EP3548691A1

EP3548691A1 - Method, apparatus and holder for mounting of a drill bit

Info

Publication number: EP3548691A1
Application number: EP17875615.1A
Authority: EP
Inventors: Johan Engblom
Original assignee: Epiroc Rock Drills AB
Current assignee: Epiroc Rock Drills AB
Priority date: 2016-11-29
Filing date: 2017-10-31
Publication date: 2019-10-09
Anticipated expiration: 2037-10-31
Also published as: CN110036176A; EP3548691C0; RU2750372C2; CA3043152A1; AU2017366970A1; AU2017366970B2; RU2019120025A; EP3548691A4; ZA201902985B; WO2018101870A1; SE541693C2; EP3548691B1; RU2019120025A3; CL2019001291A1; SE1651565A1; CN110036176B

Abstract

Herein a method (100), a device (21) and a holder (17) for rock drilling is described. The method (100) comprises the steps of: aligning (101 ) a drill rod (3) arranged at a first drilling unit (11) by using a first arm (9) towards a drill bit (1) placed in a fixedly arranged holder (17) adapted to hold at least two drill bits so that the axis of rotation of the drill rod (Ab) substantially coincides with an axis of rotation (Ak) of the drill bit (1), wherein a free movement of the first drilling unit (11) in relation to the holder (17) is permitted, to displace (103) the drill bit (3) axially forward towards the drill bit (1) to a first position of the drill bit (3) permitting mounting of the drill bit (1), mounting (105) the drill bit (1) on the drill rod (3) and displacing (107) the drill rod (3) axially backward to a second position in which the drill bit (1) has been removed from the holder (17).

Description

METHOD, APPARATUS AND HOLDER FOR MOUNTING OF A DRILL BIT

TECHNICAL FIELD

Present invention relates to equipment which may be used in, for example, mining industry. More specifically, the invention relates to a method and to an apparatus for mounting a drill bit adapted for rock drilling, for example in conjunction with tunnelling, and to a holder that can be used for the mounting.

BACKGROUND

In conjunction with tunneling or work in a mine, you need to drill holes for an explosive to be placed in the holes. Mountain drilling is usually carried out with specially designed machines adapted for mining and tunnels. The number of boreholes in a round of shots may vary depending on the bedrock. At tunneling in a harder rock, up to 70 well holes may need to be drilled for a blast. Hard bedrock causes drill bits in the drill to wear quickly and need to be replaced for regrinding. A drill bit is usually only enough to drill 1 to 2 holes before it needs to be replaced.

Historically, the replacement of a worn drill bit was performed manually by an operator. In case of manual change, the drilling machine must be switched off which interferes with the operating process. Manual switching can also cause damage to the operator who performs the change.

Recently, a number of solutions have been developed to automate the change of drill bit. These solutions usually use a magazine and a complicated equipment to handle the magazine's movement when changing. A disadvantage of known solutions is that they often include many moving parts, which results in increased risk of downtime due to increased risk of breakdown of the parts in the very demanding and often dusty environment they are used in.

SUMMARY

An object of the present invention is thus to improve operational reliability at rock drilling. This object is achieved according to one aspect of the present invention by a method for mounting a drill bit on a drill rod at a rock drilling machine comprising a base unit and a first arm freely movably attached to the base unit. In other words, the first arm is mounted to the base unit, for example via the one end of the first arm so that an opposite end of the first arm can move freely relative to the base unit.

The rock drilling machine comprises a first drilling unit freely movably attached to said first arm. Thus, the first drilling unit is mounted at the first arm so that the first drilling unit can move freely relative to the first arm.

The first drilling unit comprises the drill rod, a frame and a feeding device for moving of said drill rod axially along an axis of rotation of the drill rod relative to said frame. Thus, the drill rod can be moved, i.e. the position of the drill rod can be changed along the axis of rotation of the drill rod relative to the frame by means of the feeding device. The method comprises the following steps:

Aligning the first drilling unit by using the first arm towards the drill bit located in a fixedly arranged holder configured to hold at least two drill bits, so that the axis of rotation of the drill bit substantially coincides with an axis of rotation of the drill bit, wherein a free movement of the first drilling unit relative to the holder is permitted.

The holder is thus fixedly arranged, which means that the holder is fixedly mounted to a support and can thus be held in substantially the same position relative to the support during assembling of the holder. This, the design and the attachment of the holder is simplified. Since free movement of the first drilling unit relative to the holder is allowed, the position of the first drilling unit relative to the holder can be changed freely, i.e. the first drilling unit can be moved freely relative to the holder and by this it can be directed towards the drill bit in a simple and efficient manner and with high precision.

Further, because the method comprises the step of directing the first drilling unit by means of the first arm towards the drill bit so that the axis of rotation of the drill rod substantially coincides with an axis of rotation of the drill bit, the position of the first drilling unit can be changed by means of the first arm relative to the holder so that the first drilling unit and thus the drill rod are directed towards the drill bit. In this way the drill rod can be directed towards the drill bit with high precision and in a simple and efficient manner by means of the first arm. Thereby the need of a complicated equipment is eliminated, which according to the prior art methods is required to align a drill rod relative to a drill bit, this because the first arm is used to align the first drill assembly and thus the drill rod to the drill bit positioned in the fixedly arranged holder.

Further, the method comprises:

displacing the drill rod axially forward towards the drill bit to a first position of the drill rod permitting mounting of the drill bit,

mounting said drill bit on said drill rod and

displacing said drill rod axially backward to a second position in which the drill bit has been removed from said holder. This means that the drill bit leaves the fixedly arranged holder by following the movement of the drill rod backwards to the other position. Thus the drill bit can be mounted on the drill bit with a few simple steps.

Accordingly, a method of rock drilling is provided which enables the installation of a drill bit in a simple and efficient manner without the need of several moving parts. In this way, reliability at rock drilling can be improved as fewer moving parts imply a lower risk of stoppages. Thus, the above-mentioned purpose is achieved.

For example, the method may also comprise selecting the drill bit intended to be mounted on the drill rod. This means that the drill bit can be selected from several drill bits in the holder. This allows you to decide in advance which drill bit in the holder is to be mounted. According to some embodiments, the rock drill machine comprises a second arm freely movably attached to the base unit, the holder being mounted at the second arm. In other words, the second arm is fixedly mounted to the base unit, for example by the one end of the other arm, so that an opposite end of the other arm can move freely relative to the base unit. Because the holder can be mounted on the other arm, which is freely movable attached to the base unit, the position of the holder relative to the base unit can be changed by means of the second arm. Thus, the position of the holder relative to the first arm can also be changed by means of the second arm which facilitates positioning of the first drilling unit and by this of the drill rod relative to the holder because both the first arm and the second arm can be used to align the drill rod towards the drill bit mounted in the holder.

For example, the drill rod may comprise external threads and the drill bit may comprise corresponding internal threads, wherein the step of mounting the drill bit on the drill rod may comprise to screw tight the drill bit on the drill rod. Thus, the drill bit can be mounted on the drill bit in a simple and efficient manner.

The method may, for example, also comprise bringing back the drill bit into the holder by the first arm for disassembling the drill bit from the drill rod.

The above-described object can also be achieved according to a second aspect of the present invention by a rock drilling device intended to be used for mounting of a drill bit on a drill rod comprising a first arm freely movably attached to a base unit, a first drill unit freely movably attached to the first arm, wherein the first drill unit comprises the drill rod, a frame and a feeding device for axial displacement of the drill rod along the axis of rotation of the drill rod relative to the frame. Further, the device comprises a fixedly arranged holder configured to hold at least two drill bits, wherein a free movement of the first drilling unit in relation to the holder is permitted and a control unit arranged to:

align the first drill unit, by the first arm against the drill bit located in the fixedly arranged holder so that the axis of rotation of the drill rod substantially coincides with a rotation axis of the drill bit, displace the drill rod axially forward towards the drill bit to a first position of the drill rod permitting mounting of the drill bit, attach the drill bit to the drill rod and displace the drill rod axially backward to a second position in which the drill bit has been removed from the holder.

The holder is fixedly arranged, which means that the holder is fixedly mounted to a

The holder is fixedly mounted, which means that the holder is fixed to a support and can thus be held in substantially the same position relative to the support during assembling of the holder. Because free movement of the first drilling unit relative to the holder is allowed, the position of the first drilling unit relative to the holder can be changed freely, i.e. the first drilling unit can be moved freely relative to the holder. Further, because the device comprises the control unit designed to align the first drilling unit by means of the first arm against the drill bit so that the axis of rotation of the drill rod substantially coincides with an axis of rotation of the drill bit, the position of the first drilling unit can be changed by means of the first arm relative to the holder so that the first drilling unit and thus the drill rod are directed towards the drill bit by means of the first arm. In this way the drill rod can be directed towards the drill bit in a simple and efficient manner and with high precision by the first arm. This eliminates the need for complicated equipment which, according to known methods, is needed to align a drill rod relative to a drill bit.

Accordingly, a rock drilling device is provided by which above-mentioned object is achieved.

The device may for example comprise a second arm freely movably attached to the base unit, wherein the holder is mounted at the second arm. In other words, the other arm is attached to the base unit, for example by the one end of the other arm so that an opposite end of the other arm can move freely relative to the base unit. Because the holder can be mounted on the other arm, which is freely movable attached to the base unit, the position of the holder relative to the base unit can be changed by means of the second arm. Thus, the position of the holder relative to the first arm can also be changed by means of the second arm which facilitates positioning of the first drilling unit and by this of the drill rod relative to the holder because both the first arm and the second arm can be used to align the drill rod towards the drill bit mounted in the holder. According to some embodiments, the device comprises a second drilling unit freely movably arranged at the second arm. Thereby, the second arm may be used for drilling holes.

The above-described object can also be achieved according to an additional aspect of the present invention by a holder adapted for use for rock drilling, comprising a housing and an inner part adapted to receive at least two drill bits, wherein the inner part is adapted to hold the at least two drill bits at transport and to permit mounting of each drill bit on a drill rod. In other words, the inner part of the holder is adapted to prevent the at least two drill bits from leaving the holder during transport while allowing at least one of the at least two drill bits to be removed from the holder for mounting on the drill rod. Thus, a holder is achieved adapted for rock drilling which facilitates the transport of drill bits and which enables mounting of some of the drill bits on a drill rod,

Accordingly, a holder is provided which can be used for rock drilling and the like, by means of which the process of mounting a drill bit is simplified.

According to some embodiments, for example the inner part is arranged to counteract a rotational movement and to permit an axial displacement of the drill bits in relation to the inner part upon mounting of these on the drill rod. By this it is prevented that the drill bit rotates within the inner part at mounting of the drill bit while allowing the drill bit to be axiaily displaced out of the holder along the drill bit axis of rotation during assembling. In this way, facilitates mounting of the drill bit on a drill rod.

The inner part may for example comprise a flexible material such as rubber. Thus, the shape of the inner part can be changed thanks to the flexible material.

The inner part may for example comprise at least two openings where each opening is arranged to receive a corresponding drill bit, each opening having a diameter less than the largest diameter of the corresponding drill bit. As a consequence, friction forces between the inner part and the drill bit are achieved when the drill bit is placed in the holder, which friction forces facilitate keeping the drill bit in the holder, for example during transport, while allowing axial movement of the drill bit from the holder.

BRIEF DESCRIPTION OF THE DRAWINGS

The further aspects of the subject matter, including their particular features and advantages, will be readily understood from the following detailed description of one or several embodiments provided with reference to the accompanying drawings.

Fig. 1 is a side view of a device for rock drilling mounted at a mobile rock drilling machine, Figure 2 is a perspective view of the device in Figure 1 comprising two arms and a holder,

Fig. 3 is a perspective view of the holder in Fig. 2,

Fig. 4 is a side view of the holder according to Fig. 2 and 3 and

Fig. 5 is a flowchart showing a method at rock drilling.

DESCRIPTION OF POSSIBLE EMBODIMENTS

The present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the invention is not to be considered as limited to the described embodiments.

Corresponding features and details have the same reference in the description below.

Fig. 1 illustrates a device 21 for rock drilling comprising a first arm 9 which is freely movab!y attached to a base unit 7 and a first drilling unit 1 1 which is freely movabiy attached to the first arm 9. With free movable attachment is meant a coupling that allows mobility in several different directions and/or around several axes of rotation. According to embodiments illustrated in Figure 1 , the first arm 9 is attached to the base unit 7 by means of a first joint 2. The first joint 2 is arranged to enable rotation of the first arm 9 about the axes of rotation A1 , A2 and A3. The axis A2 of Fig. 1 is illustrated to extend perpendicular to the plane of the drawing. The rotation of the first arm 9 about the axes of rotation A1 , A2 and A3 can be controlled by means of hydraulic or pneumatic cylinders for rotation about a respective axis of rotation. For simplicity, only one cylinder 4 is shown in Fig. 1. As illustrated in Fig. 1 , a drill unit 1 1 is freely movabiy attached at the first arm 9. This can be done by means of a second joint 6. The second joint 6 is arranged to enable rotation of the drilling unit 1 1 about axes of rotation A4, A5 and A6. The axis A5 in Fig. 1 is also illustrated to extend perpendicular to the plane of the drawing. The rotation of the drilling unit 11 around the axes of rotation A4, A5 and A6 can be controlled by means of hydraulic or pneumatic cylinders for rotation about a respective axis of rotation. For simplicity only one such cylinder 8 is shown in Fig. 1.

According to the embodiment shown in Fig. 1 , the device 21 is mounted on a mobile rock drilling machine 5 comprising wheels. The device 21 can be mounted, for example, at a rock drilling machine comprising a caterpillar band. The device 21 may in some cases be mounted at a platform or directly at the bedrock.

The first drilling unit 1 1 comprises a drill rod 3, a frame 13 and a feeding device 15 for axial displacement of the drill rod 3 along the axis of rotation Ab of the drill rod relative to the frame 13. The axial displacement of the drill rod 3 can be carried out, for example, by means of a chain 10 or wire connected to a sled 12 the drill rod 3 is mounted on and to a cylinder (not shown) for driving the chain 10. Such a feeding device is common in the art and is therefore not described in detail. In this way, the drill rod 3 can be moved axiaiiy by means of the feeding device 15. in Fig. 1 it is also shown that a drill bit 1 is mounted on the drill rod 3.

Figure 2 shows the device 21 for rock drilling illustrated in Figure 1. According to some embodiments in Figure 2, the device 21 comprises a first arm 9 freely movably attached to the base unit 7, a first drill unit 11 freely movably attached to the first arm 9, a second arm 19 freely movably attached to the base unit 7 and a second drill unit 23 freely movable arranged at the second arm 19. As illustrated in Fig. 2, the holder 17 is mounted at the second arm 19 and more specifically at the second drill unit 21. As an alternative the holder 17 can be mounted directly at the second arm 19 or at the first arm 9 or at a base such as a stand or the like firmly mounted in the bedrock. When the holder is mounted at the above base, the base must be fixed to the bedrock so that it can withstand the forces it is exposed to during operation and during installation of a drill bit.

According to some embodiments illustrated in Fig. 2 and also in Fig. 1 , the first arm 9 comprises two parts pivotaliy articulated to each other by means of a joint 14. The second arm 19 in Fig. 2 also comprises two parts arranged in a similar way as the first arm 9. Alternatively, the first arm 9 and the second arm 19 may comprise only one part or more parts than two and the device 21 is generally not limited in this regard. As illustrated in Fig. 2, the first drilling unit 1 1 is directed, by means of the first arm 9, towards a drill bit 1 which is located in the fixedly arranged holder 17 so that the axis of rotation Ab of the drill rod 3 substantially coincides with an axis of rotation Ak of the drill bit 1. Thereby, the drill rod 3 has been positioned relative to the drill bit 1 in order to mount the drill bit 1 on the drill rod 3. The device 21 is controlled by means of a control device 25. The control means 25 may for example include electronic components connected to a hydraulic or pneumatic system (not shown) for controlling the device. The control can be done manually or can be programmed and done fully automatically. Because the holder 17 according to some embodiments illustrated in Fig. 2 is mounted at the second driiling unit 23, positioning of the drill rod 3 relative to the holder 17 is facilitated because a position when the axis of rotation of the drill rod Ab substantially coincides with the axis of rotation Ak of the drill bit 1 , thus, a position for mounting of the drill bit 1 on the drill rod 3 can be achieved by means of movements of the first arm 9, the first drilling unit 11 , the second arm 19 and the second driiling unit 23. This increases the flexibility and the accessibility at positioning the drill rod 3 relative to the holder 17, compared with the known technology presented, for example, in WO0061907. The second drill unit 23 can be mounted at the second arm 19 in a similar manner as the first drill unit 1 1 is mounted at the first arm 9, i.e. freely movably. Alternatively, the holder 17 can be mounted by means of a control device (not shown) that allows movement of the holder 17 relative to the second driiling unit 23 or relative to a base at which the holder is mounted. The second arm 19 and the second driiling unit 23 may for example be constructed similarly to the first arm 9 and the first drilling unit 1 1 , respectively. Fig. 3 illustrates the holder 17 in Fig. 2 in more detail. The holder 17 comprises a housing 25 and an inner part 27 adapted to receive at least two drill bits 1. This is possible because the inner part 27 comprises at least two openings 29, 31 where each opening 29, 31 is arranged to receive a corresponding drill bit 1. The housing 25 also comprises at least two openings 33, 35 adapted to cooperate with the at least two openings 29, 31 of the inner portion 27 to enable receiving of respective drill bit. The holder in Fig. 3 comprises an attachment portion 37 for attachment, i.e. mounting, of the holder at a base. The housing 25 is, for example, of metal or of a plastic material adapted for mining environment. The inner part 27 comprises a flexible material such as rubber or a suitable plastic material.

Each aperture 29, 31 has a diameter d1 which is smaller than a largest diameter d2 of a corresponding drill bit 1 to be placed in the corresponding opening. Thus, friction forces are provided between an inner surface of the respective aperture and an outer surface of the respective drill bit. These frictional forces make it easier to hold drill bits in the holder, preventing the drill bits from slipping out or shaking out of the holder, for example during transportation or other handling.

The difference between the second diameter d2 and the first diameter d1 may, for example, be between 5-10 mm. This means that upon placing a drill bit in the holder 17 and more specifically in the inner part 27 of the holder 17, the drill bit is pressed into an opening of the inner part 27 during deformation of the flexible material of the inner part. Since the inner part comprises a flexible material, the inner part 27 and more specifically the opening where the drill bit is positioned to the drill bit dimension is adapted. In this manner, the above-described frictional forces are created between the inner portion 27 and the drill bits located in the inner portion 27. The magnitude of these frictional forces depends on the difference between the second diameter d2 and the first diameter d1 so that the greater the difference, the greater the frictional forces. As described above, the inner part comprises at least two openings 29, 31 where each opening 29, 31 is arranged to receive a corresponding drill bit 1. The openings 29, 31 may be formed with the same diameter or with different diameters. This also applies to drill bits intended to be placed in the holder 17. Thus, the drill bits may have the same outer diameter or different outer diameters. Thus, drill bits of different dimensions and or different characteristics can be placed in the holder 17.

For example, the inner part 27 may be placed in the housing 25 by inserting the inner part 27 into the housing 25 from above, viewed in the position of the housing 25 illustrated in Fig. 3. Alternatively, the housing 25 may comprise an openable cover (not shown) through which the inner part 27 can be placed into the housing 25 of the holder 17.

Alternatively, the inner portion 27 may be configured so that the drill bits are held by magnetic forces, such as electromagnetic forces. The inner part 27 may for example comprise grooves on the inside of said openings 29, 31 in order to provide a coupling according to the bayonet coupling principle when placing a drill bit in a respective opening. Fig. 4 illustrates a side view of the holder 17 shown in Fig. 2 and Fig. 3 where a plurality of crowns have been placed in the holder 17. According to Fig. 4, the drill rod 3 has been positioned so that the axis of rotation of the drill rod Ab substantially coincides with the axis of rotation of a drill bit 1 Ak. When the drill bit 1 is intended to be mounted on the drill rod 3, the drill rod 3 is displaced axiaily in a direction w towards the holder 17. The holder 17 may for example include a stop plate 39 mounted to prevent the drill bit movement out from the holder in the direction w when mounting the drill bit 1 on the drill rod or at placing the drill bit in the holder 17.

As previously described, the drill rod 3 may comprise, for example, outer threads with an outer diameter dy. Corresponding drill bit may comprise corresponding internal threads with an inner diameter di to enable mounting of the drill bit on drill rod 3.

Fig. 5 shows an exemplary method 100 for rock drilling. The method 100 can be performed, for example, by a control unit (not shown).

The method 100 comprises:

aligning 101 a first drilling unit by using a first arm towards a drill bit located in a fixedly arranged holder configured to hold at least two drill bits, so that the axis of rotation of the drill bit substantially coincides with an axis of rotation of the drill bit, wherein a free movement of the first drilling unit relative to the holder is permitted,

displacing 103 the drill rod axiaily forward towards the drill bit to a first position of the drill rod permitting mounting of the drill bit,

mounting 105 the drill bit on the drill rod and

displacing 107 the drill rod axiaily backward to a second position in which said drill bit has been removed from the holder.

The method 100 may comprise selecting 109 the drill bit intended to be mounted on the drill rod. Further, the method may comprise bringing back 1 1 1 the drill bit into said holder by the first arm for disassembling the drill bit from the drill rod.

Claims

A method (100) for mounting a drill bit (1 ) on a drill rod (3) at a rock drilling machine (5) comprising a base unit (7) and a first arm (9) freely movably attached to the base unit (7), said rock drilling machine (5) comprises a first drilling unit (1 1 ) freely movably attached to said first arm (9) and having said drill rod (3), a frame (13) and a feeding device (15) for moving of said drill rod (3) axially along an axis of rotation of the drill rod (Ab) relative to said frame (13), the method comprising the following steps:

a) aligning (101 ) said first drilling unit (1 1 ), by using said first arm (9), towards the drill bit (1 ) located in a fixedly arranged holder (17) configured to hold at least two drill bits, so that the axis of rotation (Ab) of the drill rod substantially coincides with an axis of rotation (Ak) of said drill bit (1 ), wherein a free movement of said first drilling unit (11 ) relative to said holder (17) is permitted,

b) displacing (103) said drill rod (3) axially forward towards the drill bit (1 ) to a first position of said drill rod (3) permitting mounting of the drill bit (1 )

c) mounting (105) said drill bit (1 ) on said drill rod (3) and

d) displacing (107) said drill rod (3) axially backward to a second position in which said drill bit (1 ) has been removed from said holder (17).

The method according to claim 1 , comprising selecting (109) said drill bit (1 ) intended to be mounted on said drill rod (3).

The method according to claim 1 or 2, wherein said rock drill (5) comprises a second arm (19) freely movably attached to said base unit (7), said holder (17) being mounted at said second arm (19).

The method according to any of the preceding claims, wherein said drill rod (3) comprises external threads and said drill bit (1 ) comprises corresponding internal threads, wherein said step of mounting (105) said drill bit (1 ) on said drill rod (3) comprises to screw tight the drill bit (1 ) on the drill rod (3).

The method according to any of the preceding claims, comprising bringing back (1 1 1 ) said drill bit (1 ) into said holder (17) by said first arm (9) for disassembling the drill bit (1 ) from the drill rod (3). A rock drilling device (21 ) intended to be used for mounting a drill bit (1 ) on a drill road (3) comprising:

- a first arm (9) freely movably attached to a base unit (7),

- a first drill unit (1 1 ) freely movably attached to said first arm (9), wherein the first drill unit (1 1 ) comprises said drill rod (3), a frame (13) and a feeding device (15) for axial displacement of said drill rod (1 1 ) 3) along the axis of rotation of the drill rod (Ab) relative to said frame (13),

- a fixedly arranged holder (17) configured to hold at least two drill bits, wherein a free movement of said first drilling unit (1 1 ) in relation to said holder (17) is permitted and

- a control unit (25) arranged to:

align the first drill unit (11 ), by said first arm (9) against said drill bit (1 ) located in the fixedly arranged holder (17) so that the axis of rotation of the drill rod (Ab) substantially coincides with a rotation axis (Ak) of the drill bit (1 ),

displace said drill rod (3) axially forward towards the drill bit (1 ) to a first position of said drill rod (3) permitting mounting of the drill bit (1 ),

attach the drill bit (1 ) to the drill rod (3) and

displace said drill rod (3) axially backward to a second position in which said drill bit (1 ) has been removed from said holder (17).

The device (21 ) according to claim 6, comprising a second arm (19) freely movably attached to said base unit (7), wherein said holder (17) is mounted at said second arm (19).

The device (21 ) according to claim 7, comprising a second drilling unit (23) freely movably arranged at said second arm (19).

A holder (17) adapted for use for rock drilling, comprising a housing (25) and an inner part (27) adapted to receive at least two drill bits, wherein said inner part (27) is adapted to hold said at least two drill bits at transport and to permit mounting of each drill bit on a drill rod.

10. The holder (17) according to claim 9, wherein the inner part (27) is arranged to counteract a rotational movement and to permit an axial displacement of the drill bits in relation to said inner part (27) upon mounting of these on said drill rod.

1 1 . The holder (17) according to any one of claims 9 or 10, wherein said inner part (27) comprises a flexible material such as rubber.

12. The holder (17) according to any one of claims 9-1 1 , wherein said inner part (27) comprises at least two openings (29, 31 ) where each opening (29, 31 ) is arranged to receive a corresponding drill bit, wherein each opening (29, 31 ) has a diameter that is less than a largest diameter of said corresponding drill bit.