Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
2001-06-12
2002-05-14
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
C072S351000
Reexamination Certificate
active
06386013
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Technical Field
The invention generally relates to receptacles and to the end wall structure of a container such as a metal can, bottle, or jar. More specifically, as applied to a metal can, the invention relates to the joint or seam between the sidewall and end wall of a metal can. As applied to a glass bottle, the invention relates to the side wall or skirt of a crown style bottle cap. As applied to a glass jar with threaded engagement to a lid, the invention relates to the side wall or threaded wall of a jar lid. The invention also relates to method and apparatus for forming the wall structure. The invention discloses several embodiments of a contoured lid or shell, especially a lid of variable thickness. In four specific embodiments, the invention discloses a multi-layer lid structure, a single layer lid structure with reduced thickness in the curl or peripheral lip portion, a crown style bottle cap with reduced thickness in the skirt portion, and a jar lid with reduced thickness in the shirt portion. In addition, the invention discloses apparatus and method for forming lids with a peripheral lip, curl, or skirt of reduced thickness.
2. Background Art
Metal containers are produced in two-piece and three-piece constructions. Three-piece containers are constructed from a cylindrical sidewall piece and two independent end wall pieces. The latter are applied to the respective ends of the sidewall to form a closed container. Two-piece containers are constructed from a single can body piece that includes both an integral sidewall and end wall, plus one end wall piece that is applied to the open end of the body to form a closed container. Both types of containers are produced in extremely large numbers, which creates an economic incentive to save even small amounts of metal in producing each one.
The manufacture of two-piece containers such as metallic beverage cans by the draw and iron process is widely practiced. The body of a two-piece container is efficiently produced from a single disc of sheet stock. For efficient use of metal, the thickness of the sheet stock is chosen with consideration for the maximum needed wall thickness, since most metal working processes reduce wall thickness rather than increase it. According to this known technique, sheet metal coil stock of the chosen thickness is fed into a machine called a cupper. There, the sheet is blanked into round discs of metal. After these discs are cut, the cupper processes the discs by forming them into shallow cups, which are substantially wider in diameter than the finished can body. The cup is further processed in a bodymaker machine. Here, a punch pushes each cup through a series of dies. The first die is a redraw die that reduces the diameter of the cup to the eventual diameter of the finished can body. Subsequent dies draw and iron the side walls of the can body, extending them to increased height, generally greater than the finished height of the can. At the termination of the punch's stroke, the punch engages a doming die that configures the bottom wall or closed end of the can body. The opposite, open end of the can body is quite irregular after bodymaking and, thus, the can body is further processed in a trimming machine. There, the irregular wall of the open end is trimmed off, leaving behind a can body of standard dimensions and with a finished lip at its open end. After trimming, the lip is necked-in and flanged as preparation to receive the can lid. The can body is filled with its intended contents, after which the can body is closed by applying the lid to the flanged lip and seaming the edge of the lid to the flanged lip.
Container ends or lids have been formed in a variety of cross-sectional shapes and by a variety of methods that typically share a basic scheme. Metal sheet stock of a preselected thickness, such as 0.009-inches, is placed in a shell press between shearing dies that come together to shear the edge of a blank in the resulting shape of a disc. The sheet metal stock is chosen to be as thin as possible, with consideration for needed strength to resist pressure in the assembled can. Aluminum having a thickness of 0.009-inches is approximately the thinnest stock that can be used in a can that will hold a pressurized beverage such as a soft drink or beer. The thickness of the stock is substantially the same as the thickness of the blank, and the lid formed from the blank similarly is of approximately the same thickness as the original sheet stock.
After the blank has been formed, and typically within the same cupper or shell press used to shear the blank from sheet stock, a punch having a ring configuration is applied against the blank, producing a circular lid with a countersink or groove near its periphery and with an upstanding frustoconical wall or chuckwall rising from the outer edge of the groove. Other portions of the punch apparatus in the shell press form a peripheral flange extending outwardly from the top of the chuckwall. In a further step, the peripheral flange is formed into a downwardly curled or hooked shape that is better suited to mate with the lip of a container body. The lid is applied over a flanged top edge of a container body as mentioned above, and the peripheral curled wall of the lid is seamed to the top edge of the container body to form a seal.
Various methods of strengthening a lid are known, which typically enable a small amount of metal savings by reducing the necessary thickness of the lid. The process of reworking the countersink to deepen it and sharpen its curvature was found to increase the strength of the lid. Such reworking might draw the metal of the lid and thus thin it. U.S. Pat. No. 4,109,599 to Schultz taught that such drawing was undesirable and would reduce the pressure resistant capabilities of the lid. Thus, Schultz developed a method of reworking the countersink without drawing the metal. In fact, Schultz was able to slightly increase the thickness of metal in the countersink groove.
As shown by the following example patents, additional technologies have followed this approach of reworking the countersink or nearby structures to strengthen the lid. U.S. Pat. No. 4,606,472 to Taube et al. provides another method for reworking the countersink groove to increase metal thickness to form a strengthened lid and countersink. U.S. Pat. No. 6,065,634 to Brifcani et al. shows a lid configured in the traditional form with center panel, surrounding countersink wall, and chuck wall. The chuck wall is reworked for greater pressure resistance by extending it at a specified inclination that improves the closeness of the side wall to the lip of the container body. U.S. Pat. No. 5,950,858 to Sergeant strengthens the lid by forming an upward fold either surrounding the central panel or at the bottom of the depending countersink wall. U.S. Pat. No. 4,832,223 to Kalenak et al. teaches the use of coining to form a frustoconical surface at the junction of the central lid panel and the countersink wall for increasing strength of the lid. U.S. Pat. No. 4,809,861 to Wilkinson et al. strengthens the countersink wall by employing curves of several different radii. U.S. Pat. No. 4,333,582 to Bloeck et al. adds a stiffening groove that surrounds a pour outlet of a lid. This added groove allows the lid material to be thinner. The various modifications to the lid made in these patents appear to have helped save metal.
An asymmetric thinning technique is used in U.S. Pat. No. 5,152,421 to Krause. A blank is thinned by rolling portions of the blank to leave only a diametric central spine or belt of the original thickness to support a pull ring opener. Such asymmetric processing may produce irregularly shaped lids that would be difficult to apply and seal with standard equipment.
It would be desirable to reduce the thickness of the metal or other material of construction in a lid at selected locations where materi
Container Solutions, Inc.
Larson Lowell A.
Rost Kyle W.
LandOfFree
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