Slip preparation determines rheology, mould filling, dewatering speed, green-body strength and demoulding performance in ceramic sanitary ware production. Changes in raw-material ratios, water content, particle-size distribution, deflocculant dosage, water quality or temperature can cause incomplete filling, uneven wall thickness, sticking, deformation and drying cracks.
Slip preparation is the process of batching, grinding, mixing, screening and ageing clay, kaolin, quartz, feldspar, water and deflocculants to create a stable suspension suitable for casting.
A production-ready slip should not simply have low viscosity. It must provide an appropriate balance of solids loading, fluidity, thixotropy, suspension stability and dewatering performance.
A study published in Applied Clay Science explains that sanitary ware slips exhibit non-Newtonian and thixotropic behaviour. This means that one viscosity reading cannot fully describe how a slip will behave during storage, pumping and mould filling.
· Solids loading affects casting time and shrinkage.
· A low-solids slip contains more water that must pass through the mould before sufficient wall thickness develops.
· This can extend the casting cycle and increase drying shrinkage.
· However, excessively high solids loading without adequate dispersion can make pumping and filling difficult.
Viscosity and thixotropy affect mould filling. A highly viscous slip may not reach narrow waterways, corners or detailed surfaces. Rapid structural recovery after the slip stops moving may also reduce flow before the mould is completely filled.
Deflocculation affects stability and release. Insufficient deflocculation causes particle agglomeration and high viscosity. Excessive deflocculation may lead to settling, unstable drainage, non-uniform green bodies and mould sticking.
Digitalfire explains that the objective of deflocculation is not simply to achieve the lowest possible viscosity. The slip must remain fluid while maintaining suspension stability and suitable casting behaviour.
Measure density, viscosity, temperature, sieve residue and thixotropic recovery together.
Adjust deflocculant dosage when raw materials, process water or temperature change.
Connect slip data with filling time, wall thickness, demoulding and actual defects.
Do not use one viscosity target for every product, mould and forming process.
Establish an operating range rather than relying on a single laboratory value.
Sunlets combines sanitary ware manufacturing with the development of ceramic forming equipment. This allows slip rheology, resin-mould permeability, product geometry, casting pressure and demoulding procedures to be optimized as one integrated production system.
Stable slip preparation does not mean maintaining one permanent recipe. It means controlling the relationship between solids loading, rheology, casting speed, green-body strength and release performance.
When slip properties remain within a reliable process window, pressure, casting time, drying and firing parameters can be optimized effectively. When the slip is unstable, adjusting machine settings alone will rarely solve the root cause.
Is lower viscosity always better?
No. Very low viscosity may indicate over-deflocculation and increase settling or demoulding problems.
Why can filling remain incomplete when viscosity is acceptable?
Possible causes include rapid thixotropic recovery, particle agglomeration, excessive sieve residue, restricted feeding paths or poor mould venting.