FIELD OF THE INVENTION

The invention relates to a method and an apparatus for drawing metal blanks to form articles, typically drawn bodies can bodies or cups, or shells for easy open can ends. It relates to a method and apparatus for the manufacturing of deep drawn shells used to make said easy open ends, with a removable can end panel for easy opening. Metallic easy open can ends have a scoreline of reduced thickness surrounding said removable panel, and they are used to seal metallic can bodies typically by seaming. Can bodies sealed with said easy open ends, typically with a double edge seam, are adapted to withstand the temperature and pressure conditions developed during sterilisation.

STATE OF THE ART

Cups or shells are made as follows : a) planar sheet metal blanks are provided from a strip of metal or coil, typically steel coated with tin, or tin free steel, or aluminium, said strip of metal being preferably lacquered or laminated with a plastic film, said blanks being stamped from said strip or coil of metal, b) said blanks are drawn with a drawing tool to make frusto-conical cup or bodies having a recessed central panel and a peripheral flange, with a sloped skirt in between known as chuck wall. Said blanks may be drawn in one to three steps depending on the ratio H/L or D, H being the height of the end body, L or D being the largest dimension or diameter. Easy open can ends are generally made as follows : a) planar sheet metal blanks are provided from a strip of metal or coil, typically steel coated with tin, or tin free steel, or aluminium, said strip of metal being preferably lacquered or laminated with a plastic film, said blanks being stamped from said strip or coil of metal, b) said blanks are drawn with a drawing press (or shell press) to make shells having a recessed central panel and a peripheral seam flange, with a sloped intermediate portion in between, c) a sealing compound is applied in the curved peripheral seam flange to ensure an airtight seal of the easy open end when seamed to the can, d) said shells are then provided with easy open means, a rivet being formed in the central panel, a scoreline being formed in said central panel to define a removable panel portion, a pull tab being secured to said rivet and optionally the central panel being beaded.

Said drawing press comprises basically blank holders (an upper blank holder and a lower blank holder) and a punch cooperating with die.

PROBLEMS TO SOLVE

Standard easy open ends are converted from shells of comparatively low depth, i.e. of about 5 mm or less in depth. But, in some cases, deep easy open ends shells are needed. Some ends require to form shells of about 15 mm in depth, i.e. with a higher drawing ratio. A first problem arises because said stepped or sloped portion of the shell or of the easy open end may exhibit pleats. It is an object of the invention to have deep easy-open shells with no pleats nor wrinkles, because pleats may give rise to problems of mechanical strength and of airtightness of the ends, stacking, destacking and transportation of the ends of the shells. Of course, it is known to prevent the build up of pleats with an increased thickness of the metal strip serving to manufacture said shells. But another purpose of the present invention is to get easy open ends being at the same time of high deepness and manufactured out of comparatively low gauge metal. Another purpose of the present invention is to have easy open shells in which said sloped portion is a stepped portion with a ledge portion defining an upper sidewall portion and a lower sidewall portion, both sidewall portions being drawn without pleats or wrinkles.

The same problems arise in the case of frusto-conical cups or can bodies.

DESCRIPTION OF THE INVENTION

A first object of the present invention is an apparatus for drawing metal blanks in order to make stepped articles, typically can bodies, cups or shells for easy open ends, said articles comprising a recessed central panel and a peripheral seam flange with typically a seaming panel and a lip, with, in between, a sloped stepped portion having at least one ledge and defining an internal profile, said ledge defining an upper sidewall portion and a lower sidewall portion, comprising : a) a cut edge able to cut said blanks from a metal strip, b) a pair of blank holders with an upper punch and a lower draw ring, c) a lower tool, typically in a fixed position, comprising a die core ring and a die core, said die core ring having a shaped profile with a flat portion and a sloped stepped part having typically said internal profile with at least one step, d) an upper tool, typically moving down axially to and from said lower tool, comprising a knock out or upper ring due to cooperate with said shaped profile of said lower tool, and a punch core due to cooperate with said die core and typically with said sloped stepped part of said die core ring, and actuating means. Said apparatus is characterised in that said punch core comprises at least one upper pressure sleeve able to cooperate axially with said step so as to form said ledge, and a said "small" punch core able to cooperate axially with said die plate.

The applicant has found that such an apparatus could solve the problems of pleated walls encountered whenever the depth of the recessed central panel was too high and typically of 8 mm or higher. Moreover, the applicant has found that it was possible to reduce the gauge or thickness of the metal strip from which the blanks are cut. For instance, for shell making, it has been found possible to use a steel metal strip having a thickness of 0,16 mm, instead of a metal strip having a thickness of 0,20 mm, i.e. a 15 % reduction of the metal thickness and cost without any pleat form. Finally, the applicant has found that the power of the drawing press necessary to actuate its moving part to draw and form the blanks was significantly lower with the apparatus according to the invention, with respect to usual practices. All these fact make the apparatus according to the invention highly advantageous when compared to the standard apparatus.

DESCRIPTION OF THE FIGURES

Figures Ia to 5f deal with the apparatus and the corresponding process for making stepped articles (9, 9', 9"). These figures are partial sectional views in a vertical plane comprising the axial direction (10) disclosing the position of the different parts of the drawing tools or apparatus (1) at different stages of the drawing process. Figures Ia to Id deal with prior art apparatus and process. Figures 2a to 5f deal with apparatus and processes according to the invention.

Figures Ia to 2f deal with an article (9, 9', 9") having one ledge (920). In figure Ia, the strip of metal (6) has been clamped by the blank holders (3). In figure Ib, the cutting ring or cut edge (2) has been actuated, and the blank cut (7), still maintained by the blank holders (3), has been put in contact with flat part (400) of die core ring (40), and started to be formed. In figure Ic, the upper tool (5) has been lowered at an intermediate position. In figure Id, the upper tool (5) has got its final lowest position, the stepped article (9) being formed.

In figures 2a to 2f, the die core ring (40) of figures Ia to Id is replaced by a small die core ring (40') and by a lower pressure sleeve (43). Figure 2a corresponds to figure Ia. In figure 2b, the blank (7) has been cut and started to be formed by the flat portion of sid shaped profile (400). Figure 2c corresponds to figure Ib. Figure 2d and 2e are successive intermediate positions similar to the one of figure Ic. Figure 2f corresponds to figure 1 d.

In figures 3a to 3f, the punch core (51) comprises two shoulders (510, 510'), and the lower tool (4) comprises a die core ring (401) with a lower pressure sleeve (43) forming a step (430). Figures 3a to 3f deal with an article (9, 9', 9") having two ledges (920, 920'). In figures 3a to 3f, said lower pressure sleeve (43) forms a step (430). Figures 3a to 3f correspond to figures 2a to 2f.

In figures 4a to 4g, the upper tool (5) comprises one upper pressure sleeve (52) and a small punch core (53), and lower die (4) comprises a die core ring (40) with a slopped stepped part (41) forming a step (410). Figure 4a is similar to figures Ia, 2a, 3 a. Figure 4b is similar to figures 2b, 3b. Figure 4c is similar to figure Ib, 2c and 3 c. In figure 4d and 4e, said upper pressure sleeve (52) is activated and acts as part of said upper tool (5) to form said blank, while small punch core (53) is not yet activated, said upper pressure sleeve (52) being stopped by the step (410) in figure 4e. In figure 4f, small punch core (53) is activated. Figure 4g is similar to figures Id, 2f and 3f.

In figures 5a to 5f, the upper tool (5) comprises two upper pressure sleeves, one outer upper pressure sleeve (52) and an inner upper pressure sleeve (52'), and a small punch core (53), the lower die (4) comprises a die core ring (40') with a lower pressure sleeve (43) forming a step (430). Figure 5 a corresponds to figure 4a. Figure 5b corresponds to figure 4b. Figure 5c corresponds to figure 4c. In figure 5d, the outer upper pressure sleeve (52) and the top (431) of said lower pressure sleeve (43) are activated to grasp said blank. In figure 5e, the inner upper pressure sleeve (52') is activated and lowered to draw said blank up to the level of said step (430). In figure 5d, similar to figure 4g, small punch core (53) has been activated up to the level of the die core (42).

Figure 6 is a sectional view of the complete tooling of apparatus (1) corresponding to figures 4a to 4g.

Figure 7a is a partial sectional view of the stepped shell (9, 9'), with a depth H of 15 mm, having one ledge (920), manufactured with the process and apparatus of figures 4a to 4g according to the present invention. Figure 7b is a photograph (lateral view) of a stepped shell (9, 9') manufactured with the process and apparatus of figures 4a to 4g. Figure 7c is a photograph (lateral view) of a pleated stepped shell (9, 9') manufactured with the process and apparatus of figures 2a to 2f corresponding to the prior art. Figure 8a, similar to figure 7a, is a partial sectional view of a stepped shell (9, 9') having two ledges (920, 920') manufactured with the process and apparatus of figures 5a to 5f according to the present invention. Figure 8b is a partial sectional view of a stepped can body (9, 9"), with a depth H of 45 mm, manufactured with the process and apparatus similar to the ones of figures 5a to 5f according to the present invention.

DESTAILLED DESCRIPTION OF THE INVENTION

According to the invention, said punch core (51) may comprise as many upper pressure sleeves (52, 52') as steps (410, 410') so as to form as many ledges (920, 920') present in said slopped stepped portion or chuck wall portion (92).

According to an embodiment, as illustrated in figures 4a to 4g, and in figures 7a and 7b, said punch core (51) may comprise only one upper pressure sleeve (52), only one ledge (920) being present in said slopped stepped portion or chuck wall portion (92). According to another embodiment, as illustrated in figures 5 a to 5 f, and in figure 8, said punch core (51) may comprise two adjacent pressure sleeves, one outer pressure sleeve (52) and one inner pressure sleeve (52'), two ledges (920) and (920') being present in said slopped stepped portion or chuck wall portion (92). Said actuating means may actuate said upper pressure sleeves (52, 52') until said upper pressure sleeves (52, 52') are stopped typically by step (410) of said lower die (4), each upper pressure sleeve (52) and (52') being stopped by its corresponding step (410) and (410').

According to another embodiment, as illustrated in figures 5a to 5f, or in figures 2a to 2f, said die ring (40, 40') may comprise at least one lower pressure sleeve (43) to form said step (410, 430) or to form a stop (431). Another object of the invention is a method of making stepped articles (9), typically cans (9"), cups or shells (9') for easy open ends, said stepped articles (9) comprising a recessed central panel (90) and a peripheral seam flange (91), with a sloped stepped portion (92) in between, by drawing of metal blanks (7), with the apparatus (1) according to the present invention. In this method, and as illustrated in figures 4a to 5f : a) said metal strip (6) may be cut by said cutting ring or cut edge (2) to form said blank

b) then, said blank (7) may be clamped at its periphery by said pair of blank holders (3), with said upper punch holder (30) and said lower blank holder or drawing ring (31), c) then, said blank holders (3) may be moved down to put said blank (7) in contact with said flat part (401) of said die core ring (40), so as to form all or part of said lip (911) of said peripheral seam flange (91), d) then, the said upper pressure sleeve (52) and the small punch core (53) may be moved down until typically the upper pressure sleeve (52) is stopped by said step (410), or each of said upper pressure sleeves (52, 52'), if more than one upper pressure sleeve (52, 52') is present with an outer upper pressure sleeve (52) and an inner upper pressure sleeve (52'), is moved down in turn, the said outer upper pressure sleeve (52) being first actuated, until each said outer upper pressure sleeve (52) is typically stopped by its corresponding step (410), so as to form at least said upper sidewall portion (921), e) finally, said small punch core (53) may continue to move down until typically stopped by said die core (42), so as to form the rest of said stepped shell (9).

Another object of the invention is a stepped article (9) made according to the process of the invention. According to an embodiment of said stepped article (9), as illustrated in figure 7a to 8b : a) said recessed central panel (90) may have a depth H of at least 8 mm, said depth being relative to top of said seaming panel (910) of said peripheral seam panel (91), b) said sloped stepped portion (92) may comprise one ledge (920) which defines said upper sidewall portion (921) of height Hl and said lower sidewall portion (922) of height H2, with H = H1+H2, and H2/H1 > 1, and preferably >2. According to another embodiment of said stepped article (9), as illustrated in figure 8a : a) said recessed central panel (90) may have a depth H of at least 8 mm, said depth being relative to top of said seaming panel (910) of said peripheral seam panel (91), b) said sloped stepped portion (92) may comprise two ledges (920) which defines said upper sidewall portion (921) of height Hl, said intermediate side wall portion (923) of height Hl1 and said lower sidewall portion (922) of height H2, with H = H1+H1'+H2, and H2/(H1+H1') > 1, and preferably >2. In these two embodiments, said lower sidewall (922) may have a slope going from 5° to 15°, preferably from 8° to 12°, and typically of 10°, angle relative to an axial direction (10).

These stepped articles (9) may be made from a metal strip (6) chosen among steel coated with tin, or tin free steel, or aluminium, or alloys, said strip of metal being preferably lacquered or laminated or co-extruded with a plastic film, the thickness of said metal strip (6) being in range 0,13 mm - 0,22 mm, and preferably in the range 0,16 mm - 0,18 mm.

Another object of the invention is a stepped article according to the invention wherein said depth H is in the range 8 mm to 20 mm, and preferably in the range 12 to 18 mm, so as to form a stepped shell (9, 9') for an easy open end, said stepped shell (9, 9') having said peripheral seam flange (91) with said seaming panel (910) and said lip (911). See figures 7a to 8a.

Another object of the invention is a stepped article according to the invention wherein said depth H is in the range 20 mm to 70 mm, so as to form can bodies or cups (9, 9"). See figure 8b.

EXAMPLES Some stepped articles (9) have been manufactured from a metal strip of 0,15 mm or 0,17 mm or 0,20 mm of thickness of lacquered tin free steel, using the type of apparatus of figure 6, with different tools - lower die (4) and upper punch (5), said apparatus being devised to measure the power required to draw the blanks (7).

Example 1 Stepped shells (9, 9') according to figure 7a have been manufactured with the process and apparatus disclosed in figures 4a to 4g, and 6.

Example 2 According to another embodiment, stepped shells (9, 9') according to figure 8a have been manufactured according to the process and apparatus disclosed in figures 5a to 5f.

Example 3 Stepped can bodies according to figure 8b have been manufactured according to the process and apparatus similar to the ones disclosed in figures 5a to 5f.

Comparative examples Stepped shells (9, 9') according to figure 7a have been made using the process and apparatus of figures Ia to Id (example 3), and 2a to 2f (example 4), and 3a to 3f (example 5).

Results The stepped articles (9, 9', 9") have been analysed with regard to the presence of pleats. See the table below with "Y" or yes if pleats are present, or "N" or no, if pleats are not present. The process and apparatus have been compared with regard of the power required, example 1 being taken as the reference. See the table below with "+" when more power is significantly required (at least 5%), or "-" when less power is significantly required (at least 5 %).

As a conclusion, the apparatus and the process according to the invention allows for a high reduction in thickness of the strip of metal used, and as a consequence a very significant gain in the metal cost. Moreover, the process itself is less energy consuming.

LIST OF REFERENCES

APPARATUS 1 AXIAL DIRECTION 10 CUT EDGE (CUTTING RING). 2 BLANK HOLDER 3 UPPER PUNCH 30 LOWER DRAW RING... , 31 LOWER TOOL 4 DIE CORE RING 40, 40' SHAPEDPROFILE 400 FLATPORTION 401 SLOPED STEPPED PART of 40 41 STEP of 41 410 DIECORE 42 LOWERPRESSURESLEEVE 43 STEP of 43 430 TOP of 43 = STOP 431 UPPERTOOL 5 KNOCKOUT-UPPERRING 50 PUNCHCORE 51 SHOULDER 510,510' UPPER PRESSURE SLEEVE (outer / inner) ... 52,52' SMALLPUNCHCORE 53 STRIPOFMETAL 6 BLANK 7 INTERMEDIATEARTICLE 8 STEPPEDARTICLE 9 STEPPEDSHELL 9' STEPPEDCANBODY 9" CENTRALPANEL 90 PERIPHERALSEAMFLANGE 91 SEAMPANEL 910 LIP 911 CHUCK WALL or SLOPPED STEPPED PORTION.... 92 LEDGE 920,920' UPPER SIDE WALL PORTION 921 LOWER SIDE WALL PORTION 922 INTERMEDIATE SIDE WALL PORTION.. 923