Note: Descriptions are shown in the official language in which they were submitted.
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Method and grinding appliance for grinding
Technical field
The present invention relates to a grinding appliance for grinding of button
drill bits
which comprise a drilling head with a plurality of buttons, and a method for
manufacturing such a grinding appliance.
State of the art
A button drill bit intended for rock drilling comprises usually a plurality of
buttons
which are made of, for example, hard metal and are embedded in a drilling head
which
is made of a relatively softer material, e.g. steel. Each button usually has a
cylinder-like
portion partly embedded in the steel, a cupola-shaped end profile shape
protruding from
the steel. The end profile shape of the button may be of various shapes, e.g.
semi-
ballistic, as depicted in the drawings in this specification, hemispherical or
semi-
cylindrical or some other desired shape. Such a button is often made of a hard
metal,
usually a material comprising tungsten carbide grains combined with a binding
phase
which comprises cobalt or material with similar characteristics. During the
drilling
process, the button becomes worn in such a way that it becomes flat, thereby
substantially reducing the drilling effectiveness of the button drill bit. As
button drill
bits are expensive to purchase, the button is therefore reground to restore
its original
shape so that the button drill bit can be reused instead of being scrapped.
Swedish patent specification SE434356 refers to a grinding facility for
grinding of drill
bits. The grinding facility comprises a grinding appliance comprising an
abrasive wheel
fastened to a powered spindle, and a rotatable table with a holder for the
button drill bit.
In this specification, a spindle is a machine part which, via a shaft,
transmits a rotary
motion to a tool, in this case the abrasive wheel, fastened in the shaft. The
abrasive
wheel has running round it a profile groove corresponding to an intended end
profile for
the button drill bit. The end profile is obtained by rotating the tool about
the geometric
axis of symmetry of the button. The abrasive wheel is also fastened in such a
way that it
can grind a button to its original shape in conjunction with the button drill
bit being held
firmly on the rotating table.
Such an abrasive wheel for grinding of button drill bits with the object of
restoring a
worn button to its original shape is known from European patent EP397955. The
abrasive wheel according to that patent takes the form of a pulley with a
groove situated
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between two flanks, with the shape which the drilling button originally had
and which is
to be recreated by the abrasive wheel.
The groove on the abrasive wheel is provided with a grinding agent, usually a
diamond
facing, intended to be able to grind away the hard metal which the drilling
button is
made of.
In grinding with such an abrasive wheel, the situation is aggravated by the
fact that the
hard metal button is fastened in a softer material, usually steel, with the
result that, in
cases where the hard metal button is severely worn down or has been reground
more
than once, both the hard metal and the drilling head, which is made of the
softer
material, e.g. steel, have to be ground on the same occasion. However, this is
a difficult
material combination to grind simultaneously, in that the tools and grinding
methods
used also cause severe wear of the edges of the abrasive wheel, which are
caused to
grind down the surrounding steel, thereby also reducing the service life of
the abrasive
wheel. During the removal of the material round the hard metal buttons of
button drill
bits, the abrasive wheel quickly becomes clogged because of the relatively
soft material
of the button drill bit's drilling head in which the hard metal button is
fastened.
To solve this problem, a grinding appliance according to Swedish patent
SE458425 is
used. The grinding appliance according to that patent takes the form of a disc-
shaped
abrasive wheel provided with an abrasive facing of boron nitride adapted to
grinding the
steel material of the drilling head. Using such an abrasive wheel for grinding
the button
of the drill bit makes it possible for the shape of the button to be restored,
thereby
greatly lengthening the service life of the drill bit. In normal use, a drill
bit can be
reground about 8-10 times.
A problem is that if a boron nitride facing intended for grinding the steel of
the drilling
head comes unintendedly into contact with a hard metal button, the abrasive
facing is
veryquickly destroyed and the abrasive wheel has to be scrapped. Moreover, the
boron
nitride facing used as the abrasive medium for grinding the drilling head,
e.g. cubic
boron nitride (c-Bn), functions badly in the grinding of hard metal. Dividing
the
grinding process into two stages, firstly steel grinding and thereafter hard
metal
grinding, is also a time-consuming process. There is therefore within the
industry a
desire to improve the grinding process and make it more efficient.
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Summary of the invention
A first object of the invention is to propose a grinding appliance of the kind
indicated in the
introduction which may solve the above problem, and a method for manufacturing
such a
grinding appliance.
In accordance with one aspect, a grinding appliance is provided.
Such a grinding appliance for grinding a button drill bit which has a drilling
head provided
with a plurality of buttons comprises a first element provided with a first
abrasive facing
comprising diamonds of a first average grain size as the abrasive medium
adapted to grinding
a button to an intended end profile shape, and at least one second element
adapted to grinding
the drilling head, at least one section of the second element being provided
with a second
abrasive facing comprising diamonds of a second average grain size adapted to
grinding the
material of the drilling head.
Manufacturing a grinding appliance in such a way that it comprises a plurality
of separate but
mutually assembled parts made of different materials makes it possible for
each part of the
abrasive wheel to have a function of its own, i.e. for each part to be adapted
to grinding
different portions of the drill bit. This makes is possible for each part to
be adapted according
to the material, e.g. hard metal or steel, which is ground by the various
parts of the grinding
appliance. It is also possible to change the parts separately if they become
worn at different
rates.
Using an abrasive facing which comprises coarser diamond grains on the
abrasive wheel's
flanks adapted to grinding the material of the drill bit may cause the
abrasive facing to last for
more grinding operations than is the case with an abrasive facing which
comprises finer
diamond grains, since the coarser abrasive facing will grind away larger
material fragments,
thereby making the grinding process quicker. This may make it possible for the
abrasive
wheel to be not worn down as quickly as one used with an abrasive facing which
comprises
finer diamond grains on all the abrasive surfaces. Nor are large material
fragments trapped as
easily in the coarser abrasive facing as smaller material fragments. Given
that the second
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element adapted to grinding the drilling head is diamond-faced, since diamond
grains are
more durable than, for example, boron nitride, this may make it possible for
the second
element not to become worn prematurely if the grinding appliance inadvertently
comes into
contact with the hard metal button, thus allowing for less careful or careless
handling. The
average grain size for the diamonds in the second abrasive facing is
preferably different from
that in the first abrasive facing, since the respective abrasive facings are
thereby adapted to
grinding materials which have different characteristics.
In an embodiment according to the invention, the diamonds in the second
abrasive facing have
an average grain size within the range 210-500 fim, corresponding to US mesh
70/80-35/40.
In a preferred embodiment, the diamonds in the second abrasive facing have an
average grain
size of 250-354 pm, corresponding to US mesh 60/70-45/50. The diamond grain
size of the
abrasive medium determines the amount of material which can be removed with a
certain
amount of abrasive media. The material of the drilling head is softer than
that of the drilling
button. The material of the drilling head is ground by the second abrasive
facing. The
material of the drilling head is, for example, steel or a material with
characteristics similar to
steel, e.g. titanium alloys, aluminum alloys and bronzers. The larger the
diamond grains, the
more steel can be removed per unit time. Larger diamond grains increase the
amount of
material removed, and the drill bit is ground quicker. The abrasive wheel may
also last for
more grinding operations with coarser diamond grains.
In an embodiment according to the invention, the diamonds in the first
abrasive facing have
an average grain size within the range 37-320 m, corresponding to US mesh
400/500-45/60.
In another embodiment according to the invention, the diamonds in the first
abrasive facing
have an average grain size within the range 37-229 pm, corresponding to US
mesh 400/500-
60/80. The size of the diamond grains is less significant as regards grinding
speed and wear
resistance when grinding the button made of, for example, hard metal than when
grinding the
drill bit made of, for example, steel. For certain applications, however,
diamond abrasive
grains which are too large may cause deep scratches in hard metal, which may
lead to the hard
metal cracking during the grinding process. Smaller diamond grains limit
surface roughness
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and result in small depth of scratches, thereby increasing the durability, and
allowing more
regrindings, of the button.
In an embodiment according to the invention, the average grain size for the
diamonds in the
second abrasive facing is larger than the average grain size in the first
abrasive facing. An
advantage of using an abrasive facing comprising coarser diamond grains on the
flanks of the
abrasive wheel is that the abrasive wheel may not become worn down as quickly
on the flanks
as when diamonds with a smaller average grain size are used as abrasive
facing, with the
result that more grinding operations can be effected with a
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grinding appliance according to the invention. Another advantage of using an
abrasive
facing comprising coarser diamond grains on the flanks of the abrasive wheel
than in
the abrasive facing on the waist is that the flanks of the abrasive wheel can
inadvertently
reach the button without the abrasive medium on the flanks being damaged,
since
5 coarser diamond grains have better durability than finer diamond grains,
making it
possible for more grinding operations to be done with the same grinding
appliance
without the abrasive facing becoming worn or clogged and the abrasive flank
having to
be scrapped.
In an embodiment according to the invention, the first element is a first
separate
component, the second element is a second separate component, and these
components
are connected for joint rotation so that a complete profile groove with an
intended end
profile shape is formed. This is an advantage in that the elements can be
produced
separately. It is also an advantage in that they can be changed separately.
In an embodiment according to the invention, the grinding appliance is an
abrasive
wheel and the first element has running round it a concave profile groove
corresponding
to the intended end profile shape, and the second element is a concentric
circular flank,
a concentrically circular side portion. The elements with the profile groove
and the
flank are connected for joint rotation so that a complete profile groove with
an intended
end profile shape is formed. The circular profile groove is provided with the
first
abrasive facing intended for grinding the button. The concentric circular
flank is
provided with the second abrasive facing intended for grinding the drilling
head. The
abrasive wheel is with advantage mounted on a spindle in a grinding facility.
In a
preferred embodiment, the profile groove has a shape such that a button with a
convex
shape corresponding to the through-section of a substantially spherical zone
of a
trapezoid can be ground.
In an embodiment according to the invention, the grinding appliance comprises
a third
separate element connected for joint rotation with the first element and
opposite to the
second element, which third element is provided with a third abrasive facing
comprising
diamonds as the abrasive medium adapted to grinding the drilling head. In a
preferred
embodiment, the third element is a second concentric circular flank. In this
embodiment, the abrasive wheel comprises a middle portion made of one material
and
separate flanks made of another material. The grinding appliance is thus
specially
adapted to grinding a soft material, e.g. steel or a material with similar
characteristics to
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steel, with the flanks of the abrasive wheel while at the same time the hard
metal button
is ground by the middle portion, the waist of the abrasive wheel.
In an embodiment according to the invention, the first element is an inner
portion of a
grinding cup and the second element is an adjacent firmly connected outer
portion of
the grinding cup intended to grind the drilling head. The inner portion of the
grinding
cup is provided with the first abrasive facing intended to grind the button to
an intended
end profile shape. The second element of the adjacent firmly connected outer
portion of
the grinding cup, is provided with the second abrasive facing adapted to
grinding the
drilling head. This embodiment makes it possible for the grinding cup to
rotate while
the button is stationary, or vice versa. This is also an advantage in that the
parts can be
changed separately.
In an embodiment according to the invention, at least one of the abrasive
facings
comprises diamonds with protrusions. The diamonds with protrusions have
preferably
only one layer of diamonds so that a thin abrasive layer with a well-
controlled surface
profile can be applied. The diamonds with protrusions will grind steel or a
material with
characteristics similar to steel quicker, without the abrasive wheel being
destroyed, than
if boron nitride is used as the abrasive facing, resulting in more efficient
grinding.
In an embodiment according to the invention, at least one of the abrasive
facings
comprises matrix diamonds. An advantage of matrix diamonds is that the
diamonds will
be in two or more layers, so the layer can be made thicker. This is
particularly an
advantage in the manufacture of a homogeneously made second element for
grinding
the drill bit, in which the shape of the drill bit is of no great importance
and it is
therefore not important if the flank becomes worn down. In the manufacture of
grinding
cups, a thick layer is also of advantage for longer service life of the
grinding cup.
Another object of the invention is to propose a grinding facility for grinding
of button
drill bits which have a drilling head with a plurality of buttons, comprising
a grinding
appliance according to any one of claims 1-13.
A third object of the invention is to propose a method for manufacturing a
grinding
appliance of the kind indicated in the introduction which solves the above
problem.
The solution is a method which has the characterising features of claim 15.
Such a method for manufacturing a grinding appliance for grinding of button
drill bits
which comprise a drilling head with a plurality of buttons comprises:
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According to one aspect of the present invention, there is provided a grinding
appliance for
grinding of button drill bits which comprise a drilling head with a plurality
of buttons, which
grinding appliance comprises a first element provided with a first abrasive
facing comprising
diamonds of a first average grain size adapted to grinding a button to an
intended end profile
shape, and wherein the grinding appliance also comprises a second element
adapted to
grinding the drilling head, and at least one section of the second element is
provided with a
second abrasive facing comprising diamonds of a second average grain size
adapted to
grinding the material of the drilling head, the average grain size of the
diamonds in the second
abrasive facing being larger than the average grain size in the first abrasive
facing, and the
diamonds in the second abrasive facing having an average grain size within the
range
210-500 tim, corresponding to US mesh 70/80-35/40.
According to another aspect of the present invention, there is provided a
method for
manufacturing a grinding appliance for grinding of button drill bits which
comprise a drilling
head with a plurality of buttons, wherein the method comprises providing a
first element of
the grinding appliance with an abrasive facing comprising diamonds as the
abrasive medium
of a first average grain size adapted to grinding a button to an intended
profile shape, wherein
in that the method further comprises: providing at least one section of a
second element of the
grinding appliance with an abrasive facing comprising diamonds as the abrasive
medium, and
the average grain size for the diamonds in the second abrasive facing is of a
second average
grain size adapted to grinding the drilling head, and the average grain size
for the diamonds in
the second abrasive facing is larger than the average grain size in the first
abrasive facing, the
diamonds in the second abrasive facing having an average grain size within the
range
210-500 tun, corresponding to US mesh 70/80-35/40.
In an embodiment, the method further comprises:
joining the first element and the second element together for joint rotation
so
that a complete profile groove is formed.
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Figure 5 depicts a through-section of a grinding cup according to the
invention,
Figure 6 depicts a detail of a through-section of an abrasive facing
intended for a
grinding appliance according to the invention,
Figure 7 depicts a further detail of a through-section of an abrasive
facing
intended for a grinding appliance according to the invention, and
Figure 8 depicts a method according to the invention for manufacturing
a grinding
appliance according to the invention.
Description of embodiment examples
The following description refers to both the method and the device.
Figure 1 depicts a grinding facility intended to grind buttons of a button
drill bit with a
grinding appliance according to the invention. The grinding facility is in
this case
intended to be mounted on a drilling rig and includes a supporting frame 1
intended to
be fastened in the drilling rig, not depicted in the drawing. The supporting
frame 1 has
an upper arm 2 running outwards which supports a grinding machine 3 via a
supporting
structure 4 which is movable in the horizontal plane. The grinding machine 3
can be
raised and lowered in the supporting structure, i.e. it is adapted to pivoting
to and fro in
the vertical plane. The supporting frame 1 also comprises a fastening means 5
situated
below the grinding machine 3. The fastening means 5 is adapted to firmly
holding a
drill bit 6. The drill bit 6 can easily be fitted into and locked in the
fastening means 5 by
means of a locking handle 7. The drill bit comprises a number of buttons 8,
the size and
positioning of which on the bit 6 may vary. The grinding machine 3 comprises
also a
grinding unit 9 which includes a motor unit 10 and a spindle 11 which is
driven by the
motor. The grinding unit 9 is thus also adapted to pivoting to and fro about a
vertical
axis which coincides with the geometric axis of symmetry of the button 8. A
grinding
appliance, in this case an abrasive wheel 12, is supported at the end of the
spindle 11.
The abrasive wheel 12 is adapted to grinding the buttons of the drill bit. The
grinding
unit 9 is so arranged that the spindle 11 will slope somewhat relative to the
horizontal
plane, so that the abrasive wheel 12 rotates about the spindle. The grinding
unit is
supported by a supporting means 13 on the grinding facility and can be pivoted
about a
substantially vertical axis 14 by means of a pivot cylinder 15. The geometric
axis about
which the grinding unit 9 moves forwards and rearwards is a generally vertical
axis
which coincides with the geometric centre of the button 8 when the grinding
machine 3
is adjusted relative to the button drill bit. During the grinding process, the
grinding unit
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moves forwards and rearwards in a pendulum movement in the horizontal plane
when
the button 8, which protrudes substantially vertically, is being ground. The
original
shape of the button can be recreated by moving the abrasive wheel towards the
button
while at the same time the grinding tool rotates about its own axis.
A grinding appliance according to the invention may also be used in other
variants of
grinding facilities intended for drilling rigs, not depicted. Such a grinding
appliance may
also be used in a fixed station, not depicted, for grinding of button drill
bits.
Figure 2A depicts a grinding appliance 20 for grinding a button 8A of a button
drill bit
6A. In this case the grinding appliance is an abrasive wheel 20. The grinding
appliance
comprises a first element 22 and the second element 24 which are connected to
one
another for joint rotation with respect to the axis of rotation of the spindle
so that a
complete profile groove with an intended end profile shape is formed. The
first element
22 is a first separate component and the second element 24 is a second
separate
component. The first element 22 has running round it a profile groove in the
form of a
concave surface corresponding to an end profile shape 26 intended for the
button 8A.
The profile groove thus forms a waist round the first element 22. The waist is
limited to
the cap-shaped end profile shape of the hard metal button. The first element
22 is thus
adapted to grinding the button 8A to, for example, a spherical or fully
ballistic end
profile shape. The grinding appliance also comprises a second element 24 which
is a
concentric circular flank situated at one of the planar outsides of the
grinding appliance.
The flank has running round it an outer portion with a substantially arcuate
cross-
section adapted to grinding the drilling head 28 round the button 8A. The
grinding
appliance further comprises a third separate element 29 connected for joint
rotation with
the first element and opposite to the second element. The third element 29 is
a second
concentric circular flank.
The first element is provided with, running round it, an outer layer 30 with
an abrasive
facing comprising diamonds as the abrasive medium.
The abrasive facing 31 of the second element is depicted in the same Figure 2A
in a first
embodiment illustrated on the second element 24. The second element 24 is
provided
with, running round it, an outer layer with an abrasive facing 31 comprising
diamonds
as the abrasive medium. On the second element 24, the abrasive facing is
applied on the
circular outer portion 32 with a substantially arcuate cross-section.
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Figure 2A depicts a further embodiment on the third element 29, the second
flank. The
third element 29 is a component which is homogeneously made of the second
abrasive
facing 32 so that the whole flank comprises the abrasive medium.
It should be noted that both flanks in the two embodiments illustrated in
Figure 2A may
5 have an abrasive facing of the same kind.
The hatched portions which follow the waist 30 and the flanks 31, 32 in Figure
2A
show where the diamond facing is applied on the first element 22 and the
second
element 24 respectively. The average grain size for the diamonds in the first
abrasive
facing 30 is adapted to grinding of hard metal. The average grain size for the
diamonds
10 in the second and third abrasive facings is of an average grain size
adapted to grinding
the drill bit. The diamonds are, for example, fastened in a layer which is
nickel-based or
chrome-based or a mixture of these materials or some other material with
similar
characteristics, so that the layer is softer than hard metal but nevertheless
retains its
shape and tolerates impacts.
The grinding appliance in Figure 2A is firmly clamped to a grinding facility,
not
depicted, by a screw 33 and a nut 34. They may also be joined together by, for
example,
adhesive bonding or welding or by bolts, not here depicted, or by other
similar fastening
devices.
Within the industry, diamonds are sold in, for example, dimensions stated in
US mesh
size specifications. US mesh sizes are defined by the mesh apertures of the
sieves used
for the separation of diamond grains. The sieve sizes are graded and defined
according
to the number of wires per inch of the respective sieve, e.g. 50 wires per
inch or 20
wires per inch. The diamonds are then sold in overlapping mesh sizes. The
bodies
which set out and monitor the US mesh dimension specifications are the
American
National Standards Institute (ANSI) and the Florida Emergency Preparedness
Association (FEPA). The specifications for the sizes are entirely
interchangeable. ANSI
indicates a US mesh size, whereas FEPA indicates a DIN size.
In an embodiment, the diamonds have in the first abrasive facing an average
grain size
within the range of 37-320 pm, corresponding to US mesh 400/500 ¨ 45/60. The
average grain size for the diamonds in the second abrasive facing is adapted
to grinding
of drilling steel.
In an embodiment according to the invention, the diamonds in the second
abrasive
facing have an average grain size within the range 210-500 pm, corresponding
to US
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mesh 70/80 ¨ 35/40. In another embodiment, the diamonds in the second abrasive
facing have an average grain size of 250-354 p.m, corresponding to US mesh
60/70 ¨
45/50. The average grain size for the diamonds in the second abrasive facing
is adapted
to grinding the drill bit, so it is preferable that the average grain size for
the diamonds
in the second abrasive facing be larger than the average grain size in the
first abrasive
facing.
Figure 2B depicts an exploded diagram of a through-section of the drawing in
Figure
2A. It shows the separate elements of the grinding appliance before they are
joined
together. The first element 22 is a first separate component, the second
element 24 is a
second separate component and the third element 29 is a third separate
component. The
second element 24 is a first concentric circular flank. The third element 29
is a second
concentric circular flank. The first element 22 has running round it a concave
profile
groove 26 corresponding to an end profile shape intended for the button 8A.
The second element 24 is a concentric circular flank and is adapted to being
joined
together with the first element 22, the respective end portions 22A, 24A being
adapted
in size to one another so that the continuous end profile shape 26 is formed.
Similarly,
the third element 29 is adapted to being joined together with the first
element 22, the
respective end portions 22B, 29B being adapted in size to one another so that
the
continuous end profile shape 26 is formed. The second element 24 has in this
embodiment a smaller outside diameter than the largest diameter of the first
element 22.
The third element 29 has a larger outside diameter than the largest diameter
of the first
element 22. Thus the grinding appliance is adapted to being angled during the
grinding
of a button so that the device, not depicted, fastening the grinding appliance
to the
grinding facility will be clear of the other buttons in the button drill bit.
It should be
noted that the second element 24 and the third element 29 may also be equal in
size, not
depicted.
Figure 2C depicts a side view of the abrasive wheel in Figure 2A. It shows the
second
element 24 as a concentric circular flank. The outer layer 31 with abrasive
facing
comprising diamonds is applied to the concentrically outermost portion of the
flank.
Figure 2D depicts a perspective view of the abrasive wheel in Figure 2A. The
grinding
appliance 20 comprises the first element 22, the second element 24 and the
third
element 29 connected for joint rotation with respect to the spindle's axis of
rotation A.
The first element 22 has running round it a profile groove 26 in the form of a
concave
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surface corresponding to an end profile shape intended for the button 8A. The
second
element 24 and the third element 29, the flanks, each have running round them
an outer
portion with a substantially arcuate cross-section adapted to grinding the
drilling head
round the button. The first element 22 is provided with, running round it, an
outer layer
30 with a first abrasive facing comprising diamonds adapted to grinding of
hard metal
buttons. The second element 24 and the third element 29 are provided with,
running
round them, an outer layer with a second abrasive facing 31 and a third
abrasive facing
32 comprising diamonds with an average grain size adapted to grinding a soft
material,
e.g. steel or a material with characteristics similar to steel, as the
abrasive medium.
Figure 3 depicts a further embodiment of a grinding appliance for grinding a
button 8B
of a button drill bit 6 comprising a drilling head 6B with a plurality of
buttons. In this
case the grinding appliance is an abrasive wheel 40. The grinding appliance
comprises a
first element 41 and a second element 42 adapted to being joined together for
joint
rotation with one another with respect to the spindle's axis of rotation C so
that a
complete profile groove with an intended end profile shape 43 is formed. The
first
element 41 is a first separate component and the second element 42 is a second
separate
component. The first element 41 has running round it a concave profile groove
with an
end profile shape 43 corresponding to an end profile shape intended for the
button 8B.
The first element 41 is thus adapted to grinding the button 8B to, for
example, a
spherical or fully ballistic end profile shape. The second element 42 of the
grinding
appliance is a concentric circular flank. The flank has running round it in
this
embodiment an outer concentric ring homogeneously made of the abrasive facing
adapted to grinding the drilling head, and an inner concentric ring 44 adapted
to being
fastened to the grinding facility. The outer ring has a substantially convex
cross-section
adapted to grinding the drilling head 28 round the button 8B. The flank may
also have
an outer circular shaped portion of a ring made of abrasive media and with a
substantially convex cross-section. The flank may also have an inner ring of
other than
concentric shape adapted to being fastened to the grinding facility.
The profile groove 43 on the first element 41 is provided with a first
abrasive facing 46
comprising diamonds with an average grain size adapted to grinding of hard
metal, as
the abrasive medium. The second element 42 is provided with a second abrasive
facing
48 comprising diamonds as the abrasive medium with an average grain size
adapted to
grinding a soft material, e.g. steel or a material with characteristics
similar to steel. It
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should be noted that this abrasive wheel also has an undepicted embodiment in
which
the second element 42 is homogeneously made of the abrasive medium 48
comprising
diamonds as the abrasive medium with an average grain size adapted to grinding
a soft
material, e.g. steel or a material with characteristics similar to steel.
Figure 4 depicts another embodiment of a grinding appliance for grinding a
button drill
bit 6C comprising a drilling head with a plurality of buttons 8C. In this case
the grinding
appliance is a half abrasive wheel 50. The grinding appliance comprises a
first element
52 and a second element 54 adapted to being joined together for joint rotation
with one
another with respect to the spindle's axis of rotation D so that a complete
profile groove
is formed. The first element 52 is a first separate component and the second
element 54
is a second separate component. The first element 52 has running round it a
profile
groove 53 corresponding to a half end profile shape intended for the button
8C. The
grinding appliance also comprises a second element 54 which is a concentric
flank with
a parabolic shape. By rotating the abrasive wheel about the button's geometric
axis of
symmetry B the first element 52 is thus adapted to grinding the button 8C to,
for
example, a spherical or fully ballistic end profile shape while at the same
time the
second element 54 is adapted to grinding the drilling head 6C round the button
8C. The
flank has running round it an outer convex portion with a substantially
arcuate cross-
section adapted to grinding the drilling head 28 round the button 8C.
The first element 52 is provided with an abrasive facing comprising diamonds
with an
average grain size adapted to grinding the button 8C. The second element 54 is
provided with an abrasive facing comprising diamonds with an average grain
size
adapted to grinding the drilling head 6C. The profile groove on the first
element 52 is
thus provided with a first abrasive facing 56 comprising diamonds as the
abrasive
medium with an average grain size adapted to grinding of hard metal. The
second
element 53 is thus provided with an abrasive medium which is a second abrasive
facing
58 comprising diamonds with an average grain size adapted to grinding a soft
material,
e.g. steel or a material with characteristics similar to steel. It should also
be noted that
this abrasive wheel also has a undepicted embodiment in which the second
element 54,
the flank, is homogeneously made of the abrasive medium 48 comprising diamonds
with an average grain size adapted to grinding a soft material, e.g. steel or
a material
with characteristics similar to steel.
CA 02701017 2014-10-24
29312-75
14
Figure 5 depicts a further grinding appliance, in this case a grinding cup 60,
for grinding
a button 8D of a button drill bit 6D. The first element 62 is a grinding cup
filled with an
abrasive facing comprising diamonds as the abrasive medium. The second element
64 is
an outer portion applied round part of the grinding cup 60. The profile groove
on the
first element 62 is filled with an abrasive medium with a first abrasive
facing 66
comprising diamonds with an average grain size adapted to grinding of hard
metal. The
second element 64 is provided with a second abrasive facing 68 comprising
diamonds
as the abrasive medium with an average grain size adapted to grinding a soft
material,
e.g. steel or a material with characteristics similar to steel. The second
abrasive facing
may also comprise boron nitride, silicon carbide, aluminium oxide, titanium
carbide and
titanium nitride, or similar material. The grinding cup 60 or the button 8D is
rotated
during grinding or both the grinding cup and the button are rotated.
Figure 6 depicts a detail of an abrasive facing 70 intended for a grinding
appliance as
described above. The abrasive facing 70 comprises an abrasive medium with a
single
layer of diamonds 72A, 72B, 72C, 72D , 72E, 72F fastened in a layer which is
nickel-
based or chrome-based or a mixture of these or some other material with
similar
characteristics, such that the layer is softer than hard metal but
nevertheless retains its
shape and tolerates impacts. The diamonds in this abrasive facing have a
protrusion,
which means that one portion of each diamond is fastened in the layer and the
other
portion protrudes. This abrasive facing is applied preferably on the first
element for
grinding the hard metal of the button. This abrasive facing may also be
applied on the
second and third elements for grinding the layer of a soft material, e.g.
steel or a
material with characteristics similar to steel.
Figure 7 depicts a further detail of an abrasive facing 80 intended for a
grinding
appliance as described above. The abrasive facing 80 comprises an abrasive
medium
with diamonds 82A, 82B, 82C, 82D, 82E, 82F, fastened in this case in a nickel-
based
layer. Some other material with similar characteristics may also be used. The
diamonds
in this abrasive facing comprise matrix diamonds. The matrix diamonds are
situated in
two or more layers in the abrasive facing so that a layer of diamonds may be
ground
away and uncover a new layer of diamonds. This abrasive facing is applied
preferably
on the second and third elements for grinding the drilling head made of, for
example,
steel.
CA 02701017 2010-03-26
WO 2009/045142
PCT/SE2008/000538
Figure 8 depicts a method for manufacturing a grinding appliance 90 for
grinding of
button drill bits which comprise a drilling head with a plurality of buttons.
The method
comprises:
a) providing a first element of the grinding appliance with an abrasive facing
5 comprising diamonds as the abrasive medium of a first average grain size
adapted to
grinding a button to an intended profile shape (92),
b) providing at least one section of a second element of the grinding
appliance with an
abrasive facing comprising diamonds as the abrasive medium of a second average
grain
size adapted to grinding a drilling head (94),
10 c) joining the first element and the second element together for joint
rotation so that a
complete profile groove is formed (96).
The invention is not limited to the embodiment examples referred to but one
skilled in
the art can of course modify it in a plurality of ways within the scope of the
invention
15 defined by the claims.
