IES86382Y1 - Footvalve assembly for percussion drill tools - Google Patents

Description

FOOTVALVE ASSEMBLY FOR PERCUSSION DRILL TOOLS Field of the Invention The present invention relates to a footvalve assembly for fluid-operated percussion drill tools. In particular, the invention concerns a footvalve assembly for use with “down— the—hole” hammers.

Background to the Invention Some designs of conventional down-the-hole hammers and fluid—operated percussion drill tools comprise an external cylinder or outer wear sleeve, within which is mounted an inner cylinder which in turn engages with a backhead assembly. A sliding reciprocating piston co-operates with the inner cylinder and backhead assembly, which when air pressure is supplied through the backhead assembly, acts with a percussive effect on a drill bit retained within a chuck on the outer wear sleeve.

Typically the inner cylinder is mounted co-axially within the outer wear sleeve. The sliding piston is mounted for reciprocating movement within the inner cylinder and the outer wear sleeve, to strike the hammer bit mounted for sliding movement in the chuck located at the forward end of the outer wear sleeve, in well known manner. A foot valve is positioned above the bit.

When the piston strikes the hammer bit, the footvalve cooperates with a nose of the piston to prevent pressurised air from entering an exhaust bore of the hammer bit, and the piston is caused to lift. Once the piston nose moves upwards past the top of the footvalve, air in the lift chamber starts to exhaust through the exhaust bore in the bit.

A typical footvalve arrangement is shown in Figure l. A hammer bit 1 is is formed with an exhaust bore 2 of diameter 3. A counterbore 4 having a diameter 5 larger than bore diameter 3, is formed at an upper end of the bit 1. Bore 2 and counterbore 4 are formed coaxially, in that both are centred on a central longitudinal axis of the bit 1. A shoulder 6 is defined at a lower end 7 of the counterbore 4. A portion 9 of the counterbore 4 intermediate the lower end 7 and an upper end 8 thereof is formed with a slightly larger diameter than that of the counterbore 4 itself. 886382 Footvalve 10 comprises a cylindrical exhaust tube 1 1 formed from a flexible material such as plastic or rubber. An outer diameter 14 of the tube 1 l is selected to be the same as or slightly larger than that of the counterbore 4. In addition, the cylindrical tube 1 l is formed with a region of increased diameter 12 adjacent a lower end 13 thereof.

A press is used to assemble the footvalve 10 into the counterbore 4 of the bit 1. Because the outer diameter 14 of the exhaust tube l l is the same or slightly larger than the diameter 5 of the counterbore, the tube deforms slightly as it is forced into the bit. The footvalve is pushed into the counterbore until the region 12 of increased diameter seats within the portion 9 of the counterbore. Once the footvalve is in place, the flexible material of the tube I 1 expands against the inner walls of the bit so that the footvalve 10 is held in the counterbore 4 by way of an interference tit and also by way of the engagement between the region 12 of the footvalve and the portion 9 of the bit.

A disadvantage of this arrangement is that, over time, due to the heat generated at the bit and the relative movement between the bit and the piston, this type of footvalve tends to loosen and ultimately fail through breakage or removal from the bit counterbore due to forces acting on it.

United States Patent Application Publication No. US 2011/0232922 relates to a footvalve assembly for a down hole drill in which an exhaust tube is reinforced on an inner surface with a rigid support sleeve, so that when the assembly is inserted into the bit counterbore, the footvalve is sandwiched between the support sleeve and the counterbore. However, in this arrangement, the vibration caused by operation of the drill would be likely to damage the exhaust tube.

It is therefore desirable to provide a footvalve assembly which resists loosening and breakage during operation of a percussion drill tool.

Summary of the Invention According to an aspect of the present invention, there is provided a footvalve assembly for a percussion drill tool, comprising: a substantially cylindrical exhaust tube; and a substantially annular retaining member having an inwardly directed lip provided at a lower end thereof; wherein the exhaust tube comprises a recess provided in an outer wall thereof and wherein the exhaust tube is insertable into the retaining member such that the lip is received in the recess.

An advantage of this arrangement is that when forces are applied to the footvalve assembly during operation of the tool which act to push the footvalve assembly out of the bit, the recess in the exhaust tube cooperates with the lip on the retaining member to retain the valve in the tool.

The terms “inward” and “inwardly” as used herein are intended to indicate a direction towards a central longitudinal axis of the retaining member and/or exhaust tube. The term “lower” as used herein is intended to indicate a portion or end which is oriented towards the forward end of the percussion drill tool, that is, towards a bit of the percussion drill tool. Conversely, the term “upper” as used herein is intended to indicate a portion or end which is oriented towards the rear end of the percussion drill tool, that is, away from the bit of the percussion drill tool.

The lip may be substantially annular in shape. A free end of the lip may have a smaller diameter than that of an upper portion of the retaining member.

According to an embodiment of the invention, the lip is angled downwards. The terms “downward” and “downwardly” as used herein are intended to indicate a direction towards a lower or forward end of a percussion drill tool, that is, towards the bit of the percussion drill tool. The lip may be arranged at an acute angle to a cylindrical wall of the retaining member. In preferred embodiment, the lip is arranged at an angle of between about 30° and about 60° to the cylindrical wall of the retaining member prior to assembly with the exhaust tube.

An advantage of this arrangement is that the downward angle of the lip allows the exhaust tube to be inserted therewithin relatively easily during assembly of the footvalve assembly. However, when forces are applied to the footvalve assembly during operation of the tool which act to push the footvalve assembly out of the bit, the angle of the lip is such that it acts to prevent the assembly from being pushed out of the bit counterbore. It has been determined that the force required to push the exhaust tube out of the bit is much greater than the force required to push it into the bit, since in order to do so, it would be necessary to shear the lip off the retaining member.

According to an embodiment of the invention, the lip is deformable to allow the exhaust tube to be inserted into the retaining member during assembly of the footvalve. In certain embodiments, the retaining member may be formed from a flexible material, such as plastic or rubber, such that the lip is capable of deforming reversibly as the exhaust tube is inserted into the retaining member. In other embodiments, the retaining member may take the form of a circlip, whereby the lip is capable of expanding radially to allow the exhaust tube to be inserted into the retaining member. Preferably, the exhaust tube is substantially rigid.

Preferably the lip is integrally formed with the retaining member.

An internal diameter of a cylindrical wall of the retaining member may be substantially the same as an external diameter of the exhaust tube.

The footvalve assembly may be receivable within a counterbore of a percussion bit and the assembly may be dimensioned to provide an interference fit with the counterbore.

According to a further aspect of the invention, there is provided a down-the—hole hammer comprising: a percussion bit, comprising a counterbore provided therein; a substantially annular retaining member, having an inwardly directed lip provided at a lower end thereof, received within the counterbore; and a substantially cylindrical exhaust tube, comprising a recess provided in an outer wall thereof, wherein the exhaust tube is inserted into the counterbore and the retaining member such that the lip is received in the recess.

The counterbore may comprise a portion of increased diameter and the retaining member may be received within the counterbore such that it is seated within the portion of increased diameter.

The retaining member may be dimensioned such that an outer diameter thereof provides an interference fit with the portion of increased diameter of the counterbore.

The thickness of the retaining member may be such that when the retaining member is seated within the portion of increased diameter, an inner surface of a cylindrical wall of the retaining member is substantially flush with the counterbore of the bit.

The exhaust tube may be dimensioned such that an outer diameter thereof is selected to provide an interference fit with the counterbore.

Brief Description of the Drawings Figure 1 is a cross-sectional View of a conventional footvalve arrangement; Figure 2 is a cross—sectional view of a footvalve assembly according to an embodiment of the present invention, prior to assembly; Figure 3 is a cross—secti0nal view of the footvaive assembly of Figure 2, during assembly; Figure 4 is a cross-sectional View of the footvalve assembly of Figure 2, in situ; Figure 5 is an exploded perspective view of the footvalve assembly of Figure 2; and Figure 6 is an exploded perspective view of a footvalve assembly according to an alternate embodiment of the present invention.

Detailed Description of the Drawings Figure 2 illustrates a ‘footvalve assembly according to an embodiment of the invention, prior to assembly. A hammer bit 1 is formed with a bore 2 of diameter 3. A counterbore 4 having a diameter 5 larger than bore diameter 3 is formed at an upper end of the bit. Bore 2 and counterbore 4 are formed coaxially, in that both are centred on a central longitudinal axis of the bit 1. A shoulder 6 is defined at a lower end 7 of the counterbore 4. A portion 9 of the counterbore 4, intermediate the lower end 7 and an upper end 8 thereof, is formed with a slightly larger diameter than that of the counterbore 4 itself.

Footvalve assembly 20 comprises a cylindrical exhaust tube 21 formed from an engineering plastic. In alternative embodiments, the exhaust tube may be formed from other materials such as aluminium, steel, rubber or other materials, An outer diameter 24 of the tube 21 is selected to provide an interference fit with the counterbore 4. The exhaust tube 21 further comprises a circumferential groove 25 provided in an outer wall thereof. As shown in the drawings, the groove is provided towards the lower end 26 of the tube 21. In the embodiment shown, an upper surface of the groove is tapered and a shoulder is formed at the lower end of the groove.

The footvalve assembly 20 further comprises a plastic retaining ring 30 having a cylindrical wall 36 and an inwardly directed deformable lip 31 integrally formed at a lower end 32 thereof. In other embodiments, the ring may be formed from rubber or other flexible materials. An outer diameter 33 of the retaining ring 30 is the same as or slightly larger than the diameter of portion 9 of the counterbore 4. As shown in Figure 2, the retaining ring is dimensioned to be received within portion 9 of the counterbore 4.

As also shown in the drawings, the lip 31 is substantially annular in shape and a free end 34 of the lip has a smaller diameter 35 than that of an upper portion 36 of the retaining ring. The lip 31 is angled downwards, that is, towards the head of bit 1. In the embodiment shown, the lip is tapered so that an inner wall of the lip is angled at about 34° to the cylindrical wall of the ring and an outer wall of the lip is angled at about 43° to the cylindrical wall of the ring prior to assembly with the exhaust tube. In other embodiments, the lip may be angled downwards at an angle of between about 30° and about 60°.

To assemble the footvalve assembly 20 within the bit 1, retaining ring 30 is first inserted into the counterbore 4 so that it is seated in the portion of increased diameter 9, as shown in Figure 2. As shown in Figure 3, a press is then used to assemble the exhaust tube 21 into the counterbore 4 of the bit 1. As the tube is forced into the bit I, the lower end 26 of the tube forces the deformable lip 31 on retaining ring 30 to open, allowing the tube to push past the lip. The downward angle of the lip 31 allows it to deform relatively easily to allow the exhaust tube 21 to be inserted therewithin. As shown in Figure 4, the tube 21 is pushed into the counterbore until the lip 31 is received within groove 25. The tapered upper surface of the groove 25 eases insertion of the lip into the groove. As shown in the Figure 4, when the footvalve assembly is assembled, the angle of the lip on the retaining ring is altered as compared with the pre-assembled ring. The groove 25 is positioned on the tube 21 such that when the lip 31 is received in the groove, the lower end 26 of the tube is seated against the shoulder 6.

Because the outer diameter 33 of the retaining member 30 is the same or slightly larger than the diameter of portion 9 of the counterbore and the outer diameter 24 of the exhaust tube 21 is substantially the same as the diameter 5 of the counterbore, the footvalve assembly 20 ‘is held in the counterbore 4 by way of an interference fit between the eounterbore and the retaining ring and the retaining ring and the exhaust tube, and also by way of the engagement between the lip 31 and the groove 25. When forces are applied to the footvalve assembly 20 during operation of the tool which act to push the assembly out of the bit counterbore 4, the shoulder formed at the lower end of the groove 25 “picks up” or engages with the lip 31, and the angle of the lip is such that it acts to prevent the assembly from being pushed out of the bit counterbore. Because of the inward and downward bias of the lip, the force required to remove the exhust tube is considerable. It has been determined that the force required to push the exhaust tube out of the bit is much greater than the force required to push it into the bit. In fact, in order to push the exhaust tube out of the assembly, it would be necessary to shear the lip off the retaining ring, which requires considerable force.

An alternate embodiment of the invention is shown in Figure 5. In this embodiment, the retaining ring 30’ takes the form of a plastic circlip. In alternative embodiments, the circlip may be made from other materials, such as metal or rubber. The ring 30’ has an inwardly directed lip 31’ integrally formed at a lower end thereof. As in the previous embodiment, the retaining ring 30’ is dimensioned to be received within portion 9 of the counterbore 4. The lip 3 I ’ is part annular in shape and a free end 34’ of the lip has a smaller diameter than that of an upper portion 36’ of the retaining ring. The lip 31 ’ is angled downwards, that is, towards the head of bit 1 at an angle of about 45°. In other embodiments, the lip may be angled downwards at an angle of between about 30° and about 60°.

To assemble the footvalve assembly 20 within the bit 1, retaining ring 30’ is first inserted into the counterbore 4 so that it is seated in the portion of increased diameter 9, as shown in Figure 2. The circlip 30’ is biased such that when it is inserted into portion 9 of the counterbore 4, it exerts an outward force on the counterbore which tends to hold the ring 30’ in place. As before, a press is then used to assemble the exhaust tube 21 into the counterbore 4 of the bit I. As the tube is forced into the bit 1, lower end 26 of the tube forces the lip 31’ on retaining ring 30 to expand radially, allowing the tube to push past the lip. Because the ring 30’ is formed as a circlip and due to the downward angle of the lip 31’, the lip deforms relatively easily to allow the exhaust tube 21 to be inserted therewithin. As for the previous embodiment, the tube 21 is pushed into the counterbore until the lip 31 ’ is received within groove 25.

The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub—c0mbination.

Claims (5)

Claims

1. A footvalve assembly for a percussion drill tool, comprising: a substantially cylindrical exhaust tube; and a substantially annular retaining member having an inwardly directed lip provided at a lower end thereof; wherein the exhaust tube comprises a recess provided in an outer wall thereof and wherein the exhaust tube is insertable into the retaining member such that the lip is received in the recess.

2. A footvalve assembly as claimed in claim 1, wherein the lip is angled downwards, and optionally, the lip is arranged at an acute angle to a cylindrical wall of the retaining member, and optionally, the lip is arranged at an angle of between about 30° and about 60° to the cylindrical wall of the retaining member.

3. A footvalve assembly as claimed in claim or claim 2, wherein the lip is deformable to allow the exhaust tube to be inserted into the retaining member during assembly of the footvalve.

4. A down-the-hole hammer comprising: a percussion bit, comprising a counterbore provided therein; a substantially annular retaining member, having an inwardly directed lip provided at a lower end thereof, received within the counterbore; and a substantially cylindrical exhaust tube, comprising a recess provided in an outer wall thereof, wherein the exhaust tube is inserted into the counterbore and the retaining member such that the lip is received in the recess.

5. A footvalve assembly and/or a down-the-hole hammer substantially as hereinbefore described with reference to and/or as illustrated in