Liquid driven hammer machine

Abstract: Liquid driven hammer machine with a machine housing (1) and a hammer piston (2) moveable to-and-fro in guides (4,5) in the machine housing. The guides are made with an intermediate section (6) and end sections (7,8) on either sides thereof. The slot between the intermediate section and the hammer piston is less than, preferably one half of, the slot between the end section and the hammer piston at the end of the end section turned away from the intermediate section. The intermediate section has according to an advantageous embodiment an axial extension which is approximately one third of the length of the guide.

Description: The present invention relates to a liquid driven hammer machine, more particularly the invention relates to a guide for the hammer piston included in the hammer machine. In previously known hammer machines, see EP-A-127885, which are provided with cylindrical guides for the to-and-fro movement of the hammer piston, the problem occasionally arises that the lubrication in the guide is insufficient, which causes the hammer piston to seize with damages on hammer piston and guide as result. The cause of this problem is that the hammer piston is not centered in the guide but comes into metallic contact with the guide. DE-A-2719190 discloses an apparatus where combustion gases are used to drive a piston into a water chamber so that a high speed water jet is produced. The piston is provided with conical surfaces through which a centering force on the piston is obtained during the working stroke of the piston. US-A-3487752 discloses a percussive tool in which the hammer piston is centered by means of seals extending about the hammer piston. US-A-4047595 discloses a hydraulic-powered impact machine in which the hammer piston is centered by means of seals extending about the hammer piston. The present invention, which is defined in the subsequent claims, aims at doing away with the above mentioned problem by providing the hammer device with at least one guide member of predetermined length which guarantees that the hammer piston is exerted to a centering force if its position deviates from the centered position, i.e. where the slot between the hammer piston and the guide is equal about the hammer piston. This is achieved through providing the guide member with an intermediate section and two end sections, one on each side of the intermediate section, wherein the slot between the intermediate section and the hammer piston is narrower than the slot between the end sections and the hammer piston. Thus the liquid pressure between the hammer piston and the guide becomes larger on the side of the hammer piston where the slot is narrower when the hammer piston is situated in an eccentric position relative to the guide member. This increased pressure causes a side force which strives to bring the hammer piston back to a central position in the guide member. It has turned out to be advantageous to make the intermediate section with an axial extension which is less than half the length of the guide member. It is particularly advantageous with an axial extension which is about one third of the length of the guide member. It has turned out to be advantageous to have a slot between the intermediate section and the hammer piston which is less than three fourths, preferably approximately equal to one half, of the slot between the end section and the hammer piston at the end of the end section situated furthest away from the intermediate section. For production reasons it is advantageous to form the intermediate section and the end sections as cylindrical sections so that a step is created at the transition between the end section and the intermediate section. It is also possible to form the end sections as conical sections or as a number of cylindrical sections being something between the transition in one step and the conical transition. In order to obtain a large centering force the intermediate section should be given a short axial extension in order to give a large pressure rise when liquid is drawn into the slot between the intermediate section and the hammer piston. At the same time the axial extension of the intermediate section must not be too short because that leads to increased leakage which counteracts the pressure rise. An embodiment of the invention is described below with reference to the accompanying drawing in which fig 1 shows a rock drilling machine partly in section. Fig 2 shows a guide member included in the invention. Fig 3 shows a section of an alternative guide member. The rock drilling machine shown in the drawing comprises a machine housing 1, a hammer piston 2 moveable to-and-fro in the machine housing and intended to exert a tool 3, inserted into the machine housing, to impacts. The hammer piston is guided in guide members 4,5 and provided with surfaces 11,12 which are alternately connected to a pressure source and to low pressure in order to reciprocate the hammer piston. The tool 3 is rotated by means of a motor 13 and a not shown transmission. In the shown example both guide members 4,5 are made in the way shown in fig 2. In certain cases sufficient guiding can be obtained if only one of the guide members are made as shown in fig 2. As shown in fig 2 guide member 4 is formed with a cylindrical intermediate section 6 and on both sides thereof with cylindrical end sections 7,8. The intermediate section should have an axial extension which is less than half, preferably one third, of the length of the guide member. The diameter difference between the intermediate section and the hammer piston 2 should be less than three fourths, preferably approximately equal to one half, of the diameter difference between the end sections and the hammer piston at the end of the end sections turned away from the intermediate section. In the shown example the end sections 7,8 are cylindrical for production reasons. They can also be conical or have some other form. In fig 3 a transverse section through an alternative embodiment of the intermediate section of the guide member is shown. In this case the guide member has been produced by rolling so that the intermediate section comprises a number of ridges 21 and intervening grooves 22. In this case the centering pressure is built up between the ridges and the hammer piston, which is not shown in fig 3. When the hammer piston moves in the direction shown by arrow 14 liquid is drawn into the slot between the guide member and the hammer piston so that the axial pressure distribution on the side of the hammer piston where the slot is narrowest gets the form indicated by curve 16 and on the other side the form indicated by curve 17. When the hammer piston 2 moves in the direction shown by arrow 15 pressure distributions indicated by curves 18 and 19 are obtained. These pressure distributions give a side force on the hammer piston which strives to center the hammer piston in the guide member. In the shown example the pressure distributions are given in the most critical situation when neither side of the guide member is pressurized. The guide member functions in the same way if either side of the guide member is pressurized. However, the pressure distribution will look differently.

Claims: Liquid driven hammer machine comprising a machine housing (1), a hammer piston (2) moveable to-and-fro in the machine housing and intended to exert a tool (3) inserted into the machine housing to impacts, and two guide members of predetermined length (4,5) arranged at a distance from each other in the machine housing for guiding the movement of the hammer piston, characterized in that at least one of said guide members of predetermined length (4,5) comprises an intermediate section (6) and two end sections (7,8), wherein the diameter difference between said intermediate section and the hammer piston (2) is less than the diameter difference between said end sections and the hammer piston, whereby a centering pressure for the piston is built up at said intermediate section. Liquid driven hammer machine according to claim 1, characterized in that said intermediate section (6) has an axial extension which is less than half the length of the guide member (4). Liquid driven hammer machine according to claim 2, characterized in that said intermediate section (6) has an axial extension which is approximately one third of the length of the guide member (4). Liquid driven hammer machine according to any of the preceding claims, characterized in that the diameter difference between said intermediate section (6) and the hammer piston (2) is less than three fourths of the diameter difference between said end sections (7,8) and the hammer piston at the ends of the end sections at the ends (9,10) turned away from the intermediate section. Liquid driven hammer machine according to claim 4, characterized in that the diameter difference between said intermediate section (6) and the hammer piston (2) is approximately one half of the diameter difference between said end sections (7,8) and the hammer piston at the ends (9,10) of the end sections turned away from the intermediate section. Liquid driven hammer machine according to any of the preceding claims, characterized in that said intermediate section (6) and said end sections are cylindrical sections. Liquid driven hammer machine according to any af claims 1-5, characterized in that said end sections (7,8) are conical sections.

Inventors: WIJK GUNNAR, WIJK, GUNNAR
Applicants: ATLAS COPCO ROCKTECH AB
Application year: 1993
Main classification: B25D17
IPC codes: F16C29, B25D17, F15B15