Boring or penetrating the earth – Bit or bit element – Impact or percussion type
Reexamination Certificate
1999-10-25
2001-08-21
Neuder, William (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Impact or percussion type
C175S418000
Reexamination Certificate
active
06276467
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to percussive rock drill bits, such as used in percussive down-the-hole hammers and top-hammer drills, for example, which bits comprise a steel body carrying hard button inserts. The body includes a plurality of wings. In particular, the invention relates to such drill bits wherein only a single gauge button is disposed in each wing of the drill bit.
Such a drill bit
10
is depicted in
FIG. 1
(and also in U.S. Pat. No. 5,025,875). The drill bit includes a steel bit body
12
forming a front cutting face that is intersected by two fluid passages
14
for conducting a flushing/cooling medium (e.g., air) to the front cutting face. Each passage
14
communicates with a radial channel
16
in the cutting face for conducting the flushing/cooling medium to an outer periphery of the bit body, in particular, to respective longitudinal flushing grooves
18
′ formed in the bit body for facilitating the longitudinal flow of the medium. Additional longitudinal flushing grooves
18
are provided, all of the flushing channels
18
,
18
′ being in circumferentially spaced relationship with one another. Disposed between successive flushing channels in the circumferential direction are so-called wings
20
,
20
′ of the bit body, wherein the wings
20
′ are situated immediately behind the flushing grooves
18
′ with reference to the rotation direction d.
Mounted in longitudinal holes formed in the front cutting face are button inserts
22
,
23
,
23
′ formed of a hard material such as cemented carbide, especially tungsten carbide. The inserts
23
,
23
′ are mounted in the wings
20
, and are known as gauge inserts because they define the diameter of the hole being cut. Two of the gauge inserts
23
′ are mounted in the wings
20
′ that are situated immediately behind the flushing grooves
18
′. The remaining gauge inserts
23
are mounted in the other wings
20
.
FIG. 1
depicts a type of drill bit wherein only a single gauge insert
23
,
23
′ is disposed in each wing
20
,
20
′ (other conventional types of drill bits may have more than one gauge insert in each wing, but the present invention does not pertain thereto.) Typically, in such a drill bit, each gauge insert is located at the center of the respective wing, with reference to a circumferential dimension of the wing. In other words, if the direction of rotation of the drill bit is in the direction d, then the distance A from the center of the gauge insert
23
,
23
′ to a leading edge
24
of the wing
20
,
20
′ is equal to the distance B from the insert center to the trailing edge
26
of the wing, this being the case for all of the gauge inserts.
During rotation of the drill bit, the leading portion of each wing, i.e., the leading edge
24
of the wing, is more exposed than is the trailing edge
26
. Consequently, the leading edge wears more rapidly, sometimes limiting the life of the bit. This can happen while the trailing edge remains relatively intact. That is especially true of the wings that are situated immediately downstream of the flushing grooves
18
′ disposed at radially outer ends of the radial channels
16
.
It has been proposed in the prior art to deal with the above-described wear problem by making the flushing grooves narrower, thus extending the total wing length and the total amount of steel. Another solution is to increase the hardness and wear resistance of the steel. Yet another solution is to add wear protection buttons on the outside of the wing. It is not uncommon to put the wear protection buttons on the leading ledge. However, these solutions have drawbacks in regards to flushing capacity of the design, fatigue resistance of the steel and/or manufacturing cost.
SUMMARY OF THE INVENTION
A percussive rock drill bit includes a bit body and a plurality of button inserts mounted in the bit body. The bit body forms a front cutting face and a peripheral surface. At least one passage intersects the front cutting face for conducting a flushing/cooling medium to the front cutting face. The peripheral surface has a circumferentially spaced flushing grooves formed therein. Portions of the bit body which are disposed between successive flushing grooves comprise wings. Each wing having a leading edge and a trailing edge. The button inserts are formed of a material harder than the material of the bit body. Some of the button inserts constitute gauge inserts and are mounted in the wings. There is only one gauge insert mounted in each wing. At least one of the gauge inserts is offset circumferentially from a center of the respective wing by a distance equal to at least five percent of a circumferential length of the wing.
REFERENCES:
patent: 3519092 (1970-07-01), Miller
patent: 4440244 (1984-04-01), Wiredal
patent: 5025875 (1991-06-01), Witt
patent: 5947215 (1999-09-01), Lundell
Burns Doane Swecker & Mathis L.L.P.
Driltech Mission LLC
Neuder William
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