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Slip Casting (Stages involved (Pouring of slurry/ suspension/ slip of…
Slip Casting
Stages involved
- Pouring of slurry/ suspension/ slip of ceramic body composition into a porous mold
- Extraction of water into moulds through pores or voids in mould
- Forming of solid layer on surface of mould
- Excess slip removed ( except solid cast)
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Parameter
Slip density
Affected by addition of deflocculant or dispersant. The higher the percentage of deflocculant used, the higher the solid content and therefore higher the slip density. Cast body when denser, produced better physical and mechanical properties.
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Viscosity
Viscosity refers to the mobility of the slip; its "thickness" or "runniness". A slip that has high viscosity is thick like syrup and one that has low viscosity is fluid. A slip with a viscosity that is too high is said to be "thick". A deflocculant is used to lower the viscosity of a slip.
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Thixotropy
Thixotropy refers to changes in a slips runniness or viscosity over moments, minutes or hours of time. It also refers to differences in the way the slip responds to stimuli to make it move once it has become motionless for varying amounts of time.
Thixotropy can prevent sedimentation from occur, So that during casting, the composition can be remained as same. However, if too high the thixotropy, viscosity is too viscous until water cannot flow. Eventually, it leads to soft product and easily failed.
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Disadvantages
Differential shrinkage can be caused by a packing factor gradient that can be induced in a mold during water removal
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Requires large working area ( the mold used have low toughness thus fracture easily and large mold inventory must be maintained to insure a constant production rate)
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Production rate is lower than the rate of dry pressing, injection molding or extrusion
Advantages
Any form of ceramic suspension is possible as long as the suspension is chemically stable with right concentration
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Type
Drain Casting 
- Slip is poured into plaster of Paris mold cavity
- Water is absorbed into plaster mold to form a firm layer
- Excess slip is poured out.
- Partial drying to form shrinkage resulting in release of cast from wall of moulds
- Green body is removed from the mold.
Solid Casting
- Slip is poured into plaster of Paris mold cavity
- Water is absorbed into plaster mold.
- Green casting takes place
- Water absorbed from slip into porous mold.
Excess water can be removed by external
pressure.
- Finished piece is removed from slip and trimmed. Sometimes, a mould releasing agent like oil, starch and graphite are used.