|Monthly Tech-Tip |
This deflocculated slurry of 1.79 specific gravity (only 28% water) has just been poured into a mold. The mold is dry, the wall thickness of the bowl will build quickly and the liquid level will sink only slightly. It can be drained in minutes (for a wall thickness of 3-4 mm). The clay is not too plastic (too fine particle sized) so it is permeable enough to enable efficient water migration to the plastic face. If the specific gravity of this slip was too low (too high a percentage of water) the liquid level would sink drastically during the time in the mold, take longer to build up a wall thickness and water-log the mold quickly. If the slip contained too much deflocculant it would cast slower, settle out, form a skin and drain poorly. If it had too little deflocculant it would gel in the mold and be difficult to pour out. The rheology is just right.
Understanding the Deflocculation Process in Slip Casting
Understanding the magic of deflocculation and how to measure specific gravity and viscosity, and how to interpret the results of these tests to adjust the slip, these are the key to controlling a casting process.
In ceramics, this term refers to the flow and gel properties of a glaze or body suspension (made from water and mineral powders, with possible additives, deflocculants, modifiers).
In ceramics, the specific gravity of slurries tells us their water-to-solids ratio. That ratio is a key indicator of performance and enabler of consistency.
Deflocculation is the magic behind the ceramic casting process, it enables slurries having impossibly low water contents and ware having amazingly low drying shrinkage