Moulding methods in the ceramic world are quite diverse and one of these methods is the casting technique. This method, which is preferred especially for mass production, involves the shaping of ceramics with liquid mud (casting mud) with the help of plaster moulds. The casting technique is carried out by pouring or pumping deflocculated (separated) liquid mud with low water content into moulds.
Advantages of Casting Method The casting method has several important advantages in the production of ceramics: Mass Production: Hundreds of identical parts can be produced using many moulds. Production of Difficult Shapes: Casting enables the creation of complex forms that cannot be made on a potter's wheel. It is especially ideal for the production of thin-walled and complex parts. Flexibility: With this method, both fine porcelain pieces and large and heavy ceramic products can be made. Equipment Requirement: The fact that it does not require special machinery and equipment makes it easily applicable in the workshop environment. This method became widespread about 200 years ago with the invention of plaster of paris and has been used ever since, especially for large tonnage production such as sanitary ceramics (washbasins, toilet bowls, etc.).
Which Slurries are Suitable for Casting? The muds used for the casting process can either be purchased ready-made in liquid form or powdered and mixed with water. Many ceramic slurries can be made into casting slurries with suitable recipes. The plasticity (elasticity) of casting slurries is generally lower, enabling rapid drying of products with less risk of cracking. Chamotte muds are not suitable for the casting process because chamotte (ground baked clay used in porcelain and ceramic production) is not well suspended in the mud and adversely affects the flowability properties of the casting mud.
Preparation of Casting Sludge Specific Gravity and Deflocculation For the ideal consistency of the casting slurry, the correct ratio of water and slurry must be observed. Specific gravity is used to understand the accuracy of the water and mud ratio of the casting mud. This ratio can be found by measuring the weight of 100 ml of mud in grams. Generally, a specific gravity of around 1.80 is considered a good mud-water ratio. Chemical separators (deflocculants) are added to make the sludge more fluid. This process is called deflocculation. In this way, a sludge with better fluidity is obtained with less water.
How is the Casting Process Performed? The casting process is applied step by step. Here are the basic steps to be considered: Mould Preparation: Make sure the moulds are clean, never use water in the moulds. Organising Moulds: Line up the moulds according to their size and join them tightly. Preparation of Sludge: Mix the casting slurry and make sure there are no air bubbles. Casting: Pour the mud into the mould slowly and evenly, filling the mould every 5-10 minutes. Mould Drying: When the mud thickness is reached, drain off excess mud and dry the mould. Aging and Recycling of Foundry Sludge Casting mud should usually be used within 2-3 weeks. Over time, carbon dioxide in the air causes the sludge to lose its fluidity. The sludge should therefore be stored in airtight containers. Residual casting sludges can be recycled by adding a maximum of 20 per cent to new mixes. However, using more can adversely affect the quality of the sludge. When recycling casting sludge, attention should be paid to contamination from gypsum particles.
Final Thoughts The casting method is a technique that stands out with its practicality and flexibility in ceramic production. It can be used in a wide range from mass production to complex forms and it is possible to achieve successful results with careful planning.