Note: Descriptions are shown in the official language in which they were submitted.
CA 02752611 2015-03-17
GEOLOGICAL DRILL
This invention relates to an apparatus for use in geological exploration
including a transport trailer having a rear plate and a top platform, a mast
carried on
the trailer having a base of the mast arranged to be located at the ground, a
diamond core drill for drilling into the ground along the drive axis to
extract a core
sample and an auger for driving along the auger along the drive axis into the
ground
for extracting an augered soil sample.
BACKGROUND OF THE INVENTION
This invention provides a drill which is directly applicable to geologic or
geotechnical investigations where information and data on soil or rock are
required.
In particular, the arrangement described herein provides a portable,
lightweight and
mobile drill with capability for both efficient soil augering and rock coring,
typically in
remote areas where most mineral exploration is carried out; where access is
limited
= due to non existent or limited road access; where low load-bearing soils
typically
cannot support heavy equipment, and other features such as dense bush, swamps
and steep slopes make access difficult or impossible. This drill can also be
used for
other applications such as geotechnical (engineering), shallow groundwater and
soil
investigations.
In mineral exploration, soil sampling of overburden deposits where
soils are overlying rock, also often referred to as till sampling, is
increasingly being
used as a tool in the search for minerals, precious stones and precious
metals. This
is due to a number of factors, including advancements in knowledge of mineral
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deposit features and relationship to glaciation, the capability of analytical
laboratories to conduct and provide concise details on soil grain properties
and
composition and the increased costs of completing traditional core drilling
investigations such as diamond drilling.
Soil sampling and the subsequent
analytical data can be used to improve understanding of surficial geologic
environments which may provide important clues to the presence of underlying
mineral deposits such as nickel, copper or precious stones such as diamonds.
Soil sampling for mineral exploration can be conducted using a variety
of methods. The general purpose, however, is the same: to obtain a
representative
sample of soil and use the propel ties and composition to assist in gaining
knowledge
of the surface features and underlying hard rock environment.
Hand trenches, normally less than one meter width and less than two
metres depth can be hand dug in overburden covered areas to expose the
underlying bedrock for additional observation or rock sampling of the
potential
mineralized zone. This type of investigation is labour intensive,
difficult, time
consuming and often provides a rather limited exposure (view) of the bedrock.
A
similar type of excavation, known as borrow pits are also used for subsurface
investigations.
At some locations, hand augering of boreholes typically 10-20 cm in
diameter and up to a few metres depth is possible for reconnaissance type
mineral
investigations. However, this is also labour intensive and additional problems
such
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as hole caving and intersection of pebbles or stones make it difficult to
auger and
sample at some locations.
Backhoe trenches, where possible, provide additional ease, depth and
amount of exposure of bedrock compared to hand trenching. Most regular sized
backhoes can provide trench or pit depths of 5-7m and are often necessary
where
"channel" sampling, that is rock cut with a diamond blade and power saw,
across a
vein or in a sulphide exposure is required. However, due to the weight of such
equipment, lack of roads, soft soils etc. it is often impractical to transport
and use a
backhoe for reconnaissance style or "quick look" prospecting at most locations
where mineral exploration is conducted.
Augered boreholes using a machine driven auger can also be used.
The surficial deposits that cover the underlying bedrock are variable
dependent on
the location and geologic processes that occurred in different regions.
However, for
much of Canada deposits of till, that is a mix of clay, sift, sand, gravel,
cover the
underlying bedrock. As glaciers advanced from Canada's north, large quantities
of
bedrock were gouged and the material imbedded in the ice only to be deposited
at
other locations as the glaciers retreated. Generally, the glacier advance
directions
can be determined from striations (gouges) in the bedrock. It is mainly the
sampling
and analysis of these till deposits that can provide prospectors with
important clues
as to the potential location of valuable ore deposits and precious stones such
as
diamonds. However, for large regions of the country, the till directly lying
on bedrock
is covered by lake sediments, of mainly clay and silt, which vary from 0 to
10's of m
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in depth. To obtain samples of the till overlying the bedrock, boreholes must
first
drilled through the sediments and then into the till.
The most efficient, cost effective and practical method for till
prospecting is the recovery of soil samples using conveyor augers. Conveyor
augers refer to the coupling of one auger onto another to form a continuous
spiral
that augers into soils and delivers the soil to ground surface where it can be
sampled. These samples are also often referred to as "auger returns".
On mineral claims or other prospective mineral areas, successful
mineral zone delineation often requires numerous test boreholes, sometimes
hundreds. Therefore, it is cost effective and time saving to have a
lightweight,
portable and mechanized soil drill for augering boreholes for till prospecting
in
remote locations.
Core Sampling or "Diamond Drilling" is also desirable in many cases.
While most of Canada is covered by soil deposits, there are also areas where
bed
rock is near or exposed at surface and prospecting for minerals can be
conducted by
methods such as direct observation and sampling, geophysical measurements of
rock properties and coring or diamond drilling into the bedrock. Coring is
also
referred to as "Diamond drilling" because the bits used to cut into the hard
bedrock
have diamonds encased in a metal matrix. Diamond is the hardest mineral and is
best suited for use in drill bits for efficient coring of the softer rocks.
Diamond drilling
to test the rock is an important and necessary procedure for determining the
concentration and quantity of mineralization and is used to determine if
mineralized
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zones warrant additional exploration and expenditure. The procedure is more
complex than soil augering and sampling and is normally completed after other
less
costly soil and surface rock sampling, geophysical surveys, and other tests
have
been completed to increase the chances of intersecting a prospective mineral
zone
5 with the diamond drilled boreholes.
Diamond drills consist of a power unit, normally diesel or gasoline
engines, which engages a clutch and transmission unit, which in turn rotates
the drill
string consisting of: flush jointed drill rods that are coupled together; a
core barrel;
and a reaming shell with a diamond bit. The cylinder of cut rock or core
advances
into the core barrel as drilling progresses. The bit and core barrel and rods
are
rotated at higher speeds compared to soil augering and the drill cuttings are
returned
to surface by pumping water in the drill rods, core barrel and diamond bit.
The
rods are withdrawn from the borehole at regular intervals as the core barrel
is filled
with core. The core is retained in core boxes for a record of the type of rock
intersected by the borehole.
As such, diamond drilling an important part of the exploration for
minerals and a portable drill that has coring capability, in addition to soil
augering is
most useful for prospecting and exploration in remote areas.
SUMMARY OF THE INVENTION
According to the invention there is provided an apparatus for use in
geological exploration comprising:
a transport trailer having a rear plate and a top platform;
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a mast carried on the trailer having a base of the mast arranged to be
located at the ground;
a diamond core drill for drilling into the ground along the drive axis to
extract a core sample;
an auger for driving along the auger along the drive axis into the
ground for extracting an augered soil sample;
a motor housing mounted for sliding movement along the mast;
a first hydraulic motor for driving the auger and a second hydraulic
motor for driving the drill where the first motor has a lower rate of rotation
and higher
torque than the second motor so that the motor is changed when changing from
the
auger to the drill;
the motor housing being arranged to receive carried therein a selected
one of the first and second hydraulic motors so that the selected one of the
first and
second hydraulic motors is inserted into the housing and the other of the
first and
second hydraulic motors is removed from the housing depending on whether the
diamond core drill or the auger is selected to be driven;
a hydraulic cylinder connected to the motor housing at one end and to
a top bracket of the mast at the other end for driving the housing in the
sliding
movement;
a pump driven by an engine both carried on the trailer for supplying
hydraulic fluid to the hydraulic cylinder and to the selected one of the first
and
second hydraulic motors;
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and a coupling extending along a drive axis downwardly from the
motor housing and driven by said selected one of the first and second
hydraulic
motors in the housing;
the coupling being arranged for releasable attachment to said auger for
driving along the auger along the drive axis into the ground for extracting an
augered
soil sample and being arranged for releasable attachment to said diamond core
drill
for drilling into the ground along the drive axis to extract a core sample.
Preferably there is provided a first motor for the auger and a second
motor for the drill where the first motor has a lower rate of rotation and
higher torque
than the second motor so that the motor is changed when changing from the
auger
to the drill.
Preferably the motor housing includes an inner motor support into
which the motor can be inserted for the quick change operation.
Preferably the motor housing includes a transverse mounting plate
onto which the motor is mounted and includes a bottom mounting plate parallel
to
and spaced from the transverse plate to form a compartment for containing a
flexible
coupling, commonly known as a spider coupling, for the motor which flexes
sufficiently to allow slight misalignment between the motor shaft and the
driven
element.
Preferably the motor housing includes a bottom plate onto which is
mounted a thrust bearing for receiving thrust forces from the coupling when
driving
the auger or the drill.
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Preferably the motor housing is mounted for pivotal movement about
an axis along the mast so as to move the housing and the motor therein away
from
the drive axis to allow upward pulling of the auger or drill along the drive
axis for
extraction.
Preferably the mast includes a bottom bracket arranged for attachment
to the ground and wherein the mast is arranged for pivotal movement about a
transverse axis relative to the bottom bracket to change an angle of the drive
axis
relative to the ground.
Preferably the bottom bracket is attached to the ground by a bolt
extending into a split sleeve contained within a drilled hole in the ground.
Preferably the vehicle is arranged for transporting sections for the
auger and sections for the drill.
Preferably the vehicle is a trailer with the mast mounted at a rear of the
trailer.
Preferably the vehicle has the mast mounted at a rear plate of the
vehicle for pivotal movement about a pivot axis transverse to the vehicle for
lying of
the mast forwardly across the vehicle and for adjustment of an angle of the
drive
axis relative to the rear of the vehicle.
The arrangement described herein provides the capability to efficiently
and effectively conduct both soil augering and diamond drilling of boreholes
with a
lightweight, portable drill that does not require a drill transmission or gear
reduction
unit.
Soil augering requires higher torque, low rpm drill rotation while diamond
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drilling requires much less torque than soil augering but a higher rpm for
productive
coring. Traditional, portable drills such as the Winkle Drill, have both a two
(or more)
speed transmission built into the drill and a bulky, heavy gear reduction unit
that is
added to the drill frame to achieve the necessary torque for soil augering. In
addition, drills such as the Winkie drill are labour intensive as the soil
augers and
drill string are raised and lowered by manual hand turning of a sprocket and
chain
mechanism. Transmissions are expensive to build and maintain, and repair at
remote field sites is often not practical.
Another feature of the arrangement herein is the ability to efficiently
maintain or replace any component in the field. Drill components are
independent,
that is the diesel engine, hydraulic pump and hydraulic motors are all
separate, as
compared to traditional units where transmission, drive motor and water
swivels are
housed together. Break-down of one renders the drill inoperable. Therefore
repair
and or replacement can be readily completed on individual components when
necessary.
The arrangement described here provides an innovative method for
both soil augering and diamond drilling. This is achieved by maintaining some
of the
desirable features of larger drill rigs such as hydraulic drive power and
hydraulic
control of drilling functions that reduce labour but also providing an
innovative
method with use of a motor box and hydraulic motors.
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The arrangement described herein provides a compact, portable,
hydraulically controlled and operated drill for both soil augering and rock
drilling.
The unit is comprised of:
a) trailer type drill carrier with capability for highway/road transport on
5 standard tires with quick change option to high flotation all-terrain
tires;
b) hydraulic controlled, lightweight and adjustable drilling angle beam
support unit mounted on the trailer but also readily detachable and available
for
transport and drilling exclusive of the trailer carrier unit;
c) a motor box housing unit with quick change capability for hydraulic
10 drive motors specific for the soil augering drilling application
requiring higher torque,
lower rotation speeds for soil augering or lower torque, high rotation speed
for rock
coring;
d) a fully adjustable drilling penetration rate hydraulic cylinder;
e) a hydraulic control panel.
BRIEF DESCRIPTION OF THE DRAWING:
One embodiment of the invention is described in conjunction with the
figures as follows:
Figure 1 is an isometric view of the main components of one
embodiment of the drill rig according to the present invention including the
drill mast,
motor box and anchor plate;
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Figure 2 is a front elevational view of the motor box of the drill rig of
Figure 1;
Figure 3 is a bottom plan view of the motor box of the drill rig of Figure
1;
Figure 4 is a vertical cross sectional view along the lines 4-4 of Figure
3 of the motor box of the drill rig of Figure 1;
Figure 5 is a rear view of the all-terrain carrier or trailer, mast pivot
mounting and jack stands of the drill rig of Figure 1;
Figure 6 is a side elevational view of drill components, mast, hydraulic
control panel, diesel engine, hydraulic oil reservoir and drill carrier of the
drill rig of
Figure 1.
DETAILED DESCRIPTION
The apparatus for use in geological exploration shown in the Figures
includes a transport vehicle 10, E? mast 1 carried on the vehicle 10 having a
base of
the mast arranged to be located at the ground, a hydraulic motor 12 carried in
a
motor box 8 mounted for sliding movement along the mast 1, a hydraulic
cylinder 9
connected to the motor housing at one end and to a top bracket 1A of the mast
at
the other end for driving the housing in the sliding movement. A pump 10B is
driven
by an engine 10A both carried on the vehicle 10 for supplying hydraulic fluid
to the
hydraulic motor 12. A coupling 16 extends along a drive axis downwardly from
the
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housing and driven by the hydraulic motor 12. The coupling is arranged for
releasable attachment to an auger for driving the auger along the drive axis
into the
ground for extracting an augered soil sample and being arranged for releasable
attachment to a diamond core drill for drilling into the ground along the
drive axis to
extract a core sample.
There is provided a first motor 121 for the auger and a second motor
122 for the drill (both shown schematically in Figure 1) where the first motor
has a
lower rate of rotation and higher torque than the second motor so that the
motor is
changed when changing from the auger to the drill.
The drill mast 1 in Figures 1, 5 and 6 is constructed of an aluminum I-
beam with a top bracket 1A defined by a planar top plate 2 welded to the end
of the
beam. The plate 2 is reinforced with angled support gussets 3 to provide a
stable
bracket 1A that can connect to the hydraulic cylinder 9 and accommodate force
from
the cylinder 9 used to lift and lower the drilling components, that is the
soil augers
and diamond drill rods and attachments. The top bracket 1A also has additional
side
brackets 1B with bored holes 10 through the reinforced bracket to allow for
the
coupling of a hydraulic cylinder to the bracket. A removable pin 4 joins the
cylinder to
the bracket to facilitate easy removal of the hydraulic cylinder.
The mast further includes at the bottom an anchor plate 5 including a
main base plate 5A which has been reinforced by welded angle brackets 5B. A
. bored pivot hole 6 extends through the brackets 5B so that the anchor plate
is
fastened to the mast by a removable pivot pin 6A. The pivot point at the pivot
pin 6A
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allows the mast to be inclined forwardly and rearwardly relative to the base
plate 5A
at angles from 0 to 90 degrees thus facilitating angled borehole drilling at
an angle to
the ground. This is often preferred and necessary as boreholes are drilled in
a
manner to try intersect mineralized zones. Anchoring of the base plate 5A and
therefore of the mast 1 is necessary for diamond drilling procedures to
prevent
movement and off-set of the drill rig. This ensures and maintains proper
alignment of
the drill mast, drill rods, core barrel and the motor box 8 with the borehole.
Failure to
keep the drill string in alignment results in drill vibration, additional
drill rod wear and
impingement of the drill rods as they are lowered or removed from the
borehole.
The drill mast can be securely anchored by drilling a short auxiliary
borehole of the order of 0.3 m in depth adjacent to the main borehole prior to
drilling
the borehole and inserting a split steel sleeve into the auxiliary borehole
and through
the anchor plate 5A. A bolt within the split sleeve is then tightened which
forces the
split sleeve against the auxiliary borehole walls to provide a secure bolt
anchor. The
bolt in turn extends through the anchor plate 5A and another bolt is tightened
onto
the top of the anchor plate 5A to securely fasten the base plate and drill
mast to
bedrock.
Figure 2 illustrates the motor box which is coupled to a hydraulic
cylinder 9 that controls the penetration or downward feed rate for both soil
augering
and diamond drilling. The motor box is coupled to the feed cylinder 9 with a
welded
aluminum bracket 11 and a removable pin 11A. This method of coupling of the
two
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components allows for quick and easy de-coupling of the motor box 8 and
cylinder 9
for either transport or for drilling operations, such as auger or drill string
retrieval.
The motor box 8 provides a housing 8A for a hydraulic motor 12
connected by a motor drive shaft 12B to a flexible coupling 13 for a drive
shaft 14
and a thrust bearing 15 which in turn attaches to the coupling 16 provided by
a hex
adapter box that couples to the soil augers and the diamond drilling rods. The
motor
box 8 also has a separate base 17 that is fitted with notched polyethylene
sliders 18
which act as spacers that allow the motor box to slide up and down on the I-
beam
aluminum mast 1. The notched polyethylene insert 18 allows for relatively
friction
free slide action as the motor box 8 and drill string are extended or
retracted as
drilling operations proceed.
The motor box 8 is also affixed to the motor box base 17 by an
aluminum hinge 19 providing a vertical axis on one side of the housing
bridging the
butting faces 17A and 8B of the base 17 and housing 8A allowing the pivotal
movement of the housing away from the mast while the base 17 remains attached
to
the mast. A set of aluminum latches 20 on the opposite side of the motor box
hold
the housing closed against the base 17 but can be released to allow the
housing to
move away from the mast. This :-inge allows the motor box 8 to be swung open
and
to the side of the mast to allow efficient retrieval by hoisting of soil
augers or
diamond drilling rods using a winch 1W coupled to the top of the mast. Thus
with
the motor box and coupling removed to one side the cable from the winch can
pull
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along the line of the drill axis and remove the soil augers or diamond
drilling rods
while pulling them along their length.
By unlatching the two bolts on the motor box housing, to decoupling
the hydraulic cylinder 9, this allows retrieval of up to 3 metres length of
drill rods or
5 soil
augers in one stroke up to the top of the mast. This significantly increases
efficiency, reducing labour and increasing productivity when hoisting longer
lengths
of drill rod or augers from deeper boreholes.
The motor box also serves as an additional purpose and that is
providing a housing or support box for the thrust bearing 15, which transfers
the
10 stress
and load of the soil augers and drill strings to the hydraulic cylinder 9
which in
turn is coupled to the top bracket of the mast 1. This also allows the
hydraulic motor
12 to be free of any external load apart from the required torque and prevents
pressure forces from impinging on the hydraulic motor shaft, shaft seals and
bearings of the hydraulic motors.
15 As
shown in figure 4 there is a hydraulic motor mount box 12A that fits
tightly inside the housing 8A. The inside box 12A to which the hydraulic motor
is
bolted has an access opening 22 in a bottom plate 21 through which the motor
drive
shaft 12B of the hydraulic motor 12 extends. The hydraulic motor drive shaft
12B is
coupled by flexible spider couplers 13 to the drive shaft 14 which in turn
extends
through the thrust bearing 15 and bearing housing. Hydraulic hose lines 23 are
connected, through the motor box cover, to the two ports 24 of the motor 12.
One
port receives pressurize hydraulic fluid from the hydraulic pump 10B driven by
an
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internal combustion engine 10A, while the opposite port returns the fluid to
the
hydraOlic control panel 10C which is then returned to the hydraulic reservoir
10D.
The hydraulic motor 12 selected for soil augering or diamond drilling is
a standard industrial size and therefore completely inter-changeable with
other
replacement motors, often of a different capacity. The hydraulic motor 12 can
be
selected by torque, volume and rotation specification to match drilling
requirements
of the auger and drill and rock or soil conditions. A wide range of torque,
volume
and rpm hydraulic motors are available from most hydraulic service firms. Soil
augering requires higher torque and lower rpm motors to turn the auger string
in the
high friction soils while best results for diamond drilling is achieved with
higher rpm
of the drill bit and core barrel. The rotation rates can also be further
controlled by
speed of the diesel engine 10A and the hydraulic valve controls 10C.
The hydraulic motor 12 is mounted in the container 12A within the
motor housing SA by easily accessible bolts this allows for quick and easy
change of
hydraulic motor. However, it should be noted that normally only one motor is
required for soil augering for example 0 to 200 rpm and a single change to a
second
higher rpm hydraulic motor for diamond drilling for example 1000 to 2000 rpm.
The
change of one hydraulic motor to another can be made in a matter of minutes.
As such, efficient drilling of both soils and diamond drilling can be
achieved with a lightweight portable drill without the need for an expensive,
heavy
and cumbersome transmission and/or add-on auger unit reduction gears. In
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addition, hydraulic motors used for these operations are inexpensive,
typically in the
range of 200 to 500 dollars.
In Figure 5 is shown a rear-view of the drill mast, and an aluminum
channel box 25 and an aluminum pivot mounting 26 that attaches the drill mast
1 to
the rear face of the all terrain trailer 10. The horizontal pivot mounting 26
consists of
a heavy walled pipe that is welded to the mast and two channel brackets
attached to
the box 25 and is secured by a pipe-type pin that allows the mast to be
pivoted
about the horizontal axis of the mounting 26 by activation of a hydraulic
cylinder 27
connected between the mast and the trailer 10 that controls the angle of the
mast.
For travelling the mast is positioned horizontally laid across a support plate
10X of
the trailer 10 between the motor 10A and the pump 10B. For soil augering, the
mast
it tilted by the cylinder 27 to an upright position. As previously described
the drill
mast can be positioned at any angle between 0 and 90 degrees for diamond
drilling.
The pin of the pivot 26 is also constructed for easy removal for disengagement
from
the trailer 10 should it be necessary to independently transport the aluminum
mast,
motor box and cylinder, for example in a cargo plane transport.
The reinforced and adjustable jack stands 28 and 29 located at the
rear face of the trailer 10 are deployed during set-up at a drilling or soil
augering
location. The jack stand legs 28A, 29A are independently adjustable to
accommodate field terrain irregularity and are fastened with a retractable pin
to
facilitate easy adjustment and retraction for travel. The jack stands can be
made of
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aluminum and are bolted to a main upstanding rear wall 10E of the trailer to
provide
a stable platform during drilling operations.
Figure 6 shows a side view of the carrier trailer 10 including the
primary mover or engine 10A and hydraulic fluid reservoir 10D for the pump
10B.
Also shown is the hydraulic control panel 10C.
The trailer is specifically designed for transport of the drill and drill
tools
and for travel pulled by a 4 wheel All-Terrain Vehicle on terrain typical of
the
Canadian Shield. The All-terrain carrier 10 has a flat deck 10X for work
surface and
drill mount and a centre storage at a dropped section 1OF that houses the mast
control cylinder 27 and storage and transport of augers and other drilling
equipment.
The tandem wheel configuration of the wheels 10G has large all-terrain type,
low
pressure wheel assemblies installed for additional flotation and travel in
swamp-type
terrain. The
drill carrier is also constructed for highway travel and off road tire
assemblies can be removed and replaced with on-road type wheels.
Another
feature of the trailer is the mounting of the tandem wheels. The wheels are
mounted
directly to the side of the reinforced trailer frame. This eliminates the need
for an
axle running beneath the trailer and thus reduces trailer carriage profile,
resulting in
fewer hang-ups on stumps, rocks or brush while travelling off-road.
The directional control valves of the control 10C allow for a wide range
of speed and directional control for:
1)
tilting the mast 1 to horizontal positions for transport on the AT
carrier and for vertical to angled position for soil augering and diamond
drilling. The
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hydraulic control valves in conjunction with the hydraulic cylinder activation
allows
for positioning the mast and for drilling boreholes at any angle between
horizontal
and vertical. Angled boreholes are most often drilled to try intersect
mineralized
zones which often are tabular and occur in a vertical or near-vertical sheet.
As such,
capability to drill a wide range of angled boreholes is a valuable feature for
mineral
exploration.
2)
controlling the rate of soil auger or rock coring. For soil
augering the depth and type of soil dictates the rate of penetration and may
range
from cms to meters/minute. For soft organic-rich soils the penetration rate is
rapid
and the ability to quickly extend the cylinder 9 increases productivity.
Conversely for
dense, firm soils such as some tills or lake clays, the augering rate may be
significantly reduced and ability to control the downward penetration rate is
important, so as to not overload the engine, overheat the hydraulic fluid or
cause
undue stress on the drill mast and other components. For
these reasons it is
advantageous to have a fully controllable hydraulic cylinder 9 to dictate even
and
smooth drilling operations.
3) Control of auger and drill bit rotation speed. Integral to the drill
rig efficiency and reliability is the control of soil auger and drill bit
rotation speed.
This is controlled and also dependent on 2 above, penetration rate, and
optimization
of drill performance. Drilling productivity is a balance between these two
functions.
For this invention, a wide range of torque and drill speed is achieved by
selecting
and installing the hydraulic motor 12 that best provides the torque or torque
and
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speed required. For example, for soil augering, soil auger rotation speeds of
0-200
rpm are suitable and selected for these operations. These hydraulic motors
have a
higher hydraulic volume intake/rpm motors and thus provide the increased
torque
needed for soil augering. In addition to the hydraulic motor specifications
the
5 hydraulic control allows for control of the rotation speed from near zero
to the
maximum rpm specified for the hydraulic motor. For diamond drilling,
efficiency in
rate of penetration is gained by having a higher bit rotation speed (1000-
2000) rpm
and a lower torque requirement. This is because the friction on the drill rods
in a
water filled borehole is much less than soil augers rotating in dense, firm
and plastic
10 soils where considerably more torque is required to rotate the auger
string.
