How Porcelain Tiles Are Made

Types of Tiles

Most tiles made of clay or clay mixture are ceramic tiles. Within that classification, there are porcelain and non-porcelain tiles. Porcelain tile uses dust pressed under high pressure and other special techniques that differ from ceramic tile. These methods make porcelain more durable, finer grained and less absorptive than its non-porcelain counterpart, normally called ceramic tile. Porcelain tile starts with a combination of quartz or silica, clay and feldspar or flint. The clay contains a minimal amount of impurities and has an ample amount of kaolinite. The major difference is the water absorbing ability when finished. It must be less than 0.5 percent.

Crushing

The manufacturers select the combination of the primary ingredients and use the proportions they need for the green, unfired mixtures to get the qualities they want in the final product. The materials are crushed using several machines. The jaw crusher has metal jaws which swing to crush the bigger pieces. Those pieces then go to a hammer mill that reduces them to less than 0.1 inch by pounding them with a succession of moving steel hammers. The final grinding stage uses the ball mill that grinds the particles inside a rotating cylinder.

Washing

While the machines crush most of the rocks finely, it doesn't do them all or remove impurities. In order to remove larger pieces and undersized pieces, the material gets a shaking. The ground rocks are put on a series of sloped screens which mechanically vibrate to shake the smaller particles out and leave the larger ones on the screens. Other mixers remove any excess iron from the dry powder.

Forming

The most accepted method for creating porcelain tile from the crushed material is pressing. The machine presses and shapes the tile into flexible molds or rigid die. There are uniaxial pressers that create pressure from one direction or isostaic pressers that keep the pressure equal on all sides.

Bisque Firing and Glaze

Bisque firing occurs first if the porcelain is to receive a glaze. It fires the porcelain at lower temperature and vaporizes the contaminants. It also reduces any shrinkage later. The next step involves the application of a glaze, which is normally a combination of silica, alumina and calcia. For a matte glaze, the silica is decreased and the alumina increased. If the porcelain is unglazed, the manufacturer omits these steps.

Final Firing

The porcelain then travels through a long tunnel kiln. There are temperature zones throughout so that it first preheats the ceramic tile and then moves it to the main firing area where it burns out impurities and the materials bond. The last area of the kiln is the area where the tile cools before it's packaged.