Abstract
In order to know the relations between castabilities and rheologcal properties of casting slips, several coagulants were added to the alkaline deflocculated slips. The body used was a typical porcelain body, its calculated mineralogical composition was 53.6% kaolin, 0.8% mica, 20.6% feldspar, and 25.0% quartz, and exchangeable capacity was 4.6m.e./100g. Sodium silicate was used as a deflocculant and the water contents in slips were all 34.7%, selected flocculants were sodium bicarbonate, sodium fluoride, potassium ferrocyanide, sodium citrate, Rochelle salt, chloride of ammonium, magnesium, calcium, manganese, barium, aluminium, and magnesium fluosilicate. The following properties were carried on these slips, i.e. plastic viscosity and Bingham yield value from the slope of the down curve, plasticity ratio (lower yield value/Bingham yield value), rate-on-cast and retained water in cast body; and also an cast bodies, modulus of rupture and apparent porosity.
There was no relations between above-mentioned casting properties and rheological characteristics, but the thixotropic breakdown characteristic of the slip is of considerable importance to the rate-on-cast. Among used coagulants, Rochelle salt is a satisfactory modifying agent, but as the anion takes the major role to castabilities therefore the amount of additions was selected cautiously, many coagulants are useful to the accelerator to the rate-on-cast. The usual control of casting slips is through specific gravity or water content and rheological measurements, but these are inadequate and the working trials to determine casting behavior are very important.
