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Tools and Machinery of the Granite Industry
Chronicle of the Early American Industries Association, Inc., The, Jun 2006 by Wood, Paul
In the mid 1900s, the jet piercing (or torch cutting) technology was developed. It burned fuel oil and oxygen at a temperature of 4,000 degrees F, causing spalling (flaking off) of the granite due to the stresses set up by the differential heating of the granite. (This same spalling causes the destruction of granite exposed to the intense heat of building fires.) Jet piercing created the necessary twenty-foot-deep channels without the need of drilling deep holes. The burner was a complex tool, requiring water, electricity, compressed air, oil, and oxygen. The burner itself consisted of a long "pole" carrying fuel oil, pure oxygen, and cooling water. At the end of the pole was a copper tip where the oil and oxygen were mixed and burned. The initial design was manual, requiring two operators. Later, an automatic design was introduced requiring only a single operator.
In the late 1880s, M. Paulin Gay of Marseilles, France, designed and manufactured a wire saw that was used in quarries of France, Germany, Spain, Italy, and other European countries. The saw used three-strand twisted wire with a sand and water abrasive. The wire moved at a speed of sixteen feet per second and could cut about five hundred square feet of stone before wearing out. The wire was held in a pulley carrier and was forced down onto the stone by a screw feed mechanism. Two-and-a-half-foot diameter starter holes were required to accommodate the pulley carrier. Diamond-encrusted wire saws are now used for cutting the side faces. A one-and-one-quarter-inch diameter deep hole and lift hole joined at their bottoms are drilled for each side face. The saw wire is threaded through the holes, soldered into a loop, and driven by an electric motor mounted on a track. A set of gears moves the motor back an adjustable distance from the stone for every revolution of the wire. A diamond wire saw makes a very narrow cut-approximately one-half inch wide-and leaves spiral cut marks on the rock face. If a wire has to be replaced, it is a costly event since the wire costs approximately three dollars per foot.
Another currently used channeling technique employs a slot drill. First, two-and-one-half-inch diameter deep holes are drilled about four and one-halfinches on center and then the cores are drilled out using a core drill with a three-inch diameter drill bit. A bit guide, inserted into an adjacent deep hole, is used to center the drill bit on the core. An experimental technology, water jet channeling, cuts channels at a rate of forty square feet per hour with high pressure (40,000 psi) water. This is a costly technology -a water jet power pack is valued at a hundred thousand dollars.
Shooting (Blasting)
Black powder is used where less explosive force is desired, as is the case with quarrying dimension granite, which is used for building stones or monuments. Black powder consists of the granular ingredients sulphur, charcoal, which provides carbon to the reaction), and saltpetre (potassium nitrate), which provides oxygen to the reaction. It deflagrates at five hundred meters per second if contained and is termed a low explosive. Dynamite is a high explosive with a shattering and somewhat unpredictable effect and is often used to blast waste granite. Initially, loose black powder was loaded into the drilled holes and tamped in with a sparkless brass tamper. A sparkless pricker, also called a priming needle (Figure 31) was then used to make a hole in the compressed powder for insertion of a fuse. The fuse was typically a one-quarter-inch diameter cloth fiber wrapping a black powder core. Finally, loose sand was tamped into the hole to contain the blast and direct the blast forces perpendicular to the sides of the hole.
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