Processing of clay slip to print ceramic castings formation is actually almost the same as the preparation of clay materials for the formation of other techniques, the difference is in the addition of a material called deflocculant, this material allows the clay particles remain in suspension fluid and does not form a sediment at the bottom of the mold.
In the process of this material will be absorbed by the mold and stick to the walls of the mold, after several of minutes the excess clay slip is issued, the process can be formed hollow ceramic objects with the same relative wall thickness. In the ceramic industry forming technique is very necessary to be able to mass-produce ceramics, skill preparing printed material therefore cast an important requirement to be able to do the printing technique of forming the cast.
Mass slip cast molding is typically used to print three-dimensional ceramic objects, using a mold so that the two parts or more objects have the resulting cavity and has a wall thickness that is relatively the same. Castings printing techniques mentioned above are often referred to as hollow casting.
Natural clays such as the type of Earthenware and Stoneware and processed minerals such as kaolin, feldspar, whiting (chalk), quartz, ball clay, bentonite, and others can be used to make the formula (recipe) print castings as soil bodies: Earthenware , Stoneware, Earthenware white, white stoneware, soft porcelain, and porcelain.
Such materials must be dry and preferably ingredients that have been finely ground, it is intended to be more accurate weighing to obtain the viscosity of clay slips appropriately.
Deflokulan materials are materials such as alkali silicate electrolytes (usually sodium) or carbonate (soda ash). Electrolyte changes will alter the molecular or soil particles repel each other, helping the spread of the particles in the liquid slip, improve fluidity, as well as help the suspension particles and reduces shrinkage in the ceramic body, thus not clumped particles of clay that will be able to accelerate the deposition. In addition, it can also reduce the amount of water that is at least 25% is required with the same level of fluidity.
Deflocculant used may be sodium silicate (waterglass), sodium hydroxide (soda ash) and sodium carbonate. The number needed just a little deflocculant usually between 0.2% -0.5% of total dry clay is used, while the amount of water by about 35% – 50%. Number deflocculant to soil types commonly used Earthenware approximately 0.25% to 0.50% of total dry weight.
The use of too many will make the molds easily fragile and printouts are more difficult to cut or trimmed. That needs consideration is how to reduce the water content in the mold but also maintain a level of fluidity of the clay slip. There are some chemicals that are commonly used as deflokulan, namely:
1. Sodium silicate / waterglass (2Na2O.SiO2); additions to the clay slip between 0.2% -0.5% by weight of dry clay.
2. Sodium carbonate / soda ash (Na2CO3); additions to the clay slip is less than the sodium silicate.
3. Sodium polyacrylat; additions to the clay slip between 0.3% -0.5% by weight of dry clay.
4. Calgon.
5. Dispex (combination product of sodium silicate and soda ash)
6. Darvan (equivalent to dispex), the advantage of this product is not easily absorbed by the mold so that it can extend the life of the mold