Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02312100 2000-06-22
v
s
GRINDING CUP FOR DRILL BITS
Background to the Invention
This invention relates to grinding cups used to refurbish or reprofile drill
bits.
In particular, the grinding cup is for use in association with hammer bits
which are
typically tungsten-carbide bits driven by a rotary tool powered by pneumatic
or
hydraulic means, intended for drilling rock.
It is commonly known to use non-circular, solid drive shafts which fit into
tools with corresponding non-circular openings in order to create rotary
motion for
the operation of various tools and bits. Typically, in the field of grinding
cups used
to refurbish hammer bits, a steel drive shaft contacts a steel, or steel-
diamond matrix,
grinding cup in order to transmit motion from the drive shaft to the grinding
cup.
Grinding cups have a leading surface which is recessed and profiled to match
the ideal profile of the multiple tungsten-carbide buttons located on the face
of a drill
bit. Such buttons may be hemispherical, parabolic or conical (bullet-shaped)
in
profile. When a rotating grinding cup is placed over such buttons, the
grinding action
generated by the grinding cup reprofiles the buttons from a somewhat flattened
or
distorted shape to a more ideal, rounded shape.
Problems can arise during reprofiling of drill bits as a result of this direct
contact between two hard surfaces, namely the drive shaft and the grinding cup
to
which the drive shaft imparts rotary motion. In order to make the grinding cup
fit
easily onto a drive shaft, some clearance must be left between the drive shaft
and the
grinding cup. In operation, vibration between the two parts results. This can
create
r
CA 02312100 2000-06-22
-2-
discomfort or potential injury to the worker holding the pneumatically or
hydraulically driven tool. Moreover, the vibration may damage the surfaces of
both
the drive shaft and the grinding cup. Since this vibration and hard contact
tends to
generate heat, and cause the metal parts to expand to some degree, the parts
may lock
when heated unless sufficient clearance is provided. As discussed above,
however,
the more the clearance, the greater the vibration problem. In some cases, the
profile
of the drive shaft or of the grinding cup in contact therewith can be
distorted and/or
stripped as a result of the clearance and vibration problem.
In addition, when pressure is applied by the operator in the direction of the
drill bit being reprofiled, the stress on the forward edge, or crown, of the
grinding cup
can be significant. On occasion, the crown of a grinding cup can chip around
its
periphery. Moreover, when the forward end of the grinding cup contacts the
surface
of a drill bit, the escape of steel shavings created by the cutting action of
the grinding
cup, and of the coolant fluid typically used to facilitate the cutting action
and keep
the grinding cup and work piece cool during operation, can be impeded.
Typically, as set out above, one or more passageways is provided from the
grinding tool through the grinding cup for flow of cutting fluid to the drill
bit face to
assist in the grinding operation. In some prior grinding cups, the opening to
allow
escape of this coolant fluid from the grinding cup to the working surface is
centrally
disposed in the front end of the grinding cup. When a circular opening is
located
centrally in the grinding cup, the grinding cup may create an undesired bump
or
nipple on the leading surface of the drill bit button being ground.
CA 02312100 2000-06-22
-3-
Summary of the Invention
Accordingly, it would be an advantage to provide a grinding cup with means for
reducing the vibration between the grinding cup and the drive shaft of the
grinding
tool. In addition, it would be an advantage to provide means for strengthening
the
periphery of the forward crown end of the grinding cup to prevent peripheral
chipping. In addition, it would be an advantage to provide means to permit
steel
shavings and coolant to escape from the forward end of the grinding cup more
easily
and to permit a wider cut of steel around the button of the drill bit being
profiled.
Moreover, it would be an advantage to provide a grinding cup which is
conformed so as to prevent the formation of bumps or nipples on the leading
end of
the drill bit buttons being ground.
The instant invention overcomes these problems in the prior art.
In a major aspect of the invention, a grinding cup for detachable connection
to a drive shaft of a grinding machine for grinding buttons on drill bits
comprises top
and bottom surfaces, and a lower grinding section having a centrally disposed
recess
formed in the bottom surface of the grinding cup, and having the desired
profile for
the button to be ground, wherein the periphery of the lower grinding section
comprises a series of reinforcing ribs extending longitudinally towards the
bottom
surface thereof, and wherein the peripheral edge of the bottom surface is
bevelled to
facilitate during grinding the removal of cutting fluid and steel from the
face of the
bit around the button, through the spaces between the ribs, said grinding cup
further
comprising an upper body section having a centrally disposed cavity formed in
the
CA 02312100 2000-06-22
-4-
top surface of the grinding cup, said cavity being shaped and sized to permit
the drive
shaft of the grinding machine to fit snugly within the cavity without
retaining means.
In further aspects of the invention, the cavity further comprises a non-metal
liner adapted to receive the drive shaft and to absorb vibrations generated
between
the drive shaft and the grinding cup during grinding operations.
In further aspects of the invention:
(a) The non-metal liner comprises artificial rubber, a thermoplastic
material, or a carbon-based composite material;
(b) A single passageway connects the top and bottom surfaces of the
grinding cup to permit a coolant to be provided to the surface of the
button during grinding;
(c) The centrally disposed recess in the bottom surface of the grinding
cup comprises multiple slots radiating from the centre of the surface,
but not joining at said centre;
(d) The multiple slots comprise three slots each disposed at an angle of
60° to the adjacent slots;
(e) The grinding cup comprises a material capable of grinding tungsten-
carbide button bits;
CA 02312100 2000-06-22
-$-
(f) The grinding cup comprises a steel and diamond matrix.
Further aspects of the invention will become apparent from the following
description of an illustrative embodiment of the invention.
$
Brief Description of the Drawings
An illustrative embodiment of the invention is shown in the following
drawings in which:
Figure 1 A is a perspective view of the grinding cup illustrating the cavity
in the upper
end of the cup;
Figure 1 B is a plan, elevation view of the grinding cup of the invention;
Figure 1 C is a perspective view of the grinding cup illustrating the recess
in the lower
1$ end of the cup;
Figure 2A is a plan, cross-sectional, elevation view of a first embodiment of
the
grinding cup illustrating the vibration damping liner;
Figure 2B is a plan, cross-sectional, elevation view of a first embodiment of
the
vibration damping liner;
Figure 2C is a lower, end view of the grinding cup illustrating a first
embodiment of
the vibration damping liner;
Figure 3A is a plan, cross-sectional, elevation view of a second embodiment of
the
grinding cup illustrating the vibration damping liner;
Figure 3B is a plan, cross-sectional, elevation view of a second embodiment of
the
vibration damping liner;
CA 02312100 2000-06-22
-6-
Figure 3C is a lower, end view of the grinding cup illustrating a second
embodiment
of the vibration damping liner;
Figure 4A is a plan, cross-sectional, elevation view of a third embodiment of
the
grinding cup illustrating the vibration damping liner;
Figure 4B is a plan, cross-sectional, elevation view of a third embodiment of
the
vibration damping liner;
Figure 4C is a lower, end view of the grinding cup illustrating a third
embodiment
of the vibration damping liner;
Figure SA is a plan, cross-sectional, elevation view of a fourth embodiment of
the
grinding cup illustrating the vibration damping liner;
Figure SB is a plan, cross-sectional, elevation view of a fourth embodiment of
the
vibration damping liner;
Figure SC is a lower, end view of the grinding cup illustrating a fourth
embodiment
of the vibration damping liner;
Figure 6 is an upper, end view of the grinding cup illustrating the ribs and
slots.
Detailed Description of the Invention
Refernng to Figures 1 A, 1 B and 1 C, a grinding cup 1 having an upper end 3
and a lower end 5 comprises a hard material. Typically, the grinding cup, or
at least
the grinding portion thereof, comprises steel or a steel - diamond matrix.
Running
longitudinally and located adjacent the lower end 5 of the grinding cup, are a
series
of ribs 7 lying around the perimeter of lower end S. The leading edge 9 of the
lower
end 5 is bevelled towards said perimeter and the upper end 3 of the grinding
cup 1
to assist in removal of cutting fluid and cuttings from the drill bit button
being
reprofiled. The ribs 7 extend substantially to the leading edge of lower end
5. These
CA 02312100 2000-06-22
_7_
ribs provide reinforcement to the leading edge of lower end 5 and prevent
chipping
of the grinding cup in this area. The spaces between the ribs 7 also provide
areas
where cutting fluid and cuttings may more easily pass. Moreover, the ribs
widen the
cutting area around each drill bit button, thus clearing away burrs which can
develop
at the base of such buttons using conventional grinding cups. This leads to
cleaner
button profiles.
Refernng to Figure 6, the leading lower end 5 of grinding cup 1 is illustrated
in end view. Ribs 7 are spaced evenly around the perimeter of the crown 11 and
extend at least to the leading end of bevelled surface 9. A series of slots 13
radiating
from the centre of the grinding cup 1, but not joining at the centre, provide
grinding
and cutting action as the grinding cup rotates about the button being
reproflled.
Cutting fluid flows through these slots to assist in keeping the work piece
cool.
Since the slots do not join at the centre, and thus there is no opening at the
centre of
the grinding cup, no bump or nipple is formed at the centre of the button.
Refernng to Figure 2A, the grinding cup 1 typically comprises steel. The
crown 11 maybe comprised of steel or a steel diamond matrix. A recessed
opening
in the lower end of the grinding cup provides a grinding surface 15 which is
profiled
to conform to the shape and size of the drill bit button being reprofiled. The
recess
may be concave, parabolic or conical (bullet-shaped) depending on the shape of
the
drill bit buttons to be reprofiled.
A channel 17 running along the longitudinal axis of the grinding cup conducts
drilling fluid or coolant from a coolant source (not shown) to the button
being
reprofiled. Such coolant supplies are well-known in the art.
CA 02312100 2000-06-22
-$_
At the upper end 3 of the grinding cup is an opening or cavity 19 profiled
slightly larger than the corresponding profile of the drive shaft 20 of the
rotary tool
to be inserted into the grinding cup in order to impart rotary motion to the
grinding
cup. Only that portion of the drive shaft which fits into the cavity is
illustrated.
S
Figure 2B illustrates a non-metal liner 21 adapted to be snug-fit and,
optionally, fixed with some adhesive or vulcanized, into cavity 19 located in
the
upper end of grinding cup 1. The exterior wall 23 of said liner contacts the
surfaces
of the grinding cup 1 adjacent the upper end 3 which define the cavity 19. The
inner
surface 25 of the liner is sized and profiled to fit snugly around the drive
shaft 20 of
the grinding tool. These features are also illustrated in Figure 2C, an end
view of the
upper end of the grinding cup.
Three alternative embodiments of the grinding cup with different non-metal
liners are illustrated respectively in Figures 3A, 3B and 3C, Figures 4A, 4B
and 4C,
and Figures SA, SB and SC. The liner may extend only partially into the cavity
as
illustrated in Figures 3A, 3B, 4A and 4B. It may extend the full length of the
cavity
as illustrated in Figures 2A, 2B, SA and SB. In Figures SA and SB, the liner
extends
beyond the longitudinal internal walls of cavity 19, but does not block
channel 17;
thus, cooling fluid can flow in all cases.
When the drive shaft is placed into contact with the liner 21, vibrations
which
occur when a hard metal drive shaft contacts a hard metal grinding cup are
dramatically reduced. The liner may be comprised of artificial rubber,
thermoplastic
materials, or carbon based composite materials. These materials tend to
provide
significant durability while absorbing vibrations from the grinding tool. In
this way,
CA 02312100 2000-06-22
-9-
damage to the grinding cup and potential stripping of the profile of cavity 19
at the
upper end of the grinding cup where the grinding cup contacts the drive shaft,
or of
the drive shaft itself, can be prevented.
Apart from preventing stripping of the grinding cup or the drive shaft, the
vibration-damping liner provides quieter running and may contribute to fewer
work-
related injuries caused by vibration of the grinding tool.
Although an illustrative embodiment of the invention has been described,
modifications of the structure will be apparent to those skilled in the art
without
departing from the spirit and scope of the invention.
