Note: Descriptions are shown in the official language in which they were submitted.
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A one-piece drill bit for single-pass anchor bolting and
single pass drilling apparatus
Background of the invention
The present invention relates to a drill bit and a single pass drilling
apparatus according to the preambles of the independent claims.
The installation of anchor bolts to reinforce excavations is usually carried
out in two distinct steps. Usually, a bore is drilled and the drill steel and
bit
extracted before the bolt is inserted into the bore and tightened or grouted.
Single pass anchor bolting involves carrying out these two steps
simultaneously,
with the task of removing the drill steel to insert the bolt being eliminated.
The
advantages of single pass bolting include minimizing the time required for
bolt
installation, improving safety for drilling equipment operators, when
comparing
with manual or semi manual bolting, and enhancing prospects for full
automation
of the process. A further advantage is improved quality and precision of
anchor
bolt installation, when comparing with manual or semi manual bolting. The
diameter of the bore is critical for anchor bolt performance in the case of
friction,
e.g. Split set bolts. Still a further advantage with single pass bolting is
that the
bore cannot collapse when retracting the drill bit since the bolt is already
in the
bore. This leads to much better efficiency as the bolt is always installed;
i.e. there
will be no lost holes.
Prior attempts at single pass bolting have generally been targeted at
innovative anchor bolts, which also act as the drill steel, having a drill bit
provided
about an end thereof. Such apparatus are used via a rotational drilling method
or
a rotary/percussive drilling method and are generally unsuitable for hard
ground
conditions. Existing hard ground percussive anchor bolts that do not reuse the
drill bit suffer from cost problems. A wide variety of roof bolts exist and
one
particular form is tubular (e.g. split-sets, Swellex, etc.), having a central
bore
formed lengthwise through the bolt. Drill bits adapted to be extracted through
a
casing have been complex and accordingly expensive. Cost competitiveness of
drilling speed versus bit cost are complicated in prior single pass anchor
bolts
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due to the use of specialized anchor bolts and the exclusive use of either
complex retractable bits. It nevertheless remains the case, that the
installation
advantages of a self-drilling roof bolt outweigh those of the non-self-
drilling type.
Objects of the invention
The drill bit according to the present invention has as one object to
substantially overcome the above-mentioned problems associated with the prior
art, or at least to provide an alternative thereto.
Another object of the present invention is to provide a single pass drill bit.
Still another object of the present invention is to provide a drill bit and a
single pass drilling apparatus that are less costly to use and so to make use
of
single pass bolting in the mining industry more attractive.
Still another object of the present invention is to provide a drill bit having
good wear resistance.
Throughout the specification, unless the context requires otherwise, the
word "comprise", or variations such as "comprises" or "comprising", will be
understood to imply the inclusion of a stated integer or group of integers but
not
the exclusions of any other integer or group of integers.
Brief description of the drawings
The attached drawings show an example embodiment of the invention of
the foregoing kind. The particularity of those drawings and the associated
description does not supersede the generality of the preceding broad
description
of the invention.
Figs. 1 A - 1 G schematically show a sequence of single pass roof bolting
using a drill bit according to the present invention. Fig. 2A shows the drill
bit
according to the present invention and a rod portion in a side elevational
view.
Fig. 2B shows the drill bit in a front view. Fig. 3A shows the drill bit
during drilling
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of a hole in the rock in a side elevational view. Fig. 3B shows the drill bit
in a front
view during drilling of the hole in the rock.
Detailed description of the invention
Figs. 1 A - 1 G show a single pass drilling apparatus 10 according to the
present invention using a drill bit 16 according to the present invention and
Figs.
2A-3B more closely show the drill bit 16 according to the present invention.
The
single pass drilling apparatus 10 comprises several parts; e.g. an elongated
drill
steel 11 having a leading end 12 and a trailing end, not shown, reference
being
had to a drilling direction F. The leading end 12 has a connection portion
comprising a thread 15, a taper or a bayonet connection, not shown. A one-
piece
drill bit 16 is provided having rock machining means 17 and 18A, 18B, 18C. The
drill bit 16 is connectable to the drill steel via a connection portion 20
comprising
a thread, a taper or a bayonet connection (not shown). The drill steel 11 and
the
drill bit constitute drilling means. The single pass drilling apparatus 10
further
comprises an anchor bolt 21 adapted to at least partially enclose the drill
steel
11. The anchor bolt 21 has open ends. The greatest diametrical dimension of
the
drill bit is smaller than the smallest diameter of the anchor bolt 21.
The basic idea of the single pass drilling apparatus 10 is to drill the bore
while the bolt encloses the drill steel, and then to retract the bit to be
used again.
There are no losses of bit parts. The single pass drilling apparatus 10 has
been
more closely described in Swedish Patent Application No. 0400597-1, the
disclosure of which is hereby incorporated by reference.
The drill bit 16 can be designed as follows, reference being had to Figs. 2A
and 2B. The one-piece drill bit 16 has two integral parts, i.e. a pilot part
14, long
enough, i.e. the length L, to guide the entire apparatus 10 properly, and a
reamer
part 19. The center line or middle line CL1 of the pilot part 14 forms an
acute
second angle a with an axis CL3 extending parallel to a first center line CL2
of
the reamer part. The angle a is -20 to +20 , excluding 0 , preferably not
less
than +0.1 and not more than +15 , index "+" being shown in Figs. 2A and 3A.
The middle line CL1 will during drilling substantially coincide with the axis
of the
bore 22. The middle line CL1 of the pilot part 14 also substantially coincides
with
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the center line of the anchor bolt 21 during drilling, but not during
retraction of the
drill bit. The center line or middle line CL2 of the reamer part 19 and the
center
line of the drill steel 11 coincide when not drilling. It should be noted that
neither
the pilot part 14 nor the reamer part 19 has to be circular or symmetrical in
radial
cross-section, so the reference to lines CL1 and CL2 shall be understood as a
reference to average middle lines in the respective parts.
The one-piece rock drill bit 16 comprises a body 25 and cemented carbide
means, i.e. chisels and/or buttons 17, 18A, 18B and 18C. The body of the drill
bit
is made of steel. The body 25 comprises the substantially cylindrical pilot
part 14
and the substantially conical reamer part 19. The pilot part 14 can have a
conical
shape and the reamer part 19 can have a cylindrical shape. The pilot part has
a
front face carrying a diametrically extending chisel 17 or two or more
diametrically substantially aligned front buttons, not shown. The reamer part
19
can have a circular radial cross-section. The reamer part has a front face
carrying one or more front buttons; in this case three front buttons 18A, 18B
and
18C. The front faces may be convex or substantially planar. The buttons 18A,
18B and 18C may form a peripheral arch on the reamer part. The buttons 18A,
18B and 18C may project somewhat outside the periphery of the reamer part in
order to machine a bore 22 during drilling which has a bigger diameter than
the
steel body 25. The number of cemented carbide buttons in the reamer part can
be varied depending on how great the diameter of the drill bit is. Chipways or
recesses can be provided in areas between adjacent reamer buttons, through
which flush medium can pass. The rock drill bit 16 is to be coupled to the
drill
steel 11 by means of a connection portion, so as to transfer rotational
movement
and percussion in the usual manner. The drill steel 11 includes a channel for
conveying a flush medium. A main channel for flush medium is provided inside
the drill bit. This main channel communicates at its forward end with a number
of
branch channels, which exit in the front faces. The flush medium will in
practice
be water, cement or air. The pilot part drills a pilot bore 22A of less
diameter and
length in relation to the bore 22. The length L of the pilot part 14 is
defined as the
distance between the forward most portion of the pilot part and the forward
most
reamer button 18A, 18B or 18C, in a direction parallel to the reamer part
center
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line CL2. The length L is at least 10 mm and not more than 60 mm to provide
good guidance of and good service life for the drill bit. The reamer buttons
in this
embodiment comprises a leading button 18A, an intermediate button 18B and a
trailing button 18C. During drilling, the greatest reactional forces on the
reamer
5 19 act on the leading and intermediate rock machining means 18A, 18B.
Therefore, an axial plane through the chisel 17 is angled such that it passes
between the leading and intermediate rock machining means 18A, 18B. Stated
another way, an imaginary line S, preferably a midline through the rock
machining means or chisel 17 and perpendicular to the center line CL2 of the
reamer part 19, forms an acute first angle B with a normal N to the center
line
CL2. The normal N intersects the rock machining means or button 18A that leads
in the rotational direction R of the drill bit 16. The angle B is preferably
not less
than 0 and not more than 200. If the leading rock machining means in the
reamer part 19 is a button then the normal N intersects its center line. If
the
leading rock machining means in the reamer part 19 has another shape then the
normal N intersects its forward most point in the rotational direction R.
During
drilling, the greatest reactional forces on the reamer 19 act on the leading
and
intermediate buttons 18A, 18B. The rock machining means 17 will inter alia
extend at least to the envelope surface 50. Therefore, by positioning the rock
machining means 17 in a certain relation to the leading button 18A the
envelope
surface 50 of the pilot part the rock machining means 17 will form a wear
resistant means 17' during drilling at the position of the reamer most
subjected to
wear. Said wear resistant means 17' is thus integral with the first rock
machining
means 17. A tangent T, touching the envelope surface 50 or a skirt 51 of the
drill
bit and being parallel to the center line CL2, forms a radial distance X with
the
periphery of the pilot part at its forward end. The distance X is not zero and
is
preferably not less than -5 mm and preferably not more than +5 mm.
The discussed shape gives good drilling results and a better contact
surface between the pilot hole 22A and the pilot part 14. By having the pilot
part
inclined towards the reamer part by some degrees better drilling results are
achieved because the drill steel always bends in the same direction when
drilling, and the bending of the drill steel 11 is limited by a contact at the
axially
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lower end 52 of the skirt 51 axially below the buttons 18A-18C. The lower end
52
of the skirt, where it is supposed to be in contact with the rock, can be
either
harder than the rest of the steel body 25 by means of surface treatment, or be
provided with hard inserts to reduce wear.
The operation of the single pass rock bolting apparatus 10 is shown in Figs.
1 A - 1 G. Figs. 3A and 3B corresponds to for example Fig. 1 C. The degree of
bending of the drill steel 11 is exaggerated in Fig. 3A. The drill bit 16 is
connected, for example threaded, to the drill steel 11. A drilling machine
such as
a standard drill jumbo holds the drill steel. The bolt 21 is preferably
automatically
fed around the drill steel and positioned behind the drill bit 16 in the
drilling
direction F. In Fig. 1A the pilot part 14 primarily will abut against the rock
such
that for a short while it will machine the rock surface during circular
interpolation.
Then the pilot part 14 will find its correct center and begin to drill
centrally while
the drill steel 11 simultaneously starts wobbling about the pilot part middle
line
CL1 1 B. Then the reamer part 19 gets in contact with the rock surface and
begins to ream the hole made by the pilot part 14. After a short while, the
bolt 21
reaches the hole and is forced into the hole as shown in Fig. 1 C. Usually the
bolt
21 is spaced axially from the drill bit 16. The bolt 21 diameter is preferably
less
than that of the bore 22. The drill bit 16 will continue to drill and ream the
bore
22, while the bolt is pushed forwardly by a coupling sleeve 26 of the drilling
machine, see Fig. 1 D, until feed of the different parts is stopped. The depth
of
the bore 22 is substantially determined by the length of the bolt 21, i.e.
when a
washer 23 positioned at the trailing end of the bolt reaches the rock face or
entrance of the bore further feed will be stopped, see Fig. 1 E. There is an
anchor
bolt pusher on the drilling machine. The bolt pusher is a coupling sleeve 26
or a
dolly tool, which is driven by the drill steel. The dolly tool usually rotates
together
with the drill steel and the bolt during insertion. However, for instance the
bolt
may be held such that it does not rotate during insertion, e.g. in the case of
a
mechanical anchor bolt. The dolly tool can torque the anchor bolt when fully
inserted. The dolly tool can also slide along the drill steel to allow an
easier
installation of mechanical shell bolts and grouted bolts. Fig. 1 E shows the
anchor
bolt 21 fully inserted, with the drill steel and drill bit still in the anchor
bolt. A
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pusher pushes the plate to the rock face. The washer could be a loose
conventional plate having a central hole that cooperates with a bulge 24 at
the
trailing end of the bolt. Then the drill bit is retracted from the pilot hole
22A, see
Figs. 1 F. It is preferable that the axial space between the bolt and the
drill bit is
greater than the depth of the pilot bore 22A such that the leading end of the
bolt
does not interfere with the retraction of the drill bit. The drill bit and the
drill steel
can be completely retracted and can be reused for repeated drilling
operations.
The machine driving the apparatus 10 can be a top hammer drilling
machine, a pure rotary machine or a down-the-hole equipment.
The drill bit according to the present invention provides good wear
resistance since wear on its side facing away from the reamer part is received
by
a wear resistant rock machining means 17' and provides favorable drilling
results.
The invention described herein is susceptible to variations, modifications
and/or additions other than those specifically described and it is to be
understood
that the invention includes all such variations, modifications and/or
additions
which fall within the scope of the claims.
