Porcelain tiles are a type of ceramic tile produced by pressing and have a water absorption of less than 0.5% (EN 14411) - the lowest for all floor and wall tiles. Initially, ceramic granite arose as a purely technical tile of increased strength for use in industrial and industrial buildings and structures. However, after improving the aesthetic characteristics of this product - expanding the range of colors and chromatic effects, reproducing the surfaces of natural stone, granite, marble and other artistic effects - it quickly conquered all areas of application, including public and residential spaces. The beginning of the production of ceramic granite dates back to the 1970s. It developed in Italy in the Sassuolo region, but a similar product was produced in other regions in the form of mosaic tiles measuring 5x10 cm. In Sassuolo, the first producers of porcelain tiles were Casalgrande Padana, Nordica, Mirage, Flaviker, Graniti Fiandre, Marazzi. The main distinctive characteristic of ceramic granite is low water absorption, which determines its properties: frost resistance, strength, hardness, resistance to staining.
Technical and commercial name
There are several names for this product: Gres Porcellanato (Italy), Gres Porcelanico (Spain), Fully Vitrified Porcelain Tiles or Vitrified Stoneware (England), Porzellan Steinzeugfliesen (Germany). The translation of these names into Russian is porcelain clay (tiles). The Russian technical and commercial name for this type of tile is ceramic granite (abbreviated porcelain stoneware).
Production technology
The technological production process takes place in several stages.
Raw materials
Conventionally divided into main and auxiliary. The main raw materials determine the technological properties of the processed mass, the appearance and technical data of the finished product. Auxiliary – regulates individual properties of the initial masses, helps optimize technological processes.
Basics:
- fireproof clay, it gives porcelain stoneware all the necessary ceramic properties;
- kaolin - clay enriched with the mineral kaolinite, increases the strength and hardness of the finished product;
- quartz sand is a skeleton-forming component in the structure of the silicate melt formed during firing;
- feldspar, it is a flux (lowers the sintering temperature) and a source of formation of the glassy phase;
- a pigment based on metal oxides (manganese, iron, chromium, cobalt), it gives color to ceramic granite.
Auxiliary:
- engobe, which is applied to the installation side of the raw tile as a protective coating;
- an electrolyte that increases the fluidity of clay suspensions and slips.
Preparation of slip
Clay components (clay, kaolin) are dosed in a set proportion, a loosening stage is carried out, and with the addition of a certain amount of water and electrolyte, dissolution is carried out in special containers with mixers. Rocky components (feldspar, quartz sand) are dosed in accordance with the proportion and sent via belt conveyors to the mill, where the already dissolved clay suspension, water and electrolyte are also supplied. In a ball mill, the mass is crushed and homogenized, thereby obtaining a slip that is ready for further processing. The humidity of the slip for spraying is 31-34%, density 1.71-1.74 g/cm 3 , grinding fineness no more than 1.0%.
Obtaining press powder
The prepared slip is dried in automated tower spray dryers. The suspension is fed under pressure through nozzles into the closed volume of the dryer. Moisture is removed as the drop flies in the coolant flow. The moisture content of granules obtained from slip is 4.8-5.2%, they have a shape close to spherical and are characterized by good flowability.
Obtaining colored press powder
The principle is the same as when obtaining unpainted (base), only in this case the slip colored with pigment is dried.
Storage and transportation of press powder
The resulting press powder is sent via conveyors to storage silos, where it is aged. Next, in a set proportion, each powder is dosed onto a common conveyor belt, which sends it through a mixer to the dosing hoppers of the press. The moisture content of the press powder is 4-4.5%.
Pressing
Pressing is the process of giving a mass given shapes and sizes, i.e. obtaining a semi-finished product. Pressing is carried out on a hydraulic press in two stages. During the first pressing, there is an initial compression of the press powder, as well as the air that is in the mass. Then the pressure is released for a fairly short time. This is done to ensure that any remaining air escapes from the under-pressed tiles. The second pressing completes the complete pressing process. The pressure for pressing ceramic granite reaches 450-500 kg/ cm2 . The use of isostatic molds allows for uniform compaction density, which reduces the likelihood of low-quality products being produced after firing.
Drying
Drying is a process that reduces the water content of the ceramic body after molding. The purpose of drying is to increase mechanical strength and reduce the moisture content of the tiles to 0.5-1%. When tiles with a relative humidity of more than 1% are loaded into the oven, the residual moisture instantly evaporates in the heating zone. Since the volume of steam is many times greater than the volume of water, the tile breaks into small pieces. Drying is carried out in vertical or horizontal dryers. Drying time from 20 to 100 minutes. depending on the design of the dryer.
Burning
When firing ceramic granite, various chemical and physical processes occur: thermal decomposition of the original raw materials, polymorphic transformations, chemical reactions between components, dissolution of some solid phases in the melt and crystallization from the melt of others. All these processes are accompanied by changes in mass, volume, chemical and phase composition, porosity, and density. The most important phenomenon that occurs during firing is the sintering process, which causes the transformation of a porous semi-finished product from a conglomerate of loosely bound particles into a dense, durable body with a given structure and properties. The firing temperature of ceramic granite is 1200 degrees Celsius, the cycle is 40-50 minutes. After firing, porcelain stoneware is a finished product that has all the necessary properties. It should be noted that the color and tone of the tile depend not only on the raw materials, but also on the temperature and firing conditions in general.
Quality control, sorting
The operations required at this stage are carried out at the output of products from automatic lines. Computerized electronic equipment checks the flatness, squareness and dimensions of each tile to ensure compliance with European and Russian standards. Special staff sorts tiles by tone and appearance. Defective tiles are destroyed.
Package
Using computerized electronic equipment, grade and caliber information is transferred along with the product, which is moved to the output appropriate for its intended purpose. When a certain number of tiles have accumulated at the output, which make up one package, this group in the form of a stack is sent to a packaging machine, where it is automatically packed into boxes. Next, markings are applied to the box: grade, caliber, tone, code, date of manufacture, etc. Packed boxes are automatically placed on pallets by special robots.
Rectification
Rectification is the process of additional processing of the ends of porcelain tiles with diamond tools after firing. The tolerances for deviations from the correct shape for rectified porcelain stoneware of the 60x60 cm format are no more than 0.5 mm, while for untreated material it is up to 1.5 mm. Thus, the tile is shaped like an ideal rectangle or square, which greatly facilitates and speeds up the process of laying it, as well as installation in systems of suspended ventilated facades. The uniqueness of this proposal lies in the fact that rectified porcelain stoneware is ideal in its geometry and is produced in a given caliber.
Sanding and polishing
Ceramic tiles can have natural, textured, profile, relief, ground, polished surfaces. Special grinding machines with abrasive discs grind and polish the surfaces of the tiles, giving them a mirror or matte shine. This increases the range of tile processing versatility and opens up new artistic possibilities.
The article was based on the following materials:
“Ceramic tiles: a modern encyclopedia” comp. Sergeeva E.E. Estima company .