Note: Descriptions are shown in the official language in which they were submitted.
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HYDRAULIC DO~N-THE-HOLE ROCK DRILI
Technical Fieid
The present invention refers to a hydraulically operated down-the-hole
rock drill adapted for drilling deep, thick and rough holes in the rock and
in firm ground.
Background Art
Today so-called rotary drilling is mainly used when drilling holes oF
the type mentioned above, which mPans that a specially shaped drill bit is
pressed down and simultaneously rotated into the ground. Due to the fact that
10 the drill bit is provided with inserts of different shapes, the rock or earthmaterial is crushed or ground. Usually the drill bit is mounted on a tubular
drill string, the diameter of which is smaller than the diameter of the drill
bit' The drill string is imparted a rotational movement by means of a machine
assembly placed above ground. This machine assembly also comprises means for
15 supporting the drill string. The rock and earth material (called the cuttings)
ground by the drill bit is transported to the ground level by flushing with
water or any specially composed washing or flushing fluid, so called drilling
~mud. The flushing is performed by pressing the drilling mud by means of a pump
through a centre hole ;n the drill string and through flush openings in the
20 drill bit at the bottom of the bore hole, whereupon the drilling mud flows
to the ground level on the outside of the drill string and thus carries away
the cuttings. At the ground level the main parts of the cuttings are separa-
ted from the drilling mud, e.g. by settling the mud in basins, whereupon it
is again pumped down through the drill string.
It is also known to perform rotary drilling by using an engine which is
sunk down into the bore hole and is attached to the lower end of the drill
string, which is non-rotating. The engine is directly driven by the drilling
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Rotary drilling of the above type is mainly used for soft sedimentary
rock types. When drilling in harder crystalline rock, the method is expen-
sive since the drilling rate will be very low and the wear of the drill bi-t
severe. To this type of rock a completely different drilling method is used
called hammer drilling, which means that an impact piston is brought to stri-
ke against the drill string and/or the drill bit at a high frequency and the
drill string is simultaneously slowly rotated.
The machines used for this application are usually driven by compressed
air, i.e. the impact piston is driven by compressed air. The compressed air
10 is normally also taking care of the flushing up ~f the cuttings. When drill-
ing deeper and thicker holes (up to about 200 m) this method uses a so-called
sinker hammer, which means that the bore hammer with its impact piston is
mounted on a tubular drill string and is sunk down into the bore hole by means
of a rotary machine with essentially the same constructionas the one described
15 above for rotary drilling.
At hammer drilling the compressed air is taken from an air compressor
on the ground level and is blown through the drill string and driving the im-
pact piston, which directly strikes against the drill bit, whereupon the com-
pressed air flushes the cuttings up to the ground level outside the drill
20 string. One drawback of this method is that its capacity of deep drilling is
limited. However, the method is substantially faster than rotary drilling,
especially in hard rock.
In later years hydraulically driven hammer rock drills have been de-
veloped, which in principle differ from the compressed-air driven hammer
25 drilling machines by the fact that the impact piston is operated by hydrau-
lic oil under high pressure. The flushing of the cuttings is taken care of
separately by compressed air or a drilling mud. Such hydraulically driven
hammer rock drills have so far only existed in the form of so-called "above-
ground machines", i.e. with the bore hammer machine working in a machine unit
30 placed on the yround level. Thus, these machines have a limited capacity in
drilling deep and thick holes. However,itheirdrilling capacity is substantial-
ly higher than the capacity of the compressed air driven at the same energy
consumption.
It is desirable to use a sinkable hydraulically driven hammer rock drill
35 to drill deep and rough holes at high speed. However, this has so far not been
possible as the long hydraulic cables to the hammer rock drill at deep holes
imply too great losses.
As mentioned above the cuttings must be removed from the hole, which
with regard to deep holes always is performed by means of a drill;ng mud
;~¢ 40 since the hydrostatic pressure in the hole is too great to use compressed air.
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It might be possible to use the drilling mud in order to drive a hydraulic
hammer rock drill but this would be out of the question to a skilled person.
No matter how careful the drilling mud is settled before it is recirculated,
the drilling mud always contains great amounts of sand and abrasive partic-
~5 les which would rapidly abrade and destroy the valve mechanism of the hammerrock drill. Such a hammer rock drill must be driven with clean hydraulic oil
and especially when one wishes to drive the hammer rock drill at high pres-
sures, in the order of 150 bar, the hydraulic oil must be of a very hiah
grade.
Disclosure of invention
In accordance with the present invention the drilling mud drives a ro-
bust hydraulic engine placed immediately in connection with the drill bit
in the bore hole. The output shaft of the engine is used to drive an impact
15 apparatus which strikes against the drill bit, i.e. so.called hammer dril-
ling. If the impact apparatus is hydraulically driven the output shaft of ~~-
the engine is adapted to drive a hydraulic pump to provide high pressure
hydraulic fluid to the impact apparatus. The hydraulic fluid is thus enclo-
sed in a closed circuit and a very clean hydraulic oil of hiah grade may
20 be used in order to guarantee a safe operation.
The hammer rock drill in accordance with the invention which has been
sunk down, may be brought to rotate by means of a machine unit placed at
the ground level or alternatively, the output shaft of the hydraulic en-
gine may also provide rotation of the drill bit.
It is an advantage that the drill bit only carries the load of the
hydraulic engine and the impact apparatus and is independent of the length
of the drill string supplied in the hole, which easily can be provided by
means of a pilot control.
The present invention also relates to an apparatus for carrying out
30 the above mentioned hammer drilling.
_rief description of drawing
The invention is described in detail below with reference to the ac-
companying drawings, in which Fig. 1 is a longitudinal view in section of
35 one embodiment of the invention and Figs. 2 to 7 are cross-sectional views
of the embodiment of Fig. 1 taken alonn the lines II-II, III-III, IV-IV, V-V,
VI-VI and VII-VII.
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Best mode of carryinn out the invention and industrial applicability
The apparatus mainly consists of seven interconnected or integral
units, which in Fig. 1 are denoted A - ~.
Unit A consists of a tubular drill strin~ of known construction,
which is composed of separate pie~es interconnected by means of tapered
thread joints and extends to the ground level. The drill strina is brought
ro rotate by means of a machine unit on the nround level, which also com-
prises devices of known contruction for insertina and takina up the drill
string of the bore hole. The drill string is dimensioned to withstand not
10 only any appearing torque or axial forces but even a comparatively hinh in-
side hydraulic pressure from the drilling mud.
Unit B consists of a feeding or pilot control unit by means of which
it is assured that the drill bit is pressed aqainst the bottom of the bore
hole with an adequat force.
Unit C consists of a hydraulic engine of known constructi.on, which =~
during an acceptable time of life may be driven by means of the hydraulic
energy of the drillina mud. This drilling mud may be water or any other
drilling mud or liquid and is mixed with soil particles. The length of the
hydraulic engine is great compared to its diameter.
Unit D consists of a hydralic pump of known construction, but with a
special construction. The hydraulic pump emits clean high pressure hydrau-
lic oil.
Unit E consists of anoil tank with an oil filter. The length of the
oil tank is great compared to its diameter and it is provided with passa-
25 ges in the wall of the tank for the drillina mud and the hydraulic oil.
Unit_ consists of a hydraulically driven hammer rock drill, whose
fundamental mode of action with regard to the impact mechanism does not
differ from known constructions. In this case the hammer rock drill is
adapted to be able to work as a sinkhammer downwards in the bore hole, and
30 so it is i.a. provided with flushing passages for the drilling mud and an
adapter for transferring of torque, axial forces and strokes directly to
the drill ~it.
Unit G consists of a drill bit of known construction including inserts
or pins made of hard carbide steel as well as flushing passages for the
35 drilling mud.
The apparatus of the invention comprises a drill string 1, which con-
sists of a number of interconnected drill strina sections. The drill string
1 is the connecting link to the ~round level. The pilot unit (B) is connec-
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~ed to the drill string. This consists of a top unit 2, a cylinder tube 3and a base unit 4, all units being interconnected by means of thread
joints. The lower portion of the cylinder tube 3 is provided with four
circumferentially spaced openings 5. The base unit ~ is provided with a
square passage 6. A piston 7 is movably arranged inside the cylinder tube 3
and sealed thereagainst. The piston is fixedly attached to a piston rod 8,
which is tubular with a square outer shape. The piston rod 8 runs with a
small or loose fit in the square passage 6 of the base unit 4. The upper
portion of the piston rod is provided with a valve mechanism 9, consisting
10 of a cylindrical tube with a valve opening 10. This cylindrical tube is
closed at the top end and fits closely in a cylindrical hole 11 in the top
unit 2.
Drilling mud is pressed through the boring tube 1, and the direction
of the drilling mud appears from the solid line arrows in Fig. 1. Usually
15 the drilling mud flows through the valve openings 10, through,~he piston
rod 8, which is hollow and through a hydraulic engine 12. Simultaneously
the drilling mud presses the piston 7 downwards as the fluid pressure is
lower in the cylinder tube 3 under the piston 79 which space communicates
with the bore hole outside the cylinder tube.
The hydraulic engine 12 is provided with an inlet opening 13 and an
outlet opening 14 for the drilling mud and is also provided with an outlet
shaft 15 which is brought to rotate when the drilling mud flows through
the engine. The engine is of a well-known construction and will not be de-
scribed more closely herein' Any engine may be used that can be driven by
25 the drilling mud without being destroyed in a short period of time.
The outlet shaft 15 of the hydraulic engine is connected to the inlet
shaft 17 of a hydraulic pump 16. When the drilling mud reaches the hydrau-
lic engine, the engine is rotated and so is the hydraulic pump. This means
that the hydraulic pump emits high pressure hydraulic oil (15-20 MPa) to a
30 damping accumulator 19~ which is comprised in the hammer rock drill 18.
The hydraulic oil is transferred to a slide mechanism 20 of the hammer
rock drill, the construction of which implies that an impact piston 21 is
given a rapid reciprocating impact movement. The impact piston 21 strikes
with its lower portion against an adapter 22, at which the drill bit 23
35 is firmly threaded. The impact from the impact piston is thus transferred
to the drill bit, which crushes soil or rock material in the bottom of the
bore hole. The hydraulic oil is returned from the slide mechanism 20 to an
oil tank 24 and thence back to ~he hydraulic pump 16. The path of the hydrau-
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lic oil appears from the dotted arrows in Fig. 1.
When the drilling mud has left the hydraulic engine 16 it is transpor-
ted through passages 26 past the oil tank 24 and the hammer rock drill 18
to the adapter 22 and out through a flushing hole 25 in the drill bit 23.
The bottom of the bore hole is flushed from crushed material (cuttings),
which is carried by the drilling mud upwards along the outside of the ap-
paratus between the apparatus and the wall 27 of the bore hole up to the
ground level, where the drilling mud is collected in separate basins in
which the main part of the cuttings is separated from the drilling mud
lO whereupon it is pumped down once again through the clrill string.
The torque from a rotary machine (not shown) placed at the ground
level is transferred through the drill string l and the pilot unit(B)through
the square passage 6 and the square piston rod 8 to the other integral units
C-F. From the hammer rock drill (F) the torque is transferred to the adapter
15 and the drill bit 26 since the adapter is provided with splines 28. _~
The operation of the apparatus according to the invention is as follows.
When the drilling is to be started the apparatus is connected by means
of thread jounts to a rotary machine placed on the ground level, whereupon
20 the apparatus is sunk down into the bore hole until the drill bit reaches
theground level or the bottom of the bore hole. At continued sinking of the
drill string l,the top unit 2 moves towards the valve mechanism 9, of which
the outside cylindrical part is inserted into and cooperates with the upper
cylindrical holes ll of the top unit with a good fitting. In this way the
25 inner channel, i.e. the cylindrical hole ll, of the drill string is sealed
so that the drilling mud is prevented from passing further through the pis-
ton rod 8. Thereafter the drill string l is lifted a small distance until
the top edge of the valve mechanism 9 exposes the cylindrical hole ll in
the top unit and gives free passage for the drilling mud. Simultaneously~
30 the rotary machine starts to rotate the drilling string and thus the appa-
ratus as well as starts the pump placed at ground level for the drilling
mud. Thereafter the hydraulic engine and the hydraulic pump set the impact
piston into operation and the hammer rock drill is moved downwards as the
drill bit crushes soil or rock material. The drill string l, the top unit 2
35 and the cylinder tube 3 rotate without moving vertically. ~he feed pressure
on the drill bit 26 only consists of the dead weight of the units C-G, the
piston 7 and the piston rod 89 and the hydraulic differential pressure on
the top of the piston 7.
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When the drill bit and thus the piston 7 has sunk so deep inthe bore
hole that the piston has passed underneath the openings 5 in the side of
the cylinder tube 3, the drilling mud flows out through these openings and
further up to the ground level on the outside of the apparatus. This en-
tails that the hydraulic engine 12 and thus the impact piston 21 stop, whichmeans that the back pressure of the drilling mud decreases due to the lower
flow resistance, as it does not have to pass through the hydraulic engine
12. This may be monitored by means of for example a manometer at the pump
on the ground level. When this has been taken care of the drill string 1 is
10 again lowered downwards into the bore hole by means of the rotary machine.
As the drill bit rests on the bottom of the bore hole the piston 7 will
once again cover the openings 5 in the side of the cylinder tube 3 making
the drilling mud to pass through the piston rod 8 to the hydraulic engine
12, and the impact piston starting to strike against the adapter and the
~5 drill bit; When the drill string has been sunk so far that ther~valve me~
chanism 9 seals the cylindrical hole 11 in the top unit 2 the hydraulic
pressure of the drilling mud is instantaneously raised. At this moment
the drill string 1 is lifted a small distance until the passage for the
drilling mud is free, whereafter the drill string is vertically kept un-
20 movable and is only rotated until the drill bit and thus the piston 7 onceagain reaches below the openings 5 and the cycle is repeated.
The step-by-step sinking of the drill string 1 into the bore hole a
distance corresponding to the piston stroke may be done automatically for
example by means of the mechanism of the rotary machine which performs the
25 vertical movements of the drill string (feed unit). This mechanism may be
adapted to sink the drill string when the hydraulic pressure instantaneously
decreases in the drilling mud and to stop when the pressure instantaneously
increases in relation to preset values. The drill string may also be fed
with a constant preset feeding rate, the feeding rate being modified by the
30 sensor signals disclosed above.
Thus, the apparatus provides a comparatively constant and limited pres-
sure on the drill bit during drilling, which is desired for example in or
der to decrease the wear oF the drill bit and the torque required. Moreover,
it is prevented that the inpact piston strikes against the drill bit when-
35 it is not resting on the bottom of the bore hole, which is essential in or-
der not to damage the dr;ll bit.
Furthermore, the pilot control makes it possible for the drill string
to move vertically a limited di~tance during drilling if the pump -For the
drilling mud is provided with an overflow valve, so that the drilling mud
overflows at the pump on the ground level, if the pressure in the drilling
mud exceeds a preset value. This makes it possible for example to perform
drilling with a drilling machine mounted on a raft which is moving verti-
cally during high sea.
One preferred embodiment has been described above. Apparently differentmodifications and alterations may be made of the described apparatus within
the scope of the invention. For example the hydraulic pump may be any known
type of pump, e.g. a diagragm pump. Alternatively the hydraulic engine and
10 the hydraulic pu~p may be replaced by two mechanically interconnected hy-
draulic cylinders, one of which works as an engine and is driven by the
drilling mud and the other works as a pump for the hydraulic oil. By choos-
ing a suitable ratio for the cross-sectional areas of the two hydraulic cy-
linders of e.g. 3:1 the desired pressure for the hydraulic oil may be ob-
15 tained.The slide and valve mechanism of the hydraulic pistons ~ay be in~terconnected for mutual movement.
The apparatus in accordance with the invention is intended for drill-
ing very deep holes, e.g. drilling for oil. Especially at drilling for oil
at sea, the costs of operation per day are very high. For this reason the
20 apparatus in accordance with the invention only has to be constructed in
such a way to safely manage to drill one complete bore hole, after which
operation the apparatus may ge discarded. However, if the apparatus stops
working or gets stuck when the drilling of the hole has come half way, the
costs for taking up the apparatus or possibly drill a new sloping hole ad-
25 jacent the apparatus that has got stuck may be very high. Due to the fact
that the apparatus in accordance with the invention manages a bore rate
which is approximately twice the bore rate of known drills for drilling
oil, a substantial saving may be obtained when drilling such deep holes,
especially when drilling for~oil at sea.
Thus, the invention described above refers to a method and an appara-
tus for making bore holes in the ground or rock where the drilling mud has
the double function of driving a hydraulic hammer rock drill at the bottom
of the bore hole on the one hand, and on the other hand to flush out crush-
ed soi,l or rock material from the bore hole. Due to the invention it will
35 now be technically possible to make bore holes of up to several thousand
meters depth with a hammer rock drill where an impact piston strikes the
drill bit which is simultaneously rotated. This means that the drilling
capacity (drilling rate) with regard to known methods may be doubled and
in some cases even tenfolded, i.a. depending on the hardness of the rock.
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