Mechanization is the process of development in terms of production and safety. Continuous miner is a big step in this process. it began to take off in the mining industry in the 1940s and now make up of 45 percent of the underground coalmine production worldwide. Today, ultramodern continuous miners are being developed as driverless machines controlled via remote control. A brief history is presented here regarding development of continuous miner.2.1 A modern Continuous miner Early Miners

The continuous miner has been available in some form since the late I 800s. The first machine to resemble a continuous miner was known as the English Channel Machine. The pneumatically driven machine could travel 1.5 miles (2.4 km), mining 70 m (2I m) per day. Developed in 1870 to work on the English Channel, the machine ceased operation when political turmoil brought the project to a quick halt. The continuous miner did not appear again until 1912 when the Hoadley-Knight Machine was produced to reduce the size of coal to that of a nut. This machine was electrically driven by a rotor and consisted of a hydraulic swing and a set of water sprays. In addition to the Hoadley-Knight, several machines appeared in this decade: the Jeffrey MM32 in 1911, a machine capable of cutting and loading coal; the Jeffrey MM34 in 1913, known as the Jeffrey Entry Driver; and the McKinlay Entry Driver, a British boring machine produced in. These machines were moderately received in the mining industry. Mckinlay Entry Drivers were used in the New Orient Mine in 1926 and developed a positive reputation for the amount of work they could efficiently complete. This machine went on to become the standard prototype for the Marietta Miner, a mining machine produced and manufactured by Marietta Manufacturing Co., based in Point Pleasant, West Virginia.

The early twenties saw the development of a new type of miner constructed by Colonel O'Toole. The miner had a capacity that could complete 154-tons of work in 10 hours. The machine evolved to feature a pneumatic conveyor belt for the coal but such a development only reduced the power of the machine.Modern Miners

The first ripper-type continuous miner appeared in the early 1900s but did not prove to be immediately successful. The first machine to see success was built by an American, Harold Silver, in 1943 and was used for work in the Consolidated Coal & Coke Co. mine. The machine attracted the interest of Joy Manufacturing Co. three years later and Joy purchased the patents for the machine, developing two prototypes deriving from the original. They became known as the JCM models and were used for mining projects beginning in 1948.Joy Manufacturing Co. laid its claim to fame in its early years in the mining industry with several continuous miners. By the I 950s, a series of continuous miners had been produced and manufactured. The company's 3JCM model was so successful it stayed in production for the next 18 years with 212 being built in total. Although successful, it was only gradually accepted as an efficient miner.

A modern continuous miner

Fig. 2.1

Though there are many variations in design, continuous miners mostly consist of five main elements:

* A central body to carry all other components mounted on some type of drive mechanism to provide mobility (most commonly caterpillar tracks).

* A "cutting head" usually rotating drum(s) and/or chains with cutting picks attached * A loading mechanism to pick up cut coal and deliver it into the central part of the machine.

* A conveying system, usually a chain conveyor running in a steel trough from front to rear of the miner

* A rear jib section capable of a degree of vertical and horizontal movement to enable the coal to be delivered into a transport or loaded at a desired point.2.2 Cutting Elements of a Continuous MinerCutting Components Cutting Drum

This consists of a steel cylinder on which are mounted blocks, in the form of a scroll or scrolls, carrying clevis boxes or pick boxes. The drum can be caused to rotate by gears or by chain-driven sprockets. (These chains may also be equipped with pick boxes to present a continuous array of picks to the coal face.)Clevis Boxes

These are welded or bolted to the drum and enable the pick box to be positioned and fastened by a pin that passes through the sides of the clevis box and the pick box. The clevis base forms the seat on which the pick box sits. Pick box This is a casting specially shaped to

hold picks, and contains a slot, a hole for the pick shank, a hole for the clevis pin, and a seat. The pick is located into the pick hole, and the base of the pick passes through the slot and rests on the seat. The slot enables fasteners to be fitted to the pick shank, which prevents the pick from being ejected from the box during operation.Pick box

This is a casting specially shaped to hold picks, and contains a slot, a hole for the pick shank, a hole for the clevis pin, and a seat. The pick is located into the pick hole, and the base of the pick passes through the slot and rests on the seat. The slot enables fasteners to be fitted to the pick shank, which prevents the pick from being ejected from the box during operation.Pick The picks themselves consist of a steel body containing a recess into which a cemented carbide tip is brazed. The cemented carbide tip is the cutting portion of the pick, and consists of two materials, tungsten carbide and cobalt, sintered together to form a matrix of carbide grains within a cement of fused carbon. The most important physical properties of the cemented carbide are hardness and toughness. The value of both these properties can be varied by the amount of cobalt present. If the carbide is too hard. premature fracturing will occur, and, if it is too soft, the material will wear away too quickly. Thus, for optimum cutting performance, a balance between the two properties is necessary, dependent upon the quality of the coal being cut.

Direction of cutting

Fig 2.2Design Definitions of Cutting Heads Attack AngleThe angle of attack of a pick can be defined as the angle formed by a line drawn longitudinally through the shank and point of the pick and a line forming the radius of the pick point (through the centre of the drum and the point of the pick). Some manufacturers use the 'complementary angle' as their definition of attack angle.Clearance Angle

In a point-attack pick with a point 'cone angle' of, say, 60 degrees, the sum of the back and front clearance angles will be equal to 30 degrees. The individual values of the clearance angles will depend upon the attack angle in use at the timePick Spacing

For a single scroll, the position of the picks on an auger is usually determined. Multiscroll drums can be made by the interspersing of pick boxes to the required pattern. Thus, more

than one pick per line can be made available.Pick 'Off-set' AngleWith point-attack picks, the self-sharpening capability of the picks, due to normal rotation,

can be increased by the setting of each pick box slightly out of line by a small amount, say

2 to 3 degrees. This induces rotation, and hence self-sharpening of the tips. Factors

affecting the performance of coal cutting

(i) Provision of higher and variable Bumping force.This was achieved by an integrated hydraulic 'goalpost' anchor structure at the rear of the machine. When jacked between roof and floor, the machine can be thrust forward from it by the use of two hydraulic rams. These provide a much greater sumping force than can be obtained from the crawlers, which are now allowed to'free-wheel'. A wide range ofsum ping forces can be generated by variation of the hydraulic supply to the rams. and this enables the sumping rate and corresponding depth of pick penetration per drum revolution to he controlled and varied.(ii) Enhanced shearing force.

After generating the required depth of sumping, which is normally done at roof level, a conventional production machine shears the face by hydraulic rams pulling the cutting boom down. To increase the magnitude of the available shearing force, a shear assist assembly was mounted above the boom, consisting of a heavy cantilevered arm connected to the boom by a double-acting hydraulic ram. When activated, the ram forces the arm to the roof and thereafter provides a downward force on the boom additional to the normal arrangement. Hydraulic flow and pressure to the total system are controlled so that varying rates of shearing and depth of cut per drum revolution can be achieved.(iii) Variation of cutting-drum speed.The rotational speed of the cutting drum can be varied by the changing of gear boxes. Each

of the two drive trains between the motor and the cutting drum includes four gear boxes, three of which can be interchanged or replaced to provide different gear ratios. In addition to the normal production speed of 66 r/min, four other speeds of approximately 42, 35, 15, and 7 rhnin are available.(iv)Pick spacing pattern.

A specially modified drum makes provision for variations in the lateral and radial spacing of picks in the cutting array. The position and number of detachable pick boxes can be changed to give 4 levels of lateral spacing (50, 100, 150, and 200 mm) using picks of either chisel or conical profile. The centre line of a pick box makes an angle of 36,5° with the drum radius at the pick tip. The type and location of gauge cutters were not varied but remained the same as for a normal production machine. The role of the gauge cutter is somewhat different from that of the line cutter. Because they account for not more than 9 per cent of the coal cut by the drum, it was considered preferable to maintain constant gauge-cutting energy and vary only the main pick array, rather than to attempt an assessment of the effects of different types and dispositions of gauge picks.(iii) Variation of cutting-drum speed.The rotational speed of the cutting drum can be varied by the changing of gear boxes. Each

of the two drive trains between the motor and the cutting drum includes four gear boxes, three of which can be interchanged or replaced to provide different gear ratios. In addition to the normal production speed of 66 r/min, four other speeds of approximately 42, 35, 15, and 7 rhnin are available.(iv)Pick spacing pattern.

A specially modified drum makes provision for variations in the lateral and radial spacing of picks in the cutting array. The position and number of detachable pick boxes can be changed to give 4 levels of lateral spacing (50, 100, 150, and 200 mm) using picks of either chisel or conical profile. The centre line of a pick box makes an angle of 36,5° with the drum radius at the pick tip. The type and location of gauge cutters were not varied but remained the same as for a normal production machine. The role of the gauge cutter is somewhat different from that of the line cutter. Because they account for not more than 9 per cent of the coal cut by the drum, it was considered preferable to maintain constant gauge-cutting energy and vary only the main pick array, rather than to attempt an assessment of the effects of different types and dispositions of gauge picks.

2.3 Safety Aspects of Continuous Miner

Unfortunately, machine operator positioning has become an often unrecognized safety concern, particularly when remote control continuous mining machines excavate a turn (turn a crosscut). From January 2001 through July 2004, remote control CM operators or helpers have been involved in ten roof fall fatalities and eight machinery crushing fatalities. These 18 fatalities represent 41 % of the 44 total underground coal mining fatalities over the time period. The machinery crushing accidents occurred while the CM was being positioned in the cut, moved for maintenance, or while it was being moved to another place. 10 roof fall fatalities or 23% of the underground coal total emphasized that roof falls remain a major hazard to the remote CM operator. Three of the ten roof fall fatalities occurred while a crosscut was being turned (turn-out). A fourth fatality occurred while mining was being conducted adjacent to a crosscut that had been turned.

New technologies such as proximity detection sensors on remote control CMs is being pursued, but a disproportionate number of fatal accidents are associated with activity of mining turnouts and these fatalities represent 40% of all CM operator roof fall fatalities in the period January 2001 through July 2004. In an effort to reduce CM operator exposure to roof fall hazards while turning crosscuts, several mining techniques or practices have been identified.

A straightforward way to reduce hazards associated with turning crosscuts is to minimize the number of turnouts

With "head-on" mining, the CM and haulage vehicles approach the crosscut being mined through a previously developed cross cut, traverse across the intersection, and mine the next crosscut without any turn maneuvering. This allows for improved visibility and reduced miner operator exposure to haulage equipment with the operator remaining away from unsupported roof.

With red zones and visual indicator, individual remote control CM operators are responsible for selecting a safe operating position based on personal preferences and site specific conditions. Many mines have opted to establish "no work or travel zones" or `'red zones" around the continuous mining machine to rule out unacceptable positions (see Figure 3). Green reflectors that mark the second row of bolts from the rib line has helped shuttle car

operators stay out of the red zone.

Varying mine site conditions make it impractical to establish a mandatory operator position for turning crosscuts. Some mine operators have taken the proactive position of installing additional roof support at projected work positions, such as extra bolts per bolt row, extra bolts installed between the regular bolt rows, larger bearing plates installed on outside bolt in each row, and rib bolts installed just out by the location where the crosscut is to be started.

Another means to minimize hazards associated with turning crosscuts is to implement a mining sequence using a "notch" cut. A "notch" or "niche" Curt is a shallow, initial cut made at a planned intersection. The notch is a wedge-shaped side cut, typically in the 10 to 15 feet depth range and limited to the width of the machine cutter head. The notch cut is taken after completion of the cut mined in by the planned intersection. No attempt is made to fully turn the crosscut at the time the notch is mined.

Remote control affords a CM operator some degree of flexibility to achieve a safe and effective operating position. Depending on specific mining circumstances, one such non-traditional location from which the remote CM operator is inby the turn cut being mined. For example, if turning a right hand crosscut, the miner operator could be positioned to the rear left side of the machine as shown in Figure 6. This work position removes the operator from the proximity of the haulage equipment, reduces the possibility of wandering into unsupported roof, and greatly improves visibility into the crosscut being mined.

Several suggestions were presented to reduce the incidence of operator injuries and fatalities while turning 90-degree crosscuts. These techniques include: minimizing the number of turn cuts, limiting turn cut depth, establishing no work zones and using visual warning devices to designate these zones, installing more roof/rib support in the vicinity of the turn cut, using notch cuts, prior to initiating a full turn cut, and positioning the remote control miner operator in non-traditional locations. These suggestions are used successfully at mining operations across the nation. Several of the items may be applicable in a given mining scenario and conversely, individual conditions may limit their applicability. Mines are encouraged to examine the procedures they currently employ and make every effort to adopt practices that will enhance CM operator health and safety.

2.4 Development with continuous miner

The B&P mining method fits in the category of open stoping and is often applied to excavate horizontal deposits with reasonably competent hanging wall. The coal is extracted from between three and eleven entries in the seam. Pillars are left between the entries to support the roof. Crosscuts connect the entries generating a grid similar to a chessboard. Very often the pillars are rectangular to simplify the planning and mining operations.

A typical B&P section or panel in a coal mining operation is equipped with a CM, two or three shuttle cars (SC), a roof bolter (RB) and a scoop for auxiliary jobs. In total eight miners are working on the panel. The CM cuts one entry while the RB installs the roof bolts in the recently mined entry. This procedure is called place-change. In doing so the whole mining operation is very flexible and can easily be adjusted to changing conditions.

The CM extracts the coal in a two-pass operation - meaning it changes its place to cut the full width of the entry (5 to 6 m). The length of the cuts (6 to 12 m) varies, depending on the roof conditions as well as the ventilation requirements and features of the CM.

The SC hauls the coal from the CM to the stationary feeder breaker (FB). As the SC is operated electrically the cables restrict flexibility. so the planning of the optimal tramming routes requires special care. Besides the change-out procedure, while loading the SC, results in an operation that is. despite the misleading name, not continuous at all. The FB is moved after an advance of two or three crosscuts to minimize the haulage distance.

Sequence of development-

Coal has been developed with continuous miner using 5 headings. • One heading for cutting by continuous miner.• One heading is for roof boiling.

• One heading is for ventilation.

• Two headings are ready for cutting

Continuous miner being used having 3.3 m cutter head is usually sumped between 0.5 to 0.75 m at roof level. The rear stab jack on machine is lowered and head sheared down to floor level. This cycle is repeated 3-4 times in a day. I Size of the pillar shall not be less than 35*35 centre to centre and solid pillar shall not be less than 29*29 corner to corner. Width of gallery shall not exceed 6.0 m and height shall not exceed 3.5. Development shall be done always along the roof and some coal may be left on the floor. Scientific body should be

engaged to study the strata monitoring during development. No person is allowed to work under unsupported roof and maximum cutout distance shall not exceed l2rn.

2.5 Depillaring with continuous miner

Depillaring is done in same manner as development is being done except the dimensions and sequence which is as follows