Foundry mold

Abstract

Foundry mold The invention relates to a foundry mold (10) for centrifugal casting of a molten metal by rotating the mold about a vertical rotation axis (101), said mold comprising at least: - a molding cavity (14); - a feed arm (13) of the molding cavity in fluid communication with the molding cavity by means of an opening (22); the mold being characterized in that the molding cavity is arranged between the feed arm of the molding cavity and the rotation axis (101). Figure for abstract: Fig. 1

Description

Title of the invention: Foundry mold Technical field

[0001] The invention relates to the field of metal foundry, in particular molds for obtaining parts and more precisely molds allowing casting by centrifugation. Prior art

[0002] Casting of molten alloys is used in many technological fields to obtain parts directly in the desired shapes without requiring lengthy additional process steps.

[0003] Known foundry processes generally comprise at least one step of casting a molten metal in the liquid state into a molding cavity in the desired shape, followed by cooling and solidifying the metal in the molding cavity before demolding the solidified metal.

[0004] A technical difficulty of known foundry processes is to overcome defects created due to the temperature difference between the mold and the cast metal.

[0005] Indeed, the different thermal contraction coefficients between the mold and the metal can be the cause of crystalline defects, in particular cracks or recrystallized zones, which are difficult to overcome using such processes.

[0006] One proposed solution is to reduce the temperature difference between the mold and the cast metal, i.e. increase the temperature of the mold before pouring the metal. This solution imposes a significant industrial constraint, because it then becomes necessary to have a larger furnace capable of accommodating the mold and having higher power heating elements and the costs of the process are increased.

[0007] In order to minimize the thermal losses of the liquid metal during its introduction into the mold, it has also been proposed to accelerate the metal, for example by rotating the mold. In this way, the centrifugal force works to send the metal into the molding cavity more quickly, which results in lower thermal losses, due to faster filling of the mold.

[0008] However, during centrifugal casting, other defects are observed, in particular non-metal discharges, i.e. the molding cavities are not necessarily completely filled, drips or even cold drops, due to the uncontrolled and rapid projection of metal into the mold. This results in non-compliant parts, which cannot be used and therefore represent material losses.

[0009] Centrifugal casting also causes a liquid metal filling front which is not homogeneous in the molding cavity, because the flow of liquid metal is accelerated by the action of centrifugal force, and it is difficult to ensure very homogeneous progressive filling of the mold.

[0010] To achieve an even more efficient molten metal casting process that limits the number of non-conforming parts, it remains desirable to propose a process free from certain disadvantages described above. Statement of the invention

[0011] The invention aims precisely to meet this need.

[0012] For this purpose, the invention proposes a foundry mold for the centrifugal casting of a molten metal by rotating the mold around a vertical axis of rotation, said mold comprising at least:

[0013] - a molding cavity;

[0014] - a feeding arm of the molding cavity in fluid communication with the molding cavity by means of an opening;

[0015] the mold being characterized in that the molding cavity is arranged between the feed arm of the molding cavity and the rotation axis.

[0016] In this application, the term "metal" will independently refer to a pure metal or a metal alloy if no specific mention is made of one or the other.

[0017] In a mold of the invention, when the mold is rotated around the axis of rotation, the work of the centrifugal force on the liquid metal wanting to enter the molding cavity is negative.

[0018] In the application, the “work” of a force takes the classical meaning of this term in general physics and is understood as the scalar product of the force by the path traveled expressed vectorially.

[0019] "Centrifugal force" is understood here as the force created by a rotating object whose direction is included in the plane perpendicular to the axis of rotation. The centrifugal force applied to the object considered is oriented along the straight line joining the axis of rotation to the center of mass of the object considered, in the direction away from the center of rotation. Its value F can be written F = mco2r where m is the mass of the object on which it is applied, co the angular velocity (here squared), and r the distance separating the object from the axis of rotation.

[0020] In a mold of the invention, the centrifugal force works positively on a portion of metal moving away from the axis of rotation, and negatively on a portion of metal wishing to move closer to the axis of rotation.

[0021] Note that the centrifugal force is not modified in any way by the direction of rotation of the mold and that the latter is only important for the Coriolis force which will be considered in other embodiments of the invention.

[0022] It may seem counterintuitive to rotate the mold so that the work of the centrifugal force induced by the rotation of the mold on the liquid metal wishing to enter the molding cavity is negative.

[0023] Nevertheless, the inventors have found that a rotating mold of the invention ensures that the driving force for filling the molding cavity is generated indirectly by the metal present in the feed arm, and not by centrifugal force as in the methods of the prior art.

[0024] Indeed, since the liquid metal is pushed into the cavity by the metal feeding the feed arm, and this against the centrifugal force, the filling of the cavity is much less turbulent than in the molds of the prior art, which reduces the appearance of defects such as cold drops, metal folds or non-coming material or even shrinkage.

[0025] Also counter-intuitively, the filling of the molding cavity is certainly slower than in a mold where the centrifugal force works positively, but not slow enough to harm the productivity of the process, provided that the feed arm is continuously supplied with metal.

[0026] In particular, the filling speed of a mold of the invention remains faster and more uniform than that of gravity casting of the prior art, that is to say a casting in which there would be no application of centrifugal force at all.

[0027] Furthermore, and as will be detailed in more detail below, productivity is also increased by the advantage that a mold of the invention can be used at lower temperatures than those of prior art methods, which shortens the duration of the heating steps.

[0028] In the application, and unless otherwise stated, when a direction is said to be “substantially vertical”, “substantially horizontal” or “substantially aligned with ...”, it should be understood that the disorientation between the direction considered and the reference direction is less than or equal to 45°, or even less than or equal to 20°. Thus, a “substantially horizontal” direction may present with a horizontal direction a disorientation of between -45° and +45° preferably, or even between -20° and +20°, and the same applies to a “substantially vertical” direction, or a direction substantially aligned with another.

[0029] As described above, the molding cavity is entirely comprised between the axis of rotation and the feed arm. It is therefore understood that, in any projection of the mold in a plane comprising the axis of rotation, the molding cavity is projected between the axis of rotation and the feed arm.

[0030] Another geometric way to verify this condition is to verify that the cavity molding is entirely included in the envelope obtained by rotating the feed arm around the rotation axis.

[0031] The arrangement of the molding cavity between the axis of rotation of the mold and the feed arm geometrically ensures that the work of the centrifugal force on the metal wishing to enter the molding cavity from the feed arm is negative, when the mold is rotated around the axis of rotation.

[0032] In one embodiment, molten metal can only be fed into the molding cavity through openings between the feed arm and the molding cavity.

[0033] In one embodiment, the mold further comprises:

[0034] - a feed channel extending along the axis of rotation between an opening main, intended to allow the supply of molten metal to the feed channel, and a transverse arm;

[0035] - a transverse arm, extending along a second substantially horizontal axis, the cross arm being connected to the feed channel and the feed arm.

[0036] The assembly formed by the feed channel, the transverse arm and the feed arm makes it possible to propose a relatively simple mold architecture, in which the metal is fed from the middle of the mold while ensuring that the filling of the molding cavity is carried out by ensuring negative work from the centrifugal force.

[0037] The foundry mold of the invention is not limited by the position of the transverse arm relative to the molding cavity. Several embodiments are possible for the mold of the invention, some of which will be described below in connection with the figures.

[0038] According to a first alternative, the transverse arm can be arranged above the molding cavity.

[0039] This embodiment makes it possible to shorten the feed channel as will be explained below in connection with the figures. In particular, a feed channel thus shortened makes it possible to place the molding cavity very close to the axis of rotation of the mold, which makes it possible to limit the size of the mold in the transverse direction. In addition, this makes it possible to reduce the mass of metal to be used during a process of the invention.

[0040] According to a second alternative, the transverse arm is arranged below the cavity.

[0041] In this embodiment, the cast metal must rise up the feed arm before entering the molding cavity, since the latter is then arranged above the transverse arm.

[0042] In a mold according to this alternative, it has nevertheless been found that the cast metal very quickly clogs the molding cavity and the transverse arm. The cast metal in gorging these elements then allows sufficient force to be exerted so that the cast metal can rise in the feed arm despite the negative work of the force of gravity and then enter the cavity despite the negative work of the centrifugal force. In fact, the metal is forced into the cavity by the engorged metal and advances in the transverse arm under the effect of centrifugation.

[0043] Note here that, generally in this description and unless otherwise stated, the work of the force of gravity is relatively small compared to the work of the centrifugal force. Note also that the work of the force of gravity is neglected in the horizontal elements, as is the work of the centrifugal force in the vertical elements, except for the description of the collar which will be given below, and whose technical effect is linked to the effect of the centrifugal force on the metal in the feed channel.

[0044] This arrangement therefore makes it possible to slow down the molten metal even further before it enters the molding cavity, compared to an embodiment according to the first alternative.

[0045] Slowing down the molten metal and clogging the molding cavities allows for a more homogeneous metal progression front and therefore a final part with even fewer crystalline defects.

[0046] In particular, this embodiment makes it possible to avoid any projection of metal in front of the filling front in the feed arm and in the molding cavity, which avoids the appearance of defects such as cold drops. In addition, this embodiment makes it possible to ensure more homogeneous heat exchanges at the end of filling, which avoids shrinkage defects as well as the appearance of mechanical stresses.

[0047] In one embodiment, the mold further comprises a retention arm, substantially parallel to the feed arm positioned between the axis of rotation and the molding cavity.

[0048] In this embodiment, the retention arm allows on the one hand to play a role of weight during solidification, and allows to have a solidification front which starts from the center of the cavities and goes towards the retention and feed arms; and on the other hand to exert an overall compressive force during cooling and avoid the stresses and the associated crystalline defects.

[0049] In an embodiment where a feed channel is further present, the retention arm is then disposed between the feed channel and the molding cavity.

[0050] It is important, however, that there is no direct fluid communication between the feed channel and the molding cavity, i.e., it is not possible for cast metal to pass from the feed channel to the retention arm without first passing through the feed arm and then the molding cavity. This ensures that the casting cavity is supplied with molten metal on which the centrifugal force exerts negative work.

[0051] In one embodiment, the feed arm extends along an axis, called the feed axis, which has a disorientation with the vertical direction of less than or equal to 20°.

[0052] The disorientation of the feed axis with respect to the vertical direction, that is to say also with respect to the axis of rotation, makes it possible to arrange the molding cavity obliquely, and thus to increase the space available between the axis of rotation and the feed axis without having to increase the spacing between these two axes accordingly. This makes it possible to reduce the radial size of the mold.

[0053] In one embodiment, the invention relates to a foundry mold for centrifugal casting of a molten metal by rotating the mold around a vertical axis of rotation, said mold comprising at least:

[0054] - a feed channel extending along the axis of rotation, between an opening main, intended to allow the supply of molten metal to the feed channel, and a transverse arm;

[0055] - a transverse arm, extending along a second substantially horizontal axis, the cross arm being connected to the feed channel and the feed arm;

[0056] - a feed arm, connected to the transverse arm and to at least one cavity of molding ;

[0057] - at least one molding cavity extending between the feed arm and an arm retention;

[0058] - a retention arm, parallel to the feed arm, the retention arm being connected to the at least one molding cavity,

[0059] the mold being characterized in that each molding cavity is entirely comprised between the axis of rotation and the axis of the feed arm, each cavity being connected on the one hand with the feed arm and on the other hand with the retention arm.

[0060] In an embodiment in which the mold comprises a feed channel and a transverse arm, the largest dimension of the molding cavity defines, in a plane perpendicular to the axis of rotation, a disorientation relative to the second axis less than or equal to 45°.

[0061] In this embodiment, the largest dimension of the molding cavity is therefore not aligned with the transverse arm.

[0062] In the application, "the largest dimension of the molding cavity" is understood as the length of the largest straight line segment that can be inscribed in said molding cavity.

[0063] This embodiment makes it possible to place larger molding cavities in the mold. large, without increasing the length of the transverse arm, and therefore without increasing the largest dimension of the mold.

[0064] The “largest dimension of the mold” can be understood as the diameter of the envelope obtained by rotating the feed arm around the axis of rotation. By construction, all the parts of the mold intended to be fed with metal are included in this envelope.

[0065] In one embodiment, the feed channel comprises a cylindrical body and a flange extending in a direction substantially perpendicular to the diameter of the cylindrical body.

[0066] A collar is understood here as an annular hollow space, arranged around the feed channel and open onto the latter, the collar having a diameter greater than the diameter of the feed channel, for example at least one and a half times larger, or even twice as large, or even three times as large, than the diameter of the feed channel.

[0067] The presence of a collar in the feed channel makes it possible to trap any metal projections created in the feed channel by the molten metal or to trap the liquid metal which, in contact with the walls of the feed channel and under the effect of centrifugal force, can rise along the walls of the feed channel and be expelled outside the mold.

[0068] In one embodiment, the collar may have an angle α with the horizontal direction of between 0° and 20°.

[0069] Such an orientation of the collar allows better capture of any projections of rising metal, without metal being able to remain in the collars at the end of the process, the latter descending into the feed channel by gravity due to the inclination of the collar. This results in less loss of metal once the mold is completely filled.

[0070] In one embodiment, the molding cavity has the shape of a turbomachine blade.

[0071] In an embodiment where the molding cavity has the shape of a blade, and where the largest dimension of the molding cavity defines, in a plane perpendicular to the axis of rotation, a disorientation relative to the direction of the transverse arm less than or equal to 45°, the part of the molding cavity defining the trailing edge of the turbomachine blade is further from the axis of rotation than the part of the molding cavity defining the leading edge of the turbomachine blade.

[0072] Generally, the trailing edge is thinner than the leading edge for aerodynamic reasons. When the mold cavity is arranged with the indicated misorientation, the centrifugal force is not perfectly aligned with the mold cavity. By choosing to arrange the trailing edge further from the axis of rotation than the leading edge, which will be called the outer edge of the molding cavity, we ensure that the centrifugal force allows a preferred filling of the part of the molding cavity corresponding to the trailing edge. It has been found that this allows a better obtaining of the finest shapes of the blade, and generally a smaller number of non-conforming parts. Indeed, the filling of the thin parts of the molding cavities can be a significant source of defects on the final parts obtained by centrifugal molding, in particular non-metal parts.

[0073] The reasoning developed here applies to any form of molding cavity having a thin part and a thick part, and it will then always be preferable to arrange the thinner part of the molding cavity further from the axis of rotation than the thicker part.

[0074] In an embodiment in which the cavity has a thinner portion and a thicker portion, it may be preferred to arrange the thin portion of the cavity so that the thin portion leads the way when the mold is rotated. It may also be said that the thin portion of the molding cavity is ahead in the direction of rotation relative to the thick portion. In other words, the thinner portion of the molding cavity is arranged so that it passes first at a given point when the mold is rotated.

[0075] This arrangement of the thinner part of the molding cavity, compared to the thicker part, ensures that the Coriolis force exerted by the rotation drives the metal into the thinner part of the molding cavity.

[0076] Thus, the thinnest part of the molding cavity fills more easily than the thickest part, and again, it has been found that this allows for better obtaining of the finest shapes of the blade, and generally a smaller number of non-conforming parts. Indeed, the filling of the thin parts of the molding cavities can be a significant source of defects on the final parts obtained by centrifugal molding.

[0077] The "Coriolis force" is understood in the sense that it has in the field of general physics, that is to say as an inertial force (or fictitious, because resulting from the non-linear movement of the frame of reference) acting perpendicular to the direction of movement of a body moving in a medium itself in uniform rotation. The value of this force is not important in the present invention, only its presence and direction will be important in certain embodiments.

[0078] In one embodiment, and in particular when the molding cavity comprises a thin portion and a thick portion, it is possible to benefit from the two technical advantages described above by arranging the cavity so that the thin portion of the cavity is on the front edge of the cavity, and that this front edge is also the outer edge with respect to the disorientation of the cavity in a plane perpendicular to the axis of rotation, and relative to the direction of the transverse arm.

[0079] In this way, both the Coriolis force and the centrifugal force ensure that the thin part of the molding cavity is filled first, which reduces the number of non-conforming parts by ensuring good filling of the thin parts of the molding cavity.

[0080] In one embodiment, the mold further comprises a filter element between the feed arm and the mold cavity.

[0081] Such a filter element makes it possible, for example, to retain oxides or inclusions which may be created during the path of the molten metal in the feed arm or, where appropriate, the entire path taken. Also, a filter element arranged at the entrance to the molding cavity makes it possible to ensure that the filling of the molding cavity is carried out in a non-turbulent regime, which further limits the risk of creating defects in the molding cavity.

[0082] In one embodiment, the filter element may be a ceramic filter.

[0083] In one embodiment, the described mold may also comprise ra- disseurs.

[0084] Stiffeners are elements that are not passed through by the molten metal, and which are intended to ensure the mechanical integrity of the mold. For example, stiffeners can be placed between an element external to the mold and an element of the mold or between two elements of the mold.

[0085] In one embodiment, a stiffener may be placed between the feed channel and the retention arm, between the feed arm and the retention arm, between the feed channel and the mold cavity, between the mold cavity and the feed arm.

[0086] In one embodiment, the stiffeners may be composed of a ceramic material.

[0087] Although it has been described in an embodiment facilitating its understanding, the invention is not limited by the number of cavities included in the mold.

[0088] In one embodiment, the mold may comprise, for each feed arm, a plurality of molding cavities, each molding cavity being connected to the feed arm and extending between said feed arm and the axis of rotation.

[0089] The molding cavities connected to the same feed arm can be aligned in the same plane, for example a vertical plane.

[0090] In one embodiment, a mold of the invention may comprise one or more repetitions of the mold parts already described arranged radially about the axis of rotation. That is, a mold of the invention may exhibit rotational invariance about the axis of rotation.

[0091] This embodiment is particularly advantageous because it allows a greater number of cavities to be provided for the same mold footprint. Furthermore, the effects of the invention are obtained for each of the molding cavities present in the mold, without requiring review of the molding process parameters, in particular the temperatures and / or the rotation speed.

[0092] For example, a mold of the invention may comprise 2, 3, 4, or even 5 or even 6 repetitions of an assembly comprising a transverse arm, a feed arm, at least one molding cavity and a retention arm, the mold further comprising a single common feed channel.

[0093] According to another of its aspects, the invention relates to a method of casting a metal part by centrifugal casting comprising: - a step of heating a mold as described above to a temperature Tl; - a step of feeding the mold with molten metal at a temperature T2, so that the difference T2-T1 is less than or equal to 350°C; and - rotating the mold around the rotation axis.

[0094] For the proper implementation of the invention, the metal must be melted at temperature T2, and the latter is therefore higher than the melting temperature of the metal, or the liquidus temperature in the case of a metal alloy.

[0095] For example, the temperature T2 may be more than 20°C higher or equal, or even more than 40°C higher than the melting temperature of the molten metal, or the liquidus temperature in the case of an alloy.

[0096] In one embodiment of the method, the temperature difference T2-T1 may be between 300°C and 150°C, or even between 250°C and 200°C.

[0097] It should be noted that these temperature differences between the molten metal and the mold are much greater than the temperature differences permitted by the casting processes of the prior art. This results, on the one hand, in a considerable gain in terms of energy and a simplification of the industrial process. Indeed, for the casting of the same alloy, it is no longer necessary to heat the furnace as much as with a process of the prior art.

[0098] Furthermore, since the heating temperature T1 of the mold is lower than in the methods of the prior art, the method allows a saving of time, thanks to a reduction in the heating and cooling cycle times.

[0099] Also, since the permissible temperature difference between the mold and the cast metal is greater, the method of the invention allows the molding of metals inaccessible to molds of the prior art.

[0100] In one embodiment, the molten metal may be a titanium aluminide.

[0101] In such an embodiment, the temperature T2 may be 1550°C and the temperature T1 greater than or equal to 1200°C.

[0102] In other embodiments, the molten metal may be selected from a nickel-based superalloy.

[0103] In such an embodiment, the temperature T2 may be 1450°C and the temperature T1 greater than or equal to 1150°C, for example between 1150°C and 1200°C.

[0104] In one embodiment, the step of feeding the mold with the molten metal can be carried out in air at atmospheric pressure.

[0105] This embodiment allows a simplification of the methods of the prior art, some of which need to be carried out under vacuum.

[0106] In another embodiment, the step of feeding the mold with the molten metal can be carried out under vacuum, for example at a pressure less than or equal to 0.1 Pa.

[0107] In one embodiment, the method further comprises a controlled cooling step to a temperature T3, for example between 700°C and 900°C, then air cooling.

[0108] For example, the cooling during the controlled cooling step may be less than or equal to 7°C / min.

[0109] This upper limit to the cooling rate also makes it possible to limit the forces exerted on the metal by the difference in thermal contraction between the mold and the cooling metal.

[0110] In one embodiment, the foundry method may comprise a step of demoulding, i.e. destruction of the mold in order to obtain the desired part.

[0111] For example, the mold can be detached mechanically. Brief description of the drawings

[0112] [Fig-1] [Fig. 1] schematically represents a mold in one embodiment of the invention.

[0113] [Fig.2] [Fig.2] schematically represents a mold in one embodiment of the invention.

[0114] [Fig.3] [Fig.3] schematically represents a mold in one embodiment of the invention.

[0115] [Fig.4] [Fig.4] schematically represents a mold in one embodiment of the invention.

[0116] [Fig.5] [Fig.5] schematically represents a mold in one embodiment of the invention.

[0117] [Fig.6] [Fig.6] schematically represents a feed channel of a mold in one embodiment of the invention.

[0118] [Fig.7] [Fig.7] schematically represents a feed channel of a mold in one embodiment of the invention. Description of the embodiments

[0119] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0120] [Fig.l] schematically represents a mold 10 according to the invention.

[0121] Such a mold 10 comprises:

[0122] - a supply channel 11 extending along the vertical axis of rotation 101, extending between a main opening 21, intended to allow the supply of molten metal to the supply channel, and a transverse arm 12;

[0123] - a transverse arm 12, extending along a second axis 102 substantially ho rizontal, the transverse arm 12 being connected to the feed channel 11 and to the feed arm 13;

[0124] - a feed arm 13, extending along an axis 103 called the “feed axis”, the feed arm 13 being connected to the transverse arm 12 and to at least one molding cavity 14, here three are shown;

[0125] - three molding cavities 14 extending between the feed arm 13 and a feed arm 14. retention 15;

[0126] - a retention arm 15, parallel to the feed arm 13, the retention arm 15 being connected to said molding cavities 14.

[0127] In this mold 10, the molding cavity 14 is entirely comprised between the rotation axis 101 and the feed axis 103 and each molding cavity is connected to the feed arm 13 and to the retention arm 15 via the openings 22.

[0128] Furthermore, in this embodiment, the transverse arm 12 of the mold 10 is present below the molding cavities 14.

[0129] The mold 10 shown in [Fig.l] further comprises a feed cup 23 allowing easier feeding of the feed channel 11 with molten metal, via the main opening 21.

[0130] Also, the mold 10 comprises in the embodiment shown stiffeners 16 between the feed channel 11 and the retention arm 15 or between the retention arm 15 and the arm 13.

[0131] In [Fig.l], the molten metal path is represented by arrows, and, as shown, the molten metal passes successively through the main opening 21, the feed channel 11, the transverse arm 12, the feed arm 13 before entering the cavities 14 through the openings 22, and exiting through the openings connected to the retention arm 15.

[0132] In [Fig.l] is also shown the centrifugal force applied when the mold 10 is rotated co around the axis of rotation 101.

[0133] Along this path, the centrifugal force Fc works positively for metal passing through the transverse arm 12, because the displacement of a metal element takes place in the same direction as that of said centrifugal force Fc.

[0134] On the other hand, when the metal wishes to enter the molding cavity 14 from the feed arm, the centrifugal force Fc then works negatively. In other words, it opposes the entry of the metal into the molding cavity 14. Nevertheless, and for the reasons already explained above, the negative work of this centrifugal force on the metal entering the molding cavity makes it possible to obtain a part comprising fewer defects than a part obtained with a mold of the prior art, in which the centrifugal force works positively.

[0135] Indeed, the molten metal, which clogs the feed arm, exerts sufficient force on the metal located at the opening 22 of the molding cavity 14, despite the centrifugal force Fc.

[0136] In [Fig. 1], it can also be noted that the force of gravity Fg, also called simply “gravity”, is applied along the Z axis, and downwards, that is to say in the -Z direction. Thus, in [Fig.l], gravity works positively on the metal going down the feed channel 11, but negatively on the metal wishing to go back up along the feed arm 13.

[0137] As described above, it is advantageous for the force of gravity to work negatively on the metal filling the feed arm 13 since this allows a more homogeneous metal progression front, and in particular avoids any projection of metal in front of the filling front.

[0138] [Fig.2] describes an alternative embodiment for a mold 10 of the invention.

[0139] In this alternative mode, the transverse arm 12 of the mold 10 is present above the molding cavities 14. This results in a feed channel 11 whose dimension can be greatly reduced. This also makes it possible to arrange the retention arm 15 much closer to the axis of rotation 101, which limits the overall size of the mold.

[0140] Indeed, for molding cavities of identical sizes, since the latter can be brought closer to the axis of rotation 101, the transverse arm 12 can be shortened.

[0141] In the embodiment shown, stiffeners 16 make it possible to structurally reinforce the mold, without of course preventing it from rotating co around the axis of rotation 101.

[0142] [Fig. 3] represents a mold 10 of the invention which is still different.

[0143] On the mold 10 of [Fig. 3], the feed arm 13 extends along a feed axis 103 which has a disorientation y relative to the direction vertical, marked by segment 301.

[0144] In the mold 10 of [Fig. 3], we also see that the disorientation y of the feed arm relative to the vertical is reproduced between the molding cavity 14 and the horizontal direction, marked by the line 302.

[0145] This inclination y of the molding cavity makes it possible to increase the maximum size of the cavities Lmax, separating the feed arm 13 and the feed channel 11 without needing to lengthen the transverse arm 12, and therefore increasing very little the size of the mold 10 as a whole.

[0146] The additional bulk in height, due to the disorientation introduced there, may be preferable to additional bulk in the radial X direction for industrial processes, and in particular for reasons of homogeneity of the heating obtained in the furnaces.

[0147] Indeed, conventionally, industrial heating furnaces have heating elements arranged circumferentially to the substantially cylindrical heating chamber. Such furnaces guarantee better uniformity of heating in the vertical direction than in the radial direction, and this is why it is generally preferred not to increase the radial dimensions of industrial furnaces.

[0148] An optimum between space saving and homogeneity of cavity filling seems to be achieved for an angle y of 20°, and this is why in one embodiment y is between 0° and 20°, preferably between 10° and 20°.

[0149] Indeed, with a disorientation along an angle y that is too large, the centrifugal force could have a component along a vertical axis which destabilizes the movement of the molten metal that one wishes to preserve globally along the axis of the cavity 104.

[0150] The mold 10 of [Fig.4] still presents an alternative to the geometry of the mold 10 of [Fig.l], making it possible to increase the size of the molding cavities 14, without increasing the overall size of the mold. On the mold 10 of [Fig.4], the mold is shown seen "from above", that is to say that the Z direction is now perpendicular to the plane of the sheet.

[0151] The mold 10 of [Fig.4] is shown in a plane perpendicular to the axis of rotation 101, and in this plane, the largest dimension of the molding cavity, extending along the axis 105, has a disorientation δ relative to the second axis 102 along which the transverse arm 12 extends.

[0152] This embodiment makes it possible on the one hand to lengthen the molding cavities 14, without increasing the length of the transverse arm 12, and consequently, without increasing the largest dimension of the mold.

[0153] This has the same advantages as above, namely allowing larger molding cavities 14, without having to lengthen the size of the furnaces, and therefore without adding an additional constraint on the homogeneity of the heating delivered by the oven.

[0154] In the embodiment of [Fig.4], since the molding cavity is offset relative to the second axis 102, the centrifugal force Fc is therefore not aligned in the main direction of the molding cavity 14, i.e. along the axis 105.

[0155] Due to this disorientation δ, the cast metal filling the molding cavity 14 will be pressed, by the positive component of the centrifugal force Fc towards the outer edge 51 of the molding cavity 14. The outer edge 51 of the molding cavity is understood as the edge of the cavity 14 furthest from the axis of rotation.

[0156] Nevertheless, in an embodiment where the molding cavity has a thinner portion than another in the main direction 105 of the molding cavity 14, it is advantageous to arrange the thinnest portion of the molding cavity 14 on the side of the outer edge 51, and the thickest portion towards the inner edge 52 of the molding cavity 14. The inner edge 52 is understood to be the edge of the molding cavity 14 furthest from the axis of rotation. By construction, the inner 52 and outer 51 edges are arranged on either side of the molding cavity 14.

[0157] For example, in the case where the molding cavity 14 has the shape of a turbine blade, it is preferable for the trailing edge of this blade, thinner than the leading edge for known hydrodynamic reasons, to be positioned on the side of the outer edge 51 of the molding cavity 14.

[0158] As described above, it is in fact preferable for the thinnest parts of the molding cavity 14 to be filled first during the propagation of the filling front, in order to avoid material not coming in, and therefore to reduce the number of defects in the part finally obtained.

[0159] In this embodiment where the mold 10 has molding cavities 14 having a disorientation δ, the inventors have not observed any degradation of the parts even for disorientations δ of 45°. In one embodiment the disorientation δ is between 0° and 45°, or even between 10° and 45°, or even 25° and 45°.

[0160] The closer the disorientation δ is to 45°, the more the length of the molding cavity 14 can be increased for a given length of the transverse arm 12.

[0161] In the embodiments already described, it should also be noted that increasing the length of the molding cavities, without increasing the length of the transverse arm 12 makes it possible to reduce the quantity of metal to be used for the complete filling of a mold 10, which can represent a substantial gain at the end of the molding process.

[0162] The embodiments described above are not incompatible with each other, and an embodiment in which the molding cavities 14 have several non-zero disorientations δ and γ, and conforming to the values ​​described above, must be considered covered by the invention. This allows the joint obtaining of the different technical effects described for the different embodiments.

[0163] The mold shown in [Fig.4] further has stiffeners 16, arranged between the feed channel 11 and the retention arm 15, between the feed channel 11 and the molding cavities 14 and between the retention arm 15 and the feed arm 13.

[0164] These stiffeners 16 ensure the mechanical integrity of the mold 10, in particular when the latter is rotated.

[0165] [Fig.5] shows a mold 10 of the invention in another embodiment.

[0166] As described above, a mold 10 of the invention may comprise several re petitions of an assembly comprising a transverse arm 12, a feed arm 13, at least one molding cavity 14, the mold further comprising a single common feed channel 11.

[0167] [Fig.5] represents such a mold having four repetitions of this set, and therefore proposes a mold having an invariance by rotation of 90° around the axis of rotation 101.

[0168] All of the characteristics described above can be taken in association with this embodiment. In particular, the molding cavities 14 of the different assemblies are not necessarily strictly identical and / or the latter can be oriented according to the needs of the parts to be produced.

[0169] [Fig.5] also illustrates an embodiment applicable to molds already described.

[0170] In [Fig.5] is represented the Coriolis force Fcor, generated when the mold is rotated co around its axis of rotation 101.

[0171] The Coriolis force exerts a force on the metal entering the molding cavity 14 from the feed arm 13.

[0172] If we do not consider the Coriolis force Fcor, the path of the metal would be represented by the arrow 401, in this case aligned with the axis 102 which is also here the main axis of the molding cavity and the transverse arm 12.

[0173] Nevertheless, due to the Coriolis force Fcor, the actual path of the metal in the cavity is represented by the arrow 402. Thus, the metal is pressed by the Coriolis force Fcor against the front edge 41 of the molding cavity 14. The front edge 41 of the mold is understood as the edge opening the step when the mold is rotated.

[0174] For the same reasons as those described in connection with [Fig. 4], it is advantageous, when the molding cavity 14 has areas that are thinner than others, to arrange the thinner areas on the side of the front edge 41, and to arrange the thicker areas on the side of the rear edge 42. In contrast to the front edge 41, the rear edge 42 is the edge of the cavity closing the step when the mold is rotated. In this way, the cast metal entering the molding cavity 14 preferentially fills the thin areas of the molding cavity 14, which reduces the number of non-conforming parts.

[0175] In one embodiment, it is possible to arrange the thin portion of the cavity so that it is both on the outer edge 51 and on the front edge 41.

[0176] This embodiment is most preferable because it ensures excellent filling of the thinnest portion of the mold cavity 14, since both centrifugal force and Coriolis force ensure preferential filling of the thinnest portion of the mold cavity.

[0177] However, it should be noted that this embodiment of the mold construction then imposes a choice for the direction of rotation of the mold. Indeed, the Coriolis force depends on the direction of rotation. Figures 6 and 7 show different alternative geometries of an introduction channel of a mold 10 described above.

[0178] In the embodiment described in [Fig.6], the feed channel 11 has, in addition to a feed bucket 23 and the opening 21, a collar perpendicular to the axis of rotation 101.

[0179] This collar has a section SI greater than the section of the rest of the supply channel 11.

[0180] Such a collar makes it possible to avoid metal projections possibly generated when the mold is rotated in the feed channel 11.

[0181] The use of such a collar makes it possible to use a feed channel 11 whose section is constant from top to bottom, which allows a potentially quite substantial saving on the quantity of metal to be introduced into the mold to ensure its filling.

[0182] Indeed, for feed channels not having such a collar, and to overcome the same disadvantages, a feed channel of variable section is generally proposed, which requires introducing more metal so that the latter reaches the molding cavities.

[0183] The embodiment of [Fig.7] proposes an improvement of the collar of [Fig.6]. The collar is again understood as the area whose section SI is greater than the section of the rest of the supply channel 11. As described in [Fig.7], the main direction of the collar 202 has a disorientation a relative to the horizontal 201.

[0184] Unlike the collar of [Fig.6], this embodiment ensures that the metal projections caught in the collar can subsequently fall back into the introduction channel 11, and thus the quantity of metal retained in the collars at the end of the process is reduced and also allows more effective “trapping” of any projections.

[0185] The nature of the molds 10 described above is not limiting of the invention, provided that it allows the latter to be filled with molten metal.

[0186] Similarly, the method of obtaining the molds is not limiting, and the latter can for example be obtained by means of processes already described, in particular by a successive process of dipping in a slip and sprinkling with refractory sand, as disclosed for example in patents FR 2870147 and FR 2870148.

[0187] As described above, the invention also relates to a method for obtaining a metal part.

[0188] As described above, the particular geometry of a mold 10 of the invention makes it possible to obtain parts of satisfactory quality without requiring casting with molds at temperatures as high as in the prior art.

[0189] In one embodiment, once casting has been completed, the mold may be placed in an oven to perform controlled cooling.

[0190] The mold may still be maintained in the furnace during a first step of cooling and solidification of the metal in the mold, in which the cooling rate of the furnace may be controlled and limited, for example, to a rate less than or equal to 7°C / min. This upper limit to the cooling rate also makes it possible to limit the forces exerted on the metal by the difference in thermal contraction between the mold and the cooling metal. However, the thermal contraction of the metal, greater than that of the refractory walls of the mold, will cause buckling of the metal in the feed arms. This buckling will exert a compressive stress on the metal in the molding cavities, so as to at least partially balance the tensile stresses caused by the thermal contraction of the metal in the molding cavities.This avoids concentrations of stress that could disrupt the crystallization of the metal and create weak points in the parts produced by this foundry process.

[0191] During this cooling and solidification step, the liquid metal solidifies in the mold 10 and in particular in the molding cavity 14.

[0192] To avoid shrinkage defects, the Heuvers circle method can be applied, as described, for example, by R. Wlodawer in “Directional Solidification of Steel Castings”, Pergamon Press, 1966.

[0193] For example, the mold 10 may be chosen such that the area of ​​any cross-section of the feed arm and the retention arm, perpendicular to the feed axis or the retention arm axis, is greater than the area of ​​any cross-section of the mold cavities, perpendicular to the main axis of the mold cavity. Furthermore, the most massive portion of each mold cavity may have a cross-section with an area, perpendicular to the horizontal axis X, greater than the area of ​​any cross-section of the corresponding mold cavity, perpendicular to the mold cavity axis 104, but less than the area of ​​any cross-section of the feed arm and the retention arm perpendicular to the feed axis.

[0194] Furthermore, each of the feed arm and the retention arm may have cross-sections with increasing area upwards along the feed axis, or the axis of the retention arm.

[0195] For this purpose, in a mold 10, the feed arm 13 and / or the retention arm 15 may have a divergence angle of between 5 and 15°. The divergence angle is understood as the angle between the opposite edges of the feed arm 13 and / or retention arm 15. Thus, the solidification of the metal which is triggered within each molding cavity 14, where the cross-section is narrowest, will be able to extend to the feed arm 13 and / or the retention arm 15 with two opposite and ever wider solidification fronts, thus avoiding shrinkage defects which may be caused by constrictions in the cavities of the mold 14.

Claims

Claims

1. Foundry mold (10) for centrifugal casting of a molten metal by rotating the mold about a vertical axis of rotation (101), said mold comprising at least: - a molding cavity (14); - a feed arm (13) of the molding cavity in fluid communication with the molding cavity by means of an opening (22); the mold being characterized in that the molding cavity is arranged between the feed arm of the molding cavity and the axis of rotation, the mold further comprising: - a feed channel (11) extending along the axis of rotation (101) between a main opening (21), intended to allow the feed channel to be fed with molten metal, and a transverse arm (12); - a transverse arm, extending along a second substantially horizontal axis (102), the transverse arm being connected to the feed channel and to the feed arm (13);and wherein the largest dimension of the molding cavity (14) defines, in a plane perpendicular to the axis of rotation (101), a disorientation (δ) relative to the axis of the transverse arm less than or equal to 45°.;

2. A foundry mold (10) according to claim 1, further comprising a retention arm (15), substantially parallel to the feed arm (13) positioned between the rotation axis (101) and the molding cavity.

3. Foundry mold (10) according to claim 1 or 2, in which the feed arm (13) extends along an axis (103) and which has a disorientation (y) with the vertical direction less than or equal to 20°.

4. A foundry mold (10) according to claim 1 to 3, wherein the feed channel (11) comprises a cylindrical body and a flange extending in a direction substantially perpendicular to the cylindrical body.

5. A foundry mold (10) according to any one of claims 1 to 4, wherein the molding cavity (14) has the shape of a turbomachine blade.

6. A foundry mold (10) according to claim 5, wherein the portion of the mold cavity (14) defining the trailing edge of the turbine blade is further from the axis of rotation than the portion of the mold cavity defining the leading edge of the turbine blade. bomachine.

7. A foundry mold (10) according to one of claims 1 to 6, further comprising a filter element between the feed arm (13) and the molding cavity (14).

8. Method for casting a metal part by centrifugal casting comprising at least: - a step of heating a mold (10) according to any one of claims 1 to 7 to a temperature T1; - a step of feeding the mold with a molten metal at a temperature T2, so that the difference T2-T1 is less than or equal to 350°C; and - rotating the mold, around the axis of rotation (101).

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