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Slip preparation

SLIP PREPARATION

Difficult blunging of clays or too high residue

Problems adjusting density or rheology

Too low density or too high viscosity

Too high thixotropy

Ageing

Difficult blunging of clays or too high residue

Blunging the plastic materials (clays) is the first step of the casting slip preparation. It is a key step to ensuring the formulation is consistent and that it has the right rheological parameters.

To ensure the clay phase preparation is efficient, the blunging system (power installed, propeller type, sieving capacity) and the clay type have to be compatible.

Potential issues are generally related to sieving and due to un-dispersed clay particles. This leads to an inconsistent formula, waste of good material, longer blunging and sieving time. Too high residue levels in the clay can also lead to similar issues.

To speed up clay dispersion and lower residue levels, we recommend the use of pre-processed clays.

  • UK : Hycast Plastic, Hycast LR
  • Thailand: Thaicast S1, Thaicast S2, Modiscast S1, Modiscast S4
  • India : Certicast
  • US: OM4, KTS Classic in air floated form

Problems adjusting density or rheology

Basically, sanitaryware casting requires high solid percentage (density around 1800-1820 g/L for vitreous china, and 1960-1980 g/L for fine fireclay) together with good fluidity. The slip has to present low viscosity with adjusted thixotropy in order to produce difficult and complex pieces with good yield.

In some cases, the use of poor quality or unsuitable plastic raw materials (clays with a high illite or smectite / montmorillonite content) presents manufacturers from achieving the right rheological parameters.

Too low density or too high viscosity

To increase density, we recommend you use products with higher fluidity that will enable you to boost the solid content of the casting slip. The same applies if increasing the deflocculant level does not enable you to achieve the proper viscosity or if the slip contains too much deflocculant, causing casting cords and mold corrosion.

High fluidity clays

  • UK: Hycast Rapide, Hycast FFC, Hycast Plastic
  • Thailand: Modiscast S4
  • US: M#5

High fluidity kaolins

  • UK: NSC, Remblend,
  • US: KT Cast, OptiKast
  • Brazil: Paracast Plast

Too high thixotropy

Too high thixotropy generates many issues during the casting process of sanitaryware pieces such as soft and flabby pieces causing bad drainage, deformation and cracks.

When the thixotropy cannot be adjusted using deflocculants, solubles (salts), such as sulfates (SO₄²-, Cl-, NO₃-, etc., from either the water supply (especially well water) or from the raw materials themselves are a potential cause. The return slip may also be contaminated with plaster from the molds, bringing sulfates, and increasing thixotropy.

The use of low sulfate clays from selected feeds and fully refined clays (soluble salts have been removed by filter pressing the clay) may help decrease the total soluble salt level in the casting slip.

  • Thailand: Modiscast S1, Modiscast S4
  • UK: Vigor DV60

Ageing

Ageing is an important way of stabilizing the rheology of the slip before casting. However, some important issues may arise during the maturation of the slip.

Slip sedimentation

Slip sedimentation usually arises when density is too low. A part from accidents such as excess water, and if an increase in density is not possible (slip already at optimal defloculation), we recommend replacing a low fluidity clay or kaolin by a material with better properties.

High fluidity clays

  • UK: Hycast Rapide, Hycast FFC, Hycast Plastic
  • Thailand: Modiscast S4

Still having issues with slip preparation? Have a question you need to ask us?

Please contact us. We will be only too happy to help.

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Ceramics