1. BASICS OF DRILLING-1
I. Satyanarayana,
M.Tech,MBA,MCA
Dy. Manager, Project Planning, SCCL,
isnindian@gmail.com,
visit at
www.slideshare.net/isnindian
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2. Mine operation
Drilling
Blasting
Overburden Removal
Loading
Haulage
Reclamation
Water and Air Management
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3. DRILLING
In virtually all forms of mining, rock is broken
through drilling and blasting.
Except in dimension stone quarrying, drilling and
blasting are required in most surface mining.
Only the weakest rock, if loosely consolidated or
weathered, can be broken without explosives, using
mechanical excavators (ripper, wheel excavators,
shovels etc.) or occasionally a more novel device,
such as a hydraulic jet.
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4. In the mining cycle, drilling performed for the
placement of explosives is termed production
drilling.
Drilling is also used in surface mining for purposes
other than providing blast-holes.
There are minor applications of rock penetration in
surface mining other than drilling.
In quarrying, dimension stone is freed by cutting,
channeling, or sawing.
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5. 2. Classification of methods
A classification of drilling methods can be made
on several bases.
These include size of hole, method of mounting
and type of power.
The scheme that seems the most logical to
employ is based on the form of rock attack or
mode of energy application leading to
penetration.
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6. (1) Mechanical attack
The application of mechanical energy to rock can
be performed basically in only one of two ways:
by percussive or rotary action.
Combining the two results in hybrid methods
termed roller-bit rotary and rotary-percussion
drilling.
The mechanical category, of course, encompasses
by far the majority (probably 98%) of rock
penetration applications today. In surface mining,
roller-bit rotaries and large percussion drills are the
machines in widest current use, with rotaries
heavily favored.
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7. (1) Mechanical attack
Generally speaking, percussion drilling with top hammers is appropriate for drilling
small holes in hard rock, DTHs for large holes in hard rock, and rotary drilling for
large holes in soft to medium hard rock.
When drilling in rock, the sharp end of the drilling tool, or bit, is driven into the rock by
means of a dynamic (percussion, in which the bit rotates slightly in response to
each stroke) or static force (rotation).
The material excavated by the bit is stripped out of the hole by shearing as the bit
advances.
The bit generally has a knife-edge made of steel alloy or an inserted carbide tip, or is
composed of multiple round, conical, ballistic, or parabolic button tips made of
hard alloy that are inserted into the leading face.
• In some cases, the rotary cutting method can be used without percussion in drilling
very soft rock such as coal or limestone that contains little silica. In the rotary
crushing method, a three-cone bit similar to that employed in oil well drilling is
used. The bit is constructed of three cones covered in variously shaped teeth or
buttons that rotate freely like planetary gears and crush the rock as the drilling rig
rotates the bit.
• Teeth made of steel alloy are used at shallow levels in soft rock, and carbide
buttons are used for hard rock.
• Air is blown through the drill-rod to remove cuttings and to cool the rotation
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bearings and the bit.

8. (1) Mechanical attack
It is important to note that rotary drills are capable of two methods of drilling.
The majority of the units operate as pure rotary drills, driving tricone or fixed-type bits.
The fixed-type bits, such as claw or drag bits, have no moving parts and cut
through rock by shearing it. Thus, these bits are limited to the softest material.
The other method utilized by rotary drill rigs is down-the hole (DTH) drilling. High-
pressure air compressors are used to provide compressed air through the drill
string to drive the DTH hammer.
The primary difference between rotary drilling and other methods is the absence of
percussion. In most rotary applications, the preferred bit is the tricone bit. Tricone
bits rely on crushing and spalling the rock. This is accomplished through
transferring downforce, known as pulldown, to the bit while rotating in order to
drive the carbides into the rock as the three cones rotate around their respective
axis.
Rotation is provided by a hydraulic or electric motor-driven gearbox (called a rotary
head) that moves up and down the tower derrick or mast) via a feed system. Feed
systems utilize cables, chains or rack-and pinion mechanisms driven by hydraulic
cylinders, hydraulic motors or electric motors. The preference is to use cables for
pulldown, as they are light weight and inexpensive, and allow easier detection of
wear to help avoid catastrophic failures.
Pulldown is the force generated by the feed system. The actual weight on bit, or bit
load, is the pulldown plus any dead weight such as the rotary head, drill rods and
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9. Schematic drawings of three types of drill
A) top hammer, B) DTH, C) simple rotary drill
a) tip, b) bit, c) rod, d) sleeve, e) drill pipe, f) piston, g) cylinder, h) percussion
mechanism, i) rotation mechanism, j) flushing
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10. Down-The-Hole method Rotary drilling method
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11. (1) Drill Adaptability
The type of rock drill used in mining drilling is generally determined by the hole
diameter required and the mechanical properties, principally hardness, of the rock.
A top hammer is commonly employed for drilling of holes less than 125 mm in
diameter in all but the hardest rock, although a rotary cutting method may instead
be used for soft rock.
For hole diameters greater than 125 mm, rotary crushing with a three-cone bit is used
in rock weaker than an upper limit that depends on the diameter of the hole, and
DTH drilling is used for harder rocks. If rotary drilling is feasible, drilling
performance will generally be higher than obtainable with DTHs.
In practice, small-diameter drilling is required in underground mining and tunneling,
medium-diameter drilling in quarries, and large-diameter drilling in large-scale
open pit mining.
• For large-scale open pit mining, it is common to use rotary drilling rigs equipped
with three-cone bits or DTHs to drill blastholes. These tools are mechanically
compatible with each other, and make it possible to choose the most efficient
method according to the particular rock hardness.
• Most drilling functions are hydraulically driven. Powering these hydraulic systems,
along with the air compressor, is a diesel engine or electric motor.
• Most rotary drills are diesel powered for good mobility. Electric powered units
offer some advantages such as lower power cost (in most areas), no diesel
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emissions, no refueling requirement and less maintenance.

12. a) underground mining and tunneling, b) quarrying, c) strip mining
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13. Construction of Drilling Equipment
The essential components of a drilling system are
• the rock drill,
• feed equipment,
• drilling rods,
• bit,
• supports against the drilling reaction,
• power source, and
• cuttings disposal equipment.
a) rock drill, b) feed equipment, c) drilling rod, d) bit, e) support,
f) operating media, g) cuttings discharge system, h) carrier, i)
accessories
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14. Thrust and Feed Equipment
All drilling methods require a feeding system that pushes the drilling tool against the
rock, maintains the advance of the bit as drilling progresses, and withdraws the tools
once drilling is complete.
A heavy weight or a pneumatic (pusher-) leg is used with hand-held rock drills.
For larger mechanized rock drills, whether pneumatic or hydraulic, the feed
equipment is designed so that the drill sits on a carriage that travels along a feeder
called the guide shell.
An alternative system used with light pneumatic drills comprises a screw that is
inserted into a nut built into the drill body itself and rotated by a feed motor that
drives the drill bit (screw feed).
Most feed systems, however, are either chain or rope feeds.
The chain feed incorporates a chain running along the guide shell that is driven by a
pneumatic or hydraulic motor via a rotating sprocket.
In a rope feed, the expansion and contraction of a hydraulic cylinder is transmitted
to the drill via a rope passing through a sheave connected to the feed cylinder body.
In hydraulically driven drilling systems, a hose reel is usually attached to the feed
equipment.
An anti-jamming feed control for controlling the thrust is indispensable in hydraulic
drilling systems, in order to avoid uncontrolled jamming of the bit.
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15. Rotation System
For percussion rock drills, a mechanism is necessary to rotate the bit between blows
and monitor the torque on the bit to avoid jamming.
Hydraulic or pneumatic rotation motors are most frequently used to rotate the rod,
Drilling Rod
The role of this element is the transmission of percussion or rotation power to the bit
and the removal of cuttings from the bottom of the hole.
Consequently, the drilling rod must be hollow in order to transmit fluid carrying the
cuttings. When drilling long holes, it is usually necessary to connect a series of
drilling rods together via threads; these threads need to be easily unscrewed to
detach the drilling rods, but firmly secured during drilling operation.
Rods have male threads on either end and are connected to each other by means of
coupling sleeves, which are short pipes tapped with female threads. Long holes are
drilled by connecting a series of these rods together.
Drilling rod coupling sleeve
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16. Cuttings Removal (Flushing)
Compressed air is generally used in surface mining to discharge cuttings from the
bottom of the hole, because of its efficiency in long downward-sloping holes and
versatility.
Care must be taken to ensure that the annular gap between the rod and the hole wall
is neither too narrow nor too wide: if the gap is too narrow, it will become clogged
with coarse cuttings, whereas if it is too wide the air velocity will be too low to carry
the cuttings. In the latter case, the cuttings will be reground at the bottom of the hole,
wasting drilling energy.
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17. (2) Thermal attack
The only thermal method having practical application today
is flame attack with the jet pierce.
It penetrates the rock by spalling，an action associated
with hard rocks of high free-silica content.
Because of its ready capability of forming various shapes of
openings, oxygen or air jet burners are used not only to
produce blast holes but to chamber them as well and to cut
dimension stone.
Jet piercing of blast holes, however, has decreased in
popularity in recent years as mechanical drills have
improved in versatility and penetrability.
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18. (3) Fluid attack
While disintegration of rock by fluid injection is an
attractive concept, the end result is more likely
fragmentation than penetration.
To produce a directed hole with pressurized fluid
from an external source, jet action or erosion
appears to be more feasible, but commercial
application to date is limited.
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19. Hydraulic monitors have been used for over a
century to mine placer deposits and to strip
frozen overburden, and more recently, high-
pressure hydraulic jets have been applied
successfully to the mining of coal, and other
consolidated materials of relatively low strength.
Hydraulic and mechanical attack mechanisms
assist and complement one another. For large
holes, the hydraulic jet alone may be competitive
with drilling.
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20. (4)Sonic attack
Sometimes referred to as vibratory drilling, this
method as presently conceived is a form of ultra-
high-frequency percussion.
Attractive but not presently commercial, actuation
of sonic devices by hydraulic, electric, or pneumatic
means is possible.
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21. (5) Chemical attack
Chemical reaction, because of the time element, may
be more attractive as an accessory rather than a
primary means of penetration.
The use of explosives is a distinct possibility, however,
and several alternative systems are under investigation.
Additives to the drilling fluid, termed softeners, have
shown some improvement in penetration rate in
conventional drilling.
(6) Other methods of attack
While some attempts to employ other forms of energy
(electrical, light, or nuclear) have been made in
experimental or hypothetical category at present.
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22. 3.1.2 Drilling application
1. Percussion drills
Percussion drills generally plays a minor role as
compared with rotary machines in surface mining
operations.
Their application is limited to production drilling for
small mines, secondary drilling, development work
and controlled blasting
There are two main types of drill mounting. The
smaller machines utilize drifter-type drills placed on
self-propelled mountings designed to tow the
required air compressor. Typical hole sizes are in
the 63 to 150mm range
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23. The larger machines are crawler-mounted and self-contained
Drill towers permit single pass drilling from 7.6 to 15.2 m with hole
sizes in the range of 120 to 229mm in diameter.
These larger machines are almost exclusively operated using down-
the-hole hammers
Percussive drilling breaks the rock by hammering impacts transferred
from the rock drill to the drill bit at the hole bottom. The energy
required to break the rock is generated by a pneumatic or hydraulic
rock drill. A pressure is built up, which, when released, drives the
piston forwards. The piston strikes on the shank adapter, and the
kinetic energy of the piston is converted into a stress wave travelling
through the drill string to the hole bottom. In order to obtain the
best drilling economy, the entire system, rock drill to drill steel to
rock, must harmonise.
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24. For many years, these machines were exclusively operated
using pneumatic hammers. ( pneumatic leg drill ）
Recently hydraulic machines have been used in the smaller
size range.
The higher capital cost of these hydraulic drills is offset by
lower operating costs and increased productivity compared
with pneumatic machines.
Another aspect that is becoming increasingly more important
is the reduced noise produced by the hydraulic drills.
With percussion drilling, the bit is driven into the rock by either
a top hammer, in which case the drill rods transmit the
impact of a blow at the surface, or a “down the hole drill” in
which the hammer itself is in the hole and impacts the bit
directly.
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25. (1) Percussion drill productivity
It will be observed that penetration rate decreases with both
increasing hole size and increasing rock strength.
As the piston area and stroke length are fairly inflexible for a
given hole size, one main thrust to help improve percussion
drill productivity has been to improve the drill penetration
rate by increasing the hammer operating pressure.
A typical increase in penetration rate experienced when
changing from 0.7Mpa to 1.7Mpa would be of the order of
200% with an approximate doubling in the actual hole
production rate.
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26. Some attempts have also been made to improve drill
penetration rate using high frequency blow. However it has
been found difficult, especially at the higher air pressures.
The other option is to use hydraulic machines to improve
the energy available at the drill bit. The penetration rate
for the hydraulic drill is shown to be from 20 to 100%
higher than the pneumatic machines.
• Recently, many percussion rock drills have been converted
from pneumatic operation to hydraulic operation, because
of associated gains in efficiency and performance.
• The rig weight of percussion rock drills can be made quite
light because of the small thrust required, whereas the rig
weight of rotary drills strongly influences their ultimate
drilling performance. ISN

27. (1) Percussion drill costs
the costs are dependent on both the blast-hole size
and the strength of the rock.
The high cost for hammer drilling is partly a result of
lower penetration rates obtained as compared with
rotary machines. The penetration rate of rotary
machines is about 15m/hr, while the rate of
hammer drilling is about 10m/hr.
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28. While an increase in operating air pressure has
greatly improved blast-hole penetration rates, the
drilling cost improvements have been less
impressive because of higher maintenance costs,
lower machine availabilities, etc.
The results is that high pressure 178mm hammer
drilling cost is approximately 100% higher than
250mm rotary drill per unit volume of material
blasted.
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29. A comparison between pneumatic and hydraulic
surface mounted drill costs follows:
Pneumatic hydraulic
Investment cost 1.0 1.27
Energy cost 1.0 0.24
Drill steel cost 1.0 0.86
Overall operating cost 1.0 0.78
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30. 2. Jet-piercing drills
The jet-piercing process relies upon a characteristic
of rock known as spallability.
The rock is broken down, or spalled, as a result of
differential expansion of the rock crystals by
thermally induced stresses.
The jet-piercing drill essentially consists of a burner
fixed to a blowpipe that produces a high
temperature flame (of the order of 43000F) by
burning fuel oil in oxygen.
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31. The drills have a typical drilling depth capacity of
15.2m.
In addition to fuel oil and oxygen, water is also used
to cool the burner and, in the form of steam, it
helps eject the spalled rock cuttings from the
blasthole.
Hole diameters range from a minimum of
approximately 229 mm up to 457 mm.
At present very few jet-piercer drills are in
operation. One of the main problems with the
system has been the high cost of oxygen and fuel oil
which has helped to make the drill uneconomic.
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