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how many mining equipments are used in india

colliery equipment's used in mines (with diagram)

colliery equipment's used in mines (with diagram)

This article throws light upon the top nine types of colliery equipments used in mines. The types are: 1. Coal Cutter 2. Power Loader 3. Controls 4. Conveyors 5. Telemetry 6. Gate-End Box 7. Overload Protection System 8. Multi-Control (Static Switch) Gate-End Box 9. Gate-End or In-Bye Substation.

A coal cutter is a low machine, being designed for stability and use in low slams where necessary. The motor unit of a coal cutter is usually divided into two chambers; one chamber contains the motor itself, whilst the starting and reversing switches are situated beside the motor in the other compartment.

Generally, the cage motors with long rotors of small diameter, delivering up to about 150 horse power, are in use on the face. Sometimes multi-cage motors are employed in most face machines in order to give a high starting torque and to reduce starting current.

Coal cutters are usually designed to be air cooled. Moreover, the motors body is designed with cooling fins to provide maximum possible area. As the motors used underground are all totally enclosed, the cooling is done by internal air cooling, and by conduction through the body.

These types of motors are generally of double shaft type, that is, with shaft at both the ends. One end of the shaft is used to drive the cutting end. The power is transmitted by a driving spline or pinion at each end of the shaft.

Separate gear boxes and special clutches are provided for the haulage unit and cutting chain. The clutches enable the machine operator to start the motor off load, and then to engage the haulage and cutter chain, separately or both together, as required.

Moreover, the haulage unit of some power loaders is driven by a hydraulic motor working from pressure supplied by a pump in the gate. The electric motor is, therefore, used only to drive the cutting gear. The motor drives its load through a gear box and special clutch called dog clutch. Generally, the haulage unit comprising by hydraulic motor pump and ancillary controls, forms an integral part of the machine.

In fact, the motor unit of many power loaders including the pilot and reversing switches, is a development of the type of motor unit used in coal cutters, and similar in shape to a coal cutter motor unit in general design and layout. These motors are cooled by water. Water is supplied continuously to the machine from a main supply in the gate.

After passing through the water jacket round the motor, some of the water may pass to the dust suppression unit. Water-cooled motor now-a-days, in the latest design of the power loader, are commonly used, as the motors temperature rise is more due to the operation of power loaders. Ordinary air-cooled ventilation has proved insufficient to keep the temperature rise down.

However, in order to ensure that the motor was not suddenly overheated by being run without an adequate water supply, a water flow switch is an accepted practice. However, in the latest design, instead of water flow switch, thermal switch is used as a safety measure.

These switches interrupt the pilot circuit and stop the motor if, at any time, the motor temperature rises above a predetermined safe value, due to the flow of water falling below the minimum rate required for adequate cooling. In fact, thermal switch has been found more effective and is sure to save a motor better than a water flow switch in water cooled motor.

The contacts of both the pilot and reversing switches are usually controlled by a switch handle at the haulage end of the machine. This arrangement in fact provides an interlock between the pilot and reversing switches to ensure that, on starting, the reversing switch close before the pilot switch and, on stopping, the pilot switch opens before the reversing switch.

The switch handle has an OFF position in the centre position, and is operated in one direction to obtain forward rotation of the motor and in the opposite direction to give reverse rotation to the motor.

When the switch is operated, the reversing switch contacts first complete the appropriate connections to the stator and then the pilot contacts make to close the gate-end contactor, and thus ensuring that the main contacts are not called upon to make and break the motor load current.

However, in addition to reversing the connections to the stator, the reversing contacts provide a means of isolating the motor of the machine. In fact the reversing contacts are not usually designed to break the circuit while current is flowing and they are likely to sustain damage from arcing if current is flowing when they open. On many machines, therefore, the switch lever has a double action return to OFF.

In fact, a pause between the first movement (during which the pilot switch opens) and the second movement (which breaks the power lines) is sufficient to ensure that the contactor has dropped out and broken the power circuit before the reversing contacts are opened.

The reversing contactor, however, could be used successfully to stop the motor in an emergency, if, for instance, the gate-end contactor failed to open when the pilot circuit was broken. Now, we know that the pilot contacts complete the pilot circuit, which operates the pilot relay and so closes the contactor.

When the pilot contacts close, a timer is started and after a short time delay, the economy (anti-self-starting) resistor is connected into the pilot circuit. The economy resistor then remains in circuit until the control lever is moved back to the OFF position.

The delay provided by the timer ensures that the pilot relay has operated before the economy resistance comes into circuit. The pilot relay may be slow to operate because of the copper sleeve or short-circuited winding incorporated in it to provide intrinsic safety. The most up-to-date machines now-a-days being manufactured, can have push button control, and still retain the stator control switch with reversal features.

It has been found that the most cutter loaders embody a system of control which enables the haulage speed to adjust itself to accommodate changes in load on the cutter motor if the machine begins cutting a section of exceptionally hard coal, for instance, the load on the cutter motor is increased and the motor may be in danger of overheating and eventually get burnt.

The load on the motor can be relieved by slowing down the rate at which the machine moves forward. If the load on the motor becomes severe, the haulage should stop completely. Conversely, if the machine is cutting soft coal, the cutter motor may not be running at full load, and the haulage can then speed up so that full motor power is used.

The response in the hydraulic haulage is obtained by using the current in the power circuit to control the rate at which hydraulic fluid is delivered to the haulage motor. One system of control was a three phase torque motor with its current coils connected in series with the power line to the cutter motor. The torque motor controls a hydraulic valve as is shown in Fig. 8.1.

If the load on the cutter motor is increasing, the torque motor moves the valve piston against spring tension, thereby opening the speed control of hydraulic circuit to pressure. The pressure in the speed control circuit reduces the output of the hydraulic pump, and therefore the speed of the haulage, until the load on the cutter motor is reduced and the torque motor allows the valve piston to return to neutral.

Conversely, if the load on this cutter motor is reduced, the torque motor allows the spring to move the piston so that the speed control hydraulic circuit is connected to exhaust. The hydraulic pump then increases its output, and therefore the speed of the haulage, until the cutter motor is under normal load and the torque motor moves the valve piston back to neutral.

If there is a serious overload on the cutter motor, the torque motor continues to move the valve piston until pressure is connected to the overload speed reduction pipe. The output of the hydraulic pump in then immediately reduced to zero, so that the haulage stops.

The other system of control makes use of three solenoids connected in series with the power lines to the cutter motor. The three solenoids together control a single hydraulic valve. In fig. 8.2 we see the system with the valves and solenoids in their normal operating position.

If there is a sustained overload on the cutter motor, the armatures of the solenoids pull in and operate the hydraulic valve. Pressure is connected to the offloading hydraulic circuit, and the manual control circuit is opened to exhaust. The output of the hydraulic pump is immediately reduced to zero, and the haulage stops.

The machine will continue to cut only if the operator restarts it with the haulage control reset to a slower speed. This system does not achieve complete automatic control of the hydraulic haulage, but is simply an overload cut-out interlocking the electric and hydraulic circuits. New machines having a mechanical haulage end can now be purchased as an alternative to hydraulic unit.

Conveyors are most essential in mines. Without conveyors a mine today can hardly operate. These conveyors are electrically operated by driving units. The driving unit of a conveyor is usually located at the discharge end, although in certain circumstances, such as when the conveyor operates on a gradient which favour the load, it may be found at the tail end. Some longer conveyors have two or even four driving motors.

A conveyor with four-motor driving unit has two motors driving at each end. A two-motor conveyor may have both motors driving at one end or one driving at each end. Most of the conveyors use Squirrel Cage Induction motors. Among them are double cage motors. And most of these motors are started by direct switching.

In fact, most of the time, the conveyors start on load, that is, with load already loaded on the bolt throughout its length. Due to starting direct online the motors need heavy torque coupled with excessive high starting current and most of the time with sustained stalling effect.

In fact, to eliminate these effects of high torque and current at the direct starting, the motors are mechanically coupled to the load through a fluid coupling. In this system of coupling at the moment of starting, the motor is not really connected to the load due to the fact that the fluid coupling is in between the load and the motor shaft.

In reality, what happens at the time of start is that when the direct online starter ON button is pressed, the fluid coupling automatically picks up the drive, and as the motor speed increases, it transmits gradually (instead of a sudden increase which would have occurred without the fluid coupling) more and more torque to the load. And in the end when the full speed is achieved, the coupling provides a solid drive.

A brief description of operation of fluid coupling should be given here, as this type of coupling has established its place in the industry due to its extremely useful application. In construction, a fluid coupling consists of two cupped discs each with radial fins which face each other in a fluid-tight housing, partly filled with oil or, when used underground, fire resistant fluid.

In fact one disc, which is called the impeller, is driven by the motor. When the motor starts, the impeller picks up fluid and directs it at the other disc, which is called the Runner, as explained in Fig. 8.3.

The Runner is driven round by the stream of fluid, the amount of torque transmitted depending upon the speed of the impeller. It is of course very much essential that the type of fluid used is suitable to the coupling and in the case of oil; oil of proper grade must be used. In this case, the manufacturers guidance and advice should be strictly followed.

The purpose of this type of coupling is to cushion the mechanical parts from the jamming start of a high horse power motor and to allow the motor to attain the speed at which it gives greatest torque output before the total is applied to it. The amount of fluid in the coupling decides the point at which the total load is applied to it.

In fact, under-filling will allow the motor to reach full speed with the internal radial fins of the coupling slipping, until heating will cause the safety plug to burst. On the other hand, overfilling applies the load before the motor can reach the speed at which it gives its greatest torque, this generally causes it to stall and trip out electrically.

However the proper fill of a fluid coupling is dependent on voltage of the motor at start and the motor characteristics. Therefore the filling of the oil to the proper level is most important. And the method of determining the proper level of fill, using a tachometer, is given by the manufacturer which has to be carefully followed by the operators, as improper filling may cause many problems as mentioned above.

Many belt conveyors are provided with a belt protection switch with the motor, in the event of the belt slipping excessively or breaking. One type of switch consists of a centrifugal mechanism driven by the belt.

While the belt is running normally, a pair of contacts in the pilot circuit are held closed by the centrifugal action of the switch but, if the belt speed falls below a predetermined level i.e. if the belt breaks or slips excessively, the contacts open, and then the pilot circuit opens and the motor stops. This is explained in Fig. 8.4.

Another type of belt protection device consists of a small a.c. generator and a relay. The output of the generator is connected directly across the operating coil of the relay. The output voltage of the generator varies with the speed of the belt, and is sufficient to hold in the relay only when the belt speed is normal. This is explained in Fig. 8.5.

The switch is connected in series with the pilot relay holding resistance, so that it is out of circuit when the pilot switch is at START, but in circuit when switch is at RUN. This arrangement is adopted because the belt protection switch is open when the conveyor is at rest.

It is, therefore, necessary to bypass the belt protection contacts in order to complete the pilot circuit and start the motor. The pilot switch is normally of the type which moves automatically to the RUN position after a predetermined time.

Because of the length of the gate two or more conveyors may have to operate in tandem. Since they form a continuous route for coal, their starting switches are interlocked in order to prevent the possibility of a moving conveyor depositing a load on a stationary conveyor.

Conveyors at the same time would draw a heavy current which might very well disrupt the whole supply system. Therefore, in order to safeguard the conveyors and at the same time prevent a heavy current, a system of sequence switching is introduced. This is explained in the block diagram as in Fig. 8.6.

With sequence switching system the conveyor at the out-bye (discharge) end of series of conveyors is the only one controlled directly by an operator. Each of the others is controlled by a sequence switch (a centrifugal mechanism or generator and relay device) fitted to the conveyor on to which it discharges. This sequence switch takes the place of this normal starting switch in the pilot circuit.

To start the conveyor system, the operator closes the pilot switch which controls the out-bye conveyor. This conveyor starts up, after a pre-start warning has been given, and as it approaches full speed, the sequence switch fitted to it completes the pilot circuit of the next conveyor. The second conveyor then starts up, after a prestart warning, and when it is up to speed, starts the third conveyor and so on in the same sequence.

The speed at which a sequence switch operates is adjusted so that it closes only when the surge of current taken by the conveyor to which it is fitted, has subsided. The time interval between the starting of a conveyor and the next one in sequence is about five to six seconds.

The sequence control switches also provide a measure of protection, ensuring that if any conveyor stops for any reason; all conveyors in-bye of it will automatically stop. Sequence switching is usually combined with belt protection switches.

The fact that a series of conveyors can be controlled from a single switch eliminates the need of each conveyor to have it own operator. The operator at the control point, however, needs to know whether or not all the conveyors are working normally, so that he can take prompt action if a fault develops.

Since it is impractical for him to leave his control position to inspect the conveyors, this information is brought to him by electric indication circuit circuits which operate fault indicators like signal lights, hooters or flags, at the control position.

In Fig. 8.7 a fault indication circuit is shown. We see that the relay in the belt protection switch is provided with two sets of contacts, one set in the pilot circuit controlling the conveyor motor, the other set in the indicator circuit. If the speed of the conveyor belt falls for any reason, the output voltage of the belt protection generator falls and the relay is de-energised.

The contacts in the pilot stop the motor, while the contacts in the indicator circuit close, lighting the panel which informs the operator of the fault. A safety factor is introduced by the hold-out relay. This relay is held open when the indicator circuit is live. It ensures that the pilot circuit remains inoperative so that the motor can be restarted only after the indicator circuit has been interrupted by the reset button.

Besides indicating belt-slip, all systems must be equipped to give information about other fault or condition which may require action by the operator or automatic tripping device. Warning must be given remotely by indicator circuits, of fire, overheated driving drums or bearings, blocked transfer chute, torn or misaligned belt.

For each of these faults or conditions there is a type of detection unit which will complete indication and automatic tripping circuits. These detection devices, therefore, are most important in avoiding any major faults.

What is telemetry? In fact this sophisticated system of control is mostly in use in Britain and U.S.A. The basic principle of telemetry is that information is sent down the line by a transmitter, which emits a pulse of a certain frequency, and is received at the other end of the line by a receiver tuned to the same frequency.

A second transmitter and receiver can operate on the same line using a different frequency, without interfering with the first pair. In fact, more than thirty such channels are possible in a single line circuit. However, the transmitters do not all work simultaneously.

The control point scans the transmitters, that is, calls each one in turn and receives the pulse from it and then passes on to the next transmitter and so on until a message has been received from each transmitter on the line.

Then it returns to the first transmitter for a second scan and so on. Since a complete scan of thirty or more transmitters is possible within three or four seconds, each channel is effectively giving a continuous indication.

The modern development, therefore, is towards the centralized remote control of conveyor systems. The operator of a remote control system is stationed at a control point which may not be near any conveyors in the system and in most modern installations is situated in a surface control room.

The operator is, therefore, able to start or stop any conveyor in the system from his position and continuously receives the information about the state of each conveyor. Information may be displayed on illuminated mimic diagram which enables the operator to see at a glance what is happening throughout the system. Fig. 8.8, in a block diagram, explains the basic principle of a simple telemetric link.

It is a must that, with a multi-drive conveyor, a system of sequence control is employed to avoid the simultaneous starting of two or more motors. At the same time, the system also ensures that the motors start with a minimum of delay, so that they share the load equally and effectively.

Fig. 8.9 also illustrates a block-diagram control of multi-drive conveyors. Usually a conveyor is started by a pilot switch at the discharge end. If the conveyor is driven at both ends, the pilot switch usually starts first a motor at the in-bye-end of the conveyor to take up the slack in the return belt or chain. The starting of the other motors is controlled by time delay switches in the contactor panels.

The contactor panels are to be interlocked electrically so that in the event of any one panel tripping out, all the other motor circuits are also broken. The interlock provides a safeguard against motors being overloaded if one or more of the driving motors stop working. Therefore, design of an efficient interlock control in a multi-drive conveyor system is most important.

In principle and in practice a gate-end panel is a contactor panel provided with earth leakage and overload protective systems. The components of the pilot circuits are also an important part of the gate-end box. The contactor in this box is supposed to have a heavy duty of making and breaking a motor circuit.

Therefore contactors in gate-end box must be of heavy duty type subjected to heavy electrical and mechanical (ON-OFF) duty. These gate-end panels are used deep in the mines as a source of control and supply for various types of practical use. For example, to operate a coal drill, it contains a transformer which provides the necessary 125 volt supplies or as it may be necessary.

In fact, drill panels are designed so that two drills can work from one transformer. These types of panels consist of two contactors each with its own control and protective system housed in a single enclosure together with a transformer.

The busbar chamber is arranged so that when several panels are side by side, the busbar sections are coupled together, forming, in effect, three busbars running through all the panels, there being only one cable entry from the substation.

In fact, the busbar chamber is completely separated from the remainder of the panel by flameproof enclosure. Connections are made from the busbar chamber into the main contactor chamber by means of flameproof terminals. In the busbar chamber also, an isolator has to be provided. It is operated by a handle projecting through the front wall of the chamber.

The isolators main function is to isolate the contactor, the entire circuit, and the pilot circuit from the busbars. It is also provided that work can be carried out in the contactor chamber without disturbing the busbar connection which, in-fact, would mean interrupting the supply to the other panels in the area.

However it must be ensured that the busbar chamber is not opened unless the entire face system has been isolated from the substation. In this case no chance should be taken, as it is a question of safety. The isolator is provided with four positions, Forward, OFF, Reverse, and Test.

To move the isolator from either forward or reverse position the isolator must be moved to the OFF position. The isolator should not be normally be operated when current is flowing in the power circuit.

The isolator is designed to break the circuit in an emergency i.e. if the contactor fails to open. Now moving the isolator to the TEST position means that it energises the control circuit only to facilitate testing of various circuits within the gate-end box.

In gate end boxes, the contactors in use are usually of air-break butt-contact type, with wipe and rolling action under spring pressure. The moving contacts are spring loaded with spring capacity as per the required specification, to meet the electrical effect of the rate of current passing through the contacts.

The moving contacts are mounted on a perfectly insulated spindle which is actuated by a magnet coil called main operating coil. The contactors have to be filled with a set ofauxilliary contacts which are held for control or sequence operation.

However, an arrangement for guided arc extinction is done by means of specially designed magnetic blow-out coil, which is fitted in series with the main motor line, so that at the time of making and breaking, full current passes through the blow-out coil.

Over and above, specially designed arc-chutes or blow-out checks are provided to confine and interrupt arcs inside these arc-chutes. Although not yet manufactured in India, the latest development in contactor line is the vacuum contactor, which are nowadays being used in Britain, U.S.

Overloading is a regular phenomenon in any electrical system operating drive. Therefore, providing overload protection in a control circuit is a must, and this is provided by a series of over-current coils or current transformers in each phase, with oil dashpots to ensure that a brief overload, particularly the heavy current of starting a motor, can be accommodated without tripping.

However, variation in overload protection system for different h.p. drives is achieved by changing the current transformers and ammeter. Current transformer rating are designed to meet the requirements as 5/10, 10/20, 5/100, 5/300 amps.

So when the current passing through reaches 100% or 125% or 150% of FLC, the overload coil magnetizes the plunger, which is pulled upwards, hitting a contact bar called trip bar, and as such the O/L trip bar contact opens which in turn opens the main contractor, as the contactor coil gets supply through the O/L contacts in series.

As the main contactor opens, the motor circuit is broken. However, after resetting the overload contacts by a reset button the contactor can again be closed by using the pilot switch. Sometimes, for special application and also where time delay is required, timers are fitted with the O/L contactors to prevent re-closure of the contactor.

Nowadays a new electronic device called static switch is sometime used as an overload protection. This static overload system consists of a current transformer feeding a solid state circuit. The whole range is covered by a set of adjustable links covering settings from 5 to 300 amps. In this equipment short circuit protection is also provided.

Recent developments in many developed countries have shown us the introduction of the multi-control or multi-contactor gate-end box. This equipment has been designed by using vacuum contactors and solid state circuitry as protective devices.

Besides being much more trouble free and requiring less maintenance the main advantage of these units is that they occupy space almost 25% less than that occupied by conventional gate-end boxes. Due to this valuable space saving, the gate-end boxes have become very useful inside the mines where space is so important a factor. Therefore recently in U.K., the gate-end boxes have become very popular.

In India, however, these type of gate-end boxes are not only not manufactured, but are also not yet in use. In fact the author feels that for better economy and better performance these static-switch gate-end boxes should be manufactured and used in Indian mines.

The name gate-end substation is given because these are located in the gate-end as close to the face as practicable. The gate-end or in-bye substation is a step down transformer, provided with switchgear. The transformer is protected against overload, short circuit, and earth faults, and against faults between high tension and medium voltage windings.

In fact this gate-end substation is to be so equipped that any local fault can be arrested here and will not be allowed into the main substation and trip the whole system. The main air circuit breaker is on the high tension side so that the transformer can be isolated, but for better safety and protection, another air circuit breaker should be provided. The transformer, in this gate-end substation, should be flame proof.

If the transformer is fully flameproof, it may be installed close to the gate-end boxes. Sometimes, however, substation and the gate-end boxes are mounted together on the same chassis frame, so that these can be moved forward in a single operation.

This provides better handling. In India, many oil-filled transformers are still in use inside the mines. Therefore, when transformer is not fully flameproof, it is a must that it should be installed at least 300 meters from the face.

However, sometimes the substation is located in the gate, and away from the gate-end boxes. In that case the gate-end boxes should be connected to the substation by a pliable wire armoured cable. It is normal practice to use a cable which is longer than is at first necessary to make the connection. The extra cable is taken up by coiling it into a figure of eight formation, or supporting it on a mono-rail.

The cable is kept of sufficient length so that the substation does not need to be moved off and on. However, for easy handling some gate-end substation transformers are fitted with flanged wheels so that they can be moved forward easily on rails. Others stand directly on the ground or on skids, or suspended from mono-rails.

A most important factor to remember is that the cable length should be kept as minimum as possible between the gate end substation and the gate end boxes to avoid voltage drop. This is most important as the efficiency of the system depends mostly on this point. In fact, the heavy current carried by the medium voltage system would cause a considerable voltage drop in a long cable.

A voltage drop in the cable causes the motors operating from the cable to lose power. In an extreme case, a motor may not at all start due to the heavy voltage drop, when the motor is switched on, and if this persists on load, the motor will soon be burnt.

Therefore, it should be remembered that if the gate-end substation is of a type which must be installed in the gate at a distance from the face, the efficiency of the face system will depend upon the substation being moved forward at frequent intervals.

Therefore, if the substation is not moved, and the run of medium voltage cable is increased, the serious resulting loss of power may reduce considerably the output of coal from the face. Therefore location of a gate-end substation is a vital point as far as the operation of the machines in the mines is concerned.

mining equipment market share, statistics | industry report 2024

mining equipment market share, statistics | industry report 2024

Mining Equipment Marketsize was valued at over USD 70 billion in 2017 which is expected to grow at over 5% CAGR from 2018 to 2024. The global shipments are expected to surpass 450 thousand units by 2024.

Rapid evolution in mining processes and a rise in the adoption of automated solutions in recent years are predicted to drive the mining equipment market demand over the forecast timespan. Several players are providing smart solutions to their customers for improving productivity and enhancing the efficiency of industrial operations. These smart solutions offer features such as real-time control & monitoring, will optimize production management, and enhance the decision-making approach. This has led to players integrating these advanced solutions into their products to enhance the productivity and reliability in mineral extraction processes. For instance, smart extraction solutions offered by Wipro Limited include advanced analytics, short interval control, mobile asset visibility, remote operation centers, digital work management, and mobility platform. With the integration of advanced digital technologies, customers are able to maximize the Return on Investment (ROI). Such factors are anticipated to facilitate the expansion of the market in industrialized countries.

With an increase in demand for exploration machines and robotics, companies are replacing legacy mining methods, providing an impetus to the mining equipment industry growth. The replacement of automated solutions in place of manual processes helps in reducing the number of accidents in handling and performing activities. Moreover, automation and robotics technology incorporated with the complex and heavy machines is enhancing the overall productivity. High investments of market players in R&D activities to provide technically-advanced machinery with greater efficiency, reliability, and the ability to sustain the rising competition are creating several growth opportunities. Over the coming years, the commodity prices are anticipated to witness an upswing, thereby fueling the market demand. In addition, a renewed strength in construction activities and the rise in manufacturing output in the developed markets will support the market growth.

In 2017, surface mining machinery market accounted for over 30% of the overall industry share. These machines are experiencing a high adoption due to the rise in demand for extraction of minerals such as non-metallic ore, metallic ore, and coal. Several new techniques are being developed depending on mining tasks such as mountain removal, strip, and open pit. The rising demand for mineral and metal commodities is projected to drive the market growth. This equipment aids in cost optimization due to its ability to cut, crush, and load in a single working process. The growing demand for technically-advanced solutions and a rise in mining activities in developed markets will fuel the industry growth over the coming years. Countries including Brazil, Russia, India, and China have a high abundance of natural resources and a high rate of coal production. These countries are experiencing a high adoption of this equipment for performing coal extraction activities.

Metal mining is anticipated to witness a steady growth over the coming years owing to the rise in disposable incomes and improved living standards that have fueled the demand for precious metals such as gold, platinum, silver, and other commodities. The rise in demand for this equipment for metal extraction will drive the market demand. Metals such as aluminum, copper, zinc, lead, and nickel are being utilized in several industrial sectors such as construction, chemical, and energy & utility for performing manufacturing operations. The rise in industrialization and urbanization trends in developing countries are providing numerous growth opportunities to the market players. Manufacturers are offering products with GPS technology and other electronic control modules and database tools for improving the product offering. Moreover, the replacement of aging infrastructure and development of new buildings for the safety is generating a high adoption of the metals such as iron and steel in construction activities, thereby driving the mining equipments demand.

Asia Pacific is anticipated to grow at over 6% CAGR over the forecast timeline. Lack of mechanization rates in Asia Pacific countries is anticipated to drive the sales. Many developing countries in the region have sizable coal producing areas and significant coal and metal mining industries that need a substantial level of capital investment. Increasing demand for lower emissions, low cost, and high energy-efficiency machines is being witnessed in the region. Growing availability of lease-based model will encourage end users to use advanced machinery. A rapid increase in the construction activity and manufacturing output in China, coupled with government efforts to boost the mechanization of mines, have led to a rapid growth of the mining machinery market in the country. Moreover, the India market is anticipated to witness a steady growth owing to a rise in mining output growth and a significant need for mine mechanization.

Major players operating in mining equipment market share include Caterpillar, Inc., Metso Corporation, Komatsu Ltd., Atlas Copco AB, Sandvik AB, CNH Industrial NV, Hitachi Co., Ltd., AB Volvo, Doosan Group, Liebherr Group, Astec Industries Incorporated, Bell Equipment Limited, China Coal Energy Company Limited, Bradken Limited, Corum Group, Hyundai Heavy Industries Company Limited, Kopex SA, RCR Tomlinson Limited, Techint Group, Terex Corporation, and Wirtgen Group Holding GmbH, among others. These companies are offering several products to governments as well as the private sector for performing mineral extraction processes. The products offered by the players are designed based on the industrial specifications and requirement for performing specific tasks. These players have a strong presence in the countries where the demand and availability of the minerals are high.

Technological advancements and innovations are expected to drive the mining machinery industry growth. Several technologies that are revolutionizing the industry include automation, Internet of Things (IoT), 3D imaging, and plasma technology. These machines are developed using materials and technologies that can withstand high temperature and pressure. The machines are exposed to high radiation and chemical substances that can directly affect the functioning of the parts. The players in the market are focusing on such challenges and are developing machines that can be used for the extraction of specific minerals or metals. Remote monitoring and control devices are integrated into these machines to provide careful observation of the processes and activities from centralized systems. It provides maximum efficiency, improves safety, decreases the variability, and allows better identification of performance issues. Such factors are expected to drive the market growth.

list of equipment used in opencast coal mining | mining

list of equipment used in opencast coal mining | mining

List of equipment used in opencast coal mining are: 1. Bulldozer 2. Craper 3. Ripper 4. Tractor Shovel 5. Dipper Shovel 6. Stripper Shovel 7. Pull Shovel or Hoe 8. Dumpers or Tippers 9. Drag Line 10. Road Grader 11. Rock Drills.

Opencast mining is the oldest method of excavating minerals but the mining operations have been mechanised by the use of heavy earth moving machinery during the last 50 years resulting in excavations on a scale which was unthinkable half a century ago.

A bulldozer is often referred to simply as a dozer. It is a tractor with a pusher blades attached to the front portion. The tractor is the diesel-operated power unit equipped with either crawler chains or rubber tyred wheels for lifting. The pusher blade can be raised or lowered or tilted through small angles horizontally by rams operated through hydraulic pressure or by ropes.

The dozer blade is used for pushing loose material or for digging in earth, sand and soft weathered rock. The machine is also engaged for leveling or spreading earth, for leveling of rock spoil in the dumping yard, grading and compacting temporary roads, pushing mineral into sub-ground level bunkers through grizzly, for towing dumpers, etc.

It also serves the purpose of pushing boulders, pulling down trees, and is an essential equipment to push scrapers. A dozer equipped with a fork like attachment is known as ripper and operates like a plough to loosen moderately hard rock. The loosened rock may be loaded by a scraper. A dozer can dig 1.2 m to 1.5 m below ground in earth or weathered rock.

This machine is diesel-operated with pneumatic tyred wheels and has at the centre a bowl fitted with a cutting blade at bottom. The blade is reversible and can be replaced when blunt. Its working may be compared to that of a lawn power.

As a scraper is pushed forward by a dozer, its blade cuts a thin slice of earth usually between 75 mm and 225 mm thick over a distance of nearly 30 m. The earth is automatically collected in a central bowl whose capacity ranges from 3 m3 to 22 m3 and it takes nearly one minute for loading.

When the scraper is fully loaded its bottom opening is closed by the operator through manipulation of a cable (rope) and the loaded scraper, with the bowl lifted, travels to the dumping yard on its own power. At the dumping yard, as the scraper moves, the bottom opening of the bowl is opened and the contents are unloaded in a layer 150 mm to 250 mm thick, over a distance of 30 to 70 m.

The bowl is always bottom discharging. Scrapers are unsuitable in soils with stumps, large boulders and hard rocks. When the ground is hard, it is necessary to rip the surface with the help of a ripper before loading by a scraper. Sandy soil is best for a scraper which has to be stopped during rains, if engaged, in aluminum.

Scrapers are used in coal mines for cutting and transporting weathered sandstone as well as coal. The coal excavated by it is however smaller in size. A Scraper may take 5 to 6 minutes for a complete cycle of loading and unloading if the total up-and-down distance of a trip is nearly 300 m. One-way traffic of loaded and empty scrapers is desirable for good results. One dozer is normally sufficient for every two scrapers used.

A ripper is a machine which cuts, as it travels, 0.6 to 1 m deep furrows in the ground, and it can be well compared with the farmers plough. The ripper is essentially a crawler mounted heavy duty diesel tractor with a ripper attachment.

Like a farmers plough, the ripper with the ripping tool thrust into the ground by hydraulic pressure, travels along close paths, 1.2 to 1.5 m apart and during the travel rips open the ground. The broken ground or rock can be dozed to form a stockpile for convenience of loading or can be loaded by a scraper.

If the overburden or mineral is suitable for ripping its breaking is possible with the help of a ripper and the process of drilling and blasting can be dispensed with. Soft rocks and medium hard rocks, below hardness 5 on Mohs scale, which are laminated and stratified, provide suitable material for ripping.

The alluvial surface deposits, weathered sandstones and shales underlying them in the coalfields can be easily ripped and the relative rippability of the rocks can be known with the help of an instrument known as Refraction Seismograph.

The Refraction Seismograph operates on the principle that Sound waves travel subsurface material at different velocities, depending upon the degree of consolidation of the material. It is believed that the same factors that affect consolidation also affect rippability. Thus poorly consolidated material with low seismic wave velocities could be ripped easily, while highly consolidated material with high velocities would be difficult to rip.

ii. Geophone Receiver of sound waves. A geophone is a velocity gauge suitable for detecting frequencies in the range of 1-100 Hz. The geophone converts the mechanical vibrations into its electrical analogue. The electrical signal is then amplified and transmitted to the monitoring station.

The seismic wave is produced by a sledge hammer striking a steel plate at various distances from a geophone receiver. Immediately upon impact, a wave front composed of innumerable seismic waves travels in all directions away from the point of impact, or source.

The geophone receiver is sensitive only to the first seismic wave that reaches it. Thus, either the wave which travels the shortest distance, or one which travels, a longer path but which includes a high velocity segment, arrives first at the geophone.

In iron ore areas of Goa the practical results obtained with seismograph were as follows- Seismic velocity in overburden (practically laterite) was 600 to 1,200 m per second. In iron ore it was 1,050 to 1,500 m per second, but in some cases velocities as high as 1,800 to 2,100 m per second were also recorded.

The tractor speed is 0.8 to 2.5 km/hr during ripping. If the rock is soft it is advisable not to increase the speed but to add one or more ripping teeth. The distance between adjacent furrows during ripping may be 1 to 2 m and the harder the rock, the closer are the furrows. In some rock formations ripping is possible after sparse blasting of widely spaced charges.

It is essentially a diesel operated tractor with a bucket as the front attachment and is called a front-end loader or pay-loader. It may be on pneumatic tyres or crawler chains. The tractor shovel attachment consists of a push frame and a bucket that can be raised, lowered and dumped hydraulically or mechanically. The shovel usually has a pusher fan so that the dirt falling form the bucket will not be sucked back towards the operator and engine air intake.

For digging, the complete tractor shovel has to move forward toward the bench and for unloading the contents of the bucket the entire unit has to come back and position itself conveniently to empty the bucket on to a dumper. Its rate of digging and loading cannot, therefore, be as fast as with a revolving shovel.

Tractor shoveIs have been employed in some mines to load the stacked mineral at the siding into railway wagons or to push it into ground-level bunkers. Capacities of the buckets are from 0.57 m3 upwards. Heavy rock buckets for handling blasted rock carry teeth as standard equipment though the buckets used for coal handling need not be so equipped. Main specifications of two wheel-loaders (B.E.M.L.)

An excavator, technically speaking, is any machine which excavates the rock or earth and swings or transports it, within narrow limits, to an adjacent place or dumps it on to a receptacle like a dumper or railway wagon.

In this sense, a tractor shovel which cuts or digs to some extent below the flow on which it stands, may well be considered an excavator the name traxcavator for the tractor shovel manufactured by one company apply conveys the meaning- but, in earthmoving terminology the term excavator covers machines of the following type:

A power shovel is a shovel using electric or diesel motive power for its operation, as distinct from a hand-operated shovel. The functions of power shovels are very simple. Basically, these machines lift fragmented rock, and swing it to a different location such as dumpers or spoil heaps.

2. A deck or cab mounted on a turn table and housing the prime mover, all the controls for operation, cable (wire rope) drums and the operators seat. The deck or cab can swing through 360 independently of the propelling crawler chains or tyres.

A shovels is made in three structural divisions. An automatically, the top or revolving unit is the head and torso, the mounting or travel unit is the legs, and the various attachments are the arms and hands.

A revolving and a travel unit together make up a basic shovel which may be fitted with any of the five front attachments. The machine may thus become any one of the following- a crane, a clam shell, a dipper shovel, a drag line, a pull shovel or a back-hoe.

This is a machine employed for excavating soft rock or loading fragmented rock from a bench and is very commonly used in mines. It is usually mounted on crawler chains. The cab carries the power unit which may be an electrical motor at 3300 V, supplied with power from an external source through a flexible electric cable, or a diesel engine.

The bucket (also called dipper) commonly used may be of 1 m3 to 4.5 m3 capacity. It is used for loading dumpers and for this purpose it has to stand on the floor of the bench. Watery conditions in the quarry are not suitable for efficient operation of this machine, as dumpers have to move inside the quarry.

During operation, the crawlers are stationary within 3 to 5m of the toe of the bench. To load the bucket, the operator crowds it into the fragmented rock with the dipper stick and hoists it. As it moves through an arc in the rock pile.

It is then retracted and the cab, along with all the machinery mounted on it, the boom and the bucket, is swung horizontally through nearly 90 to position the bucket over the dumper. The bucket is bottom discharging and its door is opened by the trip cable. Normally five buckets are required to load a dumper.

The teeth of the bucket wear out fast and when worn out, have to the built up to size by welding. The trip cable lasts for nearly 35 hours and the hoist cable, for nearly 100 hours. In one shift a shovel loads 450 to 500 buckets. Where the dumping yard is away from the quarry a dipper shovel loading into dumpers is advantageous.

Hydraulic shovels which eliminate use of wire ropes (cables) have become popular in recent years. The electric motor or diesel engine mounted on the shovel drives the hydraulic pump and the pressure developed is utilised for various operations of the shovel. Hydraulic motors are of low speed, high torque with hydrostatic braking. One example of such hydraulic excavator is Porcelain shovel of Larsen Toubro Ltd.

Dipper shovels commonly employed in our mines are of 2 m3 4.6 m3 bucket capacities. Only a few mines employ shovels of 8.3 m3 or 10 m3 capacities, e.g. Malanjkhand Copper Project employs 10 m3 dipper shovels.

A pull shovel, is also known as a hoe, back hoe, drag shovel. It is used for loading dumpers and its best application is for digging below the level on which it stands. The shovel and the dumpers can stand at a higher level free from water and mud of the quarry floor. As the attachments to the bucket are by dipper stick and not by cables, the bucket is under positive control of the operator and therefore suitable for hard digging.

The shovel is used for stripping top soil, and making shallow cuts and trenches upto a depth of 3.5 to 6 m. Compared to dipper shovel, the hoe is slower in digging and less efficient for loading trunks.

These are heavy duty trucks with a container-body of steel open at the top for receiving material loaded mechanically by tractor shovel, dipper shovel, dragline, etc. All dumpers/ tippers are provided with arrangements to lift the loaded body by utilizing hydraulic pressure to force a ram out.

The body swings from its horizontal position round a fulcrum through nearly 70 to dump its load and the hydraulic system also functions to pull the body back on its seat i.e., the chassis. A typical hydraulic system layout for the tipping gear of a dumper. From an oil tank oil flows by gravity to hydraulic pump.

When the driver engages the power take off (P.T.O.) control lever, power from the engine is transmitted from the transmission countershaft to the power take off which drives the pump. The oil under high pressure from the pump goes to the control valve whose lever can be manipulated for 4 different positions.

High pressure oil goes through the hose pipes to the bottom of the hoist cylinder and the ram is then forced out. Oil at the top of the hoist travel back to the control valve through the hose connected to the piston rod.

Both hose passages between the control valve and hoist are open so that oil at either end of the hoist can flow either way. The hoist can then travel in either direction depending upon the direction in which the force is applied.

High pressure oil goes to the top of the hoist which then telescopes itself by the oil pressure and the oil at the bottom of the hoist travels back to the tank via the control valve. The body is thereby lowered on to the chassis.

Steering on all the heavy duty dumpers is mechanical but assisted by hydraulic power, generated by the engine. The dumper operators exertion in thereby considerably reduced. Mechanical transmission from the engine to the rear wheels is the standard practice now-a- days, though for some years the rear wheels were driven by individual electric motors controlled from operators cabin.

Medium sized mechanised quarries employ dumpers of 25-50 te carrying capacity. 50-60 te coal haulers are on the manufacturing line of B.E.M.L. and Hindustan Motors. Future planning of large projects is for employment of 100-150 te dumpers which will be fed by shovel of 8-10 m3 capacity. Bottom discharging coal haulers of 55 te payload, 43 m3 struck capacity (model GB 60C) are manufactured by BEML.

Brakes on dumpers are operated by compressed air. Some dumpers are equipped with hydraulic retarder (hydrotarder). This is a device used on some trucks and dumpers to prevent the speed from exceeding certain limits when travelling a steep down- slope and also to produce a breaking action on the vehicle.

In a way, it acts as a governor. It uses the hydraulic friction to produce the breaking action. Unline the regular brakes, the hydrotarder will not completely stop the vehicle but will slow it down preparatory to stoppings with the familiar friction brakes, operated by compressed air or hydraulic pressure. The retarder essentially consists of a vane type rotor turned by the driven shaft, a fixed casing or stator fitted with vanes and an oil circulation system.

The machines deployed in the opencast mines, at the crushing and ore preparation plant have to be of matching capacities. At Kudremukh Iron Ore Project, one of the largest opencast mines in India, the capacities of some of the machines are : shovels 10.7 m3, production trucks 108 te, front end loaders 10 m3 , electric drills for 310 mm dia. blast holes, gyratory crushers 4000 te/hr.

A drag line is a machine used for excavating earth, sand or soft rock and consists essentially of a revolving deck, a long light boom, crawler chains, and a special type of bucket held in position and controlled by cables. The bucket, when it has to be loaded, is lowered in the earth or loose rock by manipulation of the cables and is dragged by them.

As it is dragged it gets loaded. Hence the name dragline. A dragline is operated by diesel engine or a motor which is supplied power at high voltage from external source through a trailing cable. The depth to which a dragline digs is limited by the capacity of the drums to hold the hoist cable. When digging, the bucket, after it is loaded, is hoisted up, the boom given a swing through 90 and the contents then unloaded by manipulation of the cable.

A dragline is suitable for digging alluvium, sandy soil, unconsolidated rock or blasted coal/rock. It digs below the level, at which it stands and from position can dig over a wide working place and cast the earth over a wide area within the reach of the boom.

It is generally not employed to load dumpers as the accurate positioning of the dragline bucket over a limited area of the dumper delays the cycle of operation and the common application is for dumping overburden. It is suitable for working a quarry with watery conditions as the dragline works from a higher and, therefore, dry position.

This is a machine for leveling the road surface by smoothening out the ups and downs and for casting aside the boulders on the road. It is always pneumatic tyre mounted with only rear wheel drive and the front wheels are small.

The grading blade is attached to a circle that is hung from the overhead frame and pulled by a drawbar fastened to the front of the frame. The blade is usually 3.5 to 4 long having replaceable edges on the sides and bottom. Steering is direct-connecting mechanical by a hand wheel though a hydraulic booster is fitted on some models.

The motor grader (Mode GD 605 R-2) of B.E.M.L. has the following main specifications- Engine flywheel HP 145 at 1800 RPM; operating weight 12,650 kg; Max. Drawbar pull 7,280 kg; Max. speed forward 43.6 kmph; steering full hydraulic; overall length-8415 mm; width 2375 mm; height-3200 mm, minimum turning radius 10.4 m.

A jack hammer, so familiar to mine workers, is a hand-held and unmounted drill used for vertically downward drilling. It weighs from 15 to 25 kgf and is used for drilling upto a depth of 2 m (rarely 3 m); hole dia. is generally 30 to 37 mm and rarely 50 mm. In a few cases a jack hammer may be mounted on an air leg. Though ordinary used for dry drilling, it can be adapted for wet drilling as well.

A drifter is a mounted drill, generally designed for horizontal drilling. It is heavier than the Jack hammer and is used in quarries and for tunnel driving. The widely used mounting is the column and arm and the drill may be used for wet as well as dry drilling. Its working is like a jack hammer.

A wagon drill is essentially a drifter type drill capable of movement up and down a vertical guide and mounted on a portable frame fitted with wheels. The hole dia. is from 50 to 100 mm and the depth drilled ranges from 3 to 15 m.

It is a compressed air operated drill to which air is supplied from external compressors through hose pipes at a pressure of about 6 kgf/cm2. The drill weighs 15 to 25 kgf and drills holes of dia. 30 mm to 38 mm (rarely upto 50 mm) upto 3 m depth. The drill rod is hexagonal in cross-section, suitably shaped at one end to form the shank and the other end is so shaped as to form a non-detachable single chisel bit with a tungsten carbide insert.

Drill rods may also be equipped with detachable X type tungsten carbide drill bits. In a shift of 8 hrs, two workers who hold the drill can drill 60 holes, each 1.2 to 1.5 m deep in sand stone, laterite, etc. When hand-held, the machine drills vertically downward holes only but if mounted on air legs, it may be used for drilling inclined holes.

An oil bottle placed between the drill and., the air receiver, and connected by hose pipes to both, provides lubrication to the drill when working. For dust suppression a jack hammer can be adapted to wet drilling by some modifications so that the drill cuttings mixed with water come out of the hole in the form of a sludge. The air consumption is generally 2-2.5 m3 of free air/min.

A compressed air operated drifter mounted on a mobile frame and capable of travel up and down a mast is known as wagon drill. The frame is usually tyred wheel mounted though crawler chain mounting is provided in a few models. Tyred wheel mounted wagon drills can be pulled by the operator and his helper to the hole sites on a level ground.

A wagon drill, is used to drill holes of dia., varying from 50 mm to 100 mm for depth of 3 m to 15 m. The mast for the drifter is usually 3 m long providing for nearly 3 m vertical travel of the latter. This travel is possible with the help of a compressed, air driven feed motor through chain (known as chain feed).

The drifer provides the rotary motion as well as the percussive action to the drill rods, and in turn, to the drill bit. The drill bit is detachable X type with tungsten carbide insert. Compressed air fed through the hollow drill rods blows away the cuttings to the surface.

Total meter age drilled in an 8-hours shift is 60-70 m in rocks like sandstone, coal, etc. including the time spent on shifting the drill from hole to hole. The mast is capable of swiveling from vertical to a horizontal position and it can be kept fixed at any angle between the horizontal and the vertical, thereby facilitating vertical, horizontal or inclined drilling upto 40. The drill is not self-propelling, and receives air from external compressor.

In a large size wagon drill using a drifter a considerable portion of the drifters energy is utilised in overcoming the inertia of the drill string making up the column of the drill rods and in rotating them. Such loss of the drill energy increases with depth. This waste of energy is considerably reduced by the use of the down-the-hole hammer.

The drill bit used may be a carset bit (a X-bit with little modification) or a button bit which is fitted in the hammer. The compressed air going down the hollow drill rods forces the piston which directly hammers the drill bit without any drill rod in-between. The number of blows is from 500 to 2400 per min.

When using down-the hole hammer the drifter is replaced by a rotary head placed at the top of the drill string and driven by a built-in piston type air motor. The rotational speed of the drill rods is nearly 15-25 r.p.m. The rotary head is also used to tighten and loosen threaded joints on rods.

The up and down travel of the drill rods is by a chain feed. The down-the-hole hammer, type 100 ASS used on HALCO drills for holes of 100 mm to 125 mm dia. Its specifications: Outside dia. 89 mm, length without bit 94 cms; weight without bit 31 kg.

Some of the heavy duty wagon drills are powered by hydraulic pressure system. It is equipped with a rock drill model COP 1308 HB manufactured by the same company. In the drill, compressed air is replaced by hydraulic pressure and the prime mover for the hydraulic power pack is an air cooled diesel engine.

The absence of exhaust air results in a much lower noise level when compared with air-powered rock drill. It can drill holes of dia. 65 mm to 127 mm and can therefore be used as a well hole drill for 127 mm dia. holes for depth upto about 12 m. The hole is flushed with compressed air at 10 kgf/cm2.

The rate of penetration in hard rock is generally 1 m/min using 90 mm dia bit. The rock drill 1038 HB is equipped with a hydraulic system incorporates indicators rock condition. The hydraulic system incorporates indicators which point out any fault or malfunction in the system. The boom system is operated by hydraulic pressure.

This is usually a crawler mounted drill operated by a diesel engine or by an electric motor which is supplied power from an external source through a trailing cable. It drills holes of 125 mm to 300 mm diameter, depth varying from 6 m to 18 m. It has a long mast, 3 m to 6 m, to accommodate the length of the drill rod.

The mast is collapsible and the drill should not be moved over an appreciable distance with the mast raised. The drills are of percussive as well as rotary type but the latter is common in coalmining areas. The drilling tool of rotary drill is a tricone bit on most of the drills but on the machines which are known as down-the-hole percussive drills (sometimes called down-the-hole hammer drill), the drilling tool is a cross bit (carset bit), or a button bit. In down-the-hole hammer drill the assembly of the drill and its short length pipe is called down-the-hole hammer.

In the rotary drill the string is rotated by the prime mover through suitable gearing. The tricone bit attached at the end of the drill string is thus rotated and it is kept pressed against the rock by hydraulic or pneumatic pressure.

In down-the-hole percussive drill the rotation of the hollow drill rods is provided by a rotary placed at the top of the drill string and driven by a built-in air motor. The air motor is also used to tighten and loosen threaded joints on rods and bits. The up or down travel of the drill rods is by a chain, operated by a reversible piston type air motor (Chain Feed).

A compressor mounted on a well hole drill helps to clean the hole as it is drilled. During drilling, the machine is leveled with the help of 3 hydraulic jacks. Normally twenty holes, each 9 m deep, can be drilled in one shift in sand stone, shale and coal.

Only vertically downward drilling is possible on most models though holes 20 off vertical can be drilled by a few machines. On some machines the drill-rods and the tools are at one end and on others, in the middle of the machine.

The latter arrangement is permissible where the burden of blast hole is large and the ground at the quarry edge strong enough to support the weight of the machine; but where this is not practicable drills rigs with the drill rods and tool at one end have to be used.

A well hole drill appears like a wagon drill suitable for large diam. A rotary well hole drill can drill in a shift of 8 hours nearly 20 holes, 200 mm dia. each 9 m deep, in sandstone, coal, shale and similar rocks.

Where the overburden consists of soft rock which can be conveniently removed by ripper and scraper-dozer combination an alternative to ripper and scraper-dozer combination an alternative to ripper is the method of drilling nearly horizontal blast holes and blasting them. Vertical (or nearly-vertical) blast holes have to be drilled where the overburden consists of hard rock like sandstone, laterite, etc.

30 off vertical may be considered to be the limit for inclined drilling of nearly-vertical holes on a bench. Larger angle increases the length of the hole, difficulties in charging it with explosives of fixed shaped cartridges, proportion of stemmed section of the hole and gives face inclination unsuitable for travel of the shovel bucket.

The toe of a bench can be removed by extra drilling of short length horizontal holes only in the toe and blasting them, or by resort to inclined drilling of the main (nearly vertical) blast holes. In vertical as well as inclined blast holes for the face, it is always essential to extend the hole slightly beyond the level of bench floor to secure proper fragmentation of toe if the hole is terminating in hard rock.

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