Cement is typically made of limestone and clay or slate. These raw materials are extracted from the quarry ground to a fine powder and then mixed in the correct proportions.
This mixed raw material is referred to as "raw feed" or "bake feed" and is heated in a rotary kiln where it reaches a temperature of about 1400 ° C to 1500 ° C. In its simplest form, the rotary kiln is a tube of up to 200 meters long and perhaps 6 meters in diameter, with a long flame at one end. The raw food enters the oven at the cold end and gradually passes down to the hot end, then exits the oven and cools.
The material formed in the furnace is described as "clinker" and is typically composed of rounded nodules between 1 mm and 25 mm in diameter.
After cooling, the clinker can be stored temporarily in a clinker store, or can pass directly into the cement mill.
The cement mill grinds the clinker to a fine powder. A small amount of gypsum - a form of calcium sulfate - is usually ground with the clinker. Gypsum controls the setting properties of cement when water is added.