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the process of giving natural stone a required shape and external finishing (surface). Stoneworking includes the production of architectural elements (such as columns, cornices, and balusters) and facing (including slabs and blocks) from limestone, marble, and granite and other rock widely found in nature and suitable for dressing.
Stoneworking consists of three basic operations: sawing the stone into blocks, roughing out the slabs (blocks) for size, and giving the stone the required shape and finish of the face surface. The raw material for stonework is large blocks (at least 0.45 cu m in volume) cut out of a rock bed in a quarry (more rarely a mine). The stone blocks are cut on sawing rigs. The slabs or blocks are cut for size on shaping machines that are equipped with one or several diamond wheels. The finishing of the face surface of the stone can be done by two methods: by shearing or by grinding. In the first instance, the surface produced is somewhat rough (“rough cut”) or relatively smooth (picked and batted finishes). The shearing is done with tools with hard-alloy teeth. Through grinding (abrasive working), the stone acquires a smooth surface; if needed it can be given a mirror sheen. The sheen is produced with a polishing powder (usually chromium, lead, or iron oxide) with a felt wheel. A recently proposed finishing method suggests using hard polishers on a polymer base to obtain higher productivity and better quality.
The large stoneworking enterprises of the USSR are equipped with conveyer grinding and polishing machines that simultaneously shape, grind, and polish. A highly productive grinding and polishing machine with numerical control automatically determines the trajectory of the tool’s movement and its pressure on the stone; the machine can process marble (up to 15, 000 sq m per year) and granite (around 5, 000 sq m per year). The stoneworking machines are set in a processing line, and the material to be worked passes through all operations in sequence. Annual productivity of the line is around 80, 000 sq m for marble and around 25, 000 sq m for granite.
The working of stone such as rhodonite, nephrite, jasper, and amber for mosaics and small articles is carried out on small-sized machines equipped with a diamond tool. The stone is cut into tiles using small diamond wheels 200-320 mm in diameter. The mosaic work from this type of stone produced in the USSR on a wide scale is done using thin (not more than 4-5 mm) tiles glued with durable glues on a marble or metal base.
At the end of the 1960’s, the USSR developed the thermojet method for fracturing stone. The method is used both in working and in mining hard rock; its underlying principle is the effect produced by a high-temperature gas jet (obtained by burning kerosene in oxygen or gasoline in a jet of compressed air) when hitting the surface of the stone at supersonic speed. Under the effect of the jet, thermomechanical stresses are created that cause the cleavage fracture of the surface layer.
A special type of stoneworking is the faceting of precious stones for jewelry work (seeGEM CUTTING).
REFERENCESOrlov, A. M. Obrabotka prirodnogo dekorativnogo kamnia. Moscow, 1956.
Rusakov, K. I., and Iu. I. Sychev. Mashiny dlia dobychi i obrabotki kamnia. Moscow, 1966.
Orlov, A. M., and Iu. I. Shychev. Sovremennye stanki dlia obrabotki oblitsovochnogo kamnia i tekhnologicheskie skhemy [a review]. Moscow, 1968.
Sychev, Iu. I., and V. N. Seliuanov. Konveiernaia obrabotka oblitsovoch-nogo kamnia. Moscow, 1970.
A. M. ORLOV