Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
1998-08-13
2001-12-04
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S552000, C148S692000
Reexamination Certificate
active
06325872
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to aluminum alloy sheet and methods for making aluminum alloy sheet. Specifically, the present invention relates to aluminum alloy sheet and methods for making aluminum alloy sheet wherein the sheet is particularly useful for forming into drawn and ironed container bodies.
BACKGROUND OF THE INVENTION
Aluminum beverage containers are generally made in two pieces, one piece forming the container sidewalls and bottom (referred to herein as a “container body”) and a second piece forming the container top. Container bodies are formed by methods well known in the art. Generally, the container body is fabricated by forming a cup from a circular blank of aluminum sheet and then extending and thinning the sidewalls by passing the cup through a series of dies having progressively smaller bore size. This process is referred to as “drawing and ironing” the container body.
A common aluminum alloy used to produce container bodies is AA 3004, an alloy registered with the Aluminum Association. The physical characteristics of AA 3004 are appropriate for drawing and ironing container bodies due primarily to the relatively low magnesium (Mg) and manganese (Mn) content of the alloy. A desirable characteristic of AA 3004 is that the amount of work hardening imparted to the aluminum sheet during the can making process is relatively minor.
Aluminum alloy sheet is most commonly produced by an ingot casting process. In this process, the aluminum alloy material is initially cast into an ingot, for example having a thickness of from about 20 to 30 inches. The ingot is then homogenized by heating to an elevated temperature, which is typically 1075° F. to 1150° F., for an extended period of time, such as from about 6 to 24 hours. The homogenized ingot is then hot rolled in a series of passes to reduce the thickness of the ingot. The hot rolled sheet is then cold rolled to the desired final gauge.
Despite the widespread use of ingot casting, there are numerous advantages to producing aluminum alloy sheet by continuously casting molten metal. In a continuous casting process, molten metal is continuously cast directly into a relatively long thin slab and the cast slab is then hot rolled and cold rolled to produce a finished product. However, not all alloys can be readily cast using a continuous casting process into aluminum sheet that is suitable for forming operations, such as for making drawn and ironed container bodies.
Attempts have been made to continuously cast AA 3004 alloy. For example, in a paper entitled “Production of Continuous Cast Can Body Stock,” which was presented by McAuliffe, an employee of the assignee of the present application, on Feb. 27, 1989, at the AIME meeting in Las Vegas, it is disclosed that limited testing was conducted with two manufacturers of 12 ounce, 90 pound cans (i.e., a minimum buckle strength of 90 p.s.i.). One test produced 3004 can stock. The paper discloses that “[b]oth tests, in the 2-3% earing range, verified that the surface and internal quality and structure were sufficient to produce cans of acceptable quality.” However, it has been found that the continuously cast AA 3004 alloy is unsuitable for typical high carbonation beverages, such as soda, because it has insufficient buckle strength when employed using current typical stock gauges (e.g., from about 0.0112″ to 0.0118″) as opposed to stock gauges used at the time of the McAuliffe article (e.g., from about 0.0124″ to 0.0128″). This is due to the poor after-bake characteristics of continuously cast AA 3004 alloy that is produced having suitable earing levels. This is discussed in more detail hereinafter in connection with examples of the physical characteristics of continuously cast AA 3004 alloy.
U.S. Pat. No. 4,238,248 by Gyongos et al. discloses casting an AA 3004 type alloy in a block casting apparatus. The alloy had a magnesium content from 0.8 to 1.3 percent and a manganese content from 1.0 to 1.5 percent, with up to 0.25 percent copper. As used throughout the present specification, all percentages refer to weight percent unless otherwise indicated. However, there is no disclosure of processing the cast strip into sheet suitable for container bodies.
U.S. Pat. No. 4,235,646 by Neufeld et al. describes the continuous casting of an AA 5017 aluminum alloy that is useful for beverage container bodies and container ends. The alloy includes 0.4 to 1.0 percent manganese, 1.3 to 2.5 percent magnesium and 0.05 to 0.4 percent copper. However, it is also disclosed that “copper and iron are included in the present composition due to their inevitable presence in consumer scrap. The presence of copper between 0.05 and 0.2 percent also enhances the low earing properties and adds to the strength of the present alloy.” In Examples 1-3, the copper content of the alloys was 0.04 percent and 0.09 percent. In addition, the process includes a flash anneal step. In one example, the sheet stock disclosed by Neufeld et al. had a yield strength after cold rolling of 278 MPa (40.3 ksi) and an earing percentage of 1.2 percent.
U.S. Pat. No. 4,976,790 by McAuliffe et al. discloses a process for casting aluminum alloys using a block-type strip caster. The process includes the steps of continuously casting an aluminum alloy strip and thereafter introducing the strip into a hot mill at a temperature of from about 880° F. to 1000° F. (471° C.-538° C.). The strip is hot rolled to reduce the thickness by at least 70 percent and the strip exits the hot. roll at a temperature of no greater than 650° F. (343° C.). The strip is then coiled to anneal at 600° F. to 800° F. (316° C.-427° C.) and is then cold rolled, annealed and subjected to further cold rolling to optimize the balance between the 450 earing and the yield strength. The preferred annealing temperature after cold rolling is 695° F. to 705° F. (368° C.-374° C.).
U.S. Pat. No. 4,517,034 by Merchant et al. describes a method for continuously casting a modified AA 3004 alloy composition which includes 0.1 to 0.4 percent chromium. The sheet stock has an earing percentage of 3.12 percent or higher.
U.S. Pat. No. 4,526,625 by Merchant et al. also describes a method for continuously casting an AA 3004 alloy composition which is alleged to be suitable for drawn and ironed container bodies. The process includes the steps of continuously casting an alloy, homogenizing the cast alloy sheet at 950° F.-1150° F. (510° C.-621° C.), cold rolling the sheet, and annealing the sheet at 350° F.-550° F. (177° C.-288° C.) for a time of about 2-6 hours. The sheet is then cold rolled and reheated to recrystallize the grain structure at 600° F.-900° F. (316° C.-482° C.) for about 1-4 hours. The sheet is then cold rolled to final gauge. The reported earing for the sheet is about 3 percent or higher.
U.S. Pat. No. 5,192,378 by Doherty et al. discloses a process for making an aluminum alloy sheet useful for forming into container bodies. The aluminum alloy includes 1.1-1.7 percent magnesium, 0.5-1.2 percent manganese and 0.3-0.6 percent copper. The cast ingot is homogenized at 900° F.-1080° F. for about 4 hours, hot rolled, annealed at 500° F.-700° F., cold rolled and then annealed at 750-1050° F. The body stock can have a yield strength of 40-52 ksi after the final cold rolling.
U.S. Pat. No. 4,111,721 by Hitchler et al. discloses a process for continuously casting AA 3004 type alloys. The cast sheet is held at a temperature of at least about 900° F. (482° C.) for from about 4 to 24 hours prior to final cold reduction.
European Patent Application No. 93304426.5 discloses a method and apparatus for continuously casting aluminum alloy sheet. It is disclosed that an aluminum alloy having 0.93 percent manganese, 1.09 percent magnesium and 0.42 percent copper and 0.48 percent iron was cast into a strip. The composition was hot rolled in two passes and then solution heat treated continuously for 3 seconds at 1000° F. (538° C.), quenched and cold rolled to final gauge. Can bodies made from the sheet had an earing of 2
Ivy Jackie S.
Newton William
Selepack Mark S.
Nichols Aluminum-Golden, Inc.
Sheridan & Ross P.C.
Wyszomierski George
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