WO2015126315A1

WO2015126315A1 - Rock drilling machine, method for rock drilling and rock drill rig

Info

Publication number: WO2015126315A1
Application number: PCT/SE2015/050179
Authority: WO
Inventors: Per-Erik Larsson; Erik JAKOBSSON
Original assignee: Atlas Copco Rock Drills AB
Current assignee: Epiroc Rock Drills AB
Priority date: 2014-02-18
Filing date: 2015-02-17
Publication date: 2015-08-27
Anticipated expiration: 2016-08-18
Also published as: WO2015126315A9; SE538090C2; SE1450188A1

Abstract

A rock drilling machine (2) which is adapted to intermittently produce shock wave pulses for transfer over a drill string (3) to a rock disintegrating drill bit (6). The rock drilling machine includes: a force setting unit (8) which is arranged to periodically subject the drill string (3) to a setting force in said drilling direction, and a control unit (11) which is arranged to activate the force setting unit to initiate said setting force before a point of time for producing at least a selection of said shock wave pulses in order to ensure enhanced rock contact of the drill bit (6) when performing an impact. The invention also concerns a method and a rock drill rig.

Description

ROCK DRILLING MACHINE, METHOD FOR ROCK DRILLING

AND ROCK DRILL RIG

FIELD OF THE INVENTION

The invention relates to a rock drilling machine which is adapted to intermittently produce shock wave pulses for transfer over a drill string to a rock disintegrating drill bit in a drilling direction. The invention also relates to a method for rock drilling and a rock drill rig.

BACKGROUND OF THE INVENTION

For the purpose of ensuring contact between a drill bit and rock to be worked, according to today's technology, a feed force is applied to the drill bit through the drill string. This feed force acting in the drilling direction is typically provided by forcing means acting on a slide supporting the rock drilling machine and being guided on a feed beam.

In today's rock drilling machines, the feed force is transferred to a shank adapter, which comprises a first element in the drill string, as seen from the rock drilling machine. The transfer of feed force to the shank adapter is normally provided by a damping unit for also provides damping of shock wave reflexes which emanates from the drill bit striking against rock and which i.a. varies with the degree of rock contact of the drill bit.

Besides the feed force, during percussive rock drilling, there are initiated intermittent shock waves through the drill string against the drill bit emanating from a percussive piston which is arranged movable to and fro inside a

percussion device of the rock drilling machine and which performs strikes against the shank adapter. The impulse flow of these shock waves can be expressed as m f, where m = piston weight, v = striking velocity of the piston and f = frequency.

The damping force that is transferred as a force to the shank adapter over the damping piston can be expressed as damp " A_damp where P_damp is the mean value of the damping pressure and Adamp is the pressure area of the damper.

A thumb rule for describing what the magnitude of the feed force should be in relation to the impulse flow is:

Pfeed = 3 · ITTVf.

A reason why the feed force needs to be that high is to ensure that the drill bit has contact with the rock in order to make it possible for it to crush rock with the aid of the shock wave. If the drill bit would not be in contact with the rock it would, besides reduced drilling capacity, also result in that the shock wave energy could not be delivered to the rock resulting in heating and increased wear of the threads between the individual drill string components.

Another reason for having relatively high feed force is that during drilling with threaded drill string components, there will be problems of maintaining threads tightened if the feed force is low.

Since high feed forces requires correspondingly powerful equipment for the entire rig, resulting wear of the drill string and problems with hole straightness , there is ongoing development work aiming to provide more reliable and durable components .

AIM AND MOST IMPORTANT FEATURES OF THE INVENTION

It is an aim to provide a rock drilling machine and a method according to the above that address the problems of the background art and at least reduces these problems.

These aims are obtained in respect of a rock drilling machine and a method according to the above in that the rock drilling machine includes:

- a force setting unit which is arranged to periodically subject the drill string to a setting force in said drilling direction, and

- a control unit which is arranged to activate the force setting unit to initiate said setting force before a point of time for producing at least a selection of said shock wave pulses in order to ensure enhanced rock contact of the drill bit when performing an impact .

Hereby is achieved that it is made possible to momentary apply a higher force of the drill string to the drill bit when this force is really required, which is prior to a shock wave reaching the drill bit. With the aid of said shock wave, the drill bit will crush the meeting rock. Hereby several

advantages are obtained. The mean value of the feed force delivered from the rig can hereby be set lower but in spite of that the force pressing the drill bit against the rock when the drill bit performs the strike can be as great as during conventional rock drilling or even be allowed to be greater. This gives potential for higher working speed - better

drilling rate.

Furthermore, components in the rock drill rig can be dimensioned for lower continuous forces and/or better

application against the rock for the drill bit before the strike itself is performed. By in practice the setting force in the drill string being pulsed, the buckling risk can be reduced compared to if a correspondingly great constant force would be applied, which increases operational security and enhances drill string economy which can also result in that drill string components can be dimensioned for lower forces.

Hole straightness can also be enhanced since lower continuous feed force can be used and the straightness problems that are typical results from high feed forces can be avoided.

According to the invention, the force setting unit can also be activated to initiate said setting force for a

selection of said shock wave pulses whereby it is possible e.g. to initiate said setting force in respect of every second, every third etc. shock wave pulse. In respect of high frequency percussion devices it can be sufficient for reaching a totally seen effective drilling this way by ensuring high force setting with greater time distances when at least in some operational cases it can be sufficient with lower force application for the rest of the strikes in order to have good rock disintegration.

It is preferred that the force setting unit includes a damping piston which is arranged for transferring feed force to the drill string. Hereby is advantageously used a component already existing inside the rock drilling machine which is integrated in the force setting unit in a simple and effective way and to a low cost. Suitably a chamber associated with the damping piston is connectable to a pressure source for achieving said setting force. If said chamber is a damping chamber being used for normal damping function, the costs of manufacture and development can be minimized.

It is also possible that the force setting unit includes at least one setting piston being independent from the damping piston, which results in that the different functions can be held independent from each other.

The invention is particularly applicable when the rock drilling machine includes a percussion device with a

percussive piston for action against a shank adapter and being movable to and fro in a cylinder. The control unit then advantageously includes a valve body portion being carried by the percussive piston, the position of which inside the cylinder being arranged to control activation of the force setting unit through cooperation with a valve mouth.

In a preferred aspect the rock drilling machine includes an impulse device with an impulse piston adapted for action against a shank adapter which is only movable to a very limited degree in an axial direction of the rock drilling machine. In this case the control unit suitably includes a setting valve, which for activation of the force setting unit is controllable in dependence of a main control valve of the impulse device.

The invention also concerns a method for rock drilling, wherein shock valve pulses are produced intermittently in a drilling direction and are transmitted over a drill string to a rock disintegrating drill bit, wherein a setting force is periodically brought to subject the drill string in said drilling direction, and said setting force is initiated before a point of time for producing at least a selection of said shock wave pulses in order to ensure enhanced rock contact of the drill bit when performing an impact. Advantages

corresponding to the above are obtained according to the dependent method features :

- the feed force is advantageously transferred to the drill string through a damping piston.

- a chamber being associated with the damping piston is suitably connected to a pressure source for achieving said setting force.

- a damping chamber is suitably connected to a pressure source for providing said setting force.

- said setting force can also be set by a setting piston being independent of the damping piston.

- the shock wave pulses are preferably produced by a

percussion device with a percussive piston being arranged for action against a shank adapter and being movable to and fro in a cylinder.

- activation of the force setting unit is then preferably controlled by a valve body portion being carried by the percussive piston.

- in a variant of the invention the shock wave pulses are produced by an impulse device having an impulse piston being arranged for action against a shank adapter.

- a setting valve being controllable in dependence of a main control valve of the impulse device then suitably activates the force setting unit.

The invention also relates to a rock drill rig including a rock drilling machine according the above.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in greater detail by way of embodiments and with reference to the annexed drawings, wherein :

Fig. 1 diagrammatically illustrates a rig equipped with a device according to the invention,

Fig. 2 shows a partial axial section of a percussion device according to a first embodiment of the invention,

Fig. 3 shows a partial axial section of a percussion device according to a second embodiment of the invention,

Fig. 4 shows a partial axial section of a percussion device according to a third embodiment of the invention,

Fig. 5 shows a partial axial section of a percussion device according to a fourth embodiment of the invention,

Fig. 6 shows a partial axial section of an impulse device according to the invention, and

Fig. 7 shows a diagram illustrating forces influencing the drill bit in respect of a rock drilling machine according to the invention.

DESCRIPTION OF EMBODIMENTS

In the following embodiments like or similar elements are allotted the same reference numerals. The figures are

simplified and illustrate for clarity reasons in certain cases not all elements on both sides of a symmetry axis.

Fig. 1 shows diagrammatically a rock drill rig with a carrier vehicle which over a carrier arm supports a feed beam 4 whereon a rock drilling machine 2 is movable. As usual, the rock drill rig is equipped with (not shown) means for applying a feed force in a drilling direction R to the rock drilling machine 2. Furthermore, the rock drilling machine 2 produces intermittent shock wave pulses in the drilling direction R via a drill string 3 to a drill bit 6 which is positioned most distally on the drill string 3 and which performs crushing strikes against the rock in a borehole 5.

In the embodiment of a percussion device, which is diagrammatically illustrated in fig. 2, a shank adapter 14, which is a most proximal element in the drill string, is subjected to percussive action form a percussive piston 7 which is movable to and fro inside a cylinder in a housing H of the rock drilling machine. The percussive piston 7 is driven with the aid of a drive fluid which is controlled to intermittently act on surfaces on parts of the percussive piston that are exposed to pressure in order to drive the percussive piston in a striking direction and in a return direction respectively.

Radially outside the percussive piston 7, there is applied a damping piston 9 against the shank adapter 14 via a sleeve 19. In this case the damping piston is part of a single damper device. The damping piston 9 has the purpose of transferring feed force to the shank adapter 14 and is for that purpose applied with a damping force emanating from a damping chamber 10 which is pressurizable from a pressure source P whereby a piston portion of the damping piston 9 is active inside the pressurizable chamber 10. In case of shock wave reflexes from the drill string, the damping piston in principle acts as a spring, pressing the damping piston opposite to the striking direction against the action of the damping force .

According to the invention, a force setting unit 8 is arranged, through which the damping piston 9 is also

intermittently affected by a setting force in the striking direction. Hereby the setting force influences the shank adapter 14 and is transferred over the drill string all the way to the drill bit in order to ensure that it has good rock contact during a short period of the cycle of the percussion device when the percussive piston 7 performs its strike against the shank adapter 14.

For that purpose is with the aid of this force setting unit 8 according to the invention provided that the hydraulic pressure on the damping piston 9 is increased in said drilling direction R and in the shown embodiments in that during these short time periods into the damping chamber 10 there is supplied pressure fluid from an auxiliary pressure fluid source 18 which provides a higher fluid pressure than the damping pressure.

This can be arranged for in many different ways but is in fig. 2 illustrated with a control unit 11 including a valve mouth 13 which cooperates with a valve body portion 12

comprising a land portion on the percussive piston 7. When the percussive piston 7 moves to the striking position, according to this aspect of the invention, the valve mouth 13 will be opened by said valve body portion 12 uncovering the valve mouth before the percussive piston 7 hits the shank adapter 14. Through a suitable adapted arrangement of fluid conduits which in an open position of the valve mouth 13 leads pressure fluid from said auxiliary pressure fluid source to a setting inlet 20 in the damping chamber 10, a pressure increase will occur in the damping chamber 10 and the damping piston 9 will be pressed against the shank adapter 14. The so created setting force will now be transmitted over the drill string to the drill bit before the point of time of the impact of the percussive piston against the shank adapter. Hereby the impact performed by the drill bit onto the rock will be performed with the drill bit more reliably pressed against the rock which results in better impact efficiency and better

conditions for crushing rock in different operational

conditions .

In fig. 3 is shown a percussion device with a differently constructed damper which in this case is a double damper device. Hereby a damping flow Q is continuously supplied to a first damping chamber 15. A damping slot/throttle slot is established between this camber and a second damping chamber which is indicated with 16. According to the invention, in analogy with the embodiment according to fig 2, there will be provided setting of the damping piston 9 against the shank adapter 14 immediately before the percussive piston 7 strikes against the shank adapter 14 in that a pressure increase will occur in the first damping chamber 15 through for example a conduit and valve mouth arrangement corresponding to what is described in connection with fig. 2. This damper is

advantageously used in order to provide a specified striking position even when it is used and adapted to be part of the present invention. A specified striking position or floating position is ensured through a per se previously known

arrangement with one (or more) float hole 40 in the wall of a cylinder space containing the damping piston 9 in combination with a control edge 41 on the damping piston 9.

In the embodiment according to fig. 4, the damping piston 9 has been provided with one additional piston portion which is active in a special setting chamber 17. This setting chamber 17 is pressurizable corresponding to what is described in connection with figs. 2, 3, wherein in this case the setting function is thus integrated with the damping piston 9 but separate from the first damping chamber 15 and the second damping chamber 16 being included in a double damper system.

In the embodiment according to fig. 5 is arranged a setting piston 23 concentrically between the percussive piston 7 and a damping piston 9, wherein the setting piston 23 cooperates with a setting chamber 24, axially on the opposite side of the setting piston 23, as seen from the shank adapter 14. The setting chamber 24 is pressurizable corresponding to what is described in connection with the above embodiment. In the embodiment according to fig. 6 is shown an impulse device, including an impulse piston 26 which is active in an impulse chamber 29 and is arranged to emit shock wave pulses to a shank adapter 25. A counter chamber 30 is arranged in the drilling direction as seen from the impulse piston 26.

Shock wave pulses can for example be produced in that a high pressure increase abruptly occurs in the impulse chamber 9 on the side of the impulse piston 26 being directed from the shank adapter 25.

Alternatively, shock wave pulses can be produced in that high pressure is initiated in the impulse chamber 29 as well as in the counter chamber 30, whereupon the pressure in the counter chamber 30 is abruptly released.

In order to provide a setting force according to the invention, a force setting unit with a setting piston 27 is arranged radially outside a rod-shaped portion belonging to the impulse piston 26, said setting piston 27 being arranged to be allied against the radially outer part of the shank adapter 25. The setting piston can be alternatively arranged to act against a radially inner part. The setting piston 27 is active in a setting chamber 28 which is pressurizable

corresponding to what is shown and described in connection with the above embodiments. Since no percussive piston can be used as a valve, in the case of an impulse device, a control unit can be used having a valve device being controlled to pressurize the setting chamber 28 to set the setting piston 27 against the shank adapter 25 immediately before a shock wave pulse is intended to be initiated.

Fig. 7 is a force (F) - time (t) - diagram showing forces affecting the drill bit of a rock drilling machine according to the invention. With full lines are illustrated very short shock wave pulses 30 with high intensity for transmittal to a drill bit and being produced in a percussion device having a to and fro movable percussive piston or in an impulse device. The curve 31 with dot interrupted line illustrates the

principle of the invention by showing the sum of a feed force and a setting force affecting the drill bit. The lower force level 32 which prevails essentially between the shock wave pulses 30 produced by the impact in the percussion device (or the impulse device) are comprised of feed force delivered from the drill rig according to the above. The force increases at 33 indicate that a setting force has been applied in the drill string which together with the feed force can be greater than a conventional feed force which is indicated with interrupted line and reaches the force level 34.

As is clarified from this diagram, the force affecting the drill bit for force setting purposes can be greater during performing the rock disintegrating strikes but smaller as seen over an impact cycle.

The invention can be modified within the scope of the following claims. Pressurization of setting pistons can thus also in respect of percussion devices with percussive pistons be made in different ways than through control units with valve portions on the percussive piston. As an example, a control unit can be arranged with which the position of the percussive piston is detected and the detected position can be arranged for controlling initiation of the setting force.

The position of the percussive piston can thereby be measured over a sensor whose signal is transferred to a control unit which in turn controls the variation in the setting force according to the above. Examples of sensors that are suitable for this purpose are capacitive sensors,

inductive sensors or laser sensors.

The periodic setting force can also, beside the hydraulic mechanical methods described above, be produced electro- mechanically over an electromagnet which can be activated such that the drill string is subjected to the periodic setting force or pneumatically over pressure variations in a gas affecting a force-producing area for the same purpose.

Also purely mechanical solutions are possible, for example by having the percussive piston pressing against the shank adapter over a spring immediately before the percussive piston hits the shank adapter.

Claims

1. Rock drilling machine (2) which is adapted to

intermittently produce shock wave pulses for transfer over a drill string (3) to a rock disintegrating drill bit (6) in a drilling direction (R) , characterized in that the rock drilling machine includes:

- a force setting unit (8) which is arranged to periodically- subject the drill string (3) to a setting force in said drilling direction, and

- a control unit (11) which is arranged to activate the force setting unit to initiate said setting force before a point of time for producing at least a selection of said shock wave pulses in order to ensure enhanced rock contact of the drill bit (6) when performing an impact.

2. Rock drilling machine according to claim 1, characterized in that the force setting unit includes a damping piston (9) which is arranged for transferring feed force to the drill string (3) .

3. Rock drilling machine according to claim 2, characterized in that a chamber (10; 15; 17) associated with the damping piston (9) is connectable to a pressure source (18) for achieving said setting force.

4. Rock drilling machine according to claim 3, characterized in that said chamber (10; 15) is a damping chamber.

5. Rock drilling machine according to claim 2, characterized in that the force setting unit (8) includes at least one setting piston (23) being independent from the damping piston (9) .

6. Rock drilling machine according to any one of the claims 1

- 5, characterized in that the rock drilling machine (2) includes a percussion device with a percussive piston (7) for action against a shank adapter and being movable to and fro in a cylinder.

7. Rock drilling machine according to claim 6, characterized in that the control unit (11) includes a valve body portion (12) being carried by the percussive piston, the position of which inside the cylinder being arranged to control activation of the force setting unit (8) through cooperation with a valve mouth .

8. Rock drilling machine according to any one of the claims 1

- 5, characterized in that the rock drilling machine (2) includes an impulse device with an impulse piston (26) adapted for action against a shank adapter (25) .

9. Rock drilling machine according to claim 8, characterized in that the control unit (11) includes a setting valve, which for activation of the force setting unit is controllable in dependence of a main control valve of the impulse device.

10. Method for rock drilling, wherein shock valve pulses are produced intermittently in a drilling direction and are transmitted over a drill string (3) to a rock disintegrating drill bit (6) ,

characterized in

- that a setting force is periodically brought to subject the drill string (3) in said drilling direction, and

- that said setting force is initiated before a point of time for producing at least a selection of said shock wave pulses in order to ensure enhanced rock contact of the drill bit (6) when performing an impact .

11. Method according to claim 10, wherein the feed force is transferred to the drill string through a damping piston (9) .

12. Method according to claim 11, characterized in that a chamber being associated with the damping piston is connected to a pressure source for achieving said setting force.

13. Method according to claim 12, characterized in that a damping chamber is connected to said pressure source (18) .

14. Method according to claim 11, characterized in that said setting force is set by a setting piston (23) being

independent of the damping piston (9) .

15. Method according to any one of the claims 10 - 14, wherein the shock wave pulses are produced by a percussion device with a percussive piston (7) being arranged for action against a shank adapter and being movable to and fro in a cylinder.

16. Method according to claim 15, characterized in that activation of the force setting unit is controlled by a valve body portion being carried by the percussive piston (7) .

17. Method according to any one of the claims 10 - 14, wherein the shock wave pulses are produced by an impulse device having an impulse piston (26) being arranged for action against a shank adapter.

18. Method according to claim 17, characterized in that a setting valve being controllable in dependence of a main control valve of the impulse device activates the force setting unit.

19. Rock drill rig including a carrier vehicle which over a carrier arm supports a feed beam (4) where a rock drilling machine (2) is arranged, wherein the rock drilling machine is a rock drilling machine according to any one of the claims 1 - 9.