the annealing treatment is performed prior to the subsequent lacquering and/or printing treatment. Accordingly, annealing is avoided after applying lacquer and/or print to the container preform as high temperature annealing generally has a negative effect on the lacquer and/or print.
The outwardly shaping may be carried out with various different mechanical and non-mechanical techniques, such as mechanical expansion or stretch, but blow forming may be used because of the high quality of the outwardly shaping. In addition, it is possible, when desired, to impart the outer surface of the blow formed wall with strengthening or aesthetic structures extending inwardly and/or outwardly. Such structures are frequently present in the body wall of glass container or bottle for beverages, such as soft drinks.
The outwardly shaping by necking results in an axial load on the container preform. Such axial load may amount to about 1000N-1800N, and more preferably to about 1300N-1600N which is generally an axial load too large to withstand by the foot of the preform for the blow formed preform. When a top section that is too soft is subjected to the necking operation, formation of undesired wrinkles results. This could be overcome by the selection of another metal temper, or an increased number of necking dies used or change in the thickness of the container top section. In one embodiment according to the present invention, it is preferred to carry out under such circumstances the necking operation on a container preform or a blow formed container preform with the preform accommodated and supported, particularly at its sections or parts having a lower strength and susceptible to collapse the axial load, by a supporting sleeve.
Often, the shaped metal container is to be provided at its opening with a thread unto which a screw cap may be screwed for closing the shaped metal container. It is generally preferred after filling the metal container, to apply the cap while applying an axial capping force. The cap is mounted on the thread and over the opening. For such capping, but also for a traditional handling of the metal container before and during filling and later transport, the necked container top section may be provided with a so called cap bead.
It will be apparent to the skilled person, that the formation of this cap bead and/or the thread reduce the strength of the necked container top section, so that this container top section may have an insufficient strength for withstanding the axial load. Accordingly, the principles of the present invention provide a solution to this problem in the form of at least one axial interruption provided in the circumferential bead and/or in the thread. This interruption in the bead restores part of the original shape and therefore increases the axial strength. For an increase of the axial strength over the circumference of the container top section, two, three or more axial interruptions may be spaced apart over the circumference of the cap bead. Similarly, such axial interruptions may also be provided in the thread of the container top section, where the axial interruptions may be spaced apart over the circumference as long as the axial interruptions do not interfere with the screwing action of the cap. The application of these axial interruptions increases the axial strength such that the axial load to be applied during the capping operation is generally withstood without collapse of the container top section.
After the annealing of the preform in particular the cap middle section, resulting in a softer middle section wall, the transition to the bottom is less soft and becomes stronger with the increase of the thickness towards the bottom. Accordingly, this transitional section between the container middle section and container bottom section may be difficult to outwardly shape by blow forming. Accordingly, the ultimate shape of the foot of the bottom section may not be as desired. This problem in relation to the difficulty of blow forming the transition between the container middle section and the container bottom section may be overcome by applying an axial compression onto the container metal preform during the blow forming. Applying an axial compression results in a larger flow of material outwardly, but also more in the direction of the bottom and the foot, and thereby to a better formation of the desired shape of in particular the transition part for the foot part.
After necking or outwardly shaping, the free ends of the opening may be trimmed and curled. Trimming is generally required for providing a shaped metal container with the specified (height) dimensions. Curling of the free end not only improves the aesthetic appearance, but also provides a smooth surface for sealing, and when the consumer intends to drink with the mouth directly from the shaped metal container. Obviously, such curling of the free end results in some material loss, as will be the result of the trimming operation.
The shaped metal container may be a one-piece container, such as a metal beverage bottle. Such bottle is generally characterized by a container bottom section having a diameter Db that is generally greater than or equal to the diameter Dc of the cylindrical part of the preform, the container middle section may have a first diameter D ml larger than or equal to Dc, and a second diameter Dm2 equal or smaller than the diameter D ml but larger or equal to the diameter Dc, and the container top section is smaller than the diameter Dc. Accordingly, this metal beverage bottle is formed by annealing the preform followed by blow forming and thereafter necking, or formed by necking followed by blow forming. The necking operation reduces the diameter below the diameter Dc of the preform, whereas blow forming increased the diameter beyond the diameter Dc of the preform. The container may have gradually changing diameters between the various container sections, which are greater, equal and/or smaller than Dc.
Another aspect of the principles of the present invention relates to a shaped metal container of which at least a section has been subjected to annealing, whereby the annealed section acquires a rounded grain structure, as defined by an average aspect ratio being shortened below about 4.0. The annealed section becomes more multidirectional in properties because of the acquired rounded grain structure through recovery reduction in stress in metal and recrystallization morphology grain structure changes from elongated to more rounded shape. It is noted that the grain is no longer elongated as initially provided from a rolled, work hardened sheet metal, and although still non-uniform in nature, typically has an average aspect ratio in cross-section (of the largest diameter over the smallest diameter) that is in the range of less than about 4 to 1 (i.e., 4), less than about 3.5, less than about 3, less than about 2.5, or less than about 2. As a result of the annealing treatment, the hard worked elongated or flat “pancake”-like grain form has a large average aspect ratio (e.g., greater than 7), converts towards an rounded grain shape (e.g., less than about 4 or less than about 2), thereby decreasing hardness and increasing elongation of the metal. Subsequent blow forming and die necking result of a metal preform in an increase in hardness and strength of the metal.
Another aspect of the principles of the present invention relates to a preform for a shaped metal container, where the preform or a preform section has a rounded grain structure with an aspect ratio in the range of less than about 4, less than about 3.5, less than 3, less than about 2.5, or less than about 2.
Another aspect of the principles of the present invention relates to a shaped metal container, such as a one-piece or two-piece container, having a container middle section connected at one end to a container bottom section, and at the other end to a top section. At least part of the container top section, the container middle section and/or the container bottom section, being shaped by necking and another part shaped by outwardly shaping, such that at least one of the middle section diameter Dm, the bottom section diameter Db, and the top section diameter Dt is greater than, and at least one of the middle section diameter Dm, the bottom section diameter Db and the top section diameter Dt is smaller than the cylinder diameter Dc of the container preform from which container preform the shaped metal container has been made. The diameters may gradually change between the container sections.
As indicated here and before, the necked container top section is often provided with a thread and/or a bead provided with at least one axial interruption. For obtaining a metal beverage bottle, one embodiment of the container middle section is outwardly shaped, and the diameter Dm is greater than the diameter Dc, and the bottom section may be outwardly shaped with the diameter Db greater than the diameter Dc.
Finally, for mimicking closely a glass bottle, such as a glass beverage bottle, the container top section, container middle section and/or container bottom section may be provided with inwardly and/or outwardly extending strengthening of aesthetic structures.
The aforementioned and other features and characteristics of the method for making a shaped metal container and of the shaped metal container according to the invention will be appreciated from the following description of several embodiments of the method and shaped metal container according to the invention although the invention is not restricted thereto.
Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein:
The skilled person will appreciate that the structures 202 and 302 may also be incorporated in the other sections of a shaped metal container according to the principles of the present invention, and may be present in one and the same shaped metal container. The structures 202 and 302 may also be configured to provide the appearance of a logo of the company that has filled or will fill its content into the shaped metal container. In addition to such logo, imprints may also be applied to the outer surface of the shaped metal container.
The container middle section 102, container bottom section 110 and the container top section 118 all have been subjected to a blow forming shaping, whereas in the container middle section 102, the structures 18 have been formed. The blow formed preform 418 may then subjected to an inwardly shaping by necking of the top section 420 of the blow formed container shown in
The enlarged view of the container top section 118 as shown in
Produced by the process 500 is essentially the same preform 422 as produced in the method 400 according to the principles of the present invention illustrated in
Hereafter, the preforms 426, 430, and 432 are produced as shown in
The shaped metal container may be formed from aluminum or steel from suitable alloys and/or tempers.
Generally, the blank 420 may have a diameter of 100-150 mm, such as 125 to 135 mm and a thickness that may be of 0.30 to 0.60 mm, such as 0.40 to 0.50 mm. The cups 404-412 may have a diameter of 80-100 mm, 60-70 mm and 40-50 mm, respectively. The preform 414 may have a diameter of 40 to 50 mm, such as 45 mm, for producing the shaped metal container 100 or 200, as described in
As shown by the droplet magnification of
Instead of a cylindrical body wall 418, it is possible to provide the foot 114 with an outward bulging transitional section 616 as shown in
In addition, and as discussed above, it is beneficial that at least the container middle section 102 and the bottom section 110 have been subjected to the annealing treatment, thereby reducing the yield strength and increased ductility and elongation to failure. The axial load applied may be in the order of 1000 to 1800N, such as 1200-1700N, such as 1600N.
As shown in
The elongation-to-break of, in particular, the container middle section and bottom section may be about 10% to 25%, such as 15% to 20%, such as 18%. Such elongations are possible due to the prior annealing treatment, as described further herein, and the selection of the proper thickness and preferably the alloy and/or temper used. Obviously, these selections can be made by the skilled person and will also be dependent on the selection and type of work hardened Al metal, such as aluminum and steel. A suitable alloy, for example, is the aluminum alloy 3104-H19.
Work-hardened metal, such as aluminum or steel, and its alloys is a term known to one skilled in the art as the strengthening of a metal by plastic deformation. It is further understood that work hardened aluminum alloy will also result in the presence of greater residual stresses and the high dislocation density in the metal. The residual stresses and dislocation density can lead to higher strength and reduced elongation.
The term “rounded” used herein when describing annealed grain structure means any type of shape (i.e., geometric or non-geometric) that includes space both inside lines defining the shape and the lines of the shape.
A shaped metal container 900b according to
The annealed upper middle section 1210a, as shown, is subjected to an inwardly shaping illustrated by arrow 1214, which may be carried out by inward necking or other suitable technique. From the inward necking process, an inwardly shaped upper middle section 1210b results.
The annealed lower middle section 1212a is subjected to outward shaping by any suitable technique illustrated by arrows 1216, such as blow forming or mechanical shaping to cause an outwardly shaped lower middle section 1212b to be created. The end product 1200b is tailored having at the same time and inwardly shaped section with diameter D1m, and outwardly shaped section with diameter D2m, which arc both different from the original diameter Dc.
In accordance with the principles of the present invention, a shaped metal container, such as an aluminum bottle configured is to be lightweight such that shipping and packaging costs may be reduced. Such a lightweight shaped metal container may be reduced. Such a lightweight shaped metal container may be reduced to less than 20 grams, and as low as about 17 grams or lower. The lightweight shaped metal container is to be strong enough to endure shipping and consumer use environments. To achieve such results, annealing, blow forming and multi-die necking processes (see
With regard to
At step 1308, a body maker step may be configured to significantly elongate the cup formed by the cupper step 1306. The body maker step 1308 may include a wall ironing stage that uses ironing rings that progressively reduce sidewall thickness, while at the same time, significantly increase tensile properties. As an example, the sidewalls of the cup may be thinned from 0.60 mm to around 0.15 mm. Additionally, a base dome profile may also be formed in the body maker, which is conventional practice for making cans. Resulting from the body maker is an extended cylindrical preform (see
The cylindrical metal preform may be washed and dried at steps 1312 and 1314. In drying the cylindrical metal preform, a washer oven may heat the cylindrical metal preform to less than about 200° C. In being about a certain temperature, the temperature may be a few degrees higher or lower than the certain temperature and be within an appropriate temperature range in accordance with the principles of the present invention. It should be understood that other temperatures may be utilized to dry the cylindrical metal preform, but that the temperatures used do not exceed a temperature that would alter the structural composition (e.g., grains) of the metal, such as by annealing to reduce tensile strength. By washing and drying the cylindrical metal preform, lubricant and dirt are removed from the surface so as to ensure that the metal surface is suitable for coating application and adhesion processes.
In accordance with the principles of the present invention, an annealing step 1316 is utilized to anneal a portion of or an entire cylindrical metal preform. Contrary to conventional heating, annealing heats a portion of or the entire cylindrical metal preform (i) to temperatures that exceed typical heating processes for rolled sheet metal used for beverage and/or aerosol containers. Moreover, as a result of the annealing process described herein, further processing and fabrication of a “useable” container from a fully annealed preform may be performed.
As a result of the significantly altered grain structure from the increased heated cylindrical metal preform is the ability to perform blow molding at room temperature to produce larger expansion than possible with lower or no annealing having been performed. As an example, blow molding of the rolled sheet metal with little or lower temperature annealing at room temperature results in a maximum expansion of about 8%, and generally below 3%, whereas it has been realized after annealing that an increase expansion of the cylindrical metal preform of upwards of or over 18% can be achieved at room temperature. As an example, one high-pressure blow may expand a 45 mm diameter cylinder to a 53.0 mm diameter cylinder in a single blow operation at room temperature. The annealing may be performed in the number of different ways, including (1) full body annealing using a recirculating air box oven, (2) full body annealing using a single station induction unit, and (3) localized annealing using a single station induction unit. It should be understood that additional and/or alternative annealing processes may be utilized in accordance with the principles of the present invention. Moreover, at least one section along the sidewall may have grains with an average aspect ratio less than about 4 to 1, where the section(s) along the sidewall is a horizontal section along a particular height of the sidewall that extends around the sidewall. In one embodiment, grains on opposing sides of the section(s) along the sidewall have an average aspect ratio higher than the average aspect ratio of the section(s) along the sidewall.
As previously described, rolled sheet metal is work hardened and has a highly organized grain structure with elongated grains (e.g., aspect ratio greater than 7) as a result of stretching the metal when forming the sheet. TABLE I shows a few data points of the average aspect ratio for the rolled sheet metal that undergoes the annealing process, as described herein.
Continuing with
As it is conventionally performed on metal bottles used for consumer goods, a multi die necking process 1334 is performed. As understood in the art, the conventional multi-die necking process 1334 may include upwards of 50 or more steps depending on the configuration of the metal container. In the event of the metal container appearing in a bottle shape, a higher number of die necking operations are utilized to provide for a smooth transition along a neck of the metal bottle. However, the use of die necking can be used to either increase or decrease a diameter of the metal container, so the multi-die necking operation 1334 is generally used to form a body shape and/or a neck of a metal bottle. Because die necking is a complex and time consuming operation, the more die necking steps that can be eliminated, the faster manufacturing of bottles can occur with a reduction in loss due to errors in the die necking processes.
In accordance with the principles of the present invention, rather than simply performing the multi-die necking operation 1334, a blow forming operation 1336 and multi-die necking operation 1338 may be performed on the annealed cylindrical metal preform. The blow forming operation 1336 may be performed at 40 Bar or higher using high-pressure air or other medium. Again, the blow forming operation 1336 may be performed at room temperature and produce a significantly expanded container due to the annealing performed at step 1316, as previously described. As a result of performing the blow forming operation at step 1336 and multi-die necking operation at step 1338, the metal may be work hardened, whereby the grains of the metal may be stretched to have a higher aspect ratio than that after being annealed, as previously described, along with having increases in tensile strength in the neck area following successive die necking operations. By expanding and contracting annealed cylindrical metal preform, the metal is work hardened and the aspect ratio of the grains may increase and decrease, respectively (see TABLE I).
Following the multi-die necking at step 1338, a leak testing step 1340, washing step 1342, and palletization step 1344 may be performed. Once palletized, the shaped metal containers may be provided to a filling line to fill the metal containers with a product, such as a soft drink. Although the annealing 1316 is shown to be performed prior to decoration of the shaped metal container, decoration technology that is capable of being heated to temperatures of 300° C. or higher may enable the annealing 1316 to be performed at a different position within the process 1300.
As a broad generalization, steps 1302-1314 define a process for forming the cylindrical metal preform, steps 1318-1332 define a decoration process, steps 1336 and 1338 define a reshaping of the cylindrical metal preform into a shaped metal container, and steps 1340-1344 define a post-metal container shaping process including inspection, cleaning, and packaging.
As previously described, the annealing and blow forming/multi-die necking steps 1316 and 1336 enable the ability to produce shaped metal containers that have heretofore been unable to be produced due to limited expansion capabilities of rolled sheet metal for use in consumer packaging, such as soft drinks and carbonated beverages. With the inclusion of the annealing and blow forming/multi-die necking steps 1316 and 1336/1338, non-symmetrically shaped containers may be produced using a single blow at room temperature making lighter weight metal packages.
As a result of utilizing the principles of the present invention, a number of features and/or results are provided that are not otherwise available through use of a conventional multi-die necking approach, including:
(1) A smaller diameter preform may be used, which reduces a finished shaped metal vessel weight, and also benefits downstream processes by eliminating metal shaping processing steps that would have to be performed or simplifying the metal shaping processing.
(2) The annealing of the cylindrical preform may recrystallize the work hardened “pancake”-like grains of the rolled sheet metal, which eliminates built-in stresses that are inherently part of the rolled sheet metal. Such elimination of the built-in stresses considerably increases ductility and, thus, formability. As an example, in the case of using 3014 H19 alloy, an increase in elongation extends from less than 3% (after wall ironing) to about 18%.
(3) The use of the blow forming between the shaping and decoration steps enables the annealed cylindrical metal preforms to be shaped in ways that would be impossible by multi-die necking alone. For example, the blow forming stage allows inclusion of flutes, surface patterning, embossing, etc., to be included in the overall design without having to perform additional necking processes. These flutes and the other patterns may provide for work hardening at those locations, which provide structural support for the shaped metal vessel.
(4) Because the blow molding process is frictionless, the vast majority of the elongation generated by the annealing process may be used in body shaping.
(5) A combination of annealing and blow forming means that a large number of multi-die necking stages are significantly reduced, and mechanical expansion stages may be eliminated.
(6) An entire lower body of the shape metal container can be formed in a single operation without inducing any work hardening or stresses in the neck area.
(7) A potentially more robust and less complex production process may be achieved, and a number of multi-die necking stages may be reduced significantly (e.g., 40 or more multi-die necking stages for producing a particular shaped metal container may be reduced to about 20 multi-die necking stages).
(8) A reduction in the number of neck forming stages may be reduced, which necessarily reduces the number of trimming and lubrication stages plus the associated equipment for trimming and lubricating.
(9) A significant reduction of risk of splits during curl formation of a lip of the shape metal vessel may results from recrystallization of the finish area of the metal container.
(10) Quick shape change-overs on a production line may be possible if the shaped differences are limited to an area of the sheet metal vessel formed by the blow forming or other metal shaping processes.
The effect of annealing and blow forming on hardness and grain structure of various sections of preforms achieve results previously not possible. Preforms made with the process of
Annealed test shells were subjected to a tensile test (LO: 49.3 mm, 3 mm/min, at 20° C.), according to NF EN ISO 6892-1 method A. The annealed test shell had the following tensile strength characteristics:
Rm: the tensile strength Rm indicates the limit at which the metal tears under pressure, i.e., the maximum tensile stress;
Rp 0.2: Stress at which the metal undergoes a 0.2% non-proportional (permanent) extension during a tensile test;
Elongation: the maximum elongation at break.
After annealing or after annealing and blow forming, the preforms were subjected to a test for hardness. The Vickers Hardness (MPa) was measured in various sections over the height of the annealed preforms, and of the annealed and blow formed preforms. The Vickers hardness was measured according to NF ISO 6507-1. The results were as follows in TABLE II:
The sections at a height of 170 mm and 130 mm were sections subjected to a necking operation and were not subjected to blow forming. The sections at 90 mm and 15 mm were sections that had been subjected to blow forming. The section at 50 mm substantially retained the original diameter and was not, or to a minor extent, subject to blow forming. The hardness results given in TABLE II above, show that the blow forming, which is a form of work hardening, resulted in an increased hardness.
The effects in relation to the change in grain structure may be explained in that the flat, “pancake”-like grain structure is asymmetrical and two-directional, so that the properties are different in both directions. The rounded grain structure is symmetrical and omni-directional, so that the properties are more uniform in any direction. The flat, “pancake”-like grains extend parallel to the rolling direction, and are therefore prone to splitting during necking or flanging. Moreover, the structure includes undue stress. The rounded grain structure is far less prone to splitting during necking and flanging. Because the grains extend more omni-directional, the structure includes less stresses and is thus more formable.
As indicated hereinbefore, in the making of a shaped metal container provided with a container bottom section, container middle section, and container top section that have different diameters larger, equal, and smaller than the preform diameter Dc, conflicting shape making conditions exist. Because in the making of such shaped metal container the sections or section parts having a diameter larger than the diameter Dc should be less hard such as a lower yield strength, and a high ductility and elongation at break, whereas sections or section parts that have a diameter smaller than Dc and produced by necking use a relatively high strength or hardness. Above that, situations have been described in which the preforms may be first subjected to necking and subsequently other parts subjected to blow forming. These conflicts of manufacturing processes may be overcome or surpassed by utilizing the principles of the present invention inclusive of inward shaping and outward shaping, where the outward shaping is performed after annealing treatment to enable greater expansion of the annealed preform.
It will be obvious to the skilled person that the method for making the shaped metal container makes use of various techniques already existing in the container making process. Accordingly, the processes described herein can be easily incorporated in existing container producing lines.
The annealing process provides for an elegant form of outwardly shaping, particularly by to incorporate aesthetic and ornamental designs, such as logos, may be carried out in an oven that is relatively slow or by induction that is relatively fast. Induction annealing or annealing provides the further advantage of locally fast annealing or annealing a section or part of the section of the preform. In addition, it is possible to first have the preform annealed in an oven as a whole, and after a blow forming step, a further annealing process may be carried out in a particular section or section part where after that part is further subjected to a blow forming step as desired or dictated by the desired shape or form of the shaped metal container. The annealing results in the reduction of the hardness, in particular of the yield strength, whereas the elongation at break is increased, such as to 10-25%, more particularly 15-20%, such as 18-20%.
The shaped metal container is generally produced from a metal, such as aluminum or steel, or from alloys, which may have a particular temper. It is also possible to use combinations of metal with plastics and with glass.
Finally, although not described in detail, in making the shaped metal container, it is also possible to make a shaped metal container that does not have a circular cross-section, but may have a non-circular cross section, such as an oval, ellipse, or any other geometrical or non-geometrical shaped cross-section.
Although particular embodiments of the present invention have been explained in detail, it should be understood that various changes, substitutions, and alterations can be made to such embodiments without departing from the scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13187775 | Oct 2013 | EP | regional |
This application is a divisional of co-pending U.S. patent application Ser. No. 15/027,969 filed Apr. 7, 2016, which application is a 371 National Stage application of International Application No. PCT/US2014/059533, filed Oct. 7, 2014, which claims priority to co-pending Patent Application having Serial No. EP 13187775.5, filed Oct. 8, 2013, the contents of which are incorporated herein by reference in their entirety.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 15027969 | US | |
| Child | 17085668 | US |
