Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/04—Use of lost patterns
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C13/00—Moulding machines for making moulds or cores of particular shapes
  • B22C13/08—Moulding machines for making moulds or cores of particular shapes for shell moulds or shell cores
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/12—Treating moulds or cores, e.g. drying, hardening
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
  • B22D21/025—Casting heavy metals with high melting point, i.e. 1000 - 1600 degrees C, e.g. Co 1490 degrees C, Ni 1450 degrees C, Mn 1240 degrees C, Cu 1083 degrees C
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
  • B22D27/045—Directionally solidified castings

Definitions

• the present invention relates to the field of metal foundry.
• metal means both pure metals and metal alloys.
• the known foundry processes comprising at least one step of casting a metal in the liquid state in a mold, followed by cooling and solidification of the metal in the mold before demolding the solidified metal, it is possible to meet defects, especially when producing parts with particularly thin parts, such as the trailing edges of turbomachine blades. Indeed, the difference in temperature between the metal and the mold at the time of casting can cause premature cooling and solidification of a portion of the metal at the narrowest passages of the mold cavity, which can cause cracks, voids or other defects in the part thus molded.
• the present disclosure aims to remedy these drawbacks by proposing a foundry process which makes it possible to avoid more effectively defects, while reducing mold movements and simplifying the process.
• this object is achieved by virtue of the fact that, after the preheating of the mold to a first temperature, the casting of a metal in the liquid state, at a second temperature higher than the first temperature and, for example, at least 1250 ° C., is carried out in the mold maintained in a main oven at the first temperature since preheating, the difference between the first and the second temperature not being greater than 170 ° C. , and preferably not higher than 100 ° C or 80 ° C, and the cooling and solidification of the metal in the mold is performed while the mold is maintained in the main oven at a pressure of less than 0.1 Pa at less since pouring, before extraction of the mold from the main oven.
• the step of cooling and solidifying the metal in the mold maintained in the main oven at a pressure of less than 0.1 Pa can be carried out with a oven cooling rate less than or equal to 7 ° C / min.
• Such controlled cooling makes it possible to avoid the occurrence of cracks and other similar defects, in particular caused by the different rates of thermal contraction of the metal and the mold material.
• the preheating step of the mold can be performed at least partly in a preheating oven different from the main oven.
• the metal can solidify into equiaxial grains. This method is therefore not limited to the directed growth smelter of crystals, but is well applicable to conventional equiaxial polycrystalline metal alloys which form, in the solid state, a plurality of grains of substantially identical size, typically of the order 1 mm, but more or less random orientation.
• the mold may in particular be a shell mold formed around a molding cavity, for example by the so-called lost wax method or lost model.
• at least a first part of the mold around the molding cavity may have a wall thickness smaller than a second part of the mold. mold around the molding cavity.
• the second mold portion may have a greater number of layers than the first part of the mold.
• the wall thickness of the mold By thus modulating the wall thickness of the mold, in particular according to the thickness of the cavity in the same place, it is possible to prevent the different rates of thermal contraction of the metal and the mold material causing excessive mechanical stresses. on the metal during its cooling and solidification, constraints that could cause the appearance of cracks and other similar defects.
• This foundry process can in particular be used to form, with the solidified metal, parts with particularly fine parts such as for example at least one turbomachine blade.
• FIG. 1 illustrates a cluster of wax models created in a first step of a foundry process according to a first embodiment of the invention
• FIGS. 2A and 2B illustrate two following steps of the method, in which the cluster is dipped entirely in a slip bath and then sprinkled to form a layer of a shell mold;
• FIGS. 3A and 3B illustrate two following steps of the method, in which the cluster is partially immersed in the slip bath and then sprinkled to form an additional layer of the shell mold;
• FIG. 5B illustrates the shell mold of FIG. 5A after the addition of a heat shield
• FIGS. 6A, 6B and 6C illustrate consecutive steps of preheating the shell mold, casting, and controlled cooling, carried out in the same main oven
• FIG. 8 illustrates a preheating step according to an alternative embodiment, in which the mold is initially preheated in a preheating oven before being introduced into a main oven, different from the preheating oven, in which the steps are carried out. casting and controlled cooling.
• a first step of a casting process according to a first embodiment of the invention is the creation of a non-permanent cluster 21 comprising a plurality of models 22 connected by a shaft 23 supported by a plate 19, such as that illustrated on FIG. Figure 1.
• the parts of the shaft 23 for forming hollow volumes in the mold 1 are formed of a low melting point material, such as a wax or modeling resin, while other parts of the shaft 23, forming stiffeners, may be of refractory material (hatched in Figure 1).
• Models 22, which will form molding cavities in the mold, are also formed of a low melting temperature material.
• the Models 22 represent such blades, with the blade head pointing downwards.
• the batch 21 is quenched in a slip, and then sprinkled with a refractory sand, that is to say refractory material.
• a refractory sand that is to say refractory material.
• the materials used for the slip and the refractory sand, as well as the particle size of the refractory sand may be for example those disclosed in the French patent application publications FR 2,870,147 A1 and FR 2,870,148 A1.
• the slip may, for example, For example, it may contain particles of ceramic materials, in particular in the form of flour, with a mineral colloidal binder and optionally adjuvants depending on the rheology desired for the slip, while the refractory sand may also be ceramic.
• the ceramic materials that can be considered for slip and / or refractory sand are alumina, mullite and zircon.
• the inorganic colloidal binder can be, for example, a mineral-based mineral colloidal solution, such as in particular colloidal silica.
• Adjuvants may include a wetting agent, a fluidizer and / or a texturizer. These quenching and dusting steps can be repeated several times, possibly with slips and different sands, to form a slip-like impregnated sand shell around the bunch 21.
• the method according to this first embodiment it is intended to produce a mold in which at least a first part of the mold has, around the molding cavities, a wall thickness smaller than that which a second part of the mold has around the molds. same mold cavities. More specifically, in this first embodiment, as illustrated, it is intended to obtain thinner walls at the blade heads than at the blade roots.
• FIG. 2A initial quenching
• FIG. 2A partial tempering is carried out, illustrated in FIG. 3A in which the cluster 22 is dipped, inverted, only halfway up the blade before being sprinkled as illustrated in FIG. 3B.
• the upper part of the carapace thus formed will therefore comprise a greater number of layers than its lower part.
• the cluster 21 coated with this shell can then be heated, for example in an autoclave at a temperature between 160 and 180 ° C. and at a pressure of 1 MPa, to melt and evacuate from the inside of the shell the material at low temperature. melting temperature of the cluster 21.
• a firing step at higher temperature for example between 900 and 1200 ° C, the slurry solidifies so as to consolidate the refractory sand to form the refractory walls of the mold 1, as illustrated in Figure 4.
• the mold 1 thus formed is a shell mold having a central shaft 4 extending, in the direction of the main axis X, between a casting bucket 5 and a base 6 in the form of plate.
• the mold 1 also comprises a plurality of molding cavities 7 arranged in a cluster around the central shaft 4.
• Each mold cavity 7 is connected to the tapping bucket 5 by a feed channel 8 through which the molten metal is deposited. is introduced during its casting.
• the base 6 of the mold 1 is in the form of a tray.
• inclined column stiffeners 20 connect the top of each molding cavity 7 to that of the casting cup 5, and other vertical column-shaped stiffeners 30 connect the bottom of each mold cavity 7 to the base 6.
• the thickness d has walls of the upper portion 1a of the mold 1 around each mold cavity 7 is larger than the thickness d b of the walls of the lower part lb of the mold 1 around the same mold cavities 7.
• the thickness d may be, for example, between 2.5 and 9 mm, while the thickness d b can be, for example, between 1.5 and 6 mm.
• At least one heat shield 40 for example graphite, perpendicular to the main axis X, and refractory insulators 50 locally located in preferential zones of the mold can be added to this mold 1. mold 1.
• a preheating step of this mold 1, illustrated in FIG. 6A is carried out before proceeding to the casting of the metal in the liquid state in this mold 1.
• the mold 1 is heated in the main oven 100, which reaches a first temperature Ti.
• the casting of the metal in the liquid state in the mold 1, as illustrated in Figure 6B so as to fill the hollow volumes of the mold 1, and in particular its molding cavities 7.
• the metal is poured into the mold at a second temperature T 2 , greater than the first temperature Ti.
• the temperature difference ⁇ between the second temperature T 2 and the first Ti temperature is limited, for example not greater than 170 ° C, or 100 ° C, or even 80 ° C.
• the metal is, for example, a René-type nickel-based equiaxed alloy 77, with a solidus at about 1240 ° C. and a liquidus at about 1340 ° C.
• the second temperature T 2 can be, for example, 1450 ° C
• the first temperature Ti is then 1350 ° C, with a difference ⁇ no greater than 170 ° C.
• the mold 1 is still maintained in the main oven 100 during a first stage of cooling and solidification of the metal in the mold 1, in which the pressure p v is maintained and the The dT / dt cooling of the furnace is controlled and limited, for example, to about 7 ° C / min maximum.
• the pressure p v close to the vacuum, prevailing inside the main oven 100 makes it possible to restrict, or even eliminate, any convective cooling of the mold 1, so that the cooling of the mold 1 during this step is essentially radiative, and therefore easier to regulate inside the main oven 100.
• the heat shield 40 divides the interior of the main oven 100 into two thermally independent zones, to ensure a more homogeneous cooling of the mold 1 and the metal to inside of it.
• the upper limit of the cooling rate also limits the forces exerted on the metal by the difference in thermal contraction between the mold 1 and the metal that cools.
• the thickness d b of the walls of the lower part lb of mold 1 is smaller than the thickness d a of the walls of the upper part of the mold 1 also makes it possible to limit the forces on the metal in the narrower portions of the molding cavities 7, which are those corresponding to the blade heads, in particular near the trailing edge.
• the narrower walls of the mold 1 at these locations will yield under the constraints, rather than the metal. Thus, any cracks will form in the mold 1, rather than in the metal.
• Rene alloy 77 is a polycrystalline equiaxed 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 orientation. more or less random.
• Thickness at 1 mm 0.25 - 0.45 mm 0.5 - 0.6 mm trailing edge Maximum thickness of 1 - 2 mm 1.8 - 3mm dawn profile
• the preheating step of the mold 1 is carried out entirely in the main oven 100, it is also conceivable to carry out this preheating, in part or in full, in a furnace of different preheating, before introducing the mold in the main oven, so as to reduce the time that the mold will occupy the main oven, and thus increase the rate of production.
• the mold 1 which may be equivalent to that of FIG. 5, and produced by steps analogous to those of FIGS. 1 to 4, may be introduced into a preheating furnace 200, which may be at normal atmospheric pressure outside the vacuum chamber 101, to be initially preheated to a preheating temperature T 0 , less than or equal to the first temperature Ti, before being transferred to the main oven 100, where it can be further heated to reach and / or maintain the mold 1 at the first temperature Ti, up to the casting step of the metal, which can be also similar to that of the first embodiment, as are the subsequent steps.
• a preheating furnace 200 which may be at normal atmospheric pressure outside the vacuum chamber 101, to be initially preheated to a preheating temperature T 0 , less than or equal to the first temperature Ti, before being transferred to the main oven 100, where it can be further heated to reach and / or maintain the mold 1 at the first temperature Ti, up to the casting step of the metal, which can be also similar to that of the first embodiment, as are the subsequent steps.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Mold Materials And Core Materials (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=60627695

Family Applications (1)

Country Status (5)

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Family Cites Families (20)

• 2017
  • 2017-06-29 FR FR1755990A patent/FR3068271B1/fr active Active
• 2018
  • 2018-06-29 WO PCT/FR2018/051617 patent/WO2019002797A1/fr not_active Ceased
  • 2018-06-29 US US16/627,060 patent/US11235379B2/en active Active
  • 2018-06-29 EP EP18749852.2A patent/EP3645191B1/de active Active
  • 2018-06-29 CN CN201880043791.2A patent/CN110831712A/zh active Pending

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