IES20000221A2 - Down-the-hole hammer with variable pressure chamber - Google Patents

Abstract

A "down-the-hole" hammer or percussive drill tool is provided, operated by a supply of compressed air, comprising a backhead assembly (11) and an air distributor (41) secured to an outer cylinder (6), an inner cylinder (47) mounted adjacent the outer cylinder for defining a porting arrangement (14), the air distributor extending within the inner cylinder, a piston (4) slidably mounted with respect to the inner and outer cylinders and adapted to reciprocate therein so as to repeatedly strike a bit (5) mounted in a chuck at the forward end of the outer cylinder, wherein the rear end of the piston, the air distributor and the inner cylinder together define a rear pressure chamber (2), which when fully pressurized drives the piston towards the bit, and wherein the forward end of the piston, the bit and the outer cylinder together define a forward lift chamber (1), which when pressurized lifts the piston away from the bit after it has struck the bit, wherein a sliding valve member (42,60) is provided within the rear pressure chamber (2) adapted to vary the effective pressurizable volume of the rear chamber during the cycle of operations which causes a piston to reciprocate within the hammer. Preferably, the sliding valve member is a first ring (42) mounted on the portion of the air distributor which extends within the inner cylinder, defining to the forward side thereof a primary pressure chamber, and to the rear side thereof a secondary pressure chamber. Preferably, a second ring (43) is fixedly mounted between the inner cylinder and the portion of the air distributor which extends within the inner cylinder, which second ring acts as a stop for forward sliding movement of the first ring. Preferably, said secondary pressure chamber is adapted to receive a constant supply of pressure air throughout the cycle of operations. <Figure 5a>

Description

The present invention relates to a “down-the-hole” hammer or percussive drill tool, operated by a supply of compressed air, in particular to a hammer in which the volume of one of the internal pressure chambers may be varied during the cycle of operations which causes a piston to reciprocate within the hammer.

Background to the Invention In a typical prior art down-the-hole hammer, which is illustrated with reference to the accompanying Figures 1 to 3, a piston 4 oscillates between a bit strike position shown in Figure 1 and a top of stroke position shown in Figure 3. Figure 2 shows an intermediate position for the piston. Referring to Figure 1, it will be seen that in the bit strike position, there is a pressure chamber 1 formed between the piston 4, the bit 5 and the outer cylinder 6. This pressure chamber is supplied with high pressure air through a porting supply conduit shown by 11,12,13,14,15,16,17 and 18. Also in this position of the piston, the rear pressure chamber 2 is open to exhaust to the exterior through the piston bore 7 and the bit holes 8 and 9, at the same time being cut off from high pressure air supply by the piston 4 sealing with the inside diameter of the inner cylinder 19. As a result there will be a pressure differential between chambers 1 and 2 and this will cause the piston to lift, beginning the next cycle.

Referring to Figure 3, the piston 4 is shown at the top of its stroke. In this position the upward momentum of the piston (which was initiated by the forces created in pressure chamber 1) has been overcome by the pressure created in chamber 2 formed between the piston 4 the inner cylinder 19 and the air distributor 21. High pressure air is supplied into chamber 2 through the porting supply conduit shown by 11,12,13,14,15 and 20. Also in this position of the piston, pre: ure chamber 1 is tree to exhaust to the OPEN TO PUBLIC INSPECTION UNDER SECTION 28 AND RULE 23 JNL Nn nr qa- io, cm ,.

IE000221 exterior through holes 8 and 9 in the bit 5 and is cut off from high pressure air supply by the piston 4 sealing with internal diameter of the outer cylinder 6.

From the top dead centre position shown in Figure 3, the piston is driven back down to the strike position by the force created by compressed air supplied to pressure chamber 2. The force with which the piston strikes the bit is determined by a number of factors. As can be seen in Figure 1, the piston 4 is cushioned by a certain extent when it strikes the bit 5 because the pressure chamber 1 starts to pressurize before the piston strikes the bit. Chamber 1 starts to pressurize when the ports 17 on the piston pass over the undercut 18 in the outer cylinder 6, The chamber 1 must start to pressurize before the piston strikes the bit or the piston will not receive an effective lift for the return stroke. However the cushioning effect referred to above reduces the blow energy of the piston.

One solution for increasing the blow energy would be to maximize the time that the top pressure chamber 2 is supplied with high pressure air during the down stroke. Referring to Figures 2 and 2a, it can be seen that the point at which high pressure air is supplied to or cut off from chamber 2, is reached when ports 15 in the piston line up with the end of undercut 20 in the inner cylinder 19. If this point were moved closer to the bit, chamber 2 would have high pressure air supply for longer. However, a side effect of this would be to reduce the overall length of the piston stroke which would reduce the length of time chamber 1 has to exhaust, as shown in Figure 3. Hence, this approach would not achieve the desired result and would have the effect of cushioning the blow even more.

Another solution for increasing the blow energy would be to increase the volume of chamber 2 so that the piston would lift to the same top of stroke position as before. However, the effect of increasing the volume of chamber 2 would be to increase the usage of compressed air by the tool. As the output of the compressors used to supply the compressed air is limited, increasing the air consumption of the tool can IE000221 be detrimental as it could lead to a decrease in the pressure output of the compressor and thus the power output of the tool.

The present invention seeks to overcome these constraints by providing a system that allows for the effective volume of chamber 2 to be increased during high pressure air supply while maintaining stroke length and maintaining or reducing air consumption levels of the tool.

Summary of the Invention The present invention provides a “down-the-hole” hammer or percussive drill tool, operated by a supply of compressed air, comprising a backhead assembly and an air distributor secured to an outer cylinder, an inner cylinder mounted adjacent the outer cylinder for defining a porting arrangement, the air distributor extending within the inner cylinder, a piston slidably mounted with respect to the inner and outer cylinders and adapted to reciprocate therein so as to repeatedly strike a bit mounted in a chuck at the forward end of the outer cylinder, wherein the rear end of the piston, the air distributor and the inner cylinder together define a rear pressure chamber, which when fully pressurized drives the piston towards the bit, and wherein the forward end of the piston, the bit and the outer cylinder together define a forward lift chamber, which when pressurized lifts the piston away from the bit after it has struck the bit, characterized in that a sliding valve member is provided within the rear pressure chamber adapted to vary the effective pressurizable volume of the rear chamber during the cycle of operations which causes a piston to reciprocate within the hammer.

Preferably, the sliding valve member is a first ring mounted on the portionjpf the air distributor which extends within the inner cylinder, defining to the forward side thereof a primary pressure chamber, and to the rear side thereof a secondary pressure chamber. Preferably, a second ring is fixedly mounted between the inner cylinder and the portion of the air distributor which extends within the inner cylinder, which second IE000221 ring acts as a stop for forward sliding movement of the first ring. Preferably, said secondary pressure chamber is adapted to receive a constant supply of pressure air throughout the cycle of operations.

Advantageously, the area of the rear face of the sliding valve member is less than the area of the forward face of the sliding valve member, such that less force is required to urge valve member rearwardly than forwardly.

Detailed Description of Preferred Embodiments Drawings Figures 1 to 3 show a cross-section of a prior art down the hole hammer arrangement, respectively showing the piston in a bit strike position, a mid cycle position, and a top dead centre position, Figure 2a is an enlarged view of area A in Figure 2, Figures 4 to 6 show similar cross-sectional views to Figures 1 to 3, of a down the hole hammer arrangement according to a first embodiment of the invention, Figure 5a is an enlarged view of area B in Figure 5, and Figures 7 to 9 show similar cross-sectional views to Figures 4 to 6, of a down the hole hammer arrangement according to a second embodiment of the invention.

Description A first preferred embodiment of the invention is shown in Figures 4,5 and 6. In Figure 4 the piston 4 is shown in the strike position. As before the high pressure air for lifting the piston is supplied into chamber 1 through porting supply chain ΪΕ000221 11,12,13,14,15,16,17 and 18. Also as before chamber 2 is free to exhaust through holes 7,8 and 9. However, the air distributor 41 and inner cylinder 47 assembly has been substantially modified to include a sliding ring or valve 42 which is seated on a fixed ring 43, both mounted on that portion of the air distributor 41 which extends into the inner cylinder, which is effectively lengthened. The fixed ring 43 has concentrically drilled holes to ensure air can pass freely through it from chamber 2, and serves as a stop lor ring 42. Ring 43 is mounted concentrically on the air distributor 41 and is fixed in place by an external circlip 44. Sliding ring 42 slides on the air distributor 41 and within the inside diameter of the inner cylinder 47.

A secondary rear pressure chamber 40 is formed between the ring 42, the inner cylinder 47 and the distributor 41. High pressure air is constantly supplied to this chamber through ports 12 in the air distributor. In the piston strike position the sliding valve is forced onto stop ring 43 because the pressure on face 46 is greater than on face 45 due to the greater pressure in rear chamber 40 compared to forward chamber 2. Referring to Figures 5 and 5a we see the point where chamber 2 is starting to pressurize as ports 15 pass over the beginning of undercut 20. The pressure in rear chamber 40 is still greater than in forward chamber 2 so ring 42 remains seated on 43. Referring to Figure 6, it can be seen that ring 42 has moved up into chamber 40. This is due to the pressure in chamber 2 increasing beyond that in chamber 40, which results in a greater force on face 45 than face 46. The piston is then forced back down to hit the bit and the ring 42 also moves back down to seat on ring 43 as shown in Figure 4.

As can be seen the sliding ring 42 acts like a valve for varying the effective pressurizable volume of chamber 2 thus eliminating the problems outlined above.

One of the problems with the first embodiment as shown in Figures 4, 5 and 6 is that the area of faces 45 and 46 is the same. This means that the point at which the ring 42 lifts is fixed. A way of varying this would be to have different cross-sectional areas on faces 45 and 46, which is shown in a second embodiment of the invention Figures 7, 8 and 9. The assembly is the same as described above with reference to Figures 4, 5 and 6, except the sliding ring 60 has a forward face 61 which has a greater area than IE000221 rear face 62. This means that it will take less force for ring 60 to slide up as there will be a greater force on face 61 than on face 62 for equal applied pressure.

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Claims (5)

1. A “down-the-hole” hammer or percussive drill tool, operated by a supply of compressed air, comprising a backhead assembly (11) and an air distributor (41) secured to an outer cylinder (6), an inner cylinder (47) mounted adjacent the outer cylinder for defining a porting arrangement (14), the air distributor extending within the inner cylinder, a piston (4) slidably mounted with respect to the inner and outer cylinders and adapted to reciprocate therein so as to repeatedly strike a bit (5) mounted in a chuck at the forward end of the outer cylinder, wherein the rear end of the piston, the air distributor and the inner cylinder together define a rear pressure chamber (2), which when fully pressurized drives the piston towards the bit, and wherein the forward end of the piston, the bit and the outer cylinder together define a forward lift chamber (1), which when pressurized lifts the piston away from the bit after it has struck the bit, characterized in that a sliding valve member (42,60) is provided within the rear pressure chamber (2) adapted to vary the effective pressurizable volume of the rear chamber during the cycle of operations which causes a piston to reciprocate within the hammer.

2. A drill tool according to claim 1, wherein the sliding valve member (42,60) is a first ring mounted on the portion of the air distributor (41) which extends within the inner cylinder, defining to the forward side thereof a primary pressure chamber (2), and to the rear side thereof a secondary pressure chamber (40).

3. A drill tool according to claim 2, further comprising a second ring (43) fixedly mounted between the inner cylinder and the portion of the air distributor which extends within the inner cylinder, which second ring acts as a stop for forward sliding movement of the first ring (42,60).

4. A drill tool according to claim 3, wherein said secondary pressure chamber (40) is adapted to receive a constant supply of pressure air throughout the cycle of operations, and optionally wherein the area of the rear face (62) of the sliding valve IE000221 member is less than the area of the forward face (61) of the sliding valve member (60) such that less force is required to urge valve member rearwardly than forwardly.

5. A drill tool according to any one of the preceding claims substantially as 5 described herein with reference to and as shown in Figures 4 to 6, or 7 to 9, of the accompanying drawings.