WO2008145927A1

WO2008145927A1 - Culinary article with improved contact surface and manufacturing method

Info

Publication number: WO2008145927A1
Application number: PCT/FR2008/050737
Authority: WO
Inventors: Jocelyn Bonnel; Christophe Jeandenand
Original assignee: Seb Sa
Priority date: 2007-04-27
Filing date: 2008-04-23
Publication date: 2008-12-04
Also published as: AU2008257251A1; FR2915359B1; KR20100017416A; RU2009143922A; FR2915359A1; JP2010524617A; EP2142053A1; CN101668459A; RU2458616C2

Abstract

This is a culinary article comprising a metal dish (1b) defining locally a base where the dish is lined with an added insert (1a) made of a harder metal than the metal of the dish and typically fixed to the dish by perforations or teeth defining male/female engagements (231, 310). Around the perforated or toothed area (231) of the insert (1a) is a peripheral contact surface area (25) lower down, continuously solid, in the shape of a crown, in said harder metal. The insert is inserted from a shape in the form of a flat plate or cap.

Description

CULINARY ARTICLE WITH IMPROVED RANGE AND METHOD OF

MANUFACTURING

The present invention relates to a culinary article whose bottom has, on the lower outer face, at least one insert metal insert at least partially covering the bottom. The article, including its bottom, is typically made of a soft metal such as aluminum.

The manner of manufacturing the article and / or its bottom with an insert metal insert is also concerned.

In the present application, the term "metal" covers metal and metal alloy.

From EP-A-0960667, there is known a culinary article comprising: a metal cap defining locally a bottom bottom portion for the article, wherein said cap has, in a section perpendicular to this bottom, a crenellated zone,

and at least one bottom insert doubling below said metal cap, at least locally at the location of its bottom portion, this insert, which has an apparent lower face, being made of metal harder than that of the cap. metal and having, in section, at least one perforated or crenellated zone fixed by embedding with the crenellated zone of said metal cap.

"Crenellations" are folds or stampings of the plate defining a plurality of studs creating, under the bottom, discontinuities support when placed on a support.

These "crenels" or pads, like the possible orifices made in the insert, are typically organized in concentric circles.

If the insert is perforated, the holes are filled by the soft metal of the metal cap. Different disadvantages are noted: - The attachment insert / bottom "soft" is similar to a stapling or crimping (in the manner of a stone that enchased), essentially,

this fixation is imperfect; on the lower face, the "soft" bottom that receives the insert is pre-stamped,

- the orifices may be imperfectly filled,

- If softer filling material exceeds the lower level of the insert insert, contact with eg a glass ceramic plate may scratch the latter, especially if the softer material is aluminum.

An object of the invention is to overcome all or part of these disadvantages. Another goal is to prevent imperfections, related to the manufacturing process or use, or foreign elements appearing at the soft metal interfaces / reported insert, further induce risks of scratches on fragile surfaces and / or range defects.

Indeed, defects of scope may, when the article is laid, cause stability defects and / or the deposition of the soft metal on the support.

On the other hand, in the case where the hard metal insert has the function of allowing the article to be heated by induction, via a suitable generator, the greater the number of orifices through the insert, the greater the effectiveness of the invention. Induction heating may be impaired.

In order to at least limit all or part of these drawbacks and to improve the situation, the invention proposes, according to one characteristic, that around said perforated or crenellated zone of the bottom insert is a lower zone defining a peripheral bearing. , continuously solid, crown-shaped, in said harder metal. Thus, it is favorably anticipated that this range zone covers the bottom portion of the cap, around said recesses, and has a lower face, all or part of which is at least slightly lower than the lower limit of said perforated or crenellated zone and / or the crenellated zone of said metal cap. In this way, the support of the culinary article on a stand will focus there.

It is furthermore advised that said "zone of peripheral reach" has a width (hereinafter L) greater than the shortest distance (d ^) separating two successive crenellations, along a line joining the center of the bottom and a peripheral edge of this one.

Two manufacturing processes are also proposed hereinafter. They can be used to obtain the aforementioned article, at least in the case where the insert insert comprises perforations. In addition or alternatively, these methods already make it possible to manufacture a bottom, in particular for a culinary article.

Once obtained such a strengthened, stable and low aggressive bottom, the rest of the article can be realized. It is proposed for this to continue the deformation under pressure of the original block of soft metal to develop a side wall for the article.

Other advantages and features of the present invention will now be presented in the embodiments given below by way of non-limiting examples.

By the practice of this invention, it is considered that it is also possible to improve the thermal and mechanical properties of the bottom of the article, including during induction heating or high temperature cooking of the coating (s) to add, such as anti-adherent typically provided on the inner face including the bottom (delamination problems, blistering), or during repeated thermal shocks. On the drawings that support the examples: FIG. 1 shows a diagram of a culinary article, in a section perpendicular to the bottom, according to a first embodiment according to the invention,

- Figures 2 and 3 show more widely, according to the same view, respectively a second and third embodiments of the article according to the invention; the parts, zones, means ... are marked with the same references as fig.l, but provided respectively with a premium (') and a D, - Figure 4 shows a bottom variant at least partly castellated , following the same cut,

FIGS. 5a, 5b, 5c and 6a, 6b, 6c show stages of implementation of two manufacturing methods that can be used in the context of the invention; FIG. 7 shows a view from below of FIG. 2;

- And Figure 8 shows the bottom actually bent of the article of fig.l.

In the present description, the term "culinary article" any kitchen article comprising, typically, at least one handle and a cap (hollow) receiving the product or the preparation to be heated or cooked. The bottom of the cap is a sensitive part, since the most subject to the heat of a suitable source. The stoves, pans .... are concerned.

In Figures 1 to 3, the culinary article

1.1 ', 1' 'comprises a hard metal portion, la, la', la "and a softer metal portion Ib, Ib ', Ib". These two parts are assembled under the article to constitute a powerful reinforced bottom.

Part la, la ', la "may be stainless steel, part Ib, Ib', Ib" aluminum.

Part Ib, Ib ', Ib "is preferably monobloc, as illustrated, and has a bottom cross wall 21, 21', 21 '' from which rises a side wall 3, 3 ', 3". It has a hollow crown shape. At least a portion of the bottom wall is lined from below by the hard metal portion, la, la ', la "which is a perforated bottom insert.

Fig.l, the insert la has a central zone 23 surrounded by a bearing area 25 through which the culinary article 1 can bear on a support. The bearing area 25 is continuously solid (i.e., without orifice) and crown-shaped.

The central zone 23 is traversed right through by holes 230 filled tightly by the soft metal of the bottom wall 21, for assembly. These orifices are evenly distributed or not, in one or more zones, typically following several rays that can be concentric and start near the center of the plate la (see on this point figs.2 and 3).

Thus, the insert 1a, which has a lower surface 11a apparent, has Figure 1, in section, at least one perforated area 231 fixed by embedding with a crenellated zone 210 of the metal cap Ib. Around all or part of the area 210 is a continuously solid area 211 covered, or doubled, from below by the peripheral area of reach 25.

So that the support of the article 1 on its support is concentrated towards the bearing area 25, it has a lower face of which all or part is at least slightly below (d) with respect to the limit (1) the lowest of the zones 231 and 210. Thus, it is to be understood that the illustrations of the article bases figs.1,2,3 are on a large scale and are in fact not with a lower face (such as lia fig.l) planar, but curved or recessed to ensure a position below the bearing area 25, as shown in Fig.8 where the curvature is exaggerated.

If for example the orifices 230 were not completely filled by the soft metal of the bottom wall 21, the guard height (d) would appreciate compared to the only lower limit of the perforated area 231.

Fig.8, 25a has been identified the line joining the center of the bottom and the peripheral edge 27 thereof. Following this straight line (that is to say in a section perpendicular to the bottom and containing the straight line), the peripheral bearing zone 25 has a width (L) greater than the shortest distance (d1) separating two successive teeth 210a, 210b of the zone 210. Preferably, this width (L) will be greater than or equal to that (L ') between the inner and outer limits 12 and 11 respectively of a group of two respectively outer (21Oc') and inner (21Oa) ') of the metal cap separated by at least one third slot (21Ob'); is typically of the order of 7mm, see fig.2.

Thus the compromise support / fixation / induction yield will be efficient.

To ensure the guard height (d), and thus place below it (s) at least a portion of said bottom face 11a of the bottom, here of the peripheral area 25, the perforated area 231, and here the entire bottom plate from the center to its bearing area 25 extends along a curved lower surface 100a, concave downwards (and confused here with

To fix the parts la, la ', la "and Ib, Ib', Ib" between them, the bottom insert is favorably also embedded in the metal cap, in an area 29, 29 ', 29' '. situated away from the bearing area 25 and said more central recesses, such as 210,231 fig.l and 210 ", 231" fig.3.

This complementary embedding zone such as 29 is favorably located beyond the periphery the bearing area such as 25 and the surface such as 211 of the cap that it covers.

1, the zone 29 receives the attachment to the cap Ib of a fixing portion 31 which extends the periphery of the bearing area 25, in one piece with

1 'insert, and which defines a recessed rim with respect to this zone 25.

This flange 31 externally surrounds the zone 25, to which it is connected by a fold 33 of stiffening, and has orifices 310 filled tightly by the metal of the cap Ib, thus achieving the aforementioned complementary recesses of the zone 29.

The fold 33 is inclined at an angle, towards the outside. Figures 2 and 3, there is therefore also a fastening portion 31 ', 31 "in one piece with the peripheral bearing area 25', 25" and the bottom insert insert la ', the ", which may have the same previous characteristics as that -idem for the cap Ib ', Ib "bottom 21', 21" vis-à-vis Ib and 21-, except that the fixing portion 31 ', 31 "defines, for the piece la ', the "a peripheral edge raised 35', 35" where there is a retention recess of this piece in (under) the bottom of the metal cap Ib ', Ib ", in an area thus set back of said bearing area 25 ', 25 ". 2, the retaining recess 29 'comprises orifices 310' passing through the fixing portion 31 'and filled closely by the metal of the cap. The orifices 310 'are located in the curvature, here the radius.

Figs. 1 and 2, the raised peripheral portion 35,35 'is embedded only on the edge of the cap and is fully visible. Fig.l, this portion has at its base a curvature which connects the edge 35 'and the zone 25' and is traversed by the orifices 310 '. Fig.l, said raised portion 35 defines the perforated outer peripheral rim 31. Fig.3, the curved peripheral edge, folded 35 "ends in the cap Ib" where it is thus embedded, recessed.

Among the characteristics that are useful for the implementation of the invention, but not essential, it should be noted that the zone 25, 25 ', 25 "can be at least globally flat,

this zone of full span is a continuous crown; the crown could be in several portions, a continuously solid zone can surround the crenellated zone 210, 210 ', 210 "of the cap Ib, Ib', Ib",

- The fixing portion 31, 31 ', 31 "is in one piece with the insert, the same for the bearing area, otherwise the fixing portion can be used to set the bearing area, the central portion of the insert being recessed elsewhere, as for example in the previous embodiments, however, this complicates the manufacture,

- insert reported la, la ', la "may not include perforated area 231, 231', 231" -or only one or more such (s) area (s) - but, in replacement -or in addition- at least one crenellated embedding zone, as in FIG. 4,

the perforated or crenellated zone of the bottom plate and / or the crenellated zone of the metal cap under which this plate is applied extends (ent) along a lower curved concave bottom surface; concerning this characteristic, one could provide a shoulder, such as a fold down. 4, 241d shows a crenellated recess zone of the insert 10a cooperating with the crenellated zone 21Od of the cap 10b under which this insert is plated, with its bearing area 25d below. This is less efficient in terms of fixation, but beneficial for induction. Two manufacturing processes are more particularly proposed to obtain the illustrated cookware, or at least one background for such items. Indeed, it is explained below that the bottom can be obtained alone, on the one hand, the rest of the article can be achieved elsewhere, especially after the bottom.

Hereinafter the insert la, la 'or la "is monobloc and perforated rather than crenellated, the modifications for a crenellated solution (see for example fig.4) being within the reach of the skilled person, the filling of the orifices It is then possible to replace both crenellated and crenellated joists, and this is done according to the first method illustrated in FIGS. 5a and 5b.

Firstly, on the one hand, a raw, unpreformed block 37 is made of light metal, or light alloy, and on the other hand, of the desired insert. This insert is already perforated (and / or crenellated) where it should be as described before.

Let us consider that this is the one of Fig. 3. Typically (see Fig. 5a), we have the origin of a hollow insert (called capsule) made of metal or metal alloy harder than that of the block. 37 and having in the central part the through holes 230 ". These orifices are arranged in successive rays with, around, the solid zone 25 "with its width (L) greater than the shortest distance (dl) separating two successive mean radii of orifices from this central part. so bordered on its perimeter by the peripheral edge raised 35 ".

This hollow plate and the block are then pressed against each other under pressure (see FIG. 5b) until: - (re) pushing under pressure (via a press) the metal or the softer alloy of the block by compelling it to fill the hollow 41 and said holes 230 "of the plate whose raised peripheral edge is embedded in the material of the block by embedding its end, as we also see fig.3, and,

placing at least a portion of the lower face of said solid zone 25 "at least slightly below (d) with respect to the lowest limit of the orifices of the central part, so as to achieve the peripheral bearing area, full, sought after support of the assembly obtained.

Typically if, as shown in FIG. 5a, the peripheral edge 35 "is initially vertical, it may be deformed inwards and / or outwards during the pressure application of the capsule and the block, and will position itself skew with respect to the central part of the insert (fig.5b) .This may strengthen the attachment.

According to the second method illustrated in FIGS. 6a and 6b, the following steps will be carried out, in particular to obtain the solutions of FIGS. 1 and 2.

Suppose that we seek to realize the solution of fig.l: We start on the one hand again of a block 37 crude, not preformed, of light metal or light alloy, and on the other hand of desired insert.

The insert is already perforated (or crenellated) where it needs to be, as described before. At this moment, it is still in the state of plane plate, or already slightly curved as fig.βa, with then the aforementioned concavity, to ensure the position below (d) sought (a shape shouldered at the periphery for the same purpose a priori could also be considered, as already indicated). The orifices 230 in the central portion may be arranged in successive rays with, therefore, around the solid zone 25 and its width (L) greater than (dl). This zone 25 is here itself, on its perimeter, surrounded by the orifices 310 which can be distributed regularly, all following the same radius. But the zone 25 could be surrounded only irregularly by the orifices 310.

We will then, as before, apply under pressure (still via a press) this plate and the block 37 against each other (see fig.βb) to:

- (re) pushing under pressure the softer metal (alloy) of the block, by forcing it to embed in said surface plate la and to fill (all) its orifices, by creep,

- Fold the plate to the block, at the periphery of said solid zone, creating here the fold 33 in the insert, between the periphery of the zone 25 and the outer edge 250, this fold being positioned at an angle to the central portion 23 and creating the rim 31 which surrounds it externally and therefore, like all the insert, recessed at the edge of the block 37 (see also fig.l),

- And also place at least a portion of the aforementioned lower face of said solid zone 25 at least slightly below the lowest limit of the orifices 230 of the central portion, so as to realize, as already indicated, the below range range searched.

Favorably, we will have created the fold 33 between said zone 25 and the peripheral orifices 310, so that the latter are at the edge of the rim.

Conforming according to the alternative of the figure

2, the outer peripheral edge raised 35 'will be folded just once to be recessed at the edge of the block, the peripheral holes 310' located in the rounded connection having favored a high-performance fixation, without hindering the support.

Figures 5a, 5b and 6a, 6b also illustrate that the pressure applied between each insert and the block 37 has of course caused a deformation of this block which finally takes the form of the bottom, here 21 or 21 ''. As shown, it is furthermore anticipated that beyond this stage, the deformation under pressure of the block will be favorably continued until developing the side wall (3 fig.5c or 3 '' fig.βc), then one-piece with the background.

As regards the aforementioned application under pressure between the retained insert and the block 37, this will preferably take place within the framework of a "striking"

(coining) cold, with a press of up to 2000 tons. Embossing is provided between a die and a punch, including the skirt constituting the lightweight metal sidewall. Alternatively, fluo-turning can be used to make the side wall. Regarding the height of the insert embossing of the insert, it will be favorably at least equal to the thickness of this insert.

Regarding the realization of the bearing area so that its underside is below the rest of the bottom, it may intervene from the manufacture of the 1 'insert (or plate), for example with a form immediately bent, or later, when pressurizing between the insert and the soft metal block, or when developing the side wall of the article, or in the context of a subsequent recovery, via a pressure exerted on this background. Different techniques are known.

Regarding also the type of embedment made if the insert is perforated, it may in particular use lip perforations, as taught in EP-A-688525.

It will also be recalled that an insert solution incorporating both perforated zones and crenellated zones is covered by the invention.

Figure 7, the bottom view, which refers to the half sectional view of Figure 2 (section II-II), shows a concentric organization of perforations or holes central 210 ', with the non-perforated peripheral bearing surface 25' of width L and the outermost additional attachment holes 310 '. The 'hardest' inserted insert is peripherally interrupted at 35 'and the softer bottom Ib appears at the location of the peripheral crown, between 35' and 27, and at the location of the filled perforations (210 ', 310'). ').

Claims

claims

1. Culinary article (1, 1 ', 1' ') comprising: - a metal cap (Ib, Ib', Ib '', 10b) locally defining a bottom bottom portion for the article where said cap has, in accordance with a cut perpendicular to this bottom, a crenellated zone (210, 210 '', 21Od) - and at least one insert (la, la 'Ia' ', 10a) reported bottom doubling below said metal cap, at least locally to the place of its bottom part, this insert, which has an apparent lower face, being of metal harder than that of the metal cap and having, according to said section, at least one zone (231, 231 '', 24Id) embedded battlement (230, 230 '', 210a, 210a ') with the crenellated zone (210, 210' ', 21Od) of said metal cap and around which there is a zone (25, 25', 25 '') , 25d) with a downwardly peripheral, continuously solid, crown-shaped surface in said harder metal, characterized in that the peripheral bearing area that (25, 25 ', 25' ', 25d) has a width (L) greater than the shortest distance (dl) separating two successive crenellations (210, 210' ', 21Od), along a straight line (25a) joining the center of the bottom and a peripheral edge (27) thereof.

2. Culinary article (1, l ', l' ') comprising:

a metal cap (Ib, Ib ', Ib' ', 10b) defining locally a bottom bottom portion for the article in which said cap has, in a section perpendicular to this bottom, a crenellated zone (210, 210' ', 210d)

- And at least one insert (la, la 'Ia'', 10a) reported bottom doubling below said metal cap, at least locally at the location of its bottom portion, this insert, which has an apparent lower face, being of metal harder than that of the metal cap and having, according to said section, at least one zone (231, 231 '', 24Id) perforated fixed by recesses (230, 230 '') , 210a, 210a ') with the crenellated zone (210, 210'', 21Od) of said metal cap and around which there is a region (25, 25', 25 '', 25d) of continuously solid peripheral surface, crown shape, in said harder metal, characterized in that this area of peripheral bearing (25, 25 ', 25'', 25d) is below and has a width (L) greater than the shortest distance (dl) separating two successive crenellations (210, 210 '', 21Od) along a line (25a) joining the center of the bottom and a peripheral edge (27) thereof.

3. The article of food according to claim 1 or 2, characterized in that the peripheral area (25, 25 ', 25' ', 25d) is in one piece with the insert (la, la', Ia '' , 10a) reported from the bottom.

4. Cooking article according to one of the preceding claims, characterized in that 1 'insert (la, la' Ia '', 10a) of hard metal is suitable for heating the article by induction.

5. The article of cooking according to claim 3 or claim 3 and claim 4, characterized in that, in a remote area set back from the peripheral bearing area (25, 25 ', 25' '), 25d) and said recesses (230, 230 '', 210a, 210a '), the bottom insert insert is also locally recessed (29, 29', 29 '') in the metal cap (Ib).

6. Cooking item according to claim 3 or claim 3 and claim 4, characterized in that in an area beyond and away from each other, said recesses (230, 230 '', 210a, 210a ') from the periphery of said peripheral bearing area (25, 25', 25 '', 25d) and the surface of the cap that the latter covers, the bottom insert insert is, in a complementary manner, locally recessed (29, 29 ', 29'') in the metal cap.

Culinary article according to claim 3 or claim 3 and one of claims 4 to 6, characterized in that the peripheral bearing area (25,

25 ', 25d) is extended, for attachment to said metal cap, peripherally, by a fixing portion

(31, 31 ') in one piece with the bottom insert (la, la, 10a) and defining a raised portion recessed from said circumferential bearing area (25, 25', 25d) and having orifices (310, 310 ') filled closely by the metal of the metal cap (Ib, Ib', 10b).

8. Article of cooking according to claim 7, characterized in that said raised peripheral portion (31 ') is embedded only on the edge of the cap (Ib') and has at its base a curvature through which orifices (310 ') filled tightly. by the metal of the metal cap.

9. Cooking item according to claim 7, characterized in that said raised peripheral portion defines an outer peripheral rim (31) where orifices (310) are filled tightly by the metal of the metal cap (Ib).

Cooking item according to Claim 3 or Claim 3 and one of Claims 4 to 6, characterized in that the area of peripheral reach (25 '') extends, for attachment to said metal cap (Ib ''), peripherally, by a fastening portion (31 '') in one piece with the insert (Ia '') reported from the bottom and which defines a folded edge (35 '') whose end is embedded in the material of the block and which is positioned obliquely with respect to the central part of the insert (see Figures 5b and 5c).

11. Cooking article according to one of the preceding claims, characterized in that the peripheral bearing area (25, 25 ', 25' ', 25d) has, in a said section perpendicular to the bottom and containing a line (25a) joining the center of this bottom and a peripheral edge (27) thereof, a width (L) greater than or equal to that (L ') between the inner and outer limits respectively of a group of two crenels (210) respectively outer (21Oc ') and inside (21Oa') of the metal cap separated by at least a third slot (21Ob ').

12. A manufacturing method that can be used to obtain the cooking utensil according to claim 2 or claim 2 and one of claims 3 to 11, including the insert (la, la ', Ia'', 10a). metal will comprise at least one said perforated zone (231, 231 '', 24Id), or at least one bottom of a culinary article, this method comprising the following steps: - providing a raw block (37), non-perforated, of light metal or of a light metal alloy, - to provide a hollow insert (Ia '') made of metal or metal alloy harder than that of the block, the insert having in the central part orifices (230 '') passing therethrough in successive radii with, around, a solid area (25 '') having, along a straight line (25a) joining the center of the insert (1a) and its periphery (27), a width (L) greater than the most short distance separating two successive radii of orifices (230 '') from this central part, this solid zone (25 '') being bordered by a raised peripheral edge (35 "), - applying under pressure the hollow plate and the block against each other until:

* pressurizing the metal or the softer alloy of the block (37) by forcing it to fill the recess and said orifices (230 '') of the insert whose raised peripheral edge (35 '') is embedded in the material of the block, by drowning its end, and,

* placing at least one part (Ib, Ib ', Ib' ') of the underside of said solid zone (25' ') at least slightly below the lowest limit of the orifices (230' ') of the central part, so as to achieve a peripheral scope area, full (25 ''), which focuses the support on a support of the assembly obtained.

13. The method of claim 12, characterized in that during the application under pressure, the raised peripheral edge (35 '') is deformed and is positioned obliquely relative to the central portion (231 '') of this insert (the) .

14. A manufacturing method that can be used to obtain the culinary article (1,1 ') according to claim 2 or claim 2 and one of claims 3 to 11, including the metal insert (la, la' ) will comprise at least one said perforated area (23, 231), or at least one culinary article bottom, said method comprising the steps of: providing a raw, non-preformed block (37) of light metal or light metal alloy - provide an insert (la, la ') in the form of a plate, metal or metal alloy harder than that of the block, the insert having central openings

(230) passing therethrough in successive radii with, around, a solid zone (25, 25 ') having, along a line joining the center of the plate and its periphery, a width greater than the shortest distance separating two successive radii orifices (230) of this central part, this solid zone itself being at least locally surrounded by peripheral orifices (310, 31), - applying under pressure the insert and the block (37) against each other. other until:

* fold the plate towards the block (37), at the periphery of the said solid zone (25, 25 '),

* pressurize the metal or the softer alloy of the block, forcing it to insert the insert

(la, la '), in edge, by filling said orifices of this insert,

* placing at least part of the lower face (11a) of said solid zone (25, 25 ') at least slightly below the lowest limit of the orifices (230) of the central part (23, 231) , so as to achieve a zone of peripheral scope (25, 25 '), full, which focuses the support on a support of the assembly obtained.

15. The method of claim 14, characterized in that the fold (33) produced is between the full bearing area (25) and said peripheral orifices (310), so as to create a raised peripheral peripheral edge (31), recessed at the edge of the formed block.

16. The method of claim 14, characterized in that the fold (33) is made so that said peripheral orifices (310, 31) are located in its curvature.

17. Method according to one of claims 12 to

16, characterized in that the deformation under pressure of the block (37) continues until developing a side wall (3, 3 ', 3' ') monobloc with the portion lined externally by said insert (la, la', the' ' ) .

18. Method according to one of claims 12 to

17, characterized in that said insert is provided so that it has, on the side of the lower face (11a) of said solid zone (25, 25 ', 25' '), a concave curved surface (100a) down.