Note: Descriptions are shown in the official language in which they were submitted.
1~3~3~56
The present invention relates to a drill bit for use
in percussion drilling, the front end of which is provided
with one or more cutting inserts of cemented carbide
fastened in a slot or slots in the drill bit, the rear end
being provided with a central bore for fastening the drill
bit to a drill rod, said rod having a forwardly tapering
conical portion and said central bore in said bit having
a rearwardly tapering matching conical internal surface for
supporting said bit on said rod by engagement between said
conical surfaces.
Such what is called conbits are already known in
the art but have hitherto been of disadvantages due to in-
sufficient frictional engagement between said conical portions
of the bit and the rod. The result has oftentimes been that
the bit and the rod become disengaged and the bit remains
in the drill hole which causes much trouble. An earlier
suggestion for solving this problem is to provide the conical
portion of the rod with recessed portions. This solution
has the substantial drawback that the rod has become weakened
which increases the risk for failure incidence.
In one aspect of the present invention there is
provided a drill bit for use in percussion drilling
comprising a solid bit body having one or more cutting eQges at
its front end and a centrally proviced rod receiving hole
having a conical internal surface, characterized in that
the hole is bottomed in the bit and comprises a cylindrical
internal surface in front of said conical surface, and that
said cylindrical surface has an internal thread on a location
spaced from the bottom of said hole.
In a furth~r aspPct of the pre~ent invention th~re
is provided a arilling assembly for u~e in percussion drill-
~i ing comprising a solid drill bit having one or more cutting~
, " .. , . . , , . .. --. _ . . . . . . . . . . . . .. .. .
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edges at its front ena and a centrally pro~ided hole, and
a rod having a forwardly .apering conical portion, and said
central hole in the bit having a matching conical internal
surface fc,r supporting said bit on said rod by ensagement
between said conical surfaces, characterized in that said
central hole is bottomed in the bit and comprises an internal
cylindrical surface in front of said conical surface, said
cylindrical susf~ce having an internal thread matching an
external thread on the foremost part of said rod, said
external thread on said rod being positioned axiall~ in
front of said internal thread and at a location spaced
from the bottom o said hole in the bit when said bit is
in operating position having its conical surface engaged
with the conical surface on the rod.
Closer details of the invention appear ~rom the
~ollowing specification and the accompanying drawings in
which Fig. 1 is a side view of a drill bit according to
the invention.
- la -
` 1~388S6
~ig. 2 i~ a longitudianl section o~ the d:rill bit,
~ . S is an e:nd view of the drill bit,
Fig. 4 1s a ~ide view oY one embodimerlt of the rod,
F~g. 5 i~ a ~ide view of another embodiment o~ the rod,
Fig. ~ i~ a section on line ~I-VI in ~`ig. 5 and
Fig. 7 is a l.ongitudinal section of the drlll bit; in engagement with
the rod according to the embodiment shown in Fig. 4.
The drill bit according to the invention comprises a bit body 10 of
solid structu:re the rear end of ~hlch having a central bottomed hole 11
for fa~tening the bit to a drill rod 12.
The bit i9 at it~ front end provided with four croe~wi~e arranged
cutting ln~ert3 13 of cemented carbide fas-tened in slots in the drill
bit, The number of in#erts can of course be varied from a single
chi~el insert to more than four inserts and the po~ition o:f the
ln~ert~ can a}90 be varied. ~or the removal of drill cuttings recesse~
14 are prov.ided between the in~erts ~hlch ad~oin rearwardly tapering
exlt channel3 15. A oentral plug 16 i8 arranged for ~upporting the
insert~. ~ flushing channel 1'7 extends a~lally from the bottom 24 of
the hole through said plug to the front surf'ace of the bit. Exoept
thi~ channel the drill bit 19 provided ~ith two auxiliary diverging
channel~ 18 and 19.
~he central bottomed hole 11 in the drlll bit has a con.ical portion
20 and interiorly provided thread 21 at a cylindrical fore portion
in front of the conical portion 20. The thread 21 is ~uitably rounded-,
forming a wave shaped longitudinal ~ection. The thread 21 is located
at a distance from the bottom 24 of the hole such that cylindrical
portions 22 and 2~ of ~ub~tantially equa]. length are provided on
oppo~lte ~ide~ of the thread 21,
The rod par-t 12 has a conical portion 25 match~IIg the conical portion20 in the bit hole 11 90 as to provide a frictional enga~ement there-
between. The rod i~ at it~ foremost part provided ~ith an external
thread 26 matchlng the internal thread 21, Thi~ e~ternal thread 26 of
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the rod i~ sep~rated from the coni.cal portion 25 by a cylindrical
portion 27. The latter portion 27 .is of suc:h length -t~lat when the
conical surface~ 20 and 25 are in engagemerlt with each other, the
external thread 26 is situclted axi.ally in :I`ront of the intèrnal thread
21, so that the threads are out oY engagement w.ith each other. 'rhis
provide3 a ~afe and easily detachable coupling between the parts 10
and 12. The cen tral ly provided channel 28 in the rod serves the purpo~e
of transport1ng flushing medium to the .~ore part of the bit.
It has been fourld sultable to ~ake the length of internal thread 21
approxiamtely one half of the length of cylindrical portlon 23. ~his
positively adds to the duration of the drill bit becau~e the stre~ses
occurring in the fore part of the drill bi.t then will be distributed
more advantageously. It has al~o been found that this contribute~ -to
better resi9tance against transver~al ruptures that usually occur at
the bottom 24 o.~ t~le central hole 11.
Acoording to an alternative embodiment the conical portion 25 of the
rod part may be provided with a number of plane surfaces 29. It has
been found that this contributes to increased frictional engagement
between the bit 10 and the rod 12. It al~o leads to a les~ened risk of
friction martensite to appear ln the conical engaging surface layers
that otherwl~e should result in dRcreased strength of the parts.
