RETENTION MEANS

Abstract: A retention means for retaining a first element (18) of circular cross section within a space of complementary cross section in a second element (11) where the retention means comprises a plurality of axially spaced annular recesses (23, 24) formed in the wall (11) of the space and a retaining ring (25) having an axial length at least equal to the spacing between the outer edges of the outermost recesses and where the radially outermost face (26, 27) is of complementary profile to the profile of the wall (11) between the outer edges. The ring (25) has an outside diameter corresponding to the diameter of the recesses (23, 24) and is in direct abutting contact with the first element (18). A particular application of the invention relates to the support for the components of a down the hole hammer within the casing of the hammer.

Description: "RETENTION MEANS" This invention relates to the retention of one or more elements concentrically within the bore of another element. It has been the practice in the past to retain a circular element of round cross- section in a journal in a particular location or space of complementary cross- section of another body to prevent some axial movement therebetween by providing a circular abutment or shoulder on the inner face of the journal or space in order to retain the element in position. The abutment has in the past comprised a shoulder which is formed in the inner surface but this requires a significant amount of material to be machined from the inner face to form the shoulder. Another form of abutment has comprised a retaining ring in the form of a resilient or solid circlip or segmented annulus receivable in a recess in the inner bore of a member such as a tubular member to provide the abutment or shoulder and which extends beyond the inner face of the bore to retain the element. A difficulty with this latter arrangement relates to the magnitude of the annular area of the bearing surface available to support the retaining ring. This is determined by the depth of the recess which is in turn governed by the wall thickness of the tubular member. It is an object of this invention is to provide a retention means which enables the amount of machining involved in the provision of the support for an element so that the dimensions of the abutment is minimal and machining of the one or more elements is reduced and where the degree of support can be increased without an increase in the wall thickness of the tubular member to allow a recess or abutment to be machined to provide sufficient support to receive and locate an element and retain it in the correct location for the service life of the elements. Accordingly, the invention resides in a retention means for retaining a first element of circular cross-section within a space of complementary cross-section in a second element said means comprising a plurality of axially spaced annular recesses formed in the wall of the space and a retaining ring having an axial length at least equal to the spacing between the outer edges of the outermost recesses and where the radially outermost face is of complementary profile to the profile of the wall between said outer edges, said ring having an outside diameter corresponding to the diameter of the recesses said retaining ring being in direct abutting contact with the first element. According to a preferred feature of the invention the retaining ring is formed of a plurality of segments. According to an alternative preferred feature of the invention the retaining ring is capable of resilient radial compression to an external diameter at least equal to the internal diameter of the second element. One application of the invention relates to the support of components within the casing of a fluid operated down hole hammer or motor. Down hole hammers utilise piston type motors which develop energy levels which are usually directly related or related, in part to the diameter of the piston and piston bore of the hammer. The larger the piston bore the greater the energy potential of the motor and thus the hammer. In designing and manufacturing such a piston type motor for a down hole hammer it is necessary to locate or contain several internal components in specified positions within a cylindrical casing and to retain such components within the casing of the motor assembly in an exact position for the life of the unit to ensure the assembly functions correctly and its maximum efficiency. Such components include drill bit bushings, guides, check valves, valve bodies, air distribution valve or valve components, internal cylinders, control rod retainers, control rods, make-up components, or assemblies. These are usually located on a shoulder, abutment or a retaining ring located within the piston case or internal cylinder in order to support the item and as to retain that item and adjacent items in their exact position. In some instances, it has been the practice to machine or form either a single shoulder in a non-reversible piston case so as to form a lip or abutment shoulder in order to locate such components or to machine a reversible piston case with a shoulder or abutment formed at either end by means of a counter bore. In other instances, it has been the practice to machine a recess within the bore and to locate a single ring in the recess. To retain such components in position it is usual practice to lock the components in place against the abutment, shoulder or retaining ring by applying a load to the component in one direction when the components are assembled in the piston case by means of pressure from a spring or elastomeric material in order to exert a load and or use face to face component contact to prevent any component that mates with a shoulder abutment or retaining ring from moving, in order that they remain in one position. Because of the high internal load or cyclic pressures which are generated by high pressure fluid acting internally on the pressure surfaces of the internal components and the constant cyclic vibration of mating parts that are not securely and firmly located, it is common for those parts to work against each other or against the shoulders of the abutment or retaining ring or recess shoulders and as a result wear will occur. This results in the components becoming loose in relation to each other or to their precise location or insecure to the extent that the motor assembly becomes incapable of operating correctly or efficiently. In addition, due to the need to maximise the piston bore to maximise energy levels, the or each abutment, counterbore shoulder or retaining ring provide insufficient annular surface area to adequately locate or maintain the mating parts securely without premature or undue wear taking place. One reason for such is that a single locating shoulder for a given wall thickness with a single retaining ring may have insufficient area and is therefore prone to deformation or wear resulting in movement and mislocation of the internal components that are located and supported by it. However, the need to form a shoulder by the machining of a counter bore at one or either end of the cylinder or piston case of sufficient area will reduce or minimise the piston bore. Similarly the need to machine or form a recess of sufficient depth or provide a shoulder of adequate area to locate a single retaining ring in order to locate and retain internal components will also reduce, either the size of the bore, or reduce the wall thickness of the cylinder or piston case in the region of recesses, which in turn reduces the strength of the casing and the capacity of the casing to accommodate for wear which reduces the life of the component. For example, in the case of a down hole hammer the outer face of the hammer is subject to wear and therefore the casing needs to have sufficient thickness to be able to accommodate for normal wear of the exterior face of the casing. Accordingly the invention also resides in a down the hole hammer wherein at least some of the components are supported within the casing by a retention means of the form as described above and wherein the casing comprises the second element and the at least some components comprise the first element. According to a preferred feature of the hammer the casing is reversible. According to one particular embodiment of the invention the first element comprises the air delivery or valving assembly of the hammer. In one form the air delivery or valving assembly is supported at one end of the hammer casing between a make-up ring and the top-sub and where the make-up ring is in direct contact with the retaining ring. If desired the air delivery or valving assembly is formed with a radial flange received in a rebate provided in the abutting faces of the make-up ring and the top-sub. The flange can be resiliently supported within the rebate and the resilient support can comprise a resiliently compressible member located to at least one side of the flange. Alternatively the flange can be located precisely face to face contact of the components. In regard to down hole hammers, the use of a retaining ring located in the internal bore of a down hole hammer cylinder or piston case where the ring has a plurality of shoulders which locate on a similar number of recesses machined in the cylinder or piston case bore avoids the need to machine a single recess of sufficient diameter to create sufficient shoulder area to support the retaining ring and to maintain the wall thickness to ensure the integrity or strength of the cylinder causing. Therefore, the load support area available to support or locate internal components can be maximised by increasing the number of recesses and shoulder in the ring for higher energy generation by the piston motor assembly. The retaining ring can be accurately located by means of closely machined tolerances in forming recesses and the retaining ring in order for movement of the retaining ring to be contained not only in one direction but in both directions. As a result the undue or unwanted movement of the component being retained is restricted in both directions which results in reduced wear. As well as allowing the piston bore to be maximised, the plurality of shoulders provides a sufficient load area in order to minimise deformation or wear in comparison to a single shoulder or single recess. This greatly increases the life of the assembly and minimises the need to replace or repair components by maintaining the location of the components through the support provided by the retaining ring and by the retaining ring being firmly locked in the recess. The piston case and retaining ring can be made reversible so that wear in one direction on similarly facing shoulders of piston case recesses or shoulders on the retaining ring can be overcome by installing the retaining ring in the reverse manner. This serves in prolonging the effective file of the piston case and retaining ring and the ability to form a shoulder and locate mating components correctly. In the event that the plurality of recesses or counter bores in the internal bore of the piston case or cylinder become worn in one direction the piston case can be made reversible and the retaining ring will locate on shoulder recesses that have not been worn or which are worn to a lesser extent than if there had been only one locating shoulder abutment or internal recess in the piston case or cylinder. The retaining ring can also be machined in such a manner that the external and internal diameters can be used to locate the retaining ring concentric to the piston bore and in turn accurately align a component fitted through the centre of the retaining ring, concentric to the piston bore. Alternatively, or if desired by machining the centre bore of the retaining ring eccentric to the outer diameter it is possible to align a component fitted in the centre bore to be held and located securely in an eccentric manner. This can be done to ensure that uneven loads on the shoulders of the recesses of the piston case or cylinder are supported in a manner which will prevent eccentric wear as would be the case with a single shoulder or recess. The invention will be more fully understood in the light of the following description of two specific embodiments. The description is made with reference to the accompanying drawings of which:- Figure 1 is a sectional elevation of a down the hole hammer of the type described above where the components shown are supported according to the first embodiment of the invention and; Figure 2 is an enlarged sectional view illustrating the interengagemeπt between a portion of a down the hole hammer, a make-up ring and a retaining ring according to the second embodiment. Figure 1 illustrates a first embodiment of the invention in use in a down the hole hammer which comprises a hammer casing 11 which supports a top-sub 12 from its one end. The other end (not shown) of the hammer casing 11 supports a drill chuck (not shown) and a piston (not shown) is accommodated between the top- sub 12 and the drill chuck for reciprocation in the space so defined. Operation of the hammer is effected by means of high pressure air which is delivered to the hammer via the top-sub 12 through a check valve assembly 1 and a control rod 13. The abutting ends of the check valve assembly 14 and the control rod 13 are formed with flanges 16 and 17 of corresponding diameter. The flanges 16 and 17 are clampingly received between the inner end of the top-sub 12 and make-up ring 18. The abutting faces of the top-sub 12 and the make-up ring 18 are each formed with a recess 19 and 20 at their inner edges and the flanges 16 and 17 of the check valve assembly and control rod are received in the recesses which have a diameter corresponding to the diameter of the flanges. To support the flanges 16 and 17 in the recesses, a compressible ring 21 and 22 is received in each recess 19 and 20, to each side of the flange. To support the control rod assembly 21 within the hammer casing 11 , a pair of closely adjacent annular recesses 23 and 24 are formed in the wall of the hammer casing 11. The recesses receive and support a retaining ring 25 which has an outer surface defined by a pair of annular ribs 26 and 27 each having an outer diameter corresponding to the inner diameter of the recesses 23 and 24. The retaining ring 25 has an inner diameter which is less than the inner diameter of the hammer casing 11 such that it extends into the space defined within the hammer casing 11. The retaining ring 25 is formed of two semicircular segments to facilitate its location in the recess 22 during assembly of the hammer. The external face of the make-up ring is formed with an annular rebate 30 which is received over the retaining ring 23 whereby the inner face of the retaining ring is snugly received against the radial face of the rebate. In addition, the axial faces of the retaining ring 23 are tapered inwardly and the inner end of the rebate 30 is of complementary profile which ensures positive interengagement between the make-up ring and retaining ring on the top-sub being tightened against the make-up ring. On application of the top-sub 12 to the hammer casing 11 its inner end bears directly against the make-up ring which is supported directly within the casing by the retaining ring 23 In assembly of a hammer of the form shown at Figure 1 the segments of the retaining ring 25 are located such that the ribs 26 and 27 are received in the recesses 23 and 24. The make-up ring 18 is then located in position which serves to retain the retaining ring 25 in position. The control rod 13 and check valve assembly 14 is then inserted into the hammer casing such the flanges 17 and 16 respectively are received in the recess 20 of the make-up ring over the compressible ring 22. The other compressible ring 21 is then placed in position and the top-sub 12 is then threadably engaged with the hammer casing 11 to cause the compression of the compressible rings 22 and 21 and such that the top-sub abuts directly with the make-up ring 18. It is a characteristic of the retaining ring 25 that each of the axial faces 31 and 32 of each rib 26 and 27 provide a bearing surface for the retaining ring 23 and thus serve to increase the surface area of the bearing surface which is available to support the retaining ring compared to the retaining rings which have been used in the past. In addition, the depth of the recesses accommodating the retaining ring can be reduced while ensuring the bearing surface is of an adequate area to provide the required support for the anticipated forces to be borne by the bearing surface. In fact the bearing surface area can be increased even though the depth of the recesses is reduced in comparison to conventional retaining rings This can enable the use of a cylinder casing having a thinner wall that would be the case where conventional retaining rings were used. In the utilisation of a retaining ring according to the embodiment the hammer casing may be formed with an uncontoured bore with the exception of the recess 22 and if desired may be made to be reversible by providing a set of recesses at each end of the casing. In addition, the only machining required relates to the formation of the recesses. If desired, the number of recesses may be increased beyond the two as described in relation to the embodiment to increase the surface area of the bearing surface and/or reduce the depth the recesses. Figure 2 illustrates a second embodiment of the invention in use in the make-up assembly of a down the hole hammer. The arrangement is of the same form as shown in Figure 1. The difference however in the case of the second embodiment comprises the provision of a stepped axial face 33 and 34 to each side of the retaining ring which can each be received in a complementary rebate 30 formed in the make-up ring and the absence of a tapered external face. It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiments described above and in particular can relate to any situation where a shoulder or abutment is required to support a component in a bore or cylinder of a down hole hammer at any location with that bore or cylinder or any like location. In regard to down hole hammers the invention can have application in containing components within the casing of the hammer such; as drill bit supports; cylinders or internal sleeves; valve bodies or air distribution bodies; make-up components as well as control rods or valves stems or feed tubes and top-subs as described in relation to the embodiments referred to above. Provision of a retaining ring which is supported within the casing by a plurality of recesses not only serves to increase the support area for the retaining ring but also, facilitates an increase in the internal bore of the hammer, which in turn enables maximisation of the diameter of the piston and therefore the effectiveness of the hammer. There is also the ability to be able to reduce the wall thickness of the cylinder case and to be able to manufacture the cylinder to be reversible.

Claims: The Claims defining the invention are as follows:- 1. A retention means for retaining a first element of circular cross-section within a space of complementary cross-section in a second element said means comprising a plurality of axially spaced annular recesses formed in the wall of the space and a retaining ring having an axial length at least equal to the spacing between the outer edges of the outermost recesses and where the radially outermost face is of complementary profile to the profile of the wall between said outer edges, said ring having an outside diameter corresponding to the diameter of the recesses said retaining ring being in direct abutting contact with the first element. 2. A retention means as claimed at claim 1 wherein the retaining ring is formed of a plurality of segments. 3. A retention means as claimed at claim 1 wherein the retaining ring is capable of resilient radial compression to an external diameter at least equal to the internal diameter of the second element. 4. A retention means substantially as herein described 5. A down the hole hammer wherein at least some of the components are supported within the casing by a retention means as claimed at any on of claims 1 , 2, 3 or 4 and wherein the casing comprises the second element and the at least some components comprise the first element. 6. A down the hole hammer as claimed at claim 5 wherein the casing is reversible. 7. A down the hole hammer as claimed at claim 5 or 6 wherein the first element comprises the air delivery or valving assembly of the hammer. 8. A down the hole hammer as claimed at claim 7 wherein the air delivery or valving assembly is supported at one end of the hammer casing between a make-up ring and the top-sub and where the make-up ring is in direct contact with the retaining ring. 9. A down the hole hammer as claimed at claim 8 wherein the air delivery or valving assembly is formed with a radial flange received in a rebate provided in the abutting faces of the make-up ring and the top-sub. 10. A down the hole hammer as claimed at claim 9 wherein the flange is resiliently supported within the rebate. 11.A down the hole hammer as claimed at claim 10 wherein the resilient support comprises a resiliently compressible member located to at least one side of the flange. 12.A down the hole hammer as claimed at claim 9 wherein the radial flange is in direct face to face with the rebate. 13. A down the hole hammer substantially as herein described with reference to the accompanying drawings.

Inventors: REAR IAN GRAEME, REAR, IAN, GRAEME
Applicants: REAR IAN GRAEME, REAR, IAN, GRAEME
Application year: 1996
Main classification: F16B21
IPC codes: E21B4