Tool for attaching a metal shield to a turbomachine blade, in particular an aircraft turbomachine blade
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SAFRAN AIRCRAFT ENGINES SAS
- Filing Date
- 2026-01-20
- Publication Date
- 2026-07-30
Smart Images
Figure FR2026050044_30072026_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: TOOLING FOR ATTACHING A METAL SHIELD TO A TURBOMACHINE BLADE, IN PARTICULAR AN AIRCRAFT
[0003] Technical field of the invention
[0004] The present invention relates in particular to a tool and a method for fixing a metal shield on a turbine blade, in particular of an aircraft.
[0005] Technical background
[0006] Documents US-A1 -2021 / 010377 A1, FR-A1 -2 99288 and FR-B1-3014007 are known from the prior art.
[0007] The use of composite materials is advantageous in the aeronautical industry in particular because these materials have interesting mechanical performance for relatively low masses.
[0008] A manufacturing process for a composite part for the aeronautical industry, which is well known to those skilled in the art, is the RTM molding process, the initials of which refer to the Anglo-Saxon acronym for Resin Transfer Molding.
[0009] This is a process for manufacturing a part from a composite material based on woven fibers and resin. Such a process is used, for example, to manufacture a turbomachine blade. A fibrous preform is created and then placed in a mold. If the woven fibers are not pre-impregnated with resin, resin is injected into this mold. This preform is then heated so that the resin polymerizes and forms a blade from the composite material. The composite blade consists of an upper and lower surface extending from a leading edge to a trailing edge. The composite material is relatively brittle, and particularly sensitive to impacts, and it is known to protect it with a metal shield, also called a metal plate, which is attached to the leading edge of the blade to create the blade.It helps to protect the leading edge from erosion but also to improve the strength of the blade against ingestion (hail, gravel, debris, birds, etc.).
[0010] One way to fix a shield to a blade is to glue the shield to the blade using an adhesive, after polymerization of the resin in a so-called matching operation carried out manually by an operator.
[0011] Because the pairing is done manually, the pairing parameters are very difficult to control or record. Only the distance between the shield head and the blade matters. The associated measurement corresponds to the clearance between the shield and the blade at the shield head, also known as the "tip gap." This clearance is measured by the operator using calipers. If the value is within the required tolerance, the assembly is considered complete; otherwise, the operator continues lowering the shield until the required clearance is reached. Only the final result is checked and validated by measuring the clearance between the shield head and the blade. Thus, the method for achieving the result is not monitored and remains largely dependent on the operator, i.e., the human factor, which makes it impossible to guarantee the robustness of the assembly process.Consequently, the variability of the operation is very important.
[0012] The risk of non-quality is therefore high and requires a high level of operator qualification to be controlled. Furthermore, since this non-quality is detected after the shield is bonded to the blade, any defect cannot be corrected and will result in the scrapping of the assembled blade.
[0013] Furthermore, the manual operation is time-consuming.
[0014] To address this issue, the Applicant's document FR-B1-3 127°153 proposes a system for attaching a metal shield to the leading edge of an aircraft turbomachine blade. This system allows for the automated assembly of the metal shield with the blade. More specifically, the system enables the approach, positioning according to the attachment requirements, and securing of the metal shield to the blade.
[0015] However, this automated pairing step is followed by steps that are not automated. After the shield is paired, the blade equipped with the shield is covered with a flexible tarpaulin which is sealed airtight. A vacuum is then created in the tarpaulin, and the assembly formed by the blade, the shield, and the tarpaulin is placed in an autoclave to cure the adhesive used to bond the shield to the leading edge of the blade. The present invention proposes a simple, efficient, and economical solution to facilitate, or even automate, the shield attachment steps that follow its pairing.
[0016] Summary of the invention
[0017] The invention provides a tool for attaching a metal shield to the leading edge of a turbomachine blade, particularly for aircraft, the tool comprising:
[0018] - a support configured to receive and hold the metal shield, - a mold that is independent of the support and that has an internal cavity configured to receive the blade, the mold having an end that is configured to be applied against the support, the internal cavity opening at this end to form an opening suitable for receiving at least part of the shield carried by the support,
[0019] - a heating system integrated into the mold to heat the blade housed in the cavity, and
[0020] - a tarpaulin located in the cavity and configured to completely cover the blade, and possibly also part of the shield, this tarpaulin being hermetically sealed and connected to a vacuum system integrated into the mold, the mold further comprising - two shells, preferably rigid, capable of being fixed to each other, a first of these shells having a first impression defining a part of said cavity and capable of receiving at least part of an intrados of the blade, and a second of these shells having a second impression defining another part of said cavity and capable of receiving at least part of an extrados of the blade, the tarpaulin having a first part covering the first impression and a second part covering the second impression, and
[0021] The mold comprises two additional parts adapted to be fixed to one another and to be interposed between the support and the hulls. The first of these parts has a third cavity defining a portion of said cavity and adapted to receive another portion of the lower surface of the blade, and the second of these parts has a fourth cavity defining another portion of said cavity and adapted to receive another portion of the upper surface of the blade. The mold cover has a third portion covering the third cavity and a fourth portion covering the fourth cavity, said opening being defined between the first and second parts of the mold. The invention thus proposes to facilitate the attachment of the shield to the blade and, in particular, the curing of the adhesive used to attach the shield to the blade.To achieve this, the tooling includes a mold that holds the blade in position relative to the shield and the support, and a heating system that ensures even heating of the blade. The tarpaulin and the vacuum system ensure uniform compression of the blade and guarantee a consistent and controlled thickness of the adhesive film between the shield and the leading edge of the blade.
[0022] The tooling according to the invention may comprise one or more of the following features, taken individually or in combination with each other:
[0023] - the heating system is integrated into at least one of the mold shells, or even into at least one of the mold parts; - the heating system is of the induction type and includes at least one first element, such as a plate, located at the level of the first cavity, or even also the third cavity, and at least one second element, such as a plate, located at the level of the second cavity, or even the fourth cavity, the first and second elements being able to cooperate together by induction;
[0024] - the two parts of the mold are other shells, preferably rigid, of the mold or inflatable bladders;
[0025] - the heating system is a heating and cooling system and is also capable of cooling the blade housed in the cavity; - the cover comprises a first end sealed hermetically at the trailing edge of the blade, and a second opposite end sealed hermetically at the leading edge of the blade;
[0026] - the first end of the tarpaulin is clamped between the two shells of the mold, and the second end of the tarpaulin is clamped between the support and the two parts of the mold;
[0027] - the support has a horizontal orientation and the mold is located on the support;
[0028] -- the tarpaulin is flexible and / or elastically deformable.
[0029] The invention also relates to an assembly comprising tooling as described above, and a blade comprising a leading edge on which a metal shield is to be fixed.
[0030] The blade is, for example, a rectifier blade or a blower or propeller blade.
[0031] The blade is composite and preferably comprises a fibrous preform impregnated with a resin matrix. Alternatively, the blade could be metallic.
[0032] The invention further relates to a method for fixing a metal shield to the leading edge of a turbomachine blade, in particular an aircraft turbine blade, by means of tooling as described above, in which it comprises the steps of: a) positioning the metal shield on the support, this metal shield having a general dihedral shape and comprising two wings connected together and defining a space between them, the shield being held on the support so that said space is oriented upwards,
[0033] b) Position the blade in the mold cavity, with the tarpaulin covering the blade and the leading edge of the blade located outside the mold,
[0034] c) Fit the shield to the leading edge of the blade, after applying adhesive to the shield and / or the leading edge of the blade, d) Seal the cover tightly.
[0035] e) vacuum-seal the inside of the tarpaulin using the vacuum sealing system, and
[0036] f) heat the blade in the mold cavity using the heating system. The method according to the invention may comprise one or more of the following features or steps, taken individually or in combination:
[0037] - in step d), the second end of the tarpaulin is sealed tightly by fixing this end onto the support;
[0038] - in step b), the process consists of positioning the blade in the cavities of the two shells of the mold;
[0039] - after step c) or d), the process includes a step i) consisting of mounting the two parts of the mold between the support and the shells so that the blade is also positioned in the cavities of these two parts of the mold;
[0040] - step i) takes place after step d) and the two parts of the mold are mounted between, on one side the support and the second end of the tarpaulin, and on the other side the two shells of the mold.
[0041] Brief description of the figures
[0042] The invention will be better understood and other details, features and advantages of the invention will become more apparent upon reading the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:
[0043] [Fig.1] Figure 1 is a schematic cross-sectional view of a tool for attaching a metal shield to the leading edge of a turbomachine blade,
[0044] [Fig. 2] Figure 2 is a view similar to Figure 1 and shows a step of a method according to the invention for attaching a metal shield to a turbomachine blade,
[0045] [Fig. 3] Figure 3 is a view similar to Figure 1 and shows another step of the method according to the invention for attaching a metal shield to a turbomachine blade,
[0046] [Fig. 4] Figure 4 is a view similar to Figure 1 and shows another step of the method according to the invention for fixing a metal shield onto a turbomachine blade,
[0047] [Fig. 5] Figure 5 is a view similar to Figure 1 and shows another step of the method according to the invention for fixing a metal shield onto a turbomachine blade,
[0048] [Fig. 6] Figure 6 is a view similar to Figure 1 and shows another step of the method according to the invention for fixing a metal shield onto a turbomachine blade,
[0049] [Fig. 7a-7c] Figures 7a to 7c are views similar to Figure 1 and show another step of the method according to the invention for attaching a metal shield to a turbomachine blade,
[0050] [Fig. 8] Figure 8 is a view similar to Figure 1 and shows an alternative embodiment of tooling according to the invention.
[0051] Detailed description of the invention
[0052] We first refer to Figure 1, which illustrates a tool 10 for attaching a metal shield 12 to a turbine blade 14, particularly one used in aircraft. A turbine blade 14 consists, in particular, of a fibrous preform impregnated with a resin matrix. The shield 12 is also called a shim and serves, among other things, to reinforce the turbine blade 14. The turbine blade 14 extends, in particular, from a root to a tip; the root and tip of the blade are not visible here.
[0053] The wing 14 includes in particular an intrados 16 and an extrados 17 which extend from a leading edge 18 to a trailing edge 19.
[0054] The metal shield 12 has a general dihedral shape and comprises two wings 12a, 12b connected together, defining a space into which the leading edge 18 of the wing blade 14 will fit during a pairing step. The wings 12a, 12b of the shield 12 then extend respectively over the intrados 16 and extrados 17 of the wing blade.
[0055] Pairing means precisely positioning two objects, here the metal shield 12, on the leading edge 18 of the blade 14. The attachment between the shield 12 and the blade 14 is achieved in particular by means of an adhesive positioned between them, that is to say positioned on the shield 12 and / or the leading edge 18 of the blade 14 prior to pairing.
[0056] As in the Applicant's earlier document cited above, the tooling 10 includes a support 20 used to perform this pairing. The support 20 is therefore configured to receive and hold the shield 12. In the example shown, the support 20 is intended to have a horizontal orientation so that the shield 12 is located on the support 20. The reference numeral P designates a horizontal plane, and Figure 1 is a cross-sectional view in a plane perpendicular to this plane P.
[0057] The shield 12 is held on the support 20 so that the space between the two wings 12a, 12b of the shield 12 is oriented upwards.
[0058] The support 20 may for example include clamping jaws 22 for the shield 12. The jaws 22 are for example located respectively on the two sides of the shield 12 to hold it clamped between them.
[0059] The tooling 10 further includes a mold 30 which is independent of the support 20 and which has an internal cavity 32 configured to receive the blade 14. The mold 30 has an end 30a, here lower, which is configured to be applied against the support 20. It is therefore understood that the mold 30 is located on the support 20 in the example shown.
[0060] The internal cavity 32 opens at this end 30a to form an opening 34 suitable for receiving at least part of the shield 12 carried by the support 20. Indeed, it can be seen in the drawing that the cavity 32 opens downwards to form the opening 34. It is through this opening 34 that the leading edge 18 of the blade 14 can be engaged in the shield 12. The tooling 10 also includes a heating system 40 integrated into the mold 30 in order to heat the blade 14 housed in the cavity 32.
[0061] This heating system 40 allows for even temperature distribution and faster heating of the mold and blade. Furthermore, heating can be zoned to heat only the necessary areas. This also eliminates the need for control thermocouples due to the uniformity of the heating.
[0062] Heating the blade can be useful or even necessary when it is coated with an external polyurethane film that provides protection against erosion. This type of film is generally applied to the underside of the blade.
[0063] The tooling 10 further includes a cover 50 located in the cavity 32 and configured to completely cover the blade 14, or even part of the shield 32. The cover 50 is for example made of silicone.
[0064] The 50 tarpaulin is advantageously reusable to reduce single-use consumables.
[0065] The tarpaulin 50 is sealed airtight and connected to a vacuum system 60 which is integrated into the mold 30.
[0066] In the example shown, the mold 30 comprises two shells 36, 38 suitable for being fixed to each other.
[0067] A first of these shells 36 has a first impression 36a defining a part of the cavity 32 and suitable for receiving at least a part of the intrados 16 of the blade. A second of these shells 38 has a second impression 38a defining another part of the cavity 32 and suitable for receiving at least a part of the extrados 17 of the blade 14.
[0068] In the absence of dawn, footprints 36a, 38a are opposite or facing each other.
[0069] Tarpaulin 50 comprises a first part 50a covering the first imprint 36a and a second part 50b covering the second imprint 36b.
[0070] The mold 30 further includes two additional parts 42, 44 suitable for being fixed to each other, and for being interposed between the support 20 and the shells 36, 38.
[0071] A first of these parts 42 includes a third impression 42a defining a part of the cavity 32 and suitable for receiving another part of the intrados 18 of the wing 14.
[0072] A second of these parts 44 includes a fourth imprint 44a defining another part of the cavity 32 and suitable for receiving another part of the extrados 17 of the wing 14.
[0073] In the absence of dawn, footprints 42a, 44a are opposite or facing each other.
[0074] Tarpaulin 50 has a third part 50c covering the third imprint 42a and a fourth part 50d covering the fourth imprint 44a.
[0075] The aforementioned opening 34 is defined between the first and second parts 42, 44 of the mold 30. It is therefore the two parts 42, 44 of the mold 30 which perform the pairing.
[0076] The two parts 42, 44 of the mold 30 can be rigid shells similar to the shells 36, 38, as is the case in Figure 1. In the variant shown in Figure 8, the two parts 42, 44 of the mold 30 are inflatable bladders.
[0077] The various elements of the mold 30 allow the blade to be held in place and thus guarantee the geometry of the part during the firing cycle. It can be seen in the drawing that the heating system 40 is integrated into at least one of the shells 36, 38 of the mold 30, or even also into at least one of the parts 42, 44 of the mold 30.
[0078] The heating system 40 can be of the induction type. Alternatively, the heating system could be a heating cartridge or use heat transfer fluid(s).
[0079] The heating system 40 may include at least one first element (not shown), such as a plate, located at the first cavity 36a, or even also at the third cavity 42a, and at least one second element (not shown), such as a plate, located at the second cavity 36b, or even also at the fourth cavity 42b. The first and second elements are then capable of cooperating. Thus, in the case where the heating system is of the induction type, the first and second elements are configured to cooperate by induction.
[0080] Advantageously, the heating system 40 is a heating and cooling system and is therefore also suitable for cooling the blade 14 housed in the cavity 32. For this purpose, channels 46 for the circulation of a cooling fluid can be formed in the mold 30, and in particular in the shells 36, 38, and even also in the parts 42, 44.
[0081] As regards the tarpaulin 50, it preferably comprises a first end 52 sealed tightly at the trailing edge 19 of the blade 14, and a second opposite end 54 sealed tightly at the leading edge 18 of the blade 14.
[0082] The first end 52 of the tarpaulin 50 is clamped between the two shells 36, 38 of the mold 30. To achieve this, one of the shells 36 can be associated with a first clamping element 56, which is adapted to be fixed to a second clamping element 58 of the other shell 38, in order to clamp this first end 52 together. The fixing of the shells 36, 38 to each other can generate the fixing of the clamping elements 56, 58 to each other and thus the sealing of the first end 52 of the tarpaulin 50. The second end 54 of the tarpaulin 50 is clamped between the support 30 and the two parts 42, 44 of the mold 30.
[0083] For this purpose, the support 20 can include several clamping elements 62, 64 which are suitable for clamping the end 54 of the tarpaulin 50. Clamping elements 62 are located on one side of the blade 14, for example on the side of the intrados 16, and are intended to clamp together a part of the tarpaulin 50. Clamping elements 64 are located on an opposite side of the blade, for example on the side of the extrados 17, and are intended to clamp together another part of the tarpaulin 50.
[0084] In practice, the tarpaulin 50 can comprise two skins 70, 72. A first skin 70 covers the cavities 36a, 42a and therefore the intrados 16 of the blade 14, and has its lower end which is tightened by the tightening elements 62. A second skin 72 covers the cavities 38a, 44a and therefore the extrados 17 of the blade 14, and has its lower end which is tightened by the tightening elements 64. The upper ends of the skins 70, 72 are tightened by the tightening elements 56, 58, and the skins 70, 72 are joined together on the rest of their periphery.
[0085] The vacuum system 60 is integrated into the mold 30 and allows a vacuum to be created inside the tarpaulin 50. The system 60 includes, for example, a suction duct formed in the mold 30, and for example in one of its shells 36, 38.
[0086] We will now describe a method of fixing a shield 12 onto the leading edge 18 of a blade 14 using the tooling 10 described above.
[0087] Figures 2 to 7c illustrate steps in this process.
[0088] The method comprises a first step a) illustrated in Figure 2 in which the shield 12 is positioned on the support 20. The shield 12 is preferably positioned so that the space between its wings 12a, 12b is oriented upwards. The method comprises a second step b) illustrated in Figure 3 in which the blade 14 is positioned in the cavity 32 of the mold 30, and in particular in the two aforementioned shells 36, 38 of the mold 30. The blade 14 is positioned in the cavities 36a, 38a of the two shells 36, 38 of the mold. The cover 50 covers the two cavities 36a, 38a of the shells 36, 38 and its end 52 is clamped tightly by the clamping elements 56, 58. The leading edge 18 of the blade 14 passes through the opening 34. the aforementioned mold 30 and is therefore located outside of mold 30.
[0089] The process includes a third step c) illustrated in figure 4 in which the shield 12 is paired on the leading edge 18 of the blade 14. An adhesive is first deposited on the shield and / or the leading edge of the blade.
[0090] The process includes a fourth step illustrated in figure 5 in which d) the tarpaulin 50, and in particular its end 54, is sealed tightly at the support 20. For this, the aforementioned clamping elements 62, 64 are used.
[0091] The process may further include a step in which i) the remainder of the mold 30 is assembled. In particular, parts 36, 38 of the mold 30 are mounted as illustrated by the arrows in Figure 6. The blade 14 is then positioned in the cavities 42a, 44a of these two parts 42, 44 of the mold 30.
[0092] The process includes a sixth step not shown in which e) the inside of the tarpaulin 50 is evacuated using the vacuum system 60.
[0093] The process includes a seventh step not shown in which f) the blade 14 is heated in the cavity 32 of the mold 30 by means of the heating system 40. This heating step allows the adhesive for fixing the shield 12 to the leading edge 18 of the blade 14 to polymerize.
[0094] After the adhesive has cured, the system 60 can be used to cool the blade 14 before its removal from the tooling 10. Figures 7a to 7c illustrate steps for dismantling the tooling 10. Parts 42, 44 of the mold 30 are first removed, then the cover 50 is opened by separating its end 54 from the support 20. The rest of the mold 30 is then dismantled to access the blade 14 for its removal.
Claims
DEMANDS 1. Tooling (10) for attaching a metal shield (12) to a leading edge (18) of a turbine blade (14), in particular for aircraft, the tooling (10) comprising: - a support (20) configured to receive and hold the metal shield (12), - a mold (30) which is independent of the support (20) and which has an internal cavity (32) configured to receive the blade (14), the mold (30) having an end (30a) which is configured to be applied against the support (20), the internal cavity (32) opening at this end (30a) to form an opening (34) suitable for receiving at least part of the shield (12) carried by the support (20), - a heating system (40) integrated into the mold (30) in order to heat the blade (14) housed in the cavity (32), and - a tarpaulin (50) located in the cavity (32) and configured to completely cover the blade (14), or even part of the shield (12), this tarpaulin (50) being hermetically sealed and connected to a vacuum system (60) integrated into the mold (30), the mold (30) further comprising: - two shells (36, 38) capable of being fixed to each other, a first of these shells (36) having a first impression (36a) defining a part of said cavity (32) and capable of receiving at least a part of an intrados (16) of the blade (14), and a second of these shells (38) having a second impression (38a) defining another part of said cavity (32) and capable of receiving at least a part of an extrados (17) of the blade (14), the cover (50) having a first part (50a) covering the first impression (36a) and a second part (50b) covering the second impression (38a), and - two additional parts (42, 44) suitable for being fixed to each other, and for being interposed between the support (20) and the hulls (36, 38), a first of these parts (42) having a third impression (42a) defining a part of said cavity (32) and suitable for receiving another part of the intrados (16) of the blade (14), and a second of these parts (44) having a fourth impression (44a) defining another part of said cavity (32) and suitable for receiving another part of the extrados (17) of the blade (14), the cover (50) having a third part (50c) covering the third impression (42a) and a fourth part (50d) covering the fourth impression (44a), said opening (34) being defined between the first and second parts (42, 44) of the mold (30).
2. Tooling (10) according to claim 1, in which the heating system (40) is integrated into at least one of the shells (36, 38) of the mold (30), or even also into at least one of the parts (42, 44) of the mold (30).
3. Tooling (10) according to claim 1 or 2, wherein the heating system (40) is of the induction type and comprises at least a first element, such as a plate, located at the first cavity (36a), or even also at the third cavity (42a), and at least a second element, such as a plate, located at the second cavity (38a), or even also at the fourth cavity (44a), the first and second elements being able to cooperate together by induction.
4. Tooling (10) according to any one of claims 1 to 3, wherein the two parts (42, 44) of the mold (30) are other mold shells or inflatable bladders.
5. Tooling (10) according to any one of the preceding claims, wherein the heating system (40) is a heating and cooling system and is further capable of cooling the blade (14) housed in the cavity (32).
6. Tooling (10) according to any one of the preceding claims, wherein the tarpaulin (50) comprises a first end (52) sealed tightly at a trailing edge (19) of the blade (14), and a second opposite end (54) sealed tightly at the leading edge (18) of the blade (14).
7. Tooling (10) according to claim 6, wherein the first end (52) of the tarpaulin (50) is clamped between the two shells (36, 38) of the mold (30), and the second end (54) of the tarpaulin (50) is clamped between the support (20) and the two parts (42, 44) of the mold (30).
8. Tooling (10) according to any one of the preceding claims, wherein the support (20) has a horizontal orientation and the mold (30) is located on the support (20).
9. Assembly comprising a tooling (10) according to one of the preceding claims, and a blade (14) comprising a leading edge (18) on which a metal shield (12) is to be fixed.
10. A method for attaching a metal shield (12) to a leading edge (12) of a turbine blade (14), particularly an aircraft turbine blade, using a tool (10) according to any one of claims 1 to 8, wherein it comprises the steps of: a) position the metal shield (12) on the support (20), this metal shield (12) having a general dihedral shape and comprising two wings (12a, 12b) connected together and defining a space between them, the shield (12) being held on the support (20) so that said space is oriented upwards, b) position the blade (14) in the cavity (32) of the mold (30), the tarpaulin (50) covering the blade (30) and the leading edge (18) of the blade (14) being located outside the mold (30), c) fit the shield (12) to the leading edge (18) of the blade (14), after applying adhesive to the shield and / or the leading edge of the blade, d) close the cover (50) tightly, e) to vacuum-seal the inside of the tarpaulin (50) using the vacuum sealing system (60), and f) heat the blade (14) in the cavity (32) of the mold (30) using the heating system (40).
11. Method according to claim 10, the tooling (10) being as defined in claim 6 or 7, wherein, in step d), the second end (54) of the tarpaulin (50) is sealed tightly by fixing this end (54) on the support (20).
12. A method according to claim 10, wherein: - in step b), the process consists of positioning the blade (14) in the cavities (36a, 38a) of the two shells (36, 38) of the mold (30), and - after step c) or d), the process includes a step i) consisting of mounting the two parts (42, 44) of the mold (30) between the support (20) and the shells (36, 38) so that the blade (14) is also positioned in the cavities (42a, 44a) of these two parts (42, 44) of the mold (30).
13. Method according to claim 12, the tooling (10) being as defined in claim 7, wherein step i) takes place after step d) and the two parts (42, 44) of the mold (30) are mounted between, on one side the support (20) and the second end (54) of the tarpaulin (50), and on the other side the two shells (36, 38) of the mold (30).