A metamorphic rock with outstanding beauty and variety, marble has been an important building material for several millennia. Thanks to the precision of modern technology, marble has become increasingly accessible and affordable for consumers. Improvements in marble manufacturing (marble "fabrication") include explosives, composite-tipped drills, diamond-studded wire saws, super-fast saws, epoxy sealing and computer-controlled polishing.
During the extraction process, massive cube-like pieces of marble are cut out of the ground and transported from the quarry. To minimize the risk of cracks, fissures and other aesthetic damage to the stone, fabricators use a process known at "wire sawing" to gently separate the marble (Figures 1a and 1b). First, two 3-inch wide holes are drilled perpendicularly to each other. Once the holes connect, a heavy-duty wire embedded with artificial diamonds is fed through and secured to a flywheel, forming a loop. A powerful engine applies massive torque to the flywheel, which circulates the diamond-embedded wire at a very fast rate. Since diamond is much harder than the marble, the friction quickly wears it away, leaving a smooth cut plane.
After wearing all the way through, another perpendicular hole is drilled and the process is repeated, cutting away the other vertical plane. For the horizontal plane, the wire saw cuts about 80 percent of the marble away, leaving a circle in the center remaining. At this point, the wire is removed and an hydraulic excavator machine forces a wedge into the horizontally-cut planes to break the vertical plane free. Finally, a crane loads the piece onto a truck or rail car for a transport to the fabrication shop.
In the fabrication shop, the piece is loaded onto a platform with hydraulic lifts underneath. Above this platform is the "gang saw," a row of dozens of 10 to 15 feet long steel saw blades connected to a crankshaft via pistons (Figure 2). A giant engine turns the flywheel, which turns the crankshaft and moves the saw blade back and forth horizontally at an incredible rate. Each saw blade is spaced according to the desired thickness of the resulting slabs, usually 3 cm (although 2 cm is fairly common as well). As the blades saw back and forth, the hydraulic lifts push the block up into them, cutting the slabs. Once complete, two workers will gently tilt out each slab, attach a special clamp to it and use a ceiling-mounted winch to lift it into the finishing area.
Polishing and Sealing
The slab is laid face down and a machine with a finely-graded, diamond-encrusted abrasive pad grinds down the surface of the slab until it is smooth and vaguely reflective. A worker (or machine, depending on the shop) then sprays on a uniform coat of epoxy sealer onto the surface and leaves it to dry for 48 hours. Heat lamps can expedite this process. Once dry, the slab is flipped over and the process repeated for the opposite side. Polished and sealed, the finished slabs then ship out to retailers and distributors.
Waterjet Cutting and Wet Sawing
At the retailer's show room, slabs are displayed in giant, iron oxide-coated easels for customers to view. After choosing a slab(s), the customer gives the dimensions of his project (kitchen counters, ballroom floor or bathroom) to the retailer, who maps the shapes onto the slab itself.
To cut these pieces out, fabricators traditionally used a process called "wet sawing" where circular saws coated with tungsten carbide cut through the slab while continuous streams of water spray on the blades to keep them from overheating.
Today, most fabricators use a technology called "waterjet cutting" to cut pieces, make holes for appliances and create beveled edges. In waterjet cutting, water is pressurized to 60,000 psi and allowed to shoot out in a concentrated stream. Traveling at 2.5 times the speed of sound, the stream mixes mid-air with a powdered abrasive (e.g. aluminum oxide or garnet) before striking the marble (Figure 3). The result is a precise hyper-erosion that can be used for two-dimensional and three-dimensional applications alike. Due to this degree of precision (in the micrometer range), a computer controls the entire cutting process.