U.S. patent application number 13/825416 was filed with the patent office on 2013-07-18 for rock drill bit and a drilling assembly for percussive rock drilling.
This patent application is currently assigned to SANDVIK INTELLECTUAL PROPERTY AB. The applicant listed for this patent is Mauri Esko, Markku Keskiniva, Juha Piispanen. Invention is credited to Mauri Esko, Markku Keskiniva, Juha Piispanen.
Application Number | 20130180784 13/825416 |
Document ID | / |
Family ID | 43500325 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130180784 |
Kind Code |
A1 |
Esko; Mauri ; et
al. |
July 18, 2013 |
ROCK DRILL BIT AND A DRILLING ASSEMBLY FOR PERCUSSIVE ROCK
DRILLING
Abstract
A rock drill bit for percussive drilling includes a bit head
attached at an end of a drill element of a drilling assembly. The
bit head has a diameter larger than that of the drill element. The
bit head has at a front end as seen in the intended drilling
direction a plurality of buttons distributed thereon to engage
material to be crushed. At least one of the buttons is allowed to
rotate about its own symmetry axis.
Inventors: |
Esko; Mauri; (Ikaalinen,
FI) ; Keskiniva; Markku; (Tampere, FI) ;
Piispanen; Juha; (Tampere, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Esko; Mauri
Keskiniva; Markku
Piispanen; Juha |
Ikaalinen
Tampere
Tampere |
|
FI
FI
FI |
|
|
Assignee: |
SANDVIK INTELLECTUAL PROPERTY
AB
Sandviken
SE
|
Family ID: |
43500325 |
Appl. No.: |
13/825416 |
Filed: |
September 16, 2011 |
PCT Filed: |
September 16, 2011 |
PCT NO: |
PCT/EP2011/066114 |
371 Date: |
March 21, 2013 |
Current U.S.
Class: |
175/415 ;
175/414 |
Current CPC
Class: |
E21B 10/36 20130101 |
Class at
Publication: |
175/415 ;
175/414 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2010 |
EP |
10178387.6 |
Claims
1. A rock drill bit for percussive drilling comprising a bit head
attached at an end of a drill element of a drilling assembly and
having a diameter larger than a diameter of said drill element,
said bit head having a front end and as seen in the intended
drilling direction a plurality of buttons at the front end and
distributed over said bit head and configured to engage material to
be crushed wherein at least one of said buttons is allowed to
rotate about its own symmetry axis.
2. A rock drill bit according to claim 1, wherein said plurality of
buttons include gauge buttons distributed along the circumference
of said bit head and configured to determine the diameter of a hole
to be drilled by the rock drill bit, wherein at least one of said
gauge buttons is allowed to rotate about its own symmetry axis.
3. A rock drill bit according to claim 2, further comprising a
first member having a substantially circumferential ring surface
defining a substantially frusto-conical shape as seen in the
intended drilling direction, and wherein said at least one gauge
button has a base portion resting on said ring surface configured
to transfer impact forces to the at least one gauge button and to
allow said base portion to move thereon when rotating.
4. A rock drill bit according to claim 3, further comprising a
second member defining said front end of said bit head and having
said plurality of gauge buttons extending out thereof, and wherein
said at least one rotating gauge button is arranged in a hole in
said second member and allowed to move with respect to walls
defining said hole when rotating.
5. A rock drill bit according to claim 4, wherein said at least one
rotating gauge button has a base portion with a larger
cross-section than the rest of the plurality of gauge buttons, and
wherein at least a part of said hole in said second member has a
cross-sectional area being smaller than that of said base portion
so as to maintain the gauge button received in said second
member.
6. A rock drill bit according to claim 5, wherein said hole is a
through hole, and said gauge button is arranged with the base
portion thereof on a rear side of said hole as seen in the intended
drilling direction.
7. A rock drill bit according to claim 3, wherein said first member
has means configured to secure said first member to said drill
element.
8. A rock drill bit according to claims 4, further comprising means
configured to secure said second member to said first member.
9. A rock drill bit according to claim 8, wherein said means
configured to secure said second member to said first member is
configured to releasably secure the members to each other.
10. A rock drill bit according to claim 3, wherein said first
member is a ring configured to be supported on and/or secured to an
end of a said drill element.
11. A rock drill bit according to claim 4, further comprising means
for securing said second member and said rock drill bit to a said
drill element.
12. A rock drill bit according to claim 2, wherein a majority of
said gauge buttons are is allowed to rotate about their respective
symmetry axes.
13. A rock drill bit according to claim 2, wherein all of said
gauge buttons of the rock drill bit are allowed to rotate about
their respective symmetry axes.
14. A rock drill bit according to claim 1, wherein said bit head
has a front surface provided with a plurality of front buttons
configured to engage material to be crushed.
15. A rock drill bit according to claim 14, wherein at least one of
said plurality of front buttons is allowed to rotate about its
respective symmetry axis.
16. A rock drill bit according to claim 15, wherein said at least
one front button has a design similar to that of said at least one
gauge button, said second member being configured to receive said
at least one front button similarly to said at least one gauge
button.
17. A rock drill bit according to claim 15, wherein a majority of
said front buttons or all said front buttons are allowed to rotate
about their respective symmetry axis.
18. A rock drill bit according to claim 1, further comprising a
flush channel extending through said bit head and having at least
one flushing hole opening at said front end and passing the
circumference of at least one of said buttons and being allowed to
rotate about its respective symmetry axis.
19. A rock drill bit according to claim 1, wherein said at least
one rotating button is arranged in a hole in said bit head and
allowed to move with respect to walls defining said hole when
rotating, said at least one button being provided with a
circumferential annular groove and said walls defining said hole
having a female member, wherein the rock drill bit includes means
configured to engage said groove and said female member so as to
lock said button in said hole while allowing it to rotate.
20. A rock drill bit according to claim 19, wherein said female
member is an annular groove located in said hole walls, and said
engaging means comprises a ring of elastic material.
21. A rock drill bit according to claim 19, wherein said engaging
means comprise a pin configured to be pushed into said groove and
said female member for being fixed with respect to said bit head
and to lock said button in said hole while allowing it to
rotate.
22. A drilling assembly for percussive rock drilling comprising: a
rock drill bit; power means configured to act upon said rock drill
bit to rotate the drill bit and carry out impacts for engaging
material to be crushed; and a control arrangement to control the
operation of said power means.
23. A drilling assembly according to claim 22, wherein the control
arrangement controls said power means to obtain a frequency of said
impacts exceeding 250 Hz, exceeding 350 Hz or being in the range of
350 Hz-1000 Hz.
24. (canceled)
Description
TECHNICAL FIELD OF THE INVENTION AND BACKGROUND ART
[0001] The present invention relates to a rock drill bit for
percussive drilling comprising a bit head configured to be attached
at an end of a drill element of a drilling assembly and having a
diameter larger than that of said drill element, said bit head
having at a front end as seen in the intended drilling direction a
plurality of buttons distributed over said bit head and configured
to engage material to be crushed, as well as a drilling assembly
for percussive rock drilling according to the preamble of the
independent claim therefor.
[0002] The invention is not restricted to any type of drilling
assembly for use of a said rock drill bit, but the former may be a
down-the-hole hammer drill just as well as a top hammer drill,
although the rock drill bit shown is especially intended for the
latter type.
[0003] Furthermore, said rock drill bit may have any conceivable
size and has normally a diameter of 30 mm-300 mm. The same absence
of limitations applies to the intended percussion frequency and
rotational speed of the rock drill bit in operation, although it
may be mentioned that these are typically within the ranges 20
Hz-100 Hz and 20-500 revolutions per minute, respectively, but the
invention does not exclude the use of the rock drill bit in high
frequency assemblies operating at a frequency above 250 Hz and
which may reach more than 1 kHz.
[0004] A known so-called standard rock drill bit 1 of the type
defined in the introduction will now be described while referring
to both FIG. 1 and FIG. 2. The drill bit has a bit head 2
configured to be attached at an end of a drill element, for example
in the form of a drill tube or drill rod, of a drilling assembly
and having a diameter larger than that of a said drill element.
This drill element is not shown in these figures but may be
intended to be received in a so-called skirt 3 integral with a bit
head and having a smaller diameter than the bit head. Other ways of
connecting the drill bit to the drill element are conceivable and
known within the art. The bit head has at a front end 4 as seen in
the intended drilling direction a plurality of gauge buttons 5
distributed along the circumference of the bit button head 2. The
gauge buttons are configured to engage material to be crushed and
to determine the diameter of a hole 6 (see FIG. 1) to be drilled by
the rock drill bit. These gauge buttons are made of hard material,
such as cemented carbide or tungsten carbide. Front buttons 7 also
of hard material are arranged on a front surface 8 for engaging
material to be crushed. It is also indicated how a flush channel
opens at the front by a flushing hole 9 in the front surface.
[0005] In operation the gauge buttons 5 will engage and break rock
close to the walls of a hole 6 in which the rock drill bit with
said rod is located and the front buttons 7 will break rock closer
to the centre of such a hole by impacts carried out by the rock
drill bit in the direction of the arrow A. The drill bit will
rotate somewhat, typically about 5.degree., between each such
impact.
[0006] The operation efficiency of a rock drill bit of this type is
of course an important feature and this may be expressed as the
penetration rate of the rock drill bit defined as the length of a
hole drilled per time unit (meter/minute). The penetration rate of
known rock drill bits of this type is dependent upon the wear of
said buttons, especially the gauge buttons. It is indicated in FIG.
2 that during the operation of such a rock drill bit material is
abraded at the periphery of the gauge buttons resulting in a flat
surface 10 there, which makes them less sharp and reduces the
penetration rate. These flat surfaces 10 will during the operation
of the rock drill bit grow and finally result in a diameter of a
hole drilled determined by said gauge buttons being so much reduced
that the rock drill bit has to be replaced. It is of course an
ongoing attempt to increase the penetration rate and prolong the
life time of a rock drill bit of the type defined in the
introduction.
SUMMARY OF THE INVENTION
[0007] The object of the present invention is to provide a rock
drill bit of the type defined in the introduction being improved in
at least some aspect with respect to such rock drill bits already
known.
[0008] This object is according to the invention obtained by
providing such a rock drill bit in which at least one of said
buttons is configured or allowed to rotate about its own symmetry
axis. By rotatably fitting at least one said button in the bit head
this button will while drilling be influenced by the impacts
thereof and rotation of the rock drill bit to rotate about its own
symmetry axis, so that the parts of said button engaging rock will
vary and the button will be evenly worn and by that self-sharpened.
This means that this button will thanks to the self-sharpening
effect maintain its contribution to the penetration rate of the
rock drill bit longer than would it be fixed in the bit head.
[0009] According to an embodiment of the invention said plurality
of buttons includes gauge buttons distributed along the
circumference of said bit head and configured to determine the
diameter of a hole to be drilled by the rock drill bit, and at
least one of said gauge buttons is configured or allowed to rotate
about its own symmetry axis. This means that this gauge button will
thanks to said self-sharpening effect maintain its contribution to
the penetration rate of the rock drill bit until this gauge button
has been worn so much that the diameter of a said hole drilled
determined thereby has reached a minimum acceptable level. However,
this will take longer than would said at least one gauge button be
fixed with respect to the bit head, so that the lifetime of the
rock drill bit may also be prolonged.
[0010] According to another embodiment of the invention the rock
drill bit comprises a first member having a substantially
circumferential ring surface defining a substantially
frusto-conical shape as seen in the intended drilling direction,
and said at least one gauge button has a base portion resting on
said ring surface configured to transfer impact forces to the gauge
button and to allow said base portion to move thereon when
rotating. Transfer of impact forces to the gauge button by such a
surface acting on said base portion of said at least one gauge
button may increase the efficiency of the impacts and reduce
stresses on said gauge button.
[0011] According to another embodiment of the invention the rock
drill bit comprises a second member defining said front end of said
bit head and having said plurality of gauge buttons extending out
thereof, and said at least one gauge button allowed to rotate is
arranged in a hole in said second member and allowed to move with
respect to walls defining said hole when rotating.
[0012] According to another embodiment of the invention
constituting a further development of the embodiment last mentioned
said at least one gauge button allowed to rotate has a base portion
with a larger cross-section than the rest of the gauge button, and
at least a part of said hole in said second member has a
cross-sectional area being smaller than that of said base portion
so as to maintain the gauge button received in said second member.
By arranging such a base portion in form of a shoulder said at
least one gauge button may reliably be maintained in said second
member of the rock drill bit while being allowed to rotate.
[0013] According to another embodiment of the invention said hole
is a through-hole, and said gauge button is arranged with the base
portion thereof on a rear side of said hole as seen in the intended
drilling direction.
[0014] According to another embodiment of the invention said first
member has means configured to secure this member to a said drill
element. This means that the rock drill bit may be secured to a
drill element through said first member providing said ring surface
for transfer of impact forces to said at least one gauge
button.
[0015] According to another embodiment of the invention the rock
drill bit has both a said first and second member and comprises
means configured to secure said second member to said first member,
which means that said ring surface will be located inside the bit
head behind said second member. Said means configured to secure
said second member to said first member is according to another
embodiment of the invention configured to releasably secure these
members to each other, which means that a second member with gauge
buttons may be removed and replaced when the diameter determined by
the gauge buttons has reached the minimum limit while keeping said
first member, so that not the entire rock drill bit has to be
replaced resulting in saving of costs.
[0016] According to another embodiment of the invention said first
member is a ring configured to be supported on and/or secured to an
end of said drill element. Such a so-called pusher ring is of
particular interest and results in a simple construction of the
rock drill bit if the rock drill bit also comprises means for
securing said second member and by that said rock drill bit to a
said drill element. In such a case the first member has neither to
be secured to a drill element nor to said second member, but it
will be kept in place by said second member.
[0017] According to another embodiment of the invention a majority
of said gauge buttons are allowed to rotate about their own
symmetry axis, and according to a further embodiment of the
invention all said gauge buttons of the rock drill bit are allowed
to rotate about their own symmetry axis. The advantages of
arranging gauge buttons so as to be allowed to rotate will be the
greater the more of the gauge buttons that are so arranged
resulting in a said prolonged life time of the rock drill bit and a
high penetration rate maintained over a longer time.
[0018] According to another embodiment of the invention said bit
head has a front surface provided with a plurality of front buttons
configured to engage material to be crushed. These front buttons
may be fixed with respect to said front surface, but according to
another embodiment of the invention at least one of said front
buttons is allowed to rotate about its own symmetry axis, which
will result in an even wear of said front button and by that a
self-sharpening action thereof, so that it will carry out its task
more efficiently and over a longer time than would it be fixed with
respect to said front surface of the bit head.
[0019] According to another embodiment of the invention said at
least one front button has a design similar to that of said at
least one gauge button, and said second member is configured to
receive said at least one front button similarly to said at least
one gauge button.
[0020] According to another embodiment of the invention a majority
of said front buttons or all said front buttons are allowed to
rotate about their own symmetry axes.
[0021] According to another embodiment of the invention the rock
drill bit comprises a flush channel extending through said bit head
and having at least one flushing hole opening at said front end and
passing the circumference of at least one said button allowed to
rotate about its own symmetry axis. By letting the flushing medium,
such as water, flowing over the circumference of such a button
allowed to rotate surfaces and spaces of said bit head and said
button allowing said rotation will be kept clean while eliminating
any wear problems while the button is rotating inside a hole in
which it is received in said bit head.
[0022] According to another embodiment of the invention said at
least one button allowed to rotate is arranged in a hole in said
bit head and allowed to move with respect to walls defining said
hole when rotating, said at least one button is provided with a
circumferential annular groove, said walls defining said hole have
a female member, and the rock drill bit comprises means configured
to engage said groove and said female member so as to lock said
button in said hole while allowing it to rotate. This is a
preferable and simple way of locking said button with respect to
said bit head while allowing it to freely rotate.
[0023] According to another embodiment of the invention said female
member is an annular groove in said hole walls, and said engaging
means comprises a ring of elastic material. This allows easy
mounting of said button in said hole by pushing it thereinto while
compressing said ring, which will when arriving to said annular
groove in said hole walls expand and lock the button in place while
allowing it to freely rotate.
[0024] According to another embodiment of the invention said
engaging means comprises a pin configured to be pushed into said
groove and said female member for being fixed with respect to said
bit head and lock said button in said hole while allowing it to
rotate. Such a lock pin will also by simple means provide a
reliable locking of said button in said hole of the bit head while
allowing it to freely rotate.
[0025] The invention also relates to a drilling assembly for
percussive rock drilling according to the appended independent
claim for such an assembly. Such a drilling assembly makes it
possible to carry out rock drilling with a high penetration rate
over a longer time and while replacing the rock drill bit thereof
more seldom with respect to such drilling assemblies utilizing
known rock drill bits.
[0026] The invention also relates to a use of a rock drill bit
according to the invention for percussive rock drilling into earth
material, such as rock.
[0027] Further advantages as well as advantageous features of the
invention will appear from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] With reference to the appended drawings, below follows a
specific description of embodiments of the invention cited as
examples.
[0029] In the drawings:
[0030] FIG. 1 is a very simplified view of a rock drill bit
according to prior art in operation,
[0031] FIG. 2 is a perspective view of a rock drill bit according
to prior art after some time of operation,
[0032] FIG. 3 is a perspective view illustrating the principle of a
rock drill bit according to the present invention,
[0033] FIG. 4 shows a longitudinal section through a part of a rock
drill bit according to a first embodiment of the invention in
operation,
[0034] FIG. 5 is an exploded view of the rock drill bit according
to FIG. 4,
[0035] FIG. 6 is a view corresponding to FIG. 4 of a rock drill bit
according to a second embodiment of the invention,
[0036] FIG. 7 is an exploded view of the rock drill bit according
to FIG. 6,
[0037] FIG. 8 is a simplified view corresponding to FIG. 4 of a
rock drill bit according to a third embodiment of the
invention,
[0038] FIG. 9 is a simplified view of a button allowed to rotate in
a bit head of a rock drill bit according to a fourth embodiment of
the invention, and
[0039] FIG. 10 is a very simplified view of a drilling assembly for
percussive rock drilling according to an embodiment of the present
invention in operation.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0040] FIG. 3 shows very schematically the principle of a rock
drill bit according to the present invention, in which all gauge
buttons 20 and all front buttons 21 are configured or allowed to
rotate about their own symmetry axis by being received in holes 22
in a substantially circumferential ring surface 23 defining a
substantially frusto-conical shape as seen in the intended drilling
direction and in a front surface 24, respectively. The buttons are
preferably of tungsten carbide.
[0041] A rock drill bit 30 according to a first embodiment of the
present invention will now be described while making reference to
FIGS. 4 and 5. The rock drill bit comprises a first member 31
having a substantially circumferential ring surface 32 defining a
substantially frusto-conical shape as seen in the intended drilling
direction. This first member 31 is provided with means configured
to secure this member to a drill element 33, in which this securing
means is formed by a sleeve-like portion 34 of the first member 31
provided with engagement means in the form of an internal thread 35
configured to engage engagement means in the form of an external
thread 36 on the drill element.
[0042] The rock drill bit further comprises a second member 37
defining a front end 38 of a bit head 39 of the rock drill bit.
This second member is provided with a plurality of through holes 40
receiving the gauge buttons 41 and front buttons 42 while allowing
these to rotate about their own symmetry axis. The through-holes 40
each have a diameter slightly exceeding (suitably by a diameter
difference in the order of 30-80 .mu.m) the diameter of the
respective button received therein for allowing the button to move
with respect to walls 43 in the second member 37 defining said hole
when rotating. However, this difference in diameter has been
exaggerated in this figure and also in the embodiment shown in FIG.
6 and described below for better illustrating this feature. The
gauge buttons as well as the front buttons are provided with a base
portion 44 with larger cross-section than the rest of the button
and also than the respective hole 40 so as to maintain the button
received in the second member.
[0043] A gauge button 41 rests by the base portion 44 thereof on
said ring surface 32 configured to transfer impact forces to the
gauge button and allow the base portion to move thereon when
rotating. This means that impact forces are transferred to the
gauge buttons from a surface 32 located inside the drill bit. The
first member has also surfaces 45 directed in an intended drilling
direction for supporting base portions of front buttons and
transferring impact forces thereto while allowing these base
portions to move on these surfaces 45 when rotating. Furthermore,
the bit head 39 will through a shoulder 47 on the first member 31
provide a clearance C with respect to this member 31, so that the
button 41 may rotate freely without jamming. Particular measures
are taken for flushing the surfaces and spaces surrounding the
button, which will be explained more in detail below.
[0044] The rock drill bit comprises means 46 configured to secure
the second member 37 to the first member 31. The securing means is
preferably configured to releasably secure these members to each
other, for instance by mutually securing them by engagement of
threads. This would then mean that it would be possible to remove
said second member with buttons for replacement while keeping the
first member after the buttons have been that much worn that they
have to be replaced. Welding or press fitting are other possible
alternatives of said securing means 46 easier to accomplish.
[0045] When carrying out percussive drilling with the rock drill
bit shown in FIGS. 4 and 5 as illustrated in FIG. 4 the buttons
thereof will be allowed to rotate about their own axes, which means
that the gauge buttons 41 will be worn evenly and maintain their
sharpness, so that a high penetration rate may be maintained over a
long period of time and the diameter of the hole defined by the
gauge buttons will be reduced more slowly than would the gauge
buttons be fixedly arranged in the bit head.
[0046] FIGS. 6 and 7 illustrate a rock drill bit 50 according to a
second embodiment of the invention. This rock drill bit has a first
member 51 in the form of a ring configured to be supported on
and/or secured to an end 52 of a drill element 53 and having a ring
surface 54 forming a support for a base portion 55 of each gauge
button 56 in the same way as the corresponding surface 32 in the
embodiment shown in FIGS. 4 and 5. Thus, impact forces will through
this surface be transferred to the gauge buttons while the base
portions thereof are allowed to move thereon when rotating.
[0047] A second member 57 of the rock drill bit has through holes
58 receiving said gauge buttons and allowing them to move with
respect to walls of these holes when rotating. The front buttons 59
are, as an example, in this embodiment fixedly secured to a front
end 60 of the second member 57.
[0048] The second member 57 is in this embodiment provided with
means for securing this member to a drill element 53 by having a
sleeve-like portion 61 designed to receive a drill element and
having engagement means in the form of an internal thread 62 for
engaging with engagement means in the form of an external thread 63
on the drill element for releasably securing said second member to
the drill element and by that also keeping said ring 51, a
so-called pusher ring, in place. The first member 51 is provided
with a collar 64, so that the first 51 and second 57 members are
fixed with respect to each other while leaving a clearance 66
therebetween for the button to freely rotate. Proper flushing of a
button allowed to rotate is also important. It is indicated in FIG.
6 that the rock drill bit has a conventional flush channel 67
extending through the bit head. The flush channel has also at least
one flushing hole 68 (see the arrows F indicating the flow of
flushing medium) opening at the first end 60 and passing the
clearance 66 and the circumference of the button 56 allowed to
rotate. This will keep said clearance 66 clear and eliminates wear
problems while the button rotates inside the hole 58. The function
of this embodiment of the invention in operation appears clearly
from the above discussion of inter alia the first embodiment of the
present invention.
[0049] A part of a rock drill bit according to a third embodiment
of the invention is very schematically shown in FIG. 8. This rock
drill bit is provided with alternative means to lock a button 80 to
a drill bit head 81 while allowing the button to rotate. A blind
hole 82 in the bit head designed to receive the button 80 is
provided with an annular groove 83, and the button 80 is provided
with a corresponding annular groove 84 receiving an elastic lock
ring 85, for example a ring, such as a C-ring, made from steel.
When the button 80 is pushed into the hole 82 the lock ring will
first be compressed until reaching the groove 83 in the bit head.
It will then expand outwards into that groove and lock the button
to the bit head 81 while allowing the button to rotate.
[0050] FIG. 9 illustrates an alternative way of locking a button 90
to a bit head not shown in a rock drill bit according to a fourth
embodiment of the invention while allowing the button to rotate.
This is achieved by providing the button 90 with an annular groove
91 as in the embodiment shown in FIG. 8. However, a lock pin 92 is
used instead of a lock ring, and this lock pin is after pushing the
button 90 into a corresponding hole in the bit head pushed into the
groove 91 while locking the button in place and still allowing it
to rotate about its own symmetry axis.
[0051] FIG. 10 illustrates very schematically a drilling assembly
for percussive rock drilling according to the present invention
having a rock drill bit 70 according to an embodiment of the
invention provided with gauge buttons 71. This drilling assembly is
a so-called top hammer drill acting upon the rock drill bit from a
location above the ground and has power means 72, such as diesel
engine and hydraulic pump, configured to drive the rock drill 76,
which in turn makes said drill element 73 and the rock drill bit to
rotate and carry out percussions and by that crush the rock. A
design of the drilling assembly as a down-the-hole hammer equipment
is also within the scope of the present invention.
[0052] The drilling assembly has also means 74, such as a
compressed air generator, configured to flush cuttings resulted
from engagement of the gauge buttons and the front buttons of the
drill bit away from the region occupied by the drill bit. The
drilling assembly has a control arrangement 75 configured to
control the operation of the power means 72 so as to adapt the
frequency of impacts and the rotational speed of the drill bit. It
has turned out that drill bits according to the present invention
with buttons allowed to rotate about their own symmetry axis are
particularly well suited to be used in drilling assemblies
controlled to have frequencies above 250 Hz, preferably above 350
Hz and most preferred in the range of 350 Hz-1000 Hz.
[0053] Drilling with a drilling assembly according to FIG. 8 with a
rock drill bit according to the present invention will be more
efficient than with rock drill bits already known, since the
penetration rate may be kept at a high level longer and the stops
needed for replacing the rock drill bit or parts thereof will be
less frequently occurring.
[0054] It is preferable that the base portion of each rotatable
button rests against or contacts the bottom of the hole to transfer
impact forces to the button and while allowing the base portion to
move thereon when rotating.
[0055] The invention is of course not in any way restricted to the
embodiments described above, but many possibilities to
modifications thereof would be apparent to a person with skill in
the art without departing from the scope of the invention as
defined in the appended claims.
[0056] The number and positions of the buttons of the rock drill
bit may differ a lot with respect to the embodiments shown in the
figures.
[0057] "Substantially" used in the expressions "substantially a
frusto-conical shape" and "substantially circumferential ring" also
cover the case when cutting recesses or grooves and/or gauge
buttons intersect the ring, as shown in the figures.
[0058] The disclosures in EP Patent Application No. 10178387.6,
from which this application claims priority, are incorporated
herein by reference.
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