CA1038856A

CA1038856A - Percussion drill bit

Info

Publication number: CA1038856A
Application number: CA249,433A
Authority: CA
Inventors: Hans P. O. Lundstrom; Harry A. Wiredal
Original assignee: Sandvik AB
Current assignee: Sandvik AB
Priority date: 1976-04-02
Filing date: 1976-04-02
Publication date: 1978-09-19
Also published as: FI770994A; FR2346110A1; FR2346110B1; NO771177L

Abstract

PERCUSSION DRILL BIT

Abstract of the Disclosure A drill bit for use in percussion drilling comprising a solid bit body having one or more cutting edges at its front end and a centrally provided rod receiving hole having a conical internal surface. The hole is bottomed in the bit and comprises a cylindrical internal surface in front of said conical surface, and the cylindrical surface has an internal thread located at a distance from the bottom of said hole.

Description

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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~03~3~56 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 ~1~31~856 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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A drill bit for use in percussion drilling comprising a solid bit body having one or more cutting edges at its front end and a centrally provided 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.

2. A drill bit as defined in claim 1, characterized in that a flushing channel extends axially from the bottom of said hole to the front surface of the bit, said channel having substantially smaller diameter than said rod receiving hole.

3. A drill bit as defined in claim 1, characterized in that the internal thread is provided at a middle portion of the cylindrical internal surface.

4. A drill bit as defined in claim 3, characterized in that the length of the internal thread is about one half the length of the cylindrical internal surface provided axially in front thereof.

5. A drilling assembly for use in percussion drill-ing comprising a solid drill bit having one or more cutting edges at its front end and a centrally provided hole, and a rod having a forwardly tapering conical portion, and said central hole in the bit having a matching conical internal surface for supporting said bit on said rod by engagement 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 surface having an internal thread matching an external thread on the foremost part of said rod, said external thread on said rod being positioned axially in front of said internal thread and at a location spaced from the bottom of said hole in the bit when said bit is in operating position having its conical surface engaged with the conical surface on the rod.

6. A drilling assembly as defined in claim 5, characterized in that the internal thread is provided at a middle portion of the internal cylindrical surface located axially in front of said internal conical surface.

7. A drilling assembly as defined in claim 5, characterized in that a cylindrical portion is provided on the rod between its external thread and its conical surface, and that a flushing channel extends axially through the rod.

8. A drilling assembly as defined in claim 5, characterized in that the length of the internal thread is about one half of the axial length of the cylindrical internal surface provided axially in front of it.

9. A drilling assembly as defined in claim 5, characterized in that a number of longitudinally extending planar surfaces are symmetrically provided around said conical surface on said rod.

10. A drilling assembly as defined in claim 5, characterized in that a flushing channel extends axially from the bottom of the bit hole to the front surface of the bit, and there being two diverging auxiliary channel extending from the bottom of the bit hole into exit channels provided exteriorly of the bit.