Field of the Invention

[0001] The present invention relates to a DTH hammer assembly and a drill comprising said DTH hammer assembly.

Background of the Invention

[0002] A surveyor investigating geological features in promising new locations often utilises a down the hole (DTH) drill to quickly and efficiently excavate to significant depths in order to determine the presence of valuable resources. DTH drills are commonly used in mineral exploration, quarrying, and mining applications. DTH drills are also used in civil engineering applications for piling, pole drilling, water wells, and geothermal well drilling. [0003] A DTH drill is basically a mini jack hammer that screws on the bottom of a drill string.

[0004] Often a survey is strongly time dependent and can even be a race against competitors to assess a geographic area as fast as possible.

[0005] The reliability of prospecting equipment, such as a DTH hammer, is therefore of paramount importance. Any downtime caused by preventable repairs can be very costly in the immediate and longer term. [0006] A DTH hammer generally comprises a backhead at one end thereof for connecting the hammer to a drill string and a chuck at an opposite end thereof adapted to securely hold a drill bit. Various components, such as a fluid distribution assembly and a piston, are positioned between the backhead and the chuck and housed within a wearsleeve in order to protect the components from environmental conditions. [0007] DTH hammers operate through the use of percussive and rotational forces. The fast hammer action breaks hard rock into small flakes and dust, which are blown clear by the air exhaust from the DTH hammer. DTH hammers often include flow apparatus to clear debris and force cuttings to the surface to be safely disposed of.

[0008] A DTH hammer can be subject to a number of forces at one time. These forces significantly impact the lifetime of the DTH hammer and can cause rapid wear of its parts.

[0009] The optimal transmission of impact energy from the piston to the drill is dependent on the precise alignment of the components within the wear sleeve. Once some wear has occurred to parts or between parts, slack movement or "play" can be generated between parts of the DTH hammer. This can accelerate the wear of the parts of a DTH hammer as adjoining parts with a once static interface suddenly become new wear faces. As percussive forces drive the DTH hammer, the introduction of play can cause elements of the hammer to no longer be precisely located in their intended positions. In addition, impact energy is not fully transmitted to the drill bit and will be absorbed by some components reducing their working life.

[0010] Over time, as the percussion cycle progresses, hammer parts and components will no longer be in their correct optimal position. This results in incorrect strike timing, which adversely affects the useful lifetime of a DTH hammer and reduces hammer efficiency.

[0011] Known methods for retaining the internal hammer parts in correct alignment and position with each other include the use of circlips, lock rings and the like. However such retaining means lose their effectiveness once undesired play between parts is generated. [0012] This has led to the use of wave springs or shimming to compensate for the wear of the parts. However, these solutions, while effective for a time, either do not adequately mitigate the effect of the percussive forces or introduce additional problems.

[0013] For example, wave springs are constructed from metal, which under the vibrations produced by the percussive forces eventually fatigue and require replacement thus increasing the number of services, and hence downtime, during the life of the DTH tool. Shims are generally added as the tool wears to take up the slack. However, this requires downtime to dismantle and service the tool, wasting valuable drilling time. Not to mention the increased complexity to the service process the shimming adds.

Summary of the Invention

[0014] According to a first aspect of the present invention, there is provided a DTH hammer comprising a first component in the form of a backhead; a second component in the form of a fluid distribution assembly; and at least one retaining ring located between said backhead and said fluid distribution assembly; the at least one retaining ring being compressible and having a first uncompressed state and a second compressed state, the first and second component being located at a fixed distance from each other with the at least one retaining ring positioned between first and second components in said compressed state, wherein in use the at least one retaining ring is configured to expand from said compressed state towards said uncompressed state due to a change in relative position between the first and second components.

[0015] Advantageously, this reduces accelerated wear on components of the DTH hammer. As components wear down and no longer tightly mate, the retaining ring can expand and fill the newly created space while preventing undesired movement or vibration of the components. This prevents accelerated wear thereby increasing the useful life of the tool as the retaining ring will expand as other components wear, thereby taking up any slack that may occur between parts.

[0016] Suitably the retaining ring is made of a polymer. Preferably, the polymer is elastomeric, thus allowing the material to be readily compressed from an initial dimension, to a second reduced dimension. Upon decompression, the material returns to its initial form and dimensions.

[0017] Preferably the retaining ring has a Shore® hardness in the range 65 to 95. Advantageously, in this range, materials (particularly polymers) are readily compressible. This makes materials in this range a suitable choice of buffer.

[0018] The Shore® hardness of the retaining ring may be in the range of 70 to 90. Preferably the retaining ring has a Shore® hardness in the range of about 80 to 90.

[0019] Advantageously a change in dimension of the retaining ring between the uncompressed state and the compressed state is at least 0.5mm. This allows for a change in relative position between the first and second components of up to 0.5mm at the least.

[0020] Advantageously, the backhead is the first component in the chain of components, and therefore represents a fixed point within the DTH hammer. Placing the retaining ring adjacent the backhead reduces the need for extra retaining rings, thereby reducing product cost, simplifying maintenance, and reducing the required number of parts.

[0021] The fluid distribution assembly may be a gas (e.g. air) or a liquid (e.g. water) distribution assembly.

[0022] The fluid distribution assembly may be a single piece fluid distribution assembly. [0023] Alternatively, the fluid distribution assembly may be formed of multiple parts, for example it may be in the form of a two piece fluid distribution assembly comprising a diverter and valve chest.

[0024] Preferably, the first and second components comprise at least one shoulder respectively. Advantageously, a shoulder profile provides an enlarged surface area with which to abut the retaining ring. This controls the compression applied to the retaining ring and spreads out vibrational forces, further utilising the protection effects of the retaining ring.

[0025] According to a second aspect, there is provided a drill comprising a DTH hammer in accordance with the first aspect and a drill bit coupled to the DTH hammer.

[0026] Suitably, a method of assembling the DTH hammer according the first aspect of the present invention comprises the steps of locating the at least one retaining ring between the first and second components; wherein the at least one retaining ring is in an uncompressed state; wherein as said first and second components are urged together the at least one retaining ring is put into a compressed state. Advantageously, this method ensures the correct amount of compression is applied to the retaining ring to ensure it is able to fulfil its function as the manufacturer intended. This ensures the useful life of the tool is maintained. [0027] Preferably, a kit of parts suitable for constructing a DTH hammer with a compressible retaining ring comprises at least a first in the form of a backhead and a second component in the form of a fluid distribution assembly; and a compressible retaining ring; wherein the compressible retaining ring is in an uncompressed state.

[0028] Other aspects are as set out in the claims herein. Brief Description of the Drawings

[0029] For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which:

[0030] Figure 1 displays a first embodiment of a drill in accordance with the invention; [0031] Figure 2 displays an exploded view of the DTH hammer forming part of the drill of Figure 1 ;

[0032] Figure 3 displays a partial cross section of the backhead end of the DTH hammer of Figure 2 with the joint between the backhead and wear sleeve pre torque;

[0033] Figure 4 displays a similar view to that of Figure 3 with the joint between the backhead and wear sleeve tightened; [0034] Figure 5 displays a second embodiment of a drill in accordance with the invention;

[0035] Figure 6 displays an exploded view of the DTH hammer forming part of the drill of Figure 5;

[0036] Figure 7 displays a partial cross section of the backhead end of the DTH hammer of Figure 6 with the joint between the backhead and wear sleeve tightened. Detailed Description of the Embodiments

[0037] There will now be described by way of non-limiting example a specific mode contemplated by the inventors. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the description. [0038] Referring to Figure 1 , a first embodiment of a DTH drill 10 in accordance with the invention is shown. The drill 10 is in the form of a DTH hammer 100 with a drill bit 12 attached to an end of the DTH hammer 100.

[0039] With additional reference to Figures 2 to 4, the features of the DTH hammer 100 will now be described. In a typical setup arrangement as known in the art, the DTH hammer 100 includes a backhead 101 which provides an interface between a drill string and the rest of the DTH hammer 100; a chuck 1 17 for coupling the drill bit 12 to the DTH hammer 100; and a main body in the form of a wearsleeve 109 having a first end coupled to the backhead 101 and a second opposite end coupled to the chuck 1 17.

[0040] The backhead 101 is typically constructed from steel alloy and is equipped with interface means, such as a thread to engage with a complimentary thread on the drill string.

[0041] The backhead 101 suitably includes shoulders and ridges located on an outer surface so as to provide seating positions to ensure correct engagement of the backhead 101 to the drill string and of the backhead 101 to the main body or wearsleeve 109 of the DTH hammer 100.

[0042] The backhead 101 is tubular in construction and has a passageway passing there through in order to allow fluid flow from the drill string through the backhead 101 to the rest of the DTH hammer 100. The fluid is suitably a gas (typical air) or a liquid (typical water).

[0043] The fluid serves two functions, primarily to drive the percussive action of the DTH hammer 100 to allow for drilling. Secondly, the fluid serves as a lubricant and drill cutting transport system, whisking away the freshly cut debris from the bottom of the hole, past the drill string and out to the surface.

[0044] In the embodiment shown, the backhead fluid passageway is in two sections. A first passageway section 101 1 which extends from the drill string end of the backhead 101 to approximately the centre of the backhead 101 , and a second passageway section 1012 which extends from the wearsleeve end of the backhead 101 and adjoins the first fluid passageway section 101 1 at approximately the centre of the backhead 101 . The second fluid passageway section 1012 is of a greater cross-sectional area than the first fluid passageway section 101 1 of the backhead 101 .

[0045] The backhead 101 is equipped with releasable engagement means for interfacing with the wearsleeve 109 of the DTH hammer 100. Such interfacing means is shown in the form of a thread in Figure 2, although it will be apparent to one skilled in the art that any suitable coupling means may be substituted.

[0046] The wearsleeve 109 is in the form of a substantially hollow cylinder and is configured to protect the internal components of the DTH hammer 100 from environmental conditions as well as to facilitate the alignment of the internal components with one another. As can be seen in Figure 1 , the wear sleeve 109 does not have a constant inner diameter across its length, rather the inner diameter of the wear sleeve 109 at different locations thereof is dependent on the internal components of the DTH hammer 100 which are located therein.

[0047] The chuck 1 17 includes bit retention apparatus which protrude from an interior wall of the chuck 1 17 and engages with valleys in an outer wall of the drill bit 12. This provides a degree of travel such that the drill bit 12 may oscillate as a percussion cycle progresses, but may not leave the jaws of the chuck 1 17.

[0048] The chuck 1 17 is provided with connection means to interface with the wearsleeve 109 of the DTH hammer 100. In the embodiment shown, the interface means is in the form of complimentary male and female threads located on the chuck 1 17 and the wearsleeve 109 respectively. It would be understood by the person skilled in the art that other interface means may be utilized. [0049] A release washer 1 16 is located at the interface between the chuck

1 17 and the wearsleeve 109 to facilitate easy removal of the chuck 1 17, whereby if the torque applied to couple the chuck 1 17 to the wearsleeve 109 is too great to be undone with the tooling at hand, the washer 1 16 can be cut away reducing the torque in the joint and allowing easy removal of the chuck 1 17 from the wearsleeve 109.

[0050] The bit 12 is of any suitable construction or configuration that a skilled addressee may require. An example bit consists of a rock cutting head and a key for engaging with the chuck 1 17.

[0051] A bit retainer 1 14 is positioned within the wearsleeve 109 and is held in position within the wearsleeve 109 by means of a bit retainer O-ring 1 15. The bit retainer 1 14 serves to prevent the drill bit 12 unintentionally dislocating from the DTH hammer 100 in the event of break or shankage.

[0052] The internal components of the DTH hammer 100 will now be described in further detail. In the embodiment shown, the DTH hammer 100 has a checkvalve 102 located within the second fluid passageway 1012 of the backhead 101 . The function of the checkvalve 102 is to prevent back flow of fluid during the percussion cycle of the hammer 100 along the drill string. [0053] The checkvalve 102 has a conical head 1021 . When the checkvalve 102 is in a closed position, the conical head 1021 is arranged to block off fluid communication between the first and second fluid passageways 101 1 , 1012 of the backhead 101 so as to provide a seal preventing fluid flow back through the backhead 101 .

[0054] A checkvalve spring 103 serves to bias the checkvalve 102 towards the first fluid passageway 101 1 ensuring that when fluid flow is not from the backhead 101 in a direction towards the chuck 1 17, that the checkvalve 102 is in a closed position, preventing fluid flow through the backhead 101 .

[0055] A fluid distribution assembly is positioned adjacent the backhead 101 , which in the embodiment shown is a dual part assembly in the form of a valve chest 105 and diverter 106 arrangement.

[0056] As can be seen in the figures, the checkvalve 102 is partially housed within a section 1051 of the valve chest 105, while the checkvalve spring 103 is fully housed within said section 1051 of the valve chest 105. The valve chest 105 is provided with apertures to allow fluid flow there through while retaining the checkvalve 102 and valve spring 103 in their appropriate and designated locations.

[0057] The valve chest 105 further includes a shoulder 1052 which aids in aligning the valve chest 105 within the wearsleeve 109. [0058] The diverter 106 has a cuplike section 1061 and a tubelike section

1062 protruding from the cuplike section 1061 . The cuplike section 1061 of the diverter 106 is equipped with numerous apertures 1063, to guide and regulate fluid flow through the body of the DTH hammer 100 preventing fluid pressure build up and allowing fluid to flow from one section to another. A head section 1053 of the valve chest 105 is received within the cuplike section 1061 of the diverter 106. [0059] The diverter 106 is made from a single piece of material, such as steel or other suitable metal alloy. It will be obvious to one skilled in the art which materials are suitable. [0060] The free end of the tubelike section 1062 is configured to receive a choke plug 108.

[0061] The choke plug 108 provides a further means of adapting and regulating the fluid flow within the DTH hammer 100.

[0062] The cuplike section 1061 of the diverter 106 has an outwardly protruding rim 1064 which, in use, on one side thereof engages with the shoulder 1052 of the valve chest 105 and on the opposite side thereof engages with an outer edge of an inner cylinder/sleeve 107 of the DTH hammer 100.

[0063] The inner cylinder 107 is tubular in form and serves as a partition and assists in the flow of fluid about the DTH hammer 100. Apertures are incorporated into a wall of the inner cylinder 107 to this end. [0064] A cavity 1 18 exists between the inner cylinder 107 and the wearsleeve of the DTH hammer 100. The cavity 1 18 is adjacent the apertures in the inner sleeve 107 thereby forming a conduit for fluid flow there through.

[0065] A piston 1 10 is positioned downstream of the fluid distribution assembly with an end thereof located within the inner cylinder 107 of the DTH hammer 100. The piston 1 10 is in the form of a substantially tubular member and an opposite end of the piston 1 10 is arranged to abut an end of the drill bit 12 when the drill bit is attached to the DTH hammer 100. [0066] A bit bearing 1 12 is positioned about the end of the drill bit 12 which engages the piston 1 10. In the embodiment shown, the bit bearing 1 12 is positioned between the bit retainer 1 14 and a piston retaining ring 1 1 1 located at the interface between the piston 1 10 and the drill bit 12. A bit bearing O-ring 1 13 facilitates the positioning of the bit bearing 1 12 within the wearsleeve 109.

[0067] In a DTH hammer 100 in accordance with the invention, rather than the use of a circlip or lock ring to hold the fluid distribution assembly in the correct position within the DTH hammer, are compressible retaining ring 104 is utilised.

[0068] The compressible retaining ring 104 is situated between an end of the backhead 101 and the shoulder 1052 of the valve chest 105. The compressible retaining ring 104 when located in this position also functions as a compression washer/buffer.

[0069] In the embodiment shown, the compressible retaining ring 104 is in the form of a substantially annular ring which is of similar dimension to the shoulder 1052 of the valve chest 105.

[0070] While the aperture in the compressible retaining ring 104 is shown as being circular, it would be understood that the aperture need not be circular, but may be shaped to match the shape of the part of the valve chest 105 which it surrounds in use.

[0071] Upon initial construction of the DTH hammer 100, all the parts are seated and aligned in a first, pre-torque position (for example, the parts are screwed together to the point they are "finger tight" only).

[0072] Once the constructor is satisfied of the correct location and arrangement of the parts, the constructor proceeds to apply the manufacturer specified torque to each of the joints. It will be obvious to one skilled in the art of the value of the torque to be applied, or at the very least, obvious to one skilled in the art to consult the manufacture supplied DTH hammer 100 owner's manual to look up the appropriate torque value. [0073] In the pre-torque position, a tight fit between the backhead 101 and the wearsleeve 109 is not obtained due to the compressible retaining ring 104, instead a gap 1 19 is present between the two components (see Figure 3). This gap 1 19, represents the difference in thickness of the compressible retaining ring 104 when in a compressed state compared to when it is in an uncompressed state. In the embodiment shown, the gap 1 19 is 0.5 mm. Although, depending on the amount of compression to be applied to the compressible retaining ring 104, or the amount of play to be compensated by the compressible retaining ring 104, the compressible retaining ring 104 may be designed to result in gap 1 19 when the backhead 101 and the wearsleeve 109 are in the pre-torque position which is more than or less than 0.5 mm.

[0074] When the correct torque is applied to the backhead 101 , the compressible retaining ring moves towards its compressed state and the gap 1 19 between the backhead 101 and wearsleeve 109 closes (see Figure 4).

[0075] In the compressed state, the compressible retaining ring 104, presents a well of stored, potential energy. If the pressure applied to the retaining ring 104 lessens due to a change in the relative position between the backhead 101 and the valve chest 105, the potential energy is converted to kinetic energy, and the compressible retaining ring 104 expands to fill the space created from the change in position.

[0076] Due to the arrangement of the internal components of the DTH hammer 100, a change in the relative position between the backhead 101 and the valve chest 105 will occur if the blackhead 101 is loosened from the wearsleeve 109 or wear occurs in one or more of the internal components of the DTH hammer 100 that would otherwise create play between adjacent components. [0077] The expansion of the compressible retaining ring 104 towards the uncompressed state results in the compressible retaining ring 104 acting as a buffer preventing wearing internal parts from moving and vibrating undesirably, despite there being a deterioration in those parts. The compressible retaining ring 104 expands to take up and remove unwanted play between components thus prolonging the life for the DTH hammer as the wear of the components is not exacerbated.

[0078] The compressible retaining ring 104 is sufficiently compressible to ensure it may be compressed and expand to dimensions as determined by the designer. [0079] The compressible retaining ring 104 is preferably constructed of a material with a Shore® hardness in the range of 65 - 95. Although, it will be apparent to one skilled in the art that alternative values of hardness outside of the aforementioned range may be suitable for some applications. Such suitable materials are typically polymers, particularly elastomers, such as but not limited to, rubber, polyurethane, and silicones. One skilled in the art will understand that any material that may instantly transform from a compressed state, to an uncompressed state by producing an appropriate expansion along a dimension will be suitable as a compressible retaining ring. In the embodiment shown, the compressible retaining ring 104 is formed from polyurethane with a Shore® hardness of 90.

[0080] The compressible retaining ring 104 serves two functions. Firstly, the compressible retaining ring 104 ensures that components of the DTH hammer 100 are maintained in their correct, allocated, position.

[0081] Secondly, as the internal components wear (creating a change in their original positions), the compressible retaining ring 104 expands, causing the continual contact between adjacent components so as to continue to maintain the components in their allocated positions and alignment.

[0082] Referring to Figures 5 to 7, a second embodiment of a DTH drill 20 in accordance with the invention is shown. Similar features to those of the first embodinnent are given similar reference numbers but with the prefix '2'. For example, the backhead which in the first embodiment was identified with the reference number '101 ' is identified in the second embodiment with the reference number '201 '.

[0083] As in the first embodiment, the DTH drill 20 has a drill bit 22 coupled to a DTH hammer 200.

[0084] The differences between the DTH hammer of the first and second embodiments are now described. In the second embodiment, rather than the fluid distribution assembly being formed from multiple components, the fluid distribution assembly is a single piece component in the form of a control tube identified by the reference numeral 205. [0085] The control tube 205 includes a first section 2051 in which the checkvalve spring 203 is fully housed and the checkvalve 202 is partially housed (see Figure 5). The control tube 205 also has a shoulder 2052 which functions in a similar manner to the shoulder 1052 of the valve chest 105 of the first embodiment, and a tubelike section 2053 extending from the shoulder section 2052 which functions in a similar fashion to the tubelike section 1062 of the diverter 106 of the first embodiment.

[0086] Furthermore, in the second embodiment the DTH hammer 200 does not have an inner cylinder, and the piston is ported to allow fluid flow through a conduit located in the walls of the piston at appropriate points in the piston cycle.

[0087] While the embodiments of the DTH hammer 100, 200, in accordance with the invention, have been described with a single compressible retaining ring positioned between the back head and fluid distribution assembly, other embodiments are envisaged by the inventors. For example the DTH hammer may include a plurality of compressible retaining rings at different points or a single compressible retaining ring at a different internal position within the wearsleeve. [0088] In addition, the compressible retaining ring is not limited to the DTH hammer arrangements described above and may be utilised in other DTH hammer configurations, for example, in a reverse circulation hammer in place of a lock ring arrangement.