Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
DRILLING TOOL
TECHNICAL FIELD
[0001]
The present invention relates to a so-called double pipe type drilling tool
that
performs drilling using a ring bit disposed on a tip side of a casing pipe,
and a pilot bit
inserted into the casing pipe.
Priority is claimed on Japanese Patent Application No. 2014-167602, filed
August 20, 2014, the content of which is incorporated herein by reference.
BACKGROUND ART
[0002]
As such a double pipe type drilling tool, PTL 1 suggests a drilling tool in
which
a ring bit is rotatably inserted into a tip part of a casing pipe with their
inner and outer
periphery surfaces being made to face each other; an inner bit is attached to
a tip of a
transmission member inserted into the casing pipe; striking force and
impelling force are
transmitted to the casing pipe and rotating force in addition thereto are
transmitted to the
ring bit via this inner bit so as to perform drilling; and after a borehole
having a
predetermined depth is formed, the ring bit be removed from the casing pipe
and left in
the borehole.
[0003]
PTL 2 describes a so-called under-reaming bit in which an extendable bit is
attached to an outer periphery of a tip part of a shank device rotated around
an axis; a
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borehole having a predetermined internal diameter is formed while the
extendable bit is
positioned in a extending state and protrudes to a tip of a casing pipe during
drilling; and
after the end of the drilling, the extendable bit is shrunk and then is
recovered with the
shank device through the inside of the casing pipe.
CITATION LIST
PATENT LITERATURE
[0004]
[PTL 1] Japanese Patent No. 4887857
[PTL 2] Japanese Patent No. 4501407
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0005]
In recent years, in specific drilling works using such drilling tools, there
have
been increasing numbers of cases in which a borehole is formed with a greater
internal
diameter than an internal diameter sufficient enough to insert the casing pipe
itself For
example, in a case where a steel-pipe diaphragm wall is buried; a casing pipe
in which a
joint is provided at an outer peripheral part of a steel pipe is inserted into
a borehole.
Further, in a case where the casing pipe is connected by a coupling having a
greater
external diameter than the external diameter of the steel pipe, this coupling
is inserted
into the borehole, and therefore, a borehole with an internal diameter for
which the
external diameter to the joint or the coupling is taken into consideration
must be formed.
Moreover, also in a case where the periphery of the steel pipe is cemented at
a water well
or the like for water stoppage, and a borehole with a greater internal
diameter than the
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external diameter of the steel pipe is required.
[0006]
In a case where such a borehole with a greater internal diameter is formed by
the
double pipe type drilling tool described in PTL 1, the external diameter of
the ring bit is
increased. However, as described above, the ring bit is rotatably inserted
with the outer
peripheral surface of the posterior end part thereof being made to face the
inner
peripheral surface of the casing pipe. Therefore, the internal diameter of the
ring bit
does not change and the size in the radial direction of the ring bit becomes
larger. Since
this ring bit is finally left in the borehole without being recovered, an
increase in
construction cost is caused. Further, since the rotating force is transmitted
to the ring bit
via the inner bit inserted into the ring bit through the inside of the casing
pipe, sufficient
rotating force cannot be transmitted if the external diameter of the ring bit
becomes larger,
and also there is a concern that drilling performance may degrade.
[0007]
In a case where a borehole with a greater internal diameter is formed using
the
under-reaming bit described in PTL 2, the radius of the extendable bit from
the axis in the
extending state is increased. However, there is also a limitation to enlarge
the
extendable bit in order to shrink the extendable bit and recover it with the
shank device
after the end of the drilling. Moreover, in forming a borehole having a
greater internal
diameter, load becomes larger. As a result, there is also a concern that
damage may
occur on a shaft that rotatably supports the extendable bit. Further, there is
also a
limitation to the number of drilling tips disposed on the extendable bit, and
drilling
performance degrades as the diameter of a borehole becomes larger.
[0008]
The present invention has been made in view of such a background, and the
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objective thereof is to provide a borehole that can prevent degradation of
drilling
performance, occurrence of damage, and an increase in construction cost, in a
case where
a borehole with a greater internal diameter than the external diameter of a
casing pipe is
drilled.
SOLUTION TO PROBLEM
[0009]
In order to solve the above problems and achieve the objective, the present
invention provides a drilling tool including: a cylindrical casing pipe
centered on an axis;
an annular ring bit that is coaxially disposed on a tip side of the casing
pipe and has a
greater external diameter than the casing pipe; and a pilot bit that is
inserted into an inner
peripheral part of the ring bit through the inside of the casing pipe. The
pilot bit is
rotatable around the axis and a bit head is provided at an outer peripheral
part of a tip of
the pilot bit. The bit head is rotatable around a centerline eccentric from
the axis, and is
configured that when the pilot bit is rotated in a tool rotation direction
during drilling, the
bit head is extended such that a radius of the bit head from the axis is
enlarged and
thereby is supported by the pilot bit. The ring bit is provided with: a part
to be engaged
that is configured to be engaged with the extended bit head in the tool
rotation direction
during drilling; and a first abutting part capable of abutting against the tip
side of the
extended bit head in a direction of the axis.
[0010]
In this drilling tool, the bit head provided at the outer peripheral part of
the tip of
the pilot bit is extended during drilling, and the first abutting part
provided at the ring bit
abuts against the tip side of the extended bit head in the direction of the
axis. Thus, the
ring bit can be prevented from coming off to the tip side thereof Also, since
the part to
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be engaged of this ring bit is engaged with the extended bit head in the tool
rotation
direction during drilling, rotating force can be transmitted from the pilot
bit via the bit
head to the ring bit.
[0011]
5 Therefore, even if the external diameter of the ring bit is made to
be greater than
the external diameter of the casing pipe, via the extended bit head of which
the radius
from the axis is enlarged, sufficient rotating force can be transmitted to the
ring bit, and
drilling performance can be guaranteed. Additionally, when the part to be
engaged of
the ring bit is engaged with the extended bit head in the tool rotation
direction during
drilling, in this way, the need for making an outer peripheral surface of a
posterior end
part of the ring bit face an inner peripheral surface of the casing pipe to
allow the
posterior end part to be rotatably inserted into the casing pipe is also
eliminated.
Therefore, the internal diameter of the ring bit can be increased, that is, a
required
material can be reduced by making the volume of the ring bit small. Thus, even
in a
case where after the end of drilling, the bit head is rotated in a direction
opposite to the
direction during drilling and the ring bit is left in a borehole, construction
cost can be
prevented from increasing.
[0012]
In contrast, in the pilot bit, even if the radius of the extended bit head
from the
axis is not made as large as the radius of the borehole, a borehole with a
large internal
diameter can be formed by the ring bit, and damage or the like to the bit head
can be
prevented without exerting an excessive load. Additionally, the number of the
drilling
tip disposed on the annular ring bit that drills the outer peripheral side of
the borehole can
be relatively freely set, and it is also possible to prevent degradation of
drilling
performance resulting from shortage of chips.
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[0013]
Here, when a recessed portion that is recessed to an outer peripheral side is
formed at the inner peripheral part of the ring bit, and the recessed portion
serves as the
part to be engaged, the volume of the ring bit can be further reduced, and
construction
cost can be further reduced. In addition, in this case, a tip surface of the
ring bit
adjacent to the recessed portion may serve as the first abutting part, and a
bottom surface
that faces the tip side in the direction of the axis may be formed in the
recessed portion so
as to serve as the first abutting part.
[0014]
In addition, in building the casing pipe in a borehole with the striking force
and
the impelling force to the tip side in the direction of the axis to be applied
to the pilot bit,
as in the drilling tools described in PTLs 1 and 2, a smaller-diameter part of
which an
internal diameter is one step smaller may be formed at an inner peripheral
part of a tip of
the casing pipe, and a second abutting part like a stepped part capable of
abutting against
the smaller-diameter part from a posterior end side in the direction of the
axis may be
formed at an outer peripheral part of a posterior end of the pilot bit so as
to transmit the
striking force and the impelling force. In this case, by making the internal
diameter of
the ring bit equal to or greater than the internal diameter of the smaller-
diameter part, the
volume of the ring bit can be made small as described above, and construction
cost can
be reliably reduced.
[0015]
In transmitting the striking force and the impelling force to the tip side in
the
direction of the axis to the ring bit, the striking force and the impelling
force may be
directly transmitted to the ring bit from the pilot bit as in the drilling
tool described in
PTL 1. However, in that case, when the smaller-diameter part is formed at the
inner
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peripheral part of the tip of the casing pipe and is made to be capable of
abutting against
the stepped part of the pilot bit as described above, a smaller-diameter part
of which the
internal diameter is further smaller than the smaller-diameter part of the
casing pipe must
be formed at the ring bit to abut against the pilot bit, and consequently,
there is a concern
that it becomes difficult to make the internal diameter of the ring bit small
as described
above to reduce construction cost.
[0016]
Thus, particularly in such a case, by providing the bit head with a third
abutting
part which is capable of abutting against a surface of the ring bit that faces
a posterior
end side in the direction of the axis in a state where the bit head is
extended, it becomes
unnecessary to form a smaller-diameter part having a smaller internal diameter
than the
smaller-diameter part of the casing pipe in the ring bit, construction cost
can be much
more reliably reduced, and it is possible to reliably transmit the striking
force and the
impelling force from the pilot bit to the tip side in the direction of the
axis to the ring bit
via the third abutting part of the bit head.
[0017]
Moreover, in this case, by making the greatest radius of the third abutting
part of
the extended bit head from the axis greater than a radius of an outer
peripheral part of the
tip of the casing pipe from the axis, the striking force and the impelling
force can be
transmitted to the outer peripheral side of the ring bit where drilling is
performed. In a
case where a borehole with a greater internal diameter than the external
diameter of the
casing pipe is formed, it is possible to perform even more efficient drilling,
the thickness
of the ring bit in the direction of the axis can also be made small, and much
more
construction cost reduction can be achieved.
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ADVANTAGEOUS EFFECTS OF INVENTION
[0018]
As described above, according to the present invention, even in a case where a
borehole with a greater internal diameter than the external diameter of the
casing pipe is
formed, it is possible to transmit sufficient rotating force to the ring bit
and to perform
efficient drilling, without causing degradation of drilling performance, an
increase in
construction cost, or damage to the tool.
BRIEF DESCRIPTION OF DRAWINGS
[0019]
FIG. 1 is a cross-sectional view showing a state where a bit head is extended
in
one embodiment of the present invention.
FIG. 2 is an enlarged front view when the embodiment shown in FIG. 1 in a
state
where the bit head is retracted is seen from a tip side in a direction of an
axis (illustration
of a casing pipe and a casing top is omitted).
FIG. 3 is an enlarged front view when the embodiment shown in FIG 1 in a state
where the bit head is extended is seen from the tip side in the direction of
the axis
(illustration of the casing pipe and the casing top is omitted).
FIG. 4 is an enlarged front view when the ring bit of the embodiment shown in
FIG 1 is seen from the tip side in the direction of the axis.
FIG. 5 is Z-Z sectional view in FIG. 4.
DESCRIPTION OF EMBODIMENTS
[0020]
FIGS. 1 to 5 show one embodiment of a drilling tool of the present invention.
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In the present embodiment, a casing pipe 1 is formed in a cylindrical shape
centered on
an axis 0 using metallic materials, such as a steel material, and a casing top
IA formed in
a multi-stage cylindrical shape using metallic materials, such as a steel
material, is
attached to a tip part (left side in FIG 1) of the casing pipe 1.
[0021]
In the casing top 1A, the internal diameter thereof is a constant internal
diameter
that is one step smaller than the internal diameter of the casing pipe 1, the
external
diameter of a tip part is the same diameter as the casing pipe 1, and the
external diameter
of a posterior end part is of a size such that the posterior end part can be
inserted and
fitted into the casing pipe 1. The posterior end part of the casing top 1A is
inserted and
fitted into the casing pipe 1 from a tip side of the casing pipe 1 and then
jointed by
welding or the like, whereby the casing top 1A is coaxially integrated with
the casing
pipe 1.
[0022]
By attaching the casing top lA in this way, a smaller-diameter part 1B of
which
the internal diameter is one step smaller is formed at an inner peripheral
part of the tip of
the casing pipe 1. In addition, a posterior end surface of the smaller-
diameter part 1B is
formed in the shape of a concave conical surface which is centered on the axis
0 and tilts
toward an inner peripheral side so as to become slightly closer to the tip
side.
[0023]
A pilot bit 2 is inserted into the casing pipe 1 from a posterior end side
thereof
(right side in FIG 1). The pilot bit 2 is made of metallic materials such as a
steel
material and has an outer shape that is also formed in a multi-stage columnar
shape, and a
posterior end part thereof is made into a smaller-diameter shank part 2A.
Striking force
directed to the tip side in the direction of the axis 0 is transmitted to the
pilot bit 2 from a
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down-the-hole hammer H attached to the shank part 2A.
[0024]
Additionally, a drill rod (not shown) is added if necessary and is coupled to
the
posterior end side of the down-the-hole hammer H, and a drill rod disposed at
the most
5 posterior end is attached to a drilling device. The impelling force
directed to the tip side
in the direction of the axis 0 and the rotating force directed in a tool
rotation direction T
during drilling are transmitted to the pilot bit 2 from the drilling device
via the drill rod
and the down-the-hole hammer H. In addition, the casing pipe 1 is also added
to the
posterior end side if necessary and is inserted into a borehole.
10 [0025]
A stepped part of which the external diameter becomes a maximum is formed at
an outer periphery of the pilot bit 2 at i position closer to the tip side
than the shank part
2A, and serves as a second abutting part 2B of the present embodiment. The
external
diameter of the second abutting part 2B is slightly smaller than the internal
diameter of
the casing pipe 1 and greater than the internal diameter of the smaller-
diameter part 1B
formed by the casing top 1A. Moreover, a tip surface of the second abutting
part 2B is
formed in the shape of a convex conical surface which tilts toward the inner
peripheral
side so as to become slightly closer to the tip side, and the tilt angle
thereof is equal to the
tilt angle of the posterior end surface of the smaller-diameter part 1B that
forms the
concave conical surface shape.
[0026]
Therefore, the pilot bit 2 is coaxial with the casing pipe 1 and the casing
top lA
movable integrally with the casing pipe 1 and the casing top 1A to the tip
side in the
direction of the axis 0, and rotatable around the axis 0 relative to the
casing pipe 1 and
the casing top 1A, in a place where the pilot bit 2 is inserted into the
casing pipe 1 from
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the posterior end side thereof and the second abutting part 2B abuts against
the
smaller-diameter part 1B. Additionally, the external diameter of the pilot bit
2 at a
position closer to the tip side than the second abutting part 2B is a constant
external
diameter slightly smaller than the internal diameter of the smaller-diameter
part 1B
formed by the casing top 1A, and thus a tip part of the pilot bit 2 is formed
so as to
protrude greatly from the tip of the casing top lA in a state where the second
abutting
part 2B abuts against the smaller-diameter part 1B.
[0027]
A housing recess 3 is formed at an outer periphery of the tip part of the
pilot bit
2 protruding from the tip of the casing top 1A so as to be located closer to
the tip side
than the casing top 1A. The housing recess 3 includes: a bottom surface 3A
that is
located closer to the tip side than the casing top 1A, faces the tip side, and
is
perpendicular to the axis 0; and a wall surface 3B that extends to tip side in
parallel with
the axis 0 from an inner peripheral edge of the bottom surface 3A and reaches
a tip
surface of the pilot bit 2. The housing recess 3 is formed so as to be open to
an outer
peripheral surface and a tip surface of the tip part of the pilot bit 2. In
the present
embodiment, a plurality of (three) such housing recesses 3 having the same
form and the
same size are formed at equal intervals in a circumferential direction.
[0028]
A wall surface 3B of each housing recess 3 includes: a first wall part 3a that
is a
plane facing an outer peripheral side of the pilot bit 2; a second wall part
3b that is a
plane located on a side opposite to the first wall part 3a in the tool
rotation direction T
and facing the tool rotation direction T; and a third wall part 3c that is a
plane located on
the same side as the first wall part 3a in the tool rotation direction T and
facing the side
opposite to the tool rotation direction T. The second and third wall parts 3b
and 3c are
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formed such that a gap therebetween in the circumferential direction becomes
greater
toward the outer peripheral side, and the second wall part 3b out of these
wall parts
extends toward the outer peripheral side so as to tilt to the tool rotation
direction T.
[0029]
Additionally, a fourth wall part 3d and a fifth wall part 3e are formed in the
shape of a concave cylindrical surface centered on a straight line parallel to
the axis 0 at
a boundary part between the first and second wall parts 3a and 3b and a
boundary part
between the first and third wall parts 3a and 3c, respectively. The fourth
wall part 3d
connects with the first and second wall parts 3a and 3b, and the fifth wall
part 3e
connects with the first and third wall parts 3a and 3c. The radius of the
concave
cylindrical surface as the fourth wall part 3d formed at the boundary part
between the
first and second wall part 3a and 3b is greater than the radius of the concave
cylindrical
surface as the fifth wall part 3e formed at the boundary part between the
first and third
wall parts 3a and 3c.
[0030]
Moreover, a discharge groove 2C for cuttings is formed which extends toward
the posterior end side in parallel with the axis 0 from the tool rotation
direction T side of
the bottom surface 3A of each housing recess 3 and reaches an outer peripheral
side of
the shank part 2A beyond the second abutting part 2B. Each discharge groove 2C
forms
a substantially rectangular shape in a cross-section perpendicular to the axis
0 and is
open to an outer peripheral surface of the tip part of the pilot bit 2. A
bottom surface of
each discharge groove 2C which faces the outer peripheral side of the pilot
bit 2 forms a
recessed curved shape and is slightly swept toward the outer peripheral side
in a place
where the bottom surface reaches a posterior end of the second abutting part
2B. A
portion where this bottom surface and the bottom surface 3A of the housing
recess 3
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intersect each other is chamfered by an inclined surface 2D that intersects
with both the
bottom surfaces at an obtuse angle.
[0031]
On the other hand, a fitting hole 3C that has a centerline C parallel to the
axis 0
and has a circular cross-sectional shape is formed on the side opposite to the
bottom
surface 3A of each housing recess 3 in the tool rotation direction T. The
centerline C of
the fitting hole 3C coincides with the centerline of the concave cylindrical
surface as the
fourth wall part 3d formed at the boundary part between the first and second
wall parts 3a
and 3b, and is eccentric to the outer peripheral side of the axis 0.
Additionally, the
internal diameter (radius) of the fitting hole 3C is approximately equal to or
slightly
smaller than the radius of the concave cylindrical surface as the fourth wall
part 3d.
[0032]
A bit head 4 is attached to each of the housing recesses 3 of the pilot bit 2.
In
the bit head 4, a columnar shaft part 4A to be inserted and slidably fitted
into the fitting
hole 3C and a head main body 4B provided on the tip side of the shaft part 4A
are
integrally formed using metallic materials, such as a steel material. The bit
head 4 is
attached so as to be rotatable around the centerline C. The bit head 4 is
positioned in a
state where as shown in FIG. 2, the head main body 4B abuts against the first
wall part 3a
and is housed within the housing recess 3 and the radius thereof from the axis
0 is
reduced, or is positioned in a state where as shown in FIG. 3, the head main
body 4B
abuts against the second wall part 3b and the radius thereof from the axis 0
is enlarged.
A posterior end surface of the head main body 4B is a plane perpendicular to
the
centerline C.
[0033]
A cutout 4C is formed at an outer periphery of the shaft part 4A such that the
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cutout 4C forms a semi-oval shape as shown in FIG 1 in a cross-section along
the
centerline C and extends to form a substantial L-shape as shown in FIGS. 2 and
3 in a
section perpendicular to the centerline C. A pin 5 is driven into the tip part
of the pilot
bit 2 in a tangential direction of the fitting hole 3C in the cross-section
orthogonal to the
axis 0, at a position that faces the cutout 4C in the direction of the axis 0
in a state where
the shaft part 4A is inserted into the fitting hole 3C, a posterior end
surface of the shaft
part 4A is made to abut against the bottom surface of the fitting hole 3C, and
a posterior
end surface of the head main body 4B is made to abut against the bottom
surface 3A of
the housing recessed portion 3. A peripheral surface of each pin 5 is exposed
inside the
fitting hole 3C and is engaged with the cutout 4C, and thereby the bit head 4
is prevented
from coming off to the tip side while being made to be rotatable around the
centerline C.
[0034]
Additionally, a first side surface 4a, which is located on an extension of an
outer
peripheral surface of the shaft part 4A among side surfaces of the head main
body 4B, is
formed in the shape of a convex cylindrical surface centered on the centerline
C which
flushes with this outer peripheral surface of the shaft part 4A or has an
external diameter
slightly greater than that of the outer peripheral surface of the shaft part
4A. The first
side surface 4a is made to be slidable on the fourth wall part 3d of the wall
surface 3B of
the housing recess 3. Moreover, second and third side surfaces 4b and 4c that
sandwich
the first side surface 4a therebetween are formed in a planar shape. As shown
in FIG 2,
in a state where the bit head 4 is retracted, the second side surface 4b out
of these side
surfaces is made to abut against the first wall part 3a of the wall surface 3B
of the
housing recess 3 while the third side surface 4c faces the outer peripheral
side of the pilot
bit 2. In a state where the bit head 4 is extended, the third side surface 4c
is made to
abut against the second wall part 3b while the second side surface 4b is
directed to the
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tool rotation direction T.
[0035]
Moreover, a fourth side surface 4d, which is located between the second and
third side surfaces 4b and 4c on a side opposite to the first side surface 4a,
is formed so
5 as to protrude to the outer periphery of the pilot bit 2 and be located
on a cylindrical
surface centered on the axis 0, as shown in FIG 3 in a state where the bit
head 4 is
extended. In addition, an intersecting ridgeline part between the fourth side
surface 4d
and the third side surface 4c is formed so as to be chamfered by a cylindrical
surface that
has a diameter slightly smaller than the external diameter of the tip part of
the pilot bit 2
10 and is centered on the axis 0 in a state where the bit head 4 is
retracted as shown in FIG.
2. Accordingly, the head main body 4B retracted and housed in the housing
recess 3 is
located inside a cylindrical surface of the outer peripheral surface of the
tip part of the
pilot bit 2.
[0036]
15 Additionally, the fourth side surface 4d is formed in a multi-stage
(three-stage in
the present embodiment) shape that becomes concave and convex to the inner and
outer
peripheral sides with respect to the axis 0 toward the direction of the
centerline C as
shown in FIG 1. A stage at the most posterior end among these stages is made
to
protrude to the outermost peripheral side from the axis 0, and a portion in
which the
stage at the most posterior end is formed serves as a third abutting part 4D
in the present
embodiment. The third abutting part 4D has a surface thereof facing the tip
side which
is a flat surface perpendicular to the centerline C, and a greatest radius R
of the third
abutting part 4D from the axis 0 is greater than a radius r of the outer
peripheral parts of
the tips of the casing pipe 1 and the casing top lA from the axis 0 in a state
where the bit
head 4 is extended as shown in FIG. 1.
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[0037]
In addition, an intersecting ridgeline part between the fourth side surface 4d
and
the second side surface 4b in which the third abutting part 4D is formed is
chamfered in
the shape of a convex cylindrical surface with a radius approximately equal to
a concave
cylindrical surface as the fifth wall part 3e of the housing recess 3, and as
shown in FIG
2, is made to abut against the fifth wall part 3e in a state where the bit
head 4 is retracted.
Additionally, a stage at a foremost end of the fourth side surface 4d slightly
tilts toward
the posterior end side so as to become closer to the inner peripheral side in
a stage where
the bit head 4 is extended.
[0038]
Moreover, at a middle stage located between the stage at the foremost end and
a
stage at a most posterior end in which the third abutting part 4D is formed,
the fourth side
surface 4d is formed so as to extend in parallel with the axis 0. Furthermore,
an
engaging part 4E is formed at a corner part where that the fourth side surface
4d the
second side surface 4b intersect with each other in this middle stage, such
that the
engaging part 4E cuts out the corner part in a substantial L-shape in a
section orthogonal
to the centerline C.
[0039]
The engaging part 4E has a first wall surface 4e facing the outer peripheral
side
and a second wall surface 4f facing the tool rotation direction T, in a state
where the bit
head 4 is extended, a bottom surface 4g that is made to be flush with a
surface of the
third abutting part 4D which faces the tip side, and a ceiling surface 4h that
faces the
bottom surface 4g in parallel therewith and faces the posterior end side.
Similarly, in a state where the bit head 4 is extended, the first wall surface
4e is
located on a cylindrical surface that has a slightly greater external diameter
than the
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second abutting part 2B of the pilot bit 2 and is centered on the axis 0, and
the second
wall surface 4f is formed such that the second wall surface 4f extends toward
the outer
peripheral side so as to slightly tilt to the tool rotation direction T.
[0040]
Moreover, an intersecting ridgeline part between a stage at a foremost end of
the
fourth side surface 4d and a tip surface of the head main body 4B is formed as
an
inclined surface that extends toward the centerline C so as to become closer
the tip side
in such a manner the surface forms a truncated conical surface shape centered
on the axis
0 in a state where the bit head 4 is extended. Additionally, an intersecting
ridgeline part
between the tip surface and the outer peripheral surface in the pilot bit 2 is
also formed as
an inclined surface that similarly forms a truncated conical surface shape
centered on the
axis 0 and tilts toward the inner peripheral side so as to become closer the
tip side,
except for the portion cutout by the housing recess 3.
[0041]
Furthermore, the tip surface of the pilot bit 2 and the tip surface of the
head main
body 4B of the bit head 4 except the portions made to have these inclined
surfaces are
respectively flat surfaces perpendicular to the axis 0 and the centerline C.
Additionally, the length of the head main body 4B in the direction of the
centerline C is equal to the depth from the bottom surface 3A of the housing
recess 3 to
the tip surface of the pilot bit 2. Therefore, the tip surfaces of the pilot
bit 2 and the
head main body 4B become flush with each other in a state where the bit head 4
is
housed in the housing recess 3.
[0042]
The tip surfaces and the respective inclined surfaces of the pilot bit 2 and
the
head main body 4B of the bit head 4 are provided with a plurality (large
number) of
CA 02957394 2017-02-06
18
drilling tips 6 made of cemented carbide or the like which is harder than a
steel material
or the like that forms the pilot bit 2 and the bit head 4. Each of the
drilling tips 6 is one
in which, for example, hemispherical head part protruding from the tip
surfaces and the
inclined surfaces and columnar trunk part which are integrally formed, and is
fixed by
press-fitting, hot-shrink fitting, cold-shrink fitting, or brazing the trunk
parts into each of
circular holes formed perpendicularly to the tip surfaces and the inclined
surfaces.
[0043]
Moreover, an annular ring bit 7 is disposed coaxially with the axis 0 on the
tip
side of the casing pipe 1. The ring bit 7 is also formed in an annular plate
shape using
metallic materials, such as a steel material, and a tip surface and a
posterior end surface
thereof that face the direction of the axis 0 are perpendicular to the axis 0.
However,
the intersecting ridgeline part between the tip surface and the outer
peripheral surface is
made to be a truncated cone-shaped inclined surface centered on the axis 0.
The
drilling tips 6 made of hard materials, such as cemented carbide, are also
provided on the
inclined surface and the outer peripheral part of the tip surface so as to
protrude
perpendicularly thereto, similar to the pilot bit 2 and the bit head 4.
[0044]
Additionally, the external diameter of the ring bit 7 is greater than the
external
diameter of the casing pipe 1 and the casing top lA and greater than the
external diameter
of the extended bit head 4. Further, the internal diameter of the ring bit 7
is slightly
greater than the external diameter of the second abutting part 2B of the pilot
bit 2 and
therefore greater than the internal diameter of the smaller-diameter part 1B
formed within
the casing pipe 1 by the casing top 1A. The internal diameter of the ring bit
7, is smaller
than the external diameter of the extended bit head 4 and is of such a size
that the first
wall surface 4e of the engaging part 4E is finable. Additionally, the
thickness of the
' CA 02957394 2017-02-06
19
ring bit 7 in the direction of the axis 0 is smaller than the width between
the external and
internal diameters of the ring bit 7, and is slightly smaller than a gap
between the bottom
surface 4g and the ceiling surface 4h of the engaging part 4E.
[0045]
Moreover, three recessed portions that are recessed to the outer peripheral
side
and are of the same number as that of the bit heads 4 are formed at equal
intervals in the
circumferential direction at the inner peripheral part of the ring bit 7, and
as shown in FIG.
3, each of the recessed portions serves as a part 7A to be engaged that is
engaged with the
engaging part 4E of each bit head 4 in the tool rotation direction T during
drilling.
The part 7A to be engaged includes a first wall surface 7a that recedes by one
step from the inner peripheral part of the ring bit 7 to the outer peripheral
side and then
faces the inner peripheral side, a second wall surface 7b facing the side
opposite to the
tool rotation direction T and a third wall surface 7c facing the tool rotation
direction T
which extend from the first wall surface 7a to the inner peripheral part. In
the present
embodiment, the part 7A to be engaged is formed so as to pass through the ring
bit 7 in
the direction of the axis 0.
[0046]
The first wall surface 7a among these surfaces is located on the cylindrical
surface centered on the axis 0. The radius of the first wall surface 7a from
the axis 0 is
slightly greater than the radius of the stage at the foremost end and the
middle stage from
the axis 0 in the fourth side surface 4d of the extended bit head 4 which
faces the outer
peripheral side and is smaller than the radius R of the third abutting part
4D. Further,
the circumferential length of the first wall surface 7a is slightly greater
than a length
except the engaging part 4E in the circumferential length of the middle stage
of the fourth
side surface 4d.
CA 02957394 2017-02-06
[0047]
Additionally, the second and third wall surfaces 7b and 7c extend toward the
outer peripheral side so as to tilt to the tool rotation direction T, and an
angle that the
second wall surface 7b out of these wall surfaces makes with respect to a
radial direction
5 with respect to the axis 0 is equal to an angle that the second wall
surface 4f in the
engaging part 4E of the extended bit head 4 makes with the radial direction
with respect
to the axis 0. Further, as shown in FIG. 3, the third wall surface 7c is
formed in a
concave cylindrical surface shape centered on the centerline C of the fitting
hole 3C in
the housing recess 3 of the pilot bit 2, in a state where the part 7A to be
engaged is
10 engaged with the engaging part 4E.
[0048]
In addition, in the pilot bit 2, a bottomed supply hole 8 is drilled from a
posterior
end of the shank part 2A along the axis 0 to the vicinity of a central part of
the housing
recess 3 in the direction of the axis 0 so as to be capable of supplying
compressed air
15 therethrough from the down-the-hole hammer H side. First to third blow
holes 8A to
8C, which are three for each and have a smaller diameter than the supply hole
8, branch
obliquely from the supply hole 8 and extend toward the outer peripheral side
so as to tilt
to the tip side.
[0049]
20 Each first blow hole 8A is open to the tip side of the second abutting
part 2B in
the outer peripheral surface of the tip part of the pilot bit 2. A fourth blow
hole 8D with
a much smaller diameter branches from each first blow hole 8A in parallel with
the axis
0 and is open to the center of the bottom surface of the fitting hole 3C.
Further, each
second blow hole 8B branches from the supply hole 8 at a position closer to
the tip side
than each first blow hole 8A, and is open substantially perpendicularly to the
inclined
CA 02957394 2017-02-06
21
surface 2D between the bottom surface of each discharge groove 2C for cuttings
and the
bottom surface 3A of each housing recess 3. Moreover, each third blow hole 8C
has a
greater diameter than the first and second blow holes 8A and 8B, branches at
the tip of
the supply hole 8, and is open to the fifth wall part 3e side of the first
wall part 3a of the
housing recess 3.
[0050]
In this drilling tool, the pilot bit 2 is inserted from the posterior end side
of the
casing pipe 1 in a state where the bit head 4 is retracted and the head main
body 4B is
housed in the housing recess 3, and is positioned in the direction of the axis
0 in a place
where the second abutting pail 2B abuts against the posterior end surface of
the casing
top 1A. Next, with the head main body 4B being housed, as shown in FIG 2, a
circumferential position of the part 7A to be engaged is aligned with the
housing recess 3,
and the ring bit 7 is inserted into the tip part of the pilot bit 2 from the
tip side and is
disposed at the position of the engaging part 4E of the head main body 4B in
the
direction of the axis 0.
[0051]
When, from this state, the ring bit 7 is relatively rotated to the side
opposite to
the tool rotation direction T during drilling while the bit head 4 is being
extended, as
shown in FIG 3, the second wall surface 4f in the engaging part 4E of the
extended bit
head 4 comes in close contact with and abuts against the second wall surface
7b in the
part 7A to engaged of the ring bit 7 and thereby is engaged with the part 7A
to be
engaged, and the third side surface 4c in the head main body 4B abuts against
the second
wall part 3b of the housing recess 3 and is supported by the housing recess 3.
Thereby,
the ring bit 7 becomes integrally rotatable with respect to the pilot bit 2
and the bit head 4
in the tool rotation direction T.
CA 02957394 2017-02-06
22
[0052]
Additionally, in the direction of the axis 0, as shown in FIGS. 1 and 3, when
the
portion of the part 7A to be engaged on the tool rotation direction T side in
the tip surface
of the ring bit 7 faces the ceiling surface 4h of the engaging part 4E with a
slight gap
therefrom and is abuttable against the ceiling surface 4h, the ring bit 7 is
prevented from
coming off to the tip side. That is, in the present embodiment, the portion of
the part 7A
to be engaged on the tool rotation direction T side in the tip surface of the
ring bit 7
serves as a first abutting part 7B that is abuttable against the extended bit
head 4, on the
tip side in the direction of the axis 0. Moreover, the bottom surface 4g of
the engaging
part 4E and the surface of the third abutting part 4D flush with the bottom
surface 4g
which faces the tip side abut against the posterior end surface of the ring
bit 7, and
support the ring bit 7 on the tip side thereof. Thereby, the casing pipe 1 and
the ring bit
7 are made to be movable to the tip side in the direction of the axis 0
integrally with the
pilot bit 2 and the bit head 4.
[0053]
Therefore, when, from this state, the striking force directed to the tip side
in the
direction of the axis 0 is transmitted to the pilot bit 2 and the bit head 4
and to the ring
bit 7 via the third abutting part 4D by the down-the-hole hammer H and the
impelling
force, and the rotating force directed in the tool rotation direction T are
transmitted from
the drilling device, drilling work is performed by the drilling tips 6
provided on the pilot
bit 2, the bit head 4, and the tip surface of the ring bit 7, and the casing
pipe 1 is inserted
into the formed borehole. In addition, compressed air is blown off from the
supply hole
8 via the first to fourth blow holes 8A to 8D during drilling. Thereby,
cuttings
generated by the drilling tip 6 are discharged through the inside of the
casing pipe 1 from
the discharge groove 2C, and biting of the cuttings into the fitting hole 3C
or the
CA 02957394 2017-02-06
23
smaller-diameter part 1B is prevented.
[0054]
After the borehole is formed up to a predetermined depth in this way, in the
drilling tool of the above configuration, the pilot bit 2 is rotated to the
side opposite to the
tool rotation direction T during drilling by the drilling device. Then, the
head main
body 4B of the bit head 4 is guided by friction with the borehole and by the
third wall
surface 7c of the part 7A to be engaged, and thereby the bit head 4 is
retracted as shown
in FIG. 2. Thus, the pilot bit 2 and the bit heads 4 can be recovered with the
ring bit 7
being left in the borehole by pulling out the pilot bit 2 together with the
down-the-hole
hammer H as it is from the casing pipe 1.
[0055]
In this way, according to the drilling tool of the above configuration, the
rotating
force in the tool rotation direction T is transmitted from the head main body
4B of the
extended bit head 4 to the part 7A to be engaged of the ring bit 7. Thus, the
rotating
force can be efficiently transmitted at a position farther from the axis 0
which becomes
the rotation center of the pilot bit 2 and the bit head 4. Accordingly, even
in a case
where a borehole with a greater internal diameter than the external diameter
of the casing
pipe 1 is formed, sufficient rotating force can be transmitted to the ring bit
7, and drilling
performance can be guaranteed.
[0056]
Moreover, in the present embodiment, the pilot bit 2 and the bit head 4
protrude
by one step to the tip side of the ring bit 7 as shown in FIG 1. Therefore,
the drilling
tips 6 on the ring bit 7 drill an outer peripheral part of the borehole of
which an inner
peripheral part is drilled by the drilling tips 6 on the pilot bit 2 and the
bit head 4, and
becomes apt to be crushed. For this reason, the load to the ring bit 7 can be
reduced,
CA 02957394 2017-02-06
24
and more efficient drilling can be performed. Here the tip surfaces of the
pilot bit 2 and
the bit head 4 may be made to be flush with the tip surface of a ring bit 7,
and the tip
surface of the ring bit 7 may protrude from the tip surfaces of the pilot bit
2 and the bit
head 4.
[0057]
Additionally, since the outer peripheral side of the borehole is drilled by
the ring
bit 7, in the pilot bit 2 and the bit head 4, it is not necessary to make the
radius of the
extended head main body 4B from the axis 0 as large as the internal diameter
of the
borehole. For this reason, a burden to the shaft part 4A of the bit head 4 or
the like can
be reduced, and damage can be prevented. Moreover, since the ring bit 7 forms
an
annular shape, the number and positions of the drilling tips 6 can be
relatively freely set,
for example, like the drilling tips 6 being disposed in ranges other than a
range in the
circumferential direction where the extended bit head 4 as shown in FIG 3 is
located.
Therefore, degradation of the drilling performance resulting from partial
insufficiency of
the drilling tips 6 can also be prevented.
[0058]
In the ring bit 7, the part 7A to be engaged is engaged with the extended bit
head
4 as described above, while the ring bit 7 is supported by the bit head 4 so
as to be
rotatable integrally therewith in the tool rotation direction T and the
rotating force is
transmitted to the ring bit 7. Thus, it becomes unnecessary to support the
ring bit 7 with
the casing pipe 1, and the internal diameter of the ring bit 7 can be
increased. For this
reason, required materials such as a steel material can be reduced by making
the volume
of the ring bit 7 small, and even in a case where the ring bit 7 is left in a
borehole after
the end of drilling, an increase in construction cost can be suppressed.
[0059]
CA 02957394 2017-02-06
Additionally, as described above, the inner peripheral part of the borehole is
drilled by the drilling tips 6 on the pilot bit 2 and the bit head 4. Thus, in
the present
embodiment, it is not necessary to provide the ring bit 7 with the drilling
tip 6, as shown
in FIGS. 1 and 3, in a range where the drilling tips are provided on the tip
surface of the
5 head main body 4B of the extended bit head 4 in the radial direction from
the axis 0.
For this reason, it is possible to avoid providing more drilling tips 6 made
of expensive
cemented carbide than needed in the ring bit 7 left in the borehole, and cost
reduction can
be achieved.
[0060]
10 Moreover, in the present embodiment, a recessed portion that is
recessed toward
the outer peripheral side is formed in the inner peripheral part of the ring
bit 7, and serves
as the part 7A to be engaged. In this regard, for example, it is also possible
to form a
protrusion on the tip surface of the ring bit 7 as a part to be engaged to
engage the head
main body 4B of the extended bit head 4 with this protrusion in the tool
rotation direction
15 T. However, in that case, there is a concern that the load resulting
from the rotating
force may be concentrated on the protrusion to cause damage, and the volume of
the ring
bit 7 may also become as great as the protrusion and material cost may
increase. In
contrast, in the present embodiment, it is possible to receive the rotating
force with a
main body itself of the annular ring bit 7, and the volume and cost of the
ring bit 7 can be
20 further reduced.
[0061]
In addition, in the present embodiment, the portion adjacent to the part 7A to
be
engaged at the tool rotation direction T side thereof which is formed as the
recessed
portion recessed from the inner peripheral part toward the outer peripheral
side in this
25 way in the tip surface of the ring bit 7 faces the ceiling surface 4h of
the engaging part 4E,
CA 02957394 2017-02-06
26
and serves as the first abutting part 7B abuttable against the ceiling surface
4h of the
engaging part 4E on the tip side in the direction of the axis 0. For example,
even if the
ring bit 7 collides against the ceiling surface 4h with the striking force
transmitted via the
bit head 4 from the pilot bit 2, a shock can be received over the overall
thickness of the
ring bit 7, and occurrence of damage or the like can be prevented. However,
the bottom
surface that faces the tip side may be formed in this recessed portion so as
to face the
ceiling surface 4h, and may be used as the first abutting part 7B.
[0062]
Also in the present embodiment, in inserting the casing pipe 1 into a borehole
with the striking force and the impelling force to the tip side to be applied
to the pilot bit
2, similar to the drilling tools described in PTLs 1 and 2, the casing top 1A
is attached to
the tip part of the casing pipe 1 to form the smaller-diameter part 1B, and
the second
abutting part 2B of the pilot bit 2 is made to abut against the smaller-
diameter part 1B so
as to transmit the striking force and the impelling force. However, in the
present
embodiment, the internal dialneter of the ring bit 7 is increased with respect
to the
internal diameter of this smaller-diameter part 1B. Thus, as described above,
construction cost can be reliably reduced compared to the drilling tool
described in PTL 1
in which the internal diameter of the ring bit has to be made smaller. In
addition, the
internal diameter of the ring bit 7 may be equal to the smaller-diameter part
1B.
[0063]
Furthermore, in the present embodiment, the striking force and the impelling
force are transmitted by providing the casing pipe 1 with the smaller-diameter
part 1B in
this way. In contrast, in transmitting the striking force and the impelling
force from the
pilot bit 2 to the ring bit 7, the striking force and the impelling force are
not directly
transmitted from the pilot bit 2 unlike the drilling tool described in PTL 1,
but the bit
CA 02957394 2017-02-06
27
head 4 is provided with the third abutting part 4D that is abuttable against
the posterior
end surface of the ring bit 7 in an extended state so as to transmit the
striking force and
the impelling force from the third abutting part 4D. For this reason, in a
case where the
smaller-diameter part 1B is provided as described above, it is unnecessary to
make the
internal diameter of the ring bit 7 still smaller, and it is possible to
reduce construction
cost even more reliably.
[0064]
Moreover, in the present embodiment, in a case where the striking force and
the
impelling force are transmitted from the third abutting part 4D provided in
the bit head 4
in this way to the ring bit 7, the greatest radius R of the third abutting
part 4D of the
extended bit head 4 from the axis 0 is greater than the radius r of the outer
peripheral
part of the tip of the casing pipe 1 from the axis 0, that is, the radius of
the casing top 1A.
For this reason, the striking force and the impelling force can be more
reliably
transmitted to the ring bit 7 on the outer peripheral side where drilling is
performed, and
even in a case where a borehole with a greater internal diameter than the
external
diameter of the casing pipe 1 as in the present embodiment is formed, it is
possible to
perform drilling much more efficiently.
[0065]
Then, in a case where the striking force and impelling force are transmitted
from
the third abutting part 4D that is enlarged and has the larger radius R than
the radius r of
the outer peripheral part of the tip of the casing pipe 1 to the ring bit 7 in
this way, it is
possible to reliably form a borehole with a large internal diameter without
impairing the
strength or rigidity of the ring bit 7 even if the thickness of the ring bit 7
in the direction
of the axis 0 is smaller than the width between the external and internal
diameters of the
ring bit 7 like, for example, the present embodiment. Therefore, according to
the
CA 02957394 2017-02-06
28
present embodiment, the volume of the ring bit 7 can be further reduced, and a
much
greater reduction of construction cost can be achieved.
INDUSTRIAL APPLICABILITY
[0066]
As described above, according to the drilling tool of the present invention,
even
in a case where a borehole with a greater internal diameter than the external
diameter of
the casing pipe is formed, it is possible to transmit sufficient rotating
force, striking force,
and impelling force to the ring bit and to perform efficient drilling, without
causing
degradation of drilling performance, an increase in construction cost, or
damage to the
tool. Therefore, the present invention can be industrially applied.
REFERENCE SIGNS LIST
[0067]
1: CASING PIPE
1A: CASING TOP
1B: SMALLER-DIAMETER PART
2: PILOT BIT
2B: SECOND ABUTTING PART
2C: DISCHARGE GROOVE
3: HOUSING RECESS
3C: FITTING HOLE
4: BIT HEAD
4A: SHAFT PART
4B: HEAD MAIN BODY
CA 02957394 2017-02-06
=
29
4D: THIRD ABUTTING PART
4E: ENGAGING PART
5: PIN
6: DRILLING TIP
7: RING BIT
7A: PART TO BE ENGAGED
7B: FIRST ABUTTING PART
8: SUPPLY HOLE
0: AXIS OF CASING PIPE 1
T: TOOL ROTATION DIRECTION DURING DRILLING
C: CENTERLINE OF FITTING HOLE 3C
H: DOWN-THE-HOLE HAMMER
R: GREATEST RADIUS OF THIRD ABUTTING PART 4D OF EXTENDED
BIT HEAD 4 FROM AXIS 0
r: RADIUS OF OUTER PERIPHERAL PART OF TIP OF CASING PIPE 1
FROM AXIS 0
