WO2002097232A1

WO2002097232A1 - Method and arrangement for rock drilling and tool and rock drill used in rock drilling

Info

Publication number: WO2002097232A1
Application number: PCT/FI2001/000524
Authority: WO
Inventors: Markku Keskiniva; Pekka Salminen; Jorma MÄKI; Pasi Latva-Pukkila
Original assignee: Sandvik Tamrock Oy
Priority date: 2001-06-01
Filing date: 2001-06-01
Publication date: 2002-12-05

Abstract

The invention relates to a method of rock drilling, in which method compressive stress is directed to the rock by a hammering apparatus (2) of a rock drill. After a predefined time delay from the compressive stress wave, a percussive torsional component is also directed to a bit, removing rock by cutting.The invention further relates to an arrangement for rock drilling, which arrangement comprises a rock drill (1) having a hammering apparatus (2) for creating a compressive stress wave in a tool (4) connected to the rock drill. The arrangement further comprises means for creating a percussive torsional stress wave in the bit for cutting the rock.The invention also relates to a tool used in rock drilling, which comprises an anisotropic section (7) where the primary compressive stress wave (FP) directed to the tool is divided into a secondary compressive stress wave (FS) and a torsional stress wave (FT).

Description

METHOD AND ARRANGEMENT FOR ROCK DRILLING AND TOOL AND ROCK DRILL USED IN ROCK DRILLING

The invention relates to a method of rock drilling, in which method rock is broken by creating a compressive stress wave by means of a hammering apparatus belonging to a rock drill to a tool arranged in the drill, whereby a bit at the outermost end of the tool is hit against the rock and causes compression stress in the rock.

The invention further relates to an arrangement for rock drilling, which arrangement comprises a rock drill having a hammering apparatus and a tool connectable to the rock drill, whereby the hammering apparatus is arranged to create a compression stress wave in the tool whose outermost end has a bit for breaking rock.

The invention also relates to a tool used in rock drilling, whose first end has fastening means for fastening to a rock drill and whose other end has a bit or fastening means for fastening such a bit used in breaking rock, whereby an impact impulse caused to the tool by the hammering apparatus of the rock drill is arranged to be transmitted in the tool as a compressive stress wave to the bit and to make the bit hit the rock being drilled. The invention also relates to a rock drill comprising a hammering apparatus for creating a compressive stress wave to a tool fastened to the rock drill.

Known methods of rock drilling and mining include cutting, crushing and hammering methods. Soft rock is usually drilled by pressing a tool at a certain feed force against the rock while rotating a bit, whereby the bit removes rock by cutting. The method is, however, only suited for soft rock, because hard rock would require an unreasonably great propulsive force and torque. Further, with hard rock the wear of the bit would be so intense that the method would no longer be economical. The crushing method is applied to all types of rock. In it, the tool comprises one or more rotating bits having bit studs. The tool is pushed against the rock and simultaneously rotated, whereby the bits crush the rock. In this method, a great feed force is required, since the rock is crushed by pressure. In addition, the breaking speed of rock is lower than with hammering methods. Hammering methods are most commonly used with hard rock. In a hammering method, the tool is rotated and hammered. The rock breaks mainly due to the impact. The rotation mainly ensures that the bit studs or other working parts of the bit always hit a new section. A rock drill usually comprises a hydraulic hammering apparatus, whose percussion piston creates the necessary compressive stress waves, and a rotating motor separate from the hammering apparatus. In this method, efficient rock breaking requires that the bit is heavily pressed against the surface of the rock. Thus, drilling equipment must be designed to endure heavy loads. In addition, the service life of tools is often very short. Another drawback with normal hammering drilling is that the breaking speed of the rock is not sufficient and that the breaking process requires a lot of energy.

It is an object of the present invention to provide a more efficient and economical solution for rock drilling.

The method of the invention is characterized in that when the working parts of the bit are inside the rock due to the compressive stress wave, a percussive torsional load is caused to the bit after a predefined time delay from the longitudinal impact of the bit, and that the bit rotating in a percussive manner removes rock by cutting.

Further, the arrangement of the invention is characterized in that the arrangement comprises means for directing a percussive torsional stress wave to the bit after a predefined delay from the compressive stress wave, while the working parts of the bit are inside the rock due to the compressive stress wave.

The tool of the invention is characterized in that the tool comprises an anisotropic section where a primary compressive stress wave caused in the tool is divided into two components, a secondary compressive stress wave and a torsional stress wave, and that said anisotropic section is at a predefined distance from the tip of the bit, whereby the torsional stress wave reaches the tip of the bit later by a time delay proportional to said distance than the secondary compressive stress wave. Further, the rock drill of the invention is characterized in that the rock drill or the tool being connected to it comprises means for creating a torsional stress wave to the tool and that the rock drill comprises a latch mechanism or the like allowing the tool to turn to a desired direction only, whereby the torsional stress caused in the tool is arranged to make the bit at the outermost end of the tool change position between impacts. The essential idea of the invention is that in addition to the longitudinal compressive stress wave caused by the hammering apparatus, a pulse-like torsional stress wave is caused in the rock through the bit. Then the compressive stress wave causes the working parts of the bit to penetrate the rock being drilled and possibly to cause cracks, and the torsional stress wave rotates in an percussive manner the working part of the bit which has penetrated the rock, thus making the rock cut. The two force components affecting the rock through the bit are timed in such a manner that the longitudinal impact of the tool takes place first and then, after the predefined delay, the rock is cut by means of the torsional component. The essential idea of a preferred embodiment of the invention is that the force caused by the impact of the hammering apparatus is divided into two components, the longitudinal force component of the tool and the torsional component rotating the bit, in such a manner that the energy content of said components is in desired proportion with respect to each other. Dividing the primary compressive stress wave into components is done at a predefined distance LQ_EN from the tip of the bit, whereby the force components progressing in a wave motion reach the tip of the bit at different times. Because the compressive stress wave progresses faster in the tool than the torsional stress wave, it reaches the bit first. The torsional stress wave makes the bit rotate only after a delay when the working parts of the bit have already hit the rock at full force. The length of the delay can be changed by changing the distance L_GE - Further, the essential idea of a second preferred embodiment of the invention is that the division of the primary compressive stress wave into two wave components is done by means of an anisotropic section formed in the tool on a section of a certain length. Anisotropicity can be due to the geometric properties of said section or to the internal structure of the material. According to an application, the tool comprises drill rods connectable to each other, and at least one, preferably the outermost, drill rod has a spirally grooved section at a distance LQ_EN from the tip of the bit, the grooved section forming a geometric anisotropic section in the tool. When the primary compressive stress wave encounters such an anisotropic section when progressing in the tool, a part of the energy of the primary compressive stress wave is converted to a torsional stress wave and a part of it continues as a compressive stress wave on towards the bit. The invention provides the advantage that drilling becomes more efficient that before. In drilling, first compressive stress is caused in the rock, thus forming cracks in the rock. Then after a suitable delay, cutting stress is directed to the rock material being removed. As is known, the tensile strength and shearing strength of rock are usually considerably smaller than its compression strength. The efficiency of the solution of the invention is essentially based on that a cutting impact is utilised in removing the rock. This way, the use of drilling energy is more economic. Another advantage is that the solution can be used with different rock types, since the ratio of compressive stress and cutting torsional stress can easily be altered to suit every need.

When the division of the primary compressive stress wave into components is done by means of an anisotropic section formed in the tool, the ratio between the compressive and torsional stress can be affected just by changing the tool. This way, the drill and other drilling equipment can remain the same. In extension rod drilling, it is enough that the drill rod comprising the anisotropic section is changed. Drill rods arranged between the hammering apparatus and the drill rod with the anisotropic section, and the joints between them do not affect the division into components or the timing of the compressive and torsional stress, since the division into components is only done in the drill rod after them. Geometric anisotropicity is quite easily achieved by arranging the anisotropic section by shaping the geometry of the tool arm or the drill rod. The anisotropic section can conveniently be made by making grooves, for instance, on the outer surface of a drill rod having otherwise constant dimensions.

The invention is described in greater detail in the attached drawings in which

Figures 1 and 2 show schematically the principle of some rock drills of the invention, Figure 3 shows schematically a detail of a tool of the invention,

Figure 4a and 4b show schematically the principle of drilling according to the invention,

Figure 5 shows schematically a drill rod of the invention, Figures 6a to 6d show schematically the division of a primary compressive stress wave into components when using the drill rod described in Figure 5, Figure 7 shows schematically a second way of arranging an anisotropic section based on geometric form into the tool, and

Figures 8 and 9 show schematically some arrangements according to the inventive idea. Figure 1 shows in a simplified manner drilling equipment of the invention. A rock drill 1 comprises a hammering apparatus 2 and rotating apparatus 3. The rotating apparatus transmits a continuous rotating force to a tool 4, by means of which a bit 5 connected to the tool changes its position after an impact and hits a new place in the rock with the next impact. The hammering apparatus usually has a percussion piston reciprocating by means of a pressure medium, the piston hitting the top of the tool 4 or an intermediate piece arranged between the tool and the hammering apparatus. The structure of the hammering apparatus can naturally be of another kind. The impact impulse can, for instance, be provided by means based on electromagnetism and with properties of a magnetostrictive material, for instance. Apparatuses based on such properties are also considered hammering apparatuses herein. The inner end of the tool can be connected to a rock drill and the outer end of the tool has a fixed or detachable bit 5 for breaking the rock. During drilling, the bit is pushed by means of a feeding apparatus against the rock. The bit is typically a drill bit having bit studs 5a, but other kinds of bit structures are also possible. Drilling deep holes, i.e. in extension rod drilling, a number of drill rods 6a to 6c forming a tool are added between the bit and the drill depending on the depth of the hole.

Impact energy provided by the hammering apparatus 2 is transmitted along the drill rods 6a to 6c as a compressive stress wave towards the bit 5 at the end of the outermost drill rod. When the stress wave hits the bit, the bit and the bit studs 5a hit the material being drilled causing a strong compressive stress. The rock being drilled cracks due to the strong compressive stress. According to the idea of the invention, the primary compressive stress wave caused by the hammering apparatus is divided into two components, a torsional stress wave and a longitudinal secondary compressive stress wave of the tool. The figure shows in the outermost drill rod 6c an anisotropic section 7 where the division into components takes place. The anisotropic section is arranged at a predefined distance L_GEN from the tip of the bit. The distance LQEN is defined by calculation, simulation or by experimental tests in such a manner that the secondary compressive stress wave obtained by division meets the tip of the bit first, and only after a desired time delay from the longitudinal impact of the tool caused by the compressive stress wave, does the torsional stress wave reach the bit and make it rotate. The propagation speeds of the compressive and torsional stress waves are different. In addition, the propagation speeds of the waves depend on the material of the tool. In a normal drill rod, the speed of compressive stress is approximately 5, 180 m/s and the speed of the torsional wave is approximately 3,220 m/s. Since there is a delay between the compressive stress and the torsional stress, the compressive stress has had time to use its full force before the bit is rotated. Thus, the compressive force has had time to abate slightly before the torsion, making the frictional forces smaller and the force required for rotation reasonable.

Figure 2 shows a solution in which a tool connected to a rock drill comprises a uniform arm with a bit at its free end. Such an arrangement can be used in drilling shallow holes, for instance. In this case, too, an anisotropic section has been formed in the tool at a predefined distance L_GE_N from the tip of the bit.

Figure 3 shows a detail of the tool of the invention. Metals are typically isotropic, which means that their properties in all directions are the same. Materials whose properties are different in different directions are called anisotropic. When the main rigidity axes E-, and E₂ form a 0° to 90° angle α with the longitudinal axis of the tool, a force transmitted to such a section is divided in proportion to the size of the angle α. If the angle α is 0° or 90°, division into components does not occur in the anisotropic section. Anisotropicity can be achieved by influencing the geometry of a structure or by means of the internal structure of a material. An example of the latter is rolling of metals, with which the internal structure of a material can be oriented in a certain manner. Further, reinforced fibres, for instance, of plastic and composite structures can be oriented, whereby the material acts in an anisotropic manner. Geometrically this is simplest arranged by making spiral grooves 8 on the outer surface of the drill rod on a section of predefined length and with a certain gradient (corresponding to the angle α), as shown in the figure. In this case, the dimensioning of the geometrically adjusted section, for instance the profile, depth and gradient of the grooves, decide the ratio of the division of the compressive stress wave F_P into the secondary compressive stress wave F_s and torsional stress wave F_τ in the anisotropic section. Typically, the compressive stress is designed to be greater than the torsional stress, because the compressive strength of rocks is higher than the shear strength. Compression must be made with a great force so as to make the bit penetrate the rock and create cracks. After this, only a smaller force is required to cut the rock off.

Figures 4a and 4b show the principle of the drilling of the invention. A secondary compressive stress wave F_s causes strong compressive stress in the rock, whereby the rock is typically crushed under high pressure into powder in the contact area 9 between the bit and the rock, and cracks 10 extending into the rock are created. Figure 4b shows the second stage of drilling. Because the bit studs 5a are due to the impact caused by the secondary compressive stress still inside the rock, the percussive torsional movement causes the bit studs to cut the rock material when the bit rotates. The area being cut is marked with reference number 11 in the figure. The cutting is aided by the fact that cracks have been formed in the rock due to compressive stress. The chippings created during drilling are more rough in composition than the powder-like chippings created during conventional hammering drilling, which fact also shows that in this kind of drilling, the use of energy is more economical than before. Example:

Figure 5 shows a drill rod with which experimental tests were made. The measurement results of the drilling are presented later in Figures 6a to 6d. A 500 mm anisotropic section L_A was formed at about the centre point of the drill rod whose total length is 3,660 mm. The measures L-i and L₂ marked in the figure are 1,580 mm in size. In such a case, the distance LQ_EN between the tip of the bit and the anisotropic section becomes approximately 1 ,700 mm when using conventional bits. A grooving of 500 mm having 8 pieces of 10 mm deep and about 5 mm wide spiral grooves at a 40° angle to the longitudinal axis of the drill rod was made in the anisotropic section. The angle α affecting the division of the primary compressive stress wave is thus in this case said 40°.

Figure 6a shows the primary compressive stress wave measured before the anisotropic section from the drill rod shown in the previous figure. Figure 6b shows the secondary compressive stress wave F_s created by division and measured from the bit. Figure 6c shows the torsional stress wave F_τ created by division and moving towards the rock. Further, Figure 6d shows the torsional wave reflected back towards the hammering apparatus from the grooved section. As can be seen when comparing Figures 6b and 6c, the secondary compressive stress wave is in its energy content considerably larger than the torsional stress wave. The figures further show the phase difference caused by the difference in speed in the compressive and torsional stress waves. Because the momentum of the system must be maintained, balancing torsional wave components are created in the drill rod. In the solution of the example, the rock-cutting torsional wave component F_τ is balanced by both the opposing torsional wave component F_T1 (Figure 6c) coming after the component F_τ and the torsional wave components F_T2 (Figure 6d) reflecting back from the grooved section. The interrelation of the balancing components can be adjusted by the geometry of the grooved section.

Figure 7 shows the principle of a second anisotropicity achieved by geometric form. The tool may have counter surfaces slanted with respect to its longitudinal axis, whereby the compressive stress wave progressing in the tool is divided into components in proportion to the size of the slanted angle α. In practice, it is possible to equip the end surfaces settling against each other of pipe-like drill rods connected to each other, with circular slanted counter surfaces. Alternatively, such a section can be formed on the outermost drill rod only.

A percussive torsional stress wave can alternatively be formed by means of a torsion apparatus 12 arranged to the drill, as shown in Figure 8. The torsion apparatus may be mechanical, electromagnetic or use a pressure medium. The torsion apparatus may be an apparatus which converts a part of the impact of the hammering apparatus into a torsional impact. At its simplest it resembles an impact screwdriver-type solution. On the other hand, the torsion apparatus may be independent of the hammering apparatus, in which case it produces the necessary force for the torsional impact itself. A sufficiently long time delay between the compressive stress wave and the torsional stress wave is not created automatically with especially short tools in which the distance LQEN between the drill and the tip of the bit is short. Correspondingly, if the bit is at the end of a long drill rod combination, a problem may arise from the torsional stress wave reaching the bit too late in comparison with the compressive stress wave. In such a case, the impacts produced by the torsion apparatus and the impacts produced by the hammering apparatus can be timed with each other as necessary.

One possibility is to arrange the bit to rotate by means of the torsional stress wave created in the tool. Then, the torsional stress wave alone causes the bit to rotate and the bit studs to change place for a new impact. A conventional rotating motor is thus not necessarily needed any more in a drill. The drill then becomes simpler in structure and its manufacturing and operating costs lower than before. In addition, its structure is smaller and lighter. To make the rotating of the bit with the torsional stress wave possible, the equipment must comprise means, such as a one-way clutch, a latch mechanism or the like, which allow the rotation of the tool into a desired direction only. Such a latch mechanism 13a can be arranged between the bit and the outermost drill rod (Figure 9). The bit rotates in the rock a step forward with each torsional stress wave. The latch mechanism stops the bit from rotating back. Another alternative is to arrange a latch mechanism 13b or the like to the drill between the tool and the drill. A reflecting torsional stress wave is then utilised in rotating the tool.

The drawings and the description related to them are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the claims. Thus, the solution of the invention can also be applied to rock drilling in which the bit is not rotated by means of a rotating motor. This includes some of the mining methods. Further, the invention can be applied to rock breaking apparatuses, such as impact hammers/demolition apparatuses arranged in excavators. It should be noted that a drill rod or drill rods comprising an anisotropic section need not be arranged as the outermost in an extension rod combination, but a normal drill rod can be placed outermost. The essential thing is that the distance LQ_EN is made suitable.

Claims

1. A method of rock drilling, in which method a rock drill (1) is used, the rock drill comprising a hammering apparatus (2), a tool (4) arranged to the drill, and, at the outermost end of the tool, a bit (5), and in which method rock is broken by creating a compressive stress wave into the tool (4) by means of the hammering apparatus (2), whereby the bit (5) is hit against the rock and causes compressive stress in the rock, characterized in that when the working parts of the bit are inside the rock due to the compressive stress wave, a percussive torsional load is caused in the bit after a predefined time delay from the longitudinal impact of the bit, and that the bit rotating in an percussive manner removes rock by cutting.

2. A method as claimed in claim ^ characterized in that a primary compressive stress wave (F_P) caused by the hammering apparatus (2) of the rock drill is divided in predefined proportion into two components; a secondary compressive stress wave (F_s) and a torsional stress wave (F_T).

3. A method as claimed in claim 2, characterized in that a primary longitudinal compressive stress wave is caused in the tool (4) by the hammering apparatus, the wave being divided into two components by means of an anisotropic section (7) formed in the tool.

4. An arrangement for rock drilling, which arrangement comprises a rock drill (1) having a hammering apparatus (2) and a tool (4) connectable to the rock drill, whereby the hammering apparatus is arranged to create a compressive stress wave in the tool whose outer end has a bit for breaking rock, characterized in that the arrangement comprises means for directing a percussive torsional stress wave to the bit after a predefined time delay from the compressive stress wave while the working parts of the bit are inside the rock due to the compressive stress wave.

5. An arrangement as claimed in claim 4, characterized in that the arrangement comprises means for dividing the primary compressive stress wave (F_P) caused in the tool by the hammering apparatus into two components, a secondary compressive stress wave (Fs) and a torsional stress wave (F_τ).

6. An arrangement as claimed in claim 5, characterized in that the tool comprises an anisotropic section (7) which converts a part of the energy of the primary compressive stress wave into torsional stress.

7. An arrangement as claimed in claim 6, characterized in that the tool comprises drill rods (6a to 6c) connectable to each other, and that the anisotropic section (7) is formed in at least one drill rod at a distance (L_GEN) from the tip of the bit (5).

8. An arrangement as claimed in claim 7, characterized in that the anisotropic section (7) is in the outermost drill rod (6c).

9. An arrangement as claimed in claim 7 or 8, characterized in that, between the bit and the tool, means are arranged, such as a latch mechanism, allowing the bit to rotate due to the torsional stress wave into a desired direction only.

10. A tool used in rock drilling, which comprises at its first end fastening means for fastening to a rock drill (1) and at its second end a bit (5) or fastening means for fastening such a bit used in breaking rock, whereby an impact impulse caused in the tool (4) by means of a hammering apparatus (2) of a rock drill is arranged to transmit in the tool as a compressive stress wave to the bit and to cause the bit to hit the rock being drilled, characterized in that the tool comprises an anisotropic section (7) where a primary compressive stress wave (F_P) caused in the tool is divided into two components, a secondary compressive stress wave (F_s) and a torsional stress wave (F_τ), and that said anisotropic section is at a predefined distance (LQ_EN) from the tip of the bit (5), whereby the percussive torsional stress wave reaches the tip of the bit later by a time delay proportional to said distance (L_GEN) than the secondary compressive stress wave.

11. A tool as claimed in claim 10, characterized in that the tool (4) comprises drill rods (6a to 6c) connectable to each other, whereby the bit (5) is arranged at the free end of the outermost drill rod (6c), and that the anisotropic section (7) is arranged in the drill rod.

12. A tool as claimed in claim 11, characterized in that the anisotropic section is in the outermost drill rod.

13. A tool as claimed in any one of claims 10 to 12, characterized in that the anisotropicity is formed by means of the internal structure of the tool material.

14. A tool as claimed in any one of claims 10 to 12, characterized in that the anisotropicity is formed by means of the geometry of the tool.

15. A tool as claimed in claim 14, characterized in that spiral grooves (8) are formed in the anisotropic section on the outer surface of the tool.

16. A rock drill comprising a hammering apparatus (2) for creating a compressive stress wave in a tool (4) connectable to the rock drill, characterized in that the rock drill or the tool connectable to it comprises means for creating a torsional stress wave in the tool, and that the rock drill comprises a one-way clutch (13a, 13b) or the like allowing the tool to rotate in a desired direction only, whereby the torsional stress wave caused in the tool is arranged to make a bit (5) at the outer end of the tool change position between impacts.