9851 6549 01 complete_sdopm1.pdf

7/21/2019 9851 6549 01 Complete_SDOPM1.pdf

1/152

Surface Drillingin Open Pit Mining

First edition 2006www.surfacedrilling.com


2/152

Thinking young takes practice

Atlas Copco Construction &Mining Technique

www.atlascopco.com/cmt

www.rcb2.se

Working with Atlas Copco gives you access to more than a

century of rock drilling innovation. It ensures that you work

with a solutions provider who delivers the best-performingsystems, products, and people available today and tomorrow.

Our success in construction and mining is based on the com-

bination of young minds and long experience. Get your free

copy of Success Stories at www.atlascopco.com/rock

Committed to your superior productivity


3/152

DRILLING IN OPEN PIT MINING 1

Foreword 2 Foreword by Markku Terasvasara,

Vice President Marketing Surface DrillingEquipment at Atlas Copco Rock Drills AB

Talking Technically

3Open Pit Mining 7Principles of Rock Drilling 10 Principles of Rock Blasting 12Putting Rotary Drilling Into Perspective 15SmartRig Takes Control 17Correct Selection of

Tophammer Rock Drilling Tools 20COPROD Combines the Best of DTH

and Tophammer Drilling

25 Increased Productivity with DTH Drilling 28 Selecting the Right DTH Drilling Tools

34Economic Case for Routine Bit Grinding

38Ergonomics & Safety

41Rotary Club Expands With Thiessen

42 In Search of the Right Balance 45Protection by ROC Care

Case Studies

47A Viper for the Copper King

49Best Practice at Bingham Canyon

51Rotary and DTH Work Side by Side 54The Golden Twins of Southern Mexico 58Minera Marias Pre-Split Pioneer

61ROC L8 Gains Favour in Brazil

65Hydraulic Tophammers Exceed Soquimich

Expectations 67Winning Iodine from the Atacama Desert

69 Replacing Rotary in Iron Ore 70

Multiple Tasking in Western Australia 73 ROC L8 Outperforms in Assmang Iron Ore 74Greater Geita

78DTH Choice Cuts Costs at Navachab 80 Iron Ore From Erzberg Mountain 82More Than a Match for Scotlands Coal

84Apatite for Extraction Coprod Solution for Siilinjrvi

Product Specifications

88Drilling Method Guide 90Tophammer Drill Rigs 97Tophammer Rock Drills 99 Tophammer Drilling Tools110COPROD System111COPROD Crawlers114COPROD Drill Rigs115COPROD Drilling Tools118DTH Drill Rigs124DTH Hammers126

Rotation Units127Rotary Drill Rigs131Secoroc Tricone Bits133SecorocGrinding138Drill Rig Options147Service Workshops148Conversion Table

Front cover:Blasting time at Aitik Copper Mine in Sweden.

SmartRig, COPROD, ROC and COP are Atlas Copco trademarks.

Atlas Copco reserves the right to alter its product specificationsat any time. For latest updates contact your local Atlas Copco

Customer Center or refer to www.surfacedrilling.com

Contents

Produced by tunnelbuilder ltd for Atlas Copco Rock Drills AB, SE-701 91 Orebro, Sweden, tel +46 19 670-7000, fax 7393.

Publisher Ulf [email protected] Editor Mike [email protected] Senior AdviserHans Fernberg

[email protected] Picture and Specifications EditorLisa Boyero [email protected]

ContributorsAlf Stenquist, Bo Persson, Brian Fox, Gran Nilsson, Gunnar Nord, Hans Fernberg, Jan Jnsson, Jean Lindroos,

Jessis Ng, Joanna Jester, Leif Larsson, Lennart Lundin, Lennart Sderstrm, Lorne Herron, Mathias Lewen, Therese Blomster,

all [email protected], Adriana Potts [email protected], Maurice Jones [email protected]

Designed and typeset by ahrt, rebro, Sweden.

Printed by Welins Tryckeri AB, rebro, Sweden.

2006 Atlas Copco Rock Drills AB

Copies of all Atlas Copco reference editions can be ordered in CD-ROM format

from the publisher, address above, or online at www.atlascopco.com/rock.

Reproduction of individual articles only by agreement with the publisher.


4/152

2 DRILLING IN OPEN PIT MINING

Foreword

T

o be perceived as the global market leader in providing rock drilling products, it is important that our product

and service offering has the competitive edge: that we can assist our customers to generate high profit leading to

business expansion. Our growth is a consequence of our customers success.We have also grown by making strategic acquisitions such as the drill rig division from Ingersoll Rand, and by launching new,

efficient products and aftermarket programmes during the past five years. Today, our range of drill rigs comprises more than 40

models suited for various surface drilling applications.

Our modern products are equipped not only with key components such as powerful rock drills, engines, pumps and compressors,

but also with the latest computer based technology.

We have never before been committed to such a dynamic and intensive product development, giving a whole new dimension

to quality and productivity in terms of directing and guiding the equipment to perform drill holes as close as possible to plan, to

planned depth and hole bottom locations. This is a prerequisite for optimum fragmentation of blasted rock, even benches and

rock wall contours.

High productivity, as a result of outstanding equipment availability and drilling capacity, leads to better utilization of the

investment. Our long-standing relationship with Secoroc has allowed us to develop drill string components, bits, and high pres-

sure DTH hammers to match the potential of our rock drills and rigs, together with bit grinding to maintain high performance

with economy. The second generation of Coprod for straighter small-diameter holes is a prime example of how successful this

partnership has been.

Our new computer based rigs are known as the SmartRig concept, emphasizing that they have incorporated state-of-the-art

functionality, making them easy to use and maintain. Additionally, we have spent a lot of effort in providing a good working

environment inside the operators cabin.

We trust that this book, presenting not only our current product offering, but also some examples of best practice at selected

operations, will stimulate technical interchange between people having an interest in surface drilling in open pit mining. Those

engaged in mining projects, technical consultancy, universities and our own sales and marketing efforts should, hopefully, find a

lot of valuable reading material.

Markku TerasvasaraVice President Marketing

Surface Drilling [email protected]


5/152

TALKING TECHNICALLY


Open Pit Mining

Finding the BestCombinationLarge quantities of raw material

are produced in various types of

surface operations. Where the pro-

duct is rock, the operations are

known as quarries. Where metallic

ore or non-metallic minerals are in-

volved, they are called open pit

mines. There are many common

parameters in design and choice

of equipment, and in the process

of finding the best combinationof drilling and blasting methods.

Atlas Copco has the advantage of

long experience in all types of sur-

face drilling operations, with a pro-

duct range to match. With its his-

tory of innovative engineering, the

company tends to think forward,

and is able to advise the user on

improving design elements of the

operation that will result in overall

cost savings.

Surface or UndergroundMining

Mining carried out underground can

follow and be tailor-made to suit the

mineralization zones on a selective

higher metal content basis, thereby mi-

nimizing the amount of waste rock,

which has to be extracted. The amount

of ore to be left behind varies depend-

ing on mining method between 10-35

percent. Waste to ore ratio is typically

1 to 4.As no orebodies have the perfect co-

nical shape, vast quantities of waste

have to be removed from both the hang-

ingwall and the footwall to get access

to the ore as it progresses in depth.

Waste to ore ratio varies extensi-

vely depending largely on the geomet-

ry of the orebody. Many open pit ope-

rations excavate more than 5 times the

amount of waste compared to ore. Figu-

re 1 shows a sectional layout of a typi-

cal pit. The waste to ore ratio increasesas the pit gets deeper. Eventually, for

economic reasons, the open pit will

be abandoned, or underground mining

will take over.

As the ore, compared with under-

ground mining, is more diluted and in-

termixed with waste and lower gradeore, crushing, screening, milling, flota-

tion etc need high capacity. As min-

ing progresses at depth large quanti-

ties of side rock have to be excavated

in stages, so called pushbacks. See fig.

2 Aitik.

Open Pit Mining

A typical work cycle in an open pit

mine consists of a number of work ele-

ments. Exploration drilling is conduct-

ed to define ore boundaries for futureplanning. This is commonly combined

with in-pit reverse circulation drill-

ing to confirm the mineral contents,

which is important for optimizing the

blasting and the mineral processing.

Drilling of blastholes is undertaken in

Figure 1 General principles of open pit mining.

Figure 2 Aitik open pit mine. Hangingwall extractions in stages..

orebody


6/152


7/152

TALKING TECHNICALLY


crushing/dressing system, are simple.

It should merely suit the loading and

trucking equipment used for subse-

quent removal to the waste dump. On

the other hand, good fragmentation of

the blasted ore will make great savings

in the total costs of the mineral dress-

ing process. By contrast to quarries,

where the fines fraction are regarded

as reject (especially at aggregates),

open pits delivering ore to the dressing

plant get savings in the disintegrationprocess in case high amount of fines

are present. Large holes generate a

higher spread of size distribution from

more boulders to higher amount of

fines-see fig. 4

Blasting will not only break the rock

that is planned to be excavated, but

will also cause damage to the slopes

that form the boundaries of the pit.

The extent of this overbreak is mainly

dependent on the size of the individual

charge and its proximity. A common

means of minimizing overbreak is to

use smaller diameter holes, making

provision for restricted blasting in the

zone next to the planned bench slope.

Figure 6 shows two different blast

designs.

Figure 5 shows a typical drilling pat-tern to be applied in connection with

pre-split blasting, to achieve increased

slope stability with reduced back break.

The huge Chuquicamata open pit (pro-

duction rate 650,000 tonnes per day)

in Chile being 8 km long and 2.5 km

wide and progressing towards a final

Figure 5 Drilling pattern for presplit in open pit mining.

Figure 6 Savings in

waste extraction by

increasing the pit

slope.

depth of 1,000 metres saves a stagger-

ing 150 million metres of rock excava-

tion by just making the pit slopes one

degree steeper. Consequently there are

large savings to be made if drilling and

blasting is carried out in an optimum

way.

Drilling Patterns and Typeof Drill Rigs

Traditionally, focusing on the drill-

ing cost parameter and productivity

only, the predominant method in open

pit mining is large hole rotary drill-

ing using hole sizes in the 250 to 400

mm (10-15.75 in) range. No doubt this

implies lower cost for drilling, ignor-

ing the expense of excess waste, more

explosives and less controllable frag-mentation. A survey of 36 open pit

operations in Chile using hole sizes

between 75 and 345 mm (3.0-13.75 in)

reveals that hole sizes above 200 mm

(8 in) do not generate any substan-

tial savings in total drilled metres per

tonne. This indicates that burden and

spacing cannot be increased indefinite-

ly. One important reason for replacing

rotary with other methods is the inflex-

ibility of the heavy rotary rigs, which

are restricted to vertical benches andsingle pass drilling only.

Figure 6 shows the advantages relat-

ed to using an Atlas Copco ROC L8

rig, having the ability to drill inclined

holes close to the bench wall, compa-

red to a traditional rotary rig. The best

combination of drill rigs might well


8/152

TALKING TECHNICALLY


Figure 8 Souffl blasting at Bjrkdal gold mine. Figure 9 Charging for souffl blasting.

prove to be large rotary rigs for waste

rock and high productivity in the pit

centre coupled with flexible DTH rigs

for selective mining, pre split of slopes

as well as for in-pit grade control drill-

ing. See fig 7 Aitik.

Souffl Blasting

Mining of rich, narrow and irregularly

stratified ore zones, such as gold mine-

ralizations, requires extra attention,in order not to introduce unnecessary

Figure 7 Drill pattern at

Aitik open pit, Sweden.

Production holes315 mm

8-9 m drillpattern15+2 hole depth

2 rows140165 mm

quantities of waste into the ore stream.

Consequently, this type of mining has

to be progressed on a selective basis,

in close liaison with surveyors and

geologists, by taking frequent samples

before and after each individual blast.

Short benches and small holes are used

to cope with ore zone irregularities. A

recently-developed method to ensure

maximum recovery from each blast is

called souffl blasting. Figures 8 and

9 illustrate this principle of cautiousblasting with a minimum of dilution as

practised at the Bjrkdal gold mine in

Sweden. To a depth of merely 5 m, 100

vertical holes are blasted in one round,

without free surface for expansion.

The firing sequence starts in the centre

and, thanks to 2.5 m of stemming, the

blasted ore material just swells on site

like baking a souffl. Selective extrac-

tion by backhoe loaders facilitates

maximum recovery of the rich, narrow

gold-bearing zones.

by Hans Fernberg


9/152

TALKING TECHNICALLY


Rotary Drilling

Rotary drilling can be subdivided into

rotary cutting and rotary crushing.

Rotary cuttingcreates the hole by

shear forces, breaking the rocks ten-

sile strength. The drillbit is furnished

with cutter inserts of hard metal alloys,

and the energy for breaking rock is

provided by rotation torque in the drill-rod. This technique is limited to rock

with low tensile strength, such as salt,

silt, and soft limestone not containing

abrasive quartz minerals.

Rotary crushing breaks the rock

by high point load, accomplished by

a toothed drillbit, which is pushed

downwards with high force. The bit,

being of tricone roller type fitted with

tungsten carbide buttons, is simul-

taneously rotated, and drill cuttings

are removed from the hole bottom byblowing compressed air through the

bit.

Drillrigs used for rotary drilling are

large and heavy. The downwards thrust

is achieved by utilizing the weight of

the drillrig itself, and the rotation, via

a hydraulic or electric motor, applied

at the end of the drill pipe. Common

hole diameters range from 8 to 17.5

in (200-440 mm) and, because adding

the heavy drill pipes is cumbersome,

most blasthole drillrigs use long masts

and pipes to accommodate single-pass

drilling of maximum 20 m (65 ft).

Electric power is usually chosen for

the large rigs, whereas smaller rigs are

often powered by diesel engines.

Rotation rates vary from 50 to

120 rev/min, and the weight applied

to the bit varies from 0.5 t/in of bit

diameter in soft rock, to as much as

4 t/in of bit diameter in hard rock.

Recent technical advances include:

improved operator cab comfort;

automatic control and adjustmentof optimum feed force and rotation

speed to prevailing geology and bit

type and diameter; and incorporation

of the latest technology in electric and

hydraulic drive systems.

Rotary drilling, which is still the

dominant method in large open pits,

has limitations in that the rigs are not

suited to drilling holes off the vertical

line. As blasting theories and practice

have proved, it is generally beneficial

to design, drill and blast the benchslopes at an angle of approximately 18

degrees off vertical.

Many rotary rig masts have pin-

ning capabilities permitting drilling

at angles as much as 30 degrees out

of the vertical. However, the inclined

hole drilling capabilities in rotary

drilling are limited by the heavy feed

force required, since part of this force

is directed backwards. This causes rig

stability problems, reduced penetra-

tion, and shorter life of drilling con-

sumables. Consequently, most blast

hole drilling using rotary drillrigs is

for vertical holes.

Percussive Drilling

Percussive drilling breaks the rock by

hammering impacts transferred from

the rock drill to the drillbit 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. Figure 1

Principles of Rock Drilling

Drilling forExcavation byBlasting

This reference edition deals withsurface rock drilling used for thepurpose of excavating rock in qu-arries and construction projects bymeans of blasting. Other types ofdrilling, such as for oil and water,mineral exploration and exploita-tion, and grouting, are excluded.

The reader is given a brief ex-planation of prevailing drilling me-

thods, together with an introduc-tion to blasting techniques andthe interrelation of drilling and bla-sting. Also discussed are the mainparameters involved when plan-ning and executing blasthole dril-ling at quarries and civil engine-ering projects.

The range of Atlas Copco pro-ducts, with references to the AtlasCopco websites, are presented anddiscussed by comparing their suit-ability and expected productivityrelated to a selection of applica-tions. Case studies from worksites

around the world should prove in-teresting and beneficial, especiallywhen planning and selecting me-thods and equipment for blastholedrilling applications.

Blastholes have certain uniqueand important characteristics.These are: hole diameter, depth,direction, and straightness. Drillingproduces a circular hole in the rock,the strength of which must beovercome by the drilling tool.Depending upon rock properties,there are several ways to accom-plish this, as shown in the follow-ing article.

Figure 1 Principle of tophammer drilling.


10/152

TALKING TECHNICALLY


illustrates the principle of top hammer

percussive drilling.

The piston strikes on the shank

adapter, and the kinetic energy of the

piston is converted into a stress wave

travelling through the drillstring to

the hole bottom. In order to obtain

the best drilling economy, the entire

system, rock drill to drillsteel to rock,

must harmonize.

Stress Wave

Theoretically, the stress wave has a

rectangular shape, the length of which

is twice that of the piston, while the

height depends on the speed of the

piston at the moment of impact, and

on the relationship between the cross-

sectional area of the piston and that ofthe drillsteel.

The total energy that the wave

contains is indicated diagramatically

in Figure 2. To calculate the output

power obtained from a rock drill,

the wave energy is multiplied by the

impact frequency of the piston, and

is usually stated in kW. Rock drill

designers seek to find the best com-

binations of various parameters, such

as the piston geometry, the impact

rate and the frequency. Two rock drillshaving the same nominal power rating

might therefore have quite different

properties.

The shock waves that are generated

by hydraulic (Figure 3) and pneumatic

(Figure 4) rock drills are significantly

different in shape. Drillrods used with

hydraulic rock drills will normally

show substantially longer service life,

compared with pneumatic rock drills,because of the higher stress level

obtained with the pneumatic driven

piston.

The reason is the larger cross-

section needed when operating at

substantially lower pressure, which

is 6-8 bars, compared to the 150-250

bars used with hydraulic systems. The

slimmer the piston shape, the lower the

stress level.

Figure 5 compares the stress level

generated by three different pistonshaving the same weight, but with dif-

ferent shapes and working different

pressures. The lowest stress, or shock

wave amplitude, is obtained with the

long slender piston working at high

pressure.

Efficiency and Losses

The shock wave loses some 6-10% of

its energy for every additional cou-

pling, as it travels along the drillstring.

This loss is partly due to the differ-

ence in cross-sectional area between

the rod and the sleeve, and partly due

to imperfect contact between the rod

faces. The poorer the contact, the

greater the energy loss.

When the shock wave reaches the

bit, it is forced against the rock, there-

by crushing it. The efficiency at the

bit never reaches 100%, because some

of the energy is reflected as a tensile

pulse. The poorer the contact between

the bit and the rock, the poorer the

efficiency (Figure 6).

To optimize drilling economy, thedrilling parameters for percussion

pressure, feed force, and rotation must

harmonize.

Percussion Pressure

The higher the percussion pressure, the

higher will be the speed of the piston,

and consequently, the energy. Where

the bit is in good contact with hard

and competent rock, the shock wave

energy can be utilized to its maximum.

Conversely, when the bit has poor con-tact, the energy cannot leave the drill-

string, and reverses up the drillstring

as a tensile wave.

It is only when drilling in sufficient-

ly hard rock that the maximum energy

per blow can be utilized. In soft rock,

to reduce the reflected energy, the per-

cussion pressure, and thus the energy,

will have to be lowered (Figure 7).

For any given percussion pressure,

the amplitude, and hence the stress

in the drillsteel, will be higher withreduced cross-section of the drillrods.

Figure 3 Shock wave generated by

hydraulic rock drill.

+

s

Figure 2 Stress wave energy.

5200 m/s

2 x piston length

+

s

Figure 4 Shock wave generated by

pneumatic rock drill.

+

s

Figure 5 Stress level generated by

different pistons of same weight.

Piston 1 0,8 MPa

Piston 3 20 MPa

Piston 2 12 MPa

Shock-wave amplitude

1

2

3

Piston 1

8 bar

Piston 2 120 bar

Piston 3 200 bar

Figure 6 Poor contact between bit and

rock results in poor efficiency.

+

s

Primary wave

Reflecting wave


11/152

TALKING TECHNICALLY


To get the longest possible service

life from shank adapters and rods, it is

important to ensure that the working

pressure is matched to the drillstring at

all times.

Feed Force

The purpose of the feed is to maintain

the drillbit in close contact against

the rock. However, the bit must still

be able to rotate. The feed force must

always be matched to the percus-

sion pressure. Figure 8 illustrates this

relationship.

Rotation

The purpose of rotation is to turn

the drillbit to a suitable new posi-tion for the next blow. Using button

bits, the periphery is turned about 10

mm between blows. Consequently,

the rotation rate is increased using

higher impact frequency and reduced

bit diameter. Using insert bits, the

recommended rotation rate is 25%

higher.

Setting Parameters

In practice, the driller sets the percus-

sion pressure that the rock can cope

with, and then sets the rev/min with

regard to the percussive frequency and

the bit diameter.

When drilling starts, the feed is

adjusted to get even and smooth rota-

tion. In case this is not achieved, which

will show up in low shank adapter

life, the percussion pressure can be

progressively reduced, until even and

smooth rotation is reached.

The temperature of the adaptersleeve can be checked to ensure that

the drilling parameters are correctly

set. Immediately after drilling, the

temperature should be 60-70 degrees

for dry drilling, and approximately 40

degrees for wet drilling.

Drilling problems, mainly related

to loose couplings, may arise what-

ever parameters are used. In order

to tighten the couplings during drill-

ing, the friction of the bit against the

hole bottom has to be increased. This

can be done by increasing the feed,increasing the rotation rate, or chang-

ing the bit.

Flushing

Drill cuttings are removed from the

hole bottom to the surface by air blow-

ing or water flushing. As the power

output from rock drills increases,

accompanied by increased penetra-

tion rate, efficient flushing becomes

gradually more important. The flush-ing medium is normally air for

surface drilling, and water for under-

ground drilling. The required flushing

speed will depend on:

specific gravity material having a

density of 2 t/cu m requires at least

10 m/sec, whereas iron ore, for example,

having a density of 4 t/cu m, requires

an air speed of 25-30 m/sec;

particle size the larger the particles,

the higher flushing speed required;

particle shape spherical particlesrequire more speed than flaky, leaf

shaped particles.

Productivity and

Methodology

During the past century there has

been a rapid and impressive increase

in efficiency and productivity related

to tophammer drilling. Starting from

hitting a steel manually by a sledge

hammer 100 years ago, todays hydrau-lically powered rock drills utilize the

latest state-of-the-art technology.

Every drilling method has its pros

and cons, making an objective com-

parison quite cumbersome. In view of

this, the table in Figure 9 can serve as a

guideline when comparing the various

percussion drilling alternatives which

Atlas Copco can offer. The choice of

best drilling method to apply depends

on hole size and type of application.

by Hans Fernberg

Figure 8 Feed force must be matched to

percussion pressure.

Low percussionpressure

High percussionpressure

Feeding

Figure 7 To reduce reflected energy,

percussion pressure is lowered.

Percussion pressure

Soft rock Hard rock

Percussion pressure HydraulicDrilling method Tophammer DTH COPROD

hole diameter, mm 76-127 85-165 105-165

penetration rate 2 1 3

hole straightness 1 3 3

hole depth 1 3 3

production capacity (tons rock/shift) 2 1 3

fuel consumption/drill metre 2 1 2

service life of drillstring 1 2 3

investment in drillstring 2 2 1

suitability for good drilling conditions 3 2 2

suitability for difficult drilling conditions 1 3 3

simplicity for operator 2 3 1

adjustability of flushing capacity 1 2 3

Figure 9: Comparison for 20 m bench drilling in a limestone quarry. Ratings: fair = 1,good = 2, very good = 3.


12/152

TALKING TECHNICALLY


Blasting

To understand the principles of rock

blasting, it is necessary to start with therock fragmentation process that follows

the detonation of the explosives in a

drillhole.

The explosion is a very rapid

combustion, in which the energy con-

tained in the explosives is released in

the form of heat and gas pressure. The

transformation acts on the rock in three

consecutive stages (figures 1-3).

Compression:a pressure wave prop-

agates through the rock at a velocity of

2,500-6,000 m/sec, depending on rock

type and type of explosives. This pres-sure wave creates microfractures which

promote rock fracturing.

Reflection:during the next stage, the

pressure wave bounces back from the

free surface, which is normally the bench

wall or natural fissures in the rock. The

compression wave is now transformed

into tension and shear waves, increasing

the fracturing process.

Gas Pressure:large volumes of gas

are released, entering and expanding

the cracks under high pressure. Wherethe distance between the blasthole and

the free face has been correctly calcu-

lated, the rock mass will yield and be

thrown forward.

Benching

Bench blasting is normally carried out

by blasting a large number of paral-

lel holes in each round. Considering

the blasting mechanics, with a com-

pression-reflection-gas pressure stage

in consecutive order for each charge, it

is of vital importance to have a properdelay between each row, and even

between individual holes in each row.

A proper delay will reduce rock throw,

improve fragmentation, and limit

ground vibrations. The blast should

be planned so that the rock from the

first row of holes has moved about one

third of the burden, when the next row

is blasted (figures 4 and 5).

The horizontal distance between the

hole and the free face is the burden,

and the parallel distance between ho-

les in a row is the spacing. The ratio

between spacing and burden will have

great impact on the blasting result, and

1.25 can be considered as an average

ratio. The optimum burden depends

upon a number of parameters, such as

rock type, required fragmentation, type

of explosives, hole deviation, and hole

inclination. Nevertheless, as large drill-

holes can accommodate more explosi-

ves, there is a distinct relationship bet-ween burden and hole diameter (figure 6).

As the bottom part of the blast is the

constricted and critical part for suc-

cessful blasting, it is used as a basis

for deciding all other parameters. The

bottom charge, normally 1.5 x burden,

from where the initiation should start,

requires well-packed explosives of

higher blasting power than is needed in

the column charge (figure 7).

Principles of Rock Blasting

Combination ofFactorsBlasting by design results from alarge number of factors, all ofwhich need to be brought undercontrol in order to achieve theright result. These include thechoice of drillrig and tools, thelayout of the holes, the explo-sive, and the skill of the opera-tors. Geology is the governingfactor, and experience is a majoringredient. Atlas Copco producesdrillrigs and systems to suit all

rock types, and has the experi-ence to recommend the correctapproach to all ground condi-tions in order to achieve theoptimum result. The followingoutline of the principles involvedin rock blasting is a logical startpoint in the quest for the perfectround.

Figures 1-3 Rock breaking sequence in a normal blast.

Compression Reflection Gas Pressure

Figure 4 Delay detonation of a typical bench blast.


13/152

TALKING TECHNICALLY


Stemming of the top part of the hole

is used to ensure that the energy of

explosives is properly utilized. It will

also reduce and control the fly rockejected from the blast. This tends to

travel long distances, and is the main

cause of on-site fatalities and damage to

equipment. Dry sand or gravel having a

particle size of 4 to 9 mm constitutes

the ideal stemming material.

Inclined holes give less back break,

safer benches and less boulders, when

compared to vertical holes.

Types of Explosives

The geology frequently has more effect

on the fragmentation than does the ex-

plosive used in the blast. The properties

that influence the result of the blast are

compressive strength, tensile strength,

density, propagation velocity, hardness

and structureIn general, rock has a ten-

sile strength which is 8 to 10 times

lower than the compressive strength.

The tensile strength has to be exceeded

during the blast, otherwise the rock will

not break. High rock density requires

more explosives to achieve the displace-ment.

The propagation velocity varies with

different kinds of rock, and is reduced

by cracks and fault zones. Hard, homo-

geneous rocks, with high propagation

velocity, are best fragmented by an ex-

plosive having high velocity of detona-

tion (VOD).

An extensive range of different types

and grades of explosives is available

to suit various blasting applications.

A breakdown is presented in Table 1.In dry conditions, ANFO has become

the most used blasting agent, due to its

availability and economy.

The blasthole diameter, together with

the type of explosive used, will deter-

mine burden and hole depth. Practical

hole diameters for bench drilling

range from 30 to 400 mm. Generally,

the cost of large diameter drilling and

blasting is cheaper per cubic metrethan using small holes. However, rock

fragmentation is better controlled by

higher specific drilling.

The explosives are initiated with

detonators which can be electric or

non-electric. Electric systems have the

advantage that the complete circuit can

easily be checked with an ohmmeter

to ensure that all connections and

detonators are correct before blasting.

To eliminate the risk for spontaneous

ignition from lightning, non-electricsystems, including detonating cord,

are used.

by Hans Fernberg

Firing patternThis firing pattern provides separate delaytime for practically all blastholes andgives good fragmentation as well as goodbreakage in the bottom part of the round.

Figure 6 Burden as a function of drill hole diameter.

Burden as a function ofDrill Hole Diameter

Hole Diameter, mmSpacing Equal to 1.25 x Burden

Figure 7 Charging for optimum fragmentation.

Boulders and flyrockcome from this zone

Back break

Subdrilling

= 0.3 xburden

Bottom charge

requires well packed

high blasting power

Column chargeonly light chargeneeded for good

fragmentation

Stemming

(length ~ burden) Burden

Table 1 Features of common types of explosives.

base type detonation velocity m/s featuresnitro-glycerine dynamite 5500-4500 highly adaptable cartridged gelatin excellent in smaller holes

ammonium- ANFO 2500 low cost, high safety, easynitrate to pour or blow no water resistance,

contains 5-6% fuel oilwater slurry 4000-3000 watergel basically ANFO made water resistant gel 5000 emulsion stable oil/water emulsion heavy ANFO range depends on packaged or pumpable storage time

Figure 5 Firing sequence in delay blasting.

Practical Values


14/152

TALKING TECHNICALLY


Putting Rotary Drilling intoPerspectiveRotary or DTHAtlas Copco now offers a complete

range of rotary as well as DTH

and tophammer drill rigs for most

types of open pit mining and quar-

rying applications. But how do the-

se technologies complement each

other and how do drillers know

which method to choose, and

when? As readers of M&C are well

acquainted with DTH drilling, this

article puts rotary drilling into per-spective.

Complete Range

With the acquisition of the Ingersoll-

Rands Drilling Solutions and Baker

Hughes Mining Tools (BHMT) busi-

nesses, there is now another way to

break rock within the Atlas Copco fa-

mily of products. Much of the worlds

mining output begins through drilling

of holes with rotary drills. Ingersoll-Rand built air-powered rotary drills for

many years prior to the introduction of

their first fully hydraulic unit, the T4,

in 1968.

About Rotary Drills

It is important to note that rotary drills

are capable of two methods of drill-

ing. 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 limit-

ed 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 main blasthole drilling methods

are shown in Fig 1. The primary differ-

ence between rotary drilling and other

methods is the absence of percussion.In most rotary applications, the pre-

ferred bit is the tricone bit. Tricone bits

rely on crushing and spalling the rock.

This is accomplished through transfer-

ring down-force, known as pulldown,

to the bit while rotating in order to

drive the carbides into the rock as the

three cones rotate around their respec-

tive axis. Rotation is provided by a

hydraulic or electric motor-driven gear-

box (called a rotary head) that moves

up and down the tower via a feedsystem. Feed systems utilize cables,

chains or rack-and-pinion mechanisms

driven by hydraulic cylinders, hydrau-lic motors or electric motors. 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 cables.

More Weight with Rotary

It only takes one look to see that the

biggest DTH and tophammer drill rigs

are very different to the biggest rotary

blasthole rigs. In fact, the Pit Viper

351 rotary drill rig weighs in excess

of nine times that of our largest DTH

hammer drill rig, the ROC L8. Yet it

is drilling a hole that is generally only

twice the diameter. Take a typical medi-

um formation tricone bit with a recom-

mended maximum loading of 900 kg/

cm of bit diameter (5000 lbs per inch

of diameter). With a 200 mm (7-7/8)

bit, you could run about 18,000 kg

(40,000 lbs) of weight on the bit. The

laws of physics dictate that for everyaction, there is an equal and opposite

By Brian Fox, Vice President Marketing, AtlasCopco Drilling Solutions, USA.

TONS

Fig 1. Drilling meth-

ods (1) Down-the-Hole

(DTH); (2) Tophammer;

(3) COPROD; (4) Rotary

tricone.


15/152

TALKING TECHNICALLY


Surface Drilling Applications

ConstructionAggregate

Industrial Minerals

Gold

CoalCopper

Iron

Hole Diameter2" 3" 4" 5" 6" 7" 8" 9" 10" 11" 12" 13" 14" 15" 16"

51mm 76mm 102mm 127mm 152mm 178mm 203mm 229mm 254mm 279mm 305mm 330mm 356mm 381mm 406mm

125,000 LB Bit Load PV-351110,000 LB DM-H2

90,000 LB DM-M375,000 LB PV-271/PV-27575,000 LB DM-M2

50,000 LB DMLSP60,000 LB DML45,000LB DM45

30,000 LB T4BH30,000 LB DM30

25,000 LB DM25SP

ROC L8

CM780D

CM760D

KEY:

ROC L6

ROC L7/L7CR

Rotary

ECM720

ROC F9

Rotary or DTH

ROC F6

ECM660III

DTH

ROC F7

ROC D3/D5/D7

Tophammer/COPROD

ECM585MC

ECM470

Complete Range

With the acquisition of the Ingersoll-

Rands Drilling Solutions and Baker

Hughes Mining Tools (BHMT) busi-

nesses, there is now another way to

break rock within the Atlas Copco fa-

mily of products. Much of the worldsmining output begins through drilling

of holes with rotary drills. Ingersoll-

Rand built air-powered rotary drills for

many years prior to the introduction of

their first fully hydraulic unit, the T4,

in 1968.

About Rotary Drills

It is important to note that rotary drills

are capable of two methods of drill-

ing. 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 limit-

ed 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 main blasthole drilling methods

are shown in Fig 1. The primary differ-ence between rotary drilling and other

methods is the absence of percussion.

In most rotary applications, the pre-

ferred bit is the tricone bit. Tricone bits

rely on crushing and spalling the rock.This is accomplished through transfer-

ring down-force, known as pulldown,

to the bit while rotating in order to

drive the carbides into the rock as the

three cones rotate around their respec-

tive axis. Rotation is provided by a

hydraulic or electric motor-driven gear-

box (called a rotary head) that moves

up and down the tower via a feed

system. Feed systems utilize cables,

chains or rack-and-pinion mechanisms

driven by hydraulic cylinders, hydrau-

lic motors or electric motors. 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 cables.

More Weight with Rotary

It only takes one look to see that the

biggest DTH and tophammer drill rigs

are very different to the biggest rotary

blasthole rigs. In fact, the Pit Viper351 rotary drill rig weighs in excess

of nine times that of our largest DTH

hammer drill rig, the ROC L8. Yet it

is drilling a hole that is generally only

twice the diameter. Take a typical medi-

um formation tricone bit with a recom-

mended maximum loading of 900 kg/

cm of bit diameter (5000 lbs per inch

of diameter). With a 200 mm (7-7/8)

bit, you could run about 18,000 kg

(40,000 lbs) of weight on the bit. The

laws of physics dictate that for everyaction, there is an equal and opposite

reaction, meaning that if you push on

the ground with 18,000 kg (40,000 lbs),

the same force will push back on the

unit. Therefore, the weight of the ma-chine must be over 18,000 kg (40,000

lbs) at the location of the drill string

to avoid the machine lifting off the

jacks. To achieve a stable platform

through proper placement of the tracks

and levelling jacks, the distribution of

weight results in an overall machine

weight that approaches or exceeds

twice the bit load rating. This weight

does add cost to the machine, but the

size of the components also translates

to long life. Even smaller rotary blast-

hole drills are built to run 30,000 hours

of operation.

The Importance of Air

A key parameter of rotary drilling is

flushing the cuttings from the hole. In

most rotary blasthole drills, cuttings

are lifted between the wall of the hole

and the drill rods by compressed air.

Sufficient air volume is required to lift

these cuttings.

Many types of tricone bits have beendeveloped to meet various drilling

needs. Softer formation bits are built

with long carbides with wide spac-

ing on the face of the bit. This design

yields large cuttings which increase

drill speed and reduce dust. It is impor-

tant to have sufficient clearance bet-

ween the wall of the hole and the drill

rods in order for such large cuttings to

pass. If this clearance, known as annu-

lar area, is not sufficient, the cuttings

will be ground between the wall of thehole and the rods or by the bit itself

Fig 2: The Atlas Copco product range

by application and method.


16/152

TALKING TECHNICALLY


0

2000

4000

6000

8000

10000

12000

14000

$-

$1,00

$2,00

$3,00

$4,00

$5,00

$6,00Footage/24 Hours

Bit Life (ft)

Overall Cost/Ft

299 ft/hour,1500' bit life

High Production

74 ft/hour,12,000' bit life

Great Bit Life

218 ft/hour,5300' bit life

Lowest Cost

Footage/24Hours&A

verageBitLi

fe

OverallCost/Foot

of air is required. Take for example

a Secoroc QL80 203 mm (8) DTH

hammer that is designed to operate at

25 bar (350 psi). Even with our larg-

est high pressure compressor with 686

litres per second (1,450 ft3/min), the

pressure will only build to 23 bar (325

psi), thus providing less impact energy.

In real terms, each blow of the piston

is about 45 kg (100 lbs) less than it

is designed for. In some cases, this

method will still out-perform rotary

drilling. For most large diameter

blasthole drilling, there is simply not

enough air on-board for a DTH to be

as cost effective as rotary drilling with

a tricone bit.

Rotary drilling is still the predomi-

nant method of drilling 230 mm (9)

diameter or greater. This is driven pri-marily by the current limitations of top-

hammer units and rig air systems. Tri-

cone bits also become more cost effec-

tive as the larger bits are equipped with

larger bearings which in turn can hand-

le higher loads. These higher loads

translate to improved drill rates.

Another advantage of rotary rigs is

the length of the drill rods that can be

carried on board. Longer rods mean

fewer connections. Further, some rota-

ry rigs are large enough to handle along tower that enables drilling of the

entire bench height in a single-pass. At

the largest open pit mines, rotary units

are drilling 20 m (65 ft) deep holes in a

single-pass to match the bench heights

dictated by the large electric shovels

which can dig a 17 m (55 ft) bench.

Productivity versus Cost

Studies have shown that pure penetra-

tion rate will increase linearly with

increased pulldown. The same has alsobeen said of rotation speed. So why

doesnt every operation use more of

each? Unfortunately, higher pulldown

and rpm usually results in increased

vibration and lower bit life. The vibra-

tion causes increased wear-and-tear on

the rig, but more importantly, it cre-

ates a very unpleasant environment for

the operator. What invariably happens

is that the operator reduces the weight

or rpm until the vibration returns to a

comfortable level. Some operationslimit bit load and rpm even if there is

no vibration in order to improve bit

life. This is often the wrong strategy as

the overall drilling cost per unit, also

known as Total Drilling Cost (TDC),

should be considered.

TDC is calculated using the bit cost

per metre/foot and the total rig cost per

hour. The unit cost per hour includes

labour, maintenance and power, andpossibly the capital cost. The drilling

speed really doesnt impact this cost

per hour figure. What it does impact

though is the cost per unit produced

(cost/metre/foot, cost/ton, etc). You

generally want to push the rig harder

to reduce the cost/foot, but there will

be a point where the rig overloads the

bits (see fig's 3 and 4).

Large versus Small

There are some drawbacks to rotary

rigs. Smaller crawler rigs are more

flexible with many advantages such as

articulating and extendable booms and

guides that allow drilling at many dif-

ferent angles. Some models also offer

significantly more technology with

automated rod handling systems and

automatic drilling. The components on

rotary rigs are not enclosed. They are

mounted onto the frame in an open

layout which makes them extremely

easy to service. Looks are not of pri-

mary concern for a rig that is subjected

to the rigors of breaking rock for morethan 60,000 hours.

The general trend for 165 mm (6-1/2)

or less is towards the smaller, more

flexible units. However, many large

scale quarries and small mines still

favour the durability, life and simplici-

ty of the larger rotary rigs for these

small diameters. For the large scale

open pit operations that yield a high

percentage of the total worldwide mi-

neral production, it is anticipated that

rotary drilling will remain the primarymethod for years to come.

Fig 4. The impact of bit li fe and productivity on overall cost/foot (1 ft = 0.305 metres).

Production Rate (Feet/Hour) 120 138 180

Bit Life (Feet) 10,000 8,000 4,000

Bit Cost $4,000 $4,000 $4,000

Bit Cost/Foot $0.40 $0.50 $1.00

Rig Cost/Hour $175 $175 $175

Total Drilling Cost/Foot $1.86 $1.77 $1.97

Operator Steady Eddie Smart Sam Wild Jack

Fig 3. The table compares three operators on the same drill rig Steady Eddie, Smart Sam and

Wild Jack. The cost chart, using actual data collected at a major copper mine further illustrates the

balance required.

Acknowledgements

This article first appeared in Mining

& Construction No 2, 2005.


17/152

TALKING TECHNICALLY


Control System

Via PC software, the SmartRig control

system generates electrical signals to

control the hydraulic valves. This intro-

duces the concept of a dry cab, with

no hydraulic pipework and gauges, con-

siderably reducing noise for the ope-

rator. The number of hydraulic com-

ponents has been reduced by 30%,

compared with Hydraulic Control Sy-

stem, HCS, resulting in higher effici-

ency. The need for electrical cables is

also reduced.

Control gauges and instruments are

replaced by a display unit. This releases

space in the cab, increasing visibility,

and improving operator ergonomics.

The fundamentals of the rock drill

control system are RPCF control and

anti-jamming functions. RPCF, or Ro-

tation Pressure Control of Feed pres-

sure, adjusts the feed pressure according

to the measured feed pressure. Thiskeeps the joints correctly tightened and

saves drill steel. Anti-jamming uses the

rotation pressure to detect a jamming

situation, and will reverse the feed ofthe rock drill and initiate a replacement

hole collaring.

Together, this advanced system of

drilling control will give maximum life

to the entire drill string, while ensuring

high penetration rates and easy rod ex-

traction.

Automation in SurfaceDrilling

Using the laser plane as a reference

level, all holes are drilled to the same

depth, reducing drilling, blasting and

crushing costs by way of better frag-

mentation, and cancelling the need for

secondary blasting. A flatter, more uni-

form bench surface results, making loa-

ding and transportation easier. Automatic

feed positioning reduces set-up time

and cancels out operator error. More

parallel holes result in better blasting and

smoother bench bottoms. The longer

the hole, the bigger will be the impact

of even a small deviation on blasting.For instance, a one degree error will

produce a deviation of 36 cm at the

bottom of a 20 m hole. Hence the im-

portance of automatic feed positioning,which sets the feed to pre-defined angles

at the touch of a button.

The automatic rod adding system,

AutoRAS, enables the operator to drill

a hole automatically to a given depth,

allowing him to leave the cab to carry

out other duties, such as maintenance

checks or grinding bits, while keeping

the drill rig in sight. The drilling is su-

pervised by the drillsteel break detec-

tion system, which shuts down the dril-

ling operation if a breakage is detected.

The result is better rig utilization, evi-

denced by a couple of extra holes/shift.

MWD and ROC Manager

Measure While Drilling, or MWD, is an

optional instrumentation and software

package for recording and interpreta-

tion of drilling data, and enhanced pres-

entation of geomechanical variation of

rock properties. A number of parame-

ters, such as hole depth, penetration rate,

and damper, feed, percussion and rota-tion pressures are logged at requested

SmartRig Takes Control

HCS to PLC to PCAcronyms are plentiful when it co-mes to automation, but PC-basedwill be the most important acro-nym in the years to come. Eversince Atlas Copco developed Hyd-raulic Control System (HCS) in the1970s, the search has been on forits successor. Programmable LogicControl (PLC) saw us through the1990s along with the VME-system,but in 2002 the first SmartRigsstarted to take over. SmartRig isa PC-based control system inten-ded for all kinds of automation in

simple and advanced drill rigs. Thehardware is designed to operatein every possible weather condi-tion, and the software can be up-graded at site. SmartRig has built-in logging and monitoring func-tions, together with support fordiagnostics and faultfinding. Thecontrol system is used in all AtlasCopco product families, in both un-derground and surface crawlers,making it easy to move functionsand improvements between diffe-rent products. Thats smart!

Atlas Copcos Silenced ROC D7C is a sound investment with a noise level of approximately 10 dB(A) below

that of other rigs on the market.


18/152

TALKING TECHNICALLY


intervals while drilling, and this pro-

vides input to analysis of the rock pro-

perties.

Date, time, hole length, feed angle,

and rig identity are logged once for each

hole. MWD data can be recorded forevery second centimetre up to a maxi-

mum penetration rate of 3 m/min. In

this way, data is extracted from every

production hole to provide very high-

resolution rock mass characterization.

Typical parameters being reported are

rock hardness and fracturing. Detailed

information on rock mass properties is

available immediately after drilling is

completed, without disturbing produc-

tion, since logging is carried out auto-

matically during the normal drilling

process.ROC Manager is a stand-alone PC-

based tool for making drill plans, mea-

suring hole deviation, and logging,

presenting and reporting drilling data

graphically. This information can be

presented individually or in combination

with other parameters, and used both

during drilling operations, and by trans-

ferring logged data from the rig. Advan-

ced MWD analysis is also possible as

an option. Both the SmartRig and ROC

Manager 2.0 support the IREDES for-mat for data exchange on performance,

quality and MWD logs, and on drill

plans.

In ROC Manager, the MWD data can

be illustrated in slices through the bench,

with the rock properties identified by

contrasting colours, providing a map ofthe mineral qualities and types. This

facility differentiates between good rock

and poor rock, for instance, allowing

the quarry or mine operator to select

rock for excavation, and to prepare for

loading and hauling before blasting takes

place.

Hole Navigation System

Real-time satellite-based Global Posi-

tioning System, HNS, has been chosen

for the highest possible drillrig navi-gation accuracy, within 10 cm in most

situations. With HNS there is no need

to mark out holes, and the accuracy is

such that all holes will be parallel, if

required, resulting in a controllable pro-

duct with better fragmentation and less

boulders.

The focus is on road construction

applications, but the system can be used

in any type of drilling.

Using information on his display, the

operator can navigate the rig to the co-verage position for a given hole, and

the computer will provide the informa-

tion to place and align the feed exactly

over the collaring position.

The drillplan can be provided by

ROC Manager, transferred to the rig

via a PC card. The time saved by not

having to aim visually to set angles, and

by being able to drill more than one

hole from a single set-up, results in bet-

ter rig utilization.

Silenced for NoiseSensitive Areas

The sources and characteristics of noise

are complicated, and have to be identi-

fied and analysed in order to analyze

their spectrum. Atlas Copco designed

a concept rig in 2000, and a second

prototype rig in 2004, both of whichwere used as testbeds for various sim-

ulations.

These confirmed that noise was not

just created by the drilling cycle, but

also by elements of the carrier, such as

cooling fans, hydraulic system compo-

nents, and engine.

The recently introduced Silenced

SmartRig is for use in areas where noise

levels have to be controlled. Substantial

efforts have been put into redesigning

components, systems and soundproofingenclosures, resulting in a 10dB(A) ex-

ternal noise reduction.

The most visible difference between

the Silenced SmartRig and other Smart

Rig rigs is its patented feed enclosure.

The frame and panels of the enclosure

are formed from lightweight aluminium.

There are four access doors, which are

hydraulically operated from the cab. A

rubber sliding skirt at its base encloses

the hole, and this can be hydraulically

raised for collaring. The whole enclo-

sure is designed for demounting when

not needed.

The SmartRig system, because it de-

livers the right amount of power for each

phase of the drilling operation, can re-

duce fuel consumption by up to 30%.

Add this to the productivity increase

from automatic rod adding and auto

feed alignment, and the Silenced Smart

Rig is a really sound investment!

by Jean Lindroos

With Silencing Kit Without Silencing Kit

200

400

600800

1000

12001400 m

200

400

600

800

1000

1200

1400 m

55dB (A) area

The noise carpet shows the difference with and without a Silencing Kit.


19/152

TALKING TECHNICALLY


Criteria of Choice

Since button bits are used for 99%

of surface drilling applications, a bit

with guiding wings on the bit skirt, the

Retrac-type bit, should be chosen to

give the straightest possible hole.

The bit front should not be allowed

to take on a convex shape during serv-

ice life, since this convex front has

been shown to give more deflection

than a flat or drop centre front.When a button bit is worn, it is the

gauge buttons that always show the most

wear. This means that the gauge but-

tons lose more height during regrind-

ing, leading to the tendency for the bit

front to become convex. A drop centre

bit, thanks to its lowered centre, will not

become convex during the bit life, and is

thus the best choice, wherever possible.

If the above criteria are taken into

account, the choice of bit, in descend-

ing order, should be: Retrac button bitwith ballistic buttons and drop centre

front; Retrac button bit with spherical

button and drop centre front; Retrac

button bit with spherical buttons and

flat front; Insert bit, only used when

very straight holes are required and

nothing else works.

Bit Designs

Flat Front, Standard

The standard bit is

most suitable for me-

dium-hard to hard

rock, where it gives

good performance

and long service life

in normal condi-

tions. Standard bits

are easy to regrind,

as the front and gau-

ge buttons usually are the same size.

Flat Front, Heavy Duty

Hard rock, con-taining quartz and

pyrites, often causes

considerable wear

to the gauge buttons.

When drilling in rock

with this characteri-

stic, it is common

practice to use Heavy

Duty bits, Model 20 or 21, where the

gauge buttons are larger than the front

buttons.

Extra Heavy Duty

Model 21 has better

flushing characteris-

tics, due to different

clearance angle and

shorter head.

Recommended in

extremely hard and

abrasive rock.

Drop Centre

Excellent results

are obtained with

the Drop Centre bit

in soft to medium

hard rock, with

high penetration

potential. The Drop

Centre bit has out-standing flushing

characteristics, and

the cuttings are dis-

tributed evenly around the steel body,

so minimizing steel wash. The drop

centre part of the bit front produces a

rock elevation or bump during drilling,

which gives good guidance to the bit.

Correct Selection ofTophammer Rock Drilling Tools

OptimizingPenetration RatesIn order to achieve best possiblepenetration rate, a bit should bechosen where the total contactarea between the cemented car-bide and the rock creates the bestpossible penetration per blow.As a rule of thumb, the followingpenetration rate index can be

used: button bit with ballisticbuttons, 130; button bit withspherical buttons, 115; insertbit, 100. However, when bits arecompared for hole straightness, adifferent order emerges, with theinsert bit on top, followed by thebutton bit with ballistic buttons,and lastly, the button bit withspherical buttons.

This article is intended to guidethe driller through the range ofbits, rods and shank adaptersto assist with the best choice ofrock tools for the particular job.

Bit designs and rock types

DC = Drop Centre; FF = Flat Front; HD = Heavy Duty; XHD = Extra Heavy Duty.


20/152

TALKING TECHNICALLY


Drop Centre Extra Heavy Duty

Gauge buttons are larger than the front

buttons, there are no side flushing holes,

and the head is shorter. Recommended

in extremely hard and abrasive rock,

but can also be used in medium hard

rock.

Retrac Skirt

The Retrac bit has cutting edges at the

rear of the bit, allowing it to drill in re-

verse. This is an important feature when

drilling in loose, broken or fissured rock,where it can be difficult to retract the

drillstring due to hole collapse. In addi-

tion, the Retrac bit has deep grooves mil-

led along the bit body for efficient cut-

ting removal. The good guidance of this

bit gives straighter holes.

Insert Bits

These are very seldom used, except

when very straight holes are required.

Cross bits normally have cemented car-

bide inserts with a carbide grade for high

wear resistance. X-bits normally havea carbide grade for improved toughness,

and are preferred where there is a ten-

dency for squaring of the hole.

Drillrod SelectionFor bench drilling, three types of drill-

rods can be chosen: surface hardened

rods, in which only the thread parts are

hardened; carburized rods, where all sur-

faces, including the inside of the flush-

ing hole, are hardened; and carburized

Speedrods, having integrated couplings

with male and female threads at oppo-

site ends.

Surface Hardened RodsSurface hardened rods are the toughest,

and can take more abuse than the car-

burized rods, but they have the lowest

fatigue strength. They are a good choice

when drilling in faulted or folded for-mations, when driller abuse, or lack of

care and maintenance, are factors.

Tiger RodsThe new M-F Tiger Rods from Atlas

Copco Secoroc are specially developed

for surface drilling applications. They

are composed of selected steels to give

increased service life and better per-

formance. The female thread is fully car-

burized, while the rest of the rod is sur-

face hardened. The new Tiger Rods arefriction-welded, so that the best steel

grade can be selected for each section.

This improved production techno-

logy reduces the risks of pitting on the

threads, and rod and thread end break-

age, while tighter thread tolerance im-

proves the total service life of the whole

drill string.

Rigorous tests in various locations

have shown that Tiger Rod is a drill

string without any weak parts.

Carburized RodsA carburized rod has better wear resist-

ance and a higher fatigue life compared

to surface hardened rods. Demands good

treatment, and hole deflection should be

limited by putting guiding equipment in

the string, at least when drilling holes

deeper than 10 m. Their life will be

20%-30% longer if they are handled

correctly, and guiding equipment is used

when necessary. When lighter drillrods

are required for manual rod handling,

the carburized hexagonal rod is recom-mended.

When drilling with a number of rods

in a string, using standard rods and coup-

lings, the loss of energy in every joint

is about 6%, if the connection is tight.

If drilling with open threads, the energy

loss at each joint can easily climb to

10%. Therefore, it is advantageous to

use the maximum rod length possible.

SpeedrodsIf Speedrod carburized rods with inte-

grated coupling are used, the energy loss

per joint is less, since the mass (weight)

of the joint is less than that of standard

coupling joints. The energy loss is about

3.5%, which is 60% of that of standard

joints.

In practice, the energy advantage of

Speedrod joints compared to standard

couplings is even greater, since it iseasier to keep the Speedrod joint tight

during drilling.

Field tests have shown that, when

drilling 20 m holes with 4 m rods, the

penetration increase is about 15% when

using Speedrods.

The faster penetration and easier hand-

ling increase productivity, and due to

better energy transmission, the joints are

easily loosened.

From the point of view of drilling

straight holes, rods that are as rigid aspossible for the drilled hole diameter

are best. For straight hole drilling, a

Guide Rod or Guide Tube should be

used as the first rod after the bit, to

give the drillstring guidance.

Further information about rods is av-

ailable in the yellow technical specifi-

cation pages in this reference edition.

Shank Adapters

The task of the shank adapter is to tran-

smit rotation torque, feed force, impact

energy, and flushing medium. It is made

from specially selected material to with-

stand the transmission of impact energy

and rotation from the rock drill to the

drillstring, and is hardened through car-

burizing. Around 400 different shank ad-

apters are currently available from Atlas

Copco Secoroc. Shank adapters can be

divided into three main types, based on

the technique used to transfer the rota-

tion motor torque to the drillrod.

by Alf Stenqvist


21/152

TALKING TECHNICALLY


Atlas Copco Secoroc has extended

the range of button bits for surface

drilling with two new models for

drilling in soft rock formations.

The new models are designated2166 and 4766. The designation

66 means that all the buttons are

full-ballistic in shape and protrude

2025% more than standard ballistic

buttons. Model 21 has larger gauge

buttons whereas all the buttons are

the same size on model 47 .

The longer button protrusion

helps the bit to penetrate deeper into

the rock with each hammer stroke.

Both model 21 and model 47

have excellent flushing capacity for

the removal of the cuttings from the

front of the bit head. The flushing

is concentrated to four large flush-

ing holes in the bit front plus equally

deep and wide flushing grooves in

the front and sides of the bit head. A

shorter bit head and larger clearing

angle also allow for better flushing

of cuttings on models 21 and 47.

Increased penetration rateDuring tests in soft rock in Korea,

Malaysia and Australia, these new

bits showed much higher penetration

rates than standard ballistic button

bits, while their service life remained

the same.

Model 2166 bits with drop centre

front are available with T38 thread in

sizes 76 mm (3 in) and 89 mm (3.5 in).

Model 4766 bits with flat front

design can be supplied with T45

thread in size 89 mm (3.5in) and with

T51 thread in sizes 102 mm (4 in)

and 127 mm (5 in).

More sizes and thread combina-

tions will follow.

Full-ballistic button bits for soft rock

Secoroc full-ballistic button bit (dia 76 mm.)

model 2166. Drop centre front with larger

gauge buttons.

Secoroc full-ballistic button bit (dia 127 mm.)

model 4766. Flat front with same size front

and gauge buttons.

The full-ballistic buttons protrude more from the bit body, resulting in faster penetration in soft rock.

ThunderRod T60 for the most powerful

tophammer drill rigs

Atlas Copco Secoroc has launched

ThunderRod T60, a heavy-duty top-

hammer drill string designed forgreater productivity. Specially de-

signed with a bigger rod cross-

section for 102-152 mm holes,

ThunderRod T60 is built to handle

the most powerful hydraulic rock

drills, delivering higher power output

for optimization of the drilling pat-

tern. The entire drillstring is more

rigid, offering increased hole straight-

ness, higher penetration rate and a

welcome boost to drilling producti-

vity and economy. Fewer, but larger,drill holes per blast means higher pro-

ductivity. Straighter holes result in

improved fragmentation and far less

secondary drilling and blasting.

The threads on ThunderRod T60

are designed to make the coupling

sequence as easy as possible, while

at the same time keeping energy los-

ses to an absolute minimum. Fea-

turing a cross-section 40% bigger

than standard T51 rods, the new

ThunderRod is designed to reduce

hole deviation in all rock formations.

The flushing hole is also bigger, en-

suring a 10% increase in flushing ca-

pacity for up to 30 m-deep holes.

The new shank adapters for Thun-

derRod T60 are optimally hardened,

with a balance of core and surface

properties designed to withstand the

high impact power of modern rock

drills such as Atlas Copco COP 2560,

COP 2560EX and COP 4050. This

leads to unparalleled fatigue and wear

resistance.


22/152

TALKING TECHNICALLY


Introduction

In the simplest of terms, percussive dril-

ling systems go back to manually hit-

ting a steel rod with a bit at one end

and, as recoil makes the rod jump back,

rotating it at a small angle between

blows to ensure that the hole is round.

Most drilling for benching operations

has been carried out with tophammers,

using extension rods connected by thre-

aded coupling sleeves, and an exchange-able drillbit at the bottom end. This

equipment works well for smaller hole

diameters in solid rock, but it is not so

effective in larger hole diameters, or in

deteriorating ground conditions. There

are problems in transmitting sufficientenergy to the bit, especially in deeper

holes, and in obtaining satisfactory flu-

shing.

In tophammer drilling, the thrust has

to be applied from the top to keep the

bit in contact with the bottom of the

hole. This can cause the relatively slen-

der drillstring to bend, steering the bit

off its intended alignment.

Increasingly powerful hydraulic rockdrills send more percussive energy down

the drillstring, allowing larger hole dia-

meters in benching. However, due to

the microscopic movements between

mating parts in the threaded drillstring,

COPROD drilling head arrangement.

Rock

drill

COPROD

section

COPROD

head

Tube

driver

20 40 kW

Rotation chuck

Anvil

Guide

Drill rod

Guide

Drill tube

Guide

Bit tube

Bit chuck

Drill bit

COP1838 CR/2150CR/COP 2550CR and COP 4050CR rock drills.

COPROD Combines the Bestof DTH and Tophammer Drilling

The Rock DrillersDreamDrillers always dreamed of a sy-stem that would combine the stra-ightness and accuracy of down-the-hole drilling with the enor-mous capacity of hydraulic top-hammer drilling. Efforts to com-bine the advantages of the twotechniques were unsuccessful, un-

til the development of COPRODby Atlas Copco.COPROD is not only a combina-tion of positive features, it also in-tegrates two types of drillstringfor percussive drilling by meansof a tophammer. Inner drillrodstransmit power and thrust to thedrillbit and outer tubes transferrotation, adding stiffness to thestring and improved flushing effi-ciency. These assets achieve hightophammer drilling rates and largehole diameters. The rods in the COPROD sy-

stem have no threads and aresimply stacked one on top of theother. Laterally, they are centredby the guide bushes in the tubeswhich surround them, and lon-gitudinally, contact between rodends is maintained by the thrustfrom the top. Thanks to the uni-que double recoil damping systemof the COP rock drills, the rod endsremain in permanent contact, en-ergy losses are almost nil, and dril-ling efficiency is maintained fromstart to finish of the hole.

CIAA AB

CIAAAB

COP 4050ME-CR

COP 1838CRCOP 1838CR/2150CR/COP 2550CR

COP 4050CR


23/152

TALKING TECHNICALLY


energy is lost and heat develops. The

energy loss may be considerable by the

time the shock wave reaches the bit,

and there will be thread wear and re-

duced life of the drillstring components.

The down-the-hole (DTH) system

was developed to overcome some of

the problems associated with hole strai-

ghtness suffered by tophammer drills.

Rigid guide tubes, with a large outer

diameter, were developed to keep the

drillstring on a straight course, and im-prove flushing. With a DTH hammer,

a series of tubes offers far greater stiff-

ness, and runs closer to the hole walls,

resulting in considerably less deviation

than with a tophammer drillstring.

Power with Rigidity

The COPROD system combines the

power of the tophammer with the ri-

gidity of the DTH drillstring. COP-

ROD rods move longitudinally within

each tube, transmitting the rock drill

energy to the bit. Lugs on the rods pre-

vent them from sliding out during han-dling.

During drilling operations, if the bit

enters a cavity and drops down in its

splines in the bit chuck, the hammer

senses it, and percussion is interrupted.

Rotation is maintained, however, and

percussion restarts automatically when

the bit meets resistance again.

Flushing air enters the bit via a cen-

tre channel, which connects to the cy-

lindrical surface in the bit rod. A small

amount of air, containing a little oil, es-

capes via the splines in the chuck and

the bit, and lubricates them. On its way

up, the flushing air travels between the

smooth outside of the tubes and the

hole wall, providing a constant cross

section, and ideal conditions for flush-

ing the drilling fines.

COPROD offers unique features for

drilling holes fast and straight. And the

more troublesome the ground becomes,

the more the incomparable drilling sy-stem comes into its own.

Thanks to the unique double recoil

damping system of the rock drills de-

veloped for use with COPROD, the rod

ends remain in permanent contact with

each other. Thus, there are near-zero en-

ergy losses at rod joints, and drilling

efficiency is maintained at virtually the

same level from the start to the final

depth of the hole.

Latest on COPRODThe new COPROD drill string features

a wide range of improvements. The

thickness of the drill tube has been in-

creased to 8.8 mm with a new, strong-

er female thread connection to the end

piece. This results in increased service

life, virtually eliminating tube break-

age, and helping to limit in-hole devia-

tion.

The end piece of the COPROD sec-

tion has been made shorter and rede-

signed with a new male T-thread con-

nection to the drill tube, eliminating

thread breakage. The diameter of the

CR 76 inner rod has been increased

and the end diameter of the CR 89 inner

rod matches the anvil to optimize serv-

ice life and penetration rate.

In the COPROD head, the bit rod

has been redesigned to eliminate the

rod guide. Closer tolerances reduce air

passage in the bit spline area to a mi-

nimum, preventing shank breakage,

while improved airflow reduces plug-ging of the bit. The drill bit itself is now

The new COPROD drillstring provide longer life and higher penetration rate.

ROC F9CR retrofitted with second generation COPROD drilling in Belgium.

New bit tube and bit rod

design for improved guidance

New design for improvedguidance and air flushing

New steel gradeincreases

bit service lifeStronger tube,

8.8 mm wall thickness

New rod guide design

New strong T-thread connection

between tube and end-piece

COPRODsectionCR76andCR89(lenght3.66m/12ft)

COPRODhea

dCR76-CR140


24/152

TALKING TECHNICALLY


made of a new grade of steel with high

impact and fatigue strength.

The diameter of the 89 mm COP-

ROD tube can be worn down to 80 mm

before replacement, and, with low air

pressure of only 12 bar, less airflow in

the annulus results in up to 50% longer

life.

Fractured Rock in Austria

Asphalt & Beton GmbH, the quarrying

division of Austria-based Strabag, pro-

duces 18 million t/y at 57 quarries in 11

countries. An Atlas Copco ROC F7CR

forms the backbone of the operation

at the companys 650,000 t/y Jakomini

quarry located on an Alpine slope in

the Bleiberg region of southern Au-

stria. The operation, which is mainlyquarrying fractured metamorphic dia-

base of 140-150 Mpa hardness, features

seven benches, each around 20 m-high.

Blasthole depths range from 20 m to

26 m, angled at 80 degrees. Presplit dril-

ling is carried out to maintain slope sta-

bility of the benches.

The ROC F7CR drills 92 mm-dia-

meter holes, using an impact pressure

of 120 bar during collaring, and work-

ing pressure of 200 bar. Nett penetra-

tion is 1 m/min, and each hole takesaround 20-30 minutes to drill. After

10,000 drill metres, the wear on the

drill tube was 0.5 mm, and five bits

had been consumed.

The benches are reached by steep

gradients, with inclines of up to 30%,

a real test of tractability and stability

for any drillrig, but one in which the

ROC F7CR excels.

The COPROD system of straight hole

drilling is ideal in the fractured rock,

which is subject to water influx while

drilling. It is also very fuel-efficient at

0.7 litre/drillmetre, just half of that ex-

pected from DTH rigs. Within a month

of delivery in 2005, the ROC F7CR

was averaging 25 m/h, and has since

achieved consistent monthly perform-

ances of over 31 m/h.

Abrasive Rock in Belgium

Belgian company DGO M3 is a mem-

ber of the French EPC Group, and

one of the largest drilling contractorsin Europe. With an annual production

of up to 115,000 drillmetres from 24

quarry sites around the country, the com-pany is heavily reliant on continuous

drill rig availability and production. It

has a fleet of Atlas Copco rigs, com-

prising a new ROC F9CR, a second

ROC F9CR retrofitted with the new

COPROD system and COP 2150 rock

drill, a ROC F7CR, and a ROC L6H

DTH rig.

The COPROD rigs equipped with

127 mm-diameter bits are used for hole

depths up to 30 m, while the ROC L6H

can go down to 45 m-deep. A wide

variety of rock types and formations isdrilled, ranging from medium-to-hard

limestone and sandstone to granite, por-

phyry and grit.

With COPROD, the company can

drill at any of its operations, giving it

the necessary flexibility to obtain very

high efficiencies. Using the lower air

pressure of 12 bar, the flushing air and

cuttings do not destroy the hole collar,

and a 20 % higher productivity is ob-

tained compared to the 25 bar DTH

rig. Rapid bit changeover times alsoensure that regrinding and frequent bit

changes do not cause undue delays. At

the sites, every drill pattern and blast isdesigned with Geolaser profiling of the

bench, and hole alignment is checked

with the Pulsar system.

There are currently ten COPROD

drill rigs operating in Belgium, nearly

all of which are located in the French-

speaking Walloon province. These are

served by Atlas Copco distributor SE-

MAT, based at Spy, near Charleroi.

SEMAT carries out any major re-

pairs and overhaul work for DGO,

whilst the contractor does its own we-

ekly servicing. DGO reports that, overthe last two years using the new COP-

ROD system, it no longer breaks tubes,

and has recorded a 50% improvement

in service life of the drill string. Every

six months, each rig is taken out of

operation for one week for a major ser-

vice, usually coinciding with a period

of slack demand. Nearly all COPROD

rig owners have increased the diameters

of their drill bits due to increased confi-

dence in maintaining correct hole align-

ment, allowing less holes to be drilledfor the same output.

ROC F7CR in the Jakomini quarry.


25/152

TALKING TECHNICALLY


Limestone in Taiwan

Ho Ping limestone quarry, at Hualien

in Taiwan, has a fleet of six Atlas Copco

ROC F9CR crawler drill rigs equipped

with the COPROD system and COP

1838 CR rock drills. In operation since

1981, Ho Ping is owned by Taiwan

Cement, and produces 12 million t/y of

limestone, making it the largest cementquarry in Taiwan.

Located about 1,000 m above sea

level, the quarry is one of a number

operated by Chien-Kuo Construction Co

on behalf of the country's major cement

companies. The company also operates

in the People's Republic of China, Viet-

nam, Indonesia and the Philippines.

Four Atlas Copco ROC F9CR rigs

joined the production fleet in 2001, and

another two units were delivered in 2002.

They are proving to be highly pro-

ductive at 25 drillmetres/h, and emi-

nently suited to the type of rock being

mined, which is loose and fractured.They are capable of drilling holes to

depths of up to 30 m, and diameters up

to 127 mm.

Site layout at Ho Ping is designed to

keep noise, vibration and visual impact

to a mini

9851 6549 01 complete_sdopm1.pdf

Documents