EP4061557B1 - Foundry mold, method for manufacturing the mold and foundry method - Google Patents

Description

Technical area

The present disclosure relates to the field of metal foundry. By “metal”, in the present context, we mean both pure metals and metal alloys.

Prior art

With known foundry processes, as described in US 2019/337047 A1 for example, comprising at least one step of casting a metal in the liquid state into a molding cavity through a feed channel opening onto one end of the molding cavity, followed by cooling and solidification of the metal in the molding cavity before demolding the solidified metal, defects can be encountered, in particular during the production of parts with particularly fine parts, such as for example the trailing edges of turbomachine blades. Indeed, during the cooling of the metal in the mold, the different rates of thermal contraction of the metal and the material of the mold can generate mechanical stresses to the point of causing the appearance of defects, and in particular cracks, in the solidified metal.

In particular, when the part to be molded has a central part narrower than its ends, which is often the case, for example, for turbomachine blades extending, along a main axis, from a blade root to a blade head, the mold can retain these ends during cooling and contraction of the solidified metal. This then generates tensile forces in the part which can generate cracks and local recrystallizations, particularly at the transitions between the ends and the central part of the part. This phenomenon can be further aggravated by a temperature gradient along the molding cavity, between the end connected to the feed channel and an opposite closed end.

Presentation of the invention

The present disclosure aims to remedy these drawbacks by proposing a foundry mold which makes it possible to reduce cracks and recrystallization phenomena due to internal tensions induced, during the cooling of the metal in the mold, by the differences between thermal contraction rates of the metal. and the mold.

For this, according to a first aspect, the mold can comprise at least a first molding cavity extending, along a main horizontal axis, from a first end to a second end, and a first pair of feed arms. A first feed arm of the first pair of feed arms is oriented with a main axis in a substantially vertical direction and connected to the first end of the first molding cavity, while a main axis of a second arm feed arm of the first pair of feed arms is substantially parallel to the first feed arm and connected to the second end of the first molding cavity. The mold is configured such that any cross section of the first and second feed arms of the first pair of feed arms, perpendicular to a vertical axis, has a greater area than any cross section of the mold cavity perpendicular to the horizontal axis.

Thanks to the provision of a feed arm at each end of the first molding cavity, the thermal contraction of the metal in these feed arms will cause them to buckle towards each other, which makes it possible to balance the forces generated by the thermal contraction of the metal in the first molding cavity, thus avoiding the appearance of cracks and recrystallized grains which could weaken the part thus molded. Thanks to the evolution of the cross-sectional areas of the molding cavity and the feed arms, the solidification of the metal, starting at the heart of the first molding cavity where the cross-section is smaller, can propagate towards and through the two feed arms by cross sections with increasing areas so as to avoid shrinkage defects due to constrictions in the mold cavities.

According to a second aspect, the mold can comprise docking heads connecting the first and second ends of the first molding cavity to the respective feed arms of the first pair of feed arms, each docking head having a section transverse, perpendicular to the horizontal axis, with an area greater than any cross section of the first molding cavity perpendicular to the horizontal axis, but less than any cross section of the first and second feed arms of the first pair of arms feed perpendicular to the vertical axis. Furthermore, in the same direction, the first and second feed arms of the first pair of feed arms may have cross sections, perpendicular to the vertical axis, with increasing areas upwards along the vertical axis. .

According to a third aspect, in order to allow the simultaneous molding of several parts in the same mold, the mold can comprise a first row of molding cavities, including the first molding cavity, each molding cavity of the first row of molding cavities extending, along a respective horizontal axis, from a first end to a respective second end, the first end of each molding cavity of the first row of molding cavities being connected to the first feed arm of the first pair of feed arm, and the second end of each mold cavity of the first row of mold cavities being connected to the second feed arm of the first pair of feed arms. Thus, a part can be formed in each molding cavity of the first row of molding cavities between the feed arms of the first pair of feed arms. Furthermore, to avoid shrinkage defects, the mold can be configured in such a way that any cross section of the first and second feed arms of the first pair of feed arms, perpendicular to a vertical axis, is greater than any cross section of each molding cavity of the first plurality of molding cavities perpendicular to the respective horizontal axis.

Furthermore, in order to allow the simultaneous molding of even more parts in the same mold, the mold may include at least a second row of molding cavities and a second pair of feed arms, each molding cavity of the second row of molding cavities extending, along a respective horizontal axis, from a first end to a respective second end, the first end of each molding cavity of the second row of molding cavities being connected to the first feed arm of the second pair of feed arms, and the second end of each molding cavity of the second row of molding cavities being connected to the second feed arm of the second pair of feed arms. Furthermore, in order to avoid shrinkage defects in the parts formed in this second row of molding cavities, the mold can be configured such that any cross section of the first and second feed arms of the second pair of arms feed, perpendicular to a vertical axis, is also larger than any cross section of each molding cavity of the second row of molding cavities perpendicular to the respective horizontal axis.

According to a fourth aspect, in order to ensure the supply of liquid metal to the molding cavities during casting, upper ends of the supply arms can be connected to a supply bucket, for example by supply channels of liquid metal.

According to a fifth aspect, at least the first molding cavity can be configured to mold a turbomachine blade extending from a blade head to a blade root along the horizontal axis. By “turbomachine”, in this context, we mean any machine in which a transfer of energy can take place between a fluid flow and at least one blade, such as, for example, a compressor, a pump, a turbine, a propeller, or a combination of at least two of these. To transmit this energy between the blade and a rotating shaft, this blade is typically part of a rotor comprising a journal and a plurality of blades each extending radially from a blade root to a blade head in a corresponding radial direction relative to an axis of rotation of the journal. These blades being subjected to particularly high mechanical and thermal forces, and being able to present, particularly at their trailing edges, thicknesses of material particularly fine, it is particularly desirable in this area to avoid any local defects such as cracks, shrinkage or recrystallization.

According to a sixth aspect, the mold can be configured as a shell mold. By “shell mold” is meant a mold formed by granules of a refractory material bonded by a slip cooked around the cavities of the mold. The mold can in particular be formed by a plurality of superimposed layers, each comprising granules linked by the slip.

A seventh aspect of this disclosure concerns a method of producing this mold, comprising the steps of dipping a non-permanent model in a slip, sprinkling the non-permanent model, after dipping, with granules of a refractory material to form a layer of slip-coated refractory material granules, evacuating the non-permanent model of a shell formed by the slip-coated refractory material granules, and firing the shell.

An eighth aspect of this disclosure relates to a foundry process comprising the steps of pouring a metal in the liquid state into such a foundry mold, cooling and solidifying the metal in the mold, and removing the solidified metal from the mold. Furthermore, this method can also include a step of preheating the mold in an oven before the casting step, and the mold being maintained in the oven until and during the casting step. However, it is also possible for the preheating step to be carried out in a first oven, and the casting step in a second oven, different from the first oven.

Brief description of the drawings

• [Fig. 1 A] la figure 1A est une première vue en coupe d'un moule de fonderie suivant un aspect de l'invention,
• [Fig. 1B] la figure 1B est une vue en coupe, perpendiculairement à la figure 1 suivant le plan IB-IB,
• [Fig. 2A] la figure 2A est une vue latérale d'une grappe de modèles non-permanents destinée à former le moule des figures 1A et 1B,
• [Fig. 2B] la figure 2B est une vue frontale de la grappe de la figure 2A,
• [Fig. 3A] la figure 3A illustre une étape de trempage dans un procédé de fabrication du moule des figures 1A et 1B à partir de la grappe des figures 2A et 2B,
• [Fig. 3B] la figure 3B illustre une étape de saupoudrage dans le procédé de fabrication du moule des figures 1A et 1B à partir de la grappe des figures 2A et 2B,
• [Fig. 3C] la figure 3C illustre une étape de cuisson dans le procédé de fabrication du moule des figures 1A et 1B à partir de la grappe des figures 2A et 2B,
• [Fig. 4A] la figure 4A illustre une étape de préchauffage dans un procédé de fonderie utilisant le moule des figures 1A et 1B,
• [Fig. 4B] la figure 4B illustre une étape de coulée dans le procédé de fonderie utilisant le moule des figures 1A et 1B,
• [Fig. 4C] la figure 4C illustre une étape de refroidissement dans le procédé de fonderie utilisant le moule des figures 1A et 1B,
• [Fig. 4D] la figure 4B illustre une étape de décochage dans le procédé de fonderie utilisant le moule des figures 1A et 1B, et
• [Fig. 5] la figure 5 illustre en détail la propagation de deux fronts de solidification à partir d'une zone centrale d'une cavité de moulage du moule des figures 1A et 1B.

The invention will be well understood and its advantages will appear better, on reading the detailed description which follows, of an embodiment shown by way of non-limiting example. The description refers to the attached drawings in which:

• [ Fig. 1A ] there Figure 1A is a first sectional view of a foundry mold according to one aspect of the invention,
• [ Fig. 1B ] there Figure 1B is a sectional view, perpendicular to the figure 1 according to the IB-IB plan,
• [ Fig. 2A ] there Figure 2A is a side view of a cluster of non-permanent models intended to form the mold of Figures 1A and 1B ,
• [ Fig. 2B ] there Figure 2B is a frontal view of the cluster of the Figure 2A ,
• [ Fig. 3A ] there Figure 3A illustrates a dipping step in a mold manufacturing process for Figures 1A and 1B from the cluster of Figures 2A and 2B ,
• [ Fig. 3B ] there Figure 3B illustrates a sprinkling step in the mold manufacturing process for Figures 1A and 1B from the cluster of Figures 2A and 2B ,
• [ Fig. 3C ] there Figure 3C illustrates a cooking step in the mold manufacturing process for Figures 1A and 1B from the cluster of Figures 2A and 2B ,
• [ Fig. 4A ] there figure 4A illustrates a preheating step in a foundry process using the mold of Figures 1A and 1B ,
• [ Fig. 4B ] there Figure 4B illustrates a casting step in the foundry process using the mold of Figures 1A and 1B ,
• [ Fig. 4C ] there figure 4C illustrates a cooling step in the foundry process using the mold of Figures 1A and 1B ,
• [ Fig. 4D ] there figure 4B illustrates a shakeout step in the foundry process using the mold of the Figures 1A and 1B , And
• [ Fig. 5 ] there Figure 5 illustrates in detail the propagation of two solidification fronts from a central zone of a molding cavity of the mold of the Figures 1A and 1B .

Description of embodiments

A foundry mold 1 according to one embodiment of the invention is illustrated on the Figures 1A and 1B . As can be seen in these figures, the mold 1, which is of the so-called “shell mold” type, can include several cavities of molding 2. Each of these molding cavities 2 can extend, along a first horizontal axis X, from a first end 2a to a second end 2b, in such a way that the first horizontal axis formed to mold a turbomachine blade extending from a blade head to a blade root along this first horizontal axis pieces.

The mold 1 may also include several pairs of feed arms, each of which may include a first feed arm 3 and a second feed arm 4. Each of these feed arms 3, 4 can be oriented along a main axis respective in the direction of a substantially vertical Z axis. Each pair of feed arms 3,4 can be associated with a row of molding cavities 2 offset vertically relative to each other. Thus, in each row of molding cavities 2, the first end 2a of each molding cavity 2 can be connected to the first feed arm 3 of the respective pair of feed arms 3,4 by a first docking head 5, and the second end 2b of each molding cavity 2 be connected to the second feed arm 4 of the respective pair of feed arms 3,4 by a second docking head 6. The pairs of feed arms 3, 4 can be laterally offset relative to each other in the direction of a second horizontal axis Y, substantially perpendicular to the first horizontal axis X. The molding cavities 2 can thus be arranged in several parallel rows densely occupying the volume of the mold 1. When the molding cavities 2 are configured to form turbomachine blades, the first and second docking heads 5, 6 can correspond, respectively, to the blade root and to a blade head heel.

As illustrated, the mold 1 can present, at its top, a feed bucket 7 in the shape of a funnel, connected to the tops of the feed arms 3,4 of each pair of feed arms by a network of channels power supply 8.

To avoid shrinkage defects, the Heuvers circles process can be applied, as described, for example, by R. Wlodawer in “Directional Solidification of Steel Castings,” Pergamon Press, 1966 , such that the area Ab of any cross section S _b of the first and second feed arms 3.4 of each pair, perpendicular to the vertical axis Z, is greater than the area A _c of any section transverse S _c of the molding cavities 2 of the corresponding row, _{perpendicular} to the first horizontal axis , greater than the area A _c of any cross section Sc of the corresponding molding cavity 2, perpendicular to the horizontal axis X, but less than the area A _b of any cross section Sb of the feed arm 3.4 corresponding to the first pair of feed arms perpendicular to the vertical axis Z. Furthermore, each feed arm 3, 4 can have cross sections Sb with area A _b increasing upwards along the vertical axis. As illustrated on the Figure 1A , this can be obtained with a divergence angle α of, for example, between 5 and 15° between opposite edges of the feed arm3, 4. Thus, as illustrated in the Figure 5 , the solidification of the metal, which can be triggered within each molding cavity 2, where the cross section is narrowest, will be able to extend to the feed arms 3, 4 with two solidification fronts 10,11 opposite and always wider, thus avoiding shrinkage defects which can be caused by constrictions in the mold cavities.

Furthermore, in order to limit the stresses transmitted by the mold 1 to the metal solidifying in the molding cavities 2 in places where they are thinner, for example at the level of the trailing edges of turbomachine blades, it is possible that the walls of mold 1 are less thick in these places than in other places of mold 1.

A first step of a process for manufacturing the mold 1 can be the creation of a non-permanent cluster 21 comprising a plurality of models 22, like that illustrated in the Figures 2A and 2B . The parts of the cluster 21 intended to form hollow volumes in the mold 1, such as the models 22 intended to form the molding cavities 2, the vertical arms 23 intended to form the feed arms 3,4, the cone 24 intended to form the feed bucket 7, and the connections 25 connecting this cone 24 and the arms feed channels 3,4 to form the feed channels 8, can be formed from a material with a low melting temperature, such as a wax or modeling resin. When the production of large numbers of parts is envisaged, it is notably possible to produce these elements by injection of wax or modeling resin into a permanent mold. In the illustrated embodiment, intended for the production of turbomachine blades, the models 22 represent such horizontally oriented blades.

The non-permanent cluster 21 may also include refractory elements to ensure its structural integrity, such as for example descendants (not illustrated). These descenders can be located on the sides, in order to free up the space under the feed bucket 7 to accommodate additional molding cavities 2, but it is also possible to have only one refractory descender arranged, for example example, centrally under cone 24.

To produce the mold 1 from this non-permanent cluster 21, the cluster 21 can be dipped in a slip B, as illustrated in the Figure 3A , to then sprinkle it with refractory sand S, that is to say granules of refractory material, as illustrated on the Figure 3B . Thus, the slip B can for example contain particles of ceramic materials, in particular in the form of flour, with a mineral colloidal binder and possibly adjuvants depending on the rheology desired for the slip, while the refractory sand S can also be ceramic . Ceramic materials that may be considered for slip B and/or refractory sand S include alumina, mullite and zircon. The mineral colloidal binder may for example be a water-based mineral colloidal solution, such as in particular colloidal silica. The adjuvants may include a wetting agent, a fluidizer and/or a texturizer. These soaking and sprinkling steps can be repeated several times, possibly with different slips B and sands S, until a shell C of sand impregnated with slip of a desired thickness is formed around the cluster 21. This thickness can be adapted to different locations in the mold, for example by locally limiting some of the sprinkling.

The cluster 21 coated with this carapace C can then be heated, for example in an autoclave 200 at a temperature between 160 and 180 ° C and at a pressure of 1 MPa, to melt and evacuate the material from the interior of the carapace. at a low melting temperature of the cluster 21. Then, in a cooking step at a higher temperature, for example between 900 and 1200°C, the slip B can solidify so as to consolidate the refractory sand S to form the refractory walls of mold 1, as illustrated in the Figure 3C .

In a foundry process using the mold 1, before proceeding with the casting of the metal in the liquid state in this mold 1, we can carry out a step of preheating this mold 1, as illustrated in the Figure 4A . In this step, after introducing the mold 1 into an oven 100, the mold 1 can be heated in the oven 100, which can reach a first temperature T ₁ . Then, without removing the mold 1 from the oven 100, while maintaining the oven 100 at the first temperature T ₁ , we can proceed to pour the metal M in the liquid state into the mold 1, as illustrated in the Figure 4B , so as to fill the hollow volumes of the mold 1, and in particular its molding cavities 2. The metal can be poured into the mold at a second temperature T2, higher than the first temperature T ₁ . However, the temperature difference ΔT between the second temperature T2 and the first temperature T ₁ can be limited, for example not greater than 170°C, or even 100°C, or even 80° C. Thus, if the metal is, for example , an equiaxed nickel-based alloy of the René 77 type, with a solidus at 1240° C and a liquidus at 1340° C, the second temperature T ₂ can be, for example, 1450° C, and the first temperature T ₁ be then 1350° C, with a difference ΔT not greater than 170° C. Thus, excessive fiery shock to the molten metal poured into the mold 1 is avoided, thus reducing in particular the risk of premature and untimely solidification of the metal in the most difficult passages. narrow parts of mold 1, solidification which could cause blockages and local defects in the parts thus produced. The casting of the liquid metal is carried out quickly and thus completed in a time t _v , which can for example be approximately 2 seconds, or even a single second.

In the next step, shown in the Figure 4C , the mold 1 can still be maintained in the oven 100 during a first stage of cooling and solidification of the metal M in the mold 1, in which the cooling rate dT/dt of the oven 100 can be controlled and limited, for example, to approximately 7°C/min maximum. This upper limit on the cooling rate also makes it possible to limit the forces exerted on the metal by the difference in thermal contraction between the mold 1 and the metal which cools. However, the thermal contraction of the metal M, greater than that of the refractory walls of the mold 1, will cause buckling of the metal in the feed arms 3, 4, illustrated in dotted lines on the Figure 4C , buckling which will exert a compressive stress on the metal M in the molding cavities 2, so as to balance at least partially the tensile stresses caused by the thermal contraction of the metal M in the molding cavities 2. It is thus possible to avoid concentrations of forces that can disrupt the crystallization of the metal and create weak points in the parts resulting from this foundry process.

In the illustrated embodiment, as the René 77 type alloy is an equiaxed polycrystalline alloy, the metal will form, during its solidification, a plurality of grains of substantially identical size, typically of the order of 1 mm, but of more or less random orientation.

When the oven 100 has cooled sufficiently, until it reaches a third temperature T ₃ of, for example, between 800°C and 900°C, it is possible to remove the mold 1 from the oven 100 so that it continues to cool naturally. after being placed under an insulating bell surrounded by refractory fabric, until the stage of shelling, illustrated on the figure 4D , in which the mold is destroyed to remove the solidified metal, comprising the turbomachine blades 200 thus formed, on which subsequent cutting and finishing steps can then be carried out.

Although the present invention has been described with reference to a specific embodiment, it is obvious that various modifications and changes can be made to this example 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 a restrictive sense.

Claims (11)

1. A foundry mold (1) including at least:

   a first molding cavity (2) extending, along a horizontal axis (X), from a first end (2a) to a second end (2b),

   a first pair of feeder arms comprising:

   a first feeder arm (3), oriented in a substantially vertical direction and connected to the first end (2a) of the first molding cavity (2), and

   a second feeder arm (4), substantially parallel to the first feeder arm (3) and connected to the second end (2b) of the first molding cavity (2),

   the foundry mold (1) being characterized in that any transverse section (Sb) of the first and second feeder arms (3,4) of the first pair of feeder arms, perpendicular to a vertical axis (Z), has a greater area than any transverse section (Sc) of the first molding cavity (2) perpendicular to the horizontal axis (X).
2. The foundry mold (1) according to claim 1, comprising docking heads (5,6) connecting the first and second ends (2a,2b) of the first molding cavity (2) to the respective feeder arms (3,4) of the first pair of feeder arms, each docking head (5,6) having a transverse section (St), perpendicular to the horizontal axis (X), with an area greater than any transverse section (Sc) of the first molding cavity (2) perpendicular to the horizontal axis (X), but smaller than any transverse section (Sb) of the first and second feeder arms (3,4) of the first pair of feeder arms perpendicular to the vertical axis (Z).
3. The foundry mold (1) according to any one of claims 1 or 2, wherein the first and second feeder arms (3,4) of the first pair of feeder arms have transverse sections (St), perpendicular to the vertical axis (Z), with areas increasing upward along the vertical axis (Z).
4. The foundry mold (1) according to any one of claims 1 to 3, comprising a first row of molding cavities (2), including the first molding cavity (2), each molding cavity (2) of the first row of molding cavities (2) extending, along a respective horizontal axis (X) from a first end (2a) to a respective second end (2b), the first end (2a) of each molding cavity (2) of the first row of molding cavities (2) being connected to the first feeder arm (3) of the first pair of feeder arms, and the second end (2b) of each molding cavity (2) of the first row of molding cavities (2) being connected to the second feeder arm (4) of the first pair of feeder arms.
5. The foundry mold (1) according to claim 4, comprising at least a second row of molding cavities (2) and a second pair of feeder arms, each molding cavity (2) of the second row of molding cavities (2) extending, along a respective horizontal axis (X), from a first end (2a) to a respective second end (2b), the first end (2a) of each molding cavity (2) of the second row of molding cavities (2) being connected to the first feeder arm (3) of the second pair of feeder arms, and the second end (2b) of each molding cavity (2) of the second row of molding cavities (2) being connected to the second feeder arm (4) of the second pair of feeder arms.
6. The foundry mold (1) according to any one of the preceding claims, wherein the upper ends of the feeder arms are connected to a feeder (7).
7. The foundry mold (1) according to any one of the preceding claims, wherein the first molding cavity (2) is configured to mold a turbine engine blade extending from a blade tip to a blade root along the horizontal axis (X).
8. The foundry mold (1) according to any one of the preceding claims, configured as a shell mold.
9. A manufacturing method for a foundry mold (1) according to claim 8, comprising the following steps:

   dipping a non-permanent pattern (22) in a slurry;

   dusting the non-permanent pattern (22), after dipping, with granules of a refractory material to form a layer of granules of refractory material coated with slurry;

   removal of the non-permanent pattern (22) from a shell formed by the granules of refractory material coated with slurry; and

   baking the shell.
10. A casting method comprising the following steps:

    pouring a metal in the liquid state into a foundry mold (1) according to any one of claims 1 to 7;

    cooling and solidification of the metal in the foundry mold (1); and demolding of the solidified metal.
11. The casting method according to claim 10, comprising a step of preheating the foundry mold (1) in an oven (100) prior to the pouring step, and in which the mold is held in the oven (100) until and during the pouring step.

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