EP0675773B1 - Process and apparatus for further treating a closure end made of sheet - Google Patents

Abstract

PCT No. PCT/DE93/00958 Sec. 371 Date May 17, 1996 Sec. 102(e) Date May 17, 1996 PCT Filed Oct. 8, 1993 PCT Pub. No. WO95/10373 PCT Pub. Date Apr. 20, 1995A process for further treating a closure end made of sheet material is provided, particularly for beverage cans, in which an annular fringe region is radially coupled between the central panel portion and a radius of curvature coupled to a core groove with an inner leg. The central panel portion is squeezed such that material is displaced (flows) from the fringe region in a substantially radial outward direction towards the radius of curvature. The squeezing is accomplished by a coining tool having a coining surface operable to contact the closure end. The closure surface is pressed against the closure end causing the thickness of the sheet material of the closure end to be reduced in the annular fringe region. The reduction in thickness gradually decreasing in the direction of the radius of curvature. The material displaced by the squeezing flowing towards the radius of curvature. A ring tool which is finger like in cross section can be used to exert pressure on the core groove during or after the squeezing thereby causing the inner leg of the core groove to move towards a more vertical orientation.

Description

The invention relates to a method for the further treatment of a closure lid made of sheet metal, in particular a folding lid for beverage cans or the like, with the features of the preamble of claim 1 and claim 2. The tool for carrying out the method is also affected.

Such a cover is known from US Pat. No. 3,441,170, in which the radius of curvature is reduced in thickness even from the inside of the cover, with the formation of a “coined bead”. As a result, a kind of joint is created between the inner leg of the groove and the cover mirror in order to restrict the bulging of the cover to the cover mirror, so that the tensile forces acting radially inward on the core wall of the cover are reduced. At this joint (embossed bead), the lid mirror, which bulges more strongly under greater internal pressure, is articulated to the core wall in such a way that the latter is not or only slightly touched in its vertical orientation by the bulging.

A similar measure is known from EP 88 968 A1, in which the cover plate is deformed from the outside by pressing pressure starting from the radially inner edge of the radius of curvature over a region of the radius of curvature, so that material of the cover is radially inward and outward from this radius of curvature region flows outside. The deformation area forms a flat on the outside of the radius of curvature, the major part of the flat coming to lie in a plane perpendicular to the axis of the cover or in a conical plane inclined outwards and downwards. This also improves the resistance of the cover to bulging. Due to the material flow radially inward, the outwardly arched cover mirror is placed under compressive stress to form a free doming of the "free doming of central panel", while the radially outward flowing material removes the inner leg of the cross-sectionally U-shaped groove from its original inclined position in a more cylindrical or permanently pivoted to the axis of the cover ("permanent deflection of inner leg"). In both known measures, the area deformed by coining is hardened at the same time by cold working (work hardened). Both solutions of the prior art therefore strive for an enlarged curvature of the lid mirror ("doming"). If, however, a can provided with such a strongly domed lid and filled is pasteurized, for example (whereby it is upside down), the resulting bulging leads to the cans tipping and falling over.

It is an object of the invention to change a lid with a method having the features of the preamble of claim 1 so that the bulging of the lid center can be largely reduced and nevertheless material can be displaced from the lid edge area in a controlled manner to increase the compressive strength.

This object is achieved by the teaching of claim 1 or 2 or by the teaching of claim 9 .

The ring-shaped strip portion which is formed during the further treatment under reduction in thickness, clearly lies radially within the actual radius of curvature. This means that almost no material is displaced into the cover mirror, but from its edge area over the radius of curvature (almost only) into the radially inner leg of the U-shaped core groove. This displacement process is achieved primarily by the angle which is formed and determined by the embossing surfaces acting on the strip-shaped area. This angle is determined between the embossing surfaces of the embossing tool or stamp that acts on the lid from the outside and a plane running perpendicular to the axis of the lid. The embossing surface of the lower embossing tool or stamp is preferably parallel to this plane running perpendicular to the lid axis, that is to say that the angle mentioned is also present between the two embossing surfaces. This angle should be significantly larger than 0 ° be, but in any case less than 90 °.

This angle is preferably between 2 ° and 15 °.

Lids reshaped in this way are stable in their overhead stability even with increased internal pressure, although they do not have to miss the advantage of the more precise vertical alignment of the inner leg.

For precise centering of the cover, a ring holder with a cross section which is finger-shaped can be centered in the U-shaped groove during the embossing process, without exerting forces which have an effect on the core groove.

But you can also simultaneously or during the last phase of the embossing process - displacing the material - with such a finger-shaped ring tool apply a controlled stretching pressure approximately parallel to the axis of the cover on the bottom of the core groove so that the material flow radially beyond the radius of curvature supported on the outside and at the same time the inner leg of the U-shaped groove is tightened and brought more precisely into the desired vertical position.

According to the invention, the material of the cover plate is pressed together in the region of the annular strip in such a way that in this annular strip region the reduction in plate thickness decreases steadily in the direction radially outward from a point of smallest residual thickness. In the deformed area, the remaining thickness changes radially outward, for example in the form of a straight wedge, the underside lying in a plane perpendicular to the lid axis and the top in a straight conical surface.

It has proven to be particularly advantageous if a second treatment step follows the first treatment step described. During the second treatment step, the lid material is - in the first Crushed and deformed step - strip-shaped area slightly leveled, but without making any noticeable material displacement, but only in a partial area, namely a radially outer area of the strip adjacent to the radius of curvature. This leads to a further reduction in the radius of curvature _, which contributes significantly to increasing the nose strength of the lid. If, due to the first embossing, an insignificant part of the displaced material has been shifted radially inwards, the second treatment step may plan this. The resulting slight "doming" of the cover mirror and largely creates the exact contact of the radially inner wall of the core groove with the lower mold. The radially inner "lock", which has already been cold-hardened due to the wedge effect, and the planar action of the tool prevent, during leveling, that material be displaced from a local area or even shifted inward (past the cold-hardened "lock").

The leveling step therefore does purely geometric design work, which relates to the improved alignment of the inner leg of the core groove.

US-A-4,354,784 (Westphal), which introduces a chip-free score line into a metallic cover, deals with an objective which differs from the invention. This score line runs all the way around the vertical core wall of the cover and is introduced by a tool that has a central flat area and two inclined outer areas (column 4, first paragraph). With this "trapezoidal tool" a notch line contour is obtained, which reduces the risk of metal chips when torn open. This freedom from chips is obtained by defining the score line by simultaneously displacing material from the central area to both sides (radially inside and radially outside). This tool does not cause material to be displaced only on one side.

A roughly comparable objective - the protection of children's tongues from the risk of cuts - resides in DE-A-23 03 943. She wants to avoid that the children's tongues expose themselves to cutting hazards when the thick layer of pudding on the underside of the lid is licked off. For this purpose, an S-shaped triple protective fold is proposed, which is also circumferential and is obtained by folding an initially vertical wall section. In a preliminary stage of this refolding process, a tool part is used (recognizable there with the aid of FIG. 14), which has an annular undercut and a projecting flat annular surface, which in one zone (designated 45) reduces the material thickness of the metal cover. The material displaced radially inward from the aforementioned zone by this embossing process leads to a change in the inclination of the aforementioned vertical wall section, which later forms the S protective fold. A displacement of material only radially outwards is neither proposed nor suggested here.

The invention is illustrated by the following hand-drawn drawings of several execution examples .

• Figur 1 im Ausschnitt und in einem die Achse 16 des Deckels enthaltenden senkrechten Schnitt die zum Ausführen des Verfahrens erforderlichen Werkzeuge am Ende der Weiterbehandlung eines entsprechenden Blechdeckels;
• Figur 2 den gemäß der Erfindung weiterbehandelten Blechdeckel in ähnlicher Darstellung wie Figur 1;
• Figur 3 eine abgewandelte Ausführungsform des Werkzeuges für ein abgewandeltes Verfahrensbeispiel.
• Figur 4 die Werkzeuge für einen dem Weiterbehandlungsschritt der Figur 1 oder Figur 3 nachgeschalteten weiteren Bearbeitungsschritt;
• Figur 5 in ähnlicher Darstellung wie Figur 2 einen Deckel, der mit beiden Verfahrensschritten nach Figur 1 und Figur 4 behandelt worden ist.

Show it:

• Figure 1 in a detail and in a vertical section containing the axis 16 of the lid, the tools required to carry out the method at the end of further processing of a corresponding sheet metal lid;
• FIG. 2 shows the sheet metal cover treated according to the invention in a similar representation as FIG. 1;
• Figure 3 shows a modified embodiment of the tool for a modified method example.
• FIG. 4 shows the tools for a further processing step following the further processing step of FIG. 1 or FIG. 3 ;
• Figure 5 in a similar representation as Figure 2, a cover that has been treated with both process steps according to Figure 1 and Figure 4 .

The lid 1 is shaped, as usual, from a sheet metal blank so that it has a slightly curved central lid mirror 10, which over a radius of curvature 11, R1 merges into the straight inner leg 13 of a cross-sectionally U-shaped groove 12, the outer leg 14 of which Forms the core wall of the lid, to which (not shown) the lid edge connects. The edge can be of any design and typically be a folded edge.

The lid preformed in this way is placed between the embossing tools 2 and 4. The embossing tool 2 has an embossing surface 3 running approximately perpendicular to the lid axis 16. The embossing tool 4, which can be moved relative to the embossing tool 2 in accordance with the arrow 15, has on its underside in the outer area an annular rib formed by a step 5, the effective bottom 6 of which forms a predetermined angle 25 with respect to the embossing surface 3 of the tool 2, which is noticeably greater than 0 ° and less than 90 ° and preferably approximately between 2 ° and 15 ° lies. The embossing tool 4, 5 is supported on a stamp 7, on which, in the example shown, a ring-shaped hold-down device 8 is supported via a spring 9, which is finger-shaped in cross section and engages centering in the U-shaped groove 12 of the cover.

Figure 1 shows the embossing tools in a position which they assume at the end of the squeezing or embossing process.

As a result of this further treatment of the cover, the material of the cover mirror 10 of the sheet metal cover is squeezed in an annular strip region 20, which adjoins the R1 curve 11 radially on the inside. The curvature 11 itself is largely spared from the squeezing process, but not from its effects with regard to the material moved outwards. The material displaced during the squeezing flows in a controlled manner radially outward and via the curvature 11 into the inner leg 13 of the groove 12 to be aligned.

Because of this design, the smallest remaining thickness, which is indicated at 28 in the tool position according to FIG . For example, it can be 65%. The reduction in thickness decreases in the radial direction towards the outside, preferably along 22 evenly and steadily, so that radially outside the remaining thickness 29 merges into the normal thickness of the sheet in the region of the curvature 11 essentially without steps.

The flow process is further favored if the holding-down device 8 is rigidly supported on the punch 7 via the part 8a, the axial length 27 of the centering finger 8 being dimensioned such that at the end of the embossing process, a predetermined pressure is exerted on the bottom 12 of the finger Nut is exercised. As a result, the flow of material from the strip area 20 is still significantly favored by the curvature 11, and at the same time the radially inner straight leg 13 of the U-shaped groove 12 is held and aligned under tensile stress.

The resistance to deformation of the edge profile can be significantly increased and the nose strength increased if the treatment step (stamping) according to FIG . 1 or 3 described above is followed by a treatment step (leveling) according to FIG. 4 . Tools similar to those used in the first treatment step are used here, but the upper die 31 has an embossing rib, the effective leveling surface of which runs essentially perpendicular to the cover axis 16, so that during leveling the material is geometrically shaped between two planes and the embossing surfaces running perpendicular to the cover axis 16 becomes. However, this leveling remains limited to only a part of the strip which has been previously squeezed, and that part which is adjacent to the curvature and which has the greatest remaining thickness (for example between 100% and 70%). The embossing tool 31 is supported on the punch 30, on which the centering tool 34, which is finger-shaped in cross section, can also be supported directly via part 33, as shown in FIG. 4 . The stretching effect of the tool 34 is the same as the effect of the tool 8 according to FIG. 3.

With this leveling, the radius R2 of the curvature 11 is reduced compared to the radius R1 according to FIG. 2. The reduction in the radius of curvature and the geometrical reforming of the squeezing area lead to an increase in the nose strength through clean contouring of the edge profile without additional material hardening.

The original residual thickness of the sheet in the radially outer region of the strip, as indicated at 29 in FIG. 3 , is only slightly reduced at 40, but is geometrically shaped. The outer surface, which originally runs conically over the entire width 24 of the strip 20, is deformed by the deformation in a surface region 35 which is narrower than the width of the strip 24 and is perpendicular to the cover axis 16. The remaining part of the strip 24 maintains its inclination in accordance with the angle 25 from the first stamping. The centering during the second step according to FIG. 5 can take place according to FIG. 1 , that is to say with a spring-loaded centering tool. However, a centering tool according to FIG. 4 is preferred , with which the leg 13 of the U-shaped groove 12 can be placed under yield stress.

Claims (10)

1. A process for further treating a closure end made of sheet, particularly a folding end for beverage cans or the like, in which

   - the end is punched out of a planar sheet and shaped between form tools to comprise a central panel portion (10) which changes into the radially inner wall (13) of a core groove (12) including the end edge via a radius of curvature (R1, R2), and in which,

   - for further treatment, the material of the end sheet is made flowing within the region of the radius of curvature by mold pressure thereby reducing the sheet thickness

   characterized in
   that, for further treatment, the material of the end sheet is made flowing within an annular inner fringe region (20, 24), adjoining in substantially radial fashion the radius of curvature (R1, R2), of the central panel portion (10) towards the core groove (12) and for this purpose is compressed between a form tool surface (3) oriented perpendicularly to the end axis (16) and a form tool surface (6) diverging relative thereto radially outwardly in wedge-type fashion (25).
2. A process for further treating a closure end made of sheet, particularly a folding end for beverage cans or the like, in which

   - the end is punched out of a planar sheet and shaped between form tools to comprise a central panel portion (10) which changes into the radially inner wall (13) of a core groove (12) including the end edge via a radius of curvature (R1, R2), and in which, for further treatment, the material of the central panel portion is made flowing within the region of the radius of curvature by mold pressure thereby reducing the sheet thickness,

   characterized in
   that, for further treatment, the material of the end sheet is made flowing within an annular fringe region (20, 24), adjoining in substantially radial fashion the radius of curvature (R1, R2), of the central panel portion (10) such that in the annular fringe region of the central panel portion the sheet thickness reduction (28, 29) constantly (21, 22, 25) decreases from a point of lowest residual thickness (21) in radially outward direction towards the core groove (12).
3. The process according to claim 1 or 2, characterized in that - simultaneously with the sheet thickness reduction of the annular fringe region (20) of the central panel portion (10) - a pressure tensioning the radially inner groove wall (13) towards the end axis (16) is exerted on the bottom of the groove (12), so as to support a flow of material from the annular fringe region via the radius of curvature (R1, R2) as well as to promote tightening and orientation of the radially inner wall (13) of the groove.
4. The process according to one of the above-mentioned claims, in which during flowing (squeezing) the material is displaced in controlled fashion radially outwardly via the curvature (11, R1, R2) into the inner leg (13), to be oriented, of the groove (12).
5. The process according to any one of the preceding claims,
   characterized in that,
   after flowing the material of the end within the annular fringe region of the central panel portion, the radius of curvature (R1, R2) is reduced in size by levelling (35, 40) the - or part of the - annular fringe region (20, 24) (Fig. 4).
6. The process according to claim 5, characterized in that during levelling only the region, in the vicinity of the radius of curvature (R2), of the annular fringe, which includes the greater residual thickness (29), is pressed (35, 40).
7. The process according to claim 1 or 2, characterized in that pressure is applied to the bottom of the groove (12) after reducing the radius of curvature (R1, R2) by levelling (35, 40) the - or part of the - annular fringe section (20, 24).
8. The process according to claim 1 or 2, characterized in that pressure is applied to the bottom of the groove (12) while the radius of curvature (R1, R2) is reduced by levelling (35, 40) the - or part of the - annular fringe section (20, 24).
9. A processing apparatus including a tool set (2, 3) which has a contour and a counter-contour (5, 6, 3) in an annular fringe region (20, 24), which constantly (21, 22, 25) increase (29) from a point of minimum distance (28) between contour (5, 6) and counter-contour (3) radially outwardly and are developed radially inwardly (5) such that almost no material can be displaced in this direction.
10. The processing apparatus according to claim 9, in which an annular holding-down device (8, 34) facing in finger-like fashion from the contour tool (2) to the counter-contour tool (3) is arranged radially outside the contour and counter-contour of the tool set (2, 3).

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