Underground mining (hard rock)
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals those containing metals such as ore containing gold, iron, zinc, nickel and lead, but involves using the same techniques for excavating ores of gems such as diamonds or rubies. Soft rock mining refers to excavation of softer minerals such as coal, or oil sands. Accessing underground ore can be achieved via a decline, inclined vertical shaft or adit. Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit; the decline begins with a box cut, the portal to the surface. Depending on the amount of overburden and quality of bedrock, a galvanized steel culvert may be required for safety purposes, they may be started into the wall of an open cut mine. Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies. Shaft haulage is more economical than truck haulage at depth, a mine may have both a decline and a ramp.
Adits are horizontal excavations into the side of a mountain. Adits are used for horizontal or near-horizontal ore bodies where there is no need for a ramp or shaft. Declines are started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation, but the strip ratio has become too great to support open cast extraction methods, they are often built and maintained as an emergency safety access from the underground workings and a means of moving large equipment to the workings. Levels are shaft to access the ore body. Stopes are excavated perpendicular to the level into the ore. There are two principal phases of underground mining: development production mining. Development mining is composed of excavation entirely in waste rock in order to gain access to the orebody. There are six steps in development mining: remove blasted material, installing support or/and reinforcement using shotcrete etceteras, drill face rock, load explosives, blast explosives.
To start the mining, the first step is to make the path to go down. The path is defined. Before the start of Decline all preplanning of Power facility, drilling arrangement, ventilation and, muck withdrawal facilities are required. Production mining is further broken down into long hole and short hole. Short hole mining is similar to development mining. There are several different methods of long hole mining. Long hole mining requires two excavations within the ore at different elevations below surface. Holes are loaded with explosives; the holes are blasted and the ore is removed from the bottom excavation. One of the most important aspects of underground hard rock mining is ventilation. Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity, diesel equipment, or to protect against gases that are emanating from the rock. Ventilation is used to manage underground temperatures for the workers. In deep, hot mines ventilation is used to cool the workplace.
Ventilation raises are used to transfer ventilation from surface to the workplaces, can be modified for use as emergency escape routes. The primary sources of heat in underground hard rock mines are virgin rock temperature, auto compression, fissure water. Other small contributing factors are blasting; some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms. Area ground support is used to prevent major ground failure. Holes are drilled into the back and walls and a long steel rod is installed to hold the ground together. There are three categories of rock bolt, differentiated by, they are: Point anchor bolts are a common style of area ground support. A point anchor bolt is a metal bar between 20 mm – 25 mm in diameter, between 1 m – 4 m long. There is an expansion shell at the end of the bolt, inserted into the hole; as the bolt is tightened by the installation drill the expansion shell expands and the bolt tightens holding the rock together.
Mechanical bolts are considered temporary support as their lifespan is reduced by corrosion as they are not grouted. Resin grouted; the rebar used does not have an expansion shell. Once the hole for the rebar is drilled, cartridges of polyester resin are installed in the hole; the rebar bolt is spun by the installation drill. This mixes it. Once the resin hardens, the drill spinning tightens the rebar bolt holding the rock together. Resin grouted. Cable bolts are used around large excavations. Cable bolts are much larger than standard
Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding; the muscles of mastication move the jaws to bring the teeth into intermittent contact occluding and opening. As chewing continues, the food is made softer and warmer, the enzymes in saliva begin to break down carbohydrates in the food. After chewing, the food is swallowed, it enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs. Premastication is sometimes performed by human parents for infants who are unable to do so for themselves; the food is masticated in the mouth of the parent into a bolus and transferred to the infant for consumption. Cattle and some other animals, called ruminants, chew food more than once to extract more nutrients.
After the first round of chewing, this food is called cud. Chewing is an unconscious act, but can be mediated by higher conscious input; the motor program for mastication is a hypothesized central nervous system function by which the complex patterns governing mastication are created and controlled. It is thought that feedback from proprioceptive nerves in teeth and the temporomandibular joints govern the creation of neural pathways, which in turn determine duration and force of individual muscle activation; this motor program continuously adapts to changes in food occlusion. This adaptation is a learned skill that may sometimes require relearning to adapt to loss of teeth or to dental appliances such as dentures, it is thought that conscious mediation is important in the limitation of parafunctional habits as most the motor program can be excessively engaged during periods of sleep and times of stress. It is theorized that excessive input to the motor program from myofascial pain or occlusal imbalance can contribute to parafunctional habits.
A study found that unchewed meat and vegetables were not digested, while tallow, fish and grains did not need to be chewed. Chewing stimulates saliva production and increases sensory perception of the food being eaten, controlling when the food is swallowed. Avoiding chewing, by choice or due to medical reasons as tooth loss, is known as a soft diet; such a diet may lead to inadequate nutrition due to a reduction in vegetable intake. Chewing stimulates the hippocampus and is necessary to maintain its normal function. Chewing is an adaptation for mammalian herbivory. Carnivores chew little or swallow their food whole or in chunks; this act of gulping food without chewing has inspired the English idiom "wolfing it down". Ornithopods, a group of dinosaurs including the Hadrosaurids, developed teeth analogous to mammalian molars and incisors during the Cretaceous period; this may have given them the advantage needed to usurp the formidable sauropods, who depended on gastroliths for grinding food, from their ecological niches.
They became some of the most successful animals on the planet until the Cretaceous–Paleogene extinction event wiped them out. The process of chewing has, by analogy, been applied to machinery; the U. S. Forest Service uses a machine called a masticator to "chew" through brush and timber in order to clear firelines in advance of a wildfire. Biting Gnathology Muscles of mastication Horace Fletcher Chewing Gum MeSH A02.633.567.600
The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals or clasts are embedded. The matrix of an igneous rock consists of finer-grained microscopic, crystals in which larger crystals are embedded; this porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix. In South Africa, diamonds are mined from a matrix of weathered clay-like rock called "yellow ground"; the matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt, in which larger grains or clasts are embedded. It is used to describe the rock material in which a fossil is embedded. All sediments are at first in an incoherent condition, they may remain in this state for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the ocean floor, yet they are quite friable and differ little from many recent accumulations.
There are few exceptions, however, to the rule that with increasing age sedimentary rocks become more and more indurated, the older they are the more it is that they will have the firm consistency implied in the term "rock". The pressure of newer sediments on underlying masses is one cause of this change, though not in itself a powerful one. More efficiency is ascribed to the action of percolating water, which takes up certain soluble materials and redeposits them in pores and cavities; this operation is accelerated by the increased pressure produced by superincumbent masses, to some extent by the rise of temperature which takes place in rocks buried to some depth beneath the surface. The rise of temperature, however, is never great; the redeposited cementing material is most calcareous or siliceous. Limestones, which were a loose accumulation of shells, etc. become compacted into firm rock in this manner. The cementing substance may be deposited in crystalline continuity on the original grains, where these were crystalline, in sandstones, a crystalline matrix of calcite envelops the sand grains.
The change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock also accelerates consolidations. Silica is less soluble in ordinary waters, but this ingredient of rocks is dissolved and redeposited with great frequency. Many sandstones are held together by an infinitesimal amount of cryptocrystalline silica. Others contain fine scales of mica. Argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals
In mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide. Such a force or acceleration has a greater effect than a lower force applied over a proportionally longer period; the effect depends critically on the relative velocity of the bodies to one another. At normal speeds, during a inelastic collision, an object struck by a projectile will deform, this deformation will absorb most or all of the force of the collision. Viewed from a conservation of energy perspective, the kinetic energy of the projectile is changed into heat and sound energy, as a result of the deformations and vibrations induced in the struck object. However, these deformations and vibrations cannot occur instantaneously. A high-velocity collision does not provide sufficient time for these deformations and vibrations to occur. Thus, the struck material behaves as if it were more brittle than it would otherwise be, the majority of the applied force goes into fracturing the material.
Or, another way to look at it is that materials are more brittle on short time scales than on long time scales: this is related to time-temperature superposition. Impact resistance decreases with an increase in the modulus of elasticity, which means that stiffer materials will have less impact resistance. Resilient materials will have better impact resistance. Different materials can behave in quite different ways in impact when compared with static loading conditions. Ductile materials like steel tend to become more brittle at high loading rates, spalling may occur on the reverse side to the impact if penetration doesn't occur; the way in which the kinetic energy is distributed through the section is important in determining its response. Projectiles apply a Hertzian contact stress at the point of impact to a solid body, with compression stresses under the point, but with bending loads a short distance away. Since most materials are weaker in tension than compression, this is the zone where cracks tend to form and grow.
A nail is pounded with a series of impacts, each by a single hammer blow. These high velocity impacts overcome the static friction between the substrate. A pile driver achieves the same end, although on a much larger scale, the method being used during civil construction projects to make building and bridge foundations. An impact wrench is a device designed to impart torque impacts to bolts to loosen them. At normal speeds, the forces applied to the bolt would be dispersed, via friction, to the mating threads. However, at impact speeds, the forces act on the bolt to move it. In ballistics, bullets utilize impact forces to puncture surfaces that could otherwise resist substantial forces. A rubber sheet, for example, behaves more like glass at typical bullet speeds; that is, it fractures, does not stretch or vibrate. Road traffic accidents involve impact loading, such as when a car hits a traffic bollard, water hydrant or tree, the damage being localized to the impact zone; when vehicles collide, the damage increases with the relative velocity of the vehicles, the damage increasing as the square of the velocity since it is the impact kinetic energy, the variable of importance.
Much design effort is made to improve the impact resistance of cars so as to minimize user injury. It can be achieved in several ways: by enclosing the driver and passengers in a safety cell for example; the cell is reinforced so it will survive in high speed crashes, so protect the users. Parts of the body shell outside the cell are designed to crumple progressively, absorbing most of the kinetic energy which must be dissipated by the impact. Various impact test are used to assess the effects of high loading, both on products and standard slabs of material; the Charpy test and Izod test are two examples of standardized methods which are used for testing materials. Ball or projectile drop tests are used for assessing product impacts; the Columbia disaster was caused by impact damage when a chunk of polyurethane foam impacted the carbon fibre composite wing of the space shuttle. Although tests had been conducted before the disaster, the test chunks were much smaller than the chunk that fell away from the booster rocket and hit the exposed wing.
When fragile items are shipped and drops can cause product damage. Protective packaging and cushioning help reduce the peak acceleration by extending the duration of the shock or impact. Coefficient of restitution Fall factor Compression Tension Impulse Charpy impact test Cushioning Izod impact strength test Shock Impact sensor Shock data logger Jerk Write-off Road traffic accident Goldsmith, W.. Impact: The Theory and Physical Behaviour of Colliding Solids Dover Publications, ISBN 0-486-42004-3 Poursartip, A.. Instrumented Impact Testing at High Velocities, Journal of Composites Technology and Research, 15. Toropov, AI.. Dynamic Calibration of Impact Test Instruments, Journal of Testing and Evaluation, 24
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more disposed of or recycled, or to reduce the size of a solid mix of raw materials, so that pieces of different composition can be differentiated. Crushing is the process of transferring a force amplified by mechanical advantage through a material made of molecules that bond together more and resist deformation more, than those in the material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so that its molecules separate from, or change alignment in relation to, each other; the earliest crushers were hand-held stones, where the weight of the stone provided a boost to muscle power, used against a stone anvil. Querns and mortars are types of these crushing devices.
In industry, crushers are machines which use a metal surface to break or compress materials into small fractional chunks or denser masses. Throughout most of industrial history, the greater part of crushing and mining part of the process occurred under muscle power as the application of force concentrated in the tip of the miners pick or sledge hammer driven drill bit. Before explosives came into widespread use in bulk mining in the mid-nineteenth century, most initial ore crushing and sizing was by hand and hammers at the mine or by water powered trip hammers in the small charcoal fired smithies and iron works typical of the Renaissance through the early-to-middle industrial revolution, it was only after explosives, early powerful steam shovels produced large chunks of materials, chunks reduced by hammering in the mine before being loaded into sacks for a trip to the surface, chunks that were also to lead to rails and mine railways transporting bulk aggregations that post-mine face crushing became necessary.
The earliest of these were in the foundries, but as coal took hold the larger operations became the coal breakers that fueled industrial growth from the first decade of the 1600s to the replacement of breakers in the 1970s through the fuel needs of the present day. The gradual coming of that era and displacement of the cottage industry based economies was itself accelerated first by the utility of wrought and cast iron as a desired materials giving impetus to larger operations in the late-sixteenth century by the increasing scarcity of wood lands for charcoal production to make the newfangled window glass material that had become—along with the chimney—'all the rage' among the growing middle-class and affluence of the sixteenth-and-seventeenth centuries. Other metallurgical developments such as silver and gold mining mirrored the practices and developments of the bulk material handling methods and technologies feeding the burgeoning appetite for more and more iron and glass, both of which were rare in personal possessions until the 1700s.
Things only became worse when the English figured out how to cast the more economical iron cannons, following on their feat of becoming the armorers of the European continent's powers by having been leading producers brass and bronze guns, by various acts of Parliament banned or restricted the further cutting of trees for charcoal in larger and larger regions in the United Kingdom. In 1611, a consortium led by courtier Edward Zouch was granted a patent for the reverberatory furnace, a furnace using coal, not precious national timber reserves, employed in glass making. An early politically connected and wealthy Robber Baron figure Sir Robert Mansell bought his way into the fledgling furnace company wrested control of it, by 1615 managed to have James I issued a proclamation forbidding the use of wood to produce glass, giving his families extensive coal holdings a monopoly on both source and means of production for nearly half-a-century. Abraham Darby a century relocated to Bristol where he had established a building brass and bronze industry by importing Dutch workers and using them to raid Dutch techniques.
Both materials were considered superior to iron for cannon, machines as they were better understood. But Darby would change the world in several key ways. Where the Dutch had failed in casting iron, one of Darby's apprentices, John Thomas succeeded in 1707 and as Burke put it: "had given England the key to the Industrial Revolution". At the time and foundries were all small enterprises except for the tin mines and materials came out of the mines hammered small by legions of miners who had to stuff their work into carry sacks for pack animal slinging. Concurrently, mines needed drained resulting in Savery and Newcomen's early steam driven pumping systems; the deeper the mines went, the larger the demand became for better pumps, the greater the demand for iron, the greater the need for coal, the greater the demand for each. Seeing ahead Darby, sold off his brass business interests and relocated to Coalbrookdale with its plentiful coal mines, water power and nearby ore supplies. Over that decade his foundries developed iron casting technologies and began to supplant other metals in many applications.
He adapted Coking of his fuel by copying Brewers practices. In 1822 the pumping industries needs for larger cylinders met up with Darby's ability to melt sufficient quantities of pig iron to cast large in
Vanning is a type of ore dressing by which ores are washed on a shovel. A powdered sample of orestuff is swirled with water on the blade of a shovel and given a series of upward flicking motions; the heavier ore is tossed up through the water and appears as a crescent shaped patch at the top of the charge with the lighter gangue below. Developed in western England, this process was still in use at a major tin mine until 1985. In the 19th century the process was automated and used for the separation of ore on an industrial scale; the Frue vanner was one such machine, adopted. It was invented in 1874, by W. B Frue, Superintendent of the Silver Islet Mine, Canada, who spent two years developing the system. In the Frue vanner a continuous rubber belt 4 feet wide and 27½ feet long passed over rollers to form the surface of an inclined plane on which the orestuff was concentrated; the belt travelled up hill at from 3 to 12 feet per minute while being laterally shaken about 180 to 200 times. The inclination of the belt was from 4 to 12 in. per 12 feet.
The belt received crushed orestuff from the stamps via a distributor about 4 feet from its upper end. As it travelled upwards, it met with small jets of water which washed the gangue off the bottom of the belt; as the belt travelled over the top roller with the heavier ore adhering to it, it passed into a box containing water where the ore was deposited. From 3 to 6 gallons per minute of water was required. One machine could treat 6 tons per 24 hours of stuff passing a 40 mesh screen, or 2 vanners to 5 stamps; the Embrey Concentrator and the Triumph Concentrator were similar to the Frue vanner except that the shaking was longitudinal instead of lateral. King Edward Mine in Cornwall claims to have the only working Frue vanner in the world, restored in 2008