FR3101861A1 - Method of making a tin can - Google Patents

Abstract

The present invention relates to tin-type containers, closed at one of their ends by a bottom attached to the can through a crimping ring which is a welded ring.

Description

Method of making a tin can

The field of the invention is that of the food industry. The invention relates more particularly to containers intended for the preservation of food for a long period of time, and in particular tin cans.

Metal cans allow long-term preservation of the food they contain. They consist of a metal body, and differ in the way they are closed.

Certain cans of preserves (in particular those which are used for the preserves of cooked meals or vegetables) are closed by two rigid metal bottoms which are generally secured to the body by crimping to make an airtight container. Such a closing process makes it possible to subject the food products contained in these boxes, once the latter have been closed, to a heat treatment at high temperature, in particular at a temperature above 110° C. (sterilization), in order to guarantee preservation of several months at room temperature. These cans can present difficulties in opening, due to the importance of the thickness of the metal bottom, in order to support the variations of internal pressure.

Other cans intended for sterilization are closed by flexible bottoms which are directly attached to the metal body, as described in WO2016139341. These boxes are non-peelable, but the use of flexible bottoms makes it possible to improve the opening of the boxes, which can easily be cut, in particular when the flexible bottom has a partial incision (maintaining air impermeability in order to to maintain the quality and integrity of the product contained in the can) thus creating a weakening along a line of rupture corresponding to the place of the pre-cut, and helping to open it.

There are also boxes with peelable bottoms, the boxes being closed by a lid consisting of a peelable flexible sheet secured to a conventional metal bottom which is previously hollowed out. The assembly is then crimped around the circumference of the upper part of the metal body. The peelability is in particular and preferably measured according to the method described in FR 2955844, peeling of the lid at 90° at a speed of 300 mm/min), making it possible to measure the initial tearing, flow and tearing forces. final..

There are indeed today 3 principles of openings
- opening with a can opener : the lid has no opening system.
- the total opening with ring , called easy opening : one raises then one draws a ring integral with the lid previously incised. This system implements, on one of the two metal bottoms, a gripping ring allowing the opening of part of the metal bottom, previously weakened (by an incision, for example). It is by far the most widespread system and still in constant progress. In 2007, 86% of cans were equipped with easy openings (the rate was 77% in 2002).
- the peelable opening : by pulling on the tab, a heat-sealed aluminum lid peels off the box to offer a total opening. This system is mainly used for on-the-go products (salads, desserts, etc.), but is not suitable for boxes that must undergo sterilization, excluding external counterpressure, because the force required (the opening force (initial tearing force ) is generally of the order of 20 N, but generally less than 28 N) to take off the lid is lower than that exerted by the internal overpressure observed during sterilization. Thus, if it is desired to sterilize such boxes, the conditions to be implemented are technically more complicated and more onerous.

It is important to restrict the weights and raw material costs of cans. Thus, it is preferable to use flexible bottoms rather than rigid metal bottoms. However, the methods for sealing flexible bottoms as described in WO2016139341 require preparing the metal body before supplying the flexible bottom, and changing the processes currently used in packaging plants, which induces process changes, and some additional costs.

With regard to boxes with peelable bottoms, a drawback of this technique lies in the relatively high manufacturing cost of such boxes. Indeed, the manufacturing process requires steps of cutting (recessing) the metal bottom and securing the flexible sheet to the metal bottom. This solution also leads to significant losses of material, caused during the cutting of the metal bottom to be hollowed out. Indeed, this hollow material cannot be reused.

In addition, the implementation of such a solution proves to be complex and presents risks of leaking, in particular for boxes to be sterilized, since the flexible sheet is supposed to be both peelable (this is that is, not be attached too strongly to the hollow bottom to be able to be easily removed by applying moderate force) and nevertheless resist the strong variations in pressure which occur during the sterilization of the container.

In other words, there are currently no tins:
- which has an easy opening,
- which reduces raw material needs and costs,
- which guarantees good resistance to pressure variations during sterilization and optimal sealing of the box, and
- which allows simple and inexpensive manufacture
- which can be used by industrial canners while retaining existing processes as much as possible.

The processes for adding a flexible bottom according to WO2016139341 or for strong sterilization of peelable bottoms indeed require process adaptations, depending on the destination of the can, while the most standard and fixed conditions are preferably sought.

The present application proposes a solution making it possible to use existing crimping tools, without introducing any significant change in terms of can closing practices. It also makes it possible to work on containers whose diameters or opening dimensions are not imposed by market standards linked to the manufacturing processes of the bottoms conventionally used. The methods used in the art indeed require the use of standard box formats, linked to the press tools used in the manufacture of the bases. In fact, the current methods of manufacturing bottoms are restrictive in terms of the size of the boxes, or their shape.

The present application thus aims to present a system making it possible to place a bottom on a tin can, ensuring the seal if the can must be sterilized, and reducing the loss of material. This bottom is preferably a flexible bottom. It may or may not be peelable.

It is recalled that the flexibility of a bottom or a sheet means its ability to deform reversibly (compared to a rigid bottom, than a classic metal bottom).

The invention thus relates to a method of manufacturing a tin can, characterized in that it comprises the step of placing a bottom at one end of the body of the tin can, said bottom being fixed to the body via a retaining (or crimping) ring crimped to the end of the can body, characterized in that the retaining ring is a welded ring.

The use of a ring, which can be made of any diameter or any shape, as well as a bottom cut from a flexible sheet means that there is no longer any constraint as to shape or size large containers. The top diameter of the cans can be increased beyond the generally observed largest diameter of 153 mm). Moreover, because it is easier to make small series of boxes than small series of backs that are adapted to boxes, special commercial operations can be programmed with small series of boxes of different shapes or sizes. You can also easily prepare boxes whose bottoms will not have the same size or shape.

Retaining ring / crimp ring

The crimp ring is therefore a welded ring, i.e. it has a weld line. This weld line makes it possible to maintain the shape of this ring. In the context of the present invention, the crimping ring is preferably obtained by welding the ends of a metal strip (having the length of the box perimeter) in order to close it. It should thus be noted that, in the context of the intended use, the ring may be of circular shape or of any other shape, depending on the shape of the tin can.

Thus, the crimping ring is not obtained by hollowing out a sheet of metal.

In a preferred embodiment, a welded ring is used obtained by welding a strip of metal, as described above, then folding said strip to form a groove. This groove is thus positioned facing the end of the case body during the crimping stage. The end of the can body is then inserted into the groove and the edges of the groove are then strongly pressed/tightened against the body to ensure a perfect fit.

Alternatively, one can weld a sheet of metal to form a cylinder of suitable diameter, then cut welded rings of the desired width from this cylinder.

In a particular embodiment, the welded ring also has a flat face directed towards the inside of the ring. This flat (usually a few millimeters wide) therefore creates a flat surface all around the perimeter of the can. This flat surface can be used to fix a peelable bottom, or to stretch a flexible non-peelable bottom, fixed between the can body and the crimp welded ring fitted with the flat.

It can also be noted that, compared to the peelable bottoms of the prior art, when the flexible bottom is wedged between the ring and the body of the box, the flat is located above the flexible bottom and is therefore not in contact with the products (generally food) located inside the container. Thus, the risks of oxidation of the products observed for peelable bottoms due to the presence of this metallic flat located under the bottom for this embodiment of the prior art are avoided.

Thus, in a particular and preferred embodiment, the bottom is formed by a flexible sheet.

The invention also relates to the use of a welded ring for fixing a bottom to a container, in particular a tin can body by crimping the welded ring onto one end of the container or of the body of the can. container, said bottom becoming integral with the container after crimping.

In one embodiment of this aspect of the invention, the bottom is directly attached to the welded ring (this is the case for example when the bottom is peelable).

In another embodiment, the bottom is imprisoned / wedged between the wall of the container and the crimping ring and becomes integral when the pressure applied to the hemming of the ring crimps it to the body of the container.

Peelable background

In a first embodiment, this background is a peelable background. It is then a seal sealed on the flat part of the crimping ring. This lid is formed with materials known in the art, in particular aluminum, thermoplastic polymers. This peelable background can be formed of one or more layers, identical or different. Methods for sealing the bottom to the flat are known in the art. Mention may in particular be made of heat sealing. Preferably, a tab is attached to the bottom, allowing the lid (bottom) to come off the flat.

It is preferred when this peelable bottom is attached to the crimping ring before positioning the ring on the body of the box and closing it.

It thus appears that, in this embodiment, manufacturing processes similar or identical to those already existing in the art for peelable bottoms are used, the essential difference being the use of a welded crimping ring, rather than a ring obtained by hollowing out a sheet of metal. Thus, the method according to the invention allows a substantial saving of material, insofar as only the material necessary for the manufacture of the ring is used (strip of a metal sheet) rather than losing the material hollowed out by the methods of the prior art.

Non-peelable bottom

In a second embodiment, the bottom is not peelable. In this embodiment, the bottom is formed by a flexible sheet with a surface slightly larger than the surface determined by the end of the metal body of the tin can. In the same way that the crimp ring has the same shape as this end, this flexible sheet has the same shape as the end of the metal body, but slightly larger dimensions in each of the dimensions (a slightly larger radius if the end of the metal body is circular, a greater length and width if the end of the metal body is rectangular, etc.).

Thus, the flexible sheet is wedged between the metal body and the crimping ring and is thus retained in a sealed manner during the crimping of the ring on the metal body, which thus serves to fix the bottom on the container and close it. this.

The flat surface preferentially present on the crimping ring is used to stretch the flexible film sealing the end of the can, as well as to protect the flexible bottom when transferring or stacking the cans.

In a particular embodiment, the film used to close the box is in the form of a roll, a little wider than the width of the box. This allows the use of a traditional seamer (seamer used to close cans with rigid bottoms). Traction is exerted on the sides of the roller at the crimping speed and the film is deposited between the welded ring and the can body. The film is cut during the ring removal phase (just before crimping) using the usual cutting tools.

When one wishes to use a non-peelable bottom, it can also be fixed on the flat, according to the methods described in WO2016139341, then crimp the ring bearing the non-peelable bottom thus fixed on the body of the container.

Opening the box

In a particular embodiment, the flexible sheet has a useful pre-cut part to facilitate the opening of the box. This pre-cut part consists of a partial incision, forming a break line, of said flexible sheet (while maintaining air impermeability). Thus, this partial incision weakens the sheet along the line of rupture.

In one embodiment, a tab or a small gripping ring can be glued onto the flexible bottom, and close to the pre-cut zone, which can be pulled by the end user, in order to induce the rupture of the zone. of fragility, and thus improve the opening of the case. In this embodiment, the bottom is not peelable, but the opening system (traction of a tab causing the bottom to break and the box to open) is similar to the system known by consumers for peelable bottoms.

Alternatively, the opening can be done, for example with the help of a knife or a spoon, by exerting pressure at the location of the break line.

It is preferable that this break line presenting the pre-cut is also associated with a visual marking. The pre-cut can be done on an ink pre-mark or the ink pre-mark can be added after the pre-cut step. This allows the consumer to better visualize the pre-cut in relation to the rest of the bottom of the box.

The use of flexible bottoms in the context of the invention makes it possible to solve the problem of the workability of large-diameter cans. Indeed, it is not really possible to set up easy-opening systems for boxes and bottoms with a diameter greater than 153, without there being a risk of the user being cut when opening, due to in particular the force to be exerted to open these boxes, the memory effect of the steel forming the bottom, which tends to oppose the opening, and the fact that these openings lead to two sharp parts (edge and bottom) . In addition, in general (and in particular for large boxes), the use of can openers is avoided, especially in collective environments, where these boxes are used. Indeed, the hygienic conditions linked to the use of the can opener are not always optimal, because this tool penetrates inside the container, with a risk of coming into contact with the contents and of contamination. of this one. In addition, the use of a can opener can lead to the introduction of iron filings into the contents. Finally, the lid opened with a can opener has dangerous rough edges.

The use of flexible bottoms as described above allows easy opening, the removed cover not being dangerous as a rigid metal cover can be.

Structure of flexible funds

In a particular embodiment, said flexible sheet comprises at least one metal layer. In particular, this layer can be made of aluminum. This metallic layer is particularly useful for serving as a gastight barrier.

In another embodiment, said flexible sheet comprises at least one layer of plastic material. This is particularly advantageous in order to guarantee, for a reduced thickness, sufficient strength of the flexible sheet so as to resist the deformations which take place during the heat treatment of the can.

In a particular embodiment, said flexible sheet comprises at least one layer of plastic material of plant origin.

In a particular embodiment, said flexible sheet is formed of a single layer.

In a particular embodiment, said flexible sheet is formed of several layers. Such multi-layer sheets are known in the art and can be obtained by known methods, such as rolling.

Thus, in a particular embodiment, the flexible sheet has a metal layer and is covered on at least one side by a plastic layer.

Tin can type

In a particular embodiment, the body of the can is of the drawn or drawn-drawn type. The advantage of using stamping for the manufacture of the metal body is that it is formed from a single piece, and has no welding (unlike three-piece cans whose body is formed by welding a metal sidewall). This avoids crimping two weld zones which could potentially prove to be zones of leaks, loss of tightness and lead to potential contamination.

Tin can shape

The advantage of the proposed method is that the size and shape of the bottoms (and therefore of the boxes) is free and is no longer imposed by the usual standards for the manufacture of bottoms. Thus, it is possible to envisage boxes of any shape.

In a particular embodiment, the end of the can body is circular in shape.

In another embodiment, the end of the can body is rectangular or square in shape. It usually has rounded corners.

In another embodiment, the end of the can body is oval in shape.

In another embodiment, the can body is shaped like bowls. In this embodiment, the can bodies can be stacked before filling or after use.

Manufacturing process

In a preferred embodiment, the invention relates to a method for placing a bottom on the body of a tin can, comprising the steps of
(a) Provide a can body to the end of which a bottom is to be attached,
(b) Provide a flexible sheet
(c) Cut the sheet to obtain a cut element of the same shape as the end of the box body and of a perimeter slightly greater than the perimeter of the end of the box body
(d) Affix the cut-out element to the end of the box body,
(e) Crimping the cut-out element onto the end of the can body by crimping with a retaining ring, said retaining ring being a welded ring.

In this embodiment, flexible sheets as described above are used. They may in particular contain at least one metal layer, and preferably at least one plastic layer on one of its faces.

The above method is preferably carried out continuously.

The method may also comprise one or more of the following steps, carried out before or after the step indicated above:
- a step of filling the metal body with one or more food products;
- a step of crimping a rigid bottom on the other end of the metal body so as to hermetically close the box;

Thus, in one embodiment,
(a) a tin can body (cylinder) is provided
(b) closing one end of the body with a rigid bottom as known in the art,
(c) we fill the box with the appropriate content
(d) the other end of the box is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(e) optionally, the box is subjected to sterilization.

In another embodiment,
(a) a tin can body (cylinder) is provided
(b) one end of the body of the box is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(c) we fill the box with the appropriate content
(d) closing the second end of the body with a rigid bottom as known in the art
(e) optionally, the box is subjected to sterilization.

In another embodiment,
(a) a tin can body (cylinder) is provided
(b) one end of the body of the box is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(c) we fill the box with the appropriate content
(d) the second end of the body is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(e) optionally, the box is subjected to sterilization.

In another embodiment,
(a) providing a can body (cylinder) closed at one end by a rigid bottom as known in the art
(c) we fill the box with the appropriate content
(c) the second end of the body is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(d) optionally, the box is subjected to sterilization.

In another embodiment,
(a) a can body (cylinder) closed at one end by a flexible bottom is provided
(c) we fill the box with the appropriate content
(c) the second end of the body is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(d) optionally, the box is subjected to sterilization.

In this embodiment, the flexible bottom in (a) can be attached to the body of the box by means of a crimping ring, said ring being a welded ring, according to the methods described above, or by any other method known in the art such as that described in WO2016139341.

In order to close the ends of the body of the box with the flexible bottom, one can
(a) Provide a flexible sheet
(b) Cut the sheet to obtain a cut element of the same shape as the end of the box body and of a perimeter slightly greater than the perimeter of the end of the box body
(c) Affix the cut-out element to the end of the box body,
(d) Crimping the cut-out element onto the end of the can body by crimping with a retainer (or crimp) ring, said retainer ring being a welded ring, such that the flexible sheet is wedged between the body of the case and the retaining ring during crimping.

If the box is of the stamped type, the metal body is filled before the steps of closing the box by crimping, as described above.

Thus, in this embodiment,
(a) a stamped can body is provided,
(b) we fill the box with the appropriate content
(c) the end of the body is closed with a flexible bottom, attached to the box by means of a crimping ring, said ring being a welded ring, according to the methods described above
(d) optionally, a sterilization step is carried out.

In another embodiment, it is also possible to carry out
1) a step of crimping (or equivalent) a rigid bottom at one end of the box
2) a step of filling the metal body with one or more food products
3) the steps indicated above for closing the box by crimping a bottom with a welded ring.

In another embodiment, it is also possible to carry out
1) the step indicated above of crimping a bottom, using a welded ring, to one end of a metal body
2) a step of filling the metal body with one or more food products
3) a step of crimping a rigid bottom at the other end of the box.

In another embodiment, it is also possible to carry out
1) the step indicated above of crimping a bottom, using a welded ring, to one end of a metal body
2) a step of filling the metal body with one or more food products
3) a step of closing the box by crimping a bottom, using a welded ring, at the other end of the metal body.

The above methods may also include a step of heat treatment (sterilization) of the can hermetically sealed at both ends.

According to another particular aspect of the invention, the manufacturing method also comprises a step of pre-cutting the bottom (preferably flexible) attached to the box by means of the (welded) crimping ring in order to allow easy opening of the box.

This pre-cut preferably occurs after the heat treatment since the latter causes strong pressure stresses and it is therefore preferable that the bottom (preferably flexible) is not weakened.

The invention also relates to a method for sterilizing a can as described above, comprising a step consisting in placing said can under temperature and pressure conditions inducing an internal suppression (in said can) of at least 0.8 bar (or any other value as indicated above). Preferably, in this method of sterilization, said box undergoes overpressure for at least 2 minutes (or any other duration indicated above, a preferred duration being greater than or equal to 6 minutes, or 7 minutes).

The invention thus relates to a method of manufacturing a can as described above comprising:
- a step of crimping a first flexible bottom on the lower part of the metal body by means of a welded ring;
- a step of filling the metal body with one or more food products;
- a step of crimping a second flexible bottom on the upper part of the metal body, by means of a crimping ring (preferably welded) so as to hermetically close the box;
- possibly a step of heat treatment (sterilization) of the can.

According to another particular aspect of the invention, the manufacturing method comprises a step of precutting at least one of the two flexible bottoms in order to allow easy opening of the box.

This pre-cut preferably occurs after the heat treatment since the latter causes strong pressure stresses and it is therefore preferable that the flexible bottom is not weakened.

Such a manufacturing process can be implemented efficiently, industrially.

These methods are implemented to obtain cans as described below. They can also be used to close trays of metal ready meals.

Containers / Tins

In another aspect, the invention relates to a container having at least one bottom formed by a flexible sheet, said flexible sheet being fixed to one end of the container by crimping onto the body of the container by means of a welded ring . The invention thus relates to a container having a metal body and at least one end of the metal body closed by a bottom comprising a flexible sheet, the flexible sheet being held on the metal body by means of a ring crimped on the metal body, characterized in that said ring is a welded ring.

As seen above, the flexible bottom can be attached to the crimping ring (for example on a flat part of this ring), in particular when the bottom is peelable. In another embodiment, the flexible bottom is wedged between the metal body and the crimping ring, a sealed closure of the container being obtained during the crimping of the ring on the metal body of the container.

In a particular embodiment, the flexible bottom has a pre-cut part.

In one embodiment, the container may comprise two flexible bottoms, at least one of which is fixed via a welded crimp ring. Preferably, in this embodiment, the two flexible bottoms are fixed by means of a crimping ring, at least one of which is welded. More preferably, the two crimp rings are welded rings.

In one embodiment, the container has an internal vacuum relative to atmospheric pressure.

In one embodiment, the container is of the tin can type. It is illustrated that tin cans (in Europe) are generally of the types as described in Table 1.

Dimensions in mm (dia x h) Capacity in mL Appellation Destination example 55x37 71 1/12 Tomato puree 55x73 142 1/6 Tomato puree 65x70 212 1/4 US Sauces, sweet corn, mushrooms, fruits, etc. 65x100 325 Soup 73x54 212 1/4 Vegetables, sauces, mushrooms, etc. 73x109 425 1/2 high Vegetables, ready meals, mushrooms, animal feed, fruits, etc. 83x85 425 1/2 medium Vegetables, corn, etc. 99x60 425 1/2 bass Ready meals, animal feed 99x118 850 4/4 Vegetables, ready meals, soups, fruits, mushrooms, animal feed, etc. 105x205 1,250 3/2 Animal feed, etc. 153x180 2,250 3/1 Vegetables, ready meals for communities, etc. 153x240 4,250 5/1 Vegetables, ready meals for communities, etc.

Table 1: standard data for round cans

For boxes intended for canned fish, other formats are used, the basis of which is the “4/4 fish” with a capacity of 750 ml. There are also rectangular box formats.

It may however be noted that, due to the use of flexible bottoms, and in particular due to the laying of the bottoms by a continuous process using rolls (reels), as described above, the size and shape of the boxes is no longer a constraint as it could be in the prior art. The boxes described above are therefore illustrations of boxes on which the process can be applied.

In a particular embodiment, the can is of the drawn or drawn-drawn type.

As seen above, it is possible to use flexible films made of various materials, possibly containing several layers of different materials. It is thus possible to use a metallic layer and a layer of plastic polymer.

The plastic polymer layer can be printed, which avoids the use of labels on the body of the boxes. It is also possible to use transparent films allowing the ingredients contained in the containers to be seen.

The invention is particularly interesting in the case of fish canning (such as cans of sardines). In this case, the boxes are rectangular in shape, with the bodies and easy-opening bottoms being made of aluminium. Aluminum is generally more expensive than steel for the same can, but steel easy-open lids cannot be used on these fish cans, due to their rectangular shape. Indeed, the force required to open the box (break the rigid lid by pulling on the ring) is too great and the shape memory properties of steel (tendency to go back when pulled) complicate the opening capacity of a steel bottom for these boxes. Aluminum is therefore used for these types of boxes because this material is more flexible than steel and therefore has better workability. An aluminum box body must then also be used because the use of a steel body leads to the risk of galvanic corrosion.

The use of flexible lids as described makes it possible to replace aluminum with steel for these fish cans, which greatly reduces costs.

Indeed, we can then form the pressed steel body and the welded steel crimp ring, and use a flexible film which can be easily opened, and which can contain polymer or plastic layers which eliminate the problems of galvanic corrosion.

The use of a crimping ring makes it possible to obtain a good seal, by a process that is simpler to implement than that described in WO2016139341. Indeed, crimping is well known, used and mastered in the art (method used to fix rigid bottoms) and is known as guaranteeing a good seal. In fact, crimping involves a tightening operation, which once carried out on metal ensures a link, impermeable to gases and micro-organisms, between the bottom and the body of the box.

Furthermore, the mechanical resistance will also be improved compared to WO2016139341, which may require the placement of hems protecting the sealing zone of the flexible film on the mechanical body. By using crimping, the boxes have the same type of mechanical resistance, as a whole, as the boxes with rigid bottoms of the prior art. This provides good protection during logistics operations (transfers and handling of boxes).

represents a welded ring (1) before shaping. The weld line (11) obtained when closing the ring is also indicated.

shows the view of a section of a welded retaining ring (1) usable to be crimped on a body of a container. We see the groove (12) intended to be introduced on the end of the body of the container, as well as the flat (13) which is directed towards the inside of the welded ring.

shows a top view of a welded ring of circular shape according to the invention. We observe the weld line (11) as well as the flat (13).

shows a diagram of the method of closing a box (3) according to the invention by means of a flexible bottom (2) which will be fixed by crimping between the body (3) of the box and the ring (1 ) retained. We observe the weld line (11).

shows a top view of a closed tin can, with the presence of an opening tab (22) and a weakness line (21) to allow the flexible bottom to break.

EXAMPLES

The examples below and figures describe an embodiment for cans of cylindrical shape. In these embodiments, the rings are circular. In the case of cans whose end is not circular (rectangular, oval or other), the shape of the ring is identical to that of this end.

Example 1. Manufacture of a crimping ring for a 4/4 box

A welded ring is made for crimping on a 4/4 box. This box has a diameter of 99 mm.

A strip of approximately 9 to 11 mm in width and 99-101 mm in length is cut from a sheet of steel, with a thickness of 0.20 to 0.24, in particular between 0.21 and 0.23 mm.

This steel strip is folded over and its ends are welded. It is possible to use an industrial welder such as that marketed by Soudronic (Bergdietikon, Switzerland). A welded ring is thus obtained, similar to that described in figure 1, with a useful diameter of 99 mm for the hemmed area.

The ring is then shaped to give it the shape shown in Figures 2 and 3. Thus, the inverted U-ring is bent to form a groove (12), and a flat area (13) is also formed. Apparatus known in the art, such as a "curler" moulder, can be used. A steel with suitable malleability is used (grade of steel adapted to the radius of the case) in order to allow the formation of the folds (of the groove) necessary for crimping.

The welded ring (1) is thus successively composed (from the outside inwards) of a hemmed (121) (crimping zone), of a bowl (122) (return of the hemmed) then of a flat (13). The hemmed (121) and the return hemmed (122) have a development of approximately 6 to 7 mm and form the furrow (12). The flat meanwhile has a useful width of about 3 to 4 mm. A strip of steel approximately 9 to 11 mm in useful width will therefore make it possible to form a welded ring for a box with a diameter of 99 mm.

Example 2. Crimping a non-peelable flexible bottom on a 4/4 box

The step of crimping a flexible bottom (2) on a box body (3) is shown in figure 4. A flexible bottom (2) is provided which may have been cut from a reel of film and which has the same shape as the box body (3) and the crimping ring (1), but dimensions (here a diameter) a little larger. The ring (1) is lowered on the end of the body (3) so as to imprison the bottom (2) between the ring (1) and the body (3) then the crimping is carried out by pressure on the two hemmed (121) and (122) forming a groove (12). The presence of the flat (13) helps to stretch the flexible bottom (2) during the assembly stage.

These steps can be carried out continuously using the same machines used to crimp conventional rigid ends.

Example 3. Crimping a peelable flexible bottom on a 4/4 box

A ring (1) is used as obtained according to example 1. A peelable bottom is fixed to this ring according to the methods known in the art for fixing peelable bottoms to rings obtained by hollowing out material. The ring carrying the peelable bottom is then assembled on the body of a box by crimping according to the methods known in the art.

After crimping, the container can be sterilized, then make a partial incision (described as (21) in Figure 5) on the flexible bottom (maintaining air impermeability which allows the quality and integrity to be maintained of the product contained in the can) in order to create a breaking line and facilitate opening, for example by means of a tab or a gripping ring (22) on which the user can pull to induce rupture and open the container.

Claims (17)

Method of manufacturing a tin can, characterized in that it comprises the step of placing a bottom at one end of the body of the tin can, said bottom being fixed to the body by means of a retaining ring crimped to the end of the can body, characterized in that the retaining ring is a welded ring. Method according to claim 1, characterized in that said welded ring has been obtained by welding a strip of metal then folding said strip to form a groove. Method according to Claim 2, characterized in that the welded ring also has a flat face directed towards the inside of the ring. Method according to one of Claims 1 to 3, characterized in that the bottom is formed by a flexible sheet. Method according to claim 4, characterized in that the flexible sheet has a pre-cut part consisting of a partial incision of the said flexible sheet, maintaining air impermeability. Method according to claim 4 or 5, characterized in that said flexible sheet comprises at least one metal layer. Method according to Claim 6, characterized in that the metal layer is covered on at least one side by a plastic layer. Method according to one of Claims 1 to 7, characterized in that the end of the body of the can is of circular shape. Method according to one of Claims 1 to 7, characterized in that the end of the body of the can is of rectangular or square shape. Method according to one of Claims 1 to 7, characterized in that the end of the body of the tin can is oval in shape. Method of placing a bottom on the body of a tin can, including the steps of

1. Provide a tin can body at the end of which a bottom is to be attached,
2. Provide a soft sheet
3. Cut the sheet to obtain a cut element with the same shape as the end of the box body and a perimeter slightly greater than the perimeter of the end of the box body
4. Affix the cut-out element to the end of the box body,
5. Crimp the cut-out element onto the end of the can body by crimping with a retaining ring, said retaining ring being a welded ring.

Method according to Claim 11, characterized in that the sheet containing a metallic element is a flexible sheet comprising at least one metallic layer, and preferably at least one plastic layer on one of its faces. Method according to claim 11 or 12, characterized in that it is carried out continuously. Container having a metallic body and at least one end of the metallic body closed by a bottom comprising a flexible sheet, the flexible sheet being held on the metallic body by means of a ring crimped on the metallic body, characterized in that the said ring is a welded ring. Container according to Claim 14, characterized in that the flexible sheet is attached to the crimped ring, in particular on a flat part present on the crimped ring. Container according to Claim 14, characterized in that the flexible sheet is wedged between the metal body and the seam ring. Use of a welded ring for fixing a bottom on a container by crimping the welded ring on one end of the container.