Most of the raw materials used are extracted from the earth through mining and quarrying and can be divided into the following groups: lime (calcareous), silica (siliceous), alumina (argillaceous), and iron (ferriferous). Since a form of calcium carbonate, usually limestone, is the predominant raw material, most plants are situated near a limestone quarry or receive this material from a source via inexpensive transportation.
Cement manufacturing begins with quarrying operations in which limestone in mines is quarried and brought to crusher for crushing. Limestone quarries are opencast mines. Often limestone appears as an outcrop right on the surface. At other times it is under an overburden that can vary in depth but is generally less than 3 metres thick. Limestone deposits occur in a variety of landforms. Some are in the form of a hill. Some are plain thick slabs; some are fragmented with substantial interstitial impurities. The first step is to drill holes, fill them with appropriate explosives and blast them so as to loosen the rock. Loosened rock is collected by shovels and loaded into dumpers. In manual mining stone only up to 300 mm in size is loaded into trucks / wagons.
Mining and hauling are commonly monitored by (KPI):
Blasting tonnes/kg explosive
Stripping ratio volume waste removed/volume used rock
Loading tonnes/hour of equipment
Hauling tonnes/hour per truck
All production and inventory records are most conveniently kept in dry tonnes but moisture levels of mined, hauled, and crushed rock must be considered.
Some of the important machines used in Quarrying
Wagon Drills and: Equipment commonly used for drilling holes in rock are truck mounted, compressed air operated wagon drills. Hole sizes, spacing of holes and their depth and type of explosive to be used would be decided by field experts.
Portable Compressors: Generally portable diesel engine operated compressors would be used. Compressors supplying compressed air at around 7-10 kg/cm2.
Shovels / Wheel Loaders /Front End Loaders: Commonly used are diesel operated, however electric operated shovels can be used as well. They may have 'track' to be capable to pass on rough and uneven terrain in quarries or will have 'tyres'. Size of equipment is designated by the capacity of bucket expressed in cubic metres or cubic yards. Size of bucket also decides the maximum size of stone the bucket can hold, which decides the sizing of crusher as well, as the crusher must be designed to handle the stone size and crush it to required product size for further processing. Generally, the crusher opening would be 125 % of the max. size of stone from mining.
Dumpers: Dumpers are heavy duty diesel vehicles. Most commonly used vehicles for transporting run off mine (ROM) stone to crusher feeding hopper plant would be:
- Self-tipping trucks when mining is manual, for small capacity plants.
- Rear end dumpers (are most commonly used dumpers).
Dumpers are available in standard sizes specified by carrying capacity expressed in cubic metres or in tons. Numbers are dependent on the time taken for a round trip to crusher. Generally, for each shovel there would be 2-4 dumpers.
Bulldozers: Bulldozers are used to loosen over burden and to level ground. They carry out several tasks, and are very essential part quarrying operation.
Rippers: wherever the deposits permit rippers are used, without blasting, stone is 'ripped' up from the bed. It has an advantage to avoids vibrations caused by blasting.