U.S. patent application number 10/603657 was filed with the patent office on 2004-04-08 for rock drill bit and method for the manufacture thereof.
This patent application is currently assigned to SANDVIK AB. Invention is credited to Larsson, Kenneth.
Application Number | 20040065482 10/603657 |
Document ID | / |
Family ID | 20288340 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065482 |
Kind Code |
A1 |
Larsson, Kenneth |
April 8, 2004 |
Rock drill bit and method for the manufacture thereof
Abstract
A rock drill bit for percussive drilling, especially top hammer
drilling, includes a drill head provided with rock removing
members. The rock drill bit is provided with a number of external
grooves for conducting cuttings, the grooves extending in the axial
direction of the rock drill bit. Formed between adjacent grooves
are lands which also extend in the axial direction of the rock
drill bit. The rock drill bit has a thread for connection of the
rock drill bit to a drill rod. Rear end portions of at least some
of the lands define retrac teeth. Each retrac tooth has at least
one cutting edge. At least some of the lands comprise a chip
surface and a clearance surface that form therebetween an edge
angle not greater than 100.degree..
Inventors: |
Larsson, Kenneth;
(Sandviken, SE) |
Correspondence
Address: |
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Assignee: |
SANDVIK AB
SANDVIKEN
SE
|
Family ID: |
20288340 |
Appl. No.: |
10/603657 |
Filed: |
June 26, 2003 |
Current U.S.
Class: |
175/414 ;
175/415; 76/108.2 |
Current CPC
Class: |
E21B 10/003 20130101;
E21B 10/36 20130101 |
Class at
Publication: |
175/414 ;
175/415; 076/108.2 |
International
Class: |
E21B 010/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2002 |
SE |
0201984-2 |
Claims
What is claimed is:
1. A rock drill bit for percussive drilling comprising a drill head
carrying rock-removing members at a rock-removing end thereof, the
drill head having a plurality of external grooves formed therein
and extending generally in an axial direction of the drill head for
conducting cuttings; lands defined between adjacent pairs of the
grooves and extending generally in the axial direction; the drill
head further including a connecting structure adapted to connect
the drill head to a drill rod; the lands including rear end
portions defining respective retrac teeth; each retrac tooth having
at least one cutting edge, a chip surface, and a clearance surface;
the chip surface and the clearance surface forming therebetween an
edge angle no greater than 100.degree..
2. Rock drill bit according to claim 1 wherein the edge angle is
not greater than 90.degree..
3. Rock drill bit according to claim 1 wherein the first cutting
edge is formed by an intersection between the chip surface and the
clearance surface, each retrac tooth including a second cutting
edge defined by an intersection between the chip surface and a
substantially partially conical rearwardly facing end surface of
the retrac tooth, wherein the end surface is arranged axially
inside of and radially outside of a rearwardly facing stop face of
the drill bit, an angle defined between the first and second edges
being obtuse.
4. A rock drill bit according to claim 1 wherein the structure for
connection of the rock drill bit to a drill rod comprises an
internal female thread and a front stop face arranged adjacent to a
bottom of the female thread.
5. Rock drill bit according to claim 1 wherein each groove is
asymmetrically arranged in relation to a line oriented parallel to
a center axis of the bit and comprises a first chip surface and a
second chip surface arranged substantially perpendicular to each
other.
6. Rock drill bit according to claim 3 wherein the rear stop face
is situated spaced-apart from, and adjacent to, the retrac
teeth.
7. A method for the manufacture of a rock drill bit for percussive
drilling, the bit being machined from a cast workpiece to include a
forward rock-removing section and an axially opposite rearward
connecting section adapted for connecting the bit to a drill rod,
the connecting section including a recess having an internal screw
thread; cooling medium channels extending through the bit from the
recess to a front end of the rock-removing section; the method
comprising the steps of: A) performing a turning operation on the
workpiece at an exterior of the connecting section to generate a
rearwardly facing end surface that is inclined toward the
rock-removing section at an acute angle relative to a plane
oriented perpendicular to a center axis of the bit; and B) milling
external grooves in the workpiece for conducting cuttings, wherein
the exterior grooves extend along the rock-removing section and the
connecting section and defining lands therebetween that have ends
facing rearwardly to define respective retrac teeth having cutting
edges extending generally axially along an envelope surface of the
bit.
8. Method according to claim 7 wherein during step A a stop face is
generated that is concentric with and positioned outside the end
surface, and which is perpendicular to the center axis of the rock
drill bit.
9. Method according to claim 7 further including the step of
removing some of the retrac teeth by a subsequent machining
step.
10. Method according to claim 9 wherein the retrac teeth are
removed by a milling procedure.
Description
[0001] This application claims priority under 35 U.S.C.
.sctn..sctn.119 and/or 365 to patent application Ser. No. 0201984-2
filed in Sweden on Jun. 26, 2002, the entire content of which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a rock drill bit for
percussive drilling, especially top hammer drilling.
[0003] After the completion of a bore hole, the rock drill bit
intended for percussive drilling, with the appurtenant drilling
string, consisting of drill rods, should be removed from the bore
hole. In that connection, the drill bit and the drilling string are
usually rotated in the opposite direction compared to when drilling
of the bore hole is effected. However, in connection with the
removal of the rock drill bit from the bore hole, it may occur that
rock material that has come loose from the hole wall makes the
withdrawal of the drilling string and the drill bit more difficult.
In order to overcome this problem, it is common that the drill bit
at the rear end thereof, i.e., at the end facing away from the
drill front, has cutting inserts or chisels, designated retrac
teeth below, which during rotation of the drilling string and the
drill bit, in connection with retracting the drilling string and
the drill bit from the bore hole, crushes the rock material that
has come loose from the bore wall. Said retrac teeth are made by
means of special milling operations, thus constituting additional
operations in addition to the prevalent operations for the
manufacture of a rock drill bit of the type in question. However,
the design of these known teeth at the rear end of the drill bit
means that sharp corners are formed adjacent to said teeth. This in
turn means that cracks are generated in connection with said teeth
during operation of the rock drill bit.
[0004] By Hollar et al. U.S. Pat. No. 5,743,345, a rock drill bit
is previously known, which has an appurtenant drill rod, where the
rock drill bit at the rear end thereof is provided with special
cemented carbide pins that work in a way that corresponds to the
above-described teeth at the rear end of the drill bit. To arrange
special cemented carbide pins at the rear end of the rock drill
bit, involves, however, a price rise at production of a rock drill
bit of the type in question.
[0005] In SE-C2-514 931(corresponding to {dot over (A)}sberg et al.
U.S. Pat. No. 6,494,275), a rock drill bit of the present type is
shown. The retrac teeth of the known rock drill bit have a tendency
to break down. Furthermore, the retrac teeth of the known rock
drill bit have turned out to be inadequate, from a cutting point of
view.
OBJECTS OF THE INVENTION
[0006] The present invention has the object of providing a rock
drill bit of the kind defined in the introduction, wherein the
retrac teeth of said rock drill bit are so formed that the retrac
teeth are reinforced.
[0007] Another object of the present invention is to provide a rock
drill bit that permits good rock removal.
[0008] Still another object of the present invention is that the
retrac teeth of the rock drill bit permits that transfer of shock
wave energy between the drill rod situated closest to the drill bit
and the drill bit takes place by means of a so-called shoulder
stop.
SUMMARY OF THE INVENTION
[0009] One aspect of the present invention relates to a rock drill
bit for percussive drilling which comprises a drill head that
carries rock-removing members at a rock-removing end thereof and
has a plurality of external grooves formed therein. The grooves
extend generally in an axial direction of the drill head for
conducting cuttings. Lands are defined between adjacent pairs of
the grooves and extend generally in the axial direction. The drill
head further includes a connecting structure adapted to connect the
drill head to a drill rod. The lands include rear end portions
which define respective retrac teeth. Each retrac tooth has at
least one cutting edge, a chip surface, and a clearance surface.
The chip surface and the clearance surface form therebetween an
edge angle no greater than 100.degree..
[0010] Another aspect of the invention involves a method for the
manufacture of a rock drill bit for percussive drilling. The bit is
machined from a cast workpiece to include a forward rock-removing
section and an axially opposite rearward connecting section adapted
for connecting the bit to a drill rod. The connecting section
includes a recess having an internal screw thread. Cooling medium
channels extend through the bit from the recess to a front end of
the rock-removing section. The method comprises the steps of:
[0011] A) performing a turning operation on the workpiece at an
exterior of the connecting section to generate a rearwardly facing
end surface that is inclined toward the rock-removing section at an
acute angle relative to a plane oriented perpendicular to a center
axis of the bit; and
[0012] B) milling external grooves in the workpiece for conducting
cuttings, wherein the exterior grooves extend along the
rock-removing section and the connecting section and define lands
therebetween that have ends facing rearwardly to define respective
retrac teeth that have cutting edges extending generally axially
along an envelope surface of the bit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] An embodiment of the rock drill bit according to the present
invention will be described below, references being made to the
accompanying drawings.
[0014] FIG. 1 shows a perspective view of a rock drill bit
according to the present invention.
[0015] FIG. 2 shows a partial cross-section through the rock drill
bit according to FIG. 1 and an appurtenant drill rod.
[0016] FIG. 3 shows a side view of the rock drill bit according to
FIG. 1.
[0017] FIG. 4 shows an end view of the rock drill bit according to
FIG. 1.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0018] The rock drill bit 1 illustrated in FIGS. 1-4 comprises a
drill head 3 and a shank or a skirt 5, wherein the drill head 3 and
the skirt 5 are integrated with each other. A drill rod 7 is
connected to the rock drill bit 1 via a thread coupling. In the
drill rod 7, a through-going flush duct 8 is arranged in the
conventional way. A longitudinal center axis 2, common for the rock
drill bit 1 and the drill rod 7, is drawn in FIG. 2.
[0019] As is most clearly seen in FIG. 2, the rock drill bit 1
includes a rear connecting end in which is formed a recess having
an internal female thread 9, which receives an external male thread
10 at one end of the drill rod 7.
[0020] The drill head 3 of the rock drill bit 1 according to the
present invention is provided with rock removing members in the
conventional way, in the illustrated embodiment in the form of
cemented carbide pins or buttons 11. A number of cooling medium
channels 12 extends between the internal space of the rock drill
bit 1, which is defined by the internal female thread 9, and the
front of the drill head 3. In said internal space, a first stop
face 13, a so-called bottom stop, is also arranged for the free end
of the drill rod 7.
[0021] At the rear end of the rock drill bit 1, as is most clearly
shown in FIG. 4, a second stop face 14, a so-called shoulder stop,
is arranged, which is intended to interact with a shoulder 15 of
the drill rod 7. In the illustrated embodiment, a so-called
shoulder-bottom stop is frequently used, which means that the drill
rod 7 is manufactured with such tolerances that, at establishment
of the threaded joint between the rock drill bit 1 and the drill
rod 7, the free end of the drill rod 7 initially will come to
abutment against the bottom stop 13. After a relatively short time
of wearing-in of the threaded coupling, also the shoulder 15 of the
drill rod 7 comes to abutment against the shoulder stop 14, wherein
a so-called shoulder-bottom stop has been established, i.e.,
abutment between the rock drill bit 1 and the drill rod 7 takes
place at both the bottom stop 13 and the shoulder stop 14. This
means that transfer of shock wave energy from the drill rod 7 to
the rock drill bit 1 will be effected via both the bottom stop 13
and the shoulder stop 14.
[0022] As is most clearly seen in FIGS. 1 and 3, the rock drill bit
1 is on the outside thereof provided with a number of straight,
front 16A and rear 16B grooves for conducting cuttings extending in
the axial direction of the rock drill bit 1. Each front groove for
cuttings 16A is symmetrically arranged in relation to a line
parallel with the center axis 2. Each rear groove for cuttings 16B
is asymmetrically arranged in relation to a line parallel with the
center axis. Each rear groove for cuttings 16B consists of a first
chip surface 31 and a second chip surface 32, which are
substantially perpendicular to each other. The first chip surface
31 has a radial extension that runs substantially perpendicularly
to the center axis 2. The cutting surfaces 31 and 32 meet in a
rounded portion 33 that approaches the center axis 2 in the
direction axially rearwards. Between themselves, the rear grooves
for cuttings 16B define a number of substantially straight lands 17
that also extend in the axial direction of the rock drill bit 1. A
substantially cylindrical countersunk portion 17A is arranged
between the front and the rear grooves 16A and 16B, respectively.
Among other things, the cylindrical portion 17A has the purpose of
ensuring that guiding of the rock drill bit 1 in the bore hole is
carried out by means of the portions that are located in connection
with the ends of the rock drill bit 1, and decreasing the
resistance against the release of cutting dust. The grooves 16A,
16B are in the conventional manner intended to transport away the
drill dust produced at the front of the rock drill bit 1.
[0023] The lands 17 are formed by retrac teeth 18, having the
function of crushing the material that has come loose from the hole
wall during withdrawal of the rock drill bit 1 from a drilled hole.
Each retrac tooth 18 is provided with a first edge 19A, a second
edge 19B and a third edge 19C. The first edge 1 9A is situated
farthest forward in the direction of rotation R of the drill bit at
each retrac tooth 18. The edge 19A is substantially parallel to the
center axis 2. The edges 19A coincide with an imaginary cylinder
that intersects the peripheral buttons 11 of the rock drill bit 1.
The edge 19A is formed at the intersection between a chip surface
31 and a clearance or flank surface 30. The chip surface 31 and the
clearance surface 30 form an edge angle .beta., which is not
greater than 100.degree., preferably not greater than 90.degree..
The second edge 19B is positioned at the intersecting line between
the chip surface and a substantially partially conical end surface
20. The second edge 19B is situated farthest back in the feeding
direction of the drill bit on each land 17. The end surface 20 is
arranged axially inside and radially outside of the second stop
face 14. The end surface 20 is inclined generally forwardly toward
the front end of the bit and forms an outer angle .alpha. greater
than 180.degree. with the second stop face 14. Stated another way,
the end surface 20 forms an acute angle .delta. with a plane 21
oriented perpendicular to a longitudinal center axis 2 for the rock
drill bit 1. The angle .alpha. is greater than 180.degree.. Thus,
the angle between the first 19A and the second edge 19B becomes
obtuse, i.e. greater than 90.degree.. The third edge 19C is
situated farthest forward in the feeding direction of the drill
bit, on each land 17. The edge 19C forms an acute angle with the
center axis 2 and an obtuse angle with the first edge 19A.
[0024] The retrac teeth 18 according to the present invention may
be created in a simple and efficient way in connection with the
manufacture of the rock drill bit 1 according to the present
invention. During said manufacture, the end where the retrac teeth
are to be formed is turned, wherein the second stop face 14 is
provided, as well as a concentric, outer surface, which forms the
angle .alpha. with the second stop face 14 that is greater than
180.degree.. In a subsequent step in the manufacture of the rock
drill bit 1 according to the present invention, the grooves for
cuttings 16B are provided on the outside of the rock drill bit 1,
preferably through milling. In that connection, the lands 17
situated between the grooves for cuttings 16B are automatically
formed. In connection with the automatic forming of the lands 17,
retrac teeth 18 are also automatically formed, see FIGS. 2 and 3,
at the ends of the lands 17 that are facing away from the rock
removing end of the rock drill bit 1. By the geometry of the
concentric, outer surface, the retrac teeth 18 will be formed with
the edges 19A, 19B, 19C, said edges being positioned at the maximum
diameter of the skirts 5, as well as inside of the same. Thereby,
each retrac tooth 18 will also have a surface 20, generally facing
away from the rock removing end of the rock drill bit 1, which
surface is formed from the above-mentioned concentric, outer
surface, i.e., the surface 20 also forms an angle .alpha. that is
greater than 180.degree. with the second stop face 14. The surfaces
20 are included in a cone, the imaginary cone tip of which is
directed towards the threaded end of the bit 1. A substantial
advantage of the retrac teeth 18 formed in this way is that there
are substantially no sharp corners in connection with said teeth
18. Thereby, the risk of crack formations in connection with said
retrac teeth 18 is to a large extent reduced.
[0025] In the above-described embodiment of the rock drill bit 1,
the grooves for cuttings 16 and the lands 17 are straight, with an
extension in the axial direction of the rock drill bit 1. However,
within the scope of the present invention it is also feasible that
the grooves for cuttings and the appurtenant lands could run, for
instance, helically at the outside of the rock drill bit. The
phrase ". . . extends in the axial direction of the rock drill bit
. . . ", used in the claims, should be regarded as comprising also
those cases when the grooves for cuttings and the lands are not
parallel to the center axis 2.
[0026] According to the above-described embodiment of the rock
drill bit 1, retrac teeth 18 are formed between each adjacent pair
of grooves for cuttings 16B. Within the scope of the present
invention, it may however be conceived that for instance every
second retrac tooth 18 is removed, wherein this conveniently is
carried out by the fact that the end of a land 17 that is facing
away from the rock removing end of the rock drill bit 1 is removed,
conveniently by means of milling. The amount of retrac teeth 18
that a rock drill bit 1 according to the present invention should
have is determined by a range of different parameters, wherein for
exemplifying and not limiting purposes, the diameter of the drill
bit, the type of rock in which the drilling takes place, as well as
the drilling rig that is used, may be mentioned.
[0027] Although the present invention has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions, deletions,
modifications, and substitutions not specifically described may be
made without departing from the spirit and scope of the invention
as defined in the appended claims.
* * * * *