PRODUCTION METHOD - TECHNOLOGY
Designation of the technology at the brick and roof tile plants is based upon the drying system (natural drying-artificial drying), production method (labor intense-technology intense), automation (fully automatic-semi-automatic), raw material processing and forming (vacuumed-non-vacuum) and firing method (Hoffman-tunnel). The technological designation is usually done by the firing system in Turkey. Considering from this viewpoint, the most common system is the Hoffman system in our country. The number of the plants running by the tunnel kiln system is limited. These system experienced interchanges in time and some mixed technologies emerged. Artificial drying was performed beside the Hoffman firing technology; the tunnel kiln technology was supported by natural drying; and the arched tunnel kiln system was developed by mixing the tunnel firing system with the Hoffman system. The production method may be scrutinized better by studying the brick and roof tile production stages:
- Raw material preparation
- Forming
- Drying
- Firing
RAW MATERIAL PREPARATION
Clays used in the production of bricks and roof tiles are usually found in the nature and extracted in a damp and plastic consistency, sometimes in a dry and triturable form and sometimes in a rock form. Therefore, the clay obtained in the nature and brought in the production plants must go under a series of preliminary preparation so that it may have suitable properties in terms of both size and composition. First, grinding process is carried out so that the raw material may have a processable property. The raw material must be well crushed and made into fine particles so that it may be a homogenous material, and has plasticity and cohesion properties. For this purpose, large stones and wastes it contains are separated by means of various machines (stone separator, roller, edge mill, etc.) and ground to the desired particle size. Further, in order to obtain a homogenous clay pug, the clay must be crushed and mixed with a sufficient amount of water. When water is added into the clay in small amounts, its plasticity increases to some extent. Water addition may not only be made prior to grinding but after grinding as well. Settling is the most important one of the raw material preparation stages. It is so important a factor which affects the quality of the produced material. Due to the thixotropic properties of clays, the kneaded pug gains strength during the settling. The settling process is performed prior to or after the grinding process..
FORMING
The pug which gains a property suitable for forming at the end of the raw material preparation process is formed by the use of different methods and semi-finished bricks/roof tiles of different forms and sizes are obtained. Molding, pressing and extruding methods are usually employed in forming. Molding is a method usually employed in the production of blend bricks. Pressing is usually employed in the production of roof tiles. The raw materials prepared in the form of hard biscuit in the extruder are given the form of roof tiles by means of presses of various types and sizes. In the extruding (vacuuming) method, the prepared clay is extruded from the mold by means of a worm screw and at a certain pressure. In this method, the prepared raw material conveyed to the extruder (vacuum press) is deaerated at 740 mmHg by the vacuuming method and plasticized. The raw material pushed by means of spirals takes the form of its two dimensions by means of the mouthpiece at the mouth of the vacuum press and leaves the press in the form of an infinite belt. Then, the material cut by fine wires take its third dimension and is allowed to dry.

DRYING
Drying is the process of removing the water which exists in the clay or which has been added in order to make into a consistency suitable for forming it. Two methods, namely natural drying and artificial drying, are used in the drying process. Natural drying is a system which is in intensive use in our country and which is based on the principle of utilizing the heat energy in the atmosphere. Those products leaving the extruder in a wet condition are usually aligned in a certain order in the drying stands and such stands are placed in large indoor or outdoor areas and allowed to dry. This drying method seems to be economical as it does not require an additional energy in the drying process. However, need for large areas for the drying process, very slow and long drying process, insufficient control over it, dependence of the drying upon weather conditions (temperature, humidity, wind, etc.), too much labor constitute the disadvantages of the method. Artificial drying is to carry out the drying by increasing the temperature and the air movement by the provision of an additional energy without leaving it to the natural conditions. It is based on the principle of removing the free water in the clayed material first with high steam pressure and low temperature and with low steam pressure and high temperature towards the end of the drying. This is carried out utilizing drying chambers or tunnel drying kilns.

FIRING
Firing is the last stage in the production of bricks and roof tiles. As the clay loses the water available in it in a free state and the water which it absorbs later at the drying stage thereof, some reduction (shrinkage) occurs in its dimensions. During the firing, clay is subject to chemical reactions. Organic substances completely burn at approximately 300°C and lose their molecular water at approximately 450-650°C. This new material which is formed by the firing of the clay pug between 850-950°C is now a hard product with some certain strength and color which does not change its shape. Firing usually consists of the following stages:
- Filling
- Heating
- Firing
- Cooling
- Discharging
The type of kiln which is most intensively used in Turkey is the Hoffman kilns. Tunnel kilns make up the next intensive use. There are also some 20 arched tunnel kilns which are the mixture of the Hoffman and tunnel kilns. Hoffman kiln: The cross-section of the kiln is in the form of a circular vault. The fire moves but the products stand still. This kiln is one which uses the heat obtained from the fuel at so high an efficiency and which has a high production capacity and speed. Combustion occurring over the material in a state of complete firing, the air moving in the kiln being heated in contact with the fired material on one side and the heated air being used in order to heat up the unfired material are the most important advantages of this kiln. Fuel is injected from the jets above the kiln and the injecting process progresses along the jets as the firing stage advances. Such solid fuels as coal, etc. are usually used as fuel, but liquid fuels are rarely used. In the Hoffman kilns, the use of energy is higher compared to the tunnel kilns. As it requires a labor-intensive structuring, costs are higher.

Tunnel kiln: As the main principle, the products move and the fire stands still. There is a long tunnel and moving kiln cars in it. Semi-finished products are stowed in the kiln cars out of the kiln, and the cars move one after the other at a certain speed in the kiln. The products moving in the kiln encounters an atmosphere with a gradually increasing temperature and decreasing humidity. This zone is the heating zone. The firing zone (firebox) is located in the mid section. The product fired here keeps moving forward and starts to cool down as it contacts with the air which has cooled down the material fired earlier and but which has been warmed up by passing over it. The products which move out of the kiln are then picked from the kiln cars. Liquid fuel is usually used in the firing zone, but systems using solid fuels are sometimes made as well. Tunnel kilns are such systems with a high product quality, high fuel and labor economy and short fabrication time. However, the initial investment and maintenance costs thereof are very high. The flow rate of the kiln cannot be frequently changed.

PACKAGING AND TRANSPORT
The products moving out of the kiln are transported any designated places. Trucks and lorries are usually used for transport. The products which our company produces may be transported on pallets and packages as well. Thus, the products are protected against any and all adverse external impacts which may occur during the transport.

PRODUCT STANDARDS
The following standards concerning such products as bricks and roof tiles made from baked clay which are issued by TSE (Turkish Standards Institution) are used:
- TS EN 771-1 Horizontally and Vertically Perforated Bricks, Load-Bearing Bricks and External Chimney Bricks,
- TS 1260 Load-Bearing Hollow Floor Slabs (participating in static work),
- TS 1261 Filled Hollow Floor Slabs (not participating in static work),
- TS EN 771-1 Clinker (Factory Bricks),
- TS EN 1344 Splits,
- TS EN 1304 Roof Tiles.