Rock Drilling in Open-Pit Mines

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24 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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Rock Drilling in Open
-
Pit Mines

Use of drilling for various purposes.

OPERATING COMPONENTS OF THE DRILLING SYSTEM


1.
The
drill
:
it acts as prime mover converting the original form of energy that
could

be
fluid, pneumatic or electric into the mechanical energy to actuate the
system
.


2.
The rod (or drill steel, stem or pipe)
:
it transmits the energy from prime
mover
to

the
bit or applicator.


3
.
The bit
:
it is the applicator of energy attacking the rock mechanically to
achieve

penetration
.



4
.
The circulation fluid
:
it cleans the hole, cools the bit, and at times stabilizes
the

hole
. It supports the penetration through removal of cuttings. Air, water
or

mud
.

There are four main functional components of a drilling
system
:


components of a drilling system



Using

the

drills

the

rock

is

attacked

mechanically

either

by

percussive

or

rotary

actions
.

Combinations

(roller

bit,

rotary
-
percussion)

of

these

two

methods

are

also

used
.




The

resulting

action

of

the

bit

in

each

case

is

almost

similar

i
.
e
.
crushing

and

chipping
;

what

differs

mainly

is

that

the

crushing

action

predominates

in

percussion

drilling

and

chipping

action

in

the

rotary

drilling,

and

a

hybrid

action

in

the

combination

of

the

two

systems
.



Based

on

this

logic

the

drills

are

manufactured

as

percussive
,

rotary
-
percussive

and

rotary
.


MECHANICS OF ROCK PENETRATION


Mechan
i
cs

of rock
penetrat
i
on


Rock drills classification based on application of mechanical energy to rock.



In

this

system
,

the

top
-
hammer’s

piston

hits

the

shank

adapter

and

creates

a

shock

wave
,

which

is

transmitted

through

the

drill

string

to

the

bit

.




The

energy

is

discharged

against

the

bottom

of

the

hole

and

the

surface

of

the

rock

is

crushed

into

drill

cuttings
.

These

cuttings

are

in

turn

transported

up

the

hole

by

means

of

flushing

air

that

is

supplied

through

the

flushing

hole

in

the

drill

string
.




The

feed

force

keeps

the

drill

constantly

in

contact

with

the

rock

surface

in

order

to

utilize

the

impact

power

to

the

maximum
.



In

good

drilling

conditions

use

of

these

drills,

is

an

obvious

choice

due

to

low

energy

consumption

and

investments

on

drill
-
strings
.




In

surface

mines

and

civil

construction

sites
,

76

127

mm

(
3

5
)

hole

diameters

is

the

usual

range
.

TOP
-
HAMMER DRILLING


In

this

system
,

the

down
-
the
-
hole

hammer

and

its

impact

mechanism

operate

down

the

hole
.

The

piston

strikes

directly

on

the

bit,

and

no

energy

is

lost

through

joints

in

the

drill

string
.




The

drill

tubes

(rods,

steels)

convey

compressed

air

to

the

impact

mechanism

and

transmit

rotation

torque

and

feed

force
.

The

exhaust

air

blows

the

holes

and

cleans

it

and

carries

the

cuttings

up

the

hole



DTH

drills

differ

from

the

conventional

drills

by

virtue

of

placement

of

the

drill

in

the

drill

string
.

The

DTH

drill

follows

immediately

behind

the

bit

into

the

hole,

rather

than

remaining

on

the

feed

as

with

the

ordinary

drifters

and

jackhammers
.



DOWN
-
THE
-
HOLE (DTH) DRILLING


N
o

energy

is

dissipated

through

the

steel

or

couplings,

and

the

penetration

rate

is

nearly

constant,

regardless

the

depth

of

the

hole
.

Since

the

drill

must

operate

on

compressed

air

and

tolerates

only

small

amounts

of

water,

cuttings

are

flushed

either

by

air

with

water
-
mist

injection,

or

by

standard

mine

air

with

a

dust

collector
.



This

is

very

simple

method

for

the

operators

for

deep

and

straight

hole

drilling
.

In

surface

mines

76

216

mm

(
3
.
4

6
.
5
)

hole

diameters

is

the

usual

range
.


Rotary

crushing

is

a

drilling

method,

which

was

originally

used

for

drilling

oil

wells,

but

it

is

now

days

also

employed

for

the

blast

hole

drilling

in

large

open

pits

and

hard

species

of

rocks
.




In

rotary

drilling

energy

is

transmitted

via

drill

rod,

which

rotates

at

the

same

time

as

the

drill

bit

is

forced

down

by

high

feed

force
.

All

rotary

drilling

requires

high

feed

pressure

and

slow

rotation
.

The

relationship

between

these

two

parameters

varies

with

the

type

of

rock
.




In

soft

formations

low

pressure

and

higher

rotation

rate

and

vice

versa,

are

the

logics

usually

followed
.

In

general,

if

the

rock

hardness

is

less

than

4
.
0

on

Moh’s

scale
,

the

rotary

drilling

has

established

its

advantages
,

except

when

the

rock

is

abrasive
.




The

rotary

drills

can

be

operated

using

either

compressed

air

or

electrical

power
.

ROTARY DRILLING



When

drilling

is

done

by

rotary

crushing

method,

the

energy

is

transmitted

to

the

drill

via

a

pipe

which

is

rotated,

and

presses

the

bit

against

the

rock

.

The

cemented

carbide

buttons

press

the

rock

and

break

off

the

chips,

in

principle

in

the

same

manner,

as

percussive

drilling
.



When

drilling

is

done

by

rotary

cutting

method

the

energy

is

transmitted

to

the

insert

via

a

drill

tube,

which

is

rotated

and

presses

the

inserts

against

the

rock
.

The

edge

of

insert

then

generates

a

pressure

on

the

rock

and

cracks

off

the

chips

.




It

is

unbeatable

in

difficult

drilling

conditions,

as

it

gives

high

productivity

and

good

penetration

rates

in

such

conditions
.

In

surface

mines

and

civil

construction

sites

80

400

mm

(
3
.
5
-
6
.
5
)

hole

diameters

is

the

usual

range
.

MOTIVE POWER OF ROCK DRILLS

Rock
drills
classification based on their motive power
.

Comparison hydraulic and pneumatic
power


By

the

manner

in

which

the

drilling

tool

i
.
e
.

the

drill

acts

upon

the

hole

bottom

(
percussive,

rotary

or

percussive

rotary)


The

forces

and

the

rate

with

which

the

drilling

tools

act

upon

the

hole

bottom


Hole

diameter

and

its

depth


The

method

and

speed

with

which

the

drilling

cuttings

are

removed

from

the

hole
.

Drilling
efficiency


Drilling efficiency can be measured by taking into consideration

the following parameters:

Select
i
on of
dr
i
ll

Drill
selection for a particular application should be based on
the

technological
and
cost factors. It is considered that the lower cost is obtainable in
soft

and medium
rock
with rotary
drilling
,
and
in very hard rock with percussion drilling
.


Furukawa

(top
hammer
) Akdağlar
Quarry

/ İstanbul

Button

bit Akçansa
Quarry

/
Istanbul


Track

drill

(top
-
hammer
)

Akçansa

Quarry

/

Istanbul


Track

drill

(top
-
hammer
)

Murgul
Copper

Mine
Turkey

DTH
Drilling

Machine

Button

Bit 165 mm

Sandvik

dp900

Atlas
C
opco

rock

L

Rotary

drilling

machines

Sierrita

Mine
-

A
rizona
(
Hudaverdi
, 2007)

Main

reference
:



Ratan

Raj

Tatiya
,

2005
.

Surface

and

Underground

Excavations
:

Methods,

Techniques

and

Equipment
.

Taylor

&

Francis
.