|
Ceramic tiles are the result of a manufacturing process involving various phases, which change according to the different types of product, glazed or unglazed, to be produced.Raw materials - BodyThe bodies for the manufacturing of ceramic tiles are mixtures of different raw materials, including:
- Clay raw materials, which provide the necessary plasticity for subsequent forming of the tile;
- Quartz materials, with a structural function necessary for limiting dimensional variations during drying and firing;
- Feldspathic materials, whose function is to produce a liquid phase of suitable viscosity during firing.
The body preparation consists of a series of grinding, mixing-homogenization, and water content regulation operations. At the end of this first phase, it is possible to obtain two different types of body: a powder with a 4-7% water content (suitable for shaping by pressing), or a paste with a 15-20% water content (suitable for shaping by extrusion).
Shaping and DryingMost of the tiles produced in Italy are moulded by pressing. During this process, the body - in the form of a semi-dry powder - is compressed between two surfaces. This process gives the product the desired shape, as well as the right compactness and resistance.
Terracotta and Clinker tiles are shaped mainly by extrusion: the body of raw materials is formed into the shape of a continuous ribbon, and then cut as desired. Subsequently, the body water in the product is removed by means of rapid hot air dryers.Since this process is very delicate, it must be carefully controlled in order to prevent any damage.
Glazes and GlazingGlazes are mixtures of different minerals and compounds ground in water, which are applied to the tile surface and fused onto it.During the subsequent cooling phase, the fused layer hardens to form a layer of glass, which gives particular aesthetic (brightness and colour) and technical (impermeability and hardness) qualities to the tile surface Firing and SortingThe tile firing takes place in continuous roller kilns, which reach very high temperatures (from 900 °C to over 1250 °C).Inside the kiln the tiles are first heated to the maximum firing temperature and, after a defined period at this temperature, are gradually cooled. During firing the product undergoes chemical and physical reactions and transformations which are required to obtain a mechanically resistant structure.The careful tile sorting is the concluding phase in the manufacturing process. There are three objectives to this phase: elimination of defective pieces; subdivision of tiles into first quality (first choice) and lower choice lots; grouping into homogeneous batches by shade and size
Why tiles are hard-wearing and functional
The technical properties are of fundamental importance in the choice of tiles, since it is on these that the performance and durability of the tiling depend.
These properties determine the suitability of the tiles to create a regular tiling. Regularity depends on the dimensional characteristics and appearance of the tiles, and may be influenced by the shaping method and by porosity. Shaping by extrusion usually allows for a less accurate control of dimensional characteristics, as compared to pressure shaping. Smoother and more uniform surfaces can also be obtained with pressed tiles.
These properties describe the structure of the material of which the tile is composed. The main structural characteristic is water absorption, which measures the porosity of the product.
Particularly important properties for floors, they define the resistance to loads to which the tiled surface will be subjected. The mechanical properties that are measured in tiles are the flexural modulus of rupture, which depends on the material's water absorption, the flexural
breaking strength, linked to both the water absorption and the thickness of the tile, and the impact resistance.
These properties refer to the surface of the tile. The most important is resistance to abrasion, which measures a tile's tendency to wear (in the case of unglazed tiles) or to alter its appearance (in the case of glazed tiles) as a result of wear.For unglazed tiles, this property depends on water absorption, while for glazed tiles it is linked exclusively to the composition of the glaze.
These are properties of resistance to particular temperature and humidity conditions. The most significant of these properties are resistance to thermal shock, frost resistance, depending on the material's porosity, and, in the case of glazed tiles, crazing resistance, depending on the glaze composition.
These are the properties of resistance to the chemically aggressive action of substances that may come into contact with the tile surface. Chemical properties measured include stain resistance, resistance to household chemicals, acid and alkali resistance. The compactness of the surface layer is extremely important in this aspect: in fact, a greater surface porosity promotes the absorption of these substances. Glazed products usually posses a fairly good level of chemical resistance, in particular to alkaline substances. As for unglazed products on the other hand, resistance to chemical attack is generally excellent for all products.
These properties are especially significant for the safety against risk of accidents. The main safety property is slip resistance, which is obtained by giving the tiles a rough surface. Safety properties also refer to the release of lead and cadmium (elements sometimes contained in glazes), which is especially monitored in the case of tiles whose usage brings them into contact with foods (such as worktops in kitchens). As regards slipperiness, certain types of glazed ceramic tiles are produced with a rough surface and unglazed tiles with special relieve, which ensure greater resistance to slipping.
|
