Production of natural stone materials

Production technology of natural stone materials is determined by their peculiarities, rock properties and terms of occurrence. A deposit, prepared for development of rocks, is called quarry. Preparation of a deposit starts with the removal of upper rocks and baring of minerals. Quarries are developed by one (or few) benches the height of which does not exceed 20 m.

The most mass produce material is crush stone from hard rocks. It is produced by drilling-and-blasting, related to the blasthole drilling or borehole located along ledge front; placing explosives inside (ammonite, ammonium nitrate, ammonal, etc.) and separation by the explosion of rock pieces which are ground down after that.

On crushing and screening factories and plants (Fig. 5.5) there is made one-, two- or multistage crushing of initial raw material. Multistage crushing is the most prevailing; it enables to obtain both coarse and fine fractions of crushed stone. One-stage scheme is used at the low productivity plants at maximum dimensions of rock pieces 400-450 mm.

Crushing equipment can have periodical (jaw crusher and cone crusher) and continuous pressing of crushing surfaces (roll crushers and impact crushers - the hammer and rotor ones).

The crushed material is assorted on fractions by mechanical, hydraulic and air methods. At the mechanical method stone is assorted by screens. At the enterprises of construction materials most widespread screens are vibrocribble screens, in which one or two screens are set.

The stone can be crushed by opened and closed cycle. At open-cycle, material one time passes through a crusher, goes to assorting and then on finished storehouse. At the closed cycle stone which did not pass top screen, again goes to crushing, that enables to attain the greater productivity of crushers, regulate an output and coarseness of ready-made products.

Dusty and clayey admixtures which contaminate crushed stone are withdrawn by washing, for that blade flushing, drum or vibratory machines are used. Vibration machines are less metal- and energy- consuming, they require less water.

Along to washing special methods of cleaning of stone materials are used. Processing low-grade raw material in crushed stone, the method of selective crushing is applied in particular, based on more intensive destruction of pieces of weak rocks. The gravity concentration is based on dependence between strength and density of rock. Grains of material, heterogeneous by density, are divided in the special settling machines in the alternately ascending and descending streams of water or in dense media (water suspensions of magnetite or ferrosilicon), the density of which has an intermediate value between the densities of dividing fractions.

Work stone from light-extracted rocks - marble, limestone, tuff is obtained by rock-cutting machines, the operating element of which are horizontal and vertical disk saws, set on a cart which moves in a quarry by rails along the working face. Rock-cutting machines enable to mechanize both cutting of stone and secondary operations, related to its stacking and transporting from a working face.

Except for machines with disk cuttings instruments machines with chainsaws are applied. The productivity of machines on the medium hardness rocks is increased in 4-5 times, if diamond cuttings nozzles are used.

Facing elements from hard rocks are obtained by separating from massive of large monoliths which are divided into blocks and slabs. For the separation of monoliths there are used drill and wedge, drill, fire and other methods. For quartz-containing rocks of granite groups thermal method is used. It is based on the destructive actions of internal tensions which arise up at thermal deformations of minerals under the action of high temperature.

Date: 2015-12-18; view: 1043