Chilean Rescue Tech
by Mark W. Hibben
The Drilling Technology that Cut the Rescue Time in Half
After 33 miners were trapped in the San Jose mine outside Copiapo, Chile on August 5, it was not until August 23 that the first narrow shaft reached the miners and proved that they were still alive. This shaft was barely 5 inches in diameter, enough to provide a lifeline but not rescue. At the time, estimates ranged from 3 to 4 months to complete a rescue shaft, but on October 9 the rescue shaft broke through to the trapped men and on October 13 the first miner emerged on the surface, followed by his 32 comrades over the course of the day. That the rescue shaft was completed faster than anticipated was due largely to the tireless efforts of a team of drilling experts and the technologies of two US companies, Schramm Inc. and Center Rock Inc.
You don’t cut through hard rock the way you would other materials like wood, plastic, or even steel. All these can be cut by a drill bit that scrapes away a continuous layer of material as a spiral cutting. The rock is too hard and abrasive and will just grind down a conventional drill.
Instead, drillers use a “down the hole” (DTH) hammer, which works (and sounds) much like a jack hammer. The hammer is located at the end of the drill pipe just above the drill bit, and is operated by compressed air supplied from the surface through the drill pipe. For deep holes, a DTH hammer is the only effective way to apply impact force to the drill bit, since hammering on the top of the pipe would only cause the pipe to flex and not transmit much force to the bit. The impact of the hammer, combined with the rotation of the drill bit spalls and grinds the rock while a flow of lubricating water or oil carries it away from the bit. The drill bits are rather blunt objects and are usually covered with “buttons” of ultra-hard tungsten carbide, which is only slightly less hard than diamond.
The first shaft that reached the miners on August 23 was drilled by a DTH hammer supplied by Mincon, an Irish mining equipment company, although the DTH hammers in this case were made by its Australian subsidiary.
The Mincon hammers were designed to drill only 5 inch diameter holes, but this is a typical diameter hole for a single hammer drill. To drill a hole large enough in diameter to pass a man through (20 + inches), the rescue effort turned to the unique technology of Center Rock Inc., which makes what it calls the Low Profile Canister (LPC) drill.
The LPC is an array of 6 inch diameter hammers contained within a steel cylinder. Depending on the number and arrangement of the hammers, the LPC can drill holes anywhere from 20 to 84 inches in diameter. The LPC drill was primarily responsible for the shortening of the rescue time.
Operating the Center Rock LPC drill requires great power and precision, which was the job of the Schramm T130XD drilling rig. The rig is required to apply enormous torque to the drill pipe at relatively low RPMs (0 - 140 RPM). This is provided by a compact hydraulic motor that generates 8883 ft-lbs of torque and is raised and lowered on tracks in the mast. Compare this torque to that of a modern V8 engine at about 300 ft-lbs.
But an equally important function of the drilling rig is the assembly and disassembly of the drilling pipe. Whenever the LPC drill is raised from the hole, the segments of the drill pipe are carefully disassembled and neatly stacked. This can occur frequently to replace worn drill bits or hammers, or as happened on one instance in Chile, to replace the entire canister after it struck a steel support beam. Likewise, when the LPC drill is lowered back into the hole, the stacked pipe segments are sequentially reassembled, in a carefully choreographed ballet of man and machine, as the following video illustrates.
Both Schramm and Center Rock are examples of successful manufacturing companies in the US. As capital equipment manufacturers, their customers value quality and responsiveness, thus allowing them to compete effectively against foreign competition from India, China and Korea. The Center Rock LPC drill is an innovation only just beginning to be imitated by overseas companies. Center Rock especially illustrates that American entrepreneurship can still thrive. Founded in 1998 by 26 year-old Brandon Fisher as a drilling services company, CRI now provides a wide range of drill bits, hammers and drilling accessories. Fisher himself was on site in Chile to oversee the use of the LPC drills in drilling the rescue shaft and was present when the drill broke through to the miners on October 9.