U.S. patent application number 09/837345 was filed with the patent office on 2002-01-03 for method for the manufacturing of a cone cutter for rotary drilling by crushing, a rotary cone drill bit, a cone cutter and crushing elements therefor.
Invention is credited to Claesson, Bjorn, Karlsson, Lennart, Linden, Johan, Lundell, Lars-Gunnar.
Application Number | 20020000336 09/837345 |
Document ID | / |
Family ID | 20279502 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000336 |
Kind Code |
A1 |
Claesson, Bjorn ; et
al. |
January 3, 2002 |
Method for the manufacturing of a cone cutter for rotary drilling
by crushing, a rotary cone drill bit, a cone cutter and crushing
elements therefor
Abstract
A rotary cone drill bit includes at least one leg carrying a
journal provided with bearing surfaces cooperating via bearing
elements with bearing races in a rotatable cone cutter. The cone
cutter is provided with rows of crushing elements. Each crushing
element has a greatest width (D) and a greatest height (H), wherein
HID<1.2. The crushing elements are welded to the body of the
cone cutter to form a metallurgical bond therewith.
Inventors: |
Claesson, Bjorn; (Ronnlnge,
SE) ; Karlsson, Lennart; (Sandviken, SE) ;
Linden, Johan; (Gavle, SE) ; Lundell,
Lars-Gunnar; (Sandviken, SE) |
Correspondence
Address: |
Ronald L. Grudziecki, Esq.
BURNS, DOANE & SWECKER, MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
20279502 |
Appl. No.: |
09/837345 |
Filed: |
April 19, 2001 |
Current U.S.
Class: |
175/426 ;
175/375; 175/435; 76/108.2 |
Current CPC
Class: |
B23K 9/0035 20130101;
E21B 10/22 20130101; E21B 10/52 20130101 |
Class at
Publication: |
175/426 ;
175/435; 175/375; 76/108.2 |
International
Class: |
E21B 010/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 3, 2000 |
SE |
0001598-2 |
Claims
What is claimed is:
1. A rotary cutting head for cutting rock by crushing, comprising:
a support; a cone cutter rotatably mounted by bearings on the
support; rows of welded-on crushing elements adhered to a base body
of the cone cutter by a metallurgical bond, each crushing element
comprising a body having a working portion, an opposing mounting
portion, and an intermediate portion from which the working and
mounting portions extend, each crushing element having a greatest
width D at the intermediate portion, and a greatest height H
extending from a tip of the working portion to a transition between
the intermediate portion and the mounting portion, wherein
HID<1.2.
2. The cutting head according to claim 1 wherein the cutting head
comprises a drill bit having a plurality of the supports, the
supports comprising legs.
3. A crushing element adapted for use on a rotary cone cutter, the
crushing element comprising a cemented carbide body having a top
working portion, an opposing bottom mounting portion of generally
conical shape, and an intermediate portion from which the mounting
portion extends, the crushing element having a greatest width D at
the intermediate portion, and a greatest height H extending from a
tip of the mounting portion to a transition between the
intermediate portion and the mounting portion, wherein
H/D<1.2.
4. The crushing element according to claim 3 wherein the mounting
portion includes a spigot extending downwardly from a center of a
bottom of a conical section of the mounting portion, the spigot
extending symmetrically about a central axis of the crushing
element.
5. The crushing element according to claim 3 wherein the mounting
portion forms an internal cone angle from 150.degree. to less than
180.degree..
6. The crushing element according to claim 3 wherein the
intermediate portion has a height no greater than 15 mm.
7. A rotary cone cutter adapted to be rotatably mounted on a rotary
cutting head, the cone cutter comprising a base body, and rows of
welded-on crushing elements adhered to the base body by
metallurgical bonds, each crushing element comprising a body having
a working portion, an opposing mounting portion, and an
intermediate portion from which the working mounting portions
extend, each crushing element having a greatest width D at the
intermediate portion, and a greatest height H extending from a tip
of the working portion to a transition between the intermediate
portion and the mounting portion, wherein H/D<1.2.
8. A method of manufacturing a rotary rock-crushing cone cutter
comprising the steps of: A) providing a base body, and a plurality
of crushing elements, each crushing element comprising a body
having a working portion, an opposing mounting portion, and an
intermediate portion from which the working and mounting portions
extend, each crushing element having a greatest width D at the
intermediate portion, and a greatest height H extending from a tip
of the working portion to a transition between the intermediate
portion and the mounting portion, wherein H/D<1.2; B) connecting
the base body to one pole of an electric circuit, and connecting
one of the crushing elements to another pole of the circuit; C)
bringing a surface of the mounting portion of the crushing element
toward a supporting surface of the base body and energizing the
circuit to create an electric arc between the mounting portion and
the supporting surface; D) maintaining the arc sufficiently to melt
both the surface of the mounting portion and the supporting
surface; E) pressing the melted surfaces together; F) permitting
the pressed-together melted surfaces to solidify; and G) repeating
steps B-F for the remaining crushing elements.
9. The method according to claim 8 wherein the electric circuit is
energized by a capacitor pack in step C, the mounting portion
including a spigot projecting downwardly from a center of a bottom
of a conical segment of the mounting portion, step C comprising
bringing the spigot into contact with the supporting surface to
short-circuit the capacitor pack.
10. The method according to claim 8 wherein step C comprises
contacting the mounting portion with the supporting surface and
then energizing the circuit while simultaneously lifting the
mounting portion off the supporting surface to form the electric
arc.
Description
BACKGROUND OF THE INVENTION
[0001] This application is based on and claims priority under 35
U.S.C. .sctn.119 of Swedish Patent Application No. 0001598-2, filed
May 3, 2000, the disclosure of which is incorporated by reference
herein.
[0002] The present invention relates to a method for the
manufacturing of a cone cutter for rotary drilling by crushing, a
rotary cone drill bit, a cone cutter and a crushing element.
PRIOR ART
[0003] A rotary cone drill bit is intended to drill earth by
crushing rock material. This is achieved by generating an axial
feed force and rotation force via drilling machine and transferring
those forces via tubes to the end where the drill bit is secured.
The crushing itself is achieved by crushing elements such as
buttons or chisels of cemented carbide, which are positioned in
annular external rows on the cone cutter body. The buttons are
submitted to high strains during drilling. Today the buttons or the
chisels are secured by being pressed into drilled holes. The
buttons are held by friction to the bore wall in the drilled holes.
The bore wall in the cone cutter body receives the bending moment
applied to a button. These parameters require relatively deep holes
in the cone cutter body, that is holes in the magnitude of 5-20 mm,
depending of the dimensions of the cemented carbide and therefore
the geometry of the cone cutter body must be oversized. Since the
volume of the cone cutter body is limited, also the number of
buttons and their possible positions become limited. Thereby the
options for dimensioning of the bearings in the drill bit become
limited. In addition, only a smaller part of the cemented carbide
of the button is used for drilling.
OBJECTS OF THE INVENTION
[0004] One object of the present invention is to provide a method
for the manufacturing of a cone cutter for rotary drilling by
crushing and a rotary cone drill bit and a crushing element, which
counteract the above-captioned drawbacks.
[0005] Another object of the present invention is to provide a
rotary cone drill bit and a cone cutter, which allow great
opportunities regarding cavities in the cone cutter body.
[0006] Another object of the present invention is to provide a
rotary cone drill bit, which allows more durable bearings in the
cone cutter body.
[0007] Still another object of the present invention is to provide
a crushing element, which enables a simple mounting to the cone
cutter body.
[0008] Still another object of the present invention is to provide
a method for the manufacturing of a cone cutter for rotary drilling
by crushing, which is fast and efficient.
SUMMARY OF THE INVENTION
[0009] One aspect of the present invention involves a rotary
cutting head for cutting rock by crushing. The cutting head
comprises a support, and a cone cutter rotatably mounted by
bearings on the support. Rows of welded-on crushing elements are
adhered to a base body of the cone cutter by a metallurgical bond.
Each crushing element comprises a body having a working portion, an
opposing mounting portion, and an intermediate portion from which
the working and mounting portions extend. Each crushing element has
a greatest width D at the intermediate portion, and a greatest
height H extending from a tip of the working portion to a
transition between the intermediate portion and the mounting
portion, wherein H/D<1.2.
[0010] Other aspects of the invention relate to the cone cutter per
se and the crushing elements per se.
[0011] Another aspect of the invention relates to a method of
manufacturing a rotary rock-crushing cone cutter which comprises
the steps of:
[0012] A) providing a base body and a plurality of crushing
elements, each crushing element comprising a body having a working
portion, an opposing mounting portion, and an intermediate portion
from which the working and mounting portions extend, each crushing
element having a greatest width D at the intermediate portion, and
a greatest height H extending from a tip of the working portion to
a transition between the intermediate portion and the mounting
portion, wherein H/D is less than 1.2;
[0013] B) connecting the base body to one pole of an electric
circuit, and connecting one of the crushing elements to another
pole of the circuit;
[0014] C) bringing a surface of the mounting portion of the
crushing element toward a supporting surface of the base body and
energizing the circuit to create an electric arc between the
mounting portion and the supporting surface;
[0015] D) maintaining the arc sufficiently to melt both the surface
of the mounting portion and the supporting surface;
[0016] E) pressing the melted surfaces together;
[0017] F) permitting the pressed-together melted surfaces to
solidify; and
[0018] G) repeating steps B-F for the remaining cutting
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The objects and advantages of the invention will become
apparent from the following detailed description of preferred
embodiments thereof in connection with the accompanying drawings,
in which like numerals designate like elements, and in which:
[0020] FIG. 1A shows a part of a cutting head in the form of a
rotary cone drill bit according to the present invention in a
cross-section;
[0021] FIGS. 1B and 1C show magnifications of two respective areas
of FIG. 1A having crushing means according to the present
invention;
[0022] FIG. 2A shows an alternative embodiment of a toothed drill
bit according to the present invention in a cross-section in a
perspective view;
[0023] FIG. 2B shows a magnified tooth according to the present
invention of the rotary cone drill bit in FIG. 2A;
[0024] FIG. 3A shows a first stage of a process for attaching a
cutting element to a supporting surface wherein the cutting element
is being brought toward the cutting surface;
[0025] FIG. 3B shows the cutting element making contact with the
supporting surface to close an electric circuit passing through the
cutting element and the supporting surface;
[0026] FIG. 3C shows an electric arc generated between the cutting
element and the supporting surface;
[0027] FIG. 3D shows the electric arc spreading;
[0028] FIG. 3E shows the electric arc melting a surface of the
cutting element and the supporting surface;
[0029] FIG. 3F shows the melted surfaces being pressed
together;
[0030] FIG. 3G shows a metallurgical bond formed between the
pressed-together surfaces after those surfaces have hardened;
[0031] FIG. 4 shows a button according to the present invention in
a side view;
[0032] FIG. 5A shows a first stage of another welding process for
attaching a cutting element to a supporting surface according to
the present invention wherein the cutting element is in contact
with the supporting surface prior to closing an electric circuit
passing through the cutting element and the supporting surface;
[0033] FIG. 5B depicts the cutting element being lifted away from
the supporting surface simultaneously with the creation of an
electric circuit, whereby an electric arc is formed;
[0034] FIG. 5C shows the electric arc spreading;
[0035] FIG. 5D shows the electric arc melting the surface of the
cutting element and the supporting surface;
[0036] FIG. 5E shows the melted surfaces being pressed
together;
[0037] FIG. 5F shows a metallurgical bond formed between the
cutting element and the supporting surface after the melted
surfaces have been allowed to solidify;
[0038] FIG. 6 shows a second preferred embodiment of a cutting
element according to the present invention;
[0039] FIG. 7 shows a third embodiment of a cutting element
according to the present invention;
[0040] FIG. 8 shows a fourth embodiment of a button according to
the present invention;
[0041] FIG. 9 shows a fifth embodiment of a button according to the
present invention; and
[0042] FIG. 10 shows a sixth embodiment of a button according to
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0043] With reference to FIG. 1A, a rock drill bit 1 according to
the present invention is shown, the bit designed for the rotary
crushing drilling of rock, i.e., a so called rotary cone drill bit.
The cutting head in such a device is in the form of a drill bit
which comprises three supports in the form of legs 10. One leg 10
is shown in section in FIG. 1A, on which journals 11 are provided.
A roller or cone cutter 12 equipped with crushing elements in the
form of buttons 14, is rotatably mounted on each journal by means
of roller bearings 29, a system of ball bearings 15, a radial
bearing 16 and an axial bearing 17. The buttons can alternatively
be replaced by other crushing elements, such as chisels or teeth
14' (FIG. 2A) integrated with the base body 12A' of the cone
cutter. The legs 10 are evenly distributed about the periphery of
the bit with 120.degree. partition. The journal 11 is provided with
a channel 18 for introducing the ball bearings 15, in which a plug
19 is received in order to retain the ball bearings 15. The
cylindrical roller bearing 29 receives a major part of the
reactional force from the rock while the major object of the ball
bearings 15 is to retain the cone cutter 12 on the journal 11. The
cone cutter has a shoulder 20 to abut against a collar 21 on the
journal for receiving axial forces, which are not received by a
support disc cooperating with the axial end surface of the journal.
The bit is provided with flushing channels 34 for flush medium,
such as pressurized air with an addition of water for cooling and
cleaning of the bearing system. The above-mentioned internal
bearings can be sealed and lubricated by a lubricant system
integrated with the bit. The cone cutter has intermediate grooves
between the external rows of buttons to accommodate buttons of
other cone cutters in the drill bit.
[0044] Each button has a working end and the shape of the button
end may vary considerably. It can thus be semi-spherical, conical,
ballistic, semi-ballistic or chisel shaped.
[0045] The buttons are made from wear resistant cemented carbide,
such as wolfram carbide and cobalt pressed together whereafter the
formed body is sintered. Since cemented carbide is an expensive
material the cost of the drill bit would sink if the cemented
carbide portion that normally is pressed downwards into the hole in
the steel body could be eliminated. The cost for manufacturing
should also be lower if hole drilling did not have to be performed.
In the present invention the cemented carbide is directly secured
to the steel body 12A by welding. Welding means that the surfaces
are heated and are pressed together such that a so-called
metallurgical bond with high strength is obtained between the two
materials.
[0046] A problem involving welding of cemented carbide results from
the high carbon content thereof. The carbon content in the steel
closest to the joint will increase at melting, with the risk of
brittleness. To limit this risk, a short welding time is chosen,
which puts special demands on the choice of welding method.
[0047] A suitable method where specifically short welding time is
characteristic is the capacitor charge spot welding, which is
illustrated in FIGS. 3A-3G. The method involves connecting the
button 14A and the body 12A of the cone cutter to a circuit in
which a capacitor pack, not shown, is discharged. A specially
formed integral spigot 22 on the button makes the electric current
very high locally and an electric arc 43 arises. This electric arc
vaporizes the spigot and melts the adjacent surfaces. The button is
pressed or pushed against a smooth supporting surface 13 of the
base body 12A of the cone cutter wherein the melt solidifies and a
metallurgical or chemical bond arises. The course of welding is
very fast, in the magnitude of 1-5 milliseconds (ms), and its
stages are successively shown in FIGS. 3A-3G. Welding can also be
made without a gap, i.e. without step A in the figure, and then the
welding time becomes somewhat longer but no longer than 1 second.
The stages of the method according to the present invention with
reference to FIGS. 3A-3G comprise:
[0048] A) The capacitor pack is charged and the button 14A is
accelerated towards the smooth surface 13 of the body 12A of the
cone cutter. By the expression "smooth surface" is here meant a
substantially planar surface which also can be slightly convex as
in FIG. 1A or concave, i.e., the surface is not machined into a
recess of the substantially reverse shape of the lower side of the
crushing element.
[0049] B) The spigot 22 engages the surface 13 and will short out
the capacitor pack.
[0050] C) The spigot 22 is vaporized by an electric arc 43 formed
between the button and the body of the cone cutter.
[0051] D) The electric arc spreads.
[0052] E) The electric arc melts the surface layers of both the
button and the body 12A.
[0053] F) The button is pressed downwards into the body of the cone
cutter and welds the material together.
[0054] G) The melt layers immediately solidify in an essentially
conical weld joint 41 and the welding is finished.
[0055] In FIGS. 1B and 1C it is illustrated that the solidified
material, mostly steel, forms an upset 40 about each button. The
thickness of the weld joint lies within the interval of 1-300
micrometer (.mu.m). FIG. 1C shows welded protective buttons 30 of
cemented carbide, which are applied to maintain the diameter of the
drill bit constant for a longer period and to protect the steel leg
from wear in exposed areas.
[0056] The button 14A, which has been adapted to the method
according to the present invention, is shown in FIG. 4. The button
of cemented carbide has an intermediate portion in the shape of a
substantially cylindrical shank portion 23, and a semi-spherical
working portion 24 extending downwardly therefrom. The button has a
center axis CL. The end surface defines a radius R, the center of
which lies in a plane P. The shank portion 23 has a greatest width
in the form of a greatest diameter D. The spigot 22 extends
symmetrically about the central axis CL from a lower side 25A of
the button. The lower side 25A extends from the intermediate
portion 23 and forms a mounting portion. That mounting portion is
substantially conical in shape with an internal cone angle, which
is from 150.degree. to less than 180.degree., preferably about
174.degree.. The spigot has a diameter D about 0.75 mm at the
intermediate portion. The shank portion 23 has a height h1 from the
plane P to a transition 26 between the intermediate portion and the
lower side 25A, the height h1 being from 0.2 to 2.8 mm. The spigot
22 and the lower side 25A have a height h2 of about 1.2 mm measured
from the transition 26. The height H of the button constitutes the
part of the button which is intended to protrude from the
supporting surface, and the height H is defined as extending from
the transition 26 to the peak or tip of the working portion.
Suitable values regarding button dimensions for buttons according
to the present invention with the most common button diameters for
rotary cone drill bits has been listed in the table below. When
applicable, the dimensional units are millimetres.
1 Diameter Protrusion Ratio (D) (H) (H/D) 7 3.3 0.47 7 4.9 0.7 10
3.5 0.35 10 7 0.7 12 3.7 0.31 12 8 0.67 14 4.3 0.31 14 11 0.79 16
5.1 0.32 16 14 0.88 19 8 0.42 19 15.5 0.82 21 8 0.38 21 19 0.9 max
19 0.9 mm 3.3 0.3
[0057] The H/D ratio is from about 0.3 to 0.9 as is evident from
the table, but is definitively smaller than 1.2, i.e. H/D<1.2,
preferably H/D<0.9. If the entire length H+h2 of the button is
compared to the length of a conventional button it will show that
the length of the button according to the present invention is
about 30%-50% of the length of the conventional button.
[0058] Welding may alternatively be made through resistance
welding, which is illustrated in FIGS. 5A-5G. This may be of
conventional type, where heat is generated by means of electrical
current, which is led through two surfaces under pressure.
Especially suitable are two procedures, which resemble capacitor
charge spot welding, namely the so-called SC (Short Cycle) and ARC
methods. The difference compared to capacitor charge spot welding
is that a transformer current source is used and the button has a
wholly conical side instead of a spigot. The button is in contact
with the body of the cone cutter from the start but is lifted up a
short distance simultaneously as the current is turned on. Thereby
an electric arc is formed which melts the surfaces in the manner
described above. Finally the button is pushed downwards into the
body of the cone cutter and the weld is formed. The welding time,
which is somewhat longer than for capacitor charge spot welding, is
controlled through regulation of the time between the ignition of
the electric arc and the instant when the button is pushed
downwards. The SC method is illustrated in FIGS. 5A-5F and
comprises:
[0059] A) The button is initially in contact with the body of the
cone cutter.
[0060] B) Simultaneously as the current is turned on, the button is
lifted from the body of the cone cutter whereby an electric arc 43
is formed.
[0061] C) The electric arc 43 spreads between the button and the
body of the cone cutter.
[0062] D) The electric arc melts the surface layer of both
materials.
[0063] E) The button is pressed downwards into the body of the cone
cutter and welds the materials.
[0064] F) The melt layers immediately solidify and the weld joint
41 is finished. The welding time for the SC method seldom exceeds
20 ms.
[0065] The button 14B that has been adapted to the alternative
welding method according to the present invention (FIGS. 5A-5F) is
shown in FIG. 6. The difference between the button 14B and the
above-described button 14A is that the button 14B does not have a
spigot and therefore the lower side 25B consists of a wholly
conical surface with an inner cone angle about 166.degree.. An
important common feature for both buttons 14A, 14B is that they
have a lower side 50 whose smallest diameter is smaller than the
diameter D of the button, i.e. a substantially conical weld joint
41 is obtained, which compensates for the fact that more melting of
the steel normally arises at the mid section of the button. This
button includes working, intermediate, and mounting portions 24B,
23B, and 25B.
[0066] The ARC method is used for greater dimensions and functions
in the same manner as the SC method. Since longer welding times are
used, the weld in this case is protected by means of a ceramic ring
or gas. The welding time depends on the diameter, for example
200-400 ms for a button with a diameter of 10 mm, but seldom or
never exceeds 1 second.
[0067] The cemented carbide can be covered with a layer of nickel
or cobalt before welding such to increase strength of the
joint.
[0068] Example 1: Cemented carbide buttons with a diameter of 7 mm
were welded by means of capacitor charge spot welding to a steel
body in a tempered steel of the TYPE SAE 4142 (SS2244). The
cemented carbide buttons were shaped according to FIG. 4. At the
initiation of electrical welding current, the buttons were raised
by a lifting height of 1 mm. The voltage was 160 V, and pressure
was50 N and the welding time was 3 ms. Through subsequent
metallographical investigation, it was authenticated that a
metallurgical bond was obtained between the steel body and the
cemented carbide buttons.
[0069] Example 2: Cemented carbide buttons with a diameter of 7 mm
were welded by means of the SC method to a steel body in a tempered
steel of the TYPE SAE 4142 (SS2244). The cemented carbide buttons
were shaped according to FIG. 6. At the initiation of welding
current a lifting height of 1 mm was used, the amperage was 550 V
and the welding time was 20 ms. Through metallographical
investigation it was authenticated that a metallurgical bond was
obtained between the steel body and the cemented carbide.
[0070] An additional advantage with the methods according to the
present invention is that buttons can be positioned closer to each
other on the rotary cone drill bit since no button holes need to be
pre-formed, and of course there is no risk for cracks to occur
between pre-drilled holes since there are none. The short welding
time enables welding also of diamond coated buttons. Each button
14A, 14B according to the present invention, which is to be welded,
is shorter than a corresponding conventional button, and therefor
expensive cemented carbide is saved. In addition, there is no need
for preparation of the weld joint on the body 12A of the cone
cutter 12. The button 14A, 14B is not intended to be rotated during
welding (i.e., no friction welding is used) and can therefore
alternatively be asymmetrically shaped and thus needs no driving
surfaces. In the asymmetric case in the formula in the claims "D"
depicts the greatest width of the asymmetrical button. The height
h1 of the shank of the button may be 0 to 15 mm, i.e. its working
surface 24 may connect for example directly to the lower side 25A,
25B.
[0071] FIG. 7 shows a button 14C according to the present
invention, with a ballistic basic form, which is somewhat more
aggressive than the previously described buttons. FIG. 8 shows a
button 14D according to the present invention, with a conical basic
form, which is still more aggressive than the previously described
buttons. FIG. 9 shows a button 14E according to the present
invention such as mentioned above, with an asymmetrical,
essentially conical basic form. Such as evident from FIG. 10 the
button 14F according to the present invention is formed with a
shoulder and an intermediate concave portion. The shoulder protects
the surrounding steel in the body 12A of the cone cutter 12 from
wear and gives greater welded surface. Each of the buttons of FIGS.
7-10 includes working, intermediate, and mounting portions
identified by numerals 24, 23 and 25 having suffixes C, D, E and F
in respective ones of those figures.
[0072] Alternatively the buttons 14A-14F may be formed of material
similar to the type of cemented carbide which is described in U.S.
Pat. No. 5,286,549 which describes cemented carbide bodies,
containing WC and a binder based on at least one of Co, Fe and Ni
and including a soft core of cemented carbide surrounded by a
harder surface zone of cemented carbide. It is understood that the
buttons 14C-14F can be provided with a spigot 22 to enable
capacitor charge spot welding.
[0073] FIGS. 2A and 2B show an alternative embodiment of a rotary
cone drill bit 1' according to the present invention having steel
teeth. In contrast to the drill bit 1 in FIG. 1A the cone cutter 1'
has no buttons, but rather has steel teeth reinforced by cemented
carbide tips 14' serving as crushing elements. The tip 14' has a
substantially rectangular cross-section with a greatest width D
(FIG. 2B) at the weld joint. The height H of the tip constitutes
the part of the tooth which is intended to protrude from the steel
surface on the body 12A' of the cone cutter, and the height H is
defined from the transition 26' to the peak of the tip. The H/D
ratio is about 0.3 to 0.9, but is definitively smaller than 1.2,
i.e. HID<1.2, preferably H/D<0.9. The lower side 25' of the
tooth has a convex V-shape.
[0074] The present invention consequently provides a rotary cone
drill bit for rotary crushing drilling which allows a large degree
of freedom regarding the spacing between the cone cutters in the
drill bit, i.e. less steel support is needed for these crushing
means so deeper intermediate grooves can be made, and more
available bearing space in the cone cutter. In addition, crushing
element geometries are provided, and a method, which enables a
simple and quick mounting of the crushing elements to the cone
cutter body, which in turn, provides material technical
advantages.
[0075] The present invention is also applicable to a conical cutter
for a cutter head in the form of a raise boring head as described
in U.S. Pat. No. 5,984,024, incorporated by reference into the
present description. In such a device, the conical cutters are
rotatably journalled on supports in the form of yokes or
saddles.
[0076] Although the present invention has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions,
modifications, deletions and substitutions not specifically
described may be made without departing from the spirit and scope
of the invention as defined in the appended claims.
* * * * *