EP1971452A1

EP1971452A1 - Process for producing a container and apparatus for producing a container using said process

Info

Publication number: EP1971452A1
Application number: EP06744711A
Authority: EP
Inventors: Johannes Vermeij
Original assignee: Corus Staal BV
Current assignee: Tata Steel Ijmuiden BV
Priority date: 2005-12-09
Filing date: 2006-05-12
Publication date: 2008-09-24
Also published as: WO2007066172A1

Abstract

This invention relates to a process for producing a container (1) from a blank (2) by a forming process using a mould (3), the mould defining a mould cavity (4), wherein the blank (2) is held between a blank holder (5) and the mould (3) in a first clamping position above the mould cavity (4), the forming process comprising a first forming step of deep-drawing using a punch (6) for forming the blank (2) into a cup (7) , and a second forming step of stretch-forming the cup (7) into a container (1) , the punch (6) being provided with a tapered surface (8) along its perimeter, said tapered surface (8) coinciding with a congruently shaped tapered surface (9) on the mould in the mould cavity (4) , so as to clamp the cup (7) at least partly after ending the first forming step and before starting the second forming step, wherein the angle of the tapered surface (8) on the punch (6) in respect to the direction of movement of the punch is between 5 and 45°. The invention also relates to an apparatus for forming a container according to said process.

Description

PROCESS FOR PRODUCING A CONTAINER AND APPARATUS FOR PRODUCING A CONTAINER USING SAID PROCESS

This invention relates to a process for producing a container, apparatus for producing a container using said process and the use of said process in a form-fill-seal operation.

Known process for the production of two-piece containers for the packaging of products such as products intended for human or animal consumption start out as metal sheet. The sheet enters a cupping press where blanks are created by punching holes in the coil. These blanks are then drawn into cups and conveyed to a bodymaker. The bodymaker redraws the cup, makes them longer and smaller in diameter and thereafter irons the material, decreasing its thickness, and also elongates the can body. After trimming to the desired can height a lacquer is applied to the cans, which is then cured. A necking and flanging process prepares the cans for their lids, which will be applied at a future time, after filling of the can on another location where the product is produced which is to be packed in the container.

As an alternative to these types of two-piece cans a type of can is known which is produced by forming a blank into a cup by a deep-drawing process followed by a stretch-forming step to form the cup into a container. The container can then be filled and closed by a lid. These cans are typically, but not exclusively, used for food products, including liquid or viscous food products, for human consumption, or for consumption by animals.

A problem with the production of such a container is that the material flow during the stretch-forming step is such that wrinkles occur in the wall of the container if the material is not fixedly clamped during the stretch-forming step. This requires a very high clamping force, particularly when the material to be formed is slippery, i.e. has a low friction coefficient in relation to the tooling.

It is an object of the invention to provide a process for forming a container by forming a blank into a cup by a deep-drawing process followed by a stretch-forming step to form the cup into a container in which no wrinkles occur in the wall of the container without requiring a very high clamping force.

The object of the invention is reached by a process for producing a container from a blank by a forming process using a mould, the mould defining a mould cavity, wherein the blank is held between a blank holder and the mould in a first clamping position above the mould cavity, the forming process comprising a first forming step of deep-drawing using a punch for forming the blank into a cup, the cup having a bottom part, a side wall with a bottom edge and a top edge, the bottom edge being connected to the circumference of the bottom part, and a flange part being connected to the top edge of the side wall part, the flange part being held in the first clamping position during deep-drawing, and a second forming step of stretch-forming the cup into a container, the punch being provided with a tapered surface along its perimeter, said tapered surface coinciding with a congruently shaped tapered surface on the mould in the mould cavity, so as to clamp the cup at least partly to hold the cup in a second clamping position between the said tapered surfaces, clamping being undertaken after ending the first forming step and before starting the second forming step, wherein the angle a of the tapered surface on the punch in respect to the direction of movement of the punch is between 5 and 45°.

With the process according to the invention the cup is produced without wrinkles in the bottom part by an adequate selection of the blank-holder force. By maintaining the blank-holder force, at least until the cup is clamped into a second clamping position, the flow of material is effectively prevented prior to the stretch- forming operation. After starting the stretch-forming operation when the cup is clamped into a second clamping position between the tapered surface of the punch and of the mould in the mould cavity, the material flow during stretching is controlled in such as way as to prevent the formation of wrinkles in the finished container, it was found that when the angle a of the tapered surface on the punch in respect to the direction of movement of the punch is chosen between 5 and 45° that a smooth process for forming the container is obtained resulting in excellent wrinkle-less quality of the deep- drawn and stretched wall of the finished container with a reduced clamping force. The first forming step and second forming step may be performed on one location and even in one apparatus, but the first forming step may also be performed elsewhere so as to provide cups or preforms. These cups may then be transported to the apparatus for stretch-forming.

The deep-drawn cup may be subjected to a wall-ironing step before the stretch- forming step.

It should be noted that the phrase 'congruently shaped tapered surface' is intended to include the situation in which, during the clamping of the cup in the second clamping position, the tapered surface along the perimeter of the punch and the congruently shaped tapered surface on the mould are parallel when viewed in cross section view along the axis of movement of the punch. However, it is also intended to include the situation in which the two tapered surfaces are only parallel for a part of the tapered surface. The congruently shaped tapered surface may even be unparallel to the tapered surface along the perimeter of the punch as long as the clamping action in the second clamping position between the said tapered surfaces is effectively provided. The mould cavity mirrors the shape of the container to be formed. The mould cavity preferably has an annular, circular or ellipsoid perimeter so as to produce containers having an annular, circular or ellipsoid top edge when seen from the direction of movement of the punch. It will be clear that the punch has to be shaped so as to enable to deep-draw the cup to be formed into the containers having the annular, circular or ellipsoid top edge.

In an embodiment of the invention, the angle a of the tapered surface on the punch in respect to the direction of movement of the punch is chosen between 7 and 35°, preferably between 9 and 30°, more preferably between 10 and 20°, and even more preferably between 13 and 17°. By choosing an angle a having a value in the preferred range, an even better control of the forming process and/or the surface quality of the container is obtained. The length of the tapered surface on the punch when measured along the punch in the direction of movement of the punch, and thereby also of the length of the facet formed in the container by the tapered surface on the punch as a result of the second clamping action and the following stretch-forming step is preferably lower than 10 mm, more preferably lower than 4 mm, more preferably lower than 3 mm. A suitable minimum length is at least 0.2 mm, preferably at least 0.5 mm. If the length is too small, then the surface on which the clamping action is exerted becomes too small and local pressures become too high. To large a surface results in too low a surface pressure and thereby in slippage of the material out of the clamping position.

In an embodiment of the invention the blank is a planar blank. Planar blanks have the advantage that they can be produced in large quantities from flat metal sheet, preferably by stamping. The metal sheet may be supplied in the form of a coiled sheet.

In an embodiment of the invention the perimeter of the mould cavity is substantially circular. Although the process according to the invention is suited to also accommodate shapes of perimeter of the mould cavity, it was found that the point- symmetry of the forming process using a circular mould cavity, leading to containers with a substantially circular top edge, provides very good control of the forming process and the quality of the container thus formed.

In a preferred embodiment the tapered surface on the punch is provided by chamfering the perimeter of the punch at the location where the bottom part of the punch contacts the bottom part of the cup, the chamfering angle β between the plane of the bottom part of the punch and the tapered surface being (90°-σ). This way the bottom part of the punch for contacting the bottom part of the cup has a smaller diameter than the punch at the location where no chamfering has taken place.

In an embodiment of the invention the punch comprises a surrounding part and a surrounded part, wherein the surrounding part is provided with the tapered surface of the punch for holding the cup in the second clamping position and wherein the first forming step is performed substantially by the surrounding part of the punch, and wherein the bottom of the container is embossed in an embossing step by moving the surrounded part out of the surrounding part of the punch to emboss the bottom part of the container by pressing the bottom part of the container to the bottom part of the mould cavity.

This embodiment allows for a very efficient forming of the container as well as embossing of the bottom of the container so as to provide a steady surface on which the container rests to prevent wobbling of the container when positioned on a flat surface, such as a tabletop. The embossing may also be used so as to introduce a shape in the bottom of the container, such as a trademark or any other figurative shape. For this purpose, the bottom of the mould cavity may be provided with an elastic insert, such as a rubber insert, mirroring the shape to be embossed.

In an embodiment of the invention the second forming step is performed immediately subsequent to the first forming step.

In this embodiment the cup, which is made in the first forming action is stretch- formed in one continuous process, preferably in the same apparatus, more preferably in one continuous movement in the same apparatus. This reduces the risk of damage to the cup during the time between deep-drawing and forming, for instance during transport from the cupper to the stretch-forming apparatus. The risk of polluting the cup between the deep-drawing and the stretching is also reduced, which is particularly advantageous in producing a container for containing food products. In an embodiment of the invention the stretch-forming step is a blowing step, preferably using a gas as a blowing medium, preferably wherein the medium is provided through a conduit running through the punch.

By performing the stretch-forming step according to this embodiment the inner surface of the container to be formed remains essentially clean, particularly when using a gas, which gas may be an inert gas, as a blowing medium. Also clean fluids, such as clean water, could be envisaged as a suitable blowing medium. However, depending on the contents of the container when in use, requirements to the blowing medium may be strict or relaxed. For instance, when the contents comprises food products, the demands with regard to cleanliness and toxicity are strict, whereas the requirements for packaging non-consumable products may be less strict. AN additional advantage of using a gas as a blowing medium is that the inside of the container after forming remains dry.

In an embodiment of the invention the forming process comprises a curling step so as to provide the edge of the container with a curl.

The sharp edges of the container are thus eliminated, taking away the risk of injury by cutting. The curl also eliminates the risk of corrosion at the location of the edge in case the metal is provided with a protective coating. In an embodiment of the invention the blank is a metal substrate, which substrate is coated on at least one side and preferably on both sides with an organic coating such as paint or lacquer, a polymer coating or a polymer coating system. Preferably the polymer coating or coating system comprises a thermoplastic resin. The substrate may be coated on different sides with different organic coatings, polymer coatings or polymer coating systems. A substrate may be provided with an organic coating on one side and a polymer coating or coating system on the other side. In the meaning of this invention a polymer coating is to be understood to be a coating comprising a single layer coating. A polymer coating system is to be understood to comprise at least two layers of polymer coating.

Substrates provided with an organic coating, a polymer coating or a polymer coating system are known to have a lower friction coefficient and tend to suffer from slippage during stretching. The process according to the invention provides a solution for stretch forming substrates provided with an organic coating, a polymer coating or a polymer coating system without the occurrence of wrinkles, and without requiring a high clamping force. High clamping forces should of course also be prevented to avoid damage of the organic coating, polymer coating or polymer coating system.

This process offers a big advantage because the containers this produced are already provided with a protective coating, thereby eliminating the need for a lacquering and curing treatment. This enables the forming process to be integrated in a unit which forms the container, fills the container and seals the container, because there is no risk that the lacquering step pollutes the product to be packed in the container, nor does it involve a time-consuming curing step which potentially leads to intermediate storage of unfilled container. This integrated forming, filling and sealing process offers logistical economical advantages and/or design flexibility. According to a second aspect of the invention, an apparatus is provided for producing a container from a blank by a forming process, the apparatus comprising a mould, the mould defining a mould cavity, a blank holder for holding the blank between said blank holder and the mould in a first clamping position above the mould cavity, the apparatus further comprising a punch for deep-drawing the blank into a cup, wherein the punch is provided with a tapered surface along its circumference, said tapered surface being able to coincide with a substantially congruently shaped tapered surface on the mould in the mould cavity, so as to enable holding the cup between the said tapered surfaces in a second clamping position, wherein the angle a of the tapered surface on the punch in respect to the axis in which the punch is movable during deep- drawing is between 5 and 45°.

By using such an apparatus a wrinkle free container is obtained without the need for a high clamping force.

In an embodiment of the invention, the punch comprises a surrounding part for deep-drawing the blank into the cup, and a surrounded part for embossing a bottom part of the container, the surrounded part being moveable in the direction of the movement of the punch while the surrounding part remains stationary in the second clamping position.

By using such an apparatus a wrinkle free container is obtained which is provided with an embossed bottom part in one process step.

In an embodiment of the invention the apparatus is provided with means for providing the edge of the container with a curl.

After forming the container, the flange part of the container is provided with a curl using the curling means. The advantages of a curl have been described above. According to a third aspect of the invention an embodiment is provided wherein the process according to the invention is used in an operation involving the subsequent production of the container, filling the container and sealing the container. In an embodiment these operations are combined into one operation. In this embodiment the use of the process according to the invention is provided in a form-fill-seal operation, wherein in the forming step a container is provided which is subsequently filled in a filling step, with a product, preferably a food product, and sealed with a lid in a sealing step. This process enables an operation wherein the container is produced in a forming process, preferably in one continuous movement, preferably from a blank under carefully controlled conditions, eliminating the risk of contamination of the container, filling it, again under carefully controlled conditions with the product, such as a food product, followed by sealing to avoid deterioration of the product. The production, filling and sealing may be performed in a controlled atmosphere by locating critical parts of the form-fill-seal process in a protective environment, or even by locating the entire form-fill-seal operation in a protective environment. After filling and sealing, the containers may be heat treated to further prepare and/or preserve the contents of the container.

In an embodiment of the invention the apparatus according to the invention is applied in an operation such as a form-fill-seal operation, wherein the forming step provides a container which is subsequently filled with a product, preferably a food product, and sealed with a lid.

This allows for a compact operation having the advantages as described above.

The invention will now be further explained by the following non-limitative schematic drawings in which

Fig. 1 shows a cross-section of the apparatus prior to the deep-drawing step; Fig. 2 shows a cross-section of the apparatus at the end of the deep-drawing step; Fig. 3 shows a cross-section of the apparatus at the end of the stretching step;

Fig. 4 shows a cross-section of the apparatus at the end of the embossing step;

Fig. 5 shows an enlarged part of the cross-section of the apparatus at the location of the tapered surfaces.

In Figure 1 a blank 2 is shown clamped in a first clamping position over a mould cavity 4 between the mould 3 and a blank holder 5. The blank holder 5 presses the blank 2 against the mould by a force F. In the drawing the punch 6 is movable in an upwardly and downwardly direction as indicated by the arrow in the punch. The tapered surface 8 on the punch 6 is located at the lower part of the punch by means of a chamfered part. The tapered surface 9 on the mould 3 in the mould cavity 4 is indicated as well. It should be noted that the dimensions of the tapered surfaces in relation to the other dimensions in Fig. 1 may be exaggerated for the sake of clarity. Fig. 1 represents the situation which would occur just prior to starting the forming operation.

Fig. 2 shows the situation which occurs after forming the blank 2 from Fig. 1 into a cup 7 by a first forming step of deep-drawing due to the downward movement of the punch 6, the cup having a bottom part 7a, a side wall 7b with a bottom edge 7c and a top edge 7d, the bottom edge being connected to the circumference of the bottom part, and a flange part 7e being connected to the top edge of the side wall part, the flange part being held in the first clamping position during deep-drawing between the mould 3 and the blank holder 5. The cup 7 is pressed against the inside of the mould cavity 4 by the punch 6, and particularly the cup is pressed against the tapered surface 9 of the mould cavity by the tapered surface 8 of the punch 6 thereby clamping the cup 7 between the said tapered surfaces 8,9 in a second clamping position. The part of the cup 7 clamped between the said tapered surfaces 8,9 may result in a chamfered section on the cup 7 or the container 1 , but the main intention of the clamping action is to provide a good starting position for the stretching step. In the figure, the said tapered surfaces are substantially parallel over the full length of the cross section of the tapered surfaces, i.e. the tapered surface 8 along the perimeter of the punch 6 and the congruently shaped tapered surface 9 on the mould 3 are parallel or substantially parallel when viewed in cross section view along the axis of movement of the punch 6, this axis of movement being indicated by means of the arrow on the punch 6. Fig 2 represents the situation which would occur just prior to starting the forming step of stretch-forming the cup 7 into a container 1.

Fig. 3 shows the situation which occurs after stretch-forming the cup 7 from Fig. 2 into a container 1. The cup 7 is held in a second clamping position between the tapered surfaces 8,9 and the bottom part 7a is plastically stretched so as to conform it to the mould cavity 4. The stretch-forming may be performed by a blowing step, preferably using a gas as a blowing medium, for which purpose the medium is provided through a conduit (10) running through the punch. The conduit is schematically indicated as a straight conduit through the punch, although other designs of the conduit for providing the blowing medium may be more appropriate.

Fig. 4 shows the situation in which the punch 6 comprises a surrounding part 6a and a surrounded part, the punch 6 usually being circular in planar cross-section, although the invention also related to the situation wherein the punch 6 has a non- circular planar cross-section such as an ellipsoid cross-section. Fig. 4 shows that the surrounding part 6a is provided with the tapered surface 8 of the punch 6 for holding the cup 7 in the second clamping position and wherein the first forming step is performed substantially by the surrounding part 6a of the punch 6, and wherein the bottom of the container 1 is embossed in an embossing step by moving the surrounded part 6b out of the then stationary surrounding part 6a of the punch 6 to emboss the bottom part 1a of the container 1 by pressing the bottom part 1a of the container 1 to the bottom part of the mould cavity 4a by the surrounded part 6b, while the part of the container 1 held between the tapered surfaces 8,9 is held in the second clamping position by the stationary surrounding part 6a. Fig. 5 shows an enlarged version of the encircled section in Fig. 3. The definition of the angles a and β = 90° - a is clearly indicated. The angle a is the angle between the punch wall 6c and.the tapered surface 7, whereas β is the angle between the punch bottom 6d and the tapered surface 7. Assuming the punch bottom 6d and the punch wall 6d are perpendicularly oriented with respect to each other, separated by the chamfered section defining the tapered surface 7, β = 90° - a. Fig. 5 schematically indicates both the left and right hand side of the enlarged cross-section. The center part of the punch is not shown in the drawing.

It is of course to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the description and the following claims.

Claims

1. Process for producing a container (1) from a blank (2) by a forming process using a mould (3), the mould defining a mould cavity (4), wherein the blank (2) is held between a blank holder (5) and the mould (3) in a first clamping position above the mould cavity (4), the forming process comprising a first forming step of deep- drawing using a punch (6) for forming the blank (2) into a cup (7), the cup having a bottom part (7a), a side wall (7b) with a bottom edge (7c) and a top edge (7d), the bottom edge being connected to the circumference of the bottom part, and a flange part (7e) being connected to the top edge of the side wall part, the flange part being held in the first clamping position during deep-drawing, and a second forming step of stretch-forming the cup (7) into a container (1), the punch (6) being provided with a tapered surface (8) along its perimeter, said tapered surface (8) coinciding with a congruently shaped tapered surface (9) on the mould in the mould cavity (4), so as to clamp the cup (7) at least partly to hold the cup

(7) in a second clamping position between the said tapered surfaces (8,9)_s clamping being undertaken after ending the first forming step and before starting the second forming step, wherein the angle a of the tapered surface (8) on the punch (6) in respect to the direction of movement of the punch is between 5 and 45°.

2. Process according to claim 1 wherein the punch (6) comprises a surrounding part (6a) and a surrounded part (6b), wherein the surrounding part (6a) is provided with the tapered surface (8) of the punch (6) for holding the cup (7) in the second clamping position and wherein the first forming step is performed substantially by the surrounding part (6a) of the punch (6), and wherein the bottom (1a) of the container (1) is embossed in an embossing step by moving the surrounded part (6b) out of the surrounding part (6a) of the punch (6) to emboss the bottom part of the container (1 ) by pressing the bottom part of the container to the bottom part (4a) of the mould cavity (4).

3. Process according to any one of the preceding claims wherein the second forming step is performed immediately subsequent to the first forming step.

4. Process according to any one of the preceding claims wherein the stretch- forming step is a blowing step, preferably using a gas as a blowing medium, preferably wherein the medium is provided through a conduit (10) running through the punch (6).

5.. Process according to any one of the preceding claims wherein the forming process comprises a curling step so as to provide the edge (1b) of the container (1) with a curl (11 ).

6. Process according to any one of the preceding claims wherein the blank (2) is a metal substrate, which substrate is coated on at least one side and preferably on both sides with a polymer coating or a polymer coating system.

7. Apparatus for producing a container (1) from a blank (2) by a forming process, the apparatus comprising a mould (3), the mould defining a mould cavity (4), a blank holder (5) for holding the blank between said blank holder and the mould in a first clamping position above the mould cavity (4), the apparatus further comprising a punch (6) for deep-drawing the blank (2) into a cup (7), wherein the punch (6) is provided with a tapered surface (8) along its circumference, said tapered surface (8) being able to coincide with a substantially congruently shaped tapered surface

(9) on the mould (3) in the mould cavity (4), so as to enable holding the cup (7) between the said tapered surfaces (8,9) in a second clamping position, wherein the angle a of the tapered surface (8) on the punch (6) in respect to the axis in which the punch (6) is movable during deep-drawing is between 5 and 45°.

8. Apparatus according to claim 7 wherein the punch (6) comprises a surrounding part (6a) for deep-drawing the blank (2) into the cup (7), and a surrounded part (6b) for embossing a bottom part (1a) of the container (1), the surrounded part (6b) being moveable in the direction of the movement of the punch (6) while the surrounding part (6a) remains stationary in the second clamping position.

9. Apparatus according to claim 8 or 9 also provided with means for providing the edge (1 b) of the container (1) with a curl (11).