The forming process is highly prone to quality problems because slip, equipment, mould and environmental variables interact within the same production cycle.
Temperature changes slip viscosity and dewatering speed.
Insufficient vacuum allows air bubbles to remain in the body.
Filling pressure, pressure-rise rate and holding time determine particle packing, wall thickness and green strength.
A deviation in any one of these conditions can appear as a soft green body, hidden crack, local density difference, deformation or unstable demoulding.
Ceramic sanitary ware forming is the process in which slip fills a porous mould, loses water and develops a consolidated particle layer.
Green-body density is not determined by maximum pressure alone. It results from the interaction of solids loading, rheology, air content, pressure difference, casting time and mould permeability. Forming is therefore a system-control problem rather than a single machine-setting problem.
Temperature controls rheology and casting speed. Increasing slip temperature generally reduces liquid viscosity and accelerates water movement. However, the fastest casting condition does not necessarily produce the best compaction. In one study of ceramic slurry, the casting rate was highest at 65°C, while the most favourable compaction and uniform densification occurred at 45°C. Although the material was calcium hydroxyapatite rather than sanitary ware, the result demonstrates an important process principle: temperature changes both production speed and particle consolidation. A factory should therefore stabilize slip and mould temperature instead of compensating for seasonal changes only by extending casting time. |  |
Vacuum controls internal pore defects. Air can enter the slip during mixing, recirculation, storage and pumping. If bubbles are not removed before casting, they may become internal pores, weak areas or surface defects after drying and firing.
A slip-degassing study involving reaction-bonded silicon nitride found that vacuum and heat treatment increased apparent density from 2.89 to 2.95 g/cm³, reduced porosity from 52.9% to 49.5% and increased flexural strength from 8.1 to 9.3 MPa. These values are not sanitary ware production targets, but they provide measurable evidence that removing entrapped gas can improve density and reduce pore-related weakness.
Vacuum control should cover more than the vacuum gauge. Degassing duration, slip level, foam formation, pump stability and air re-entry during transfer should also be monitored.
 | The casting curve controls density distribution. As the consolidated wall becomes thicker, its permeability decreases and the resistance to further water removal increases. A constant inlet pressure may therefore provide strong consolidation near the mould surface but weaker particle packing in later-forming regions. Research on ceramic filtration explains that a stepwise increase in slip inlet pressure can compensate for the increasing pressure drop across the growing cast layer. This is why a controlled pressure curve is usually more reliable than immediately applying maximum pressure. |
Record slip density, viscosity, temperature and thixotropic recovery.
Check vacuum level, degassing duration and bubbles during transfer.
Standardize filling, pressure rise, holding, pressure release and demoulding.
Validate the cycle using green-body weight and critical wall thickness.
Trace defects by machine, mould, slip batch, shift and process recipe.
Adjust parameters from measured results rather than operator experience alone.
Industry practice includes an integrated system that measures the thickness of the product leaving the casting cycle and uses feedback to optimize casting time when injected-slip rheology changes. This demonstrates the industrial shift from fixed cycle settings to result-based process control.
Sunlets combines ceramic sanitary ware manufacturing with forming-equipment and mould development. Slip properties, mould structure and pressure programs can therefore be tested together under production conditions, helping establish repeatable forming windows for complex OEM and ODM products.
Stable forming does not mean maximizing pressure, vacuum or cycle time individually. It means matching slip temperature, degassing conditions and the casting curve so that particles consolidate uniformly throughout the product.
When green-body density is stable, drying, glazing and firing become more predictable. When forming density is already uneven, later processes can reduce some visible symptoms but cannot fully eliminate the original structural difference.
Can a temperature change be compensated for only by adjusting casting time?
No. Temperature also changes viscosity, dewatering and particle arrangement. Adjusting time alone may produce acceptable wall thickness while leaving an uneven density distribution.
Is a higher vacuum level always better?
No. The vacuum window should match slip condition, equipment capability and production cycle. The process must also prevent the slip from drawing air back in after degassing.