GB2138729A - Compression-vacuum action percussive machine - Google Patents

Abstract

A compression-vacuum action percussive machine comprises a casing (1), a drive (2) secured inside the casing (1), a pick tool (3), and a cylinder (4). The cylinder (4) accommodates a piston (5) connected to the drive (2), and a hammer (6) engageable with the pick tool (3). The machine also comprises a means for trapping the hammer (6) for the machine to idle, this hammer trapping means being part of the cylinder (4) secured inside the casing (1). The trapping means has an axial clearance (12) and a radial clearance (11) relative to the casing (1) to define a free end of the cylinder (4) having section (13) of a diameter substantially smaller than the diameter of the hammer (6). Longitudinal slots (14) divide the wall of the cylinder (4) into resilient lobes (16) which constitute the trapping means. The invention provides reliable trapping of the hammer (16) when changing from working to idling, in the normal working position or in the <IMAGE>

Description

SPECIFICATION Compression-vacuum action percussive machine This invention relates generally to machine construction, and more particularly to compression-vacuum action percussive machines.

The machine according to the invention can find application for breaking materials and rocks in civil engineering, mining, and geological explorations.

There is known a compression-vacuum action percussive machine (cf. West German Patent No.

2,423,735; IPC E 21C 3/04, published, October 23, 1 980) comprising a casing, a work tool, a drive, a cylinder accommodating a piston connected to a drive means and a hammer connected to the piston through an air cushion and engageable with the pick tool, and idle run ports made in the cylinder.

Inherent in the above machine is insufficient reliability associated with switchover from impact operation to idling when the machine is drawn away from the rock being broken up, the lack of reliability being still more pronounced with the pick tool in an overhead position. The machine can be switched to idling by opening the idle run ports made in the cylinder and normally closed during impact operation. When the machine operates in a downhand position, raising the casing thereof upwards is accompanied by a downward movement of the pick tool relative to the casing and the cylinder.The hammer is therefore caused to also move down, and such movement of the hammer to follow the pick tool is accompanied by still greater opening of the idle run ports, after which these ports are open to such an extent that they communicate the air cushion with the atmosphere to prevent a pressure drop therein during the work and return strokes of the piston.

The hammer therefore stops responding to reciprocations of the piston and impact operation terminates to assure idling.

When the machine operates in an overhead position, removing the casing, and consequently the tool from the rock being broken up, causes the gravity force acting on the hammer subsequent to opening thereby of the idle run ports to return the hammer to its initial position, the hammer thus blocking the idle run ports to result in that the machine resumes again to deliver impacts.

Such lack of reliability of switchover from impact to idling, especially during variations in the working position of the machine, affects operability and reliability of the machine.

There is also known a compression-vacuum machine (cf. West German Patent No. 2,437,023; IPC B 25d 11/04, published August 1, 1971) which comprises a casing, a drive disposed inside the casing, a work tool, a cylinder accommodating a piston connected to the drive and a hammer connected to the piston through an air cushion and engageable with the work tool, and a means for trapping the hammer for the machine to idle, the hammer trapping means including idle run ports made in the cylinder.

In order to prevent axial displacement of the hammer subsequent to switching the machine to idling, the hammer trapping means comprises a spring ring of an inside diameter somewhat smaller than the outer mating diameter of the hammer, this ring being fixedly secured in the casing. During impact operation the spring ring fails to come into contact with the hammer. After the machine is set to idle, the hammer tends to enter into the spring ring expanding it to an extent equal to the difference between the mating diameters. Therewith, the force of friction arising between the spring ring and the hammer prevents the movement of the hammer under the gravity of its own weight and due to the movement of the work tool. This arrangement is therefore capable of putting the machine to idling in practically any working position thereof.

However, the machine suffers from a rather low reliability caused by unstable parameters of the hammer trapping means due to difficulties associated with fabrication of the spring ring whereby its inner diameter is ensured only after the ring is split laterally. This results in a considerable spread in the precise inside diameter of the rings, thus manufactured, which in turn leads either to excessive squeezing of the hammer by the ring, and consequently damage to the latter, or to a rather low squeezing force insufficient for holding the hammer and therefore for switching the machine to idling.

It is an object of the present invention to provide a compression-vaccum action percussive machine of greater reliability.

The object of the invention is attained by that in a compression-vacuum action percussive machine comprising a casing, a drive secured inside the casing, a pick tool, a cylinder accommodating a piston connected to the drive and a hammer connected to the piston through an air cushion and engageable with the pick tool, and also a means for trapping the hammer when the machine idles, this hammer trapping means including an idle port made in the cylinder, according to the invention, the hammer trapping means is part of the cylinder secured inside the casing with axial and radial clearances relative to the casing of the pick tool to define a free end of the cylinder with a section thereof having an inside diameter which is smaller than the diameter of the hammer and longitudinal through slots in length greater than the length of the section of the free end of the cylinder to divide its wall into resilient lobes.

Preferably, each slot in the free end of the cylinder terminates in a hole made in the wall thereof. Increased reliability is attained here by the provision of the holes which act to reduce stress concentrations occuring at the location where the slots terminate.

Advisably, each slot in the free end of the cylinder terminates in the idle port.

In this modified form a higher reliability is assured by that the area of stress concentrations is confined by idle ports in which the slots terminate, these concentrations being absent where the idle ports were located previously.

Alternatively, each slot extends beyond the hammer on the side of the air cushion when the hammer is brought in touch with the pick tool.

Slots positioned in this fashion, aside from their principle designation, function to compensate for the loss of air from the air cushion.

In the compression-vacuum action percussive machine according to the present invention a very high reliability of hammer trapping is achieved during switchover to idling both in the downhand and overhead or other working positions of the machine, and a more extended service life of the machine is guaranteed.

The invention will now be described in greater detail with reference to various specific embodiments thereof taken in conjunction with the accompanying drawings, in which: Fig. 1 illustrates a longitudinal sectional view of a compression-vacuum action percussive machine in impact delivering position; Fig. 2 is a section of the lower part of the machine according to the invention with a hammer trapping means when the hammer is trapped for the machine to idie; Fig. 3 is a cross-sectional view of the cylinder taken along the line Ill-Ill in Fig. 2 in the location where the slots made in its walls are disposed; Fig. 4 is a view of the lower portion of the machine provided with a hammer trapping means during idling when the slots pass through the idle run ports; and Fig. 5 is a longitudinal sectional view a modified form of the compression-vacuum action percussive machine according to the invention during impact operation in which the slots in the cylinder also serve to compensate for the air loss from the air cushion.

With reference to Fig. 1, a compressionvacuum action percussive machine comprises a casing 1 having disposed therein a crank drive 2, a pick tool 3, a cylinder 4 accommodating a piston 5 connected to the crank drive 2 and a hammer 6.

The hammer 6 is engageable with the piston 5 by means of an air cushion indicated generally at 7 to exert periodically in response to the movement of the piston 5 impact actions on the pick tool 3. A hole 8 is bored in the cylinder 4 within the volume occupied by the air cushion 7 to compensate for the loss of air in this air cushion, this hole being disposed under the piston 5 relative to its bottom dead centre position. The cylinder 4 also has idle run ports 9 arranged above an upper end face 10 of the hammer 6 confining the air cushion 7 at the point when the hammer 6 comes into contact with the pick tool 3. A means for trapping the hammer is envisaged, which means is generally part of the cylinder 4 installed on the side of the pick tool 3 in the casing 1 with a radial clearance 11 and an axial clearance 12 to form a free end of the cylinder 4.This free end of the cylinder 4 has an open section 1 3 of an inside diameter somewhat smaller than the diameter of the hammer 6, and longitudinal through slots 14 passing from an outer edge 1 5 of the free end 4 a length exceeding the length of the section 1 3 of the cylinder 4. The slots 14 separate the wall of the free end of the cylinder 4 into resilient lobes 1 6. The movement of the hammer 6 when it is being caught by the trapping means is limited by a rubber-metal shock-absorber 1 7. During idling the hammer 6 assumes a position represented in Fig. 2 to bear on the shock-absorber 17, in which position the hammer 6 engages with the section 13 of the free end of the cylinder 4. The slots 14 terminate in holes 1 8 made in the wall of the cylinder 4.The number of the resilient lobes 16 (Fig. 3) depends on their resiliency and may amount to as much as four. For better reliability of the resilient lobes 1 6 (Fig. 4) the slots 14 in the cylinder 4 pass through the idle ports 9. In order to compensate for the loss of air in the air cushion 7 (Fig. 5), the slots 14 of the cylinder 4 may extend beyond the upper end 10 of the hammer 6 facing the air cushion 7 at the point when the hammer 6 is brought into contact with the pick tool 3 to deliver an impact.

The compensation hole 8 in the cylinder 4 may, in this case, be dispensed with.

The compression-vacuum action percussive machine according to the invention operates as follows.

In the working impact mode of operation the hammer 6 (Fig. 1) executes reciprocations inside the cylinder 4 induced by similar reciprocating motions of the piston 5, engagement with the piston 5 being effected through the air cushion 7.

The hammer 6 periodically deiivers impacts against the pick tool 3, the idle run ports 9 being thus outside of the air cushion 7. For switching to idling the casing 1 is lifted upwards. The pick tool is therefore caused to be lowered relative to the casing 1 by gravity. The hammer 6 while delivering impacts on the pick tool 3 is caused to follow suit and assume a position seen best in Fig.

2. In this position of the hammer 6 the idle ports 9 communicate the air cushion 7 with the atmosphere so as to have no pressure drop during the travel of the piston 5. Therewith, there is the absence of force inside the air cushion 7 which would induce the hammer 6 to ascend and therefore it retains its down position in contact with the rubber-metal shock-absorber 1 7. While retaining this position, the hammer 6 is engaged with the section 13 of the cylinder 4. Because the inside diameter of the section 1 3 is smaller than the cooperating diameter of the hammer 6, the hammer 6 acts to force apart the resilient lobes 1 6 defined by the walls of the free end of the cylinder 4 and slots 14. The resiliency of the lobes 1 6 is such that the extent of their radial displacement caused by interaction between the hammer 6 and the section 13 of the cylinder 4 corresponds to the difference between the diameters of the hammer 6 and this section 13. Such a displacement is made possible thanks to the provision of the radial clearance 11 and axial clearance 12 between the casing 1 and the cylinder 4 in the location adjacent to the pick tool 3, as well as by that the length of the slots 14 extending along the cylinder 4 is greater than the length of the section 13 of the cylinder 4 which contributes to a greater compliance of the lobes 1 6. For improving the reliability and eliminating excessive stress the slots 14 terminate in the holes 18 provided in the wall of the cylinder 4.A friction force arising between the resilient lobes 1 6 and the hammer 6 when the latter is jammed into the former prevents their relative movement and holds the hammer 6 in a position where the idle ports 9 are open to assure idling of the machine free of percussions. In this manner a reliable switchover from the percussive mode of operation to idling is guaranteed in any position of the machine, even when the pick tool tip points overhead.

Bringing the machine out of idling is made in a reverse sequence. The casing 1 of the machine is moved together with the pick tool 3 toward the rock to be broken up. When thrust against the rock, the pick tool 3 is caused to move relative to the casing 1 to overcome the force of friction between the section 13 and the hammer 6 and thus force the latter toward the piston 5 which continues to execute reciprocations. After the hammer 6 is brought out of engagement with the section 13, it moves further toward the piston 5 and blocks the idle ports 9. The air cushion 7 is thereby rendered closed for a force to arise between the piston 5 and hammer 6 due to a pressure differential making the hammer 6 respond to the reciprocations of the piston 5 and deliver impacts on the pick tool 3.

The machine can operate even more reliably when the slots 1 4 (Fig. 4) in the cylinder 4 extend to the idle ports 9, these ports 9 now acting to reduce possible stress concentrations during resilient deformations of the lobes 1 6 and make the function of the hammer trapping means for machine idling more reliable.

Referring now to Fig. 5, when the slots 14 extend in the cylinder 4 beyond the end of the hammer 6 facing the air cushion 7, these slots 14 may also function to compensate for the loss of air in the air cushion 7. Therewith, the provision of the slots 14 along with the main hole 8 to compensate for the loss of air in the air cushion 7 improves operability of the hammer mechanism of the machine during switchover from idling to impact delivering operation. Such a switchover may be made smoothly within a wide range of supply voltages, especially when the machine is driven by a drooping-response electric motor, such as a commutator motor. When not loaded, such a motor has a substantially higher speed of rotation than under load during impact operation.The piston 5 therefore oscillates at a much faster rate than during impact operation at the point of switching the machine from idling to impact operation. During such a high frequency of oscillation of the piston 5 excess air in the air cushion 7 has no time to escape therefrom through the hole 8 which in turn hampers a switchover. The provision of slots 14 (Fig. 5) increases the passage area for the escape of excess air from the air cushion 7 to thereby improve conditions for switching the machine over to impact operation. In the course of impact operation, when the hammer 6 reciprocates, the time during which the slots 14 communicate the air cushion 7 with the atmosphere is negligeable and therefore fails to affect normal operation of the machine.

Entrapping the hammer 6 is thus effected by virtue of resiliency of the lobes 16 assured by the slots 14 in the cylinder 4 and the difference between the diameters of the section 1 3 and the hammer 6. Taking into consideration the fact that the inside diameter of the section 13 and the inside diameter of the cylinder 4 are ground for finishing to provide highly accurate and stable dimensions, the degree of deformation of the resilient lobes 16 is also stable, which on the one hand prevents excessive deformation of the means for trapping the hammer 6 to result in damage thereof, and on the other hand guarantees a more reliable trapping of the hammer 6.

Claims (5)

1. A compression-vacuum action percussive machine comprising a casing, a driv8secured inside the casing, means for mounting a tool such as a pick tool, a cylinder having a piston connected to the drive and a hammer connected to the piston through an air cushion and engageable with the tool, and also means for trapping the hammer for the machine to idle, which hammer trapping means includes idle run ports made in the cylinder and constituting part of this cylinder secured inside the casing with axial and radial clearances relative to the casing on the side of the tool to define a free end of the cylinder with a section thereof having an inside diameter which is smaller than the diameter of the hammer, and longitudinal through slots in length greater than the length of the section of the free end of the cylinder to divide its walls into resilient lobes.

2. A compression-vacuum action percussive machine as claimed in Claim 1, in which each slot in the free end of the cylinder terminates in a hole made in the wall thereof.

3. A compression-vacuum action percussive machine as claimed in Claim 1 or 2, in which each slot in the free end of the cylinder terminates in the idle port.

4. A compression-vacuum action percussive machine as claimed in any one of the preceding Claims, in which each slot extends beyond the hammer on the side of the air cushion when the hammer is brought in contact with the pick tool.

5. A compression-vacuum action percussive machine substantially as described in the description with reference to, and as shown in, Figures 1 to 3 or Figure 4 or Figure 5 of the accompanying drawings.