U.S. patent application number 16/145780 was filed with the patent office on 2020-04-02 for roof drill bit and cutting insert therefor.
This patent application is currently assigned to Kennametal Inc.. The applicant listed for this patent is Kennametal Inc.. Invention is credited to Chad A. Swope.
Application Number | 20200102793 16/145780 |
Document ID | / |
Family ID | 69945622 |
Filed Date | 2020-04-02 |
![](/patent/app/20200102793/US20200102793A1-20200402-D00000.png)
![](/patent/app/20200102793/US20200102793A1-20200402-D00001.png)
![](/patent/app/20200102793/US20200102793A1-20200402-D00002.png)
United States Patent
Application |
20200102793 |
Kind Code |
A1 |
Swope; Chad A. |
April 2, 2020 |
ROOF DRILL BIT AND CUTTING INSERT THEREFOR
Abstract
A roof drill bit has an elongate roof drill bit body having a
forward end and a rearward end. The bit body includes at least one
helical twisted surface terminating at a dust port and a feeder
ledge proximate the at least one helical twisted surface. A hard
insert is affixed to the bit body at the axial forward end thereof.
The hard insert includes a plurality of leading cutting edges for
cutting the earth strata. The at least one helical twisted surface
and the feeder ledge enhance the flow of debris into the dust
port.
Inventors: |
Swope; Chad A.; (Bedford,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kennametal Inc. |
Latrobe |
PA |
US |
|
|
Assignee: |
Kennametal Inc.
Latrobe
PA
|
Family ID: |
69945622 |
Appl. No.: |
16/145780 |
Filed: |
September 28, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 21/16 20130101;
E21B 10/60 20130101; E21B 10/44 20130101; E21B 10/55 20130101; E21B
10/46 20130101 |
International
Class: |
E21B 10/44 20060101
E21B010/44; E21B 21/16 20060101 E21B021/16; E21B 10/46 20060101
E21B010/46 |
Claims
1. A rotary drill bit for penetrating earth strata, comprising: an
elongate bit body having an axial forward end, the bit body
including at least one helical twisted surface terminating at a
dust port and a feeder ledge proximate the at least one helical
twisted surface; and a hard insert being affixed to the bit body at
the axial forward end thereof, the hard insert including a
plurality of leading cutting edges for cutting the earth strata,
wherein the at least one helical twisted surface and the feeder
ledge enhance the flow of debris into the dust port.
2. The rotary drill bit of claim 1, wherein the at least one
helical twisted surface has a helix angle, HA, of between 10
degrees and 50 degrees.
3. The rotary drill bit of claim 2, wherein the helix angle, HA, is
30 degrees.
4. The rotary drill bit of claim 1, wherein the bit body includes a
lobed socket in the axial forward end thereof, and wherein the hard
insert includes a lobed projection, and wherein the lobed
projection of the hard insert is received within the lobed socket
in the bit body.
5. The rotary drill bit of claim 1, wherein the bit body has a
lobed projection projecting from the axial forward end thereof, and
wherein the hard insert includes a lobed socket, and wherein the
lobed projection is received within the lobed socket.
6. The rotary drill bit of claim 1, wherein each one of the leading
cutting edges for cutting the earth strata have a generally radial
orientation.
7. The rotary drill bit of claim 1, wherein each one of the leading
cutting edges for cutting the earth strata have a corresponding
side clearance cutting edge.
8. The rotary drill bit of claim 1, wherein the rotary drill bit
has a central longitudinal axis passing through a center point of
the hard insert, and wherein the bit body has a peripheral surface,
and wherein each one of the leading cutting edges for cutting the
earth strata begins at a point radially outward of the center point
of the hard insert and extends in a direction away from the center
point so as to terminate at a point radially outward of the
peripheral surface of the bit body.
9. The rotary drill bit of claim 1, wherein each one of the leading
cutting edges for cutting the earth strata is formed by a
corresponding leading surface of the hard insert intersecting a
corresponding top surface of the hard insert, and wherein each one
of the leading surfaces are disposed at a rake angle of between 0
degrees and -15 degrees.
10. A rotary drill bit for penetrating earth strata, comprising: an
elongate bit body having an axial forward end, the bit body having
a peripheral surface and containing a central bore, the bit body
including at least one helical twisted surface terminating at a
dust port and a feeder ledge proximate the at least one helical
twisted surface, the bit body further including at least three
debris ports in the peripheral surface communicating with the
central bore, and each one of the debris ports has an axial forward
edge, and the axial forward edge of each debris port is spaced a
different distance away from the axial forward end of the bit body;
and a hard insert being affixed to the bit body at the axial
forward end thereof, the hard insert presenting at least three
discrete leading cutting edges for cutting the earth strata,
wherein the at least one helical twisted surface and the feeder
ledge enhance the flow of debris into the dust port.
11. The rotary drill bit of claim 10, wherein the at least one
helical twisted surface has a helix angle, HA, of between 10
degrees and 50 degrees.
12. The rotary drill bit of claim 11, wherein the helix angle, HA,
is 30 degrees.
13. A rotary drill bit for penetrating the earth strata,
comprising: an elongate drill bit body having an axial forward end,
the elongate drill bit body having a longitudinal axis, the axial
forward end being defined at least in part by a discrete first
axial forward surface that is generally perpendicular to the
longitudinal axis and a discrete second axial forward surface that
is generally perpendicular to the longitudinal axis, the first
axial forward surface being axially spaced apart from the second
axial forward surface, the bit body including at least one helical
twisted surface terminating at a dust port and a feeder ledge
proximate the at least one helical twisted surface; and a hard
insert being affixed to the axial forward end of the drill bit body
so as to form a joint between the hard insert and the bit body, the
joint being defined at least in part by the second axial forward
surface, wherein the at least one helical twisted surface and the
feeder ledge enhance the flow of debris into the dust port.
14. The rotary drill bit of claim 13, wherein the at least one
helical twisted surface has a helix angle, HA, of between 10
degrees and 50 degrees.
15. The rotary drill bit of claim 14, wherein the helix angle, HA,
is 30 degrees.
16. The rotary drill bit of claim 13, wherein the first axial
forward surface is generally parallel to the second axial forward
surface.
17. The rotary drill bit of claim 13, wherein the drill bit body
has a projection projecting away from the axial forward end
thereof, the second axial forward surface defining a distal end of
the projection, and the first axial forward surface being radially
outward of the second axial forward surface.
18. The rotary drill bit of claim 13, wherein the drill bit body
includes a socket at the axial forward end thereof, and the first
axial forward surface defines a periphery about the socket, and
wherein the first axial forward surface is radially outward of the
second axial forward surface.
19. The rotary drill bit of claim 13, wherein the drill bit body
having a central bore, the hard insert containing a first passage
therethrough, the drill bit body containing a second passage
therethrough, and the first passage in the hard insert being
aligned with the second passage in the drill bit body so as to
provide direct communication between the hard insert and the
central bore of the drill bit body.
Description
BACKGROUND OF THE INVENTION
[0001] The invention pertains to a roof drill bit, as well as a
roof drill bit body and a cutting insert (i.e., hard insert) for
use in a roof drill bit, that has a typical use of drilling
boreholes in mine roofs. More particularly, the invention pertains
to a roof drill bit, as well as a roof drill bit body and a hard
insert for use in a roof drill bit, that exhibits an improvement in
the performance of drilling boreholes in a roof bolting operation
due to an improvement in drilling debris evacuation and hard
cutting insert retention.
[0002] Expansion of an underground mine (e.g., a coal mine)
requires digging a tunnel that initially has an unsupported roof.
To provide support for the roof, an operator will drill boreholes
using a roof drill bit, wherein the boreholes can extend from about
two feet to twenty feet into the earth strata. The roof drill bit
attaches to a drill steel, which connects to a rotary driver. The
rotary driver powers the roof drill bit to drill the boreholes. The
operator then affixes roof bolts within the boreholes and a roof
support (e.g., a roof panel) connects to the roof bolts to support
the roof of the underground mine.
[0003] As one can appreciate, the drilling operation generates
drilling debris. It is important to remove this drilling debris
from the vicinity of the borehole. One typical way to remove or
evacuate drilling debris from the vicinity of the borehole is to
exert a vacuum at dust ports in the roof drill bit body. Under the
vacuum, drilling debris passes through the dust ports and through a
bore of a hollow drill steel into a debris collector. The debris
collector is away from the borehole.
[0004] Although earlier roof drill bits, which utilize a vacuum to
evacuate drilling debris, operate in a satisfactory fashion, there
remains a need to improve upon the operation of the roof drill bit.
More specifically, there is need to need to provide an improved
roof drill bit that exhibits an improvement in the evacuation of
drilling debris.
[0005] Roof drill bits operate at high rotational speeds. For
example, a typical rotational speed is 650 rpm (revolutions per
minute). When operating at such speeds, typically the drilling
debris does not directly enter the dust port, but travels about the
circumference of the roof drill bit prior to entering a dust port.
In other words, the drilling debris does not directly enter the
dust port closest to the point of engagement generating the
drilling debris. Instead, the drilling debris travels about the
circumference of the roof drill bit body prior to entry into a dust
port that is not the dust port closest to the point of engagement.
Significant disadvantages result from the inability of earlier roof
drill bits to evacuate drilling debris directly through the dust
ports.
[0006] One such disadvantage is excessive abrasive wear on the
surface of the drill bit body. The drilling debris exhibits
abrasive characteristics so that as the roof drill bit rotates at
high speeds, drilling debris between the earth strata defining the
borehole and the roof drill bit body abrades the roof drill bit
body. Such abrasion reduces the underlying support for the hard
insert, which over time may result in a premature removal of the
roof drill bit from service, i.e., a reduction in the expected
useful tool life. Thus, it would be highly desirable to provide an
improved roof drill bit that provides for an improvement in the
evacuation of drilling debris under the influence of the vacuum at
the dust ports.
[0007] Another significant disadvantage associated with the
inability of earlier roof drill bits to evacuate drilling debris
directly through the dust ports is an increase in the tendency of
the roof drill bit to become stuck once the roof drill bit ceases
operation. The presence of drilling debris between the roof drill
bit and the earth strata defining the borehole can make removal of
the roof drill bit-drill steel assembly difficult. The drilling
debris actually can frictionally hold or retain the roof drill bit
within the borehole. Thus, upon cessation of the rotation of the
roof drill bit, an attempt by the operator to remove the roof drill
bit-drill steel assembly may encounter problems. For example, the
operator may be unable to remove the entire roof drill bit-drill
steel assembly without great difficulty. As another example, during
an attempt to remove the roof drill bit-drill steel assembly from
the borehole, the drill steel may disengage from the roof drill
bit. The result is that the roof drill bit remains stuck in the
borehole. As one can appreciate, these difficulties decrease the
overall production efficiency of the mining operation. Thus, they
would be highly desirable to provide an improved roof drill bit
that better evacuates drilling debris so as to reduce or eliminate
drilling debris retained between the earth strata defining the
borehole and the roof drill bit.
SUMMARY OF THE INVENTION
[0008] In one aspect, the invention is a roof drill bit comprising
an elongate bit body having an axial forward end. The bit body
includes at least one helical twisted surface terminating at a dust
port and a feeder ledge proximate the at least one helical twisted
surface. A hard insert is affixed to the bit body at the axial
forward end thereof. The hard insert includes a plurality of
leading cutting edges for cutting the earth strata. The at least
one helical twisted surface and the feeder ledge enhance the flow
of debris into the dust port.
[0009] In another aspect, the invention is a roof drill bit body
that comprises an elongate bit body having an axial forward end.
The bit body has a peripheral surface and contains a central bore.
The bit body includes at least one helical twisted surface
terminating at a dust port and a feeder ledge proximate the at
least one helical twisted surface. The bit body further includes at
least three debris ports in the peripheral surface communicating
with the central bore, and each one of the debris ports has an
axial forward edge, and the axial forward edge of each debris port
is spaced a different distance away from the axial forward end of
the bit body. A hard insert is affixed to the bit body at the axial
forward end thereof. The hard insert presents at least three
discrete leading cutting edges for cutting the earth strata. The at
least one helical twisted surface and the feeder ledge enhance the
flow of debris into the dust port.
[0010] In still another aspect, the invention is a roof drill bit
body that comprises an elongate bit body having an axial forward
end. The elongate drill bit body has a longitudinal axis. The axial
forward end is defined at least in part by a discrete first axial
forward surface that is generally perpendicular to the longitudinal
axis and a discrete second axial forward surface that is generally
perpendicular to the longitudinal axis. The first axial forward
surface is axially spaced apart from the second axial forward
surface. The bit body includes at least one helical twisted surface
terminating at a dust port and a feeder ledge proximate the at
least one helical twisted surface. A hard insert is affixed to the
axial forward end of the drill bit body so as to form a joint
between the hard insert and the bit body. The joint is defined at
least in part by the second axial forward surface. The at least one
helical twisted surface and the feeder ledge enhance the flow of
debris into the dust port.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] While various embodiments of the invention are illustrated,
the particular embodiments shown should not be construed to limit
the claims. It is anticipated that various changes and
modifications may be made without departing from the scope of this
invention.
[0012] FIG. 1 is an isometric view of a specific embodiment of a
roof drill bit in which the hard insert is exploded away from the
drill bit body;
[0013] FIG. 2 is a top view of the hard insert of FIG. 1;
[0014] FIG. 3 is a side view of the hard insert of FIG. 1; and
[0015] FIG. 4 is a bottom view of the hard insert of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring to FIGS. 1-5, a roof drill bit 20 is shown
according to an embodiment of the invention. The roof drill bit 20
has a central longitudinal axis A-A. The roof drill bit 20 includes
a generally cylindrical elongate steel drill bit body 22 having an
axial forward end 24, an axial rearward end 26, a central
longitudinal bore 28, and a generally cylindrical peripheral
surface 30.
[0017] The preferred method to make the roof drill bit body 22 is
cold-forming. As will become apparent from the discussion
hereinafter, using cold-forming techniques to make the roof drill
bit body 22 result in a number of advantages that improve the
overall performance of the roof drill bit itself. For example, U.S.
Pat. No. 6,915,867 B2 to Bise (assigned to Kennametal Inc. of
Latrobe, Pa.) discloses a roof drill bit body made via cold-forming
techniques. Although the preferred manufacturing technique is
cold-forming, there should be an appreciation that powder
metallurgical techniques are also suitable to make the roof drill
bit body 22. Powder metallurgical techniques provide the
opportunity to employ a wide variety of materials for the
manufacture of the roof drill bit body. This is in contrast to
manufacturing processes that require machining or extensive
machining.
[0018] There should be an appreciation that the cutting insert of
the invention, as well as the cutting assembly of the invention,
can operate in a number of different applications. The cutting
insert, which has internal coolant delivery, is for use in the
removal of material from a workpiece. In this respect, the cutting
insert is for use in a material removal operation, wherein there is
enhanced delivery of cryogenic coolant to the entire cutting insert
to diminish excessive heat at the interface between the cutting
insert and the workpiece (i.e., the insert-chip interface).
[0019] The enhanced delivery of coolant to the insert-chip
interface leads to certain advantages. For example, enhanced
delivery of coolant to the insert-chip interface results in reduced
tool wear and increased tool life. Further, enhanced flow of
coolant to the insert-chip interface leads to better evacuation of
chips from the vicinity of the interface with a consequent
reduction in the potential to re-cut a chip.
[0020] The description herein of specific applications should not
be a limitation on the scope and extent of the use of the cutting
insert.
[0021] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about",
"approximately", and "substantially", are not to be limited to the
precise value specified. In at least some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value. Here and throughout the
specification and claims, range limitations may be combined and/or
interchanged, such ranges are identified and include all the
sub-ranges contained therein unless context or language indicates
otherwise.
[0022] Throughout the text and the claims, use of the word "about"
in relation to a range of values (e.g., "about 22 to 35 wt %") is
intended to modify both the high and low values recited, and
reflects the penumbra of variation associated with measurement,
significant figures, and interchangeability, all as understood by a
person having ordinary skill in the art to which this invention
pertains.
[0023] For purposes of this specification (other than in the
operating examples), unless otherwise indicated, all numbers
expressing quantities and ranges of ingredients, process
conditions, etc are to be understood as modified in all instances
by the term "about". Accordingly, unless indicated to the contrary,
the numerical parameters set forth in this specification and
attached claims are approximations that can vary depending upon the
desired results sought to be obtained by the present invention. At
the very least, and not as an attempt to limit the application of
the doctrine of equivalents to the scope of the claims, each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques. Further, as used in this specification and the
appended claims, the singular forms "a", "an" and "the" are
intended to include plural referents, unless expressly and
unequivocally limited to one referent.
[0024] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing measurements
including that found in the measuring instrument. Also, it should
be understood that any numerical range recited herein is intended
to include all sub-ranges subsumed therein. For example, a range of
"1 to 10" is intended to include all sub-ranges between and
including the recited minimum value of 1 and the recited maximum
value of 10, i.e., a range having a minimum value equal to or
greater than 1 and a maximum value of equal to or less than 10.
Because the disclosed numerical ranges are continuous, they include
every value between the minimum and maximum values. Unless
expressly indicated otherwise, the various numerical ranges
specified in this application are approximations.
[0025] In the following specification and the claims, a number of
terms are referenced that have the following meanings.
[0026] The singular forms "a", "an", and "the" include plural
references unless the context clearly dictates otherwise.
[0027] "Optional" or "optionally" means that the subsequently
described event or circumstance may or may not occur, and that the
description includes instances where the event occurs and instances
where it does not.
[0028] Furthermore, as used herein, the term "cryogenic coolant"
refers to a super cooled coolant, such as liquid nitrogen, and the
like, that is cooled to a temperature of approximately -321 degrees
Fahrenheit.
[0029] Referring back to FIG. 1, a pedestal portion (brackets 32)
is located near the axial forward end 24. The pedestal portion 32
includes a trio of helical twisted surfaces 36 (commonly known as
"flutes"). Each helical twisted surface 36 has a helical
orientation at a helix angle, HA, with respect to the central,
longitudinal axis A-A of the roof drill bit 20. The helix angle,
HA, may range between about 10 degrees and about 50 degrees. The
preferred helix angle, HA, is about 30 degrees. Each helical
twisted surface 36 has a preferred pitch equal to about 4.375
inches. The pitch of the twisted helical surface 36 may range
between about 0.1 inches and about 5 inches. The helical twisted
surface 36 extends in the axial rearward direction and leads into a
debris or dust port 38, so that as it moves in the axial rearward
direction it finally terminates at its corresponding dust port
38.
[0030] Each debris port 38 is generally circular having a diameter,
D, equal to about 0.375 inches (about 0.95 cm) near the axial
rearward edge thereof. Each debris port 38 is slightly offset a
distance, E, equal to about 0.082 inches (about 2.08 millimeters
[mm]) from the centerline F-F of each helical twisted surface 36.
The center of the debris port 38 is spaced a distance, X, equal to
about 0.939 inches (about 2.38 cm) from the axial rearward end 26
of the bit body 22. The debris ports 38 are in communication with
the central, longitudinal bore 28 to permit evacuation of the
drilling debris, including larger size pieces of debris, under the
influence of a vacuum in dry drilling. The roof drill bit 20 is
also useful for wet drilling.
[0031] The pedestal portion 32 includes a trio of pedestal lobes 40
wherein each lobe 40 is defined between each pair of the scalloped
surfaces 36. The axial forward end 24 presents a discrete first
axial forward surface 41 and a discrete second axial forward
surface 43.
[0032] Each pedestal lobe 40 has a distal peripheral edge 42
adjacent a feeder ledge 44, and a leading edge 46 near a leading
peripheral surface 48. The feeder ledge 44 of the pedestal portion
32 enhances the flow of debris along the helical twisted surface 36
and into a respective debris port 38, while providing for excellent
strength and assisting the drill bit body 22 to resist failure
during stalling of the roof drill bit 20.
[0033] The roof drill bit body 22 further contains a lobed socket
50 in the axial forward end 24 thereof. The lobed socket 50
presents a trio of generally radial socket lobes equally spaced
apart about 180 degrees. As clearly shown in the drawings, a bottom
second axial forward surface of the lobed socket 50 is generally
parallel to a peripheral first axial forward surface of the axial
forward end 24 of the drill bit body 22. As described hereinafter,
the configuration of the lobed socket 50 corresponds to the
configuration of a lobed projection that depends from the bottom
surface of a hard insert.
[0034] The roof drill bit 40 further includes a hard insert 56 that
presents three discrete leading cutting edges. However, there may
be more or less than three discrete leading cutting edges,
depending upon the application.
[0035] The hard insert 56 is preferably (but not necessarily) a
single monolithic member formed by powder metallurgical techniques
from a hard material such a cemented (e.g., cobalt) tungsten
carbide alloy wherein a powder mixture is pressed into a green
compact and then sintered to form a substantially fully dense part.
Applicants contemplate that the hard insert also could be made by
injection molding techniques. The preferred grade of cemented
tungsten carbide for the hard insert (i.e., Grade 1) contains about
6.0 weight percent cobalt (the balance essentially tungsten
carbide) and has a tungsten carbide grain size of about 1-8
micrometers and a Rockwell A hardness of about 89.9.
[0036] The hard insert 56 has a top surface 58 with a central area
60 surrounding the center point, G, (see FIG. 2) and a bottom
surface 62. The hard insert 56 has a trio of lobes 64 wherein each
lobe 64 has a generally planar leading surface 66, a trailing
surface 68, and a contoured top (or relief) surface 70. The relief
surface 70 has a leading convex upper portion and a trailing
concave lower portion wherein there is a smooth transition between
the upper leading portion and the trailing lower portion.
[0037] When the hard insert 56 is affixed to the drill bit body 22,
the leading surface 66 of each first lobe 64 is disposed at a rake
angle, H, (see FIG. 1) of about negative 5 degrees. The rake angle,
H, may range from about 0 degrees to about -15 degrees, and more
preferably range from about -5 degrees to about -15 degrees. By
exhibiting a negative rake angle, H, a hard insert 56 is provided
with a strong leading cutting edge. The negative rake angle also
provides for better powder flow during the fabrication process so
as to enhance the overall integrity (including uniform density) of
the hard insert 56.
[0038] Each lobe 64 further includes a distal peripheral surface
74. The leading surface 66 intersects the relief surface 70 at the
upper portion thereof so as to form a generally straight leading
cutting edge 76 at the intersection thereof. The leading surface 66
intersects the distal peripheral surface 74 to form a generally
straight side clearance cutting edge 78 at the intersection
thereof. While the leading cutting edge 76 presents a generally
straight geometry, applicants contemplate that the leading cutting
edge may take on a different configuration such as, for example, an
arcuate configuration in either or both the vertical and horizontal
directions.
[0039] The hard insert 56 has a lobed projection 80, which has a
trio of projection lobes spaced apart about one hundred twenty
degrees, that depends away from the bottom surface 62 of the hard
insert. Lobed projection 80 has a side surface 84 and a bottom
surface 86. The bottom surface 62 of the hard insert has a shoulder
88 that surrounds the lobed projection 80 and is generally parallel
to the bottom surface 62. Each one of the projection lobes has a
general radial orientation so that its central longitudinal axis
passes through the geometric center of the hard insert (i.e., the
point on the hard insert that lies along the central longitudinal
axis A-A of the roof drill bit 20 when the hard insert is affixed
to the bit body).
[0040] Referring back to the geometry of the leading and side
cutting edges, while these cutting edges are generally straight and
perform in an acceptable fashion, other geometries for these
cutting edges are acceptable for use. For example, the following
patent documents disclose suitable geometries for these cutting
edges: U.S. Pat. No. 4,787,464 to Ojanen, U.S. Pat. No. 5,172,775
to Sheirer et al., U.S. Pat. No. 5,184,689 to Sheirer et al., U.S.
Pat. No. 5,429,199 to Sheirer et al., and U.S. Pat. No. 5,467,837
to Miller et al.
[0041] Referring to the assembled roof drill bit 20, it is typical
that the hard insert 56 is brazed to the axial forward end 24 of
the bit body 22. More specifically, the lobed projection 80
depending from the bottom surface 62 of the hard insert 56, has a
corresponding geometry with, and thus is received within, the lobed
socket 50 contained in the axial forward end 26 of the bit body 22.
There is geometric correspondence between the shape of the lobed
socket 50 and the shape of the lobed projection 80, whereby the
projection 80 is received within the socket 50 so as to ensure that
the hard insert is correctly positioned with respect to the drill
bit body 22. There is a braze joint between the surface of the
drill bit body at the axial forward end thereof and the rearward
surface of the hard insert wherein the braze joint includes the
surfaces defining the projection on the hard insert and the socket
in the drill bit body, as well as the shoulder of the hard insert
and the peripheral surface of the bit body that surrounds the
socket, i.e., the axial forward most surface.
[0042] The preferred braze alloy is HI-TEMP 548 braze alloy
manufactured and sold by Handy & Harmon, Inc., 859 Third
Avenue, New York, N.Y. 10022. HI-TEMP 548 braze alloy is composed
of 55+/-1.0 weight percent copper, 6+/-0.5 weight percent nickel,
4+/-0.5 weight percent manganese, 0.5+/-0.05 weight percent
silicon, and the balance zinc with 0.50 weight percent maximum on
total impurities. Additional information on HI-TEMP 548 braze alloy
may be found in Handy & Harmon Technical Data Sheet D-74
available from Handy & Harmon, Inc.
[0043] When in the assembled condition, the radially outward
portion of the leading cutting edge 76 of each lobe 64 extends
forward of the leading peripheral surface 48 of its corresponding
pedestal lobe 40. This distance decreases as the leading cutting
edge 76 moves in a radial inward direction. Furthermore, for each
lobe 64 the side clearance cutting edge 78 extends a distance in a
radial outward direction past the distal peripheral surface 44 of
its corresponding pedestal lobe 40.
[0044] Referring to FIG. 2, the leading cutting edges 76 of the
hard insert 56 have a generally radial orientation. If the rake
angle is zero degrees, then a line laying along each leading
cutting edge when extended in a radial inward direction passes
through the center point, G, of the hard insert 56. The center
point, G, lies on the central longitudinal axis A-A of the roof
drill bit 20.
[0045] Each one of the leading cutting edges 76 begins at a point
that is a distance, K, (FIG. 3) [equal to about 0.125 inches (about
3.2 mm)] radially outward of the center point "G" of the hard
insert 56. Each cutting edge 76 then extends in a radial outward
direction so as to terminate at a point radially outward of the
peripheral surface of the drill bit body 22. There is an open
central area 60 (see FIG. 2) surrounding the center point, G, of
the hard insert. The portion of each leading cutting edge nearer
the center point "G" travels a shorter distance per revolution than
does the distal portion of each leading cutting edge. Because each
leading cutting edge 76 does not extend to the center point of the
hard insert 56 there is a reduction in the amount of low velocity
cutting, i.e., cutting that occurs at or near the center point of
the hard insert. Generally speaking, a reduction in the amount of
low velocity cutting increases the penetration rate of a roof drill
bit so that (all other things being equal) an increase in the
magnitude of distance "K" may increase the penetration rate.
[0046] In operation, the roof drill bit 20 rotates and impinges
against the earth strata so that the leading cutting edges 76
contact the earth strata so as to cut a borehole and the side
clearance cutting edges 78 cut the side clearance for the borehole.
The circle cut by the hard insert is about 1.024 inches (about 2.6
cm) in diameter. Although optimum parameters depend upon the
specific circumstance, typical rotational speeds range between
about 450 to about 650 revolutions per minute (rpm) and typical
thrusts range between about 1000 and 3000 pounds.
[0047] The drilling operation generates debris and dust
particulates. In certain applications the higher penetration rates
associated with the roof drill bit generates larger-sized debris
that has the potential to clog the roof drill bit. The debris, and
especially the larger-sized debris, needs to be handled and removed
from the borehole so as to not interfere with the drilling
operation. In the roof drill bit 20, the debris smoothly moves over
the leading surfaces 66 of each one of the lobes 64 and directly
into the corresponding debris port 38. By providing the trio of
debris ports 38, the roof drill bit 20 provides a way for the
debris to quickly and efficiently be removed from the vicinity of
the drilling. The removal of debris, and especially larger size
debris, is enhanced by the configuration of the helical twisted
surface 36, the feeder ledge 44 and the offset and axial location
of the debris port 38. The consequence is that the debris generated
by the drilling (and especially larger-sized debris) does not
interfere with the efficiency of the overall drilling
operation.
[0048] Because these three discrete leading cutting edges 76 have a
generally radial orientation, the roof drill bit 20 exhibits
excellent balance so as to continue to steadily advance with
little, and possibly no, wobble, i.e., side-to-side movement. While
the generally radial orientation of the leading cutting edges
appears to provide the above-described advantage, applicants would
expect that the roof drill bit would still exhibit improved
performance even if the hard insert would have leading cutting
edges that would not have a generally radial orientation.
[0049] In addition, the hard insert 56 covers the entire axial
forward end 24 (including the axial forward most surface) of the
drill bit body 22. By providing coverage of the axial forward end
24 of the drill bit body 22 the hard insert 56 protects the braze
joint between the hard insert and the drill bit body from erosion
so as to maintain the integrity of the braze joint. This is
especially true for the portion of the braze joint defined by the
bottom surface and side surface of the lobed socket of the bit body
and the corresponding surfaces of the hard insert since the braze
joint is actually within a volume of the bit body protected by the
hard insert.
[0050] The patents and other documents identified herein are hereby
incorporated by reference herein. Other embodiments of the
invention will be apparent to those skilled in the art from a
consideration of the specification or a practice of the invention
disclosed herein. It is intended that the specification and
examples are illustrative only and are not intended to be limiting
on the scope of the invention. The true scope and spirit of the
invention is indicated by the following claims.
* * * * *