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

Definitions

• the present invention relates to the manufacture of parts such as blading complex geometries according to the technique known as lost wax foundry.
• 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 production of the piece metal casting.
• the step The next step is to sink a molten metal into the mold cavity and then to the solidify.
• solidification techniques In the field of lost-wax foundry, one distinguishes currently several solidification techniques, so several techniques of casting, depending on the nature of the alloy and the expected properties of the resulting part of the casting. It may be directed solidification with columnar structure (DS), directed solidification with monocrystalline structure (SX) or solidification equiaxe (EX) respectively.
• DS columnar structure
• SX monocrystalline structure
• EX solidification equiaxe
• the shell is broken by a shakeout operation, and it completes the manufacture of the metal part.
• the carapaces can be made from different fillers, based on silico-aluminous, silica-zircon or silica.
• the first layer for each of these carapaces plays a vital role. She constitutes the interface between the shell mold and the cast alloy. It must, in the case of a solidification directed to columnar or monocrystalline structure, to be non-reactive with the cast alloy. In the case of equiaxed solidification, it must allow equiaxial germination of the grains. Moreover, the integrity of this Contact layer determines the final quality of the casting, in terms of condition surface especially.
• the first layer must meet certain requirements in order to avoid defects such as ceramic decohesions, and surface defects.
• the decohesions of the contact layer before or during the casting can generate harmful marks on parts.
• the surface defects result from excessive micro porosity of the contact that generates surplus forming reliefs on the surface of the pieces.
• Major surface defects are often the result of a phenomenon surface capillary at the interface between the wax model and the first layer.
• the grains of sand form stacks, which have many capillaries. Each acts like a sucker that gives rise to a depression. This one is all larger than the capillary is small. This corresponds to a first layer insufficient thickness. Depression promotes a capillary rise of the slip to the stucco and this, until the column of liquid thus formed restore the pressure difference. It follows the formation of a withdrawal zone with cavity which leads to the formation of surface defects. This phenomenon is accentuated by a first layer of thickness too weak.
• the properties of the contact layer must therefore make it possible to find a compromise between these antagonistic characteristics, in order to be free from all defects on parts.
• the invention achieves these objectives with the following method.
• the multi-shell ceramics mold manufacturing process layers including at least one contact layer from a wax model or other similar material, including dipping the model in a slip containing ceramic particles and a binder, and adjuvants, so as to forming said contact layer, depositing sand particles on the layer and drying said contact layer.
• the process is characterized in that the ceramic particles of said slip are mullite particles.
• the adjuvants comprise an agent wetting agent, a fluidifying agent and a texturing agent.
• composition of the slip it is possible to fulfill the objectives assigned to all foundry molds, whose properties satisfy the requirements of casting conditions in particular meeting the constraints of solidification DS and SX.
• the contact layer is not reactive against cast superalloys.
• the slip is advantageously composed of mullite flour in a quantity of between 65 and 90% by weight, without zircon.
• sand particles or "stuccos" for this contact layer, are formed from mullite grains and not from zircon.
• adjuvants in the slip allows to control deposits on wax and to ensure optimal characteristics in terms of thickness and distribution on parts.
• the binder is a water-based mineral colloidal solution, such as colloidal silica, and not a alcohol base binder.
• contact layer on wax associated with a reinforcement by dusting of a mullite sand with a particle size between 80 and 250 microns to obtain a very good cohesion of first layer and very good states of surface of castings.
• the method of manufacturing the shell molds comprises a first step of manufacture of the model in wax or other equivalent material known in the field.
• the most commonly known is wax.
• the models are shaped to the dimensions of the final pieces, at removal near alloys.
• the carapace manufacturing steps are preferably carried out by a robot whose movements are programmed to have an optimal action on the quality of the deposits made, and to overcome the geometrical aspect of different vanes.
• slips are prepared in which they are quenched successively the models or the cluster to make deposits of materials ceramics.
• the covered model undergoes a phase of dewatering and then topping.
• mullite whose granulometry in this first layer is fine. It is between 80 and 250 microns. The surface condition of the final pieces depends in part.
• the layer is dried.
• the dipping is then carried out in a second slip to form a so-called "intermediate" layer.
• the model is then quenched in a third slip to form the layer 3 which is the first layer called "reinforcement”.
• the stucco is then applied and dried. We repeat the soaking operations in the third slip, stuccing and drying to obtain the thickness of desired carapace. For the last layer, an operation of icing.
• the second and third slip may comprise a mixture of flours of alumina and mullite in quantities of between 45 and 95% by weight, and mullite grains in amounts between 0 and 25% by weight.
• the carapace can thus comprise from 5 to 12 layers.
• the baking cycle of the molds includes a temperature rise phase during a given period, a plateau at the cooking temperature and a cooling phase.
• the cooking cycle is chosen to optimize the mechanical properties of the shells so as to allow manipulations to cold without risk of breakages, and in order to minimize their sensitivity to shocks thermals that can be generated during the various pouring stages.
• contact layer An example of a shell mold manufacturing process has been described from contact layer according to the invention.
• This contact layer can be associated with all types of layers as needed, even if necessary with layers made from zircon particles.

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

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  • 2004-05-12 FR FR0405145A patent/FR2870148B1/fr not_active Expired - Fee Related
• 2005
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