Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURIZED FLUID FLOW SYSTEM FOR A DTH HAMMER AND NORMAL
CIRCULATION HAMMER BASED ON SAME
FIELD OF APPLICATION OF THE INVENTION
The present invention relates generally to pressurized fluid flow systems for
percussive mechanisms operating with said fluid, particularly for DTH (Down-
The-
Hole) hammers and more particularly for normal circulation DTH hammers, and to
DTH hammers with said systems.
STATE OF THE ART
DTH hammers
A numerous variety of percussive drilling mechanisms exist which use a
pressurized fluid as the means for transmitting power. Among these are DTH
hammers which are widely used in the drilling industry, in mining as well as
civil
works and the construction of water, oil and geothermal wells. The DTH hammer,
of cylindrical shape, is used assembling it on a drill rig located at ground
surface.
The drill rig also comprises a drill string comprising rods assembled
together, the
rear end, understood as the end that is farther to the hammer drill bit
(elemtent
described further along in these specifications), being assembled to a
rotation and
thrust head and the front end, understood as the end that is closer to the
hammer
drill bit, coupled to the hammer. Through this drill string the drill rig
supplies the
necessary pressurized fluid to the hammer for the hammer to operate.
Parts of the DTH hammer
The main movable part of the hammer is the piston. This member of the
hammer has an overall cylindrical shape and is coaxially and slidably disposed
in
the inside of a cylindrical outer casing. When the hammer is operative in the
mode
known as "drilling mode", the piston effects a reciprocating movement due to
the
change in pressure of the pressurized fluid contained in two main chambers, a
front chamber and a rear chamber, formed inside the hammer and located at
opposite ends of the piston. The piston has a front end in contact with the
front
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chamber and a rear end in contact with the rear chamber, and has outer sliding
surfaces or sliding sections of the outer surface of the piston (as opposed to
sections with recess areas, grooves or bores) and inner sliding surfaces or
sliding
sections of the inner surface of the piston (again as opposed to sections with
recess areas, grooves or bores). The outer sliding surfaces are mainly
designed
for ensuring guidance and aligment of the piston within the hammer. Besides,
in
most hammers these surfaces, together with the inner sliding surfaces of the
piston, in cooperation with other elements as described further along in these
specifications, permit control of the alternate supply and discharge of
pressurized
fluid into and from the front and rear chambers.
The foremost part of the hammer, which performs the drilling function, is
known as the drill bit and it is slidably disposed on a driver sub mounted in
the
front end of the outer casing, the drill bit being in contact with the front
chamber
and adapted to receive the impact of the front end of the piston.
In order to ensure the correct alignment of the drill bit with respect to the
outer casing, a component known as drill bit guide is normally used, which is
disposed in the inside of the outer casing. The rotating movement provided by
the
drill rig is transmitted to the drill bit by means of fluted surfaces or
splines in both
the rearmost part o the drill bit (or shank) and the driver sub. In turn the
drill bit
head, of larger diameter than the outer casing and than the drill bit shank
and
driver sub, has mounted therein the cutting elements that fulfill the drilling
task and
extend forward from the drill bit front face. The movement of the drill bit is
limited
in its rearward stroke by the driver sub and in its forward stroke by a
retaining
element especially provided for said purpose. At the rear end of the hammer a
rear sub is provided that connects the hammer with the drill string and
ultimately
to the source of pressurized fluid.
In the above description and that one hereinafter provided, the rear end of
the hammer is understood to be the end where the rear sub is located and the
front end of the hammer, the end where the drill bit is located.
Operation of the hammer
When the hammer operates in the so called "drilling mode", which is
explained further along, the front and rear chambers undergo the following
states:
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a- supply of pressurized fluid, wherein the fluid coming from the source of
pressurized fluid is free to flow into the chamber;
b- expansion or compression, depending on the direction of the piston's
movement, wherein the chamber is tightly sealed and the volume it
encloses increases or decreases;
c- discharge of pressurized fluid, wherein the fluid coming from the chamber
is free to flow towards the bottom of the hole; this discharge flow enables
flushing of the rock cuttings generated by the drill bit, dragged in
suspension in the pressurized fluid flow, towards the ground surface
(process known as flushing of the hole).
In accordance with the piston's reciprocating movement, starting from the
position in which the piston is in contact with the drill bit and the latter
is disposed
at the rearmost point of its stroke (position known as impact position), and
ending
in the same position (with the impact of the piston over the drill bit), the
respective
sequence for the states of the front and rear chambers are the following: [a -
b(expansion) - c - b(compression) - a] and [ c - b(compression) - a -
b(expansion)
- c]. The transition from one state to the other is independent for each
chamber
and is controlled by the position of the piston with respect to other parts of
the
hammer in such a way that the piston acts in itself as a valve, as well as an
impact
element.
In a first operative mode or "drilling mode", when pressurized fluid is
supplied to the hammer and the hammer is in the impact position, the piston
immediately begins the reciprocating movement and the drill bit is impacted in
each cycle by the piston, the front end of the drill bit thereby peforming the
function
of drilling the rock at each impact. The rock cuttings are exhausted to the
ground
surface by the pressurized fluid discharged from the front and rear chambers
to
the bottom of the hole. As the depth of the hole increases, the magnitude of
the
pressurized fluid column with rock cuttings also increases, producing a
greater
resistance to the pressurized fluid discharge from the chambers. This
phenomenon negatively affects the drilling process. In some applications the
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leakage of water or any other fluid into the hole increases even more this
resistance, and the operation of the hammer may cease.
In some hammers, this operative mode of the hammer can be
complemented with an assisted flushing system which allows discharge of part
of
the flow of pressurized fluid available from the source of pressurized fluid
directly
to the bottom of the hole without passing through the hammer cycle. The
assisted
flushing system allows the hole to be cleaned thorougly while it is being
drilled.
In a second operative mode of the hammer or "flushing mode", the drill
string and the hammer are lifted by the drill rig in such a way that the drill
bit loses
contact with the rock and all the pressurized fluid is discharged through the
hammer directly to the bottom of the hole for cleaning purposes without going
through the hammer cycle, thus ceasing the reciprocating movement of the
piston.
The pressurized fluid coming from the assisted flushing system has an
energy level substantially similar to that of the pressurized fluid coming out
from
the source of pressurized fluid, as opposed to what happens with the
pressurized
fluid exhausted from the chambers, which is at a pressure substantially lower
due
to the exchange of energy with the piston.
Industrial applications
These drilling tools are used in two fields of industrial application:
1) Production, where a kind of hammer known as "normal circulation
hammer"
is used, wherein the rock cuttings produced during the drilling operation are
flushed to the ground surface through the annular space defined by the wall of
the
hole and the outer surface of the hammer and the drill string, producing wear
on
the outer surfaces of the hammer and the drill string by the action of said
cuttings.
The pressurized fluid coming from the chambers and from the assisted flushing
system is discharged through a central passage inside the drill bit which
extends
from its rear end to its front end. This passage may be divided into two or
more
passages ending in the front face of the drill bit in such a way that the
discharge
of the pressurized fluid is mainly generated from the center and across the
front
face of the drill bit towards the peripheral region of the same and towards
the wall
of the hole, and then towards the ground surface along the annular space
between
the hammer and the wall of the hole and between the drill string and the wall
of
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the hole. The rock cuttings are exhausted by drag and are suspended in the
pressurized fluid discharged to the bottom of the hole.
Normal circulation hammers are used in mining in underground and surface
developments. Due to their ability to drill medium to hard rock, the use of
this type
of hammers has also extended to the construction of oil, water and geothermal
wells. In general the soil or rock removed is not used as it is not of
interest and
suffers from contamination on its path to the surface.
2) Exploration, where a kind of hammer known as "reverse circulation
hammer" is used, which allows the rock cuttings from the bottom of the hole to
be
recovered at the ground surface by means of the pressurized fluid discharged
to
the bottom of the hole. The pressurized fluid coming from the chambers is
discharged along the peripheral region of the front end of the drill bit,
therefore
producing a pressurized fluid flow across the front face of the drill bit
towards the
inside of a continuous central passage formed along the center of the hammer,
typically through an inner tube known as sampling tube extending from the
drill bit
to the rear sub, and through the double walled rods that conform the drill
string.
This central passage begins in the inside of the drill bit at a point where
two or
more flushing passageways originated in the front face of the drill bit
converge.
The rock cuttings are dragged towards the central passage by the action of the
pressurized fluid, said rock cuttings being recovered at the ground surface.
The
pressurized fluid flow with suspended rock cuttings produce wear on the inner
surfaces of all the elements that form said central passage.
Either, the drill bit or a cylindrical sealing element of the hammer which has
a
diameter substantially similar to the diameter of the drill bit head and
larger than
the external diameter of the outer casing, performs the function of preventing
the
leakage of pressurized fluid and rock cuttings into the annular space between
the
hammer and the wall of the hole and between the drill string and the wall of
the
hole when the hole is being drilled (as happens with a normal circulation
hammer),
forcing these cuttings to travel through the sampling tube and drill string to
the
ground surface by the action of the pressurized fluid. If it is the drill bit
that performs
this sealing function, it has a peripherial region that isolates the front
face of the
drill bit from said annular space.
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The use of this type of drilling tool allows for the recovery of more than 90%
of
the rock cuttings, which do not suffer from contamination during their travel
to the
ground surface and are stored for further analysis.
Performance Variables
From the user's point of view, the variables used to evaluate the
performance and usefulness of the hammer are the following:
1) rate of penetration, which is given by the power generated in the
pressurized fluid cycle in the hammer and which value depends on two
variables:
the pressurized fluid consumption and the cycle's energy conversion
efficiency,
this being defined as the power generated per unit of pressurized fluid mass
consumed;
2) durability of the hammer related to wear induced by the pressurized
fluid
flow dragging rock cuttings toward the ground surface and the interaction
between
moving parts, the durability being strongly dependent on the characteristics
of the
rock cuttings, the materials used to manufacture the hammer parts and the
thickness of the parts in contact with the pressurized fluid flow;
3) consumption of pressurized fluid, which is strongly dependent on the
passive volume of the front chamber, the passive volume of the rear chamber
and
the design of the pressurized fluid cycle of the hammer;
4) deep drilling capacity, which depends on the ability of the hammer to
deliver
pressurized fluid with a high level of energy to the bottom of the hole;
5) manufacturing costs, which depend on manufacturing complexity, the
amount of components of the hammer and the amount of raw material used;
6) reliability of the hammer, which depends on the quality of the
manufacture
process and the sturdiness of the design of the tool; and
7) rock cuttings recovery efficiency (only for reverse circulation
hammers),
which is mainly related with the capacity of the hammer to seal the hole and
prevent the leakage of pressurized fluid and rock cuttings to the annular
space
formed between the hammer and the wall of the hole and between the drill
string
and the wall of the hole.
It should be noted that the rate of penetration, durability of the hammer,
pressurized fluid consumption, reliability of the hammer and deep drilling
capacity
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are factors that have direct incidence in the operational cost for the user.
In
general, a faster and reliable hammer having a useful life within acceptable
limits
will always be preferred for any type of application.
Pressurized Fluid Flow Systems
Different pressurized fluid flow systems are used in hammers for the
process of supplying the front chamber and the rear chamber with pressurized
fluid and for discharging the pressurized fluid from these chambers. In all of
them
there is a supply chamber formed inside the hammer from which, and depending
on the position of the piston, the pressurized fluid is conveyed to the front
chamber
or to the rear chamber. In general, the piston acts as a valve, in such a
manner
that depending on its position is the state in which the front and rear
chambers
are, these states being those previously indicated: supply, expansion-
compression and discharge.
At all times the net force exerted on the piston is the result of the pressure
that exists in the front chamber, the area of the piston in contact with said
chamber
(or front thrust area of the piston), the pressure that exists in the rear
chamber,
the area of the piston in contact with said chamber (or rear thrust area of
the
piston), the weight of the piston and the dissipative forces that may exist.
The
greater the thrust areas of the piston, the greater the force generated on the
piston
due to a certain pressure level of the pressurized fluid and greater the power
and
energy conversion efficiency levels which can be achieved.
All the prior art pressurized fluid flow systems described in the following
paragraphs are described with regard to the solutions for controlling the
state of
the front and rear chambers of a DTH hammer. The examples described refer to
normal circulation hammers but they are equally applicable to reverse
circulation
hammers.
Type A Flow System, represented by patents U54084646, U55944117 and
U56135216
The designs described in these patents comprise a cylinder mounted inside
the outer casing, the cylinder creating a fluid passageway between the outer
surface of said cylinder and the inner surface of the outer casing. This fluid
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passageway extends along the rear half of the piston and ends in the supply
chamber, which is partially defined by the outer sliding surface of the
piston, near
its middle point, and the inner surface of the outer casing. The provision of
this
cylinder requires the use of a dual outer diameter piston, the outer diameter
of the
same being greater at its front end and smaller at its rear end where the
cylinder
is placed.
The region where the piston's outer diameter changes, i.e. where there is
a shoulder on the outer sliding surface of the piston, is subject to a
pressure equal
in average to the supply pressure of the hammer. Therefore, on each cycle the
.. net work exerted by this region on the piston is null, i.e. it does not
contribute with
the energy transfer process to the piston, resulting in a reduced rear thrust
area.
Moreover, in the normal or reverse circulation hammers with this type of
flow system, an air guide is provided for controlling the discharge of the
rear
chamber, the air guide being a tubular element coaxial with the piston and the
.. outer casing and located at the rear face of the rear chamber. Also, a
footvalve is
provided in order to control the discharge of the front chamber, the footvalve
being
a hollow tubular element coaxial with the piston and the outer casing and
emerging
from the rear face of the drill bit, known as impact face.
The above requires the use of a piston with a central bore, the bore
extending along its entire length and interacting with the air guide and with
the
footvalve, This central bore reduces even more the rear thrust area and the
front
thrust area of the piston, which causes as a result a cycle of even less
power.
Moreover, the alignment of the cylinder is a frequent problem in this type of
design, which if is notaddressed, induces dissipative forces that drain power
from
the hammer's cycle.
Type B Flow System, represented by patents U55984021, U54312412 and
US6454026
The designs described in these patents comprise a pressurized fluid
supply tube (inside of which the supply chamber is generated), which extends
from
the rear face of the rear chamber and is received inside a central bore in the
piston.
This bore extending along the whole length of the piston.
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In order to control the supply of the front chamber and of the rear chamber
with pressurized fluid and control the discharge of the rear chamber, the
supply
tube interacts with bores and undercuts inside the piston.
Undercuts on the outer sliding surface of the piston and on the inner surface
of the outer casing complement the piston's control of the state of the
chambers.
Further, the discharge of the front chamber is controlled by a footvalve
formed in
the drill bit (US5984021 and US4312412) or alternatively by a front portion of
the
piston of smaller diameter that interacts with a piston guide (US6454026).
This
last solution can also be used as an alternative to the footvalve in the Type
A flow
system and in the rest of the flow systems which will be described
hereinafter.
The presence of bores across the piston weakens the impact strength of
this part of the hammer and implies a more complex manufacturing process. From
this point of view, hammers with the Type A flow system have a stronger piston
and a simpler manufacturing process than the hammers with the Type B flow
system. In addition, the creation of the supply chamber inside the supply tube
produces a delay in the initiation of the flow when the supply of pressurized
fluid
to the chambers is enabled, due to the distance between the former and the
latter.
The bores also cause an increment in the passive volumes of the chambers,
being
the main consequence of this a rise in the consumption of pressurized fluid
and a
.. reduction in the energy efficiency conversion in the thermodynamic cycle.
In the particular case of hammers that have a piston with a front portion of
smaller diameter that interacts with a piston guide, the front thrust area of
the
piston is highly reduced due to the fact that a sufficiently large impact area
is still
required in order to withstand the stress generated by the impact, thus taking
away
surface from the front thrust area.
Moreover, the provision of a supply tube requires the use of a piston having
a central bore extending along its entire length, resulting in the effects on
power
already mentioned for the Type A system.
Type C Flow Systems, represented by the patent U54923018
The design described in this patent has three different sets of supply
passages built in the outer casing. The first set of passages end at the inner
surface of the outer casing and create a supply chamber between the outer
sliding
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surface of the piston and the inner surface of the outer casing. The second
and
third sets of passages allow for the flow of pressurized fluid from the supply
chamber toward the front chamber and toward the rear chamber respectively. In
order to control the supply of pressurized fluid to the front chamber and to
the rear
chamber, the supply chamber interacts with recesses in the outer sliding
surface
of the piston and with the second and third sets of passages in the outer
casing,
while the discharge of the front chamber and the rear chamber are respectively
controlled with the use of a footvalve and an air guide (refer to the Type A
flow
system applied to a normal circulation hammer).
The main disadvantages of this design is the addition of passive volume
due to the presence of the second and third sets of passages and the fact that
these passages significantly reduce the useful life of the outer casing which
is
largely dependent on the thickness of its wall. Also, the provision of an air
guide
and footvalve requires the use of a piston having a central bore extending
along
its entire length, resulting in the effects on power already mentioned for the
Type
A system.
Type D Flow System, represented by patents US5113950 and U55279371
In the designs described in these patents a supply chamber is provided in
the rear end of the piston, the designs have similar characteristics to the
Type A
and Type B flow systems. The Type D flow system uses a central supply tube as
in the Type B flow system, but differs from the latter in that the supply
chamber is
not created inside the supply tube. Instead, similarly to the Type A flow
system,
the supply chamber is created and acts on a portion of the rear end of the
piston.
In this manner the supply tube performs the function of helping to convey the
pressurized fluid toward the supply chamber and does not participate in its
creation. All this produces as a consequence a reduction in the piston's rear
thrust
area. Moreover, the need to discharge the rear chamber requires the use of a
piston with a central bore that emerges on the front face of the same, thus
reducing
even more the rear thrust area and the front thrust area of the piston, which
results
in a cycle of even less power.
Further, in patent US5113950 the presence of recesses and bores through
the piston weaken the impact strength of this component.
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Type E Flow System, represented by patents U58640794 and U57921941
The designs described in these patents comprise a cylinder mounted inside
the outer casing, the cylinder creating a supply chamber for supplying
pressurized
fluid to the front chamber and to the rear chamber of the hammer, and a
discharge
chamber for discharging pressurized fluid from the front chamber and from the
rear chamber. In this design, the supply and discharge chambers are defined by
respective recesses, disposed in series longitudinally, on the inner surface
of the
outer casing.
In these designs the flow of pressurized fluid into and out of the front and
rear chambers is controlled solely by the overlap or relative position of the
multiple
outer sliding surfaces of the piston and the inner surface of the cylinder
during the
alternating movement of the piston. The former represents and advantage
because no aligment problems must be expected as far as the piston only slides
within the cylinder. But these designs require that the piston be provided
with
multiple fluid-conducting means for supplying pressurized fluid to the front
chamber and to the rear chamber of the hammer, and for discharging pressurized
fluid from the front chamber and from the rear chamber. These multiple fluid-
conducting means represents a disadvantage as far as the presence of bores
across the piston weakens the impact strength of this part of the hammer and
implies a more complex manufacturing process. The bores also cause an
increment in the passive volumes of the chambers, being the main consequence
of this a rise in the consumption of pressurized fluid and a reduction in the
energy
conversion efficiency in the thermodynamic cycle.
In the following paragraphs the different known pressurized fluid flow
systems are described for the specific case of reverse circulation hammers,
with
regard to the solutions for conveying the pressurized fluid discharged from
the
front chamber and from the rear chamber to the bottom of the hole,
specifically to
the periphery of the front face of the drill bit, for flushing of rock
cuttings.
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Type 1 Flow System, represented by the patents US5154244, RE36002(US),
U56702045 and U55685380
These patents describe a flow system where the pressurized fluid is
conveyed from the rear end of the drill bit to the front end of the same by
means
of channels formed in a cooperative way by splines machined on the inner
surface
of the driver sub and splines machined on the outer surface of the drill bit
shank,
and with a ring or sleeve acting as sealing element, so as to create enclosed
passages through which the pressurized fluid is discharged to the periphery of
the
front end of the drill bit.
In a variant of the former solution, described in patent US6702045, a flow
system is shown where the pressurized fluid is conveyed from the rear end of
the
drill bit up to an intermediate point on the outside of the same by means of
channels created on the outer surface of the drill bit. These channels
cooperatively
work with the splines of the driver sub to create enclosed passages. From this
intermediate point the flow of pressurized fluid is deviated through bores in
the
driver sub to a passage formed between the outer surface of the driver sub and
the inner surface of the sealing ring or sleeve in such a manner as to
discharge
the pressurized fluid at the peripheral region of the front end of the drill
bit.
From the point of view of the control of the state of the front and rear
chambers, commercial designs from these patents are of the Type A and Type D
flow systems. As with the Type B flow system, a front region of the piston of
smaller
diameter that interacts with a piston guide is used as an alternative solution
to the
footvalve for controlling the discharge of the front chamber. The discharge of
the
rear chamber is controlled by means of an air guide that opens or blocks the
flow
of pressurized fluid from the rear chamber to a central coaxial channel formed
between the inner sliding surface of the piston and the outer surface of the
sampling tube, this passage extending from the rear chamber to the rear end of
the drill bit.
The disadvantages of this flow system are the same ones as those
associated with the Type A and Type D flow systems and, in particular, impact
negatively the design of the drill bit in two aspects. The first one is the
need for a
multiplicity of manufacturing processes for producing the channels in the
outer
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surface of the drill bit, which increases the manufacturing cost of the
hammer. The
second is that, due to the presence of these channels, the drag surface of the
splines, which depend on the contact area of each spline individually and the
total
number of splines, can in some applications be insufficient. This last problem
can
be counterbalanced by lengthening the drill bit, but this implies increasing
the cost
of the hammer.
Type 2 Flow System, represented by patents U55407021 and U54819746
Patents US5407021 and US4819746 describe a flow system where the
pressurized fluid is conducted from the rear end of the drill bit up to an
intermediate
point on the outside surface of the same by means of channels formed in a
cooperative way by splines machined on the inner surface of the driver sub and
splines machined on the outer surface of the drill bit shank. From this
intermediate
point the flow of pressurized fluid is deviated through mainly longitudinal
bores
created in the head of the drill bit in such a way as to discharge the
pressurized
fluid at the peripheral region of the front end of the drill bit.
The bit head has the further function of avoiding the escape of pressurized
fluid through the annular space formed between the hammer and the wall of the
hole and between the rods and the wall of the hole.
From the perspective of controlling the state of the front and rear chambers,
patent US4819746 has a Type A flow system.
In both patents, as an alternative solution to the foot valve for controlling
the discharge of the front chamber, a front portion of the piston of a smaller
diameter is used that interacts with a piston guide, as described in the Type
B flow
system.
The discharge of the rear chamber is controlled by an air guide
(US4819746) which opens or closes the flow of pressurized fluid from the rear
chamber to a central coaxial channel formed in between the inner sliding
surface
of the piston and the outer surface of the sampling tube, which extends up to
the
rear end of the drill bit.
The disadvantages in this case (patent US4819746) are the same as those
of the Type A flow system and the design of the drill bit is also negatively
impacted
in the same two aspects already mentioned for the Type 1 flow system plus a
third
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aspect. This third aspect is given by the mechanical weakness induced on the
drill
bit as a result of the mainly longitudinal bores made on the head of the drill
bit for
channeling the pressurized fluid and discharging it at the peripheral region
of the
front end of the drill bit so as to produce a flow of pressurized fluid from
the
periphery along the front face of the drill bit towards the inside of the
central coaxial
passage of the hammer and the rods.
OBJECTIVES OF THE INVENTION
According with the issues and technical antecedents stated, it is a goal of
the
present invention to present a pressurized fluid flow system that, applied to
a
normal circulation hammer, provides a better performance than the normal
circulation hammers of the previous art, and that combined with drill bit
pressurized fluid channelling means adapted to said system, provide an
improved
DTH nomal circulation hammer. Specifically and without sacrificing useful
life, it
would be desirable to have a normal circulation hammer improved in the
following
aspects:
= a high power and high efficiency in the energy conversion process,
which implies a higher penetration rate.
= a structurally simpler design and reduced manufacturing cost.
= a high reliability and sturdiness.
BRIEF SUMMARY OF THE INVENTION
With the purpose of providing an improved pressurized fluid flow system for
a normal circulation DTH hammer according to the above-defined goals, a
solution
has been deviced that makes an efficient use of the cross-sectional area of
the
hammer and employs fewer parts and is simpler to manufacture.
The pressurized fluid flow system of the invention is characterized by
comprising a set of equal diameter outer sliding surfaces for the piston thus
avoiding failure of this part due to thermal cracks induced by friction
between the
piston and misaligned parts (air guide, supply tube, foot valve, etc.).
Moreover, the
piston does not have holes, channels or passages, making it a completely solid
component.
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Specifically, the pressurized fluid flow system of the invention is
characterized by having a cylinder coaxially disposed in between the outer
casing
and the piston; and two sets of channels, a set of supply channels and a set
of
discharge channels, delimited by the outer surface of the cylinder and the
inner
surface of the outer casing. The set of supply channels is permanently filled
with
fluid coming from the source of pressurized fluid and connected without
interruption to the outlet of said source. The set of discharge channels is
permanently communicated with the bottom of the hole drilled by the hammer.
The
supply channels are disposed in parallel longitudinally with respect to the
discharge channels overlapping longitudinally and both sets of channels are
defined by respective sets of recesses on the cylinder outer surface.
The piston has a recess on its external surface that defines, in cooperation
with the inner surface of the cylinder, a supply chamber. The supply chamber
is
permanently connected without interruption to the set of supply channels. In
this
way, the supply chamber is permanently filled with fluid coming from the
source of
pressurized fluid and connected without interruption to the outlet of said
source.
The flow of pressurized fluid supplied into and discharged from the front and
rear chambers is controlled solely by the overlap or relative position of the
outer
sliding surfaces of the piston with the inner suface of the cylinder.
For channeling the pressurized fluid from the supply chamber to the front and
rear chambers of the hammer, front and rear sets of recesses are provided on
the
cylinder. For channeling the pressurized fluid from the front and rear
chambers to
the set of discharge channels multiple discharge through-ports are provided in
the
cylinder.
Therefore, the flow of pressurized fluid into and out of the front and rear
chambers takes place inbetween the inner surface of the cylinder and the outer
surface of the piston. Further, the state of the front chamber and the rear
chamber
are controlled in the invention by the interaction of a single pair of
components.
The above-mentioned configuration enables an optimal use of the cross
sectional area of the hammer compared to prior art hammers. By disposing the
set of supply channels longitudinally in parallel with the set of discharge
channels
it is possible to increase the front thrust area and the rear thrust area of
the piston.
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The front thrust area and the rear thrust area of the piston under the
configuration of the invention are identical in size. Additionally, control of
the
discharge of the front chamber and the rear chamber by interaction between the
piston and the cylinder makes it unnecessary to have either a foot valve or a
front
portion of the piston of smaller diameter interacting with a piston guide or
an air
guide for this purpose, thus avoiding the additional losses in the thrust
areas as it
occurs with the flow systems of the prior art.
Moreover, the fact that the flow of pressurized fluid into and out the front
and
rear chambers takes place inbetween the inner surface of the cylinder and the
outer surface of the piston allows the latter to be completely solid, avoiding
the
need of holes, channels or passages that can weaken it, increase the front and
rear chambers passive volumens, deteriorate the cycle efficiency and make the
piston a more expensive part.
Even more, one or more flushing channels may be provided in the dividing
walls that separates the set of supply channels and the set of discharge
channels
for permitting part of the flow of pressurized fluid available from the source
of
pressurized fluid to be discharged directly to the bottom of the hole,
conforming in
this fashion an assisted flushing system and enabling an increased deep
drilling
capacity without a noticeable reduction in the penetration rate.
The invention also refers to a normal circulation DTH hammer characterized
by having the above-described pressurized fluid flow system and a drill bit in
which
the conventional central passage in the rear end thereof and the two or more
passageways that converge to this central passage used in normal circulation
hammers have been replaced by one or more flushing passages bored across the
drill bit and extending from the channels which, as in the described Type 1
and
Type 2 flow systems, are cooperatively formed by the splines on driver sub and
on the drill bit shank, to the front face of the drill bit. This enables a
simplified and
sturdier drill bit for a normal circulation hammer.
By having the the invention a set of discharge channels delimited by the outer
surface of the cylinder and the inner surface of the outer casing., i.e.
adjacent to
the inner surface of the outer casing, it is possible not only to divert the
pressurized
fluid flow exhausting from the set of discharge channels to the outside of the
drill
bit shank and towards the channels cooperatively formed between splines on the
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inner surface of the driver sub and splines on the outer surface of the drill
bit shank,
but also, the flow of pressurized fluid can then be discharged from these
channels
to the front end of the drill bit through the one or more flushing passages
which
are bored across the body of the bit and extend from said channels to the
front
face of the drill bit.
The mentioned characteristics of the bit plus the features previously
described in relation to the pressurized fluid flow system strongly improve
the
reliability of the hammer.
For ease of understanding of the precedent ideas, the invention is
described with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 and figure 2 depicts how the cross section views of the normal
circulation DTH hammer of the invention shown in figures 3, 4 and 5 are
generated. As can be seen, the three cross section views are obtained in the
same
way.
Figure 3 depicts a longitudinal cross section view of the normal circulation
DTH hammer of the invention specifically showing the disposition of the piston
with respect to the outer casing, cylinder and drill bit when the front
chamber is
being supplied with pressurized fluid and the rear chamber is discharging
pressurized fluid to the bottom of the hole.
Figure 4 depicts a longitudinal cross section view of the normal circulation
DTH hammer of the invention specifically showing the disposition of the piston
with respect to the outer casing, cylinder and drill bit when the rear chamber
is
being supplied with pressurized fluid and the front chamber is discharging
pressurized fluid to the bottom of the hole.
Figure 5 depicts a longitudinal cross section view of the normal circulation
DTH hammer of the invention specifically showing the disposition of the piston
and
the drill bit with respect to the outer casing and cylinder when the hammer is
in
flushing mode. The front set of recesses is depicted with a dashed line for a
best
understanding of its location respect to the piston.
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Figure 6 depicts an isometric view of the cylinder of the hammer of the
invention.
Figure 7 depicts a cross section view of the cylinder of Figure 6 for a best
understanding of the different features of this element.
In all these figures, the flow system of the hammer has also been depicted
with respect to the solution designed under the invention to convey the
pressurized
fluid to the bottom of the hole from the front chamber and rear chamber, in
all the
modes and states, specifically to the front end of the drill bit for flushing
the rock
cuttings. The direction of the pressurized fluid flow has been indicated by
means
of arrows.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figures 1 to 7, a normal circulation DTH hammer is shown that
comprises the following main components:
a cylindrical outer casing (1) having a rear end and a front end;
a driver sub (110) mounted to said front end of the outer casing (1) and
having an inner surface (113) with splines (112) machined thereon;
a rear sub (20) affixed to said rear end of the outer casing (1) for
connecting
the hammer to the source of pressurized fluid;
a piston (60) slidably and coaxially disposed inside said outer casing (1)
and capable of reciprocating due to the change in pressure of the pressurized
fluid
contained inside of a front chamber (240) and a rear chamber (230) located at
opposites ends of the piston (60), the piston (60) having multiple outer
sliding
surfaces (64, 67); and
a drill bit (90) slidably mounted on the driver sub (110), the sliding
movement of the drill bit (90) limited by the drill bit retainer (210) and the
drill bit
supporting face (111) of the driver sub (110), the drill bit (90) comprised of
a drill
bit shank (95) at the rear end of the drill bit and a drill bit head (96) at
the front end
of the drill bit, the drill bit head (96) being of bigger diameter than the
drill bit shank
(95) and having a front face (99), the drill bit shank (95) having an outer
surface
(98) with splines (93) machined thereon;
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channels (97) cooperatively formed between the splines (112) on the inner
surface (113) of the driver sub (110) and the splines (93) on the outer
surface (98)
of the drill bit shank (95).
The pressurized fluid flow system of the invention includes a cylinder (40)
that is coaxially disposed in between the outer casing (1) and the piston
(60), the
cylinder (40) having an inner (47) and an outer surface (48).
The rear chamber (230) of the hammer is defined by the rear sub (20), the
cylinder (40) and the rear thrust surface (62) of the piston (60). The volume
of the
rear chamber is variable depending on the piston's (60) position. The front
chamber (240) of the hammer is defined by the drill bit (90), the cylinder
(40), the
drill bit guide (150) and the front thrust surface (63) of the piston (60).
The volume
of the front chamber is also variable depending on the position of the piston
(60).
The piston (60) has an annular recess (68) on its external surface that
defines, in cooperation with the inner surface (47) of the cylinder (40), a
fluid flow
supply chamber (66). This fluid flow supply chamber (66) is respectively
longitudinally limited at each end by the outer sliding surfaces (64, 67) of
the
piston.
The cylinder (40) has a set of supply (2) and discharge (3) channels defined
by respective longitudinal recesses on its outer surface (48), the supply (2)
and
discharge (3) channels disposed around said surface (48) for in the first case
conveying pressurized fluid from the rear sub (20) to the supply chamber (66)
and
therefrom to the front (240) and rear (230) chambers and in the second case
discharging the pressurized fluid from the front (240) and rear (230) chambers
towards the channels (97) formed between the driver sub (110) and the drill
bit
shank (95) and therefrom towards the bottom of the hole drilled by the hammer.
When the hammer is operative, the first of these sets of channels is in
permanent
fluid communication with the source of pressurized fluid and it is filled with
said
fluid while the second of these sets of channels is directly communicated with
the
bottom of the hole.
The cylinder (40) has rear pressurized fluid intake ports (41) bored
therethrough, which connect the supply channels (2) with a supply undercut
(21)
in the rear sub (20), and has elongated front pressurized fluid exit ports
(42) bored
therethrough, which fluidly and uninterruptedly communicate the set of supply
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channels (2) of the cylinder with the supply chamber (66), therefore
permanently
filling it with high pressure fluid. The cylinder (40) also has rear (43) and
front (44)
discharge ports bored therethrough, which allow the pressurized fluid to
respectively flow from the rear chamber (230) and front chamber (240) into the
set
of discharge channels (3).
The cylinder (40) further has a front set (45) and a rear set (46) of recesses
on its inner surface for allowing the pressurized fluid which flows from the
rear sub
(20) to the supply chamber (66) through the set of supply channels (2) to
respectively divert part of the flow to the front (240) and rear (230)
chambers in
cooperation with the multiple outer sliding surfaces (64, 67) of the piston
(60).
Control of the state of the front chamber (240)
When in the hammer cycle the impact face (61) of the piston (60) is in contact
with the impact face (91) of the drill bit (90) and the drill bit (90) is at
the rearmost
point of its stroke, i.e. the hammer is at impact position (see Figure 3), the
front
chamber (240) is in direct fluid communication with the supply chamber (66)
through the front set of recesses (45) of the cylinder (40). In this way, the
pressurized fluid is able to freely flow from the supply chamber (66) to the
front
chamber (240) and start the movement of the piston (60) in the rearward
direction.
This flow of pressurized fluid to the front chamber (240) will stop when the
piston (60) has traveled in the front end to rear end direction of its stroke
until the
point where the front outer supply edge (73) of piston (60) reaches the rear
limit
of the front set of recesses (45) of the cylinder (40). As the movement of the
piston
(60) continues further in the front end to rear end direction of its stroke, a
point will
be reached where the front outer discharge edge (72) of the piston (60) will
match
the front limit of the front discharge ports (44) of the cylinder (40). As the
movement
of the piston (60) continues even further, the front chamber (240) of the
hammer
will become fluidly communicated with the set of discharge channels (3)
through
the front set of discharge ports (44) of the cylinder (40) (see Figure 4). In
this way,
the pressurized fluid contained inside the front chamber (240) will be
discharged
into the set of discharge channels (3) and from the set of discharge channels
(3)
it is able to freely flow out of the hammer through the channels (97)
cooperatively
formed between the splines (93) of the drill bit shank (95) and splines (112)
of the
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driver sub (110), and through the flushing passages (92) of the drill bit (90)
to the
front face (99) of the drill bit (90).
Normally, the drill bit (90) is aligned to the outer casing (1) of the hammer
by
a drill bit guide (150) having discharge grooves (151) as shown in the
Figures. In
the current invention these discharge grooves connect the set of discharge
channels (3) with the channels (97), so that the discharge of pressurized
fluid flows
through these discharge grooves (151) before reaching the channels (97) and
thereafter flows through the flushing passages (92) of the drill bit (90).
However,
the invention is not limited to the use of a drill bit guide and alternative
alignment
solutions may be used with corresponding pressurized fluid discharge means.
Control of the state of the rear chamber (230)
When in the hammer cycle the impact face (61) of the piston (60) is in
contact with the impact face (91) of the drill bit (90) and the drill bit (90)
is at the
rearmost point of its stroke, i.e. the hammer is at impact position (see
Figure 3),
the rear chamber (230) is in direct fluid communication with the set of
discharge
channels (3) through the rear set of discharge ports (43) of the cylinder (40)
(see
Figure 3).
In this way, the pressurized fluid contained inside the rear chamber (230)
will
be discharged into the set of discharge channels (3) and from the set of
discharge
channels (3) out of the hammer and to the front face (99) of the drill bit
(90) in a
similar fashion as with the pressurized fluid discharged from the front
chamber
(240).
This flow of pressurized fluid will stop when the piston (60) has traveled in
the front end to rear end direction of its stroke until the rear outer
discharge edge
(70) of piston (60) reaches the rear limit of the rear set of discharge ports
(43) of
the cylinder (40). As the movement of the piston (60) continues further in the
front
end to rear end direction of its stroke, a point will be reached where the
rear outer
supply edge (71) of the piston (60) matches the front limit of the rear set of
recesses (46) of the cylinder (40) (see Figure 4). As the movement of the
piston
(60) continues even further, the rear chamber (230) of the hammer will become
fluidly communicated with the supply chamber (66) through the rear set of
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recesses (46) of the cylinder (40). In this way, the rear chamber (230) will
be
supplied with pressurized fluid coming from the supply chamber (66).
Flushing Mode Operation
If the hammer is lifted in such a way that the drill bit (90) stops being in
contact
with the rock being drilled and the drill bit's retainer supporting shoulder
(94) rests
on the drill bit retainer (210), the drill bit (90) will reach the front end
of its stroke
and then the hammer switches to its flushing mode. In this position the
percussion
of the hammer stops, hence leaving the impact face (61) of the piston (60)
resting
on the impact face (91) of the drill bit (90) (see Figure 5 for illustration
of the
flushing mode description while features (61) and (91) are shown in Figure 4),
and
the pressurized fluid is conveyed directly to the front end of the drill bit
(90) through
the following pathway: into the set of supply channels (2) through the supply
undercut (21) of the rear sub (20) and the rear pressurized fluid intake ports
(41)
of the cylinder (40), and from the set of supply channels (2) to the set of
discharge
channels (3) through the front pressurized fluid exit ports (42) of the
cylinder (40),
through the rear chamber (240), and through the rear set of discharge ports
(43)
of the cylinder (40). From the set of discharge channels (3) the pressurized
fluid
is able to freely flow out of the hammer and to the front face (99) of the
drill bit (90)
in a similar fashion as with the pressurized fluid discharged from the rear
and front
chambers (230, 240) when the hammer is in drilling mode.
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