Note: Descriptions are shown in the official language in which they were submitted.
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GUIDE ADAPTER
Field of the invention
The present invention generally relates to a guide adapter for guiding a
drill bit during percusion drilling, and a drill arrangement comprising said
guide adapter.
Technical background
Within the constructional work sector and the mining industry
percussion drilling, such as top hammer drilling, is an established method for
drilling vertical bore holes with a drill bit arranged in the forward end of
an
elongated drill string or cable. During drilling, a hammering impact from a
hydraulically driven piston is acting on the drill string to exert the
required
force to break the rock and generate the bore hole.
The length of the drill string is, during the drilling, increased by adding
further drill string rods as the depth of the bore hole increases. When the
depth of the bore hole increases also the risk for deviation from the intended
straight direction of the bore hole increases. The problem with deviation
could
be reduced by adding a guide adapter between the drill bit and the drill
string
or cable to provide additional support to the forward end of the drill string
and
the drill bit. One example of a guide adapter is disclosed in US8051927B2.
However, there is always a need to improve the drilling performance
without increasing the problem with deviation.
Summary
It would be advantageous to achieve a guide adapter that fulfills at
least some of the needs mentioned above. To better address one or more of
these concerns a guide adapter as defined in the independent claims is
provided. Preferable embodiments are defined in the dependent claims.
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The guide adapter for guiding a drill bit during percusion drilling, said
guide adapter is intended to be arranged between the drill bit and an
elongated drill string extending along an axis A, said drill bit having a
first
radius transverse to axis A. The guide adapter according to the invention
comprises:
a sleeve shaped adapter body intended to extend along axis A and
comprising a forward end with a first coupling intended for connecting the
guide adapter to the drill bit, and a rear end with a second coupling intended
for connecting the guide adapter to the drill string; and
a plurality of guiding elements extending substantially radially in
relation to axis A from the sleeve shaped adapter body,
wherein the guiding elements extend along 60% or less of the adapter
body length along axis A and are arranged in the rear end of the adapter
body, said guiding elements in the rear end have an extension in radial
direction from axis A substantially equal to said first radius and curved,
straight or stepwise reduced radial extension towards the forward end along
axis A.
The guide adapter according to the invention is favorable since the
guide elements with the claimed characteristics arranged in the aft end of the
guide adapter will provide the desired guiding of the drill bit, and at the
same
time reduce the weight of the guide adapter which is a considerable
advantage to improve the drilling performance. The characteristic design of
the guide elements furthermore reduces the friction between the guide
elements and the bore hole since only the aft end of the guide elements will
be in contact with the side wall of the bore hole which improves the drilling
performace further. The guiding elements in the rear end of the guide adapter
preferably have an extension in radial direction from axis A substantially
equal
to the maximum radius, i.e. the first radius of the drill bit such that the
guiding
elements of the guide adapter will provide support against the side walls of
the bore hole and reduce deviation from the desired straight bore hole
direction.
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In one embodiment of the guide adapter, the guide adapter comprises
at least five guide elements with substantially identical shape and dimension.
This embodiment is favourable since the five or more guiding elements will
provide very good guiding of the drill bit and prevent deviation.
5 In one embodiment of the guide adapter, the guide elements are
substantially straight and extending parallel to axis A along the sleeve
shaped
adapter body. This embodiment could be manufactured in an effective way
since the guiding elements are straight and parallell to axis A.
In one embodiment of the guide adapter, the guide elements, in a
10 plane transverse to axis A, have a base arranged towards the sleeve
shaped
adapter body, said guide elements have a tapered shape in radial direction
from axis A and are ended by an outer end surface. Guiding elements with
this design provide excellent support within the bore hole and are very
resistant to loads exerted during drilling since the wider base provides a
15 strong bounding to the guide adapter body while the tapered shape
reduces
the amount of material, and consequently the weight, of the guide adapter
which improves the performance of the arrangement.
In one embodiment of the guide adapter, the outer end surface is
shaped like a cirular arc with a radius corresponding to the radius from axis
A
20 to the outer end surface. The curved outer end surface provides
excellent
support against the side walls of the bore hole and are very resistant to
wear.
In one embodiment of the guide adapter, at least an area of the outer
end surface of at least one guiding element is covered by a hard layer. The
guide adapter body and the guide elements are made of a metal material and
25 the applied hard layer of a material that is harder and more resistant
to wear
increases the life time for the guide adapter.
In one embodiment of the guide adapter, the hard layer is applied on
the outer end surfaces along the entire guide elements along axis A to
increase the life time of the guide adapter by providing the hard layer on the
30 entire surface of the guide element facing the bore hole side wall. The
hard
layer is a layer made of a material that is harder and more resistant to wear
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than the metal material of the guide adapter body. The material is a material
including an iron-based alloy, a cobalt-based alloy, a nickel-based alloy, a
refractory metal, a cemented carbide, a metal matrix composite and/or a
chromium carbide alloy. These different alternative materials provide a
5 protective layer that can withstand wear and increase the intervals
between
replacement of the guide adapter. The hard layer has a thickness in a
direction perpendicular from the outer end surface within the range of 0.1 ¨
10
mm, and preferably within the range of 0.1 - 4 mm to provide the desired
protection of the guiding elements of the guide adapter.
10 In one embodiment of the guide adapter, the guide elements
comprise
a rear end surface and the rear end surface of at least one guide element is
covered by a rear end surface hard layer. The rear end surfaces are exposed
to wear since the material removed from the rock to form the bore hole
remain within the bore hole and due to gravitation tend to land on the rear
end
15 surfaces of the guiding elements. The application of the rear end
surface hard
layer exends the life time of the guide adapter since the rear end of the
guide
elements are protected by the rear end surface hard layer. The rear end
surface hard layer has a thickness in a direction perpendicular from the rear
end surface within the range of 0.1 ¨ 10 mm, and preferably within the range
20 of 0.1 - 4 mm and is made of the same type of materials as the hard
layer
arranged on the outer end surface on the guiding element
In one embodiment of the guide adapter, the guiding elements in the
rear end has an extension in radial direction from axis A of about 94¨ 96 % of
said first radius, and a radial extension the forward of the guiding elements
of
25 about 89 ¨ 91% of said first radius. Guiding elements with this design
provides excellent guiding of the drill bit and the desired drilling
performance.
In one embodiment of the guide adapter, a wear indicator is arranged
in the outer end surface of at least one of the guide elements to indicate
when
the guide adapter is worn out and needs to be replaced. This embodiment
30 helps the operator to replace the guide adapter in time to ensure the
desired
guiding of the drill bit.
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In one embodiment of the guide adapter, the wear indicator is a notch,
recess or cut out portion arranged in the top end surface, said notch, recess
or cut out portion has a depth selected such that when the guide adapter is
worn out, the notch is no longer visible in the top end surface. This
5 embodiment makes it easy for the operator to verify the condition of the
guide
adapter and, if required, replace the guide adapter.
In one embodiment of the guide adapter, the distance from axis A to
the wear indicator is within the range of 80 ¨99 % of the guiding element
extension in radial direction from axis A in the rear end of the guide
adapter,
10 and preferably within the range of 85 ¨ 95 % of the guiding element
extension
in radial direction from axis A in the rear end of the guide adapter. These
ranges are selected to ensure that the guide adapter is preplaced in time to
ensure the desired guiding of the drill bit.
In one embodiment of the guide adapter, the guide elements extend
15 along 50% or less of the adapter body length L along axis A,
alternatively
40% or less of the adapter body length L along axis A. These lengths are
selected to ensure the desired guiding of the drill bit in combination with
excellent drilling performance.
In one embodiment of the guide adapter, the guide elements extend
20 along 10-60% of the adapter body length L along axis A, preferably along
15-
50% of the adapter body length L along axis A, more preferably along 20-40
18-35% of the adapter body length L along axis A. These lengths are selected
to achieve the optimal balance between reducing the weight of the drilling
assembly which improves the penetration rate and having sufficient length to
25 be able to maintain the service life of the guide adapter. With the
length being
in this range it ensures that the desired guiding of the drill bit in
combination
with excellent drilling performance is achieved.
In one embodiment of the guide adapter, the radial extension of the
guiding elements are decreasing in the direction from the rear end towards
30 the forward end such that the guide elements will have a convex shape
along
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axis A, or a substantially straight shape angled in relation to axis A along
axis
A.
The invention furthermore relates to a drill arrangement for percussion
drilling, said arrangement comprises a drill string, a drill bit having a
first
5 radius transverse to axis A and a guide adapter according to claim 1
arranged
between the drill string and the drill bit to reduce the risk for deviation.
Brief description of the drawings
The invention will be better understood through the following illustrative
10 and non-limiting detailed description of preferred embodiments, with
reference to the appended drawings, on which:
Figure 1 is a perspective view of a drill arrangement comprising a drill
string rod, a guide adapter and a drill bit, and enlarged views of the guide
15 adapter and drill bit arranged in one end of the drill string and the
coupling
arranged in opposite end of the drill string.
Figure 2 illustrates an exploded view of the forward end of the drill
string rod, the guide adapter and the drill bit.
Figure 3 illustrates a perspective view of one embodiment of a guide
20 adapter.
Figure 4 illustrates a cross-sectional view of the guide adapter
transverse to a longitudinal axis A. The position of the cross-sectional view
is
illustrated by arrows IV in figure 3.
Figure 5 illustrates a cross-sectional view of the guide adapter parallel
25 to the longitudinal axis A through the center of the guide adapter. The
position
of the cross-sectional view is illustrated by arrows V in figure 3.
Figure 6 illustrates a side view of a drill bit and a guide adapter fitted
together.
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All figures are schematic, not necessarily to scale, and generally only
illustrating parts which are necessary to elucidate the invention, wherein
other
parts may be omitted or merely suggested.
5 Detailed description of embodiments
In figure 1 a perspective view of a drill arrangement according to the
invention is illustrated. The drill arrangement comprises a drill string rod
10, a
guide adapter according to the invention 100 and a drill bit 20. The drill
string
rod 10 comprises an elongated intermediate section 11 extending along a
10 longitudinal axis A (shown in figure 3). In the illustrated embodiment,
a male
coupling 12 is arranged in one end of the intermediate section and a female
coupling 13 in the opposite end. The male and female couplings are intended
to make it possible to connect the guide adapter and drill bit in the forward
end of the drill string rod, and the female coupling in the rear end of the
drill
15 string rod is intended for connecting further drill string rods to form
a drill
string 100 with the desired length by connecting the male coupling of an
identical drill string rod to the female coupling of the adjacent drill string
rod.
During drilling, further drill string rods 10 are connected to extend the
length
of drill string 100 as the depth of the bore hole increases. In the
illustrated
20 embodiment male / female couplings are illustrated but other coupling
arrangements could be used to adapt the arrangement for different needs.
During drilling, the rear end of the drill string 10 is connected to a
hydraulically driven piston, not illustrated, arranged to provide the desired
axial force and rotation of the drills string, the guide adapter and the drill
bit to
25 conduct the percussion drilling. The design of the drill string rod, the
guide
adapter and the drill bit are adapted to specific needs origin from different
types of rock materials and the desired bore hole diameter. Larger bore hole
diameters require larger dimensions of the different components to ensure
that they are able to withstand the loads during drilling.
30 The drill string rod could be embodied in different ways and for
example the intermediate section 10 could have a circular, rectangular,
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pentagonal or hexagonal cross-sectional shape as long as the required
strength is ensured. The intermediate section is either solid, or comprising a
passage extending in the center of the intermediate section through the drill
string rod to allow a of flushing media through the drill string to the drill
bit
5 arranged in the forward end of the drill string to remove particles and
gravel
from the rock during drilling. The flushing media is for example air, water or
a
mixture of air and water.
Figure 2 illustrates an exploded view along axis A where the forward
end of the drill string rod 10, the guide adapter 100 and the drill bit 20 are
10 illustrated separately from each other to more clearly illustrate the
design of
the different components. The male coupling 12, arranged in the forward end
of the intermediate section 11, comprises a male spigot portion 14 extending
co-axially to the intermediate section along axis A. In the illustrated
embodiment, the male spigot portion 14 has substantially the same radius as
15 the intermediate section 11, but dimensions could be changed to adapt
the
spigot portion 14 and intermediate section to different needs. The male spigot
portion 14 comprises an external thread 15 extending along the entire length
of the spigot portion along axis A. In the opposite end to the male coupling,
illustrated in figure 1, a female coupling 13 is permanently fitted to the
20 intermediate section 11. The female coupling 13, illustrated in figure 1,
has a
shape and dimension corresponding to the dimensions of the male coupling
12, i.e the male spigot portion 14 to make it possible to connect identical
drill
string rods 10 to each other to form a drill string. The female coupling 13
comprises a sleeve shaped element 16 extending co-axially to the
25 intermediate section. The sleeve shaped element 16 has internal threads 17
corresponding to the external threads 15 on the male spigot portion 14.
The guide adapter 100 is attached to the forward end of the drill string
rod to provide additional guiding of the drill bit 20 during drilling and
reduce
deviation from the desired straight bore hole direction. Different embodiments
30 of the guide adapter according to the invention will be described in
detail
further down the detailed description.
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The different embodiments of the guide adapter all comprises a sleeve
shaped adapter body 101 intended to extend co-axially to axis A. The adapter
body has a forward end 102 with a first coupling 104 intended for connecting
the guide adapter 100 to the drill bit 20, and a rear end 103 with a second
5 coupling 105 intended for connecting the guide adapter 100 to the drill
string
10.
The drill bit 20 is fitted to the forward end 102 of the guide adapter 100
by the first coupling element 104. In the illustrated embodiment the first
coupling 104 of the guide adapter 100 is a male coupling and in the rear end
10 28 of the drill bit 20 a corresponding female coupling 22 is arranged
within the
drill bit body 21. The drill bit body 21 extend co-axially to axis A. The
length of
the drill bit body 21 along axis A depends on the size and intended use of the
drill bit. The front surface 23 of the drill bit is either substantially flat,
or
convex. In the front surface 23 several buttons 24 are arranged. The buttons
15 are made of a harder and more resistant material and are intended to
form
the desired bore hole during drilling. The buttons are positioned such that
the
buttons along the periphery of the front surface define the maximum radius of
the drill bit, i.e. the first radius, and consequently the radius of the bore
hole of
the drill bit will form when the drilling is initiated. There are different
well-
20 known suitable materials for the buttons as well as a number of
different
layouts and designs of the front surface and button known in the art. Behind
the front surface 24 of the drill bit the drill bit body has a narrower
section 30
with substantially circular cross-sectional shape with a smaller radial
extension from axis A than the first radius. Behind the narrower section the
25 drill bit body comprises a rear section 29. Along the rear section 29 a
number
of guiding ribs 31 extend in a substantially radial direction from the drill
bit
body. The guiding ribs 31 extend substantially parallel to axis A along the
rear
section of the drill bit body and has a radial extension slightly smaller than
the
first radius, i.e. the maximum radius of the drill bit. The guiding ribs are
30 intended to provide support for the drill bit against the side walls of
the bore
hole to reduce deviation from the desired straight bore direction.
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In the guide adapter embodiment illustrated in figure 2, 3 and 5, the
first coupling 104 is a male coupling element 110 and the second coupling
105 a female coupling element 111 corresponding to the male coupling 12 in
the forward end of the drill string rod 10. The sleeve shaped adapter body 101
5 has a legth L along axis A, and the sleeve shaped adapteter body has a
slightly smaller outer radius along the forward half than the outer radius of
the
rear half. The design of the adapter body could however be modified in
several different ways to adapt the guide adapter to different needs.
The male coupling element 110 comprises a male spigot portion 112
10 extending co-axially to axis A from the forward end 102 of the adapter
body
101. In the illustrated embodiment, the male spigot portion 112 has a smaller
radius than the forward end 102 of the adapter body 101. The male spigot
portion 112 comprises an external thread 113 extending along the entire
length of the spigot portion along axis A. The spigot portion is ended by a
15 contact surface 114 transverse to axis A. The contact surface is
intended to
bear against a corresponding surface in the drill bit such that axial loads
are
transferred from the drill bit to the guide adapter via the contact surface
112.
The adapter body length L is defined as the total length of the guide adapter,
i.e. the adapter body including the spigot portion of the male coupling.
20 At the opposite end of the adapter body to the male coupling, the
female coupling 111 is arranged within the rear part of the adapter body 101.
The female coupling 111 is embodied as a recess 113 with a circular cross-
sectional shape transverse to axis A extending coaxially to axis A within the
adapter body from the rear end of the guide adapter 100. The radius of the
25 recess corresponds to the radius of the male coupling 12, i.e the male
spigot
portion 14 of the drill string rod to make it possible to connect the forward
end
of the drill string rod 10 to the guide adapter. The female coupling has
internal
threads 114 corresponding to the external threads 15 on the male spigot
portion 14.
30 In order to provide the desired guiding of the drill bit during
drilling, the
guide adapter comprises guiding elements 106 extending along the rear part
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of the adapter body. The design of the guide elements is illustrated in figure
3,
4 and 5.
In a plane transverse to axis A, the guide elements have a base 115
illustrated in figure 3, arranged towards the sleeve shaped adapter body 101
5 and a first 116 and second 117 side surface extending from the adapter
body.
The guide elements have a tapered shape in radial direction from axis A and
are ended by an outer end surface 107 extending between the first and
second side surface. The outer end surface 107 is shaped like a cirular arc
with a radius corresponding to the radius from axis A to the outer end
surface.
10 The design of the first and second side surface and the outer end
surface
could however be modified in many different ways.
The guide elements have substantially identical shape and dimension
and are arranged side by side at constant distance from each other around
the periphery of the adapter body. The guide elements extend along the rear
15 end 103 of the adapter body substantially parallel to axis A.
The guiding elements 106 in the rear end of the guide adapter have an
extension in radial direction from axis A corresponding to the maximum radius
Rf of the drill bit and curved, straight or stepwise reduced radial extension
towards the forward end along axis A which is illustrated in the appended
20 figures.
In order to provide the desired guiding of the drill bit it is essential that
the dimensions of the drill bit and the guide adapter correspond to each other
and in figure 6 the radial extensions of the drill bit and a corresponding
guide
adapter are illustrated. The drill bit could be embodied in many different
ways
25 but the essential feature of the drill bit is the maximum radius, i.e.
the first
radius Rf, of the drill bit that will determine the dimension of the formed
bore
hole once the drilling is initiated. The guide adapter according to the
invention
intended for use in combination with the described drill bit preferably has
guiding elements 106 with an extension in radial direction Rr from axis A in
30 the rear end of about 94 ¨ 96 % of said first radius Rf, i.e. the
maximum
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radius of the drill bit intended to be used in combination with the guide
adapter.
Since the radial extension of the guide elements is reduced towards
the forward end of the guide adapter the radial extension Rm of the guide
5 elements in the forward end of the guiding elements is about 89 ¨ 91% of
said
first radius Rf, i.e. the maximum radius of the drill bit intended to be used
in
combination with the guide adapter.
The radial extension of the guiding elements 106 in figure 6 are
decreasing in the direction from the rear end towards the forward end such
10 that the guide elements will have a convex shape along axis A. The
decresing
radial extension of the guiding element also results in that the outer end
surface will be slightly wider transveres to axis A due to the tapered shape
of
the guiding elements. The same consequence will also apply if the guiding
element radial extention is decreasing along a substantially straight shape
15 angled in relation to axis A along axis A. In the illustrated embodiment
of the
guide adapter, a transition section 124 is formed adjacent to the forward end
of the guide elements to form a smooth transition between the forward end of
the guide elements 106 and the sleeve shaped adapter body 101.
There are a number of drill bits in different sizes available on the
20 market today and consequently corresponding guide adapters will be
required
to ensure the desired performance of the drill arrangement.
Each guiding element furthermore comprises a rear end surface 109.
In the illustrated embodiment of the guide adapter the rear surfaces have an
undulating shape instead of a flat surface transverse to axis A to facilitate
the
25 transport of particles or gravel from the bore hole. The end surface
could be
modified in several ways to adapt the guide element for different conditions.
To extend the life time of the guide adapter, surfaces exposed to
severe wear during drilling could be covered by an additional protective hard
layer 108 applied on the outer end surfaces 107 of the guiding elements since
30 these surfaces will be in contact with the walls of the bore hole to
guide the
drill bit. The guide adapter is made of a metal material and either an limited
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area of the outer end surface or the entire outer end surface of one or more
guiding elements are covered with the hard layer that is more resistant to
wear. Preferably, all outer end surfaces are covered by the hard layer 108 to
ensure that all guiding elements have similar characeristics.
5 Furthermore, the rear end surface 109 of one or more of the guide
elements could be covered by a rear end surface hard layer 122.
The hard layers 108 and 122 are made of a material that is harder and
more resistant to wear than the metal material of the guide adapter to make it
possible for the exposed surfaces of the guide adapter to withstand the wear
10 for an extended period of time.
The applied hard layer on the outer end surface 107 and the rear end
surface 109 has a thickness in a direction perpendicular to the covered
surface within the range of 0.1 - 10 mm. The hard layer thickness is either
constant over the entire covered area or adapted such that a thicker layer is
15 applied where the risk for wear is higher.
The layer of material that is harder and more resistant to wear could be
different types of materials. Examples of materials are material including an
iron-based alloy, a cobalt-based alloy, a nickel-based alloy, a refractory
metal,
a cemented carbide, a metal matrix composite and/or a chromium carbide
20 alloy with the desired characteristics. Further materials are possible
as well.
The technique of applying a layer of material that is harder and more
resistant to wear is often referred to as "hardfacing". Hardfacing is a metal
working process where harder or tougher material is applied to a base metal.
The material is often welded to the base material to ensure that the applied
25 material is adhered to the base material. An alternative method involves
the
use of powder metal alloys that are welded to the surface of the product that
need the protective layer.
The guide adapter 100 furthermore comprises a wear indicator 120
arranged in the outer end surface 107 of at least one of the guide elements
30 106 to indicate when the guide adapter is worn out and needs to be
replaced.
The wear indicator is a notch 120, recess or cut out portion arranged in the
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top end surface 107 somewhere along the top end surface where it is easy for
the operator to inspect. Preferably the the notch 120, recess or cut out
portion
is arranged close to the forward end of the guiding elements 106 where the
radial extension of the guiding elements is smaller and the loads on the guide
5 elements from the bore hole is smaller than in the rear end of the guide
adapter to prevent that the strength of the guiding elements is affected. The
notch, recess or cut out portion has a depth selected such that when the
guide adapter 100 is worn out, the notch is no more visible in the top end
surface 107. The depth of the wear indicator is selected such that the bottom
10 of the wear indicator has a radial extension Rw within the range of 80 ¨
99 %
of the guiding element extension in radial direction Rr from axis A in the
rear
end of the guide adapter. In a preferred embodiment of the war indicator the
depth is within the range of 85 ¨95 % of the guiding element extension Rr in
radial direction from axis A in the rear end of the guide adapter.
15 While the invention has been illustrated and described in detail
in the
drawings and foregoing description, such illustration and description are to
be
considered illustrative or exemplary and not restrictive; the invention is not
limited to the disclosed embodiments. The skilled person understands that
many modifications, variations and alterations are conceivable within the
20 scope as defined in the appended claims.
Additionally, variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing the claimed
invention, from a study of the drawings, the disclosure, and the appended
claims. In the claims, the word "comprising" does not exclude other elements
25 or steps, and the indefinite article "a" or "an" does not exclude a
plurality. The
mere fact that certain measures are recited in mutually different dependent
claims does not indicate that a combination of these measures cannot be
used to advantage. Any reference signs in the claims should not be construed
as limiting the scope of the claims.
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