Coal Face Mechanization

• Deployment of machines at the working place from

where mineral/ coal has to be extracted is known as
face mechanization.
• During the last 50 years, significant changes have
been made in the coal face mechanization by replacing
the coal cutting machines working on ill - organized
faces to more scientific working on carefully and
systemically planned faces with the result that coal can
be extracted continuously with the cutting loading
machine and the conveyor in the same track between
the coal face and the last row of supports ( prop free
front ), so that cutting and loading of coal proceed
without hindrance and the conveyor can be advanced
after or during each strip without being dismantled.
Coal Face Mechanization
• The ultimate aim of mechanized mining is complete
flexibility without adhering to rigid cycles and in its
fully developed stage, mechanization comprises
machine cutting and loading of coal, its transport by
AFC and self advancing supports on the face.
Coal cutting machines
• Coal cutting machines were being used in
underground coal mines to assist in breaking down
the coal so that it can be loaded out.
• A coal cutter cuts into a portion of the seam, making a
slot along the coal face, after which the remaining part
of the coal is cut down by the use of hand or
pneumatic picks or is broken down by explosives.
• The coal cutter is conventionally a machine which
prepares the coal face for shot firing by making an
under cut, over cut or middle cut in the coal face
thereby reducing the quantity of explosives required to
break the solid coal face by increasing the number of
free faces in underground coal mine.
Coal cutting machines

• The slot made by the cutting machine is known as

the 'cut' or 'kerf'. Normally the cut is 5" or 6" thick and
penetrates the seam to a depth of 4' 6" or 6', although
cuts are sometimes made as shallow as 2' and as
deep as 7'.
• If the cut is made at floor level, the seam is said to
be 'undercut'. If halfway up the seam it is called a
'middlecut', and if at the top of the seam, near the
roof, an 'overcut'. Machines designed for these three
cutting positions are shown in Figure 1.
Types of CCM

Coal
Cutting
Machine

Longwall Coal Shortwall Coal Arc Wall Coal

Arc Shearer
Cutter Cutter Cutter
Double Curved Jib
Coal Cutter
Mashroom Jib
Longwall Coal Cutting Machine:
Constructional Features
• A coal cutting machine is made up of three main parts
which are bolted together as shown in Figure .These
parts are:
1. The Driving Unit containing the motor.
2. The Haulage Unit which carries the operator's
controls.
3. The Gearhead, to which are attached the jib and
cutter chain, and (if one is in use) the gummer.
Longwall Coal Cutting Machine
The Driving Unit
• This is the central section of the machine. It consists
of a casing enclosing the motor which drives, through
a series of gears, the haulage and cutting units.
• The driving unit may contain either an electric motor
or a compressed air turbine.
• The power of the driving unit may be either 40, 50 or
60 h.p., according to the type of machine.
• The supply for electrically driven coal cutting
machines is normally alternating current and is
supplied to the machine at a voltage of 440, 500 or
600 volts.
• Compressed air is usually supplied at a pressure of
about 60 lb. per square inch.
• Electrically driven machines are fed by a flexible cable, called a
trailing cable, which is coupled at one end to the main supply in
the gate end box and at the other to the machine.
• The point where the trailing cable is connected to the main
supply is a gate end switch by which the current can be
switched on to or shut off from the trailing cable.
• At the machine itself there is a controller switch which is used by
the operator when working the machine. The power may be cut
off either in the switch compartment of the driving unit, or in the
gate end switch box.
• In the former 'Direct On' type, the controller switch handle on
the machine operates directly the main switch in the machine. In
the latter 'Remote Control' type the controller switch handle
operates the main contactor switch in the gate end box through
a pilot circuit.
• The electric motor consists of two sections, a
stator and a rotor. The stator is the fixed part
of the motor consisting of a series of wires
arranged in coils set around the rotor.
• The rotor is an iron core cylinder, at each end
of which project the driving shafts. When the
current is switched on, a magnetising field is
produced in the stator windings and
magnetism is induced in the iron core; this
causes the rotor to turn.
• With compressed air driven machines the air is fed along the
gate in steel pipes through a main control valve to 2" diameter
rubber hose, and so to the machine where the air is
controlled by another valve operated by a handle attached to
the haulage end of the machine.
• The compressed air turbine is shown in Figure 3. It consists
of two cylinders called rotors, on each of which are a number
of teeth which radiate diagonally from the centre point of the
rotor to the outside edge. These are called double helical
gears and those of each rotor are designed to mesh together.
• The air is conducted through a pipe underneath the turbine
and is fed to the helical gears at the point where they meet at
the centre of the rotors. The compressed air with its high
pressure forces the teeth of both rotors apart, causing the
rotors to revolve. This movement continues as each
succeeding pair of teeth come under the influence of the
compressed air.
Haulage Unit
• Longwall coal cutters are constructed with a system
of gears designed to provide two types of haulage,
namely a variable slow speed for cutting and a higher
speed for flitting.
• The cutting haulage is intermittent in action which
gives speed in the range of 6 to 96 in/ min.
• The flitting haulage is continuous in action and
provides speed range of 20 to 72 ft/min.
• The cutting chain speed ranges from 120-170 m/
min(1.8 -2.0 m/s).
The Haulage Unit
• A flexible steel rope either ½" or 5/8" in diameter and
about 30 m long is used to pull the machine along the
face.
• At one end of the rope there is an eye or loop for
attaching to an anchor prop. The other end of the
rope is wound round and clamped to a drum attached
to the haulage unit.
• As shown in Figure 4A there may be only one drum
placed horizontally almost at floor level at the centre
of the haulage unit, or as shown in Figure 4B there
may be two vertical drums, one at each side of the
unit.
• The gearing through which the motor drives the haulage drum is
contained in the unit above the horizontal drum, or between the two
vertical drums. The haulage unit also carries the controls which the
operator uses to work the machine. These are shown in Figure 5
lettered A to E as follows :—
• (A) The starting switch handle or air control valve. (On electric
machines this switch or controller is also used to reverse the
direction of the motor.) (B) The handle for reversing the haulage
drum on compressed air machines. (C) The clutch handle
(sometimes called the gear lever) for engaging high and low speed
gears to the haulage drum. (D) The speed control handle for varying
the speed when the haulage drum is in low gear. (E) The quick
release lever for the rope or friction clutch.
• The handle for putting the cutting chain into gear is in some
machines placed with the other controls on the haulage unit. In other
machines it is situated at the side of the gearhead as shown at F in
Figure 5. With compressed air machines in which the motor is not
reversible the direction of the cutter chain is also reversed by this
handle.
The Gearhead
• The gearhead contains the mechanism by which the
cutting chain is driven round.

• A bevelled pinion from the shaft of the motor drives

the chain sprocket through a large diameter
horizontal bevelled gear, called a 'crown wheel', and
a sprocket shaft.

• Supported in the gearhead below the crown wheel is

a ring or turntable which carries the jib. This is free
to turn, thus enabling the jib to be slewed from one
position to another.
• Fastened to the turntable is a bracket into which
the support bar of the jib is fitted.
• The turntable may be locked by a jib locking pin,
which in some machines is a bolt fitted into the
framework of the gearhead.
• The gummer is also driven from the crown wheel
and used to clean the cuttings.
•
Cutting Unit
• The cutting mechanism of a coal cutter is generally
by a continuous revolving cutting chain rotating
around a jib in its chain race.
• The cutting chain is rotated by the sprocket driven by
the reducing gear from the motor.
• During cutting the jib moves with the coal cutter in a
direction perpendicular to the cutting chain, pulled
simultaneously by the haulage unit. Because of these
movements the pick penetrate in to the coal seam.
• The cutting chain of the jib consists of pick boxes
each with either one or two picks.
Jib
• This is essentially a very strong and rigid blade which
provides a guide race for the cutting chain and a
means by which the cutting chain is kept fully up to
the work of cutting in to the solid coal, a process
which is a combination of shearing, abrading and
impact actions.
• The Jib can be straight, shaped or bent up type.
• The jib head is a steel casting forming the root of the
jib and providing the means for swinging the jib about
an axis which is that of the sprocket shaft.
Jib
• Rigidity is given to the jib by a strong heat treated
support bar, secured to the tongue of the jibhead by
means of an underside clamping plate and a number
of heavy studs.
• The tongue is provided with a channel socket to
receive and secure the support bar. The jib itself fits
over the support bar and consists of an upper and
lower steel plate between which the chain guide is
rivetted.
• The Chain guide is a continuous channel section of
hardened steel.
Jib and Jib Support Bar
Jib Head and Clamping Plate
Cutting Chain and Picks
• The cutting chain of the Jib consists of pick boxes
each with either one or two picks. The pick boxes are
connected by links and by pins through them.
• The pick boxes contain pockets in to which the
cutting picks are set by set screws.
• A pick of a cutter chain consists of the shank by
which it is clamped in to the pick box and the point or
working end which is usually wedge shaped.
• The hinges between the pick boxes allow the chain to
sag slightly as well as to curve around the drive
sprocket in the chain race at the outer end of the jib.
• The pockets of the pick boxes are set at various
angles to the horizontal plane of the jib and the picks
are set to cut a slot in the coal which is little wider
than the thickness of the jib.
• The depth of cut is 200 mm shorter than the length of
the jib and the thickness of cut is 120-140 mm.
• Because the picks are set at different inclinations,
their layout projected on a vertical plane is fan
shaped. The number of cutting lines usually vary from
7 to 9 depending on the strength and hardness of
coal seam to be cut.
• Soft to medium hard coal seam- 7 line cutter chain
• Hard coal seam- 9 line cutter chain
• Round the outside end of the jib is a channel or race which
provides the track for the chain. It is made up of strips of
special wear-resisting steel.
• The cutter chain shown in Figure 9 is one of the various
types of chains which are used. They consist of a series of
pick boxes joined together in various ways.
• One end of the chain is threaded round the race on the jib,
passed round the driving sprocket, and the two ends of the
chain are then riveted together. The cutter picks are held in
the pick boxes by a set screw. The pick boxes along the
chain are set at different angles so that the picks are
fanned out to cut on a series of lines. Some of the pick
boxes are arranged to take two picks, one pointing upwards
and the other downwards. These are called double boxes.
• As the machine cuts, the chain brings out pieces of
cut coal which it has chipped off. These are called
gummings. Unless these are cleared as they are
brought out, either by hand shovelling or by some
mechanical device, they get carried back and may
choke the chain and so stall the machine. To save
hand shovelling, mechanical gummers are fitted to
undercutting machines. As mentioned previously, the
gummer is driven from the crown wheel.
Operating the Machine
• A cutting machine is usually transported on a
specially constructed trolley to the district in
which it is to work. It usually travels as one
complete unit, except for the jib and chain
which are attached when the machine has
been unloaded.
• The jib is bolted into position, the chain placed
round the sprocket and the ends riveted
together before the machine is drawn into the
face. It is again advisable to examine and run
the machine before the operator takes over.
The Operator's Preliminary
Examination
• 1. Check the trailing cables or air hoses for damage.
• 2. Couple the trailing cables or air hoses.
• 3. Turn on the compressed air in the gate or, with electric
machines, place the isolator switch at the gate end switch box in
the 'ON' position.
• 4. See that the chain is free from obstruction.
• 5. Operate the switch handle at the machine and switch on the
power momentarily to make sure that power is being supplied to
the machine.
• 6. Oil the machine.
• 7. Examine the chain for correct tension. Where necessary
tighten the chain
• 8. Place a sharp pick in every box of the chain so that the point
of each pick faces the direction in which the chain is to travel
when cutting.
• 9. Run out the haulage rope by hand or by using power.
Jibbing In
• 1. Set two stay props at the side of the machine away
from the face to keep the gearhead close to the face
whilst the operation of jibbing in is carried out. Place
a short sprag between the face and the haulage end
to keep the control handles free and also to enable
the rope to be removed after jibbing in.
• 2. Pass the haulage rope round the machine on the
face side as shown in Figure. Attach the loop of the
rope to the bracket on the turntable.
• 3. See that the jib locking pin is disengaged or
removed.
• 4. Make sure all persons are well clear of the jib.
• 5. Place the haulage clutch handle 'C' in the cutting
position; ensure that, in the case of a machine
operated by compressed air, handle 'B' is set to
draw the rope on to the drum. Switch on the power
and engage the friction clutch handle 'E'.
• 6. Operating the handle 'D', tighten the rope.
• 7. Draw the jib round until the picks are almost
touching the coal face.
• 8. Switch off the power, and, just as the motor is
stopping, engage the chain clutch 'F'.
• 9. See that the chain is free to rotate.
• 10. Switch on the power.
• 11. Jib in slowly and stop the feed, using handle 'D', as
soon as the machine shows signs of labouring.
• 12. When the jib has cut well into the coal, shovel away the
gummings to prevent the chain becoming choked up. Stop
the machine whilst this work is carried out.
• 13. As the jib reaches the cutting position, drop the jib pin
into its hole and lock the jib in position.
• 14. Allow the cutting chain to continue to spin round a few
times so that it keeps itself free; release clutch 'E' then
switch off the power.
• 15. Release the haulage rope by placing the haulage clutch
handle 'C' in the neutral position. Remove the slewing chain.
• 16. Clean the gummings from the cut.
Cutting
• 1. Prepare the cutting track when the machine is
running on the floor. Clear away loose coal, debris or
other material from the path of the machine.
• 2. Draw off the haulage rope and pass the rope round
the face side pulley as shown in Figure.
• 3. Set up an anchor prop at a distance from the
machine almost equal to the length of the haulage
rope, leaving one or two laps of the rope on the drum.
4. Make a notch hole in the roof with a pick, and
insert the top of the anchor prop into the hole. Place
the loop of the haulage rope in the hook attached to
the anchor prop.
• 4. Take up any slack rope and gradually tighten the rope,
using the slow speed to test the anchor prop to see that it is
secure.

• 5. Switch off the power, and as the sound of the motor dies
away, engage the chain by means of handle 'F'.
• 6. Switch on the power and allow the chain to pick up speed.
• 7. Engage the friction clutch handle 'E'.
• 8. By operating handle 'D' control the rate of advance of the
machine.
• 9. An assistant to the machineman should remove debris
from the cut, using the long handled shovel.
• 10. On reaching the anchor prop disengage the friction clutch
handle 'E' and then clutch handle 'C' and turn off the power.
• 11. Remove and reset the anchor prop farther along the
face, draw out the haulage rope and attach it to the prop.
• 12. Repeat the sequence of operations until the end of the
face is reached.
Jibbing Out
• Remove the anchor prop and draw off a length of haulage rope.
Reset the anchor prop in the required position for the next move
and attach the loop of the haulage rope.
• Place the stay or sprag near the centre of the machine toward the
haulage end. This will act as a pivot.
• Switch on the power and draw the machine into the required
position.
• Reset anchor prop in new position and repeat.
• Disengage the jib pin when the machine is almost at right angles
to the face.
• Reset the anchor prop. By controlling handle 'D' draw the
machine towards the anchor prop until the jib is drawn out of the
cut (Figure 20). Disengage the chain clutch so that the cutting
chain no longer revolves.
• Reset any supports that have been removed.
• Remove all the picks from the chain. Examine the chain for wear
and any damaged links.
Flitting
• A machine can be 'flitted', i.e. moved from one position to
another when not cutting, with the jib either trailing or in front.
The procedure when the jib is trailing is similar to that when
cutting except that the haulage clutch handle 'C' is in the high
speed position. To keep the machine straight the rope is
threaded round a pulley which is attached to the centre of the
haulage end.
• When flitting with the jib in front the haulage rope is passed
round the pulley at the haulage end and round a bracket and
pulley attachment fitted to the jib (Figure). The chain clutch
handle 'F' is disengaged and the haulage clutch handle 'C'
placed in the high speed position.
• The machine can be kept in its path when it is being moved by
setting sprags to the side of the machine. In seams where the
floor is soft a special iron shoe (Figure) may be fitted to the tip of
the jib to prevent its digging into the floor.
Short Wall Coal Cutter
• On Longwall faces, the operation of flitting the machine,
sumping in, cutting along the face and finally jibbing out
are more or less distinct and where conventional cycle is
being followed, it must be completed in a scheduled
time.
• A considerable proportions of the scheduled time is
taken up in running out the rope and selecting suitable
anchor prop positions.
• On shortwall or wide heading faces, the cutting
requirements are rather different.
• On shortwall faces, the face can usually be cut from
single position of anchor prop and the machine may
have to be immediately withdrawn from the face in order
to allow the remaining operations to proceed unimpeded.
• For these reasons, the design of the shortwall coal
cutter is somewhat different from that of the longwall
coal cutter although the basic mechanical features are
common to both.
• A characteristic of the shortwall cutter is that the jib
remains locked in a position in line with the body of the
machine and also the length of the jib is usually shorter
than the longwall type.
• Since the jib is in line with the body of the machine,
shortwall cutter cuts with the body at right angles to the
face.
• It has three basic units:
Haulage unit, Driving and Power Unit and Cutting unit
Which are mounted a few inches above a short base
plate. The haulage is provided with a twin rope drums
mounted on horizontal axes, one on each side of the
machine. There are independent controls on each
drum and the auxiliary pulleys and brackets on the
haulage unit and gear head allow the operator to carry
out all the necessary controls by suitably threading
and anchoring the two haulage ropes.
Shortwall Coal Cutter
Shortwall
Machine
cutting
across a
heading
Arcwall Coal Cutter
• Arcwall coal cutters are characterized by a
fixed gearhead and additional gearing for the
mechanical swinging of the jib through a wide
arc.
• They are commonly rail mounted, the drive
unit providing necessary power for propelling
the machine forward.
• Swinging of the jib through an arcing shaft.
• For operation in heading, the machine is
propelled till its jib head is against the face,
then with adjustable stelling props, the
machine is held anchored in the center of the
gallery.
• The jib then starts cutting a circular path
about the jibhead.
• The machine jib length may be up to 3 m.
Arc Shearer
• The arcwall machine can cut only in one plane and
that is horizontal unless the machine itself is tilted to
another plane. Cutting in a more or less vertical plane
is called shearing. Shearing reduces the explosive
consumption and gives better percentages of round
coal.
• The arc shearer is provided with means for rotating
the gear head as a whole about an axis in line with
the machine body. Thus it is able to cut at any angle
and in any plane from the horizontal to vertical.
Arc Shearer