EP3099438B1 - Lined mould for centrifugal casting - Google Patents

Description

The present invention relates to a mold for manufacturing by centrifugal casting of metal parts, in particular turbomachine blades. More specifically, the turbine wheel vanes of a turbojet or an airplane turbo-prop.

It is known to make turbomachine blades by machining a blank obtained by casting by casting of a metal alloy. The blank is typically a rod of generally elongated solid shape and is machined in the mass to achieve the final geometry of the blades.

• plusieurs chemises, chacune définissant un logement de réception de l'alliage s'étendant radialement autour dudit axe (A)
• au moins un exosquelette dans lequel sont disposées les chemises, ledit au moins un exosquelette retenant ces chemises vis-à-vis d'une force centrifuge.

One of the techniques of obtaining the sketch consists, as in EP992305 using a rotatable mold about an axis (A), for the centrifugal casting, of an alloy, the mold comprising:

• a plurality of sleeves, each defining a housing for receiving the alloy extending radially about said axis (A)
• at least one exoskeleton in which the jackets are disposed, said at least one exoskeleton retaining these jackets with respect to a centrifugal force.

A (first) problem to be solved concerns the control of the cooling rate to promote the production of a controlled microstructure, such as a level of homogeneous aluminum in the part, especially if the alloy is based on TiAl.

Concerning the manufacture by bar casting in a centrifuged permanent mold, it is furthermore noted that the casting conditions lead to a second problem, namely, the rapid wear of the molds, which necessitates changing them often, which is expensive and impacts the manufacturing conditions, including the rates. This also has an impact on the shapes given to the molds, and thus to the molded parts.

The present invention overcomes at least some of the aforementioned drawbacks simply, efficiently and economically.

For this purpose, it proposes that, transversely to the radial direction (B) according to which each liner extends, a space exists peripherally between said liner and the surrounding exoskeleton.

Thus, not only will we be able to dissociate the physical characteristics of the exoskeleton or physical characteristics of the shirts which may in particular be thin and / or in a material different from that of the exoskeleton (s), but also favorably manage the thermal inertia , in order to promote a homogeneous cooling of the shape of the cast alloy. Providing that the space between said jacket and the exoskeleton is defined within a peregrely extending cellular structure between each liner and the exoskeleton surrounding it will typically allow for the above two goals, including by this box structure, to promote the desired resistance to mechanical forces, and in particular the retention of shirts during centrifugation.

Achieving the open-skeleton exoskeleton (s) will also promote this mechanical resistance to efforts related to centrifugation. There is also an advantage vis-à-vis the thermal inertia which will then be lower than if the same (s) exoskeleton (s) were (in) t solid wall.

• une fixation, qui peut être amovible, sera établie entre chaque chemise et l'exosquelette qui l'entoure et/ou,
• le moule comprendra un bloc central présentant des conduits par lesquels l'alliage coulera et qui communiqueront avec l'intérieur des chemises, une fixation amovible étant alors établie entre chaque chemise et/ou l'exosquelette qui l'entoure et le bloc central.

Moreover, and preferably:

• a fastener, which may be removable, will be established between each folder and the surrounding exoskeleton and / or,
• the mold will comprise a central block having conduits through which the alloy will flow and which will communicate with the interior of the shirts, a removable attachment being then established between each sleeve and / or the surrounding exoskeleton and the central block.

Thus, especially when wear demand, we can ensure a replacement of the shirts (for example every 25 castings), while ensuring the maintenance of these shirts meanwhile.

The shirts can be changed at a lower cost, while the rest of the mold structure, particularly the exoskeleton (s), can be preserved.

In this context, it is therefore recommended that the exoskeleton (s) and the shirts be designed so that the mold is permanent, the shirts thus having to hold several castings in succession (for example approximately 25).

Concerning again the control of the thermal inertia allowing a homogeneous cooling of the metal form resulting from the mold, and in particular a mastery of the cooling rate, essential to obtain a homogeneous aluminum content in a piece of metal alloy to TiAl base and thus a mastered microstructure, it is further recommended that the mold jackets be made of steel, metal alloy and / or ceramic, and are therefore suitable for spinning centrifugally molten TiAl alloy .

It is also recommended that at least one thermally insulating structure extends peripherally between each liner and the surrounding exoskeleton.

Thus the or each exoskeleton may have a very simple shape, not or little worked for this desired control of thermal inertia, and all the more so if said thermally insulating structure is alveolar. Note also that such a solution, by its structure in boxes, typically will promote the resistance to mechanical forces, and in particular the retention of shirts during centrifugation.

Such is, moreover, an expected effect if, as recommended, the jacket in question and the honeycomb structure, which includes walls separating cavities, bear against each other or are joined by discrete zones, this being by elsewhere beneficial to a control of the thermal inertia.

It is possible to obtain a good mechanical strength, by transfer of forces via said cavity separation walls, but also if necessary to insure a thermal insulation of the jacket vis-à-vis the exoskeleton (s) via a suitable material and shapes ( s).

To further promote this resistance to efforts, it is recommended that the structure in question defines at least part of said centering means which therefore position the shirt in relation to the exoskeleton.

Furthermore, to further favor the replacement of the shirts in terms of ease of handling and / or time and costs, the modular nature of the molds will be favored, so that the jacket, the honeycomb and / or thermally insulating structure surrounding it and the exoskeleton surrounding said structure are three separable elements between them, the jacket and the thermally insulating structure being engaged in the exoskeleton, concentrically.
Including to encourage the taking into account of the questions of: control on the one hand of the efforts and on the other hand of the thermal stresses, it is furthermore proposed
that individually the jackets having an inner surface which delimits the / a central casting duct of the alloy,
a radially outer end portion of this conduit is supported.

• la figure 1 est une vue schématique de face d'un barreau cylindrique plein de la technique antérieure, dans lequel sont destinées à être usinées des aubes de turbomachine,
• la figure 2 est une vue schématique d'un moule de la technique antérieure,
• la figure 3 est une vue schématique de dessus d'un moule à chemises et exosquelettes, dans lequel seront moulés des barreaux ayant moins de ségrégation,
• les figures 4,5,6,7,8,9,10,11,12,13,14,15 schématisent des chemises et exosquelettes suivant divers modes de réalisation, en vue de face (figures 4,6), coupes schématiques longitudinales (l'un des axes radiaux B ; figures 12, 14,) ou transversale (figure 7, coupe VII-VII, figure 11, coupe XV-XV, figure15,), et vues de côté (figure 5 -vue suivant V- et figures 8,9,10), la figure 13 étant un détail d'une variante de réalisation de zones identiques à celle référencée XIII figure 12.

Other advantages and characteristics of the invention will appear on reading the following description given by way of nonlimiting example and with reference to the appended drawings in which:

• the figure 1 is a schematic front view of a solid cylindrical bar of the prior art, in which are intended to be machined turbomachine blades,
• the figure 2 is a schematic view of a mold of the prior art,
• the figure 3 is a schematic view from above of a shirt and exoskeleton mold, in which bars having less segregation will be molded,
• the Figures 4,5,6,7 , 8.9 , 10 , 11,12,13 , 14,15 schematically folders and exoskeletons according to various embodiments, in front view ( figures 4,6 ), longitudinal schematic sections (one of the radial axes B; figures 12 , 14 ,) or transverse ( figure 7 , section VII-VII, figure 11 , XV-XV cup, Figure15 ,), and side views ( figure 5 -view following V- and Figures 8,9,10 ), the figure 13 being a detail of an alternative embodiment of zones identical to that referenced XIII figure 12 .

Figure 1 we see a rod 11 made of metal foundry and in which are intended to be machined at least one blade, here two blades, 12 turbine of a turbomachine.

The bar 11 may have a cylindrical shape and is full. It is obtained by casting a metal alloy in a mold.

The figure 2 represents a conventional device for producing bars or blanks 11, by successive operations of casting, casting and molding.

The device 10 comprises a closed and sealed enclosure 120 in which a partial vacuum is applied. An ingot 16 of metal alloy, in this case containing aluminum, and more precisely in the TiAl-based example, is first melted in a crucible 14. In fusion, it is poured into a metal mold 13 permanent.

The mold 13 is used to cast the alloy by centrifugation, in order to obtain bars 11. For this, it is rotated about a vertical axis A. The mold 13 comprises a plurality of housings 17, for example cylindrical of circular section, which extend radially (axes B1, B2; figures 2,3 ) around the axis A, preferably via a motor 18. These cavities are preferably regularly spaced angularly about the axis A which is vertical here. The centrifugal forces generated by the rotation of the mold force the molten alloy into these dwellings and fill them. Thus, the casting alloy, brought to the center of the mold, is distributed to the cavities.

After cooling, the mold 13 is disassembled and the molded bars 11 are extracted. The walls of the mold surrounding the recess 17 of the metal have significant thicknesses to withstand centrifugal forces, typically more than 10 g.

These thicknesses can lead to a high thermal inertia and create significant thermal gradients during cooling of the cast metal, generating a difference in the microstructure of the bar near its center relative to that to its periphery. The parts from the bars 11 may therefore have differences in microstructures (segregations).

Furthermore, in case of wear, it is necessary to change the part of the mold surrounding the radial housing 17 concerned.

The invention makes it possible to provide a solution to the cited problem of segregations and, if necessary, to meet the requirements of resistance to centrifugal forces and rapid and frequent change of at least part of the mold.

The Figures 4 to 15 represent embodiments of a mold 130 according to the invention, it being specified that the figures 5 and following schematize variants of shirts and exoskeletons likely to replace those shown figure 4 around the central block 131. As to all the functional means of which these mold embodiments are preferably provided, they have not been illustrated or systematically taken up in all the variants described below, so as not to overload the figures or to render tedious the following. Nevertheless, the particularities of these embodiments can be combined and applied from one mode to another.

The mold 130 differs from the mold 13 in the realization of some of its structural means, in particular its radial receiving housing of the alloy.

Specifically, around the central block 131, by the bent inner ducts 132 from which the alloy is caused to be distributed radially around the central vertical axis A, are regularly spaced shirts 135 (or for example 135a, 135b figure 4 ) which together define the aforementioned dwellings. The ducts 132 open respectively into radial ducts 133 which receive the alloy through an opening 133a and each extend inside one of the jackets, in a radial direction B. The opening 133a of each jacket is thus located in the radially inner end portion 134a of the duct concerned.

The shirts, which are thus hollow, are arranged in at least one exoskeleton 137, and preferably in as many exoskeletons as there are shirts, each exoskeleton then containing a jacket 135 defining one of said housings.

The exoskeleton (s) retain the jackets with respect to the centrifugal forces generated by the rotation of the mold. Preferably, they will promote (or at least do not hinder) a limitation of the thermal inertia.

In the illustrated embodiment illustrated figure 4 the central axis A of rotation of the mold is vertical and both the shirts 135 and the exoskeletons 137 each extend along a horizontal longitudinal axis (axis B).

For balance during rotation, a concentric arrangement (axis B) of each pair of shirt 135 and peripheral exoskeleton 137 is recommended.

At its radially outer end (end portion 134b), each duct 133 has a solid bottom 135c.

In a comparable manner, each exoskeleton 137 has, at its radially inner end, an opening 137a through which, for example, a liner 135 can pass and, at its radially outer end, a bottom 137b which can participate in the radial retention of the liner. .

Figure 6 in 139a, 139b there are fixations, here removable, established between the illustrated shirt, here 135a, and the exoskeleton, here 137a, which surrounds it, so as to allow a replacement of the jacket. Screwed fasteners may be suitable.

We also note figure 4 Removable fasteners, such as 141a, 141b, are provided between each jacket (and / or the surrounding exoskeleton, references 142a, 142b) and the central block 131.

Thus it will be possible to separate the shirts from the exoskeletons and the central block 131, in particular to replace these shirts. Again, screwed fasteners may be suitable.

The removable fasteners established between shirts and exoskeleton (s) and / or between the central block 131 and shirts and / or exoskeleton (s) may form thermal break zones.

Anyway, to limit the thermal inertia, as desired, it is advised that the thermal behavior of the shirts is preponderant compared to that of the exoskeleton (s).

In a preferred embodiment, the exoskeleton (s) is / are made of mild steel, steels or alloys that are more or less refractory and the sheaths are made of mild steel, steels or alloys that are more or less refractory and / or ceramic.

Figure 7 , the peripheral wall is referenced 135d and there is seen in the center, the molded bar (blank) 110 from the casting.

The figure 8 illustrates a solution where the schematized exoskeleton 137a is provided with a movable door 143a which, in the open position, releases an opening 145 for passing through it (here laterally with respect to the radial axis B) the shirt considered here 135a. Hinges, such as that identified 147a, may facilitate the operation of each mobile door and thus for example the extraction from its exoskeleton of a used sleeve and the introduction of another, in better condition, replacing.

On the Figures 4 to 8 , it will still be noticed that the exoskeletons are / are open.

They are thus like cages somehow meshed.

To promote a low thermal inertia, it is provided here that a void space 155 exists peripherally (around the axis B) between each jacket, such as 135a, and the exoskeleton, such as 137a, which surrounds it.

Centering means 157 position, in a fixed manner during the centrifugation, the sleeve considered with respect to the exoskeleton, for casting (see FIG. figure 5 ).

The Figures 9,10 illustrate yet another solution where the shirts are individually formed of several shells, such as 150a, 150b for the shirt 135a schematically.

The respective inner surfaces of the shells define at least the major part of the cast bar 110.

These shells open and close along a joint surface of the shells, such as the joint plane 152. Thus, one of these shells (such 135a) can constitute a movable or removable door vis-à-vis the other, to unmold the piece.

In addition, a separable attachment 153, such as a latch, is established between the shells for, once the shells are separated, to be able to pull the bar 110 from the inside of the liner, here 135a, considered, through the opening 154 released.

In the solution of figures 11.12 a honeycomb structure 159, which extends peripherally between each liner, such as 135a, and the surrounding exoskeleton, such as 137a, plays this role and therefore defines at least a part of said centering means 157 above.

The honeycomb structure 159 may be annular. It can occupy a space between the bottom 135c of the shirts and that 137b of the exoskeleton considered ( Figure12 ).

Including for the heat transfers sought, the figure 13 shows that the considered liner and the honeycomb structure, such as 159, are in contact by discrete zones, such as 159a, 159b,

Rather than in separate rooms, it would be possible to make the shirt and the honeycomb structure in one piece ( figure 13 ), so that they meet by these discrete zones located at the radially inner end of the walls 161 separating in pairs the cavities 163 of the cells, equivalent, as a whole, to the space 155 above.

Alternatively, it will be possible to make each jacket, such as 135a, said structure 159 which surrounds it and the exoskeleton, such as 137a, which surrounds this structure, in three distinct elements, dissociable between them, the jacket and the structure being engaged in the exoskeleton, concentrically, thus following a radial B to the axis A.

Figures 14.15 , but this can be applied to the preceding cases, the exoskeleton (s), such as 137a, individually (comprises) a radially outer end 134b ( figures 14 where the sleeve 135 is radially supported against a transverse surface 165 of the exoskeleton.

The transverse surface 165 will preferably be an internal shoulder of the exoskeleton.

The radially outer end 134b can be opened, the exoskeleton then resembling a structure traversed from one side to the other by at least one passage, where the / each relevant sleeve is received.

An attached plug 167 (which may be removable) will then plug this radially outer end 134b, in the manner of the aforementioned bottom 135a.

Favorably, the / each plug 167 will not penetrate the exoskeleton beyond the transverse surface 165. Thus, the shirt will not come to bear against it, which is preferable during centrifugation.

At least in the case of figures 14.15 the outer structure, in particular that in exoskeleton (s), of the mold may be cylindrical tubular (structure). It will favorably be made of mild steel. Y will thus be slipped axially an insert (the aforementioned folder) of metallic material or ceramic more or less refractory, which may include shells (such as two half-shells) as mentioned above.

• que l'insert assure l'obtention de la géométrie souhaitée pour la pièce coulée et permette d'en contrôler la solidification, par maîtrise des contraintes thermiques,
• et que la structure extérieure assure le positionnement du moule sur le montage de coulée centrifuge ainsi que la résistance mécanique de l'ensemble.

It will be understood that this allows:

• that the insert ensures obtaining the desired geometry for the casting and allows to control the solidification, by controlling the thermal stresses,
• and that the outer structure ensures the positioning of the mold on the centrifugal casting assembly and the mechanical strength of the assembly.

For axial assemblies / disassemblies, a slope of a minimum degree will preferably be provided between the structure and the insert. This will allow the shirt to come in / out along the exoskeleton, along the B axis, while concentrating them coaxially, in contact with each other. In addition, a detachable fastener will be made (by tightening) between the jacket and the surrounding exoskeleton. The interior volume of the shirts 135 can be of simple geometry (cylinder, rectangle, cone or combination) or complex. In general, any demoldable shape according to the closure plane of the half-shells is a priori acceptable.

To persevere in the control of the thermal stresses, preferably in combination with that of the forces, it is advised that, transversely to the radial direction in which they extend (axis B of the jacket considered), the shirts each have at least one thickness which varies along said radial direction (length L) and which is, at least globally, smaller towards at least one of the radially inner and outer ends, 134a, 134b, than in the intermediate portion, as shown Figures 14 ,; see also thicknesses e1, e2 and e3. In other words, it is then possible to find, along an axis B, a shape 133, firstly by narrowing the section from the end 133a, towards an intermediate zone, then eventually ( figures 14 ,) widening towards the opposite end 133b.

If necessary in connection with this aspect (but it could be a form of molded part to privilege), the figure14 , show the interest in having a mold where, individually, the radially open inner end 133a of the central duct 133 for casting the alloy of all or part of the shirts 135 would have a shape 169 thus narrowing in section towards the center of the jacket, along the radial direction, B, according to which the corresponding jacket extends. It should be noted that the form 169 can thus be single or double funnel (head to tail). A truncated cone might be suitable. However, this funnel / chute shape will not necessarily have a symmetry of revolution.

As for the radially outer end of this duct, near end 134b ( figure 14 ), it can be supported, to present an end portion 133b widened.

Typically if at least one blade, for example BP (low pressure), is later machined in the cast bar, the funnel / chute shape may correspond to the heel area of this blade and the end portion 133b enlarged to the zone of the blade. extended foot.

Always for control of efforts and weight gain, in conjunction with the controlled scalability of the wall thickness of the jacket, or even control of thermal stresses, it is further specified that individually all or part of the shirts 135 may have, transversely to the radial direction B along which they extend, a radial peripheral surface 170 at least locally (or partially) machined, as schematized figure 15 .

In this figure, it can also be seen that longitudinal reinforcements 171 may be provided to ensure the rigidity, centering and / or guiding of the liner 135 concerned in the peripheral structure 137. The reinforcements are radially protruding relative to the rest of the concerned shirt.

A positioning of the reinforcements 171 towards the radial ends 134a, 134b will make it possible to disengage the intermediate zones along the length of the mold, where the presence of at least one (empty) space 155 is favorable to the control of constraints, including thermal ones.

Figure 15 the reinforcements 171 are radial to the axis of the schematized sleeve and define therebetween several free spaces, or secondary cavities, such as 155a, 155b.

For vacuum use of the mold, this (s) free space (s) or secondary cavities 155a, 155b established (es) between the peripheral structure 137 and the outer face of the shirt 135 considered, including if These are the outer surfaces of machined (half) shells, it is recommended that the space be "aired" outside of space 155.

For this, it is proposed that this space 155 be in fluid communication with the outside environment of the mold via at least one orifice 175. In a particular embodiment, each liner 135, 135 a. length L or axial dimension (axis B) of between 10 and 50 cm, an outer section (such as an outer diameter) between 5 and 20 cm, an inner section (such as an inner diameter) between 4 and 10 cm and a radial thickness e, e 1. .. between 1 and 10cm, on average at the location of a given section.

Claims (10)

1. A rotary mold mounted to spin about an axis (A), for centrifugal casting of an alloy, the mold comprising:

   - a plurality of liners (135), each defining a recess (17) for receiving the alloy, and extending radially about said axis (A); and

   - at least one exoskeleton (137) inside which the liners (135) are disposed, and that retains said liners against a centrifugal force;

   said mold being characterized in that, transversely to the radial direction (B) in which each liner extends, a space (155, 163) exists peripherally between said liner and the exoskeleton that surrounds it.
2. A mold according to claim 1, characterized in that it further comprises a central block (131) having ducts (132) via which the alloy is cast, and which communicate with the insides (133) of the liners, and a releasable fastening (141 a, 142a) is established between the central block and at least one element chosen from each liner and the exoskeleton that surrounds said liner.
3. A mold according to any preceding claim, characterized in that the at least one element chosen from among said at least one exoskeleton and the liners is individually provided with a moving door (143a,150a) that, in the open position, opens up an opening (145, 154) making it possible to pass the liner (135) in question through it, and a cast piece (110) coming from the solidified cast alloy, respectively.
4. A mold according to any preceding claim, characterized in that the space (155) is empty and centering zones (157, 159, 171) position the liner to be considered in a fixed manner relative to said at least one exoskeleton, for the casting.
5. A mold according to any preceding claim, characterized in that said at least one exoskeleton (137) is open-work.
6. A mold according to any preceding claim, characterized in that the space (155, 163) is defined within a cellular structure (159) extending peripherally between each liner and the exoskeleton that surrounds it.
7. A mold according to claim 6, characterized in that the liner to be considered and the cellular structure (159), which has walls separating the cavities, bear against each other.
8. A mold according to claim 6, characterized in that the liner to be considered and the cellular structure (159), which has walls separating the cavities, meet via discrete zones.
9. A mold according to any one of claims 6 to 8, characterized in that the liner, said cellular structure (159) and the exoskeleton that surrounds the cellular structure are three elements that are mutually dissociable, the liner and the cellular structure being engaged in the exoskeleton concentrically.
10. A mold according to any preceding claim, characterized in that the liners are made of steel, of a metal alloy, and/or of a ceramic adapted so that such a TiAl metal alloy, in the molten state, can be centrifugally cast into them.

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