EP1595620A1 - Broken mould moulding method - Google Patents

Abstract

The shell mould is made by dipping a model of wax or similar material in a slip containing ceramic particles and a binding agent, coating it with sand and drying, followed by a a series of dipping, sand-coating and drying stages to make a mould with a given thickness. The ceramic particles are of a refractory oxide or a mixture of refractory oxides, such as mullite or aluminium, with no zircon in any layer, while the binding agents are based on mineral colloidal solutions, especially colloidal silicon. The sand particles are of the same refractory oxides, without zircon.

Description

The present invention relates to the manufacture of parts such as blading complex geometries according to the technique known as lost wax foundry.

For the manufacture of turbojet blades, such as rotor parts or stators, or structural parts according to this technique, it is realized first a model wax or other equivalent material easily removable by the following. If necessary we group together several models into one cluster. We made around this model a ceramic mold by soaking in a first slip to form a first layer of material in contact with its area. Sand the surface of this layer to reinforce and facilitate the hanging of the next layer, and we dry the whole: what constitutes respectively the stuccage and drying operations. We then repeat the soaking operation in slip of possible compositions different, operation always associated with the successive operations of stuccage and drying. Thus, a ceramic shell consisting of a plurality of layers. The slips are composed of particles of ceramic materials, flour, such as alumina, mullite, zircon or the like, with a mineral colloidal binder and adjuvants, if any, depending on the rheology desired. These adjuvants make it possible to control and stabilize characteristics of the different types of layers, while avoiding the effects of different physicochemical characteristics of raw materials constituting the slips. It can be a wetting agent, a plasticizer or a texturizer based, for the latter, the desired thickness for the deposit.

The carapace mold is then dewaxed, which is an operation by which eliminates the material constituting the original model. After elimination of the model, we obtain a ceramic mold whose cavity reproduces all the details of the model. The mold then undergoes heat treatment at high temperature or "cooking", which gives it the mechanical properties required.

The carapace mold is thus ready for the manufacture of the metal part by casting. After checking the internal and external integrity of the carapace mold, the step The next step is to sink a molten metal into the mold cavity and then to the solidify. In the field of lost-wax foundry, there is currently a distinction several solidification techniques, therefore several casting techniques, according to the nature of the alloy and the expected properties of the part resulting from the casting. It may be directed solidification with columnar structure (DS), directed solidification with monocrystalline structure (SX) or solidification equiaxe (EX) respectively. The first two families of pieces concern superalloys for parts subject to high thermal stress that mechanical in the turbojet engine, such as HP turbine blades.

After casting of the alloy, the shell is broken by a shaking operation, and we complete the manufacture of the metal part.

During the molding step, several types of shells can be made at through several processes. Each carapace must have properties specific to ensure the desired type of solidification. For example, for equiaxed solidification, several different processes can be one using a silicate binder of ethyl, another using a silica binder colloid. For directed solidification, shells can be made from different fillers, based on silico-aluminous, silica-zircon or silica.

In order to simplify and standardize the processes used, it is There is a need for a shell with a "unique" structure whose properties would allow it to be used in different cases of solidification.

On the other hand, for reasons of respect for environmental standards and costs, there is also a need to avoid the use of alcohol-based binders such as ethyl silicate.

For reasons of rejection costs, it is also desirable to develop a shell structure not including zircon. This material, even low level of radioactivity, requires the establishment of treatment of highly binding waste industrially and financially.

The invention achieves these objectives with the following method.

trempage dans une première barbotine contenant des particules céramiques et un liant, dépôt de particules de sable sur la couche et à sécher ladite couche, de manière à former la couche de contact,

trempage dans une deuxième barbotine contenant des particules céramiques, un liant, dépôt de particules de sable sur ladite couche et à sécher celle-ci, de manière à former la couche intermédiaire

trempage dans au moins une troisième barbotine contenant des particules céramiques, un liant, dépôt de particules de sable sur ladite couche, à sécher celle-ci, de manière à former une couche de renfort. On répète la formation de couches de renfort jusqu'à obtenir une épaisseur de moule carapace définie.

The method of manufacturing a multi-layer ceramic shell mold, including at least one contact layer, an intermediate layer and a plurality of reinforcing layers from a wax model or the like, comprises the following steps:

dipping in a first slip containing ceramic particles and a binder, depositing sand particles on the layer and drying said layer, so as to form the contact layer,

dipping in a second slip containing ceramic particles, a binder, deposition of sand particles on said layer and drying it, so as to form the intermediate layer

dipping in at least a third slip containing ceramic particles, a binder, deposition of sand particles on said layer, drying it, so as to form a reinforcing layer. The formation of reinforcement layers is repeated until a defined shell mold thickness is obtained.

According to the invention, the method is characterized by the fact that ceramic particles of the slips comprise a refractory oxide or a a mixture of refractory oxides without zircon, none of the layers comprising zircon.

Preferably the slip for the formation of the reinforcement layers is much more fluid than the second slip.

It has been found that a shell mold having this composition and this structure, at the near contact layer, could be designed to be common to all types of castings according to the techniques reported above. We can thus advantageously adjust the mechanical properties of the mold, particular, its sensitivity to thermal shocks, to satisfy the conditions of casting corresponding to the constraints of the various solidification processes (EX, DS or SX).

Preferably and to satisfy the economic and environmental, the binder for different slips is a solution colloidal mineral such as colloidal silica. Similarly to satisfy economic constraints related to the rejects, the stucco grains for the layers of contact, intermediate and reinforcement are made from mullite grains and no zircon.

In order to control the porosity of the mold, and thereby control the sensitivity of the thermal shocks, the stuccage operations are carried out with stucco grains covering a size range between 80 and 1000 microns. In addition, stucco is preferably applied by dusting to the first layers, and is preferably applied by fluidized bed, for layers from the fourth. Stucco is applied automatically, so that the movements of the robot can make a carapace mold having a porosity after baking, between 20 and 35%. More shell is porous, the more it reduces its sensitivity to thermal shocks such as those products during different types of pouring.

In particular, in order to be applied to two distinct modes of solidification, the baking cycle of the mold comprises a heating up to a temperature between 1000 and 1150 ° C, preferably between 1030 ° C and 1070 ° C.

It suffices to adapt only the contact layer to the solidification mode. Thus the first slip can be formed from mullite flours and of alumina without zircon, with or without germinating.

In a particular case, for DS or SX type solidifications, the contact is composed mainly of mullite flour in quantity between 40 and 80% by weight, possibly of alumina flour, a binder based on colloidal silica, and organic adjuvants.

In the particular case of equiaxed solidification, the contact layer is composed of a mixture of alumina flours and mullite in quantities between 40 and 80% by weight and between 2 and 30% by weight, remainder comprising a binder based on colloidal silica, a germinant, and organic adjuvants.

According to another characteristic, the second and third slip are common to any solidification process, and comprise a mixture of alumina and mullite flours in an amount of between 45 and 95% by weight, and mullite grains in an amount of between 0 and 25% by weight.
The mold structure thus defined finds, indifferently, a use
for the manufacture of a part with solidification of directed type with a columnar structure, the contact layer being formed mainly from a mullite flour,
for the manufacture of a monocrystalline structured type solidification-type part, the contact layer being formed predominantly from a mullite flour or else
for producing a piece with equiaxed type solidification, the contact layer being formed from a mixture of alumina flour and mullite.

The invention also relates to a method for manufacturing parts by casting molten metal that, irrespective of the type of solidification, directed to columnar structure, directed at monocrystalline or equiaxed structure, molds with a common shell skeleton: intermediate layer and common reinforcement layer.

The invention also relates to an installation for the production of parts by casting a molten metal in a shell mold comprising a station of manufacture of molds and casting stations for different solidifications, said stations being fed with molds having reinforcement layers identical.

The process is described in more detail below.

The method of manufacturing shell molds for use common to all types of parts includes a first step of manufacturing the model in wax or other equivalent material known in the field. The more generally known is wax. Depending on the type of part, you can group the cluster models so that several can be made simultaneously. The models are shaped to the dimensions of the final pieces, alloys.

The carapace manufacturing steps are preferably carried out by a robot whose movements are common to all types of parts, programmed to have an optimal action on the quality of the deposits made, and to free oneself the geometric aspect of the various blades.

In parallel, slips are prepared in which they are quenched successively the models or the cluster to make a deposit of matter ceramic.

We distinguish a first slip for solidification EQX.

• un mélange de farines d'alumine (40 - 80%) et de mullite (2 - 30%) ;
• un germinant, aluminate de cobalt (0 - 10%) ;
• un liant silice colloïdale (18 - 30%) ;
• de l'eau (0 - 5%) ;
• trois adjuvants : agents mouillant, fluidifiant et texturant ;

It includes in weight percentage:

• a mixture of flours of alumina (40-80%) and mullite (2 - 30%);
• a germinant, cobalt aluminate (0-10%);
• a colloidal silica binder (18 - 30%);
• water (0 - 5%);
• three adjuvants: wetting, thinning and texturing agents;

• un mélange de farines d'alumine (2 - 30%) et de mullite (40 - 80%) ;
• un liant silice colloïdale (18 - 30%) ;
• de l'eau (0-5%) ;
• trois adjuvants : agents mouillant, fluidifiant et texturant ;

For columnar or monocrystalline columnar solidification, the composition of the first slip in percent by weight is as follows:

• a mixture of flours of alumina (2 - 30%) and mullite (40 - 80%);
• a colloidal silica binder (18 - 30%);
• water (0-5%);
• three adjuvants: wetting, thinning and texturing agents;

• un mélange de farines d'alumine (50 - 75%) et de mullite (5 - 20%) ;
• un liant silice colloïdale (20 - 30%) ;
• de l'eau (0 - 5%) ;
• trois adjuvants : agents mouillant, fluidifiant et texturant ;

The second intermediate slip, common to all types of solidification, comprises in percentage by weight the following components:

• a mixture of flours of alumina (50-75%) and mullite (5-20%);
• a colloidal silica binder (20 - 30%);
• water (0 - 5%);
• three adjuvants: wetting, thinning and texturing agents;

• un mélange de farines d'alumine (30 - 45%) et de mullite (15 - 30%) ;
• des grains de Mullite (14 - 24%) ;
• un liant silice colloïdale (10 - 20%) ;
• de l'eau (5 - 15%) ;
• quatre adjuvants : agents mouillant, fluidifiant, texturant et de frittage ;

The third reinforcing slip, common to all types of solidification, comprises the following components in percentage by weight:

• a mixture of flours of alumina (30 - 45%) and mullite (15 - 30%);
• Mullite grains (14 - 24%);
• a colloidal silica binder (10-20%);
• water (5 - 15%);
• four adjuvants: wetting, thinning, texturizing and sintering agents;

• Le fluidifiant permet d'obtenir plus rapidement la rhéologie désirée lors de la fabrication de la couche. Il agit en tant que dispersant. Il peut appartenir à la famille des acides aminés, à la gamme des polyacrylates d'ammonium, ou à la famille des tri - acides carboxyliques à groupements alcools ;
• Le mouillant permet de faciliter le nappage de la couche lors du trempé. Il peut appartenir à la famille des alcools gras poly - alkylènes, ou alcools alkoxylates ;
• Le texturant permet d'optimiser la rhéologie de la couche afin d'obtenir des dépôts adaptés. Il peut appartenir à la famille des polymères de l'oxyde d'éthylène, des gommes de xanthane, ou des gommes de guar ;

The first 3 adjuvants respectively have the following functions:

• The fluidizer makes it possible to obtain the desired rheology more quickly during the manufacture of the layer. It acts as a dispersant. It may belong to the family of amino acids, to the range of ammonium polyacrylates, or to the family of carboxylic tri-acids with alcohol groups;
• The wetting agent makes it easier to coat the layer during dipping. It may belong to the family of polyalkylene fatty alcohols, or alkoxylated alcohols;
• The texturizer makes it possible to optimize the rheology of the layer in order to obtain suitable deposits. It may belong to the family of polymers of ethylene oxide, xanthan gums, or guar gums;

For layer # 1, contact, once the model removed from the first slip after an immersion phase, the covered model undergoes a dewatering phase then topping. Then, sprinkles of stucco are applied to do not disturb the thin layer of contact. For the stuccage operation, one uses mullite whose granulometry in this first layer is fine. It is between 80 and 250 microns. The surface condition of the pieces in final depends in part.

The No. 1 layer is dried.

The dipping is then carried out in a second slip to form a layer N ° 2, called intermediate. The composition is the same regardless of the solidification mode adopted.

As before, a stucco is deposited by dusting and dried. For the stuccowork operation, we use mullite whose particle size is average. It can be between 120 and 1000 microns. The state of porosity final shells depend in part on it.

The model is then quenched in a third slip to form the layer No. 3 which is the first so-called reinforcement layer.

The same stucco is then applied to layer 2 by dusting, and dried. The soaking operations are repeated in the third slip, stuccage and drying to form the layers of "reinforcement". For these layers reinforcement, the stuccage is carried out by fluidized bed.

For the last layer, a glazing operation is performed which does not include a stuccage operation.
The carapace in final can consist of 5 to 12 layers.

Soaked for different layers are made in different ways and are adapted to obtain a homogeneous distribution of the thicknesses and to avoid the bubble formation, especially in enclosed areas.

Soak programs are optimized for each type of layer, in order to to overcome the geometrical aspect of the different types of pieces, and are therefore common to all references.

The interlayer drying range is optimized for each type of layer, to overcome the geometric aspect of the different types of parts. The range is therefore common. The range allows indeed for each type of layer, a drying of molds with geometries as different as vanes movers, distributors, or structural parts.

Final drying is carried out after the formation of the last, common layer to all types of rooms.

The baking cycle of molds is the same for all types of solidification, and thus free from the type of room. It includes a rising phase in temperature, a plateau at the cooking temperature and a phase of cooling. The cooking cycle is chosen to optimize the properties mechanical shells so as to allow cold handling without risk of breakage, and in order to minimize sensitivity to thermal shock that can be generated during the different stages of casting.

It can be seen that a single cooking can be done instead of both types of previously made to prepare the EQX, DS and SX to different casting modes.

Claims (19)

A method of manufacturing a multi-layered ceramic shell mold including at least one contact layer, an intermediate layer and a plurality of reinforcement layers from a model of the part to be made, in wax or the like, consisting in carrying out the operations following successive dipping in a first slip containing ceramic particles and a binder, deposition of sand particles on said layer and drying thereof, so as to form the contact layer, dipping into a second slip containing ceramic particles and a binder, depositing sand particles on said intermediate layer, and drying it, so as to form the intermediate layer, dipping in at least a third slip containing ceramic particles and a binder, deposition of sand particles on said layer, drying thereof, so as to form a reinforcing layer, the formation of reinforcement layers being repeated until get a defined shell mold thickness, characterized in that the ceramic particles of the slips comprise a refractory oxide or a mixture of refractory oxides without zircon, none of the layers having zircon. Process according to claim 1 wherein the refractory oxide is mullite or alumina. A process according to claim 1 or 2 wherein the binders for the different slips are based on colloidal mineral solutions, in particular especially colloidal silica. A process according to claims 1, 2 or 3 wherein said particles of sand are made of refractory oxide grains without zircon, in particular mullite grains. Process according to Claim 4, in which the grains have a grain size distribution between 80 and 1000 microns. A method according to claim 4 or 5 wherein for some layers the sand particles are applied by dusting, preferably for first three layers. A process according to claim 4, 5 and 6 wherein for certain layers the sand particles are applied by fluidized bed, preferably for layers from the fourth. Process according to one of claims 4 to 7, according to which the particles of sand are applied so that the carapace exhibits porosity after cooking between 20 and 35%. The process of claim 1 wherein the drying between two layers successives is realized according to the same range whatever the room and its geometry. A process according to claim 1 wherein the soaking is carried out by robot, programmed so that the movements of the robot are the same whatever the geometry of the piece. Method according to one of the preceding claims, according to which the deposit of sand particles on the mold is made automatically by robot so that the movements of the robot are the same whatever the geometry of the room. Method according to one of the preceding claims, according to which the cycle of baking of the final shell mold is unique regardless of the piece and includes heating up to a temperature of between 1000 and 1150 ° C, preferably between 1030 and 1070 ° C. Method according to one of the preceding claims, according to which the first slip has a different alumina and mullite composition depending on whether the manufacturing process of the part is directional or equiaxed solidification. Method according to one of the preceding claims, according to which the second and third slips comprise a mixture of alumina flours and mullite and mullite grains, and are common to any process of directed or equiaxed solidification. The method of claim 13 wherein the first slip for a directed solidification, mainly comprises mullite flour, in particular amount between 40 and 80% by weight, possibly flour alumina, a binder based on colloidal silica, and organic additives. The method of claim 13 wherein the first slip for a equiaxed solidification, comprises a mixture of alumina flours and mullite in quantities of between 40 and 80% by weight and between 2 and 30% by weight, a binder based on colloidal silica, a germinator, and organic adjuvants. The method of claim 14 wherein the second and third slips, are common to all solidification processes, and include a mixture of alumina flours and mullite in an amount between 45 and 95% by weight, and mullite grains in an amount between 0 and 25% in weight. Use of a "unique" shell mold according to one of the claims for the manufacture of parts by casting molten metal, which whatever the type of solidification directed to columnar structure, directed to monocrystalline or equiaxed structure. Installation for the production of parts by casting molten metal in a shell mold, comprising a mold making station according to one of of the preceding claims, and casting stations for different solidifications, said stations being fed with molds having identical intermediate and reinforcing layers.