Plastic and nonmetallic article shaping or treating: processes – Removal of liquid component or carrier through porous mold...
Patent
1995-02-03
1997-09-16
Czaja, Donald E.
Plastic and nonmetallic article shaping or treating: processes
Removal of liquid component or carrier through porous mold...
264 86, 264299, 264650, 501 88, 501 90, 501 97, 65 24, C03B 4002
Patent
active
056675488
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for producing ceramic green bodies, as set forth below.
Essentially five shaping processes are known for the production of green bodies, more specifically pressing, isostatic pressing, extrusion, slip casting and injection molding. The choice of a shaping process depends on the configuration, function and number of items of the desired green body. The pressing and isostatic pressing processes use starting powder materials which are capable of flow and which can be easily pressed. Extrusion which is preferably suitable for axially symmetrical components makes use of a mixture of powders and organic or inorganic plasticizers. The injection molding process which is known from plastic technology is used for green bodies of a highly complex shape. In that process a ceramic powder/thermoplastic mixture is injected into a mold and then after the shaping operation the thermoplastic material or materials are driven out of the green body. In the slip casting procedure ceramic powder with water is processed with the addition of tensides and binders to produce a slip which is capable of flow, and then poured into porous molds. Removal of the water in the porous molds, for example comprising gypsum or porous plastic materials, results in green bodies which, after being removed from the mold, are dried and then sintered.
Slip casting has long been used and is preferably employed for the production of larger hollow green bodies. In spite of its wide spread and use, slip casting suffers from a number of disadvantages.
The hardening mechanism depends on the removal of water; consequently soluble constituents have a tendency to migrate, with the result of irregular distribution in the shaped green body.
The shaping process is slow, and density gradients may also occur in the green body. In addition, a green body which is produced in accordance with the known slip casting process is sensitive to mechanical effects and thus is only suitable to a limited degree for working in the green condition. The porous molds also have to be dried very carefully end at considerable cost, before they are ever put to use again. The molds impose limits in terms of the geometrical configuration of green bodies, in that for example undercut configurations are only possible to a limited degree.
Taking the known slip casting procedure and the disadvantages from which it suffers as their basic starting point, the inventors set themselves the object of further developing the slip casting process in such a way that the known disadvantages are eliminated. In accordance with the invention the object is attained by the process of the present invention which includes adding an active substance to a slip for decomposing the slip and forming ions for gradually altering the condition of the slip over time until the slip has solidified.
The process according to the invention provides a technically simple alternative to the known shaping processes, which is quick and thus inexpensive to carry into effect. In particular, in regard to the known slip casting procedure, improvements are achieved insofar as it is possible to shape green bodies which are of a geometrically more demanding configuration than hitherto, which satisfy all requirements to be made in respect thereof, in regard to their structure, surface properties end mechanical characteristics. As the hardening mechanism in the case of the slip casting process according to the invention is no longer primarily dependent on the removal of water, migration end unequal distribution of soluble constituents is extensively suppressed. The shaping process which takes place in accordance with the invention is significantly faster than the known processes, and the development of density gradients can also be avoided. In contrast to the green bodies produced in accordance with the state of the slip casting art, green bodies produced in accordance with the process of the present invention, with a suitable slip composition, are suitable for processing in the green condition, for exa
REFERENCES:
patent: 2527390 (1950-10-01), Blaha
patent: 2979401 (1961-04-01), Szymaszek
patent: 3216841 (1965-11-01), Thellmann
patent: 4624808 (1986-11-01), Lange
Baader Felix
Gauckler Ludwig J.
Graule Thomas
Colaianni Michael P.
Czaja Donald E.
Gauckler Ludwig J.
Graule Thomas
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