Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/26—Producing shaped prefabricated articles from the material by slip-casting, i.e. by casting a suspension or dispersion of the material in a liquid-absorbent or porous mould, the liquid being allowed to soak into or pass through the walls of the mould; Moulds therefor ; specially for manufacturing articles starting from a ceramic slip; Moulds therefor
  • B28B1/261—Moulds therefor

Definitions

• the present invention relates to molds for the production of ceramic molded parts by means of the pressure slip casting process, where flowable slurries are injected into open-pore molds and the mold surface is designed in such a way that slurries with particle sizes of 0.1 to 2 ⁇ m expansion can be processed without difficulty.
• slip is understood to mean slurrying of the ceramic powder in water or organic liquids.
• surface-active substances such as organic surfactants or inorganic polyphosphates.
• the flow behavior is adjusted in a desired manner by adding further additives, such as synthetic or natural polymers that are soluble in the liquid, such as polyacrylic acid, polyacrylamides or cellulose derivatives.
• the aim is to set a high solids content with good flowability.
• pressure slip casting was proposed as a new process.
• the plaster mold is replaced by another molding material, namely open-pore sintered metal or open-pore plastic.
• the slip is first slowly pumped into the closed mold, the inner wall of the mold holding back the ceramic powder and the suspension medium passing through the mold. If the inner wall of the mold is covered with a layer of ceramic powder, the conveying speed is increased and the molded part is built up in the mold in a layer filtration analogous to the filter cake. Because of the high filtration pressure, the cullet is built up in a much shorter time than in a plaster mold at normal pressure.
• the mold When the conveyance of the slip to the mold comes to a standstill, the mold is filled.
• the maximum delivery pressure is 40 - 60 bar.
• the divisible mold is installed in a corresponding apparatus which is not the subject of this application.
• the pressure is removed and a negative pressure is applied to one mold half in order to hold the molded body on this mold half.
• the mold is then opened and the molded product is removed after the vacuum has been removed.
• the mold halves are rinsed in the opposite direction with water.
• the molds required for this process can be produced from porous sintered metal semi-finished products. For economic reasons, molds made from open-pore plastics are preferred (DOS 3 134 679). Plastic molds of this type are usually produced by foaming reactive resins. These reactive resins contain urethane and / or isocyanurate and / or urea bonds and are produced by foaming the corresponding components using conventional polyurethane technology.
• starting powder with grain sizes in the range from 0.1 ⁇ m to 5 ⁇ m are used for the production of structural ceramic parts with high temperature resistance and high strengths based on aluminum oxide, zirconium dioxide, silicon nitride, silicon carbide, mullite, sialons or other powders for structural ceramic parts.
• the pressure slip molds according to the prior art are no longer sufficient. It has also not yet been possible to produce reproducible shapes with duromer technology, the open pores of which have widths below 5 ⁇ m.
• the mold has a two-layer structure with a mechanically stable open-pore carrier with large pore sizes and a thin open-pore separation layer with a small pore size on the inside of the mold.
• the coarser-pored shape essentially serves as a support material, while the separation of ceramic powder and liquid runs on the additionally applied thin separation layer.
• separating membranes can be used as separating layers, which are used in the areas of micro- and ultrafiltration.
• Such membranes have thicknesses of up to 100 ⁇ m, consist of synthetic polymers and are produced by various processes (see Synthetic Membrane Production, Structure and Application, Angew. Chem. 94 (1982) 670-695).
• Nuclepore-type membranes with pore sizes of 0.5 to 5 ⁇ m are produced by irradiating polycarbonate or polyester films with heavy ions and then etching the areas damaged by the passage of the particles. Pores with a particularly narrow size distribution are obtained.
• monoaxially appropriate polymer films are stretched a second time perpendicular to the original stretching direction, slit-shaped to elliptical pores being created and pore sizes of 0.05 to 5 ⁇ m being able to be set.
• Such membranes are available, for example, on the basis of polyethylene, polypropylene or polytetrafluoroethylene (Celgard, Goretex or Poreflon type).
• Separating membranes can also be produced from partially crystalline polymers, such as polyethylene, polypropylene or polyamides, by dissolving the polymers in an organic solvent at elevated temperatures, knife-coating the solution into films and then allowing it to cool. On cooling, the polymer crystallizes out, leaving an open-pore structure that is filled by the solvent. After removing the solvent, there are separation membranes with pore sizes of 0.01 to 2 ⁇ m.
• partially crystalline polymers such as polyethylene, polypropylene or polyamides
• the membranes are manufactured using the phase inversion method.
• the polymer is dissolved in an organic solvent, the solution is knife-coated onto a circulating conveyor belt, part of the solvent is allowed to evaporate and the conveyor belt is then passed into a bath with non-solvent, the polymer coagulating starting at the surface of the polymer / solvent film and goes into the solid phase.
• the asymmetric membrane structure is created.
• Molds according to the invention are produced by covering the large-pore starting forms with separating membranes of the desired pore sizes. Dry membranes made of hydrophobic polymers, such as polycarbonate, polyesters or polyolefins, are heated until they become correspondingly stretchable and pressed onto the starting shape with an air stream of the same temperature, also at the same temperature level. Membranes made of hydrophilic polymers, such as polyamides or cellulose derivatives, are applied to the starting form in a moist state at room temperature.
• hydrophobic polymers such as polycarbonate, polyesters or polyolefins
• asymmetrical membranes are produced directly on the surface of the starting form, with which the best adhesion properties are achieved.
• the membrane polymer is dissolved in a water-soluble organic solvent, such as acetone, formamide or dimethylformamide or a solvent mixture in a concentration of 5 to 35% by weight, the viscous solution is degassed in vacuo and applied to the surface of the starting form. After a short evaporation time, the mold surface is sprayed with water and then immersed in water for about 10 minutes to develop the structure completely.
• a water-soluble organic solvent such as acetone, formamide or dimethylformamide or a solvent mixture in a concentration of 5 to 35% by weight
• the separating layers produced by the preferred method are so well anchored in the carrier material that they survive backwashing processes without detachment.
• the molds according to the invention are also suitable for shaping with slip based on organic solvents. Separating layers based on polysulfone, polyether sulfone, polyetherimide or polyamides are stable against aromatic-free aliphatic hydrocarbons. Subsequent crosslinking of the membrane polymer further increases the solvent resistance.
• membrane polymers with free amino or hydroxyl groups can be crosslinked by treatment with formaldehyde or epichlorohydrin.
• the molds according to the invention are used to produce molded parts made of aluminum oxide, zirconium dioxide, mullite, sialons, silicon nitride, silicon carbide, titanium boride, boron carbide or boron nitride.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Dispersion Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Producing Shaped Articles From Materials (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (5)

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Citations (5)

• 1987
  • 1987-09-08 DE DE19873730024 patent/DE3730024A1/de not_active Withdrawn
• 1988
  • 1988-09-02 JP JP21863388A patent/JPS6471705A/ja active Pending
  • 1988-09-03 EP EP19880114422 patent/EP0306865A1/fr not_active Withdrawn

Patent Citations (5)

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