AU706283B2 - Improvements in drill bits - Google Patents

Description

2 The present invention relates to drill bits and more particularly to the form of cutting tip for a drill bit having a wide range of applications which includes but is not limited to rock drilling and metal drilling.

Typically, the cutting faces of a drill bit are formed by intersecting planar faces which incline towards the drill tip. Those faces are chamfered from the leading edge to the trailing edge at an angle referred to as the back clearance angle. In order to increase the drilling rate there has been proposed the provision of a slot at the tip of a drill bit such as the form of slotted spade insert manufactured by Hard Metals Australia Pty Limited under their designation KS27N. By employing a slotted spade insert of the prior art there is the capacity to improve the drilling rate of a drill bit having such an insert as compared with a solid tip conventional type spade insert as the region about the apex of the insert only spins at low linear speeds and effects minimal cutting action. The slotted spade insert provides a further clearance zone for material being drilled thereby allowing the drilling rate to be increased over that available for conventional unslotted drill tips. The present invention consists in an improved drill tip wherein the back clearance angle is varied radially from the tip of the drill bit or spade insert.

Typically the back clearance angle is varied from of the order of 250 adjacent the tip or slot formed in the tip to of the order of 50 at its radially outermost extremity. The drill tip is preferably slotted for use in drilling rock or stone while remaining unslotted for other purposes.

The range of variation in back clearance angle applicable to the invention is not fixed in that the limits of that range will be varied to suit a particular application.

By varying the back clearance angle a spade insert or drill tip is able to more efficiently clear shavings or broken particles of the material being sheared by the drill bit. Also by varying the back clearance angle to give greater relief at the centre of the drill bit, the limitations on penetration rate due to the low linear speed in this area are greatly reduced and the performances of the drill bit is very much enhanced.

In rock drilling applications a spade bit typically includes a tungsten carbide spade insert with a bore through the centre of the bit which enables a flushing fluid to be directed to the cutting face so as to improve the flushing of material away from the cutting tip as the drill feeds through the material being drilled.

In another embodiment the tip of the drill bit or spade insert is formed with a negative land on its leading edges. By this modification the tip or spade insert is less prone to damage.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a conventional spade bit as employed in rock drilling; Fig. 2 is a perspective view of a tungsten carbide slotted spade insert of a conventional form; Fig. 3 is a perspective view of a slotted spade insert of Fig. 2 but modified to incorporate a variable back clearance angle in accordance with the present invention; Fig. 4 is a front elevation of the spade insert of Fig. 3; .70 Fig. 5 is a side elevation of the slotted spade insert of Fig. 3; 15 Fig 6 is a similar view to Fig. 4 but showing a modified leading edge :ooo.o :0 of a second embodiment of a spade insert of the invention; "Fig. 7 is plan view of the spade insert of Fig. 6; and Fig. 8 is an end elevation view of the spade insert of Fig. 6.

Referring to Fig. 1 there is shown a conventional spade bit comprising a spade body 11 and a solid spade insert 12 formed from tungsten carbide. The spade bit body 11 comprises a threaded end 13 having a central bore 14 for feeding flushing fluid to the cutting face of insert 12.

Fig. 2 shows a slotted spade insert 15 in accord with Model No KS27N as manufactured by Hard Metals Australia Pty Limited of Mount Kuring-gai, New South Wales, Australia.

Figs. 3-5 are views of a slotted spade insert 16 incorporating a back clearance angle which varies radially starting at, say, 250 adjacent the central slot 17 to 50 at the outer edge of insert 16.

The embodiment of Figs. 6-8 is a modification of that shown in Figs.

3-5 in that portions 21, of the leading edge of spade insert 20, as shown in shaded form are removed either side of the slot 22.

Even though the depicted embodiments relate to spade bit inserts it will be understood that the present invention is applicable to formed drill bits whether incorporating a central slot or not. By providing a radially varying back clearance angle to the cutting edge of a drill bit there may be an improved rate of clearance of material removed by the drill bit which 1 enables the drill having a tip in accordance with the present invention to be passed more rapidly through the material being drilled.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive.

.o* oO o o*o* THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A drill bit or spade insert for a drill bit comprising a tip, a radial extremity adjacent the tip and a radially extending surface from at least near to the tip to the radial extremity, wherein the back clearance angle of the radially extending surface increases from the radial extremity toward the location at least near to the tip.

2. A drill bit or spade insert for a drill bit as claimed in claim 1 wherein the back clearance angle at the radial extremity is of the order of 3. A drill bit or spade insert for a drill bit as claimed in any one of the preceding claims wherein the back clearance angle near to the tip is of the order of S4. A drill bit or spade insert for a drill bit as claimed in any one of the preceding claims wherein the drill tip is slotted.

A drill bit or spade insert for a drill bit as claimed in claim 4 wherein the leading cutting edges of the tip adjacent the slot are chamfered.

6. A drill bit or spade insert for a drill bit substantially as hereinbefore defined with reference to Figs. 3-5 or 6-8 of the accompanying drawings.

DATED this 9th day of November 1995 STEPHEN CHARLES AINGE Patent Attorneys for the Applicant: F.B. RICE CO.

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