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MINING
S
olving a problem that a customer ex-
perienced when drilling in abrasive
rock conditions, has led to a ground-
breaking new design for drill bits. The re-
sulting Sandvik top centre drill bits, which
incorporate the largest upgrades to face
drilling bits in decades, are now available
as standard products in three sizes. Primary
applications for the top centre drill bits in-
clude face drilling and bolting in mining and
tunnelling environments where long bit life
is essential for cutting costs and improving
productivity.
The top priority when developing the new
top centre drill bit was to increase service
life. Since the main reason for discarding a
drill bit is excessive wear on the diameter,
the simplest way to achieve longer service
life is to add more gauge buttons. However,
this can prove problematic because of the
minimal space available. Furthermore, an
increase in the number or size of the car-
bide buttons generally decreases the pene-
tration rate: the same impact force yields a
lower net force per button.
The new design solves these problems with
a so-called raised front, elevating two or
three front buttons – depending on diame-
ter size – a few millimetres above the gauge
buttons located on the periphery of the bit.
Furthermore, the front buttons are set at a
slight angle relative to the symmetric axis of
the bit. The raised front creates a somewhat
recessed hole bottom pattern that alters the
rock-breaking action to achieve improved
performance.
In addition to the new design, the top centre
bit also features a new, innovative cement-
ed carbide grade, the GC80. “The problem
with the carbides that exist on the market
today is that they are either wear-resistant
or tough,” says Robert Grandin, Product
Manager Top Hammer Tools at Sandvik Min-
ing. “When developing the GC80, we want-
ed to combine the best of those two worlds
in order to get as much as possible out of
the top centre design.”
The key to this is a completely new pro-
duction method, which makes it possible
to produce a button that improves wear
resistance on the outside, yet combines
toughness with a softer centre, pushing the
service life and long grinding intervals even
further.
Tool life improvements brought about by the
Sandvik top centre design also yield signifi-
cant health and safety benefits, since oper-
ators spend less time near an unreinforced
face. “The new bit design essentially deliv-
ers more metres per shift compared with
a standard bit thanks to less frequent bit
changes,” Grandin says.
More than 1 000 hours of testing in wide-
ly varying conditions and sites in countries
including China, Turkey, Bulgaria, Georgia,
Zimbabwe, Australia, Mexico and Sweden
have shown operators logging more drilled
metres and more holes between each re-
grind. Less regrinding means less wear on
the drill diameter. An additional benefit is
more accurate collaring, which directly im-
pacts the accuracy of drilled holes and con-
sequently blasting results. “What started as
a solution for an extreme customer problem
is now a standard solution that can be used
everywhere,” Grandin concludes.
Top centre drill bits are available in bit sizes
43, 45 and 48 mm with 2–3 raised end but-
tons and 7–8 gauge buttons in grade GC80
and connections R32, Sandvik Alpha 330
and R35.
b
Sandvik reinvents
TOP HAMMER DRILL BIT DESIGN
Sandvik top centre drill bits add value to
operations:
For mine management
Up to 80% longer grinding intervals
Up to 60% longer bit life
For drill operators
Higher productivity thanks to longer service life
Safer work environment thanks to fewer bit
changes