Wikijunior:How Things Are Made/Ceramic/Ceramic Tiles

Product
Ceramic tiles are used for house decorations. Beside as decorations, ceramic tiles have properties of being impervious to liquid, meaning that the ceramic tiles are waterproof against liquids and won't get dirty due to liquid.

Raw Materials
The raw materials used to form tile consist of clay minerals mined from the earth's crust such as sands/clay as base material / binder, talc to provide whitish colour to tile, feldspar that are used to provide glossy finish and lower the firing temperature, and chemical additives required for the shaping process. The minerals are often refined near the mine before shipment to the ceramic plant.

A glaze is a glass material designed to melt onto the surface of the tile during firing, and which then adheres to the tile surface during cooling. Glazes are used to provide moisture resistance and decoration, as they can be colored or can produce special textures.

Process
Step 1 - The raw materials determine the color of the tile, which can be red or white in color, depending on the amount of iron-containing raw materials used.It is important to mix the right amounts together to achieve the desired properties. The raw materials must be pulverized and classified according to particle size. Ball mills consist of large rotating cylinders partially filled with spherical grinding media that are used to reduce large lumps of material.

Step 2 - The raw materials are intensive mixer uses rapidly revolving plows. This step further grinds the ingredients, resulting in a finer particle size that improves the subsequent forming process. Sometimes it is necessary to add water to improve the mixing of a multiple ingredient batch as well as to achieve fine grinding. This process is called wet milling.

Alternatively, it can be performed using a ball mill. The resulting water-filled mixture is called a slurry or slip. The water is then removed from the slurry by filter pressing (which removes 40-50 percent of the moisture).

Step 3 - Most tile is formed by dry pressing. In this method, the free-flowing powder containing organic binder or a low percentage of moisture-flows from a hopper into the forming die. The material is compressed in a steel cavity by steel plungers and is then ejected by the bottom plunger. Automated presses are used with operating pressures as high as 2,500 tons.

Alternatively, extrusion plus punching is used to produce an irregularly shaped tile and thinner tile faster and more economically. This involves compacting a plastic mass in a high-pressure cylinder and forcing the material to flow out of the cylinder into short slugs. These slugs are then punched into one or more tiles using hydraulic or pneumatic punching presses.

Step 4 - Ceramic tile usually must be dried (at high relative humidity) after forming, especially if a wet method is used. Drying, which can take several days, removes the water at a slow enough rate to prevent shrinkage or cracks. Continuous or tunnel driers are used that are heated using gas or oil, infrared lamps, or microwave energy. Infrared drying is better suited for thin tile, whereas microwave drying works better for thicker tile.

Step 5 - In this process, the tile goes through a low-temperature firing ( <800°C ), called bisque firing, before glazing. This step removes the volatile organic chemical (VOC) from the material and most or if not all of the shrinkage.

Step 6 - To prepare the glaze, similar methods are used for the tile body. After a batch formulation is calculated, the raw materials are weighed, mixed and dry or wet milled. The milled glazes are then applied using the bell/waterfall method, a stream of glaze falls onto the tile as it passes on a conveyor underneath. Sometimes, the glaze is simply sprayed on.

Step 7 - After glazing, the tile must be heated intensely to strengthen it and give it the desired porosity. The body and glaze are then fired together in a process called glost firing ( > 1100°C). Both firing processes (Bisque and glost) take place in a tunnel or continuous kiln.

Step 8 - The ceramic tiles are considered finished processing and ready to be packed and sold.