Drawn can body methods, apparatus and products

Abstract

New technology for deep drawing can bodies for use in the manufacture of two-piece cans for food and beverage products from precoated flat-rolled sheet metal can stock in which damage to can stock precoated on both surfaces with an organic coating is avoided and draw-forming of the side wall is controlled to decrease metal requirements. A draw die cavity entrance (47, 74) is selected to provide at least a major portion of its curvilinear surface having a radius of curvature of about five times nominal sheet metal thickness gage, or less, e.g. a maximum radius of curvature of .04 inch is used for the more commonly used can stock materials. During cup redraw, nesting of curvilinear clamping surfaces (21, 26) of the prior art is eliminated; the compound curvilinear juncture of a work product cup, between its endwall and side wall, is reshaped about a clamping ring compound curvilinear transition zone (72) of smaller surface area than the cup juncture, and the sheet metal is clamped solely between planar clamping surfaces (63, 71) during redraw to a smaller diameter utilizing a male punch (66) with a punch nose ( 79) having a significantly larger surface area than that of the cavity entrance zone.

Description

This invention relates to new canmaking processes, apparatus and can products. More particularly, this invention is concerned with processing organically coated flat-rolled sheet metal into drawn can bodies for use in the manufacture of two-piece cans and, in one of its more specific aspects, is concerned with processing precoated flat-rolled sheet metal for direct use in canning food products.

One specific application for the invention involves cylindrical sanitary cans which must be able to withstand vacuum packing and post packing sterilization of canned foods and beverages. There has been an increasing demand to replace soldered can bodies with a can body which does not use lead in any form in contact with food products. Major efforts continuing for more than a decade have been directed toward development of a solder-free two-piece can fabricated with a unitary can body of suitable height made by progressively drawing and redrawing flat-rolled sheet metal. However, two-piece cylindrical sanitary cans have not been commercially competitive with the three-piece can in the can sizes desired for packing fruits, vegetables, soups, and the like which require deep-drawn can bodies.

In prior efforts to fabricate suitable unitary can bodies by deep drawing operations, the sheet metal thickened along the side wall height, increasing in going from the bottom wall toward the open end of the can body, so that the metal economics were not commercially acceptable. One approach, attempting to overcome that problem, provides tooling for thinning such draw thickened side wall metal by forcing the mandrel-mounted can through a restricted opening die (see e.g. U.S. Pat. No. 4,485,663); essentially, this involves ironing or burnishing of the thickened side wall metal. However, such an approach can create additional problems if the can body is driven through the tooling. Also, the open end of the can body is increased in height irregularly presenting ragged-edge formations from which small pieces of metal are broken off; these contaminate tooling and subsequent canmaking, and the irregular open end of the can body requires costly rotary shearing (in a direction transverse to the can axis) and flange metal orientation.

A major obstacle in any draw technology existent prior to the present invention has been the extent of damage to protective coatings applied prior to draw operations. Because of such damage to protective coatings, especially organic coatings, the use of precoated sheet metal in the manufacture of drawn can bodies had restricted application unless provisions were made for coating repair subsequent to can body fabrication. This has been a significant factor in preventing two-piece cans which require deep drawn can bodies from being commercially competitive with most three-piece sanitary cans for food products. Also, deep drawn can bodies have not previously been commercially competitive with drawn and ironed can bodies for pressurized contents such as carbonated beverages.

The present invention surmounts these obstacles by providing new methods and apparatus which enable commercially competitive manufacture of deep drawn can bodies for vacuum packed and carbonated beverage cans from flat-rolled sheet metal precoated on both surfaces with an organic coating. New tooling configurations and relationships are provided which enable draw process production of unitary can bodies from flat-rolled sheet metal having an organic coating, of the type required for comestibles, on both surfaces without detriment to the metal or protective coating.

These and other advantages and contributions of the invention are considered in more detail in describing embodiments of the invention as shown in the accompanying drawings. In these drawings:

FIG. 1 is a schematic cross-sectional partial view of prior art tooling with sheet metal clamped between compound curvature surfaces immediately prior to start of redraw of a new diameter;

FIG. 2 is a schematic cross-sectional partial view of the prior art tooling of FIG. 1 as the new diameter is being formed;

FIG. 3 is a diagrammatic presentation of the overall process steps and apparatus combination of the present invention for direct fabrication of one-piece can bodies for use in the manufacture of two-piece cans;

FIG. 4 is a cross-sectional view of a circular blank;

FIG. 5 is a schematic cross-sectional partial view of tooling for drawing a cup-shaped article from a circular blank in accordance with the invention;

FIG. 6 is a cross-sectional view of a cup-shaped article in accordance with the invention;

FIG. 7 is a schematic cross-sectional partial view of tooling in accordance with the present invention as arranged before start of redraw of a new cup diameter;

FIGS. 8, 9, 10, and 11 are schematic cross-sectional partial views of apparatus and work product illustrating the sequential steps in accordance with the invention for reshaping the compound curvature juncture, between the endwall and side wall of a cup, in preparation for drawing a new cup diameter;

FIG. 12 is an illustration for describing manufacture of a multiple radii surface for use at the compound curvature transition zone, between the endwall and external side wall of a clamping ring, in accordance with the invention;

FIG. 13 is a schematic cross-sectional partial view of the apparatus of FIG. 7 at the start of formation of a new cup diameter;

FIG. 14 is a cross-sectional view of a redrawn can body in accordance with the present invention;

FIG. 15 is a cross-sectional view of a doubleredraw can body in accordance with the present invention;

FIG. 16 is a cross-sectional view of a deep drawn can body showing bottom wall profiling in accordance with the present invention;

FIG. 17 is a cross-sectional view of a two-piece can showing bottom wall profiling and side wall profiling including a chime profile contiguous to the closed end of a deep drawn can body in accordance with the present invention.

FIG. 18 is a cross sectional view of a two-piece beer and carbonated beverage can embodying a deep drawn can body in accordance with the invention;

FIG. 19 is a bottom plan view of the can body of FIG. 18;

FIGS. 20, 21 and 22 are radial cross-sectional views of portions of a draw die for describing configurational aspects of a cavity entrance zone in accordance with the invention; and

FIGS. 23, 24, 25, and 26 are schematic cross-sectional partial views of apparatus illustrating final redraw, release and bottom wall profiling of a sheet metal work product in accordance with the invention.

Prior art redraw technology for can body manufacture relied on nesting of compound curvature (curvilinear as shown in cross section in FIGS. 1 and 2) clamping surfaces. An objective, as part of such nesting arrangement, was to have the curvilinear clamping surfaces match the compound curvature (curvilinear in cross section) juncture between the endwall and side wall of a cup-shaped work product while re-drawing the cup-shaped work product to a smaller-diameter cup with increased side wall height. Toroidal configuration clamping ring 20 had a radius of curvature at its curvilinear transition zone 21, between its planar surface endwall 22 and side wall 23, which was designed in the prior art to match, as closely as possible, the radius of curvature of the internal surface at the curvilinear juncture of the endwall and side wall of cup 24. Also, draw die tooling 25 had a curvilinear clamping surface 26; the attempt was made, while allowing for metal thickness, to clamp over the entire outer compound curvature surface area of sheet metal 27. The random and excessive increase in side wall sheet metal thickness experienced with prior art drawing technology added to the difficulties in attempting to obtain full surface clamping.

Also, in accordance with prior technology, radius of curvature 28, at the entrance of cavity 29, was preselected to be as large as possible without wrinkling the sheet metal during relative movement of male punch 30 into die cavity 29 (FIG. 2); and, radius of curvature 32, at the nose portion of male punch 30, was selected to be as small as possible without causing punch out of metal. Typically, prior ar radius of curvature dimensions for the tooling during the first redraw operation in forming a 211.times.400 can (2-11/16" diameter by 4" height) were as follows:

______________________________________clamping ring surface cavity entrance radius.070" "28"draw die surface punch nose radius.125" "32"______________________________________

Thickening of the side wall metal was not desirably controlled during drawing or redrawing operations in the prior art. Reasons for this may possibly be related to dimensional relationships of the tooling, inadequate clamping of the sheet metal provided by the compound curvature clamping surfaces and/or the small planar clamping surface area available (represented by radial dimension 33 in FIG. 2). However, it is known that prior deep drawing technology produced can bodies in which side wall metal thickened in excess of 15% and up to about 25% (over starting gage) in approaching the open end of the can body.

With the new technology being presented, side wall thickening is substantially eliminated, or controlled, and organically coated flat-rolled sheet metal mill product can be processed directly into can bodies ready for use without special flange metal orientation or can body repair steps of any nature. Referring to FIG. 3, can stock of predetermined gage, coated on both its planar surfaces with an organic coating, is uniformly lubricated on both such surfaces and delivered from coil 34 to blanking and cupping station 35. A large-diameter shallow-depth cup is formed from the sheet metal blank of predetermined diameter so a to present flange metal oriented in a plane substantially perpendicularly transverse to the central longitudinal axis of the cup. Draw surfaces of such cup can be re-lubricated at station 37 prior to a first redraw operation at station 38 in which the original cup diameter is decreased and its side wall height increased; flange metal is properly oriented for chime seam usage as part of the draw-technology teachings of the present invention.

Preferably, cup draw surfaces are re-lubricated before each redraw. In a specific embodiment with two redraw operations, the first-redraw cup is lubricated at station 39 prior to a second redraw at station 40. In this double-redraw embodiment, the cup is redrawn at station 40 to final dimensions of desired diameter and side wall height with flange metal in place substantially perpendicularly transverse to the can body's central longitudinal axis. Lubricants acceptable for food product cans (e.g. petrolatum) are utilized. Flat-rolled strip lubricators have been known in the art. However, the present teachings provide for relubricating work product cup surfaces before each redraw operation as may be required while enabling direct utilization of a redrawn can body, without washing or other can body preparation steps, in can manufacture. For such purposes, atomized liquid cup lubrication apparatus is provided in which a lubricant (such as petrolatum) in liquid form is atomized in an atmoization chamber and liquid lubricant particles are transported pneumatically into a lubricant deposition chamber. Such particles are directed for flow-impingement on both interior and exterior cup surfaces; and, electrostatic charging can be used to augment relubrication of exterior cup surfaces. Suitable cup re-lubrication apparatus is disclosed in copending U.S. application Ser. No. 011,112, entitled "Lubrication of Cup Shaped Can Bodies" filed Feb. 5, 1987, now U.S. Pat. No. 4,724,155 dated Feb. 9, 1988, and U.S. Pat. No. 4,831,960, dated May 23, 1989, which is included herein by reference.

As a final-redraw can body is freed from draw die tooling, bottom profiling is carried out with apparatus at station 41. Thus bottom profiling is carried out on the same press used for the final redraw. The type of flange metal trimming carried out at station 42 is dependent on can usage. If the open end of the can body is to be necked-in for a particular type of carbonated beverage can, the transversely oriented flange metal can be removed for the necking-in operation. Full periphery flange metal is provided for other types of cans and is properly oriented at the completion of the redraw, i.e. flange metal orientation is not required. Also, trimming is simplified; rotary shearing is eliminated and replaced by trimming in a direction parallel to the centerline axis of the can. Side wall profiling is carried out at station 43.

Sanitary can bodies are then ready for direct use by filling, completing closure with a chime seam and heat process treatment of contents using apparatus known in the art. Such direct processing of deep drawn can bodies into cans was not previously available without coating repair, washing or other can body preparation steps.

Teachings of the present invention enable one-piece cylindrical can bodies to be deep drawn from flat-rolled sheet metal, coil-coated on both surfaces with an organic coating, without damage to the metal or coating. This can stock is controlled during draw and redraw operations enabling can body product of the present invention to meet or exceed metal economics requirements so as to be commercially competitive with drawn and ironed can bodies for pressurized two-piece cans and, also, with three-piece cylindrical sanitary cans shown or described in the "Dewey and Almy Can Dimension Dictionary" published by the Dewey and Almy Chemical Division, W. R. Grace & Co., Cambridge, Mass. 02140. While the metal economics requirements of the can body, per se, can be met with the present invention across the full spectrum of standard three-piece cylindrical sanitary can sizes, capital requirements for extended stroke (above e.g. about five and one-half inches) presses and market volume for such extended height cans are factors which have a bearing in commercial application. Considering these factors, a preferred range for commercial application of the invention covers standard can sizes with diameters between about two inches to about four and one-quarter inches, and side wall heights between above one inch to about five inches; representative tooling dimensions and relationships for can sizes in such preferred commercial range are set forth later herein.

The invention departs, initially, from the conventional can body draw die design technology which taught that the draw die cavity entrance radius should be selected to be as large as possible without forming buckles during forming of high tensile strength light gage sheet metal. In place of such prior teachings, cupping of a sheet metal blank is carried out using a die cavity having an entrance zone including a surface formed from a radius of curvature which is selected to be as small as practicable, e.g. about five times can stock starting thickness but having a maximum value of about .04" for standard can stock gages.

The invention also teaches use of a significantly larger punch-nose radius of curvature than taught in the prior art, e.g. about forty times starting gage in first drawing a cup from a can stock blank. Such punch-nose radius can be partially dependent on the cup diameter being drawn. In the first draw for fabricating a soup can (211.times.400) from 65 #/bb flat-rolled steel, punch nose radius is selected at .275"; this radius of curvature is practical for the range of can size diameters set forth above.

FIG. 4 shows a can stock blank 44 of predetermined thickness gage and diameter which is draw formed into a work product cup with tooling as partially shown in the crosssectional schematic view of FIG. 5. Draw die tool 45 defines cavity 46 with compound curvilinear entrance zone 47 between its internal side wall 48 and a planar clamping surface 49. Male punch 50 moves relative to die cavity 46 as indicated, as the circular blank 44 is clamped about its periphery radially exterior to male punch 50, between planar clamping surface 49 of draw die 45 and planar surface 51 of clamp ring 52; such planar clamping surfaces are perpendicularly transverse to centerline axis 53. The cavity entrance zone 47 includes a .040" radius surface, or smaller radius surface, dependent on can stock thickness gage; punch-nose radius 54 presents a significantly larger surface area than that of the cavity entrance zone 47.

Drawn cup 56 (FIG. 6) includes endwall 57, side wall 58 which is symmetrically spaced from centerline axis 59, flange metal 60 which lies in a plane which is substantially perpendicularly transverse to axis 59, and a curvilinear juncture 61, between endwall 57 and side wall 58, having a curvature conforming to that of punch nose 54 of FIG. 5.

During redraw, the prior nesting arrangement of curvilinear clamping surfaces is eliminated. In the new technology, the cross-sectional curvilinear juncture between the endwall and side wall of a work product cup being redrawn is reshaped initially in a manner which creates radially outwardly directed force on the can stock and prevents wrinkling of the sheet material. This reshaping of the curvilinear juncture also significantly increases the surface area of the metal available for clamping between planar surfaces during redraw.

FIG. 7 shows the juxtaposition of redraw tooling and a drawn cup 56 in approaching a redraw operation. Draw die tool 62 can be considered as stationary for purposes of explaining this embodiment, it being understood that the required relative movement between tool parts can be carried out with various movements of the upper or lower tooling with their centerline axes coincident. In FIGS. 5, and 7, and later apparatus figures, the open end of the cup is oriented downwardly during formation.

The invention teaches use of a "flat face" draw die for redraw operations as shown in FIG. 7 i.e., first-redraw die 62 presents solely planar clamping surface 63 lying in a plane which is perpendicularly transverse to centerline axis 59. Movable clamping ring 64, which is substantially toroidal in configuration, is disposed to circumscribe cylindrically shaped male punch 66. The latter is adapted to move within cavity 68, defined by draw die tool 62, while allowing clearance for work product thickness (sheet metal including coating; e.g. about .010" around the full periphery for organically coated 65 #/bb steel plate; i.e. about one and one-half times thickness of the precoated sheet metals.

Clamping ring 64 includes external side wall 70, planar endwall 71 and curvilinear transition zone 72 therebetween. The outer diameter (peripheral side wall 70) of clamping ring 64 allows only for tool clearance (about 00025") in relation to the side wall internal diameter of a work product cup such as 56.

In accordance with present teachings, the surface area of transition zone 72 of clamping ring 64 is significantly smaller than the surface area of juncture 61 of cup 56; i.e. a projection of the transition zone 72 onto a clamping surface plane which is perpendicularly transverse to the centerline axis occupies significantly less radial distance, i.e. less than about 40% along that plane, than a projection of cup juncture 61 (this is shown in more detail in FIGS. 8-11). The interrelationship of these curvilinear surfaces is selected to provide a difference of at least 60% in their projections on the transverse clamping plane; this translates into a corresponding increase in planar clamping surface area when juncture 61 is reshaped by transition zone 72 as shown in FIGS. 8-11.

In a specific embodiment, a .275" radius of curvature at cup juncture 61 projects on the transverse clamping plane as .275"; the projection of transition zone 72 occupies .071"; this provides about a 75% difference; i.e. a projection of the clamping ring transition zone (72) onto the transverse clamping plane occupies about 25% of the projection of the .275" radius of curvature of juncture 61. This significantly increases the toroid-shaped planar clamping surface area, peripheral to the punch, over that which would be available through use of the curvilinear surface nesting arrangement of the prior art.

As clamping ring 64 is moved against spring-loaded pressure, transition zone 72 comes into contact with the inner surface of juncture 61 of cup 56; with continued relative movement, a radially outwardly directed force is exerted on the sheet material of cup 56 as juncture 61 is reshaped (FIGS. 8-11). Upon completion of such reshaping, the sheet material is clamped solely between planar clamping surfaces during redraw of a new diameter; clamping takes place, over an extended planar surface area, between draw die planar clamping surface 63 and clamping ring planar surface 71. The total planar clamping surface area is significantly increased, over that previously available, due to such controlled reshaping of juncture 61 about clamping ring transition zone 72; and, it is also increased because of the smaller projection of the cavity entrance of curvature 74 on the transverse clamping plane. As previously stated, such die cavity entrance radius does not exceed .040" which is significantly less than taught by the prior art. Combining the effect of reshaping the cup juncture and use of a smaller cavity entrance zone projection increases the planar clamping surface available by a factor of at least two over that available with the prior art nesting arrangement.

The reshaping of curvilinear juncture 61 of the cup 56 is shown sequentially in FIGS. 8, 9, 10, and 11 with relative movement of clamping ring 64 as indicated. The increase in planar clamping surface is represented by radial cross-sectional dimension 80, which extends around the full periphery. During such reshaping, a radially outwardly directed force is exerted uniformly on the sheet material, around the full 360.degree., preventing wrinkling of the sheet metal.

The concept of reshaping the peripheral juncture metal at the closed end of a work product cup about a smaller curvilinear surface area than the cup juncture adds planar clamping surface area as taught above. An additional contribution of the invention involves manufacture of the clamping ring peripheral transition zone about multiple radii which further adds to planar clamping surface area, and has other advantages.

This multiple radii concept is described in relation to FIG. 12. A single radius of curvature for the clamping ring peripheral transition zone about a radius "R" would result in a projection on the transverse clamping plane of clamping ring endwall 82 dimensionally equal to "R". In place of such single radius, a multiple radii curvature is provided through selective usage of "large" and "small" radii of curvature in forming the compound curvature transition zone for a clamping ring.

In FIG. 12, clamp ring 84 includes planar endwall 82 (defining the transverse clamping plane perpendicular to the centerline axis of the cup) and peripheral side wall 85. In preferred fabrication of the clamp ring transition zone, a radius R ("large") is used about center 86 to establish circular arc 87, which is tangent to the planar surface of clamping endwall 82. Extending circular arc 87 through 45.degree. intersects the extended plane of side wall 85 at imaginary point 88. Using the radius R about center 89 establishes circular arc 90 tangent to side wall 85; extending arc 90 through 45.degree. intersects the transverse clamping plane of endwall 82 at imaginary point 93. Straight line 94 is drawn between point 93 and center 89; straight line 95 is drawn between point 88 and center 86; line 96 is drawn to be equidistant between parallel lines 94, 95. Line 96 comprises the loci of points for the center of the "small" radius of curvature which will be tangent to the circular arcs 87 and 90 so as to avoid their abrupt intersection at imaginary part 97. Using a radius of 1/2R with its center 98 along line 96, circular arc 99 is drawn, to complete a smooth multiple-radii compound curvature for the transition zone of clamping ring 84.

As a result of the die design of FIG. 12, the projection of the multiple-radii compound curvature on the transverse clamping plane of endwall 82 is .0707 times R; resulting in an increase of almost 30% (29.3%) in the planar clamping surface over that available if a single radius R were used for the compound curvature transition zone of clamping ring 84. Also a more graduated entrance curve 87 to the transverse clamping plane is provided; and a more gradual entrance curve 90 is provided for entrance of the clamping ring onto the internal surface of the compound curvature juncture of the drawn cup for the reshaping step.

In a specific embodiment for the multiple-radii clamping ring transition zone for reshaping a .275" radius of curvature for work product cup 56, R is selected to be .100"; therefore the projection of the clamping ring multiple-radii transition zone on the transverse clamping plane comprises .0707"; rounded off as .071". Other values for R can be selected, e.g. 1.25" for reshaping a cup juncture of substantially greater radius than .275"; or .9" for reshaping a smaller radius of curvature juncture; in general selecting R as .100" will provide desired results throughout the preferred commercial range of can sizes designated.

A funnel-shaped configuration 75 (as shown in cross section FIG. 13) is established between planar surface 63 of draw die 62 and clamping ring transition zone 72 for movement of work product sheet material into the axially transverse clamping plane, without damage to the coating, as male punch moves into cavity 68; a further relief can be provided by having surface 63 diverge away from the clamping plane at a location which is radially exterior to the planar clamping surface. Male punch 66 includes endwall 77, peripheral side wall 78 and curvilinear transition zone 79 therebetween. In contrast to the small surface area of cavity entrance zone 74, a large surface area is provided at "punch-nose" 79. Overcoming the inertia of starting a new diameter is facilitated by such selection of a relatively large surface area for punch-nose 79. Coaction between such large surface area punch-nose, a small radius of curvature cavity entrance zone surface, and the elimination of the prior art curvilinear nesting arrangement, with accompanying increase in planar clamping surface area during redraw, combine to continue control of side wall sheet material which was initiated during the cupping step and prevent unacceptable thickening of such sheet material (e.g., of the type which would damage an organic coating). Through use of the present invention, side wall thickness gage is decreased through substantially the full side wall height; any minor increase in thickness which might occur is limited to a level contiguous to the open end flange metal. That is, if side wall thickening occurs, it is limited to this single level, and any increase in thickness at such level is substantially less than the prior art experience of 15% to 25%; e.g. about 10% or less with the present invention. In double-redraw practice in the above preferred range of can sizes, increase in side wall thickness contiguous to open-end flange metal, if any, has been minor, i.e. less than 3%.

The punch nose radius for a first redraw is selected to be about thirty times starting metal thickness gage; e.g., in the specific embodiment for a 211.times.400 can, 65 #/bb steel, the first-redraw punch-nose radius is 205".

The same multiple radii compound curvature which projects as .071" on the transverse clamping plane can be used, for convenience, in reshaping this compound curvature juncture (which has an internal surface radius of curvature of .205") during the second redraw; or a new surface based on R=.9" can be used in forming the multiple radii transition zone for the second redraw clamping ring as described above.

FIG. 13 shows the apparatus of FIG. 7 at the start of new diameter formation. Typical values for deep drawing a can body for a 211.times.400 size can from precoated 65 #/bb flat-rolled steel in accordance with the invention are as follows:

______________________________________ Punch- Cavity Projection of Nose Entrance Clamp Ring Tran-Work Product Diameter Radius Radius sition Zone______________________________________Circular 6.7" -- -- --blankShallow cup 4.4" .275" .028" --(first draw)First-redraw 3.2" .205" .028" .071"cupSecond-redraw 2.5" .062" .028' .071"cup______________________________________

Typical sheet metal clearance in each draw is approximately 1.5.times. sheet material thickness or .010" to .012" per side (in cross section) for precoated 65 #bb flatrolled steel.

In practice of the invention, a sheet metal blank diameter is decreased about 25% to 40% during cupping and the work product cup diameter is decreased about 15% to 30% in a first redraw; the diameter of a first-redraw cup is decreased about 15% to 30% when second redraw is utilized.

Typical diameters for a double-redraw embodiment (can size 300.times.407) are:

______________________________________circular blank 7.6"first draw 5.2"first redraw 3.6", andsecond redraw 2.9"______________________________________

Typical diameters for a single redraw embodiment (can size 307.times.113) are:

______________________________________ circular blank 6.2" first draw 4.0" redraw 3.3"______________________________________

The punch nose radius of curvature in a final redraw is selected based on requirements of can geometry; i.e. the desired radius of curvature at the closed end of the final redraw can body; e.g. about then times starting gage of the sheet material.

A first redraw can body 100 is shown in FIG. 14 and a second redraw can body 101 is shown in FIG. 15. In each instance, flange metal at the open end of the can is oriented transversely to its centerline axis.

Using prior art draw-redraw technology on organically coated tin-free steel for a can body for a 211.times.400 can size, the average increase in side wall sheet metal thickness at the open end of the double-redraw can body was about 17.5%. When the circumferentially-distributed average thickness, measured at about 1/4" increments over the entire side wall longitudinal dimension is compared, such prior art can body side wall had an average thickness about equal to starting gage (.0075" which is nominal 65 #/bb flat-rolled steel can stock with organic coating); whereas with the present invention, such average side wall thickness was 12.7% less than the starting gage. These data correspond to starting blank area requirements in practice of the present invention; the starting blank area is about 12% less with the present invention than the starting blank area requirement of the prior art; e.g. in a specific embodiment of the invention for a can body for a 211.times.400 can size, the starting blank diameter is 6.718"; the starting blank diameter with prior art draw-redraw technology was 7.267".

As stated, with prior draw-redraw technology, the metal increased in thickness along the side wall with the increase over starting gage reaching from about 15% to 25% at the open end of the can body. With the present invention, if any increase in side wall thickness occurs, it is minor and limited to a level contiguous to open end flange metal of the can body. Results of the present invention include an improvement in metal economics while maintaining adequate vacuum and crush-proof strength for the side wall.

In specific embodiments of the invention, an organically-coated, TFS steel substrate was fabricated into can bodies (as shown in FIG. 16) for 211.times.400 cans utilizing a first and second redraw; side wall gage was then measured at about 0.2" increments (tabulated as "A" through "S") starting at the open end and proceeding longitudinally throughout the side wall height. The percentage change in side wall thickness, measured around the circumference at each such incremental level, is set forth in the Table below. In Example #1, side wall thickness increased only slightly (less than 3%) solely at the first measurement location ("A") decrease in thickness over side wall height averaged slightly less than 15%; in Example #2, side wall thickness decreases slightly at such location; average decrease in thickness slightly above 16%. Percentage changes in side wall thickness gage or nominal starting gage are shown:

TABLE______________________________________Side Wall MeasurementLocations Starting at Percentage Reduction0.2" from Flange Example #1 Example #2Metal of FIG. 16 % %______________________________________A (2.2)* 2.0B 4.8 8.7C 9.7 11.2D 14.7 17.0E 17.9 18.6F 18.9 19.2G 20.4 21.2H 21.5 22.1I 21.2 23.1J 22.1 23.8K 22.8 24.1L 22.5 23.8M 14.1 23.2N 10.6 11.2O 11.8 13.1P 13.1 13.8Q 14.4 14.1R 13.8 14.4S 7.4 4.1______________________________________ *(Increase)

Additional novel tooling configuration concepts for the draw die further facilitate simultaneous multidirectional movement of precoated flat-rolled sheet metal during draw (cupping and/or redraw) operations while avoiding damage to either coating or sheet metal.

The difficulties in overcoming the inertia of the can stock during initiation of such multi-directional shape changes, and avoiding damage to the sheet material, increase as can body production rate is increased. In addition to facilitating desired movement of sheet material during draw operations, these difficulties are overcome without sacrificing draw die planar clamping surface area and while maintaining a desired radius for a major portion of the cavity entrance zone; i.e. a compound curvilinear surface portion formed about a radius which is about five times nominal starting thickness gage.

Also, the draw-operation reshaping method taught by the present invention is carried out while eliminating adherence of can stock along the draw die internal side wall surface which might damage the coating. Notwithstanding tooling clearances of about one and one-half times coated can stock gage, as taught above, the reshaping action required can cause the sheet material to follow the internal side wall surface of the draw die upon leaving the cavity entrance zone as the draw punch moves within the draw cavity. A change in cavity entrance zone configuration and a recessed taper for the internal side wall of draw die overcome this tendency.

As part of such novel draw die configurational concepts, the cavity entrance zone is reshaped to increase its surface area providing for a more gradual change in direction of movement of the coated sheet material during draw operations; and, also, providing better support of such can stock during its movement both into and from the cavity entrance zone. The surface area of the cavity entrance zone is increased by forming such surface area from multiple radii of curvature; such increase in surface area is provided without sacrificing smooth movement or support of the can stock during reshaping and without sacrificing planar clamping surface area provided by the draw die.

FIG. 20 shows an enlarged view of a cavity entrance zone for draw die 131 formed about, as previously described, a single radius of curvature 132 which is smaller than that used in the prior art. Single-radius curvilinear surface 133 is symmetrical about central longitudinal axis 134 and extends between planar clamping surface 135 and internal side wall 136. Such compound curvilinear surface 133 is tangential, at each end of its 90.degree. arc (as measured in a radial plane) to planar surface 135 and side wall surface 136, respectively.

The objective in further improving the draw die of FIG. 20 is to increase the surface area of its cavity entrance zone in a manner which will provide for a more gradual movement of the can stock both into and out of such entrance zone; that is, in a manner less abrupt, and less likely to be damaging to the sheet material, so as to facilitate overcoming the inertia in the sheet material resisting the multi-directional reshaping action taking place as the draw punch moves into and out of the draw cavity. Support for the sheet material is improved during such reshaping. These objectives are achieved while maintaining the improved smaller area of projection of the cavity entrance zone on the clamping plane which is perpendicular to the central longitudinal axis 134. That is, these objectives are accomplished without decreasing the draw pie planar surface area available for clamping. Also, these objectives are accomplished while a radius of about five (5) times can stock thickness gage (maximum of about .04" in a specific embodiment) is maintained for a centrally-located major portion of the cavity entrance zone surface.

The concept of increasing the surface area of the cavity entrance zone is carried out by reshaping the entrance zone about multiple radii rather than a single radius while maintaining a continuously curvilinear smooth surface for support of the can stock sheet material.

In FIG. 21, the compound curvilinear surface 133 (about single radius of curvature 132 of FIG. 20) is shown in dotted lines; a 45.degree. angle line 137, between the planar clamping surface and cavity side wall, is also shown in dotted lines; such 45.degree. angle line 137 meets the respective points of tangency of a single radius surface 133 with the planar clamping surface and internal side wall at 138, 139.

A larger surface area compound curvilinear entrance zone provided by the present invention is shown at 140. Comparison to single-radius surface 133 shows that multiple-radii surface 140 provides for a more gradual movement of the can stock sheet material from the planar clamping surface into the entrance zone; and, also for a more gradual movement of the can stock sheet material from the entrance zone into the side wall of the draw die.

The multiple-radii concept for increasing the surface area of the cavity entrance zone is carried out, in the specific embodiment being described, by selecting a radius equal to or greater than .04" as a larger radius for the multiple-radii surface. Such larger radius (R.sub.L, FIG. 22) provides the more gradual movement from the planar clamping surface into the cavity entrance zone; and, also, the more gradual movement of the can stock from the entrance zone into the interior side wall of the cavity.

A smaller radius (R.sub.s) which is approximately five times thickness gage of the can stock sheet material, with a designated maximum, is used to establish a compound curvilinear surface intermediate such larger radius (R.sub.L) portions at the arcuate end portions of the entrance zone surface; i.e. centrally located of such compound curvilinear surface area.

This multiple-radii, increased-surface-area concept, along with the recessed taper concept for the draw die internal side wall, are embodied in structure as shown in FIG. 22. A portion of the compound curvilinear surface 140 is formed about center 143 using larger radius R.sub.L (.04" and above); such surface portion 142 is tangential to the planar clamping surface 144 of the draw die. Such larger radius is used about center 145 to provide curvilinear surface 146 leading into the internal side wall of the cavity.

To derive the loci of points for the centrally located smaller radius (R.sub.s) of curvature portion of the compound curvilinear surface, the arcs of the larger radii surfaces 142, 146 are extended to establish an imaginary point 148 at their intersection. Connecting imaginary point 148 with midpoint 149 of an imaginary line 150 between the R.sub.L centers 143, 145 provides the remaining point for establishing the loci of points (line 152) for the center of the smaller radius (R.sub.s) of curvature; the latter will provide a curvilinear surface 154 which is tangential to both larger radius (R.sub.L) curvilinear surfaces 142 and 146.

Typically, for the can sizes and materials discussed above, the larger radius (R.sub.L) of curvature would be .04" and above, in the range of .040" to .060", and the smaller radius (R.sub.s) of curvature would be less than .040", e.g. in the range of .020" to .030". For example, an increased compound curvilinear surface area entrance zone for can stock of about .006" gage, for which a single-radius of curvature of about .028" would provide a suitable entrance zone, would be formed with an R.sub.L of .040" and an R.sub.s of .020". the projection on the clamping plane would remain at .028".

In the multiple-radii configurations of the present invention, the smaller radius (R.sub.s) curvilinear surface occupies at least about 1/3 of the compound curvilinear surface area and is located intermediate the larger R.sub.L surfaces. In the R.sub.L =.040", R.sub.s =.020" embodiment, the R.sub.s curvilinear surface occupies slightly in excess of 37% of the total surface area of a 90.degree. arc between the clamping surface and internal side wall of the draw die; and, each of the R.sub.L surfaces occupies slightly less than 32% of the surface area in such a 90.degree. arc.

However, in order to provide a 1.degree. recessed taper for the internal side wall, the arc between the planar clamping surface and the internal side wall of the draw die is increased by 1.degree.; such 1.degree. arc increase being added at the internal side wall end of the arc. Such added 1.degree. of arc enables the internal side wall to be recess tapered 1.degree.; and enables such side wall surface to be tangent to the compound curvilinear surface at point 155, i.e. 1.degree. beyond the 90.degree. point of tangency (139). A tangential recess-tapered internal side wall cannot be provided without such added arc provision as described immediately above.

The location of such 1.degree. recessed tapered internal side wall surface, in a radially oriented plane which includes the centerline axis of the draw cavity, is shown at line 156 in relation to a non-tapered side wall surface indicated by line 157.

Profiling of the bottom wall is used with one-piece can bodies because of the internal vacuum and pressure conditions which may be experienced. Profiling of a side wall is used to provide vacuum and crush-proof strength for vacuum packed cans. In accordance with the present invention, bottom wall profiling is carried out after a final-redraw can body is free from drawing operations so as to eliminate stress or strain on side wall sheet material during profiling. The configuration for the endwall profile can be in accordance with that shown in U.S. Pat. No. 4,120,419 of Oct. 7, 1978, which is included herein by referenced. The profiling of unitary endwall 102 (FIG. 16) is provided by the endwall of the final redraw punch, as described in more detail later herein; a centrally located panel 103 with circumscribing profile rings 104, 105 are provided. The unitary endwall panel 102 is recessed from bottom peripheral edge 106 by circular ring profiling 107 so that, under pressure, the central panel can move axially toward the exterior of the can body without disturbing upright stability of the can. Under vacuum conditions, the ring profiling enables the panel 103 to move toward the interior of the can. Also, the bottom wall profile of FIG. 16 sacrifices less can volume than an interior dome-shaped profile; e.g. the normal four-inch height for a condensed soup can (211.times.400) can be reduced to a height of 3-15/16" through use of the deep drawn can body of FIG. 14.

Can 108 of FIG. 17 includes chime seam 109 attaching closure 110 to the one-piece can body; closure 110 is provided with profiling of a type similar to the closed endwall, i.e. with a centrally located panel 111 which can move axially under internal vacuum or pressure conditions due to cooperation of profiling rings 112, 113 and the recessed central panel.

Chime seam 109 adds to the overall diameter of the can. As is generally known, this added diameter must be taken into consideration to provide for straight-line rolling of a can during content processing, such as heat treatment. A "chime profile" or "roll bead" 114, to provide a diameter substantially equal to that of the chime seam 109, is used for such purposes. Eccentrically mounted tooling, the operation of which is known in the art, is inserted into and rotated within the can body for side wall profiling.

Rib profiling 116, located contiguous to mid-side wall height, can be conventional side wall profiling as used with certain three-piece cans.

FIG. 18 shows the profiling used for a two-piece drawn carbonated beverage can 117 in accordance with the invention. In order to be able to use light gage sheet metal, e.g. 50 #/bb flat-rolled steel for such cans, and to provide adequately for the high internal pressure during pasteurization of pressurized contents, a bulb profile is utilized for unitary bottom endwall 118. Note that side wall profile 119 (produced by a die-sizing operation) decreases bottom wall diameter and decreases the cross-sectional area of endwall 118 which must withstand internal pressure. Loss of volume, due to this decrease in side wall diameter near the bottom wall, is more than offset by the added volume of the bulb configuration of endwall 118. The bottom bulb and side wall profiling 119 can be carried out during a single press stroke after completion of final redraw.

Reduced-diameter side wall portion 119 is provided to accommodate a fixed plastic coaster having an exterior periphery equal in diameter to the main body side wall; such plastic coaster adds to upright stability without distorting overall side wall diameter. However, for stability purposes during can body storage or can processing, protrusions 125, 126 and 127, shown in FIGS. 18 and 19, are formed in the bottom wall; these provide a tripod on which the can body can stand upright notwithstanding the bulb configuration bottom wall.

A necked-in chime seam 128 at the open end of the can body attaches closure 130, which can be of the easy-open type (not shown), without distorting overall side wall diameter.

In carrying out a final redraw for a sanitary food can body as shown in FIG. 16, the compound curvature transition zone is reshaped as described earlier in relation to FIGS. 7-12. Bottom profiling is carried out at the final redraw station after the final redraw forming is completed and after the can body is released from clamping action.

FIGS. 23 through 26 depict final redraw tooling for redrawing a cup-shaped work product and countersinking of the endwall upon completion of redraw. As shown in FIG. 23, such reshaping of the compound curvature juncture of the previous cup has been completed and the metal which is peripheral to upwardly moving redraw punch 162 is being clamped solely between the planar clamping surface 163 of draw die 164 and upper planar surface 166 of clamping ring 167; such clamping is free of nesting curvilinear clamping surfaces as taught in the prior art. The new diameter is being redrawn about the peripheral portion 170 of final redraw punch 162 so that the endwall 172 is planar at this time.

As the redraw is approaching completion (FIG. 24), the redraw punch 162 and redraw die 164 are moving in the same direction with redraw punch 162 moving at a faster rate. Final redraw forming is controlled to present flange metal 174 before release of clamping action. Male profile member 176 is fixed so that no coaction between its profiling surface 178 and the recessed profiling surface 180 of draw punch 162 has started.

As shown in FIG. 25, clamping action has been released as draw die 164 moves upwardly. As clamping action is released, final redraw punch 162 approaches and reaches top dead center of its upward stroke countersinking the endwall 102 in cooperation with fixed male profile member 176. Such countersinking takes place through movement of side wall metal into such endwall; prior release of clamping action is provided to avoid damage to the sheet metal due to such movement. Final redraw punch 162 is then withdrawn downwardly.

As shown in FIG. 26, upon completion of redraw forming and endwall countersinking operations, the upper planar clamping surface 166 of clamping ring 167 is positioned in the pass line 182 to support flange metal 174 at the open end of work product 184 providing for movement in the pass line for exit from the press. Redraw punch 162 is moving downwardly below the pass line and redraw die 164 is moving upwardly above the closed end of the redrawn can body.

Flat-rolled sheet metal for the can body applications taught by the present invention can comprise flat-rolled steel of nominal thickness gage between .005" to .012", i.e. about 50 to 110 #/bb in which thickness tolerances are generally within 10%, and nominal flat-rolled aluminum thickness gages between about .005" and .015"; both surfaces of such flat-rolled sheet metal are organically coated.

Double-reduced plate because of its cold-reduced hardness, is a preferred flat-rolled steel since the high tensile strength developed in the substrate during cold reduction makes the substrate subject to minimum modification of its properties during draw and redraw operations. However, single-reduced plate can be utilized. The preferred substrate surface for flat-rolled steel for adhesion of organic coating is "TFS" (tin free steel) which comprises a thin plating of chromium. However, with the present invention, deep drawing of flat-rolled steel with other substrate surfaces for organic coating, such as chromium oxide from a cathodic dichromate (CDC) treatment, can also be utilized without detriment to the organic coating. Such "tin mill product" materials and specifications are known in the art, see e.g. "Tin Mill Products", published by the American Iron & Steel Institute, 1000 16th Street N. W., Washington, D.C. 20036, November 1982, or "Steel in Packaging" published by the Committee of Tin Mill Products Producers of the American Iron & Steel Institute; the latter includes can and can body manufacturing nomenclature, and describes prior art manufacture of can bodies by draw-redraw and drawing and ironing processes.

The ability to manufacture deep-drawn can bodies without damage to precoated organic coatings is an important advantage of the present invention. No special properties are required for the organic coatings to withstand deep drawing as taught herein; conventional vinyl organosols, epoxies, phenolics, polyesters and acrylics, applied in a conventional manner to conventional sheet metal substrate surfaces for such coatings to conventional weight per unit area specifications, can be utilized; typical organic coating weights are about four to twelve milligrams per square inch on the sheet metal surface for the can body interior and about one and one-half to six milligrams per square inch on the sheet metal surface for the can body exterior. Such organic coatings are available commercially from companies such as the Midland Division of The Dexter Corporation, East Water Street, Waukegan, Illinois 60085, or The Valspar Corporation, 2000 Westhall Street, Pittsburgh, Pennsylvania 15233. All beer and carbonated beverage cans, regardless of organic coating, are conventionally spray coated internally with enamel which is available from the same commercial sources. The quality of the organic coating surface is maintained when precoated can stock is fabricated in accordance with the invention so that the need for enamel spray coating of the interior surface of carbonated beverage can bodies may be questioned; however, such coating can be applied in accordance with specifications presently prescribed by the carbonated beverage market.

Can body handling line equipment and profiling machinery, etc., and canmaking presses with which the present tooling apparatus teachings can be utilized, are known in the art and available through various commercial sources, such as Standun Inc., Rancho Dominquez, California 0221.

While specific can bodies and cans, tooling dimensions, sheet metal material and coating specifications have been set forth in describing the invention, those skilled in the art will recognize that modifications in specifically mentioned values can be utilized in the light of the present teachings. Therefore, for purposes of determining the scope of the present invention, reference shall be had to the appended claims.

Claims

1. A clamping ring for use in fabricating a onepiece can body from can stock including sheet metal precoated with an organic coating by redrawing a cup-shaped work product to decrease its diameter and increase its side wall height,

such clamping ring having

a toroidal configuration symmetrical about its centerline axis,

a planar clamping surface endwall,

a substantially cylindrical peripheral side wall symmetrical about such centerline axis, and

a compound curvature transition zone between such planar surface endwall and peripheral side wall,

such transition zone being in tangential contact with such planar endwall surface and peripheral side wall surface,

such transition zone having a smooth continuously curvilinear surface including multiple curvilinear surfaces formed about multiple radii of curvature of different lengths such that a projection of such multiple radii curvilinear surface transition zone onto a plane which is perpendicularly transverse to the centerline axis of the clamping ring occupies a lesser radial dimension than the maximum radius of curvature utilized in forming such transition zone.

2. The clamping ring of claim 1 in which

such multiple radii of curvature transition zone includes a pair of curvilinear surfaces formed about a larger radius of curvature and a curvilinear surface formed about a smaller radius of curvature,

with such larger radius of curvature providing a first curvilinear surface in tangential contact with such planar endwall and a second curvilinear surface in tangential contact with such cylindrical side wall, and

such lesser radius of curvature providing a curvilinear surface located intermediate of and in tangential contact with such first and second larger radius of curvature curvilinear surface.

3. The clamping ring of claim 2 in which such lesser radius of curvature is approximately one-half the length of such, larger radius of curvature.

4. A draw die for fabricating a one-piece cup from flat-rolled sheet metal can stock pre-coated with an organic coating and draw lubricant,

such draw die defining

a draw cavity into which such can stock is drawn by relative movement of a draw punch into such cavity during which the centerline axes of such draw cavity and draw punch are coincident, and including

an endwall presenting a planar clamping surface radially exterior to and circumscribing such draw cavity at its entrance end for such draw punch, such planar clamping surface being in a plane perpendicularly transverse to such cavity centerline axis,

an internal side wall surface for such draw cavity which is symmetrical about the centerline axis of the draw cavity, such side wall surface being of circular configuration in a plane which is perpendicularly transverse to such cavity centerline axis, and

a cavity entrance zone between such endwall planar clamping surface and such internal side wall surface extending over an arc of at least 90.degree. measured in a radially oriented plane which includes the centerline axis of such draw cavity,

such entrance zone at one of its arcuate ends being in tangential contact with such planar clamping surface and at its remaining end being in tangential contact with such internal side wall surface,

such entrance zone having a smooth continuously curvilinear surface including multiple compound curvilinear surfaces formed about multiple radii of curvature so as to increase its surface area over that which would be provided by a single radius of curvature surface extending over such arc of at least 90.degree. between such planar clamping surface and internal side wall surface of the draw die without increasing the area of projection onto a planar clamping plane in perpendicularly transverse relationship to such cavity centerline axis of such multiple radii of curvature cavity entrance zone over the corresponding area of projection which would have resulted from such a single radius of curvature,

such increased surface area entrance zone for such draw cavity providing for a more gradual movement of such can stock into such draw cavity, during relative movement of such draw punch into such draw cavity, without diminishing the planar clamping surface area provided by such draw die,

such multiple radii compound curvilinear surfaces including a curvilinear surface formed about a smaller radius of curvature of a dimension, measured in a radially oriented plane which includes the centerline axis of such draw cavity, which is about five times starting gage for such can stock.

5. The draw die of claim 4 in which

such compound curvilinear surface having a smaller radius of curvature is located intermediate a pair of compound curvilinear surfaces each formed about a larger radius of curvature, with

one each of such larger radius of curvature surfaces being in tangential relationship to such planar clamping surface and such internal side wall surface, respectively, and

such smaller radius of curvature surface being in tangential contact with such larger radius of curvature surfaces.

6. The draw die of claim 5 in which such larger radius of curvature surfaces are formed about equal radii.

7. The draw die of claim 6 in which such smaller radius of curvature surface occupies a greater surface area of such cavity entrance zone than each of such larger radii curvilinear surfaces.

8. The draw die of claim 5 in which such larger radii of curvature are in the range of about .040" to about .060", and

such smaller radius of curvature is in the range of about .020" to about .030".

9. The draw die of claim 4 in which such internal side wall surface is recess tapered in extending from such compound curvilinear entrance zone surface into such cavity

such recess taper increasing the cross-sectional diameter of such cavity in proceeding longitudinally along such draw cavity beyond such entrance zone.

10. The draw die of claim 9 in which

such internal side wall surface is recess tapered in the amount of about 1.degree.,

such internal side wall surface is in tangential relationship to such compound curvilinear entrance zone, and

such compound curvilinear entrance zone extends through an arc of about 91.degree., measured in a plane which includes such cavity centerline axis, from such planar clamping surface and extending into such draw cavity to establish such tangential relationship.