HOW IS CEMENT MANUFACTURED?
Basic raw materials used in cement manufacturing are limestone, clay and marn. As raw material, iron ore can be used to meet the iron need and bauxite can be used for aluminum need. Raw materials are loaded into the carrier vehicles at the quarry area. Sizes of the raw materials brought from the quarry are reduced to 25x25 millimeter at the jaw crusher equipped with dedusting unit. Raw material crushed are segregated and stocked by their types. Dust is reclaimed at the transfer points by means of bag filters. Raw materials are ground at the treadmill and turned into farin meal (raw material mixture). Calcium, oxide and silicon dioxide resources are the main components of farin, which is a mixture of carefully proportioned cement raw materials.
Calcium oxide comes into existence in the environment thanks to the rocks basically containing calcium carbonate such as limestone or marn. Main source of the silicon dioxide is clay. This is followed by aluminum and iron oxide, which are other farin components. Even in smaller quantities, the structure also includes other matters such as magnesium and alkaline oxides.
Farin is ground at vertical mills or ball mills. Taken after being weighted at farin silo, farin is fed to a pre-heater tower, which is made up of cyclones. There is hot gas circulation in the opposite direction of the material flow in the cyclones. Thanks to this gas passage, raw mixture is subject to pre-heating. In this way, less fuel is used for burning at the kiln. Farin is heated from 30°C to 1000°C with the pre-calcination process and is calcined in 90%. Calcination is fragmentation of carbonate and hydrates with the impact of heat to obtain oxide components. Calcite mineral in limestone turns into free lime mineral.
As farin is burnt in the kiln, the oxides in the raw material first become free. They form new crystals as the heat increases. Farin, which comes from the pre-heater, is burnt in the rotating kiln at 1450C and forms the clinker by-product in granular form. Coming out of the kiln at 1300C, clinker is cooled and its temperature is reduced to 100C. Clinker granules, which come to cement mill that is generally with balls, are ground with limestone here. Gypsum addition is mandatory to avoid too fast solidification (extension of setting time) during the reaction occurring when cement is mixed with water. There are partitions with steel crusher balls filled up to one third of the volumes in the mills in the form of steel cylinder with approximately 3 m diameter. As the cylinder turns, balls hit the clinker particles and break them into smaller pieces. The material is conveyed between the partitions. In the last partition, the desired fineness is reached. The temperature rise in the cement mill during grinding is prevented by giving pressured water into the mill.
The product obtained as a result of grinding is cement and stored in the silos.
Bagged Cement: Cement is put into special, three-layered craft paper bags. Although these bags are 50-kg in our country and in most countries, there are also 25-kg bags in some countries. Also cement can be carried by sacks of approximately 1 ton, which are called as “big bag”.
Bulk Cement: Cement is directly loaded into tankers (bulk trailers), which are specially manufactured for this, and shipped to the concrete plants at the ready-mixed concrete plants or construction sites.