Rock drilling machine and use thereof for hindering occurrence and spreading of cavitation bubbles

Abstract

Rock drilling machine (10) comprising a piston that is arranged to move back and forth in a chamber (12a, 12b) when the rock drilling machine (10) is in use, a cavitation-sensitive component (14), and an oil channel that is arranged to extend between the chamber (12a, 12b) and said cavitation-sensitive component (14). The oil channel comprises a series of restrictions (18) and oil volumes (20) to hinder the movement of cavitation bubbles through said oil channel.

Claims

1. Rock drilling machine (10) comprising a piston that is arranged to move back and forth in a chamber (12a, 12b) when the rock drilling machine (10) is in use, a cavitation-sensitive component (14), and an oil channel that is arranged to extend between the chamber (12a, 12b) and said cavitation-sensitive component (14), wherein said oil channel comprises a series of restrictions (18) and spaces (20) for restricting oil flow through said oil channel during decreasing pressure in the chamber (12a, 12b) to hinder the spreading of cavitation bubbles through said oil channel and to isolate the cavitation-sensitive component from cavitation damage without components having movable parts, said series of restrictions and spaces including at least one space for collecting oil flowing through said oil channel, said at least one space being disposed between two restrictions having decreased cross sectional areas.

2. Rock drilling machine (10) according to claim 1, wherein said series of restrictions (18) and spaces (20) includes at least two restrictions (18) and one space (20), or at least three restrictions (18) and two spaces (20).

3. Rock drilling machine (10) according to claim 1, wherein said series of restrictions (18) and oil volumes (20) comprises alternating restrictions (18) and spaces (20) which are sequentially arranged such that one said restriction is followed by one said space, and said one said space is followed by another said restriction.

4. Rock drilling machine (10) according to claim 1, wherein said restrictions (18) are arranged to decrease said oil channel's cross sectional area by at least 50%.

5. Rock drilling machine (10) according to claim 1, wherein at least one restriction (18) of said series of restrictions is arranged where the oil channel meets the chamber (12a).

6. Rock drilling machine (10) according to claim 1, wherein said cavitation-sensitive component of the rock drilling machine (10) is a seal (14) or a guide.

7. Rock drilling machine (10) according to claim 1, wherein said piston is a damper piston or a piston in the percussion or breaker part of the rock drilling machine (10).

8. Rock drilling machine (10) according to claim 1, wherein the total length of said oil channel (measured from the chamber (12a, 12b) to the cavitation-sensitive component (14) along the oil channel) is longer than the shortest distance between the chamber (12a, 12b) and the cavitation-sensitive component (14) (measured from one end of the oil channel to the other end of the oil channel), at least 50% longer.

9. Use of a rock drilling machine (10) according to claim 1, to hinder the occurrence and spreading of cavitation bubbles of a rock drilling machine (10) by restricting oil flow through said oil channel by said series of restrictions and spaces of said oil channel.

10. Rock drilling machine (10) according to claim 2, wherein said series of restrictions (18) and spaces (20) comprises alternating restrictions (18) and spaces (20) which are sequentially arranged such that one said restriction is followed by one said space, and said one said space is followed by another said restriction.

11. Rock drilling machine (10) according to claim 2, wherein said restrictions (18) are arranged to decrease said oil channel's cross sectional area by at least 50%.

12. Rock drilling machine (10) according to claim 3, wherein said restrictions (18) are arranged to decrease said oil channel's cross sectional area by at least 50%.

13. Rock drilling machine (10) according to claim 2, wherein said at least one restriction (18) is arranged where the oil channel meets the chamber (12a).

14. Rock drilling machine (10) according to claim 3, wherein said at least one restriction (18) is arranged where the oil channel meets the chamber (12a).

15. Rock drilling machine (10) according to claim 2, wherein said cavitation-sensitive component of the rock drilling machine (10) is a seal (14) or a guide.

16. Rock drilling machine (10) according to claim 3, wherein said cavitation-sensitive component of the rock drilling machine (10) is a seal (14) or a guide.

17. Rock drilling machine (10) according to claim 2, wherein said piston is a damper piston or a piston in the percussion or breaker part of the rock drilling machine (10).

18. Rock drilling machine (10) according to claim 3, wherein said piston is a damper piston or a piston in the percussion or breaker part of the rock drilling machine (10).

19. Rock drilling machine (10) according to claim 2, wherein the total length of said oil channel (measured from the chamber (12a, 12b) to the cavitation-sensitive component (14) along the oil channel) is longer than the shortest distance between the chamber (12a, 12b) and the cavitation-sensitive component (14) (measured from one end of the oil channel to the other end of the oil channel), at least 50% longer.

20. Rock drilling machine (10) according to claim 3, wherein the total length of said oil channel (measured from the chamber (12a, 12b) to the cavitation-sensitive component (14) along the oil channel) is longer than the shortest distance between the chamber (12a, 12b) and the cavitation-sensitive component (14) (measured from one end of the oil channel to the other end of the oil channel), at least 50% longer.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the following, the present invention will be described in more detail with reference to the accompanying schematic drawing, in which:

(2) FIG. 1 shows part of a rock drilling machine according to an embodiment of the present invention.

(3) It should be noted that the drawing has not necessarily been drawn to scale and that the dimensions of certain elements may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) FIG. 1 shows part of a rock drilling machine 10 according to an embodiment of the present invention. The rock drilling machine 10 comprises a damper piston 16 that is arranged to move back and forth in a chamber, which in FIG. 1, due to the damper piston's position in the chamber, is divided into a front part 12a, and a rear part 12b. A seal 14 is arranged at a distance from the chamber 12a, 12b around the damper piston 16.

(5) In the illustrated embodiment the rock drilling machine comprises a first oil channel that comprises a first restriction 18i, a dedicated constriction or obstruction, in order to hinder the passage of cavitation bubbles between the front part of the chamber 12a and the oil volume 20i.

(6) As can be seen in FIG. 1 there is a plurality of interconnected oil channels through which oil can flow from oil volumes 20 in the rock drilling machine between the seal 14 and the chamber 12a, 12b. These oil channels comprise a series of alternating restrictions 18 and oil volumes 20 which hinder the spreading of cavitation bubbles between the seal 14 and the chamber 12a, 12b when a low pressure occurs in the chamber. The spreading and the occurrence of cavitation bubbles is therefore limited to the chamber 12a, 12b itself, whose material is resistant to cavitation damage. In the illustrated embodiment the chamber 12a, 12b is substantially isolated from all of the spaces 20 hydraulically connected to the chamber. Cavitation-sensitive components, such as the seal 14, are consequently isolated from cavitation and are thereby protected from cavitation damage.

(7) It is favourable if the oil channel that includes a series of restrictions 18, 18i and oil volumes 20, 20i has a long extension, i.e. that its total length (measured from the chamber 12 to the seal 14 along the oil channel) is longer than the shortest distance between the chamber 12 and the seal 14 (measured from one end of the oil channel to the other end of the oil channel), at least 50% longer, at least 60% longer, at least 70% longer or even longer. A long extension can be achieved for example by the placement of oil volumes 20, 20i and restrictions 18, 18i. A long oil channel gives a long signal time for the pressure decrease and the cavitation bubbles/pressure decrease is/are forced to pass through a larger amount (volume) of oil between the chamber 12 and the seal 14.

(8) According to an embodiment of the invention a restriction 18, i.e. a dedicated constriction or obstruction, is arranged to decrease an oil channel's cross sectional area by at least 50%, at least 60%, at least 70%, at least 80% or at least 90% or more. It should be noted that the expression restriction is intended to also include a gap 18m between adjacent components of the rock drilling machine.

(9) The illustrated embodiment shows a damper piston 16. The present invention can however be used on another piston of the rock drilling machine, for example a piston in the percussion or breaker part of the rock drilling machine such as a percussion piston or a breaker piston.

(10) The present invention also concerns a method to hinder the occurrence and spreading of cavitation bubbles of a rock drilling machine. The method comprises the step of arranging an oil channel that is arranged to extend between a piston chamber and a cavitation-sensitive component of the rock drilling machine to comprise a series of restrictions that decrease an oil channel's cross sectional area by at least 50%, at least 60%, at least 70%, at least 80% or at least 90% or more, and oil volumes to hinder the movement of cavitation bubbles through said oil channel. According to an embodiment of the invention said oil channel is arranged to comprise a series of alternating restrictions and oil volumes.