Druckgießen tonmineralfreier Suspensionen am Beispiel von Siliciumnitrid

Pressure casting is a forming method which has been known for a long time. This forming technique has been accepted more and more in the sanitary ware production over the last fifteen years due its clearly higher productivity as compared with plaster mould slip casting. However the application of pressure casting in the field of non-clay ceramics is very limited and under development. A laboratory pressure casting machine was used for casting of aqueous silicon nitride slips. Several commercial polymethylmethacrylate materials were applied as the filtering and moulding material. The penetration of fine powder particles into the mould was avoided by partially flocculation of the slips. With the partially flocculated slips lower green densities were reached (maximum 54 per cent) compared with pressure cast deflocculated slips (maximum 63 per cent). In both cases the slip pressure was varied in the range 1 MPa - 3 MPa and it did not significantly influenced the green density. The bending strength of the sintered samples was between 700 and 800 MPa and it is consequently lower than the strength of dry pressed samples. Large pores because of a inhomogeneous distribution of the polyacrylate binder were detected as defects in the microstructure. Further research work is necessary to show the principle benefit of this wet forming method to advantage also for the non-clay ceramic powders.