EP0114016A1 - Drill bit for combined rotary and jet drilling - Google Patents

Abstract

The invention relates to the geometry of cutters for rotary jet-assisted drilling. The invention recommends a cutter comprising plates (20) of small radial dimension, arranged around a central spark gap (40a) through a discontinuous peripheral crown (50) extending said cutter axially, channels (60) of supply of pressurized fluid emerging from the crown near the plates. These are preferably separated by straight discharge ramps (30). A cutter according to the invention can be obtained for example by turning and milling. Application: rock drilling in mines, or other hard materials.

Description

The present invention relates to cutters for rotary jet-assisted drilling and aims more particularly at optimizing their geometry.

As is known, a cutter is a mine tool which is mounted at the end of a drilling rod driven in rotation and which is intended, thanks to sharp edges formed on its leading edge, to bite and to penetrate a rock, parallel to its axis of rotation. These sharp edges are generally constituted by plates of high hardness, tungsten carbide most often, reported by brazing; sometimes it is specified that it is a cutter with reported stakes.

Such cutters are used in practice in the drilling of relatively soft and not very abrasive rocks. For harder and / or more abrasive rocks, it has indeed been proposed to use roto-percussive drilling, with striking effect, but this has proved to have serious drawbacks insofar as, apart from that it leads to very high installation costs, it causes the appearance of noises, vibrations and very strong oil vapors which are detrimental to compliance with ergonomic and even safety rules.

Another solution has however been proposed recently for the drilling of semi-hard rocks (pressure greater than or equal to approximately 800 bars), hard and abrasive, which seems promised with a great future: rotary assisted drilling by jet.

This process consists in driving a cutter in simple rotation, without striking effect, by injecting, near its sharp cutting edges, a fluid at very high pressure which fractures the rock and therefore facilitates the felling of it by the cutting.

The implementation of this process has raised certain difficulties related to the supply, through the drill rod and the cutting edge, of said fluid under very high pressure, more often than not. However, it is note that it was already known to bring water or low pressure air to the cutting edge (around 20 to 40 bars) for the removal of drilling or logging debris.

French Patent No. 2,450,936 (G. CAGNIONCLE), filed March 8, 1979, describes one way in which these difficulties have been overcome. For the implementation of the process which is described there it is recommended to arrange there through a cutter two sets of channels of fluid under pressure: channels of low pressure fluid for the evacuation of the debris, and channels much finer for the supply of fluid under very high pressure (1000 to 4000 Lars) to assist the actual drilling, emerging through or in front of the inserts. This patent also describes the entire liquid supply device necessary for such a fluid injection under two very different pressures.

It turns out in fact that the cutters used up to now in the context of rotary assisted jet drilling have a geometry very close to that of traditional cutters (without assistance by jets).

However, the Applicant has been able to demonstrate, within the framework of its research, that the fact of assisting the rotary drilling by jets made it possible to completely review the geometry of the cutters to be used.

The present invention thus relates to a new cutting geometry leading to higher performance than that of cutting edges currently known for a lower manufacturing cost.

To this end, it proposes a cutter for rotary jet-assisted drilling, intended to be mounted at the end of a rotary drive rod, of the type comprising, opposite said rod, a plurality of drilling plates having radial and axial projecting edges angularly separated by debris discharge ramps, pressurized fluid supply channels opening near said plates, characterized in that the plates have a small radial dimension and are arranged around a spark gap central through a discontinuous peripheral ring axially extending said cutter, which ring is crossed by said fluid supply channels.

Such a cutting geometry is very clearly different from the geometries currently known. Indeed, the cutting edges of the prior art are generally compact and massive; they include inserts whose radial dimension is barely less than the largest radius of the cutting edge, so as to drill a rock over practically the entire cross section of the cutting edge. Given their size, these plates undergo significant stresses during rotation which they can only resist if they are supported on a large mass of metal. In practice, these plates are supported by helical arms obtained by forging, or else are enclosed in notches made in a solid cutting edge as shown in the aforementioned patent 2,450,936.

A cutting edge according to the invention, on the other hand, turns out to lead to the use of smaller plates adapted to exert, by their edges projecting axially, for the same axial thrust, much higher penetration stresses than in the prior art where the axial thrust was distributed over much longer radial edges. A cutter according to the invention therefore allows the drilling of much harder rocks than in the prior art, which can reach pressures of 600-800 bars and more. It should be noted that thanks to the presence of a central spark gap, which can for example be a cone, preferably in precession, or a jet of pressurized fluid, any risk of tailgating of the cutting edge against a central zone of rock not felled by the pads can be spread.

According to an important characteristic of the invention, the discharge ramps are rectilinear. This results in a significant lowering of the manufacturing costs of the cutters insofar as the invention proposes a cutter which, before the brazing of the wafers, can be shaped to using simple and inexpensive machining operations such as turning or milling.

• la figure 1 est une vue frontale d'un premier mode de réalisation d'un taillant selon l'invention ;
• la figure 2 est une vue latérale du taillant de la figure 1, avec coupe partielle d'un côté de l'axe ;
• la figure 3 est une vue frontale d'un deuxième mode de réalisation d'un taillant selon l'invention ; et
• la figure 4 est une vue latérale du taillant de la figure 3, avec coupe partielle d'un côté de l'axe.

Other objects, characteristics and advantages of the invention appear from the description which follows, given by way of nonlimiting example, with reference to the appended drawing in which:

• Figure 1 is a front view of a first embodiment of a cutter according to the invention;
• Figure 2 is a side view of the cutter of Figure 1, with partial section on one side of the axis;
• Figure 3 is a front view of a second embodiment of a cutter according to the invention; and
• Figure 4 is a side view of the cutter of Figure 3, with partial section on one side of the axis.

- As shown by way of example in Figures 1 and 2, or Figures 3 and 4, a cutter 1 according to the invention, which advantageously has an axial symmetry, comprises, in known manner, at one of its ends a fixing skirt 11 internally threaded for receiving the end of a drill rod, not shown, intended to rotate the cutting bit 1 during drilling operations.

_- The cutting edge 1 flares from the skirt 11 in a connecting section 12, and ends with a leading end 13 forming the cutting edge body. In the examples shown, the fixing skirt 11 and the body 13 are cylindrical, while the connection section is frustoconical.

In known manner, the cutting body 13 carries a plurality of plates 20, two per cutting in the examples shown, angularly distributed in an advantageously regular manner so as to distribute the forces well within the cutting edge. These plates have leading edges 21 and 22 projecting axially and radially.

These plates are attached, in known manner, by brazing, and are angularly separated by ramps 30 for evacuating slaughter debris.

According to the invention, the plates have a small radial dimension, of the order of half the radius of the body 13 in the example shown. They are arranged around a central spark gap 40, through a discontinuous peripheral ring 50 extending the cutting edge axially 1. Channels 60 for supplying pressurized fluid, generally water, pass through the discontinuous ring 50 and open near the edges 21; they are preferably straight; they open at their other end inside the skirt 11 where they are supplied with liquid through the rotary drive rod (not shown) by a device of any known type.

Several cutting edge configurations are possible depending on whether, taking into account the direction of rotation of the cutting edges indicated by the arrow F, the channels 60 open out in front of the edges 21, through the plates 20, or behind them. In order to avoid any difficulty in alignment when brazing the wafers, the invention recommends that the channels 60 preferably be provided outside of the wafers 20.

It should be noted that, for design reasons, the diameter of the channels 60 is clearly overestimated in the figures, 2 and 4 compared to reality. In practice, these channels are designed to provide, near the wafers, an injection of fluid under high pressure which can range up to 1000 bars and more, greater than the pressures currently used. The calibration of the jets thus injected, or even their orientation, is preferably ensured by injection nozzles 61 shown only in FIGS. 2 and 4.

Figures 1 and 2 illustrate a cutter according to the invention in which the fluid injection channels 60 open behind the associated plates 20.

These plates 20 have a radial thickness close to that of the crown 50. Their section is trapezoidal so that their external lateral face 23 is radially set back relative to the edge 22 and does not come into contact with the rock, or the material to be drilled. Likewise, the external front face 24 of each insert is inclined relative to the axis of rotation A of the cutting edge. Preferably, the transverse surface 51 of the crown 50 behind the plates is also inclined towards the rear, so as to keep the mouth of the channels 60 axially recessed with respect to the drilling front of the rock. In this way only the edges of the plates participate in the drilling.

The discontinuous crown 50, after the transverse zone 51 where at least one pressure fluid inlet channel opens, moves away from the rock to be drilled and is thus connected to an evacuation ramp 30.

As is apparent from Figures 1 and 2, such a ramp 30 is advantageously delimited by rectilinear surfaces 31, 32, 33, which can easily be obtained by milling. The discharge ramps 30 continue up to the height of the fixing skirt so that the debris can then be discharged between the wall of the drilled hole and the skirt 11, then the drive rod in rotation.

The surface 31 of each discharge ramp preferably terminates at the base of the following plate so as to facilitate the evacuation of rock debris along the front face of said plate from the edge 21.

In the example shown, the crown 50 surrounds a central spark gap 40 constituted by a cone 40a pointing towards the rock to be drilled. For manufacturing facilities, this cone is preferably attached. In addition, its axis is advantageously inclined relative to the axis A of rotation so as to undergo a slight precessional movement in rotation, which increases its efficiency.

FIGS. 3 and 4, on the other hand, illustrate a cutter according to the invention in which the injection channels 60 open out in front of the plates 20; these plates have a shape very close to that of the plates of FIGS. 1 and 2. Taking into account that the fluid jets are all the more effective for fracturing the rock that they are coherent, these jets preferably emerge near the rock to be drilled. The body 13 of the cutter comprises consequently a shoulder 14 rising axially towards the rock in front of each plate; the plates are thus attached in notches formed axially in the body 13. The front surface 15 of the shoulders 14 into which the channels 60 open is advantageously inclined towards the axis so as to evacuate the debris well towards the ramps. This evacuation is further facilitated by a surface 16 of connection between the front surface 15 and the straight surface 31 'of said ramp 30 which, as in the previous example, is preferably delimited by surfaces 31', 32 ', 33 'straight.

In the example shown in Figures 3 and 4, the central spark gap 40 is constituted by a pipe 40b for supplying pressurized fluid intended to burst a portion of rock not felled by the plates although already weakened and fractured. This channel 40b is preferably supplied by the same pressure source as the channels 60, so as to simplify the structure of the rotary drive rod to be implemented.

It should be noted that in the two examples shown, the plates 20 are arranged radially through the crowns 50, so that the edges 21 are not themselves radial, and that the plates thus present a drilling wedge 25 relayed during drilling by the edges 21 then 22. The drilling capacities of a wafer are thus optimized.

It goes without saying that many variant embodiments can be proposed by those skilled in the art without departing from the scope of the invention, which is defined by the appended claims. Thus, the number of plates, the position and the number of pressurized fluid injection channels, their direction, the inclinations of the various faces of the plates, of the crown or of the ramps, or even the structure of the central spark gap can be chosen according to the particular needs of each user, and each particular material to be drilled.

Claims (10)

1. Drill bit for rotary jet-assisted drilling, intended to be mounted at the end of a rotary drive rod, of the type comprising, opposite said rod, a plurality of drilling plates having edges of attack in radial and axial projection and angularly separated by debris discharge ramps, in combination with very high pressure fluid supply channels opening near said plates, characterized in that the plates (20) have a low radial dimension and are inserted, around a central spark gap (40), in a discontinuous peripheral ring (50) extending axially said cutter (1), which ring is crossed by said channels (60) for supplying fluid. 2. Cutter according to claim 1, characterized in that the discharge ramps (30) are limited by faces (31, 32, 33, 31 ', 32', 33 ') rectilinear. 3. Cutter according to claim 1 or claim 2, characterized in that it has an axial symmetry with respect to its axis of rotation (A). 4. Cutter according to any one of claims 1 to 3, characterized in that the central spark gap (40) is a cone (40a). 5. Cutter according to claim 4, characterized in that the cone (40a) is inclined relative to the axis of rotation (A). 6. Cutter according to claim 4 or claim 5, characterized in that the cone is attached. 7. Cutter according to any one of claims 1 to 3, characterized in that the central spark gap (40) is constituted by a channel (40b) for supplying pressurized liquid. 8. Cutter according to claim 7, characterized in that the various pressurized liquid supply channels (40b, 60) are supplied by the same pressure source. 9. Cutter according to any one of claims 1 to 8, characterized in that the plates have a drilling corner (25). 10. Cutter according to any one of claims 1 to 9, characterized in that the channels (60) for supplying pressurized fluid open out in front of the plates (20) through shoulders going up towards the material to be drilled. along said plates.

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