Note: Descriptions are shown in the official language in which they were submitted.
1328448
TITLE: DRILLING EQUIPMENT
This invention relates to drilling equipment for the
drilling of holes in rock by percussive techniques, where
the drill bit is subjected to repeated axial impacts, whilst
being rotated in the hole.
There is a requirement in modern mining and drilling
practice for the production of long, straight holes. Such
holes may for example be of the order of 35 metres in length
and 75 millimetres in diameter. This invention is intended
to facilitate the drilling of such holes.
According to the invention, there is provided a drilling
string for drilling long straight holes in rock using a
percussive drilling technique, the string comprising a drill
bit, an extension body, at least two drill rods with
threaded ends and at least one drill rod connector, the
extension body being threadedly connected to the drill bit,
one drill rod being threadedly connected to the extension
body and the connector connecting the one drill rod to
another drill rod, wherein all of the drill bit, the
extension body and the connector have outer cylindrical
surfaces with helical flutes formed in the surfaces.
The drill bit is preferably a button bit having buttons of a
hard material such as a carbide material mounted in the
cutting face. The invention is however also useful in
connection with blade bits.
The use of an elongated cylindrical bit surface (with
helical flutes to carry away the debris) helps to stabilise
the bit in the hole and to ensure that a straight hole is
produced.
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The diameter of the cylindrical surface is preferably 4 to 8
mm less than the gauge diameter of the cutt-ng face, when
the bit is new.
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The use of a drill string having all these features enhances
the straightness of a hole as it is drilled. Straight holes
can be drilled with rod lengths of between one metre and six
metres, ie with rods of most standard lengths.
In all three components, there are preferably four flutes
around the circumference of the cylindrical surface, and the
flutes and lands which separate the flutes preferably have
approximately equal circumferential extents.
The angle of the helix is preferably between 20 and 30,
and an angle of 26 has been found to be particularly
suitable. Such a helix will turn through less than half a
revolution over the length of a typical component which is
likely to have an overall length of about 150 - 200 mm.
The bit is preferably arranged to be rotated anti-clockwise
as it rotates, and the helix will be handed to conform to
this direction of rotation.
The invention will now be further described, by way of
example, with reference to the accompanying drawings, in
which:
Figure 1 is a schematic view of a completed drill string in
accordance with the invention;
Figures 2 and 3 are external views of two alternative drill
bits in accordance with the invention;
Figure 4 is a section through the drill bit of Figure 2;
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Figure 5 is a view in the direction of arrow A from Figure 4;
Figure 6 is an external view of an extension body in
accordance with the invention:
Figure 7 is a cross sectional view of the extension body from
Figure 6;
Figure 8 is a view of the extension body taken in the
direction of the arrow B from Figure 7;
Figure 9 is an external view of a drill rod connector:
Figure 10 is a cross section view through the connector of
Figure 9; and
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Figure 11 is an end view of the connector of Figure 10 taken
in the direction of the arrow C from Figure 10.
20 The drill string shown in figure 1 consists of a bit 10, an
extension body 12, a first drill rod 14, a drill rod
connector 16 and a second drill rod 18. The threads which
connect the various components will be one of the known
threads which are specifically designed for connecting drill
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string components in percussive, rotary drilling. It should
also be noted that the drill rods 14, 18, the extension body
12 and the bit 10 all have central flushing passages through
which flushing medium passes from the drill itself to the
cutting face of the bit.
The substantial cylindrical surface area presented by the
components 10, 12 and 16 ensures that when a hole is drilled
in rock, the forward progress of the bit is controlled for
centricity by the contact made between the cylindrical
surfaces and the walls of the hole as it is drilled. In this
way it is possible to drill a long straight hole.
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1328448
Figures 2 and 3 show respectively a button bit lOa and a
blade bit lOb. The button bit has inserted carbide buttons
20 on its cutting face 22. An outer row of buttons 24 forms
a gauge row or heel row and defines the diamet~r of the hole
which will be drilled. Although it cannot be seen in the
drawing, the outermost regions of these buttons extend
radially beyond the cutting face itself to cut the edges of
the hole, as is known in the art.
In the blade bit lOb, blades 26 of carbide material are
inserted in the head. There will normally be four such
blades equally spaced around the head, and they extend to
the outer circumference of the head.
Both bits have outlet holes 28 for a flushing medium which
is usually water, and which is passed down the centre of the
drill string, exits through the holes 28 and 42 and then
carries the drilling debris along the spiral flutes and out
of the drilled hole.
1~ Immediately behind the cutting face 22, the bit narrow!to a
neck 30, and from this neck helical flutes 32 extend towards
the opposite end of the bit 34. The flutes 32 are spaced
25 from one another by lands 36. As can be seen from figure 5,
there are four flutes 32 equally spaced around the
circumference. Figures 2 and 3 show that the flutes 32
extend all the way fronl the neck 30 to the end 34 of the t
bit.
Figure 5 shows how the bases of the flutes do not have sharp
corners but in fact have large radii 38. These radii may
amount to about 5mm.
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The bit itself is of generally massive constructions as can
be seen from figure 4, so that it can withstand repeated
percussive blows which are used to make the bit drill the
necessary hole. The bit has a socket 40 which carries an
internal thread form (not shown, but which will be of a
standard type known in this type of installation). From the
front of the socket 40, flushing passages 28 and 42 extend
towards the cutting face 22.
Figures 6, 7 and 8 show the extension body 12. On the
outside of the body, helical flutes 44 and separating lands
46 are formed in much the same way as the flutes 32 and
lands 36 in Figures 2 and 3. The lands 46 form an outer
cylindrical surface which guides the drill string in the
hole. One end of the extension body has a male threaded end
48, the thread corresponding to those on drill rods. This
threaded end 48 can then be screwed into the socket 40 on
the drill bit. At its other end the extension body has a
socket 50 which corresponds to the socket 40 in the drill
bit. A flushing passage 52 leads from the socket 50 to the
opposite end of the body. The body al80 has a neck 54
between the threaded portion 48 and the cylindrical fluted
region.
Figures 9, 10 and 11 show more details of the coupling 16
which has a tapered leading end 56 and a cylindrical body
region 58 which is provided with helical flutes 60 and lands
62 similar to those already described for the bit and the
extension body. The coupling has two female sockets 64 and
66 again with standard thread forms on them to receive
standard threads on the ends of two drill rods to be
connected.
132~448
Figure 1 shows the drill string with a length of the drill
rod 14 broken away.
When drilling a long hole there will be a considerable
number of drill rods 14, 18, etc, with the drill rods joined
end to end by connectors 16. There will be a continuous
flushing passage extending through the string.
The helix angle should be chosen so that it presents minimum
hindrance to the flow of flushing medium and debris back up
the hole. Typically the helix angle is between 20 and 30,
preferably 26, with the angle being measured between a
plane which includes the cylinder axis and one flank of one
of the flutes, where the flute cuts the plane.
The drill string is to be rotated anti-clockwise to carry
out drilling, and the fluting will be arranged so that, as
seen looking into the hole, the ends of the fluting nearest
the top of the hole trail the bottom ends wich are closest
to the cutting face of the bit.
It i5 important that the diameters of the cylindrical
surfaces on the various components be large enouyh to
perform a worthwhile guiding function in conjunction with
the walls of the drilled hole whilst avoiding the production
of excess friction which would retard drilling. It is
therefore necessary to reach a compromise which will permit
an efficient action to take place. It has been found that a
satisfactory action takes place if the diameter of the
cylindrical surface is between 3 and 10 mm, preferably 6 mm
less than the diameter of the heel row of button inserts on
the drill bit.
This invention can be applied to drill strings which drill a
35 hole having a diameter b~tween 50 and 100 mm, and
satisfactory operation has been proved at about 75mm
diameter.
