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Spanish drill-and-blast contractors invest rationally in new


  • pg 1
									                                                                                           DRAFT 2, Page 1 of 5


Spanish drill-and-blast contractors invest rationally in new Sandvik
universal button-bits for drilling big blast-holes with tophammers
Great versatility, simple choices, rational inventories, higher penetration rates, straighter
holes, longer bit life and lower energy consumption. These are the benefits Sandvik promises
when rock-drillers change to RT300 UNIFACE, a new and exceptionally versatile series of
threaded button-bits from 51-152 mm in diameter. Thanks to the use of one super-grade of
cemented-carbide throughout and one universal face design per sequence of bit diameters, the
user need now choose only the best button shape (Spherical or Ballistic) and best skirt design
(Regular or Retrac) in order to obtain the best bit for the rock formation in question.

As the leading component in the production chain, the drill bit plays a vital role in project advancement and
must be chosen skillfully and decisively. Today this is hindered by a bewildering array of drill bits in the
market, which can make it very difficult for users to choose exactly the right bit for the rock conditions. For
any given bit diameter, some manufacturers can offer up to ten or more different designs. Not only does this
make it hard to choose the right bit for the job, it also requires the „tailored‟ bit to be changed whenever the
rock conditions change, if optimal drilling is to be maintained. For years Sandvik has been trying to clear this
minefield by consolidating more features into fewer drill-bit models in order to widen each bit‟s range of
application. Hardness and toughness, two normally mutually-exclusive properties, are just two examples of
such features. Now the firm has announced a double breakthrough. The first is XT48, a new grade of
cemented-carbide that has the highest coexistence of hardness and toughness ever seen in one and the same
tool, making it the world‟s most universally applicable cemented-carbide for rock-drilling. The second is
UNIFACE, a series of three new, patent-protected universal bit-face designs, one for Ø51-64 mm bits, one
for 70-96 mm bits and one for 102-152 mm bits. The Uniface design combines, synergizes and enhances, in
a single drill-bit, diverse features that formerly necessitated two or more different models of bit. To qualify
for the RT300-Uniface label, a drill bit must have both Grade XT48 cemented-carbide buttons (indicated by
the suffix 48 in the ordering number) and a Uniface front. Expected to add value through higher productivity,
better blasting results and lower rock-excavation costs, Sandvik says that RT300-Uniface bits will
demonstrate quickly the practicality and benefits of greater universality. “With these few models,” says
Product Line Manager (PLM) Kenneth Larsson, “you can drill optimally in any rock formation that is
normally drilled with the rotary-percussive drilling method.”

In Spain, where the tophammer drilling method is very popular, the larger RT300-Uniface bits have been put
to the test in recent months in some very different environments.
New Atlantic port project for super-ships
La Coruña is a busy port city in the very northwest of Spain. In recent years the demands of the port, which
needs urgently to expand, have been conflicting with the needs of the city, which wants to limit heavy-goods
traffic to and from the port and provide better amenities for its citizens. To solve the problem, La Coruña
Port Authority ordered in 2005 a new super-port to be constructed at Punta Langosteira, a rocky headland
about 8 km west of the existing city-center port. Because the new location is exposed directly to the Atlantic
Ocean, whose wave action can be extreme, it is to be protected by a very substantial breakwater 3354 meters
long, which will provide 230 hectares of sheltered water. Consisting mainly of large chunks of blasted rock
overlain strategically with 2.6 million tonnes of high-density concrete cubes weighing up to 150 tonnes each,
the new breakwater requires more than 50 million tonnes of rock in the form of both rip-rap and aggregates.
This is being provided by a series of quarries which are effectively demolishing a large granite hill adjacent
to the new port, which will also make way for access roads and other land-based facilities. All rock
excavation and haulage to the work-site dock, where the deposition barges are loaded, and to the crushing

                                           Leigh Bartlett - LONDON
                                                                                              DRAFT 2, Page 2 of 5

plant that produces aggregates for the in-situ concrete-cube factory, are being carried out by two drill-and-
blast contractors, PEAL Obras Publicas SA and Percasa SA.
Granite and amphibolite: different origins and different characteristics
The quarry rock formation consists mainly of very hard, abrasive granite intruded substantially in places by
amphibolite which, although also hard, is less abrasive and more jointed. In order to produce the large
fragments of rock required for the breakwater fill, both contractors drill Ø127-mm blast-holes with maximal
burden and spacing in 12-15 meter benches. To ensure optimal hole-straightness and service life, both have
chosen to use the Sandvik GT60 drilling-tool solution. Until three months ago, Sandvik Flat-Face bits with
spherical buttons, the firm‟s premier model for hard and abrasive rock, were prescribed for high penetration
rates and best service-life in the granite. For the amphibolite, Sandvik recommended Drop-Center (DC)
button bits with spherical buttons; the DC design in order to prevent any hole-deviation triggered by the
Different face designs no longer needed
Sandvik Flat-Face bits have a plane face and optimized button protrusion for the hardest rocks. This design
gives an extremely robust, wear-resistant crushing structure, enabling very high impact energy to be used to
break the rock, with little risk of damaging the bit. In Drop-Center bits, the center of the bit-face is recessed.
This means that the periphery of the bit protrudes a little, with the effect that it drills a shallow pilot annulus
a few millimeters ahead of a short core, which guides the drill bit in the hole. Formerly, it was also common
to use different grades of cemented-carbide to drill different types of rock. Such tailored bits were often
limited to a fairly narrow range of rocks. Now, with Sandvik RT300-Uniface bits combining the best of the
foregoing features optimally with universal Grade XT48 cemented-carbide buttons, the firm says there are
few limitations left and drillers can use one and the same bit to drill economically in many different types of
Longer life in hard abrasive granite
According to Miguel Angel Escanciano Sánchez, PEAL‟s operations manager at Punta Langosteira, who has
been using Sandvik RT300-Uniface Ø127-mm bits with regular skirt and spherical buttons in the unforgiving
granite of Quarry B2 for more than eight weeks, they are not only superior to other brands but also perform
better than earlier Sandvik models. “Compared with Sandvik Flat-Face bits, which we used before,” he says,
“the RT300-Uniface model gives six to eight per cent more service life.” According to Oscar Alvarez,
Sandvik‟s local drillmaster, this increase would be even greater, perhaps up to 20 per cent, were it not for the
strict limitations Mr Escanciano places on gage wear. He does this in order to avoid difficulties when
charging the holes, which frequently are waterlogged. Mr Alvarez, who has tested RT300-Uniface bits
throughout Spain, says they also give higher penetration rates in the granite, particularly during the first few
hundred meters of drilling. “After this,” he says, “periodic regrinding is still needed in order to maintain
maximal drilling speeds and also to achieve the best possible bit life in hard abrasive rock.” While this
applies to button bits generally, the practice of regrinding bits is, for various reasons, not popular in Spain.
More than 30 per cent more life in amphibolite
Reviewing several pages of drilling data, Sandvik regional rock-tools manager Pedro Martinez-Herrera says
that RT300-Uniface bits are giving an even greater increase in service life in the more mixed rock conditions
of quarries A and B1 at Punta Langosteira, which are operated by Percasa. “We used to recommend Drop-
Center (DC) bits for these quarries,” he says, “for they contain large intrusions of amphibolite, which is quite
heavily jointed. Formerly the customer used DC bits with ballistic buttons, but when we tested Sandvik
RT300-Uniface drill bits with spherical buttons in these formations we recorded a 35 per cent increase in
service life, as well as a 15-20 per cent rise in penetration rates.” Since ballistic buttons are usually faster in
mixed rock conditions, this is probably due to the visibly more efficient cuttings-evacuation paths in the
Uniface design, which keep the bottom of the hole clean so that only fresh rock is crushed, thus raising
penetration rates. Percasa‟s operations manager, Jorge Sanchez, confirms the superiority of Sandvik RT300-
Uniface bits in the amphibolite and says they also perform significantly better in the more abrasive granite.

                                             Leigh Bartlett - LONDON
                                                                                              DRAFT 2, Page 3 of 5

New nickel mine also reports longer bit life
At Agua Blanca, a new opencast nickel-copper mine situated in the south of Spain, about 80 km north of
Seville, rock excavation has been subcontracted to PEAL Obras Publicas SA. On this occasion PEAL has
appointed Movimientos y Voladuras (M&V) to do most of the rock drilling. The Agua Blanca Ni-Cu deposit
is hosted by intrusive gabbroic formations whose compositions range from gabbro to gabbronorite, with
apparent contact with granite in places. The ore itself is described as a magmatic sulfide mineralization, with
the highest grades occurring in magmatic breccia. With silica contents ranging from 45 to 55 per cent, the
rocks are not overly abrasive. While the breccia is easy to drill provided it remains competent, the waste and
the disseminated ores can be very hard and also abrasive. M&V has chosen the Sandvik T51 drilling-tool
system to produce Ø110 mm blast-holes in the waste and Ø115-mm holes in the ore. The bench height is
limited to 9 meters.

According to operations manager Clemente Molina Muñoz, a mining engineer, Sandvik RT300-Uniface bits
with regular skirt and spherical buttons are performing better and lasting longer than any model of bit used
previously. This is supported by Sandvik test results, which indicate a 22 per cent increase in service life
compared with the main competitor. By all accounts, this is achieved through “one extra day‟s drilling”
made possible by one extra regrinding, which RT300-Uniface bits allow in these rock conditions, compared
with other bits. This is the equivalent of an extra 250-300 meters of drilling per bit. Periodic bit regrinding is
observed rigorously at Agua Blanca.
Good testing ground for universal bit
With a stripping ratio of about 5:1 in Agua Blanca, rocks with quite different characteristics need to be
drilled, which makes the mine a good testing ground for the versatility of Sandvik RT300-Uniface bits. From
observations in the pit, it appears that at least two different bit designs, flat-face and drop-center, would
normally have been needed in order to achieve optimal hole-straightness and good drilling economy in the
different parts of the mine. Retrac skirts, too, would be beneficial in some areas, even today. At present,
though, Sandvik RT300-Uniface bits with regular skirt and spherical buttons are being used in all parts of the
mine and there are no reports of any difficulties. Again, this could be due to their superior flushing
characteristics compared with both their predecessors and other brands.

While production demands at Agua Blanca are linked to nickel prices, Mr Clemente says that total rock
excavation is currently about 0.5 million cubic meters per month, the equivalent of about 17 million tonnes
per year. While drilling results continue to be monitored, present indications are that Sandvik RT300-
Uniface bits with regular skirt and spherical buttons are the best single choice of drill bit for the mine.
High-quality aggregates producer satisfied with Grade XT48 alone
About 150 km northwest of Madrid, near Ávila, a quarry called Canteras Cuadrado produces around 1.5
million tonnes of high-quality aggregates per year. The owner of the quarry, Amador Cuadrado, has chosen
the robust Sandvik GT60 drilling-tool system to drill Ø92, Ø96 and Ø102-mm blast-holes, depending on the
type of product in demand. While these bit diameters are at the smaller end of this tool system‟s range, Mr
Cuadrado is satisfied that GT60 is the right system for his needs, not least because he places high priority on
drilling precision. Similarly, he is satisfied with Sandvik Flat-Face Retrac drill bits equipped with Grade
XT48 cemented-carbide buttons (the first half of the RT300-Uniface solution) for he says they give the
highest penetration rates and best service life in his rock conditions. The rock is described as “corneana”, an
extremely hard and abrasive variety of hornfels, which is prized as an aggregate and is also approved as
high-speed railway ballast. In spite of the hardness of the rock, drill bits with ballistic buttons are used in this
quarry, since periodic regrinding of the bits is not practiced and ballistic buttons have been shown to last
longer than spherical buttons in such „continuous‟ drilling. Mr Cuadrado also prefers to use bits with a retrac
skirt for greater surety of hole-straightness and retractability in fractured rock.
Corresponding Uniface tests to start soon
Since Sandvik currently offers Ø92, 96 and 102-mm RT300-Uniface bits for the GT60 tool system with the
regular skirt and spherical buttons only, Canteras Cuadrado continues to use the Flat-Face retrac ballistic
models. According to Sandvik PLM Kenneth Larsson, the corresponding Ø102-mm RT300-Uniface bits

                                             Leigh Bartlett - LONDON
                                                                                             DRAFT 2, Page 4 of 5

with Sandvik GT60 thread will be available very soon. “We are hoping that Mr Cuadrado will try them as
soon as possible,” he says, “for we are certain that the Uniface version will outperform the old Flat-Face
model in every respect.” With regard to the smaller sizes for GT60, namely Ø92 and 96 mm, Mr Larsson
says Sandvik will continue to manufacture them in the Flat-Face Retrac design with Grade XT48 ballistic
buttons for the time being.
Choosing the right RT300-Uniface bit
The guidelines for choosing the right Sandvik RT300-Uniface bit are simple: Spherical buttons for very hard
rocks; Ballistic buttons for less-hard rocks; Regular bit-skirt for solid homogenous formations; Retrac skirt
for mixed, jointed or fractured formations. Thanks to the greater versatility of all Sandvik RT300-Uniface
bits, however, their respective ranges of use are now much wider than before and the changeover boundaries
are less strict. As always, Sandvik strongly recommends regrinding button bits periodically, especially when
drilling in harder and/or more abrasive rocks. This will ensure that maximal drilling speeds are maintained
and also that the full service life of the bit is obtained. Anomalistically, when regrinding is not carried out at
all, Sandvik XT48 ballistic buttons (which are in fact a robust, semi-ballistic shape) can sometimes last
longer than spherical buttons in hard and abrasive rocks. In such „non-stop‟ drilling, the Sandvik ballistic
button, while wearing more quickly than the spherical button, can still give more service life because of its
longer projection from the face of the bit. Nevertheless, periodic regrinding gives the best drilling economy.
Hardness and toughness in cemented carbide
Hardness and toughness are the two most important properties in cemented-carbide buttons for drill bits. The
hardness is needed to crush the rock and resist wear from abrasives like silica and quartz. The toughness, a
kind of elasticity, is equally vital in order to resist fracture from sharp frontal impacts, acute peripheral
overloading from irregularities in the gage rock, and fatigue. However, hardness and toughness are mutually
exclusive. Both properties cannot exist maximally in the same body, since one can be increased only at the
expense of the other. For many decades Sandvik has been manipulating this natural law, consistently finding
new ways to make higher hardness and greater toughness live together in the same tool. As a result of these
continual developments, rock drilling has become progressively more economical in real terms over the
What further distinguishes Sandvik Grade XT48
What makes Grade XT48 cemented-carbide buttons especially strong and more dualistic is a new
manufacturing technique that enables the density of the tungsten-carbide composite to be increased
significantly. This, together with the highest possible combination of hard elements and tough elements,
gives Grade XT48 cemented-carbide the durability to withstand maximally the frontal shock resistance and
abrasion from hard, quartz-bearing rocks. Due to its coexistent toughness, Grade XT48 can, at the same,
resist high gage-loading, poor rock resistance and the resultant, normally very destructive surplus impact
energy that remains trapped in the drillstring in softer rock formations. This means that bits fitted with Grade
XT48 cemented-carbide buttons can be used to drill percussively any rock formation with a compressive
strength of 100 to 400 MPa. Only the button shape (spherical or ballistic) needs to be chosen to match the
hardness of the rock.
Why the Uniface design works best
Sandvik RT300-Uniface drill bits combine the best features of the former Sandvik Flat-Face series of bits
(for hard, abrasive rock formations) with those of the former Sandvik Drop-Center series (for mixed rock
conditions and fractured formations). While the new bits exhibit characteristics of both designs, notably a
combination of high, flat surfaces and deep recesses, they are much more than just a merger of the two
designs. One striking characteristic is the high number of buttons in the face, as well as their more optimal
placement and larger dimensions, which means that more hard-metal is presented to the rock more
strategically and more efficiently. According to GPLM Kenneth Larsson, Sandvik RT300-Uniface bits
transmit a full five per cent more impact energy into the rock, compared with the former Flat-Face models.
“We have measured this increase in efficiency consistently,” he says.

                                            Leigh Bartlett - LONDON
                                                                                            DRAFT 2, Page 5 of 5

Another efficiency-driving characteristic of Sandvik RT300-Uniface drill bits is the almost exclusive use of
frontal flushing holes, placed optimally in the face of the bit and aided by deep, wide, flow-inductive
cuttings-evacuation channels. Together, these features keep the bottom of the hole clear of rock cuttings, thus
avoiding wasteful re-crushing and raising penetration rates. “No-one wants to drill in cuttings,” says Mr
Larsson. “We want to drill in rock!”

The foregoing features, together with more optimal symmetry, easier bit rotation and a long, thick skirt
assure greater efficiency, higher productivity, straighter, cleaner holes and less wear. As a result, more blast-
holes of better quality can be drilled more economically in less time using less energy.
New stepped retrac skirt balances wear and eases rotation
All Sandvik RT300-Uniface „Retrac‟ bits feature a patented new Stepped-Splines Retrac Skirt, which gives
the best possible hole-straightness and retractability in mixed and/or and fractured rock formations. Since the
long, splined skirt is stepped diametrically, bit rotatability improves immediately. What is more, any gage
wear to the bit-face and bit-skirt is now more synchronous thanks to the steps on the skirt, and the skirt
always has sufficient gage to provide good guidance in the hole. Not only does this improve the long-term
rotatability of the drill bit, it also reduces wear, cuts energy demands and gives better quality holes.
Special guide bits for high precision
A fourth Sandvik RT300-Uniface design is reserved for dedicated guide-bits in the Ø51-89 mm size range.
These special bits are used mostly in the dimensional stone industry, where there are exceptionally high
demands on hole-straightness.

                                            Leigh Bartlett - LONDON

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