Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/165—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents in the manufacture of multilayered shell moulds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds

Definitions

• the invention relates to a molding material for the fine and mold casting of metals or metal alloys comprising plastic and / or carbon aerogels and a process for the production of corresponding molding materials.
• Investment casting in ceramic molded shells is a standard casting technique for precision parts to manufacture from various alloys.
• the shapes are in usually made using the lost wax technique; d. H. a wax body
• the part to be cast is wetted with a silica sol in several steps sanded, dried and then the shell is fired, whereby the wax is melted in an autoclave or burned.
• Means Modern casting processes make it possible to cast in line with the shape and close to the final shape (J. Sprunk, W. Blank, W. Grossmann, E. Hauschild, H. Rieksmeier, H.G. Rosselnbruch; Investment casting for all industrial sectors, 2nd edition, headquarters for casting use, Düsseldorf 1987; K.A. Krekeler, investment casting, in: manual of manufacturing technology Vol. 1., editor G. Speer, Hanser Verlag, Kunststoff 1981).
• Aerogels are highly porous, open-pored, oxidic solids that usually via sol-gel processes from metal alkoxides by polymerization, polycondensation to gels and subsequent supercritical drying. For some years now, it has also been possible to add plastics using sol-gel processes gel and by supercritical drying in a highly porous organic Convert solid body. Pyrolysis of such plastic aerogels under protective gas or in a vacuum at temperatures above 1000 ° C converts them into carbon aerogels around. Like the oxidic aerogels, plastic and carbon have aerogels extremely low effective thermal conductivities (order of magnitude some mW / K / m) and are considerably lighter. The physical and mechanical Properties of plastic and carbon aerogels are in the literature documented (R.W.
• a Molding material for the fine and mold casting of metals or metal alloys comprising highly porous, open-pore plastic and / or carbon aerogels, available through sol-gel polymerization of organic plastic materials optionally followed by partial or complete pyrolysis of the obtained Plastic aerogels.
• the molding material according to the invention is particularly suitable for use in lost wax processes and need not, as in the prior art for oxidic Gels can be applied in several steps.
• the molds obtained in this way are filled with melt using customary techniques and the melt starts.
• heat is dissipated over the mold shell or the molding sand.
• pour and freeze in
• aerogels mean, since carbon aerogels are quasi adiabatic, that the heat dissipation only via feeders and risers or specifically attached heat sink takes place, skillfully the risers and feeders can be used by yourself, but do not have to. That way is one fully controlled solidification is possible and the structure can accordingly required range of properties can be adjusted.
• the airgel forms produced according to the invention are particularly suitable for the casting of aluminum alloys (whereby the casting mold practically does not heat up must be, since no heat dissipation takes place by itself). This increases the economy because energy costs can be reduced. Magnesium and titanium alloys also do not react with carbon, so that these carbon airgel forms also for these alloys under protective gas or Offer vacuum as film material.
• a particular advantage of the molding materials according to the invention is that the Sol-gel formation at room temperature, that is, in particular at temperatures completed below the pour point of the wax within a few hours can be.
• Supercritical drying as with the purely inorganic Gelling is not necessary. Nevertheless, it is possible to determine the pore size in the micrometer range adjust. When drying in the supercritical temperature range pore sizes in the nanometer range are also possible.
• the molding materials according to the invention can also be inorganic or contain organic filler materials. These are essentially Understand solid materials that are inert under solidification conditions.
• Inorganic Filler materials are selected, for example, from aluminum oxide, titanium dioxide and / or quartz, each in an amount of 5 to 30 vol .-%. used can be.
• Fillers for the purposes of the present invention further comprise Fiber materials that have a fiber reinforcement with organic, inorganic or allow carbon and / or SiC fibers with approximately equal volume fractions.
• organic fillers for example thermoplastic or thermosetting plastic particles, for example polystyrene and / or use organic (polyacrylonitrile) fibers.
• thermoplastic or thermosetting plastic particles for example polystyrene and / or use organic (polyacrylonitrile) fibers.
• these materials are also melted out during the pyrolysis of the plastic gels or be burned.
• using such materials is one Control of shrinkage possible during pyrolysis.
• Plastic aerogels based on resorcinol / formaldehyde used in suitable composition and suitable content of basic catalyst at temperatures between 20 and 50 ° C without supercritical drying in one microstructured plastic airgel can be transferred.
• the composition of the sol-gel polymerization can be set such that, for example First, a highly viscous liquid is created, which is applied to a wax mold can be applied. This is also possible in several work steps, so that the layer thickness is adapted to the needs of the applications in the foundry can be.
• the temperature of the conversion of the solution into a plastic airgel must be Melting point of the wax can be adjusted. After converting to a Plastic airgel can melt the wax and at the same time the conversion to a carbon airgel takes place in the absence of air.
• Dependent the composition of the starting solution, the gelation temperature, the density of the resulting porous body can be made into molds, as both plastic and carbon airgel, on a micrometer scale are smooth on the surface and reproduce sharp contours.
• the production of molds up to the plastic airgel usually takes 1 to 3 days, often only up to 24 hours.
• the pyrolysis time is determined by the thickness the mold shell; with a wall thickness of 1 cm, for example, the time is less than 24 hours, usually 10 hours.
• a glass container in which a wax model (weighted down with steel plates) of the Shaped body was filled with the solution until the model was complete was covered.
• the container was closed. Gelled within two hours the solution in an air circulator (Heraeus) at 40 ° 0. It became a color change the clear solution observed after ocher yellow / light brown. The drying of the gel was obtained in the air circulator over 24 hours. Subsequently the wax was melted out at a temperature of 60 ° C.
• the plastic airgel was placed in a cold muffle furnace brought in.
• the oven was slowly (3 hours) heated to 1050 ° 0, where continuous nitrogen (argon or another protective gas is possible analogously) was blown through to avoid oxidation.
• the temperature of 1050 ° C was maintained for 24 hours.
• the mixture was then cooled with a constant gas flow and the carbon dioxide airgel form taken.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)
• Catalysts (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Carbon And Carbon Compounds (AREA)

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Publications (2)

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• 1999
  • 1999-03-17 DE DE19911847A patent/DE19911847A1/de not_active Ceased
• 2000
  • 2000-03-01 AT AT00104214T patent/ATE303214T1/de not_active IP Right Cessation
  • 2000-03-01 DE DE50011046T patent/DE50011046D1/de not_active Expired - Lifetime
  • 2000-03-01 EP EP00104214A patent/EP1036610B1/fr not_active Expired - Lifetime
  • 2000-03-17 US US09/527,809 patent/US6599953B1/en not_active Expired - Fee Related
• 2003
  • 2003-05-30 US US10/449,794 patent/US6887915B2/en not_active Expired - Fee Related

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