Blasthole Drilling in Open Pit Mining

Blasthole Drilling

in Open Pit Mining

First edition 2009

www.atlascopco.com

Introducing the new and expanded line of the Pit Viper Series drills from

Atlas Copco. The venerated PV-351, PV-275, and PV-271 are being joined

by the all new PV-235 series. And throughout the line, we’re crafting a

better user experience by improving your comfort, control and visibility.

Plus, our new power systems add to your bottom line with increased

fuel efficiency. So, whether you’re mining precious metal or mineral,

follow the line and mine with us.

We’re redrawing the line between

productivity and innovation.

C M Y CM MY CY CMY K

Find out more at www.atlascopco.com/blastholedrills

Introducing the new and expanded line of the Pit Viper Series drills from Atlas Copco. The venerated PV-351, PV-275, and PV-271 are being joined by the all new PV-235 series. And throughout the line, we’re crafting a better user experience by improving your comfort, control and visibility. Plus, our new power systems add to your bottom line with increased fuel efficiency. So, whether you’re mining precious metal or mineral, follow the line and mine with us.

We’re redrawing the line between

productivity and innovation

Foreword

Talking technically

Case studies

Product specifications

For latest updates contact your local Atlas Copco Customer Center or refer to www.atlascopco.com/blastholedrills

Contents

Front cover:

Pit Viper 271 working in Southwest US copper mine. Photographer: Scott Ellenbecker

Produced by: Atlas Copco Drilling Solutions LLC, PO Box 462288, Garland, TX 75046, USA, Phone +1 972 496 7400. Publisher: Ulf Linder, [email protected]

Layout: Rafaella Turander, ahrt informationsdesign, Örebro, Sweden, [email protected]

Editing team: Ulf Linder, Diane Norwood, Patsy Thomas, Nichole Schoch, Mark Bausch, Gunilla Lindberg, Marino Wallsten, Torbjorn Viberg Adviser: Dustin Penn, [email protected]

Contributors: Brian Fox, John Stinson, Dustin Penn, Clarence Zink, Rick Meyer, Leif Larsson, Darwin Hollar, Jeff Rose, Bo Persson, Guy Coyne, Ron Buell, Gunnar Nord, Sverker Hartwig, Jim Langford, Jon Torpy, Stig Fredriksson, all name.surname@country code.atlascopco.com William Hustrulid, Hans Fernberg, Stephen Boyce, Kyran Casteel, Scott Ellenbecker, Kenneth Moffitt, Ewald Kurt,

Digital copies of all Atlas Copco reference editions can be ordered from the publisher, address above, or online at www.atlascopco.com/rock. Reproduction of individual articles only by agreement with the publisher.

Printed by: Prinfo Welins, Örebro, Sweden. www.welins.se Legal notice

© Copyright 2009, Atlas Copco Drilling Solutions LLC, Garland, Texas, USA. All rights reserved.Atlas Copco is committed to comply or exceed all applicable laws, rules and regulations. Photos in this publication may show situations which complies with such laws, rules and regulations in the country where the photo has been taken but not necessarily in other parts of the world. In any case think safety first and always use proper ear, eye, head and other protection to minimize risk of personal injury. This publication, as well as specifications and equipment, is subject to change without notice.

Foreword

“If it can’t be grown, it must be mined.” It is a common saying in our industry, but it bears repeating. As the world population grows, mining must keep up to supply the material needs of people everywhere. Open pit operations continue to account for the majority of mined materials. In their 2008 Mining Project Review, Raw Materials Group (as published in Engineering & Mining Journal) shows open pit methods accounting for over 90 percent of planned capital expenditures for known projects. Atlas Copco is proud to be part of the open pit mining industry. The rotary and down-the-hole (DTH) blasthole drills and tooling we offer account for only a small part of an open pit mine’s capi-tal and operating cost. However, they play a critical role as they kick off the material movement portion of the mining process with the drilling of blast holes. No matter how powerful shovels, draglines or loaders might be, they can’t dig solid rock. Since the acquisition of Ingersoll-Rand Drilling Solutions in July 2004, Atlas Copco has made significant investments in

product development, technology, production facilities and customer centers around the world. We have established our-selves as a leader in open pit mining with machines running in widely varying operations and conditions across the globe. We’re happy to share some of these case studies and technical articles with you, and anticipate that the information can be put to use to help improve the productivity and reliability of open pit mines everywhere.

Going forward, we will continue to aggressively develop new and improved products aimed to safely increase production and minimize operating cost and downtime. We can only do this through interaction with our mining customers. We encourage feedback from the production and maintenance personnel who work with our rigs to help guide our improvements, and hope to be able to share our mutual success stories in future editions of this Blasthole Drilling in Open Pit Mining reference guide.

We hope you enjoy this first edition.

Brian Fox

Vice President, Marketing Drilling Solutions LLC

gunpowder

The application of blasting agents apparently began in Hungarian mines sometime during the sixteenth cen-tury. To make better use of the explo-sive force, miners started to place the powder in holes and it is certain that drilling and blasting were used in sev-eral German and Scandinavian mines early in the seventeenth century, for instance at the Nasafjäll silver mine in Lappland in 1635, and in 1644 at the Röros mine in Norway.

One-man drilling with the help of a drill steel and sledgehammer was

the established technology used in the eighteenth century. This physically demanding technique evolved only slowly but, despite the mechanization of other industries, remained in quite widespread use until well into the twentieth century. However, powered drills did start to mount a challenge in the 1800’s, the competition in the USA being symbolized by John Henry who in 1870 hammered through 14 feet in 35 minutes while the steam drill only completed nine feet.

The first patented rock drilling ma-chine was a steam driven percussion drill invented by J. J. Couch in Phila-delphia in 1849 but it may have been preceded by a machine manufactured by the Scottish engineer James Nasmyth ten years earlier. This patent spurred a period of rapid development, acceler-ated in the 1860s by Nobel’s inventions of the blasting cap and safe dynamite explosives. From 1850 to 1875 some

110 rock drill patents were granted to American inventors and seven for drill carriers while 86 patents were issued in Europe during this period.

In 1851 James Fowle, who had worked with Couch, patented a rock drill that could be powered by steam or compressed air and could rotate the drill steel by means of a ratchet wheel controlled by the piston's back-and-forth movement. In the 1860’s large scale rock drilling machines were built for tunnelling by engineers in Europe and the United States. One of the most successful of these early rock drills was the second refined version of the Burleigh rock drill, which was put into service in October 1866 at the Hoosac tunnel in Massachusetts. The perform-ance at this tunnel project showed that rock drill development had taken the step from an experimental product to a proven and rather reliable technology.

The Pit Viper is designed for production drilling of large holes in hard rock conditions.

From gunpowder to Pit Viper

Drilling and blasting

Drilling with sledgehammer was the established method before the development of the rock drill.

In 1871 the American inventor Simon Ingersoll patented a steam powered rock drill, later to be operated on compressed air. Ingersoll formed the Ingersoll Rock Drill Company in the same year, during the following year purchased the Fowle-Burleigh patents and also merged with the Burleigh company. The new com-pact rock drill launched by Ingersoll was a simple and strong design with few moving parts. The designers had kept in view the tough conditions in which the rock drill had to work, and the contemporary technical opinion regarded his new rock drill as the best yet available on the market. During the years to come Ingersoll bought out many small firms and expanded his company. The Ingersoll Rand name came into use in 1905 through the combination of Ingersoll-Sergeant Drill Company and Rand Drill Company.

The AB Atlas enterprise had been founded in February 1873 at a time when the Swedish railway net was being rapidly expanded. Three years later, now with 700 employees and the Stockholm shops completed, AB Atlas had delivered more than 600 railway wagons. Diminishing demand from the railroad sector, combined with years of losses, led to a reconstruction in 1890. During the years to follow new product lines were added, including compressed

air tools, compressors, diesel engines and the first Atlas rock drill which was launched in 1905.

Further development

The design of the first Atlas rock drill featured an advanced rifle bar rota-tion but with a weight of 280 kg (617 lb) it was very heavy for manual use. Immediately and for the next 25 years Atlas focused on light weight hand rotated drills like the Cyclop, Rex, and Bob. The real Atlas winner among lightweight hand-held rock drills was the RH-65 from the year 1932. This machine had more efficient shank and chuck designs for better steel guidance

and longer shank life. Used with the new pusher leg feed system developed in the 1930s, the RH 65 was the most important element in what was later to become known as the "Swedish method" of underground drilling.

In the United States Ingersoll-Rand expanded into pneumatic tools in 1907 by acquiring the Imperial Pneumatic Tool Company of Athens, Pennsylvania. In 1909 the company bought the A.S. Cameron Steam Pump Works and en-tered the industrial pump business. Ingersoll Rand also acquired the J. George Leyner Engineering Works Com-pany. This firm had developed a small, pneumatic hammer that could be operated by one man. This “Jackhamer”

The Ingersoll rockdrill was a simple and strong design with few moving parts. In 1871, a number of patents were issued to the

inventor Simon Ingersoll, who started the Inger-soll Rock Drill Company The machine produced by Ingersoll was at this time regarded as the best rock drill yet produced, and it was followed in the mid 1880s by another success, the famous “Ingersoll Eclipse” machine.

The first drill made by Atlas "pneumatic rock drill No. 16" had a weight of 280 kg (617 lb) and was heavy and difficult to handle - at least two men were needed to move it.

introduced in 1912 became a popular item, and the company progressively developed the design as well as sup-plying compressors to the expanding construction and mining industries in North and South America

Rock drilling tools

The parallel improvement of drill steel quality had started during the 1890s with development of heat treated drill steel that could better resist deformation. But sharpening the tips required exten-sive haulage of tons of drill steel between drilling sites and the work shops. The detachable drill bit was developed in 1918 by A L Hawkesworth, a foreman at the Anaconda copper mine in Butte, Montana. The first versions used a dove-tail joint to the drill steel while later ver-sions were threaded or tapered. The rods were retained at the workings and used with new or re-forged bits.

In Europe during the German col-lapse in 1918 a team was formed at the Osram lamp factory to develop cemented tungsten carbide as a substi-tute for industrial diamonds. In 1926 the first cemented tungsten carbide became available as a “magical” machine tool for turning and milling operations. Early tests were made in 1928 trying to use tungsten carbide bits for rock drilling in German mines and before World War II promising results were obtained. By this time the research team had scattered and some members had been forced to leave the country. One of these, Hans Herman Wolff, found refuge in Sweden where he worked at the Luma lamp fac-tory. Dr Wolff manufactured a number of bits according to designs provided by Erik Ryd at Atlas. The bits were tested in the Atlas test mine. In 1942 Atlas, Sandvik and Fagersta signed a coop-erative agreement and it was not until 1945, after a long improvement process, that the new cemented tungsten carbide drill bits were as economical to use as conventional steel bits.

The post-war years saw Atlas achieve further major advances. In 1948 the com-pany introduced an RH 65 upgrade, the RH 656, which was designed to use the new cemented carbide tipped drill-steels.The superior performance of the “Light Swedish Method” was exploited

worldwide and culminated in 1962 with the completion of the Mont Blanc tunnel. With development of highly mechanized drill rigs and with the introduction in 1973 of the COP 1038 hydraulic top hammer drill Atlas Copco laid the foundation to become a world leader in top hammer drilling technol-ogy. (See article from wagon drill to SmartRig, Surface drilling, Fourth Edition 2008).

Rotary bits

Rotary drilling with drag bits was the common method used in oil drilling. These bits were suitable when drilling in soft formations like sand or clay but not in rock. The solution for drilling large diameter holes in rock was by using rotary crushing technology instead of trying to cut hard rock with drag bits. The roller cone bit was developed by Hughes and Sharp, and the US patent for a dual roller cone bit was issued to Howard Hughes Sr. in 1909. This new type of bit had two interlocking wheels with steel teeth, and penetrated the rock by crushing and chipping. The success of the new bit led to the founding of the Sharp-Hughes Tool Company, and after Sharp's death in 1912 the name was changed to Hughes Tool Company.

The company continued develop-ment of the roller cone bit and in 1933 two Hughes engineers invented the tricone bit. This bit had three conical

rollers equipped with steel teeth. Drilling was accomplished by trans-ferring a pulldown force to drive the teeth into the hole bottom. The three roller cones turned as the drill string was rotated, and the teeth crushed and spalled the rock.

While tophammer drills could be used for small blast holes in rock, this method was not suitable for large hole diameters; for these rotary drills were

the best alternative. However, as drill-ers sought to use the rotary system for progressively harder rock formations so the feed force (pulldown) available had to be increased. Roller cones with long steel teeth were used in softer forma-tions for gouging the formation while roller cones with shorter teeth were used for crushing and spalling harder formations.

The US patent for a dual roller cone bit was issued to Howard Hughes Sr. in 1909.

The Secoroc Tricone bits are now regarded as the ultimate blasthole bit solution.

A parallel development of the tri-cone bits made it possible to use these high loads on bits. To extend the life of the bits in hard and abrasive rock the steel teeth were replaced by cemented tungsten carbide inserts. Tungsten car- bide inserts have significantly increased the number of blast holes that the roller cone bits are able to drill. Improvements in materials have continued to increase the life of the bearings so the cutting structures can be fully utilized. While the geometry of the roller cone bit is much the same as the original bit pat-ented in 1933, the material and technol-ogy currently utilized is cutting edge.

Downhole drilling

technology

Meanwhile, manual lightweight pneu-matic drills had also underpinned the expansion of bench mining in open cut mines and quarries. But in the 1930’s downhole drills (DHDs ) were intro-duced for drilling deeper holes. The main initial development of this technology took place in Belgium and the United States. Atlas designed a downhole unit in the mid-thirties that was used with

good results in two Swedish limestone quarries until the 1950s but the company then ceased further DHD development, only re-entering the market in 1969 with the COP 4 and COP 6 down-the-hole hammers.

In 1955 Ingersoll-Rand introduced a new downhole drill design and started to establish downhole drilling on a truly commercial basis. The Tandematic, which at the time was claimed to pro-vide the highest drilling speed ever attained by a downhole drill, was sup-plied in two standard sizes – the DHD 275 for 4¾* inch and 5 inch holes and the DHD 1060 for 6 and 6½ inch . This later enabled the company to build drill rigs adapted to be used either for rotary drilling or with downhole hammers. The main difference is that downhole drill-ing requires more air, and consequently these drill rigs had to be equipped with a larger capacity compressor and a more powerful diesel or electric engine.

Downhole drill technology went through rapid change in 1960’s and 70’s. In fairly rapid succession I-R developed the DHD 325 ( their first 6" hammer), DHD 325A, DHD 16, DHD 1060, DHD 1060 A and B models, DHD 360 (all 6"

drills) and corresponding larger and smaller models, up to the current line of DHD’s. Probably the most significant change in DHD technology was the advent of the valveless DHD. Drill effi-ciency and life dramatically improved with the elimination of the flapper valve. Of course higher pressure and volume air from the air compressor advance-ments produced the performance one sees today. Re-entry to the downhole drill market at 6 bar** in 1969 also ena-bled Atlas Copco to take advantage of improved air compressors and develop more and more powerful downhole hammers, reaching 18 bar in the early 1980s and more recently 25 bar and 30 bar in the larger current hammer sizes.

Drill rigs

The mobilization of rotary and down-hole drills was linked to significant post-war changes in rotary drilling technology. Up until then rotary drill-ing had been used in water well drilldrill-ing and surface mining using fluid circu-lation to clean cuttings from the hole. Coal mines were using rotary drilling in soft overburden, removing the cuttings with augers. In the late 1940’s it was rea- lized that air was an effective flushing medium with considerable advantages over water, doing a better cleaning job, protecting the bits and eliminating the difficulties of supplying water.

Experience also proved that air flu-shing improved the penetration rate of rolling cutter bits such as tricone bits and extended their life. By using effi-cient air flushing to keep the bottom of the drill hole free from cuttings the rock breaking process became more efficient.

In 1948, Ingersoll-Rand entered the large-diameter blast hole market by launching the Quarrymaster. It really was not a rotary drill, but a large self

The Quarrymaster from 1948 was equipped with a huge 8" bore drifter. Secoroc downhole hammer (DHD), also named Down The Hole hammer (DTH)

propelled mounting in the 40,000 lb weight range, designed with on board air and a long drill tower to drill 6 inch to 8 inch diameter holes for mining and quarry applications. The original Quarrymasters were equipped with a huge 8" bore drifter, know as the QD8. This was a piston drill with the drill steel attached directly to the drifter piston. The blow frequency was in the range of 200-300 blows per minute. The drifter used a large rifle bar rota-tion system. Achieving decent wear life between the rifle bar and rifle nut was sometimes a problem in tight ground. This was a single pass drill system, hole depth was limited by the tower length. The steel system was a heavy wall tubular product, in the range of 4" OD, and was extremely heavy. Since there was no steel change, the weight didn’t seem to be much of an issue.

Quarrymasters were used in some large iron mines in Canada and the Atlantic City Iron Ore Mine in Wyoming. Numerous Quarrymasters were used in the rock excavation for the St Lawrence Seaway in Canada.

In the same year also Atlas intro-duced its first mobile rubber tired drill wagons for top hammer drilling, but these were not equipped with any tram-ming machinery and were intended for considerably smaller hole diameters. I-R development work with downhole drills in the early 1950’s brought about changes to the drill mounting business. First, the Quarrymaster was equipped with the newly developed QRD rotary head, and this along with the new DHD 325 down hole drill, made for a produc-tive but heavy and bulky package.

The Drillmaster design, a somewhat smaller rotary drill, was introduced about 1955. It produced the same

perform-ance as the Quarrymaster in a smaller and less costly package. Upgraded versions of the Drillmaster, the DM-1, DM-2 and DM-3 followed in quick succession. Originally equipped with sliding vane air compressors up to 900 cfm*, all were updated to the screw compressor design. The Drillmaster line was equipped with the DRD and later DRD 2 rotary head to provide drill string rotation. As with the QRD rotary head the DRD was powered by a vane air motor and several steps of gear reduction. All of these drills only used hydraulic power, from an engine driven hydraulic pump off the cam shaft, to operate the jacks, tower raising cylin-ders, break-out wrench, and dust collec-tor drive mocollec-tor. Neither rotary head was very useful in supplying straight rotary power for tricone bits, hence the future development of the T-4 and DM-4 with hydraulic powered rotary head for straight rotary drilling. I-R’s first truck drill was called the Trucm package. The drill frame package was mounted on a customer provided truck, often a used Mack truck. However, none of the standard truck designs proved very successful. The normal channel truck frames were not sturdy enough, result-ing in many cracked and broken truck

frames. I-R’s answer to this problem was to join hands with Crane Carrier Corp of Tulsa, OK, and mount the drill components and tower directly on an I-beam chassis frame, often used for mounting construction cranes. This product became the TRUCM-3 and the same style mounting carried over to the T-4 and T4W introduced in 1968.

A major new stimulus for blasthole drilling rig development generally was the introduction in the 1950’s of mil-lisecond delay blasting. This allowed

Big picture; Airpowered DM-3 with a DRD-2 Rotary head from the late 1950's. Inset; Tractor mounted Drillmaster, air powered with a DRD Rotary Head from the early 1950's.

Rotary table and Kelly bar concept.

The truck mounted T4BH was introduced in 1968. * 100 cfm = 47.2 l/s

blasters to design multi-hole large volume blasts that could be used for mass production techniques in open cut drill and blast mines. In turn this required the introduction of large, mobile drilling rigs able to drill large diameter holes using tricone bits, as well as the formulation of cheap bulk mining explosives based on ammonium nitrate and nitro-glycerine. These and other developments helped the mining industry to keep the costs of bench drilling substantially unchanged during the 1950s and 1960s, despite increasing wage costs.

The Quarrymaster and TRUCM machines were made progressively more self-contained through the 1950s. By the end of the decade the air supply was up to 10 bar and the marketing slogan “Pressure is Productivity” was promoted. The drill rigs and rock drills were sold together to maximize revenue but this did encourage other manufactur-ers to build competing rock drills.

hydraulics technology

adds to drillers options

The similarities between the air require-ments of rotary and downhole drilling

made the design of rigs able to do both an economically attractive proposition. In 1965-66 Ingersoll-Rand started work on the switch to hydraulic powered rotation for rotary and downhole drilling, launching first the truck-mounted T4W for water well drilling in 1968. In the same year this rig was modified to make a truck-mounted blasthole rig with a 5-rod carousel, the Drillmaster T4BH, which could drill holes of up to 7⅞ inch diameter and was successfully offered for coal mine drilling through-out the 1970s. The designers also used the power unit, tower and other com-ponents to create the crawler-mounted Drillmaster DM4 blasthole drilling rig. This machine was designed from the ground up for both rotary and downhole drilling. A 36 ft* high tower incorpo-rated a hydraulically indexed carousel housing seven 25 ft rods. The rotary head featured an axial piston hydrau-lic motor and single-reduction worm gear for rotation, providing 5.6 kNm of torque and rotation speeds from 0 – 100 rpm. There was a choice of diesel engine or electric motor for the spring mounted floating power pack and a range of diesel or electric compres-sors, enabling use of either rotary or downhole drilling with the company’s DHD-15, -16 or -17 downhole drills. The excavator style crawler undercar-riage had tracks with 22 inch triple bar grousers driven by hydraulic motor through a planetary gear drive and chain reduction.

In the marketplace the DM4 com-peted with the more powerful electric top drive blasthole drilling rigs. The late 1960s and 1970s saw heavy take- up of the DM4 rig by the Appalachian coal mines in the United States. And the combination of patented rig, drill and drill rod technology was very profitable for Ingersoll-Rand. The use of hydraulic power for rotation and non-drilling functions meant that more air could be made available for rotary and, especially, for downhole drilling. This engendered an “air race” in the late 1960s and 1970s. The independent downhole drill manufacturers were able to build machines that could drill at 130 ft/hour in the 6 – 8 inch diameter hole range – faster than a rotary drill could achieve in this hole size range,

particularly when drilling in harder rock types.

The development of screw compres-sors to supply air for drilling rigs at up to 20.6 bar led to the 1970s introduction of an airend to supply both low pres-sure and high prespres-sure air. These units were used in portable air compressors and also onboard drilling rigs, where they enabled downhole drills to outper-form rotary drills in the 6 - 8½ inch hole sizes in hard rock mines. However, rotary drills were still better for rock compressive strengths up to medium hard limestone.

The higher pressures were also very beneficial for water well drilling, in which air pressure must be sufficient to evacuate the ground water pressure from the hole while drilling.

expansion of the

Drillmaster range

Significant corporate developments and one major product launch impacted the Ingersoll-Rand drilling business in the mid-1970s. Firstly, in 1973 the company acquired DAMCO (Drill And Manu-facturing Company) in Dallas, Texas, who built mechanically driven pre-split drilling machines for quarrying and light coal stripping. These expanded the Drillmaster range down to the 20,000 lbf* bit weight class. The rigs also used the rotary table drive and kelly bar concept, which lightened the tower structure sufficiently to accommodate rod long enough to drill 40 – 50ft holes in a single pass if required. Ingersoll-Rand added their own compressors to create the DM20, DM25, DM25-SP (single-pass), DM35 and DM35-SP rotary rig models. Then, in 1975, the company bought the Sanderson Cyclone Drill Company in Ohio, USA, adding 12 models designed for the water well market.

The next extension of the size class range came with the launch of the Drillmaster DM50 with 50,000 lbf of weight on the bit. In this machine the diesel engine drove the hydraulic power pack from one end of the crankshaft and the compressor was directly coupled to the other. This concept was also used on the next two drills to be launched. The first one was a new crawler mounted

The DM50 could use bit loads up to 50,000 lbf and was launched in 1970.

* 1 ft = 0.304 m

rig for rotary or downhole drilling, the DM45 with 45,000lbf weight on bit. This was followed by a conceptually similar top drive rotary or DHD model, the DM30 and a specialized rotary table variant, the DM-35I, which was intro-duced in the 1980s for drilling underwa-ter in phosphate mines. It featured a dual kelly system that allowed explosives to be charged through the annulus between the outer and inner kelly. The inner kelly would then be removed for blasting. Later the DM 40SPi was developed for drilling and shooting deeper holes.

Development of large

blasthole drills

Towards the end of the seventies, the company started designing drill rigs more specifically aimed at the base metal mining market, using power pack concepts developed for deephole drilling. So far, neither air-powered nor hydraulic drive rotary nor downhole drills had challenged the electric motor top drive rotary rigs manufactured in the United States for the 12 – 15 inch diameter hole market. These machines by now had very high weights on bit in the range 100,000 – 120,000 lbf, partly due to the weight of the electric motor for the rotary head, but were not suitable for live tower operation. Ingersoll-Rand’s first response was in 1979 with the development of the Drillmaster DM70, able to drill 10 inch diameter holes in metal mines and up to 12½ inch holes at coal mines using 8.6 bar air for rotary drilling. And in 1979 the company launched the DM-H (Drillmaster – Heavy), the first truly modern large blasthole drilling rig to be used for low pressure rotary drilling of 9 7_{/8 - 12} 1_{/8 inch holes with bit loads}

up to 90,000 lbf.

The DM-H used hydraulics for both drilling and non-drilling functions and featured a hydraulic propel excavator type undercarriage with easily replace-able grouser pads and in-line compo-nents on the deck. It was equipped with a rotary screw compressor and a “live” tower with patented angle drilling system. The tower pivot point was flush to the drill deck and within the dust curtain, reducing the length of unsup-ported drill rod. It was an all-purpose

machine, with a single-pass version added in the mid-1980's. The machine has been upgraded over the years al-though replaced by the Pit Viper 351 for hard rock applications.

At much the same time the company started to offer electric powered ver-sions of the DM 45 and other models if customers wanted them, for instance for use in open pits where the other key equipment was electric powered. However, although these machines had electric motor power packs they retained the hydraulic rotation system. The first electric drill rig was the DM7B delivered to Clarksburg in 1977, followed a year later by the DM100 delivered to Rock Springs.

After recovery from the recession of the early 1980’s, Ingersoll-Rand launched a medium range Drillmaster, the DM-M designed for rotary drill-ing of 9 7_{/8 inch holes with bit loads up}

to 60,000 lbf. Three of the first four DM-M's went into operation at Peabody Energy's new North Antelope & Rochelle Mine in the Wyoming Powder River Basin, now one of the two larg-est coal mines in the world. Now, over 25 years later, the prototype DM-M is still in operation. The machine featured a carriage feed system with wire rope cables, resulting in a lighter tower and lower center of gravity.

In 1989 this model was upgraded to the DM-M2 on which maximum bit load was increased to 75,000 lbf and the hole size capability extended up to 10 5_/

8

inch. Stability was improved as well. In 1990-91 the company intro-duced the DML for multi-pass drilling to 180 ft hole depth.

This new model could drill from 6 to 9 7_{/8 inch (200 – 250 mm) diameter}

holes in rotary mode, and 6 – 8 7_{/8 inch}

using a downhole hammer. Following a development project based on a customer consultation exercise the DM-M3 was launched at MINExpo 1992. Designed primarily for deep drilling of overbur-den for cast blasting in large coal mines, the first production DM-M3 went into operation in 1993 at Arch Coal's Black Thunder Mine, one of the largest coal mines in the world.

For this new model, the designers rai- sed bit load to 90,000 lbf and the hole diameter range up to 12 ¼ inch while a

Milestones in development

Year Model Load on bit

1948 Quarrymaster drifter 1955 DM3 30,000 lbf 1968 T4BH 30,000 lbf 1969 DM4 40,000 lbf 1970 DM50 50,000 lbf 1979 DM-H 90,000 lbf 1983 DM-M 60,000 lbf 1990 DML 60,000 lbf 1992 DM-M3 90,000 lbf 2000 PV-351 125,000 lbf 2004 PV-270 75,000 lbf 2008 PV-235 65,000 lbf The DM-H, launched in 1979, could be used with bit loads up to 90,000 lbf (400 kN).

The first Pit Viper 351 was launched in 2000 and used at the Morenci copper mine in Arizona.

new patented cable feed allowed the use of 40 ft long drill rods.

The launch of the Pit Viper

Although difficult market conditions restricted investment in the mid-1990’s, during 1997 the company started work on a new generation blasthole drilling rig design.

To differentiate this new range from the Drillmaster series, which initially was designed for drilling large holes in coal mining and soft rock, this new series was - from the very beginning - specified and designed for produc-tion drilling of large holes in hard rock conditions.

The first one out was the Pit Viper 351, which was successfully launched at MINExpo 2000. Weighing 170 tonnes, measuring 53 feet long, and equipped with a CAN-bus control system with seven on-board computers, the new Pit Viper 351 was at that time the largest and most advanced drill rig of its kind. The advanced control system allowed the drill pattern to be transmitted to the drill rig via a radio network, and it also featured production monitoring, rock recognition and a GPS navigation system.

A few months after the Minexpo show, in April 2001, the PV-351 was put to work at the Morenci copper mine in Arizona for final testing and evalu-ation. The mine had a fleet of 16 drill rigs from a variety of manufacturers, so in addition to the new rig being used for drilling in the hard igneous rock condi-tions, this was an excellent opportunity for benchmarking the PV-351 with the other brands.

The application required 12 ¼ inch diameter single pass drilling of 57 ft deep blastholes using up to 90,000 lbf weight on bit (of the 125,000 lbf capac-ity). The test was successful: the PV-351 drilled some 2.2 million feet by August 2004 at a recorded average rate of 60,000 feet per month and in some months even more than 80,000 feet per month.

Later the same year the multi-pass Pit Viper 275 was launched at MINExpo 2004. Based on the experience from the PV-351, combined with customer con-sultations, a project had been initiated for development of the PV-270 series. These drills were specified for a 75,000 lbf bit load capacity and were featured a similar cable feed system and auto-matic cable tensioning to that on the larger PV-351. The multipass version PV-275 with a 195ft depth capacity was

delivered for a test in December 2003 at Peabody's Kayenta coal mine in Arizona where it was used for cast blast drilling for removal of the overburden. This first machine is still in use there and, as a result of the good performance, the mine decided to invest in several addi-tional units. One of these is prepared for quick change between a multi-pass and a single-pass tower as an option to be adapted for different applications at the mine.

The first mine to use the single pass version, the PV-271, was the Barrick Goldstrike mine near Elko, Nevada. Since the PV-271 arrived at the mine in April 2004 it has been problem-free, and holds an impressive track record with an average penetration rate of 199 ft per hour. The long component life and also the automatic tensioning adjustments for the cables are much appreciated by the mine.

Following this tradition of product launches in Las Vegas, the latest addi-tion to the Pit Viper series - the PV-235 - was shown at MINExpo 2008. This is an advanced mid- range drill for bit loads up to 65,000 lbf, with the RCS Rig Control System available as an option.

acknowledgements

Editors: Kyran Casteel and Ulf Linder Contributions: Guy Coyne, Ron Buell, Kenneth Moffitt, Brian Fox, John Stinson, Dustin Penn, Gunnar Nord, Sverker Hartwig, Jim Langford, Diane Norwood, Darwin Hollar, Ewald Kurt.

Big picture: The electric PV-351E at the Boliden Aitik Mine. Inset: The workplace of today with RCS control and automated functions.

ergonomics and safety for

operators

Today much has changed with regard to operators, machines and machine interfaces. Twenty years ago the indus-try took a macro view of an operator’s ability to complete a shift without tiring or having an accident. Today designers work to a micro requirement; neither a hand nor a finger must be injured over a 30-year career doing the same func-tion.

In the past the requirements were for gauges and levers to be properly placed to avoid human strain during the work shift. Now engineers analyze site paths, a process of ensuring that natural hand motions are used to operate equipment. The drive for safety and efficiency are integrated.

Not only does the manufacturer look at drilling as the sole function of an operator. A multi-skilled operator may also manage drilling consumables, com- plete basic maintenance and report de-tails of bench conditions. These new roles also must be designed into the ma- chine interfaces.

Also with regard to improved ergo-nomics and safety, Drilling Solutions engineers work to design systems that eliminate or reduce the hazards. In the late 1990s when the United States Mining and Safety Administration imposed stric- ter silica exposure limits for operators, engineers found that improved air qu-ality could not be achieved without re- moving the concentration levels in cer-tain applications. The drive then became to manage the dust rather than improve air quality through expensive filtration. The goal of Drilling Solutions is to al- low the operator to do what comes na- turally and to create a work environ-ment that provides superior comfort and safety.

Operator cabins and

machine interfaces

A rotary drill is recognized as one of two pieces of surface mining equipment that sits and works in its waste, heat and dust. The other piece is the shovel or ex- cavator. The operator’s cabin, or cab, is the device used to protect the operator, a design factor not seriously considered as late as 1995.

Nearly everyone would agree today’s automobiles are safer, quieter, offer a smoother drive and are very user fri-endly. The automobile is becoming the acceptable standard in industry when looking at operator cabins. The visual look of an operator cab has also become a design criteria, as personnel equate past operator cabs with a metal box that induces high fatigue. An automotive’s structure and safety systems keep passengers safe. Likewise today’s drills are engineered to protect an opera- tor against hazards that once injured or killed operators.

Reference dust management improvement.

ergonomics and safety

Machine

developments in

a new decade

The image above shows a rock fall that the operator survived without in- jury. Using proper de sign techniques and better materials. Atlas Copco en- gineers have delivered an operator cab that reduces interior noise levels signif-icantly below the industry benchmark

of 80 dBA. For example, the Pit Viper 351 with 1500 hp was measured below 70 dBA when drilling.

Like automotive climate control sys-tems are developed to maintain opera-tor comfort more efficiently, today’s systems direct the cooling effort on the operator. The systems are also used to defrost windows in cold weather cli-mates just as automobiles do. Drilling Solutions engineers also are working to advance the cleanliness of the air the operator breathes.

Engineers can use computer models to quickly improve line of site. Cabs now feature more window space, which improves visibility, due to glass and in- sulation technology. Camera technology

allows an operator to watch the areas where visibility is restricted. The com-bined effect is to give operators a full view from the operator’s chair.

The operator chair and flooring play active roles in reducing drilling vibra-tions, which add to operator fatigue. Now an operator’s chair is often referred to as an operator’s pod, and is adjust-able to fit a variety of shapes, sizes and weights. All machine interfaces are now within the operator’s reach.

Technology can also play a role in protecting the operator from dangerous work conditions. Drilling Solutions en- gineers, working with suppliers, are creating a system that allows limits of operation to be defined and to give an operator feedback when an unsafe condition exists. As drilling conditions change within the pit, the machine can be easily reprogrammed to fit the new situation.

The result of this combined effort is to deliver a safe, comfortable work environment that is suited for the long shifts required in surface mining.

Maintenance ergonomics

Nearly unheard of a decade ago, in-dustry standards now require safe, rou-tine and easy access to all maintenance points. In the 1990s the Australian New South Wales MDG-15 Act gave guide-lines for maintenance ergonomics that have become the accepted standard in industry today, and these standards, in addition to factors such as fatigue and safety, drive the machine design effort.

For example, Australian studies sho- wed a very high incident rate for person-nel getting on and off machines. These results drove the international market to look at alternatives. As a result, place- ment of key maintenance points could only be in a zone from waist to shoul-ders, based on measurements for 90 percent of the population. Until fairly recently, operator comfort and safety were only afterthoughts – if they were considered at all. Now, what was once “out of sight, out of mind,” is a critical requirement at the forefront of design innovation.

John Stinson

Operator survived rock fall.

Comfort combined with ease of operation in one package.

The image shows digital readouts of weight on bit, rotation speed, torque and rate of penetration. It also can be programmed to give an operator visual feedback. The image shows a digital leveling device on which the background can change colors, sound an alarm or remove power when an unsafe angle of operation is

an increasing demand

Today, the population of the world stands at about 6.5 billion people. In simple terms, this means that every year approximately 10 tons of material is extracted using surface mining tech-niques for every person in the world.

If one looks to the future, the UN esti-mates that in 20 years (2038) the world’s population will have reached about 8.5 billion people. By simply applying the current utilization rate of 10 tons/ person, one would expect the amount of material extracted yearly by surface mining techniques to climb to 85 billion tons. One must keep in mind, however, that today about 95% of the population growth is in the developing countries of the world. Based on their expecta-tions for improved living standards

in the future, the actual estimate of ma- terials mined using surface mining tech- niques in the year 2038 is 138 billion tons (Bagherpour et al, 2007).

The ability of the earth to meet this type of demand is not really a question of resources, since they are clearly there, but rather a matter of price and cost. In looking at the mineral resource base, one must conclude that, in gener-al, the mining conditions will be sign- ificantly more difficult than today. In addition, ever-increasing environmen-tal and health and safety conditions are expected to be in place. This means that the entire mining process from pro- specting to exploration to development to extraction and finally to reclama-tion will have to become much more advanced. In many places of the world today, mine closure must be fully and satisfactorily addressed before a surface mine can be opened. This translates into requirements for applying first rate

engineering and technology for meet-ing today’s requirements and especially those of the future. Atlas Copco is at the forefront in producing the equip-ment and technologies required today and for addressing the challenges of the future.

a brief synopsis of

quarrying and open pit

mining

This introductory chapter will focus on those surface deposits that require the application of drilling and blasting techniques as part of the overall extrac-tion process. Excluded from the discus-sion will be strip mining, the mining of sand and gravel deposits and the quar- rying of dimension stone.

As indicated, large quantities of raw materials are produced in various types of surface operations. Where the pro-duct is rock, the operations are known

Photo: Copper mine in the southwest USA.

an introduction to surface mining

The wealth

of nations

as quarries. Where metallic ore or non-metallic minerals are involved, they are called open pit mines. There are many common parameters both in design and in the choice of equipment.

When examining a deposit for poten-tial mining and even when expanding a current operation, one often employs a process called circular analysis. As

shown diagrammatically in Figure 1, the process consists of five components. Although the figure applies specifically for the open pit mining of ore depos-its, a similar procedure is followed for quarries.

One naturally begins with a descrip-tion of the deposit and using some as-sumed costs a preliminary pit design

is obtained. By adding the desired pro-duction rate into the model a propro-duction schedule is generated.Based on the schedule, one determines the required equipment fleet, staffing, etc. to satisfy the schedule. This leads allows one to calculate the capital requirements and the operating costs. With these now-estimated rather than assumed costs, the ore reserves are re-examined and design alternatives evaluated. Eventually, an overall financial evalu-ation is performed. The double-headed arrows indicate the highly repetitive nature of the process.

Quarries

A rather simple but useful definition of a quarry is a factory that converts solid bedrock into crushed stone. Quarries can be either of the common pit type or, in mountainous terrain, the hillside type. Pit type quarries are opened up below the level of surrounding ter-rain and accessed by means of ramps (Figure 2). The excavation is often split into several benches depending on the minable depth of the deposit. When the terrain is rough and bulldozers cannot provide a flat floor, a top-hammer con-struction type drill rig can be used to establish the first bench. Once the first bench is prepared, production drilling is preferably carried out using DTH- or COPROD techniques.

The excavated rock is crushed, scre- ened, washed and separated into differ-ent size fractions, for subsequdiffer-ent sale and use. The amount of fines should be kept to a minimum. Not all types of rock are suitable as raw material for crushed stone. The material must have certain strength and hardness characteristics and the individual pieces should have a defined shape with a rough surface. Igneous rock such as granite and basalt as well as metamorphic rock such as gneiss are well suited for these purposes. Soft sedimentary rock and materials which break into flat, flaky pieces are generally unacceptable. The final prod-ucts are used as raw material for chemi-cal plants (such as limestone for cement manufacturing, the paper and steel industries), building products, and for concrete aggregates, highway construc-tion, or other civil engineering projects.

Financial optimization

1. Capital and operating summation 2. Revenue 3. Cash flow statement 4. Marginal ore utilization

5. Rate of return Ore reserve analysis 1. Break-even analysis 2. Drill-hole evaluation 3. Pit design 4. Marginal analysis Production scheduling 1. Preproduction costs 2. Working room 3. Stripping ratios 4. Sequencing 5. Reclamation 6. Operating schedules 7. Financial 8. Constraints Equipment and facilities 1. Capital intensive 2. Equipment selection 3. Operating costs 4. Capital depreciation 5. selective mining Refined ore reserves 1. Cutoff grade 2. Marginal analysis 3. Design alternatives

Figure 1. Financial optimization using circular analysis (Dohm, 1979).

Quarries are often run by operators who sell their products to nearby contractors and road administrators. Because the products are generally of relatively low value, they are transport cost sensitive. Hence, wherever possible, quarries are discreetly located as close as feasible to the market. Special measures are requi- red to minimize adverse environmental impacts such as noise from drilling, vibrations from blasting, and dust from crushing and screening to the neighbor-ing areas.

Open pit mines

Two major differences between open pit mining and quarries are the geological conditions and the demands placed on the characteristics of the blasted material. For quarries, a majority of the rock products eventually delivered to the customers has only undergone crushing and screening in order to ob- tain the desired size fractions. An open pit metal mine, on the other hand, attempts to deliver the ore as pure as possible via crushers to a concentrator consisting of mills, separators, flota-tion and/or biochemical systems, etc. The resulting concentrates/products are eventually sent for further process-ing before emergprocess-ing as a final product. For certain metals, this latter process involves smelting and refining. The deposits mined using open pit meth-ods have a variety of sizes, shapes and orientations. Sometimes the distinction between the valuable material and the waste is sharp such as shown in Figure 3 and in other cases the distinction is more subtle - based upon econom-ics. As in quarries, the minerals are extracted using a series of benches. If the orebody does not outcrop, the over-lying material must first be stripped away to expose the ore. As the initial pit is deepened, it is widened. The pit geometry is controlled by a number of factors including orebody shape, grade distribution, the stability of the slopes, the need to provide access, operating considerations, etc.

For the geometry shown in Figure 3, a significant amount of waste must be removed (stripped) to access the next bench of ore at the pit bottom. Without jeopardizing slope stability, it

is of prime importance to keep the pit slope angle as steep as possible, thereby keeping the excavated waste to a mini-mum. There becomes a point where the quality of the material contained in the next “ore” bench is not sufficiently high to pay the costs of the associated waste. At this point in time either the open pit mine closes or, if conditions are

favorable, continuation may proceed us- ing some type of underground method.

Figure 4 shows the Aitik copper/gold mine in northern Sweden. It is Europe’s largest copper mine producing 18 Mton of ore per year. Currently at a depth of 480 m it is expected to reach of depth of 800 m before decommissioning. The Bingham Canyon mine in Utah (Figure 5)

Figure 4. The Aitik mine in northern Sweden (www.Boliden.se).

O

re

bo

dy

Waste

Good fragmentation needed

Good slope stability

Pit slope 45o Bench

slope 72o

has been in production since 1906 and is one of the largest man-made struc-tures in the world, measuring 1200 m

deep and 4400 m across the top. It has produced more copper than any

other mine in history and has many years remaining. With respect to waste removal, the fragmentation demands are simple. Since, the material is not required to pass through a crusher, the maximum size is controlled by the li- mitations imposed by the equipment used to load and haul the material to the waste dump. On the other hand, good fragmentation of the blasted ore offers great savings in the total costs of the mineral dressing process.

Some forward thinking

Extraction of the valuable mineral whe- ther in quarries or open pits requires a number of unit operations. Generally, the rock is drilled, blasted, loaded, hauled to a primary crusher and then transported further to a plant of some type for further processing. Figure 6 shows a schematic of the process.

Often, mines are organized so that the individual unit operations are se-parate cost centers. Although there are advantages to this approach, one result,

Photo: Blasthole drilling of 40 ft (12 m) benches at Newmont's Phoenix mine, Nevada, USA. See page 91.

Drilling Blasting Loading Hauling Primary crushing Secondary crushing Grinding Mine Orebody Further treatment O ve ra ll fr ag m en ta tio n sy st em Mill

Figure 6. Diagrammatic representation of the overall mine-mill fragmentation system and the mine and mill subsystems (Hustrulid, 1999). Figure 5. The Bingham Canyon copper mine near Salt Lake City, Utah, USA. (www.kennecott.com)

unfortunately, can be that the individual managers look at minimizing the cost of their center rather than on the overall objective of overall cost minimization. In reviewing the components in Figure 6, it can be shown that they can be replaced by two operations, fragmen-tation and transport. In the simplified view shown in Figure 7, there are five different stages of fragmentation each with a different energy – product pro-file.

One must carefully examine the best opportunities for applying fragmenta-tion energy in the various stages on the final product cost. For example, in- creased fragmentation energy can be relatively easily introduced in the mine by modifying the drill patterns and explosive characteristics. This action may provide an inexpensive alternative to adding the fragmentation energy in the grinding circuit. This process of considering all elements of the frag-mentation system, logically dubbed “mine-to-mill” is a recognized part of

mine-mill optimization. In addition to production, there are some other important customers for blast engi-neering.One is termed the “Internal Environment” and the other the “Ex- ternal Environment.” These are shown in Figure 8.

Both for safety and economic rea-sons, it is important to preserve the integrity of the pit wall. Large diam-eter blast holes, energetic explosives and wide patterns will be used in the production blasts which will be subse-quently loaded out using large excava-tors and haulage units. Near the pit wall, much more precise techniques involving smaller diameter holes, specially de- signed explosives, and special timing procedures are employed to minimize wall damage (Figure 9). Unless great care is taken, large loading equipment can easily spoil the results of the trim blasting. The result is that special loa- ding and hauling fleets may be requi- red. Failure to protect the pit walls, translates into the need for flatter slopes

and additional waste removal and/or the loss of reserves. These, in turn, translate into higher overall costs for the mining operation. In carrying out an evaluation of the appropriate drilling and blasting practices, emphasizing mine-to-mill aspects without taking into account the care of the slopes can result in lo- wer production costs but at the sake of higher investment (capital) costs due to greater stripping or lost reserves. Therefore care must be taken to include all the costs when making the analysis. The “external environment” component falls into the category of a potential “show-stopper” since if proper meas-ures are not taken to fully comply with standards, the operation could very well be shut down.

Final remarks

Atlas Copco has the advantage of long experience in all types of surface drill-ing operations, with a product range to match. With its history of innovative

Drilling

Specified Drill Pattern

External environment

Minimum: Flyrock, noise, airblast, ground vibration

Loading & Haulage

Good: Fragmentation, Pile shape, diggability

Primary crusher

High throughput and bridging preventation

Secondary crushing & grinding

Efficient crushing and grinding feed

Internal environment

Minimum wall damage Blast Engineering

Drilling

Blasting

Loading & Haulage

Primary crushing Conveyor Secondary crushing Grinding Insitu Further treatment Fr ag m en ta tio n Tr an sp or t

Figure 7. The mine-mill system represented as fragmentation and transport unit operations (Hustrulid, 1999).

Figure 8. Simplified view of the five different stages of fragmentation, each with a different energy - product profile.

References

Bagherpour, R., and Tudeshki, H. 2007. Material handling in

world-wide surface mines. Aggregates

International. Pp 10-14. June. Dohm, G.C., Jr. 1979. Circular

ana-lysis – Open pit optimization.

Chapter 21 in Open Pit Mine Plan-ning and Design (J.T. Crawford, III and William A. Hustrulid, editors). AIME. Pp 281-310.

Hustrulid, William. 1999. Blasting

Principles for Open Pit Mining.

A.A. Balkema, Rotterdam.

Fernberg, Hans 2002, New trends in

open pits, Mining and Construction

1-2002

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.

William hustrulid hans Fernberg

Photo: Blasthole drilling and haulage at a mine in the southwest USA. Figure 9. Near the pit wall more precise

a complete range

With the acquisition of Ingersoll-Rand’s Drilling Solutions, Baker Hughes Mining Tools (BHMT) and Thiessen Team businesses, Atlas Copco has a complete range of products to offer to large quarries and open pit mines. Much of the world’s 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 hydrau-lic unit, the T4, in 1968.

about rotary drills

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 mo- ving parts and cut through rock by shea- ring 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 com-pressed air through the drillstring to drive the DTH hammer (see illustration page 20). 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 crush-ing and spallcrush-ing 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 via a feed system. Feed sys-tems utilize cables, chains or rack-and-pinion mechanisms driven by hydraulic cylinders, hydraulic motors or electric motors. The preference at Atlas Copco is to use cables for pulldown, as they are lightweight and inexpensive, and allow easier detection of wear to help avoid catastrophic failures.

Atlas Copco’s largest drill, the Pit Viper 351E, operates on a blast pattern at an open pit copper mine. Rotary blasthole drills are the predominant method of drilling 9 inch (229 mm) diameter holes or greater.

Putting rotary drilling

into perspective

Mining prosperity

Pulldown

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 than the biggest rotary blasthole rigs. In fact, the Pit Viper 351 rotary drill rig weighs in excess of nine times that of Atlas Copco's largest DTH hammer drill rig, the ROC L8. Yet the Pit Viper 351 is drilling a hole that is generally only twice the diameter. Take a typical medium formation tricone bit with a recommended maximum load- ing of 900 kg/cm of bit diameter (5000 lb per inch of diameter). With a 200 mm (7-7/8 in) bit, you could run about 18,000 kg (40,000 lb) of weight on the bit. The laws of physics dictate that for every action, there is an equal and opposite reaction, meaning that if you push on the ground with 18,000 kg (40,000 lb), the same force will push back on the unit. There-fore, the weight of the machine must be over 18,000 kg (40,000 lb) 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 blasthole drills are built to run 30,000 hours of operation, and some of the large blasthole drills have clocked over 100,000 hours of use.

Rig design

With the exception of one model, the rubber-tire mounted T4BH, Atlas Copco’s rotary blasthole drills are mounted on excavator-style undercarriages. Power-ful hydraulic-drive systems allow the machine to tram over a variety of ground conditions, though rotary blasthole drills should always operate on firm, flat benches.

Principle:

The hammer is situated down the hole in direct contact with the drill bit. The hammer piston strikes the drill bit, resulting in an efficient transmission of the impact energy and insignificant power losses with the hole depth. The method is widely used for drilling long holes, not only for blasting, but also for water wells, shallow gas and oil wells, and for geo-thermal wells. In mining it is also developed for sampling using the reverse circulation technique (RC drilling). TONS Principle: Rotation is provided by a hydraulic or electric motor driven gearbox, called a rotary head, that moves up and down the tower via a feed system, generating the pulldown required to give sufficient weight on the bit. Flushing of drill cuttings between the wall of the hole and the drill rods is normally done with compressed air.

The tower supports the drill string during drilling as well as the rotation head and feed system.

The key component of a rotary blast- hole drill is the tower, which is some-times referred to as the derrick or mast. Atlas Copco towers are four main mem-ber, open front structures in which the rotary head slides up and down via a guide system. The length and weight of the tower ultimately dictates the size of the mainframe and undercarriage.

Most drilling functions are hydrauli-cally 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 emissions, no refueling requirement and less maintenance. However, some operations are not setup with the pro-per electrical infrastructure or staffing to run electric units. Even when elec-tric power is available, many custom-ers avoid electric drills as the trailing cable used to provide power makes it harder to move the unit between holes or patterns. Generally, electric power

is preferred on large single-pass units used in major open pit metals mines where electric shovels are employed, though electric power is now available on smaller units such as the Atlas Copco Pit Viper 271, Pit Viper 275 and DML.

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 been developed to meet vari-ous drilling needs. Softer formation bits are built with long carbides with wide spacing on the face of the bit. This design yields large cuttings which increase drill speed and reduce dust. It is important to have sufficient clearance between the wall of the hole and the drill rods in order for such large cuttings to pass. If this clearance, known as an- nular area, is not sufficient, the cuttings

The drilling platform is supported by a crawler undercarriage except during drilling when it is raised up by hydraulic jacks.

The ability to carry long drill rods up to 70 feet provides more time for drilling.