SE425360B - SET TO ISSTATIC PRESSURE OF POWDER FOR THE PREPARATION OF FORMAL OF CERAMIC OR METALLIC MATERIAL - Google Patents

Description

20 25 35 7903955-8 targets to be produced, and bound to a mold, after which the model is removed from it so. formed form ooh a mold space is obtained in the mold corresponding to the object to be produced and on. utilization of the mold as a gas-permeable casing in the isostatic pressing. The mold space thus has the same. shape as the object but larger dimensions.

The present invention relates to a method of producing an object of ceramic or metallic material by isostatic pressing of a powder * of the ceramic or metallic material with a gaseous tryochmedicism, the powder being arranged in a glass envelope which is made gas-permeable before the isostatic pressing. during sintering of the powder is carried out, characterized! in that the powder of the ceramic or metallic material is introduced into the mold space of in the form of glass powder with a mold space corresponding to the object to be produced, and that the mold space is covered with glass, which together with the mold forms an enclosure for the powder of the ceramic or metallic material. , that the enclosure with the powder and the connection placed in a vessel which is stable at the temperature at which the sintering is carried out are transferred into a melt with a surface limited by the walls of the vessel, below which the material in the mold space is located and that a pressure required for the isostatic pressure is applied to the melt with the gaseous pressure medium.

In the description and claims, melt means a gas-permeable mass which at least mainly consists of molten phase. It is thus not necessary for all the constituents of the enclosure to be melted in their entirety in order for a functioning gas-permeable mass, here included in the term melt, to have been formed. As the pressure medium in the practice of the present invention, noble gases such as argon and helium and nitrogen gas are preferred.

The ceramic material can, among other things. of a nitride such as silicon nitride, a methsiloxm such as smimsumoxia or a man such as rice urea.

The metallic material can, among other things, consist of steel, of an iron-based alloy, eg 5 -yá cr-mo-sfal / indenaiianae 0.55 Vø o, 0.50 in si, o, 4o 96 nn, 0.01 * íá P, 0,01% S, 2,8 * ß Gr, 0,6 7 »Mo, rest Fe eller 12 76 Gr-Mo-V-Iïb-stál: nnenaïianae one mo, 0,25 7» si, o, 6o am, 0.01 9% P, o, o1 9% S, 11.5% Gr, 0.5% Ni, 0.5% Mo, 0.30 å! V, 0.25 5% Nb, residual Fe, or an alloy in- nåiianae 1.21 aa c, o, 5 so to speak, 0.3 96 nn, 6.4 aa w, 5.0 1% Mo, 5 , 1 'ß V. 4,2 74 »Gr. residue Fe, or of a nickel-based alloy, such as an alloy containing Ünoš 3% cv 15% Crn-l? % C09 5 ß H09 305% Ti! 494% A10 0903 g 'Bi rest Ni sim en iogermg binnenållanae o, o6 mc, 12 9% »oi, 17 ø co, 5 16 mo, o, o6 7% zr 4,7 gå Ti, 5,3 fl, 111 , 0.014 73 B, 1.0% V, residue Ni. The percentage refers to weight percent. The form of glass powder into which the ceramic or metallic material is introduced is manufactured by surrounding a model of the object to be produced with the glass powder and by the glass particles. bond to each other., to a coherent unit, before the model is removed. The model is made of a material that can be removed. out of the device without it. destroyed, for example by wax or other low-melting material such as an alloy of 60 toe ni and 40 'ß sn ene: - wooas metal (50 76 m, 25 9% Pb, 14 7% sn and 11 9% ca) as of course is removed by allowing the material to drain after melting, by a plastic such as polystyrene or other material which decomposes on heating and can be released in gaseous form, or by a material which can be dissolved with a solvent, for example a metal which can be dissolved with acid. The glass particles can be bonded to each other with an inorganic binder, e.g. 13203 or S102, formed in the form of ethyl sililate. Organic binders, such as starch or a resin binder, which can be burned off, are also useful. It is also possible to achieve. a bonding of glass particles to each other by sedimentation or cold compaction without the use of binders.

The glass is preferably of the low melting type. An example of a suitable glass is a glass containing 80.3% by weight of 81202, 12.2% by weight of 3205, 2.8% by weight of Al2 O3? 4.0% by weight of Na 2 O, 0.4% by weight of K 2 O and 0.3% by weight of csu (Pyrexet, furthermore an aluminum silicate: imanant 58% by weight of SiO 2, 9% by weight of 3205, 20% by weight of Al 2 O 3, 5% by weight of Ca particles of substances, such as SiO2, 3205, b.1203 and alkali metal and alkaline earth metal oxides which, when heated, form glass.The term glass in the claims is intended to include glass-formed materials, eg mixtures just mentioned.

The ceramic or metallic material is given, if so. Prior to introduction into the mold of the glaze powder, a suitable consistency is required by the addition of an additive, for example in the form of a solvent such as methanol, ethanol or water, a binder such as polyvinyl alcohol, a blowing agent such as polyethylene glycol, an antifluxing agent. such as benzenesulfonic acid and / or a wetting agent such as ethyl pentyl glycol. The insertion into the mold space can be done by slurry casting or by means of vacuum, pressure, centrifugal force or ultrasound. The property of the mold to be porous and absorbent facilitates the production of a high filling of the mold with the ceramic or metallic material, especially in slurry casting. At the inner wall of the mold have the pores. preferably a smaller size (diameter) than the size of the grains of the ceramic or metallic material. After the mold cavity has been filled and its opening covered with glass, which together with the mold forms an enclosure around the ceramic or metallic powder, the connection is transferred as can be seen from the foregoing in a melt. To keep the melt in place, the mold is preferably arranged in a vessel which is dimensionally stable at the temperature at which the isostatic pressing during sintering of the powder of the ceramic or metallic. the powder is performed. G-rafite is preferred as the material in the vessel, but other materials such as boron nitride or molybdenum are also useful.

The enclosure can be made gas permeable while vacuum is maintained around it. The enclosure can also. is made gas permeable while being kept in contact with a gas in which a pressure is maintained which is at least as great as the pressure of gas present in the material in the mold. Thereby this can be avoided. that gas leaving the material in the mold frame damages the mold. The invention will be explained in more detail by describing exemplary embodiments with reference to the accompanying drawing, in which Figures 1-4 show different steps during the manufacture of an object according to the present invention.

A vana model is produced, the shape of which corresponds to the shape of a turbine disc with vanes but which has larger dimensions to compensate for dimensional reduction via the option of the object; In the center, of the vmeaeii, a tube of borosilicate glass was attached. This pipe was used as described below as a casting and riser in sludge casting in the finished mold. The vane model and the lower part of the glass tube are repeatedly dipped in a gruel-like slurry of 65 parts by weight of bersilicate glass with a grain size of less than 1 .mu.m in 35 parts by weight of ethyl silicate until a coating layer with a thickness of 0.5-0.5 mm is obtained. The pom size in the layer is at 0.2 - 0, S / um. The mold is further built by dipping in a slurry of borosilicate glass particles containing 47 parts by weight of particles with a grain size of 45 .mu.m, 24 parts by weight with a grain size of 177 .mu.m and 29 parts by weight of ethyl silicate to a layer of suitable thickness, about 3-5. mm, obtained around the wax model. The model is then dried with a coating.

Model with surrounding glag coating is then placed in a vessel, the bottom of which is provided with a hole corresponding to the inner diameter of the glass tube and a shoulder corresponding to the outer diameter of the glass. Model with glass coating is placed in the vessel with the glass tube facing downwards and with the glass tube resting against the shoulder in the bottom of the vessel. Then, a slurry of borosilicate glass particles having a grain size of less than 44 microns and water is cast into the mold until a mold having a wall thickness of about 20 mm is obtained. After the mold has been allowed to dry in the vessel, vessels with mold are placed in an autoclave in which steam with a temperature of about 150 ° C melts the wax. The mold is then heated gradually; to 550-600 ° C in an oven, whereby all residues of va: disappear and the strength of the mold increases. The resulting shape becomes hard and porous with good cohesion between the glass articles. It is shown in Figure 1 with the glass tube facing down. In this. In the figure, the shape of glass particles is denoted 10, the mold space formed when the vane has run out of the annulus 11 and the glass tube is denoted 12.

The mold 11 'is then filled as shown in Figure 2 with a powder 13 of silicon nitride. The silicon nitride, which has a grain size of less than š / μm and which contains about 0.5% by weight of free silicon and about 5% by weight of yttrium oxide, is then slurried with methanol to a gruel-like consistency.

The slurry is further provided with the additive consisting of polyvinyl alcohol, polyethylene glycol and benzenesulfonic acid, so. that their contents amount to 2, 4 and 1 percent of the weight of the slurry, respectively. The slurry is degassed to remove air bubbles before it is poured into the mold.

Because. because the mold is porous, the main part is sucked up by the methanol and the additives so that a successive filling of silicon nitrite powder results in the mold cavities being well filled with. the powder. Finally, when the level in the tube 12 has stopped falling so. that new material is not taken up by the mold space 11, a gas pressure of about 2 FIPa is applied over the material in the mold space. This enables improved filling of the storage space and reduced shrinkage during drying. The drying takes place for a period of about 4-5 days at room temperature and atmospheric pressure. novel with content, the asians are heated to about 500 ° C in the five, whereby the substances added to the silicon nitride in the slurry are removed from the mold and mold space. As can be seen from Fig. 3, the mold is then placed in a vessel 15 of graphite, which is internally provided with a release layer of boron nitride. The vessel is thus of a material which is dimensionally stable at the sintering temperature of silicon nitrile. The vessel is covered with powder 14 of borsilikzztgias. The powder 14 can be replaced with, for example, a sheet of glass, which covers the opening of the glass tube 12, either it has been retained in its original length or cut off at the level of the upper surface of the mold. All in the described example used borosilicate of low-melting tooth type and contains 80.3% by weight of S102, 12.2% by weight of 13205, 2.8% by weight of 7903955-8 2.8% by weight of Al2 O3? 4.0 weight percent Na 2 O, 0.4 weight percent E 2 O and 0.3 weight percent CaO. The silicon nitride has thus been provided with a glass enclosure. One or more. vessel 15 is then placed in a high pressure suction: according to Fig. 4. For the sake of clarity, only one vessel is shown in this figure.

In Fig. 5, 22 denotes a grass stand which is supported by the wheels 25 and is displaceable on rails 24 in the floor 25 between the position shown in the figure and a position where the stand surrounds the high-pressure chamber 42. The press stand of the type consisting of an upper yoke 26, a lower yoke 27 and a pair of spacers.- 28, which are held together by a prestressed belt jacket 29. The high pressure chamber 42 is supported by a pillar 49 and contains a high pressure cylinder, which is built up of an inner tube 50, a surrounding baffle belt casing 51 and end rings which axially hold the belt casing together and form suspension means with which the high pressure chamber is attached to the pillar 49. The chamber 42 has a lower end closure 55 which sails into high pressure cylinder tube 50. In the end closure there is a groove in which is inserted a sealing ring 54, a duct 55 for degassing the products to be pressed and for supplying pressure medium, preferably argon, helium or nitrogen gas, and a duct 56 for cables for supplying heating elements 57 for heating the oven. The elements 57 are supported by a cylinder 58, which rests on. an insulating bottom 59, which projects into an insulating jacket 60. The upper end closure contains an annular part 61 with a sealing ring 62 as a seal: against the pipe 50. The sheath 60 is suspended in the part 61 and gas-tightly connected thereto. The end closure also contains. a look 63 for closing the opening in the part 61, which is usually permanently anti-ag in the high-pressure cylinder. The lid is provided with a seal 64 which seals against the inner surface of the part 61 and with an insulating lid 65 which, when closed with a high-pressure laser, projects into the cylinder 60 and forms part of the insulating shell surrounding the oven space 66 itself. The lid 65 is attached to a bracket 67, which is supported by a raising, lowering and rotating operating rod 68. In the same way as described for the device according to Figs. pressure is applied in the oven compartment.

After the Lozxe container 15 is placed in the oven compartment 66, the powder 15 is degassed with surrounding glasses 10 and 14 at room temperature for about 2 hours.

During continued evacuation, the temperature is raised to approximately 1150 ° C. The temperature increase is done as follows. slowly that the pressure does not exceed 0.1 torr for any part of the time. at about 1150 ° C the temperature is kept constant for about 1 hour, the final. the degassing uksr ooh the glass forms _ a melt of low viscosity, which completely surrounds the pzzlvret 15. Then added to 10 15 20 25 50 \. \ l LW 7903955-8 7 i is fed at the same. temperature ergon, helium or nitrogen to a pressure level. which gives a pressure of 200-500 IdPa at the final sintering temperature.

The temperature is then raised to 1700-180670, i.e. to the appropriate entrainment temperature: for the silicon nitride for a period of 1 hour. The pressure then rises at the same time. suitable sintering time under the specified conditions is at least 2 hours. After completing the cycle, however, allow to cool to a suitable discharge temperature. ïförlet 15 then contains. a glossy cake, in which the sintered powder body is visible through the solidified and clear glass. The powder body is completely embedded in the glass and has thus been below the surface of the melt in its entirety during pressing. Due to the fact that the high pressure required for the pressing has been applied, it is then applied. the glass has been low viscosity and the glass in solidified form has the same. coefficient of thermal expansion such as silicon nitride, defect-free objects can be produced with good reproducibility. The cake releases easily from the vessel due to the presence of the release layer. The glass can then be blasted or pickled away from the object.

In an alternative embodiment, the furnace run 66 is then filled after the vessel 15 with the powder 15 and surrounding glasses 10 and 14 is previously degassed at room temperature for about 2 hours, with nitrogen gas of atmospheric pressure and the oven temperature is raised to 1150 ° C during successive introduction of nitrogen gas to a pressure of 0 , 1 MPa. When the temperature has reached 1150 ° G, the glass powder forms a low viscosity melt which completely surrounds the powder body 13. Thereafter, at: sz-smma temperature, argon, helium or liquefied gas are supplied and the pressing and sintering are carried out under the conditions given in the previous example.

Sintering of ciel nitride is suitably carried out at 1600-1900 ° C and the pressure should be at least 100 MPa if no sintering-promoting additive such as magnesium oxide or yttrium oxide is used and at least 20 MPa when using such additive. _ l Same. The procedure described above for the production of a silicon nitride turbine wheel was used in a modified form in the manufacture below of a milling cutter of iron-based alloy with a composition of 1.27% by weight, 0.3% by weight of Si, 0.5% by weight of Mn , 6.4 wt% w, 5.0 wt% Mo, 5.1 wt% V, 4.2 wt% Cr, residue Fe. The steel powder has a grain size of less than 177 .mu.m. In this case, the vaaunodell is coated at the innermost part of the 0.3 - 0.5 mm thick layer ß and must be 6% 8138 fl- V high melting type eg containing 96, weight percent S102, 2.9 VíWGPPOCGHÜ 13205 and 0.4 weight percent A120; Vycor with a grain size of less than 1 .mu.m. Otherwise, the same borosilicate glass was used for all glass materials as in the previous example. The high-melting glass powder sinters to the glass powder in the rest of the mold when sintering it. and prevents the penetration of glass into the steel powder body during the isostatic pressing, which is done at a temperature of about 110 DEG C. and a pressure of about 100 .mu.m for a period of 2 hours, in order to prevent deformation of the produced mill due to different coefficients of thermal expansion of glass and steel, the majority of the glass enclosure around the cutter is removed while the glass is still at such a temperature that it is melted. "Pressure and temperature at the isostatic pressing and sintering of a ceramic or metallic material are of course dependent on the type of this material. to at least 100 MPa, preferably to at least 150 MPa. For materials other than those specifically exemplified, silicon nitride and ch high-speed steel, it can be mentioned that the temperature for alumina should be at least 1200 ° C, preferably at least 1300-1500 ° C, for comparable alloys at at least 100,000, preferably at 1100-120000 and for nickernaseraae alloy gauges via at least 10o5o ° c, rareträaesvie via 1100-125 ° C.

For the manufacture of articles of ceramic and metallic materials with very high sintering temperatures, it is conceivable to use in the mold instead of low-melting type powders of high-melting type glass such as glass containing 96.7% by weight of S102, 2.9% by weight of 3203 and 0 .4% by weight of Al 2 O; Vycor 13.05 which on heating forms a gas-tight glass layer. Further quartz glass and mixtures of particles e.g. SiO., And

Claims (6)

7903955-8 PATENT REQUIREMENTS A method of producing an article of a ceramic or metallic material by isostatic pressing of a powder of the ceramic or metallic material with a gaseous pressure medium, the powder being arranged in a glass enclosure which is made gas permeable, before the isostatic pressing during sintering of the powder, it is characterized in that the powder (15) of the ceramic or metallic material is introduced into the mold rim of a mold (10) of glass powder with an antifreeze (11) corresponding to the object to be produced and that the mold is covered with glass (14) which together with the mold forms an enclosure for the powder of the ceramic or metallic. the material, that the enclosure with the powder and the enclosure placed in a vessel which is resistant to the temperature at which the sintering is carried out is transferred into a melt with a surface limited by the walls of the vessel, below which the material in the furnace chamber is located and that one for the isostatic. the pressure required pressure is applied to. the melt with the gaseous miga 'txgvclcrnediet. 2. A method according to claim 1, characterized in that the shape of glass powder is produced by surrounding a model of the object to be produced with the glass powder and bonding the glass particles to each other. to a coherent unit, before the model is removed, whereby the model is made of a material such as wax, which tends to be removed, from the unit without it being destroyed. 3. A method according to claim 1 or 2, characterized in that the connection (10, 14) - is made gas permeable while the powder of the ceramic or metallic material and the enclosure are kept under poppy. '= i 4. A method according to claim 1 or 2, characterized in that the connection (10, 14) is made gas permeable; while the powder of the ceramic or metallic material and the connection are kept in contact with a gas in which a pressure is maintained which is at least equal to the pressure at the temperature of the gas present in the powder of the ceramic or metallic material. 5. A method according to any one of claims 1-4, characterized in that the Iceramic material consists of silicon nitride. 7903955-8 6. A method according to any one of claims 1-4, characterized in that the metallic material consists of steel, an iron-based or a nickel-based alloy. 'I