Foundry mold, its manufacture and use

Abstract

Foundry mold, its manufacture and use. The invention relates to foundry work, and in particular to a mold (1), its manufacture and use. The mold (1) comprises a central descender (2), a plurality of molding cavities (4) arranged in a cluster around the central descender (2), and a first plurality of several heat shield support arms (10), extending radially from the central descender (2). A method for manufacturing the mold (1) comprises the steps of mounting a cluster (20) of patterns (21) made of fusible material around a central column, forming a shell around the cluster (20) by dipping it in a slip and dusting it with refractory sand, draining the fusible material from the patterns (21) in a liquid state, and firing the shell.The mold (1) can be used to manufacture a metal part by pouring molten metal into the molding cavities (4) through the central descender (2), cooling and solidifying the metal, and removing the mold (1) to retrieve the metal parts formed in the molding cavities (4). Figure for the abbreviation: Fig. 1.

Description

Title of the invention: Foundry mold, its manufacture and its use Technical field

[0001] The present invention relates to the field of foundry, and more particularly to a mold, as well as the manufacture of such a mold and the manufacture of a metal part with such a mold. Prior art

[0002] In the following description, the terms "top", "bottom", "horizontal" and "vertical" are defined by the normal orientation of such a mold when casting metal into its interior.

[0003] Lost wax or lost model casting processes have been known since ancient times. They are particularly suitable for the production of metal parts with complex shapes. Thus, lost model casting is used in particular for the production of turbomachine blades.

[0004] In investment casting, the first step is normally the production of a model from a material with a comparatively low melting temperature, such as a wax or resin. This model is itself coated with refractory material to form a mold, and in particular a shell-mold type mold. After evacuation or elimination of the model material from the interior of the mold, which gives its name to these so-called investment casting processes, a molten metal is poured into this mold, in order to fill the cavity formed by the model in the mold after its evacuation or elimination. Once the metal cools and solidifies, the mold can be opened or destroyed in order to recover a metal part conforming to the shape of the model. By "metal", in the present context, is meant both pure metals and, especially, metal alloys.

[0005] In order to be able to produce several parts simultaneously, it is possible to combine several models in a single cluster in which they are connected by a shaft forming, in the mold, casting channels for the molten metal.

[0006] Among the different types of molds that can be used in lost model casting, we know in particular the molds called shell molds, formed by dipping the model or the cluster of models in a slip, followed by sprinkling the model or the cluster coated with slip with refractory sand to form a shell around the model or the cluster, and by firing this shell to sinter it so as to consolidate the whole. Several successive dippings and sprinklings can be envisaged in order to obtain a shell of a thickness sufficient before firing. In the present context, "refractory sand" means any granular material with a particle size distribution fine enough to meet the desired production tolerances, capable of withstanding, in the solid state, the temperatures of the molten metal, and capable of being consolidated in one piece during firing of the shell. Such a shell mold, as well as its manufacture and use in a foundry process, has been disclosed, for example, in international patent application publication WO 2014 / 167243 A1.

[0007] In order to avoid crystallization defects, it has also been disclosed, for example in the publications of international patent applications WO 2014 / 049223 A2 and WO 2019 / 002797 A1, to install heat shields on the cluster molds. These heat shields, typically made of non-woven textile material incorporating carbon fibers, may in particular be flexible, so as to facilitate their installation on the mold. They can then be arranged horizontally at different levels of the mold, supported by discs secured to the central shaft of the mold. The flexibility of the heat shields, although it facilitates their installation, may then have the disadvantage of peripheral sagging of the heat shields under their own weight, which reduces their effectiveness.

[0008] Furthermore, during casting, it may be desirable to feed from below the molding cavities formed by the lost models and intended to shape the resulting metal parts. For such casting, called "source casting", in a cluster mold, the casting channels typically comprise a central descender and feed arms extending from this central descender to below the molding cavities. However, the arrangement of these feed arms may interfere with that of the supports of a heat shield located relatively low, and in particular below the molding cavities. However, such a low arrangement of the heat shield may in particular be desirable to avoid crystallization defects manifested for example by spotted surfaces on the metal parts resulting from the molding. Presentation of the invention

[0009] According to a first aspect, a mold is provided comprising a central descender, and a plurality of molding cavities arranged in a cluster around the central descender, in which a first heat shield can be installed in a stable and non-sagging shape.

[0010] For this purpose, the proposed mold further comprises a first plurality of heat shield support arms, extending radially from the central descender. These support arms, which can be arranged in a star shape, can thus support at least one heat shield up to its periphery, without interfering with other elements of the mold.

[0011] In order to avoid crystallization defects, this first plurality of heat shield support arms may in particular be located below the molding cavities. To allow for source casting, the mold may further comprise a plurality of feed arms opening below the molding cavities, and the heat shield support arms of the first plurality of heat shield support arms.In this case, to allow a low arrangement of the heat shield, and in particular below the molding cavities, without interfering with the feed arms opening below the molding cavities, the feed arms may descend obliquely from mouths connected to the central descender, and the heat shield support arms of the first plurality of heat shield support arms may be connected to the central descender lower than the mouths of the feed arms and each extend radially, between the feed arms, to a distal end located higher than distal ends of the feed arms.

[0012] By locating the mouths of the feed arms higher than the heat shield support arms, it is possible to prevent the weight of the molten metal in the central chute during casting from causing leaks at the feed arms. At the same time, the arrangement of the heat shield support arms, interposed between the feed arms, makes it possible to avoid their interference despite the downward inclination of the feed arms.

[0013] The mold may further comprise, in order to facilitate the production of single-crystal or oriented-crystal metal parts, a starting cavity located under each molding cavity, and a selector channel, for example in a baffle, connecting each molding cavity to the starting cavity located below. In order to allow the arrival of the molten metal at the molding cavities from below, through the starting cavities and the selector channels, each feed arm may then open, at its distal end, onto one or more of said starting cavities.

[0014] To ensure its structural integrity, particularly during casting, the mold may include stiffeners. These stiffeners may in particular include support rods laterally offset from the selector channels and connecting the starting cavities to the molding cavities.

[0015] In order to direct the flow of molten metal to the feed arms, the central downcomer may be plugged between the mouths of the feed arms and the first plurality of heat shield support arms. In addition, the molding cavities may in particular be configured for the molding of turbomachine blades.

[0016] In order to allow the installation of an additional heat shield at a different level of the mold, the mold may comprise a second plurality of arms of heat shield support, extending radially from the central descender, and vertically offset from the first plurality of heat shield support arms.

[0017] The mold may further comprise one or more heat shields supported by the heat shield support arms. The heat shields may in particular be made of non-woven material, formed for example by carbon fibers. They may have cutouts so as not to interfere with other elements of the mold, such as for example the feed arms.

[0018] Each of the heat shield support arms may extend radially in a horizontal plane, perpendicular to the central descender. At least one of the heat shield support arms may be curved, particularly in said horizontal plane, although it may alternatively be straight.

[0019] According to a second aspect, a method of manufacturing this mold may comprise the following steps: mounting a cluster of models made of fusible material around a central column, forming a shell around the cluster by dipping in a slip and sprinkling with refractory sand, removing the fusible material from the models in the liquid state, and baking the shell.

[0020] According to a third aspect, the use of this mold may comprise the following steps: pouring molten metal into the molding cavities, through the central descender, cooling and solidifying the metal, and unsticking the mold to recover metal parts formed in the molding cavities. Brief description of the drawings

[0021] The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of embodiments shown as non-limiting examples. The description refers to the appended drawings in which:

[0022] [Fig-1] [Fig.l] schematically illustrates a mold according to a first mode of realization, in side view and partial section.

[0023] [Fig.2] [Fig.2] represents a cluster of models used to produce the mold of [Fig.l].

[0024] [Fig.3] [Fig.3] is a schematic plan view of the support arms for supporting the heat shield of the mold of [Fig.l].

[0025] [Fig.4] [Fig.4] is a schematic plan view of the support arms for supporting the heat shield of a mold according to an alternative embodiment.

[0026] [Fig.5] [Fig.5] schematically illustrates a mold according to another alternative embodiment, in side view. Description of the embodiments

[0027] As illustrated in [Fig.l], a mold 1 according to a first embodiment may take the form of a shell mold and comprise a central descender 2 extending, vertically along a central axis Z, under a casting cup 3. The mold 1 may also comprise a plurality of molding cavities 4 arranged in a cluster around the central descender 2, and a starting cavity 6 under each molding cavity 4, each molding cavity 4 then being able to be connected from below, through a selector channel 5 in the form of a baffle, to the starting cavity 6 below. To allow source casting in which the molten metal can arrive from below at each molding cavity 4, the mold 1 may also comprise feed arms 7 connecting the central descender 4 to the starting cavities 6, as well as possibly vents 8 at the tops of the molding cavities 4 allowing the exit of hot air and / or gases from the molding cavities 4 from above during and / or after casting.

[0028] The mold 1 may also comprise at least one first heat shield 9, located for example in a horizontal plane under the molding cavities 4, and a first plurality of heat shield support arms 10, for supporting the first heat shield 9. These heat shield support arms 10 may be arranged in a star shape, as illustrated in [Fig. 3], each extending radially, relative to the central axis Z, from the central descender 2 to a distal end 10d. Although in this first embodiment the heat shield support arms 10 are substantially straight, they may take other shapes and in particular be curved, as illustrated in [Fig. 4], in order in particular to avoid their interference with other elements of the mold 1 and the formation of thermal bridges.

[0029] The feed arms 7 may be inclined downwards from the mouths 7p connecting them to the central descender 4, in such a way that these mouths 7p are located higher than the heat shield support arms 10, or even than the first heat shield 9 itself, but that the distal ends 7d of the feed arms 7, opening into the starting cavities 6, are located lower than the heat shield support arms 10. The central descender 7 can also be plugged under the mouths 7p, in particular between these mouths 7p and the heat shield support arms 10, so as to direct the molten metal towards the feed arms 7 and prevent it from accumulating in the central descender 4 under the mouths 7. Furthermore, as illustrated, the feed arms 7 can branch off, so that each can supply more than one molding cavity 4 with molten metal during casting.

[0030] In order to ensure its structural integrity, the mold 1 may also comprise stiffeners. These stiffeners may in particular comprise support rods 11, substantially vertical, laterally offset relative to the selector channels 5, and extending between the starting cavities 6 and the molding cavities 4. These support rods 11 may be made of refractory material, for example ceramic. In order to ensure the support around each molding cavity 4, the mold 1 may comprise lateral projections adjacent to the molding cavities 4 and receiving upper ends of these support rods 11. The first heat shield 9 may in particular be located under these lateral projections.

[0031] Although, in the embodiment illustrated in [Fig.l], the mold 1 comprises only one heat shield, it is also conceivable to have more than one heat shield. Thus, in the alternative embodiment illustrated in [Fig.5], the mold 1 comprises a second plurality of heat shield support arms 10, vertically offset upwards relative to the first plurality of heat shield support arms 10 and supporting a second heat shield 9 located above the first heat shield. The remaining elements are analogous to those of the first embodiment and receive the same references.

[0032] The mold 1 can be produced by the so-called lost wax or lost model process. A first step of such a process can be the creation of a non-permanent cluster 20 comprising a plurality of models 21 connected by a shaft 22, like that illustrated in [Fig. 2]. The models 21 as well as the shaft 22, can be intended to form hollow volumes, such as, for example, the casting cup 3, the central descender 2, the feed arms 7, the starting cavities 6, the selector channels 5, the molding cavities 4 and the vents 8, in the shell mold 1. They can be obtained from a material with a low melting temperature, such as a suitable wax or resin. When the production of large numbers of parts is envisaged, it is in particular possible to produce these elements by injecting the wax or resin into a permanent mold.The stiffeners such as the support rods 11 can already be integrated into this cluster 20, as well as a plug 23 made of refractory material, for example ceramic, to plug the central descender 2 under the mouths 7p of the feed arms 7. .

[0033] In each of these embodiments, to produce the mold 1 from the non-permanent cluster 20, the cluster 20 is dipped in a slip, and then sprinkled with refractory sand. These dipping and sprinkling steps can be repeated several times, until a shell of slip-impregnated sand of a desired thickness is formed around the cluster 20.

[0034] The cluster 20 coated with this shell can then be heated to melt and evacuate from the interior of the shell the low melting temperature material of the cluster 20. Then, in a higher temperature firing step, the shell is sintered so as to consolidate the refractory sand to form the mold 1, where the refractory material elements which were already incorporated in the cluster 20 can be permanently integrated.

[0035] The metal or metal alloy used in this foundry process can be poured into melting in the mold 1, through the pouring cup 5, to fill the molding cavities 4 after having descended through the central descender 2 and the feed arms 7, and risen through the starting cavities 6 and the selector channels 5. During this casting, the shell mold 1 can be held in a heating chamber. Then, in order to obtain the progressive cooling of the molten metal, this mold 1, possibly supported by a cooled and movable support, can be extracted from the heating chamber, along the Z axis, downwards. The mold 1 can be cooled through its base, the solidification of the molten metal can be triggered in the starting cavities 6 and propagate upwards.The constriction formed by each selector channel 5, as well as its baffle shape, can then ensure that a single grain, among those having initially germinated in each starting cavity 6, continues to extend towards the corresponding molding cavity 4, so as to produce a monocrystalline metal part in this molding cavity 4.

[0036] Among the metal alloys that can be used in this process, there are in particular single-crystal nickel alloys, such as, in particular, AMI and AM3 from SNECMA, but also others such as CMSX-2®, CMSX-4®, CMSX-4® SLS, CMSX-6®, and CMSX-10® from CM Group, René® N5 and N6 from General Electric, RR2000 and SRR99 from Rolls-Royce, and PWA 1480, 1484 and 1487 from Pratt & Whitney, among others. Table 1 illustrates the compositions of some of these alloys:

[0037] [Tables 1] a CS s SC Ss TS n es ko Ht c 8 ] Si CO 0 S,8 | OO Sc OO —]—...... ; O 5 es ] es 3.Ô O CS - ] W s ■ i O s C-.O 5.S: 3.0 4sç S,3 SC; ss WSXiS 2,¾ sc ■''s 7 8,2 i CS • orrorr-......... :• [ W , s' y V 7. y M ; CS o Ce > s: . ] SC 4.2 '■nsf v..... os - O i OS ; SCSSM 35.0; 3.0 O-: ks; SS O" O i ■■ iCC sc CsÇ ..:.......L:.........L......... [ es ^À3 iO.si O ; - •s .0 5 S ?.c: k.'.ü ; sc 5,¾ Ci.S ; 3.0 SCô ] iS "W ™ SC AT" SC "m..... - ■: xa? •: ■: ; O; SC i •O y, O CS: oc O ] 08 ' SS W" ​​5 <3 "o O 'O 8 ■■■ çs V ; sc ............~pgr ïebteM 1: Campœittons of ages of mekel mœacnstalfes in W

[0038] After the metal has cooled and solidified in the mold 1, it can be unchecked to release the metal parts, which can then be finished by machining processes and / or surface treatments.

[0039] Although the present invention has been described with reference to a specific embodiment, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. Mold (1) comprising: a central descender (2), a plurality of molding cavities (4) arranged in a cluster around the central descender (2), a first plurality of heat shield support arms (10), extending radially from the central descender (2), and the mold (1) being characterized in that it also comprises a plurality of feed arms (7), descending obliquely from mouths (7p) connected to the central descender (2), and opening under the molding cavities (4), in that the first plurality of heat shield support arms (10) is located below the molding cavities (4),and in that the heat shield support arms (10) of the first plurality of heat shield support arms (10) are connected to the central descender (2) lower than the mouths (7p) of the feed arms (7) and each extend between the feed arms (7) to a distal end (10d) located higher than distal ends (7d) of the feed arms (7).,

2. Mold (1) according to claim 1, further comprising: a starting cavity (6) located under each molding cavity (4), and a selector channel (5), for example in a baffle, connecting each molding cavity (4) to the starting cavity (6) located below, each feed arm (7) opening, at its distal end (7d), onto one or more of said starting cavities (6).

3. Mold (1) according to claim 2, further comprising, as stiffeners, support rods (11) laterally offset from the selector channels (5) and connecting the starting cavities (6) to the molding cavities (4).

4. A mold (1) according to any one of claims 1 to 3, wherein the central descender (2) is plugged between the mouths (7p) of the feed arms (7) and the first plurality of heat shield support arms (10).

5. A mold (1) according to any one of claims 1 to 4, comprising a second plurality of heat shield support arms (10), extending radially from the central descender (2), and vertically offset from the first plurality of heat shield support arms (10).

6. A mold (1) according to any one of claims 1 to 5, further comprising one or more heat shields (9) supported by the heat shield support arms (10).

7. Mold (1) according to claim 6, in which the heat shields (9) are made of non-woven material, formed for example by carbon fibers.

8. A mold (1) according to any one of claims 1 to 7, wherein at least one of the heat shield support arms (10) is curved.

9. A mold (1) according to any one of claims 1 to 8, wherein the molding cavities (4) are configured for molding turbomachine blades.

10. A method of manufacturing a mold according to any one of claims 1 to 9, comprising the following steps: mounting a cluster (20) of models (21) made of fusible material around a central column, forming a shell around the cluster (20) by dipping in a slip and dusting with refractory sand, removing the fusible material from the models (21) in the liquid state, and baking the shell.

11. A method of manufacturing a metal part with a mold (1) according to any one of claims 1 to 9, comprising the following steps: pouring molten metal into the molding cavities (4), through the central descender (2), cooling and solidifying the metal, and uncoupling the mold (1) to recover metal parts formed in the molding cavities (4).

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