GB2490336A

GB2490336A - Releasable lock for securing threaded members

Info

Publication number: GB2490336A
Application number: GB1106931.7A
Authority: GB
Inventors: Alan Mackenzie
Original assignee: MACKENZIE DESIGN CONSULTANTS Ltd
Current assignee: MACKENZIE DESIGN CONSULTANTS Ltd
Priority date: 2011-04-26
Filing date: 2011-04-26
Publication date: 2012-10-31
Anticipated expiration: 2031-04-26
Also published as: GB201106931D0; GB2490336B

Abstract

A releasable lock (10) for securing threaded engagement between respective first and second components (11, 12) having threads (13, 14), comprises a groove (17), confining an annulus (18). The annulus (18) is rotatable about a periphery defined by the groove (17). The lock (10) includes a locking member (22), and the annulus (18) includes a recess (19) for confining the locking member (22) so as to be moveable radially relative to the annulus (18). The locking member and the first member (11) include chamfers ((24, figure 2), 21); the locking member includes one or more actuator members (27) for moving the locking member radially relative to the annulus; the second component (12) and the annulus or the locking member are non-rotationally engageable; and the chamfers are such that on radial movement of the locking member caused by operation of the or each said actuator the chamfers bind to prevent relative rotation between the annulus and the first component, and hence between the second component and the first component.

Description

A RELEASABLE LOCK

The invention relates to a releasable lock for securing threaded engagement between respective first and second components having mutually engageable threads.

In particular the invention is of particular utility when connecting together tubular components of one kind or another that are intended for use in downhole environments such as wellbores, other boreholes and test bores that are employed in mining industries and more particularly in the oil and gas exploration and production industries. The invention however is additionally applicable in many other situations in which it is necessary to join together two threaded cylindrical (or sometimes rod-like) parts that otherwise might unscrew from one another and separate.

In the oil/gas exploration industries it is commonplace to wish to secure two such threaded, cylindrical components together in a manner that prevents their unintended separation after they have been inserted into a borehole. Several of many possible examples include the securing of two stands of drilipipe to one another; the securing of a drillstring or production string to the in-use downhole end of a run of drilipipe or any other so-called "tubular" conduit; the securing of internal threaded components within down hole tools; or the locking of a threaded connection between large diameter (e.g. approximately O.75m outside diameter) casing joints used in wellbore construction.

The various cylindrical components that are secured together for use in downhole environments normally include threads formed at the adjacent mating ends of the parts to be connected. Typically these threaded connections comprise a female box' (ie.

recessed) thread and a male pin' (ie. protruding) thread. These are usually straight threads, such as ACME, National V Thread and Isometric M thread types that are not tapered threads. Tapered threads, such as API NC, may also be used to connect together internal components. The parts are assembled by screwing them together until two shoulders engage preventing further rotation.

Such shouldering of the connections allows any play within the threads to be removed providing a stiff connection. During assembly of the individual parts of such downhole tools, once relative rotation has been applied to the threads and the respective shoulders have contacted, then a torque is applied. This torque may range from that generated manually using hand-operated tools through to high torque applied by a specialist piece of machinery.

I

After the connection has been assembled, shouldered and torque applied, it must now be prevented from undoing (ie. backing off or unthreading) during subsequent operation of the tool. A torque causing a force capable of causing back-off or unthreading may be due to a subsequent assembly procedure, an operational event, vibration within the system, interference by unapproved personnel or by technician error. lt is therefore essential that a reliable method of locking the connection in place to prevent back-off or unthreading be used.

Current methods to provide a locking mechanism in a shouldered threaded connection are: 1. Thread glue such as provided under the Loctite (RIM) Brand This glue is applied to the threads to be locked and, after the connection has been made up, is allowed to cure forming a bond between the two threaded elements of the connection. This will prevent backing-off of the connection up to a prescribed torque level. Preparation of the surfaces is very important. Grease or oil used to aid assembly must not be present within the glued interface.

Personal protective items must also be used to prevent contamination of the technician by the glue product. Further, during tool maintenance when the connections have to be disassembled, heat must be applied to the connection so that the glue bond is destroyed and torque applied to disassemble the connection.

This disassembly requires two technicians: one to apply heat to the connection and the second to apply torque to it. Risks must be carefully identified and mitigated during this procedure; and personal protective items must be used to protect the operators from heat. In addition, the connection tends to release suddenly which can injure the operator applying the torque.

2. Threaded screws (commonly called set or arub screws) radially assembled into preformed taed holes and grippina the adiacent component The nature of downhole technology generally limits the wall thickness of components which are to be joined via a threaded connection. This limited wall thickness in turn limits the size (the outside diameter) of set screws used to provide the grip. Smaller sizes provided smaller grip.

Also, the design of the connections generally introduces a radial gap between the outer threaded component and the inner threaded component. The set screw must bridge this gap. This results in a bending load being applied to the screw during times of possible back-off or unthreading. This also limits the strength of grip offered by this method. The simple set screw method described is not suited to the transmission of torque in either direction. For these reasons, this method is often not preferred.

3. Threaded screws assembled into preformed taed holes and subsequently into a preformed drilled hole in the matting part In this method, the components must be pre-assembled. Pre-formed tapped holes exist in the outer walls of the female thread. On pre-assembly, the position of the tapped holes relative to the component being attached is marked and noted.

Subsequently, the connection is disassembled and a machining operation performed to add a corresponding hole or a slot in the component to be attached.

Upon subsequent re-assembly, set screws may be threaded into the tapped holes and will locate precisely in the drilled holes or slots on the mating part.

This method of using set screws provides a higher locking grip than using set screws as described in Method 2 above. However, the drilled hole in the mating part can only be formed after the connection has been pre-assembled as described; the position of the hole marked on the opposing face; the components disassembled; and arrangements made for subsequent machining. This requires additional time and incurs associated costs. The same limitations as described above regarding the limits of set screw size apply to this method. in addition, the method requires access to workshop facilities not always available in remote field locations. The components moreover become matched' providing limits to inventory flexibility, and the method is not suited to the transmission of torque in either direction. For these reasons, the method is often not useable.

4. A toraue transmitting tongue assembled after the connection is made up A variation on Method 3 above is to employ a torque transmission component such as a tab or a tongue. This is generally fixed into adjacent mating profiles in each of the parts to be connected. This will generally provide a higher resistive torque than is available using Method 3. However, parts still require to be matched which increases assembly time and cost and also limits flexibility in inventory. This method is suited to the transmission of limited torque in either direction. For these reasons, the method is often not viable.

5. A pro�rietarv locking washer mechanism such as Nord-Lock (RTM brand This washer-based system requires the connection to be threaded together and a prescribed torque applied to the connection. This energises the washer device and provides a resistance to break out via a torque higher than the make-up torque. This is particularly suited to standard nuts and or bolts, where washers of the required size are readably available. It is not suited to bespoke' threaded connection sizes such as those used in downhole tool design, nor is it suited to transmitting torque in either direction.

Clearly therefore there exists a need for a reliable arrangement for securing threaded components together that resists backing-off torques, is easy to assemble, does not require modification of the parts being assembled together and generally improves on the prior art methods described. Such an arrangement would be particularly suited for use in downhole environments as arise in the oil and gas exploration and production industries, and also could be of utility in other industries.

According to the invention in a broad aspect there is provided a releasable lock for securing threaded engagement between respective first and second components having mutually engageable threads, the lock comprising a groove, formed in a surface of the first component, confining an annulus that is rotatable about a periphery defined by the groove; and a locking member, the annulus including a recess for confining the locking member so as to be moveable radially relative to the annulus; the locking member and the first component including mutually engageable chamfers; the locking member including one or more actuator members for moving the locking member radially relative to the annulus; the second component and the annulus or the locking member being non-rotationally engageable; and the chamfers being such that on radial movement of the locking member caused by operation of the or each said actuator the chamfers bind to prevent relative rotation between the annulus and the first component, and hence between the second component and the first component.

A significant advantage of the arrangement of the invention is that the torque applied to screw the threaded components together is not also required to effect securing of the threaded connection, this instead being caused by operation of the actuator members.

This means that the threaded components can be subjected to the correct torque for their intended application, without any need to compromise the applied torque to take account of a securing (anti-unthreading) function.

This benefit arises to a certain extent from the use of prior art set screws as described above. However the assembly of the invention through employing the locking member additionally avoids the problem, explained above, of limited torque transmission being possible via set screws. The locking member can be made of a size and shape that are suited to resisting the expected torque values, without concern that the dimensions of the threaded parts will limit the transmissible torques.

In addition, the inclusion of mutually engagable chamfers imparts a mechanical advantage to the operation of the actuator members, i.e. set screws, which further assists in obtaining desired securing of the threaded connection.

Furthermore during assembly of the releasable lock of the invention it is not necessary either to follow a multi-stage pre-assembly and final assembly sequence; or to machine the components being assembled together before securing occurs. Aside from the fact that this saves time and cost during component assembly this also means that matching of components does not result.

In other words, the parts of the lock of the invention need not be provided in matched sets. This in turn provides numerous advantages in terms of inventory control and in the event of parts of the assembly becoming lost or damaged in use.

Preferably the first component includes a male thread and the second component includes a female thread with which the male thread is engageable. The apparatus of the invention therefore is suitable for connecting together numerous items that are welt known in the oil and gas drilling arts. Such items include but are not limited to drillstring subs, drillpipe, jars, various forms of expandable tool, togging sondes and subs therefor, drillbit annuli, and pressure testers.

Conveniently the groove extends around a shank defined as part of the first component adjacent the male thread. This advantageously means that the groove can easily be machined into a cylindrical part of the first component, that in common with the remainder of the parts of the lock of the invention may be formed from e.g. steel or another metal alloy.

Preferably the annulus is formed as two or more part-annular segments and the second component includes one or more formations that in use lie adjacent the annulus and thereby retain it rotatably confined in the groove.

This means that the annulus is removably attachable to the first component and may be secured in place on assembly of the lock by a confining action of the second component.

In consequence the parts of the lock of the invention may be assembled together as required, and do not have to be permanently assembled together.

This reduces costs since it is necessary only for the first and second components to include the groove and the formations mentioned above. Such features may be cheaply incorporated into the first and second components. The annulus, which would otherwise add modestly to the weight, cost and complexity of the components is attached only when needed.

In a preferred embodiment of the invention the formations include one or more castellations protruding at an end of the second component so as to define an interrupted shroud that in use partially encircles the annulus; and wherein the annulus includes one or more protuberances that in use engage one or more said castellations.

This provides a ready mechanism using which the formations may achieve the retaining function described above while also providing for driving engagement between the formations and the annulus. This in turn assures that any rotation of the second component relative to the first is transmitted to the annulus the position of which relative to the second component therefore remains unchanged during such rotation.

Even more preferably the lock includes a plurality of the castellations arranged in an annular pattern about an end of the second member, wherein the annulus includes a corresponding plurality of the protuberances. This advantageously means that the transfer of rotation from the second component to the annulus takes place at locations distributed evenly about the periphery of the annulus.

Conveniently one or more said castellations includes formed therein one or more apertures via which a user may operate a said actuator member.

This means that the actuator members are shielded against damage and are confined in a manner that both promotes and permits their operation.

Preferably the lock includes an aperture passing through the locking member to permit the actuator member to protrude from the locking member in order to effect radial movement of the locking member relative to the annulus. In a practical embodiment of the invention the locking member includes at least a pair of the apertures so that more than one actuator member may be employed. This in turn ensures that the locking member can be actuated evenly, or at least in a controlled manner, along its length.

In a preferred embodiment of the invention the or each said actuator member includes a screw that is threadedly received in the aperture that is threaded in a corresponding manner to the screw. Such a screw, that preferably but not necessarily is a grub screw, may readily be accessed and operated from the side of the formations opposite the locking member via the apertures therein.

Preferably the mutually engageable chamfers include mating surfaces of the locking member and the first member respectively that are aligned to cause radial movement of the locking member on operation of the one or more actuators. This in turn means that the locking mechanism of the lock may be designed including a relatively large mechanical advantage arising from conversion of the (preferably) rotational movement of the actuators to linear relative movement of the chamfers. Such linear relative movement is such as to cause the chamfers to bind together, thereby locking the locking member relative to the first component. This in turn prevents movement of the second component relative to the first by reason of the driving engagement between the annulus and the second component.

Conveniently at least one of the mating surfaces includes formed thereon one or more bind-promoting features that promote binding with the other said surface. Preferably a said bind-promoting feature includes a pattern of grooves formed in the said mating surface.

In another preferred embodiment of the invention the recess in the annulus and the locking member include at least one pair of mutually engageable formations cooperable with one another to drive the mutually engageable chamfers of the locking member and the first component into further engagement with one another on rotational movement of the annulus in an undesired direction.

The inclusion of at least one such mutually engageable formation increases the gripping force between the locking member and the first component in the event that undesired movement of the annulus occurs.

Preferably the rotational movement of the annulus in an undesired direction arises from unthreading of the second component from the first component. As such the locking effect of the mutually engageable chamfers of the locking member and first component is actually increased in the event that an attempt is made to unthread the second component from the first component thereby resisting still further such separation of the first and second components.

Optionally the recess includes first and second pairs of mutually engageable formations separated from one another by a detent formation. The inclusion of first and second pairs of mutually engageabte formations drives the mutually engageable chamfers into further engagement with one another to a desired extent, while the inclusion of a detent formation inhibits rotation of the annulus relative to the locking member when the annulus is rotating in a desired direction, i.e. a direction opposite the undesired direction.

There now follows a description of preferred embodiments of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which: Figure 1 is an exploded perspective view of one form of lock according to the invention; Figure 2 is an enlarged, perspective view of a locking member forming part of the Figure 1 lock; Figure 3 is a perspective view of the lock of Figure 1 in assembled form, illustrating an adjustment technique; Figure 4 is an end elevation view of the Figure 3 assembly, showing the planes of sectioning represented in the sectioned view of Figure 5 and 6 respectively; Figure 7 is an enlargement of part of the Figure 6 cross-section, illustrating binding of the locking member to secure the lock; Figure 8 is an exploded perspective view of another form of lock according to the invention; and Figure 9 is an enlarged, exploded view of an annulus and a locking member forming part of the Figure 8 lock.

Referring to the figures, a releasable lock 10 according to the invention secures first and second, threadedly engageable components 11 and 12 together.

In the embodiment of the invention illustrated the first and second components may be any of the types of downhole component commonly employed and including threaded tool joints as illustrated.

When so configured the first and second components typically are formed from a steel or another metal alloy. Other materials however are possible for the construction of the lock, as would occur to the worker of skill in the art.

The lock of the invention moreover may be employed in a wide range of non-downhole applications in which it is required securely to lock two threaded components in threaded engagement with one another. Such further applications of the lock of the invention need not arise in the oil and gas exploration, drilling and production arts. However these areas of engineering activity are those in which it is envisaged that the invention will find the widest application.

In the embodiment shown the first component 11 is a hollow, tubular member including a length of its exterior at the free end 13a visible in Figure 1 formed as an external, male thread 13 of a design that is commonplace when forming tool joints in oil/gas downhole tools.

Second component 12 is also a hollow, tubular item formed adjacent its free, open end with an internal, female box thread 14 that also is essentially of conventional design.

Thread 14 is recessed by reason of being spaced a short distance inside the interior of second component 12, with the end of component 12 being defined by a formation 16 described in more detail below.

Male thread 13 is formed in a section ha at the end of first component 11 that is of reduced diameter compared with the remainder. Thread 13 is spaced at its end 13b remote from the free end 13a by a groove 17 defined in the manner of a shank that is of reduced diameter compared with both the thread 13 and the remainder of first component 11.

Thread 13 is threadedly receivable in thread 14 such that the first and second components 11, 12 are threadedly securable together. The respective components 11, 12 include formed in their exterior surfaces conventional spanner flats 11 a, I 2a that may be used to assist in tightening together the threaded connection between them. In practice the flats ha, 12a would be provided in pairs on opposite sides of the components 11, 12.

The nature of the threads, reduced diameter section ha and formation 16 is such that when so threaded together the first and second components may be tightened together so that the formation 16 overlies and encircles the groove 17.

This condition of the components 11, 12 is illustrated in Figure 3. As explained above, it is desirable reliably to prevent unintended loosening of the threaded connection achieved in the Figure 3 condition, and to permit ready releasing of the tightened threads when desired. The remainder of the parts of the lock 10 described herein are intended to realise these objectives.

Groove 17 formed in the outer surface of first component 11 is designed to confine an annulus 18 formed from a rigid material such as a metal alloy.

In the preferred embodiment of the invention shown the annulus 18 is formed from two semi-annular segments ISa, lSb. This arrangement means that the operative parts of the lock may be added to the components 11, 12 only when required by reason of the semi-annular nature of the segments 18a, 18b permitting ready insertion of the annulus 18 into and its removal from the groove 17.

Such an arrangement in turn advantageously means that the components 11, 12 themselves require only minimal modification from known designs (in the case of the first component 11 to form the groove 17, and in the case of the second component 12 to create the formation 16). Otherwise the components 11, 12 are conventional. Thereby the lock of the invention beneficially helps to contain manufacturing and inventory costs.

However in other embodiments of the invention the annulus could be formed as an in-use single, circular member that is uninterrupted or largely uninterrupted around its periphery. Such a design of the annulus could then be permanently retained in the groove 17.

In yet further embodiments of the invention the annulus may be formed from more than the two semi-annular segments illustrated, The use of two segments however is believed to be preferable from the standpoint of providing maximum assembly flexibility whilst minimising the overall number of components required to be taken to a field location for use.

As yet another variant however the annulus segments constituting the annulus 18 do not all have to be of the same angular length. As an example it is possible to construct the annulus 18 from two segments one of which extends over an arc of say 150 degrees and the other of which extends over a circular arc of 210 degrees. If the annulus segment that is 210 degrees long is made of a resiliently flexible alloy it may be "snapped" onto the groove 17 and loosely retained there while the remainder of the lock is assembled.

Such an arrangement may have advantages for example when it is required to assemble the lock in arduous conditions such as bad weather.

Regardless of the exact make-up of the annulus 18 its inner diameter is chosen to be slightly greater than the outer diameter of the groove 17. Therefore once installed encircling the groove 17 the annulus 18 is rotatable in the groove. In other embodiments of the invention the inner diameter of the annulus 18 may be the same or slightly smaller than the outer diameter of the groove 17.

Each of the annulus segments ISa, 18b includes formed therein a respective recess 19.

Each recess 19 is formed as an essentially rectangular cut-out extending along an arcuate section of the segment to either side of its longitudinal mid-point. The cut-out defining recess 19 is through-going in the sense that it extends from the radially outer face to the radially inner face of the respective segment ISa, 18b. The cut-out is open-sided along an edge 19a of the annulus that in use faces away from the free end 13a and lies adjacent a shoulder 21 defined by the transition in the first component from the diameter of the groove 17 to the diameter of the remainder of the first component 11.

On assembly of the lock 10 the recess 19 accommodates a locking member 22 that is shown in an enlarged view in Figure 2.

Locking member 22 is a rigid, arcuate piece formed from e.g. a metal alloy. Locking member is of an angular length just slightly shorter than that of recess 19. The ends 22a, 22b of the locking member are of complementary shape to the angularly spaced ends of the recess 19 such that the locking member when inserted into the recess 19 is moveable radially inwardly and outwardly relative to the annulus 18.

Locking member 22 includes one elongate edge 23 extending perpendicular to its radially inner and outer surfaces 22c, 22d; and on its opposite side an elongate edge 24 of different design.

Specifically edge 24 is, as best illustrated in Figure 2, designed as a taper or chamfer such that the locking member is wider at its in use radially inner surface 22c than at its radially outer surface 22d. Put another way, edge 24 tapers in the radially outward direction towards the edge 23. The taper is visible in Figures 2, 5, 6 and 7.

Shoulder 21 is tapered in a complementary manner to edge 24. In other words shoulder 21 is wider at its radially outermost edge than at the point of intersection with groove 17.

The angle of the taper of shoulder 21 is the same as the taper angle of edge 24. As a result when the edge 24 and the shoulder 21 are placed in abutting relationship as described below the faces of the tapers engage one another over their whole surfaces (or substantially their whole surfaces). In other embodiments of the invention the angle of taper of the shoulder 21 may be greater than or less than the taper angle of the edge 24.

Locking member 22 includes formed therein a pair of through-going, threaded bores 26a, 26b designed for threaded receipt therein of respective actuator members in the form of grub screws 27. ln other embodiments of the invention the respective actuator members may take another form such as rotary cams.

The bores 26 and grub screws 27 are such that when the grub screws 27 are screwed sufficiently far into the bores 26 from the radially outer side of the locking member 22 they protrude from the radially inner surface of the locking member 22. Assuming the locking member 22 is retained in the groove 17 this will cause jacking of the locking member in a radial direction, in dependence on the depth to which the grub screws 27 are tightened into the bores 26.

Thus the grub screws 27 when received in the bores 26 amount to actuator members that cause movement of the locking member 22 radially relative to the annulus 18.

The second component 12 and the annulus 18 are non-rotatable relative to one another, notwithstanding that the annulus 18 is rotatable in the groove 17.

This is achieved by reason of the design of the formation 16 and of the radially outer surface of the annulus 18.

In more detail, the formation 16 is formed as an annular series of castellations, i.e. alternately disposed protruding and recessed end sections 28a, 28b that are connected one to another by longitudinally extending, straight walls 28c. Thus the formation includes a shroud defined by the protruding sections 28a that is periodically interrupted around the circumference of the formation 16 by the recesses 28b.

The annulus 18 is formed on its outer surface with respective protuberances 29. Each of these is of an angular length that is slightly less than that of each recessed section 28b of the formation 16. The annulus 18 includes the same number of the protuberances 29 as the recessed sections 28b; and when the annulus is received in an assembled state in the groove 17 the spacings between the protuberances 29 corresponds to the angular spacings between the recessed sections 28c.

It will be apparent that it is possible therefore to assemble the lock 10 with the protuberances 29 each received in and in driving engagement with a respective recessed section 28b when the annulus is assembled into the groove 17. In this condition the protruding sections 28a of the formation 16 overlie the parts of the outer circumference of annulus 18 that omit the protuberances 29. In consequence a drive-transferring arrangement exists whereby rotation of the second component 12 to tighten or loosen the threaded connection with the first component 11 causes the annulus 18 to rotate with the second component 12 and hence relative to the groove 17 and indeed the remainder of the first component 11.

As a result the relative angular orientations of the annulus 18 and the second component 12 remain fixed relative to one another during screwing together and apart of the first and second components 11, 12.

Each of the protruding sections 28b of the formation 16 includes formed therein a pair of through-going access holes 31. These are sized and positioned to permit access by a tool such as a screwdriver or hex key to the grub screws 27 from a location radially outside the lock 10 when it is in its assembled condition.

Since the annulus 18 is non-rotatable relative to the second component 12 when the lock lOm is assembled assuming the access holes are formed in the correct places in the protruding sections 28b access to the grub screws will always be possible.

In consequence after the first and second components 11, 12 have been screwed together to a desired torque setting it is possible to rotate the grub screws 27 using a tool inserted via the access holes 31 and thereby cause the locking member 22 to move radially outwardly from the groove 17.

This occurs by reason of the grub screws 27 protruding from the radially inner surface of the locking member 18 to engage the groove 17 and drive the locking member radially outwardly.

This causes the taper defined by locking member surface 24 to engage tapered shoulder 21. The further locking member 18 is driven radially outwardly from groove 17 the greater is the degree of bind between the tapered surfaces 24 and 21. As a result the locking member inhibits rotation of the annulus relative to surface 21 and hence the remainder of the first component 11. Since the annulus 18 is non-rotatably engaged with the second component 12 relative rotation between the first and second components 11, 12 is prevented without any need to tighten the components together to an unattractively high torque setting, without any need to transmit a high torque across set screws (since the rotation-resisting torque resulting from binding of the surfaces 24 and 21 does not develop in the grub screws 27) and without any need for closely matched components.

As illustrated in Figure 2 the tapered edge 24 of locking member 22 includes formed thereon bind-promoting features in the form of a pattern of grooves 32. A similar pattern may be formed on the surface defined by edge 24, thereby assuring positive binding together of the annulus 18 and the first component 11.

Assembly of the lock 10 involves a process of placing the segments ISa, 18b of the annulus, and the locking member 22 including the grub screws 27 received in the holes 31, in the groove 17 and screwing the male thread 13 into the female box thread 14 until the protruding sections 28a of the formation 28 overlie the annulus parts 18 thereby retaining them in the groove 17.

Continued screwing together of the components 11, 12 causes the protuberances 29 to enter the recessed sections 28b, guided as necessary by hand, with the result that the annulus 18 and the second component 12 become drivingly connected as described herein.

Once the components 11, 12 are screwed together to a desired extent a tool is inserted into each of the access holes 31 in turn so as to engage and rotate the grub screws 27.

This causes jacking of the locking members 22 radially outwardly to lock the first and second components 11, 12 in the selected position.

Releasing of the lock involves a reversal of the process by which the locking member 22 Is is jacked to cause binding with the first component 11, thereby releasing the components 11, 12 that then are free to be unscrewed, or screwed more tightly together as desired.

The figures show a further, optional feature of the invention in the form of an 0-ring groove 33 formed as an annulus cut into the first component 11 between the male thread 13 and groove 17. A conventional 0-ring seal may be inserted into the groove 33 in order to aid the sealing of the joint between the components 11, 12.

Alternative or additional sealing means, as would occur to the worker of skill in the art, may be incorporated in a range of locations on the parts shown.

A releasable lock 50 according to another embodiment of the invention is illustrated schematically in Figure 8.

The second lock 50 shares a number of features with the first lock 10 described hereinabove and such like features are designated using the same reference numerals.

The second lock 50 differs from the first lock 10 in that the recess 19 in the annulus 18 and the locking member 22 additionally include first and second pairs 52, 54 of mutually engageable formations 56. Each pair of formations includes a cooperable inclined profile formed in each of the recess 19 and the locking member 22. In other embodiments of the invention the recess 19 and the locking member 22 may include fewer than or more than two pairs of mutually engageable formations 56.

The pairs of formations 52, 54 are separated from one another by a detent formation 58.

The second lock 50 is assembled and disassembled in the same manner as the first lock 10.

Once assembled the first and second pairs 52, 54 of mutually engageable formations 56 cooperate with one another to drive the mutually engageable chamfers of the locking member 22 and the first component 11 further into engagement with one another in the event that a back-off torque T is applied to the second component, i.e. when the second component 12 attempts to become unthreaded from the first component 11 and rotates the annulus 18 in a corresponding, undesired, direction relative to the locking member 22.

The detent formation 58 inhibits relative movement between the annulus 19 and the locking member 22 when the annulus 19 is moving in a desired direction relative to the locking member 22 and thereby assists in assembling the second lock 50 The embodiments of the invention described above include a locking member 22 that lies radially inwardly of the interrupted shroud represented by the castellations 28. The locking member 22 is moveable under the influence of the actuator members (grub screws 27) in a radially outward direction to promote the described binding effect. It is however possible within the scope of the invention to conceive of an alternative arrangement in which an equivalent of the groove 17 is formed in the radially inwardly facing surface of the second component 12 such that the annulus 18 is retained rotatably captive adjacent the second component.

In that case it might be necessary to adopt an actuator mechanism that caused radially inward driving or jacking of the locking member to cause binding with the second component 12. It would also of course be necessary for the annulus to be non-rotatably engaged with the first component on assembly of the lock in order to provide for the locking effect described.

Although this alternative version of the invention, in which the operation is effectively inverted, is possible, the described embodiments are preferred because of the ease of their assembly and the ease of access to the grub screws 27 via the access holes 31.

In another variant of the invention it is not necessary for the formation 28 to be non-rotatably engaged with the annulus 18. Instead it is possible, within the scope of the invention, for the formation 28 to engage the locking member in a non-rotatable manner.

The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Claims

CLAIMS1. A releasable lock for securing threaded engagement between respective first and second components having mutually engageable threads, the lock comprising a groove, formed in a surface of the first component, confining an annulus that is rotatable about a periphery defined by the groove; and a locking member, the annulus including a recess for confining the locking member so as to be moveable radially relative to the annulus; the locking member and the first component including mutually engageable chamfers; the locking member including one or more actuator members for moving the locking member radially relative to the annulus; the second component and the annulus or the locking member being non-rotationally engageable; and the chamfers being such that on radial movement of the locking member caused by operation of the or each said actuator the chamfers bind to prevent relative rotation between the annulus and the first component, and hence between the second component and the first component.
2. A releasable lock according to Claim I wherein the first component includes a male thread and the second component includes a female thread with which the male thread is engageable.
3. A releasable lock according to Claim 2 wherein the groove extends around a shank defined as part of the first component adjacent the male thread.
4. A releasable lock according to any preceding claim wherein the annulus is formed as two or more part-annular segments and the second component includes one or more formations that in use lie adjacent the annulus and thereby retain it rotatably confined in the groove.
5. A releasable lock according to Claim 4 wherein the formations include one or more castellations protruding at an end of the second component so as to define an interrupted shroud that in use partially encircles the annulus; and wherein the annulus includes one or more protuberances that in use engage one or more said castellations.
6. A releasable lock according to Claim 5 including a plurality of the castellations arranged in an annular pattern about an end of the second member, wherein the annulus includes a corresponding plurality of the protuberances.
7. A releasable lock according to Claim 5 or Claim 6 wherein one or more said castellations includes formed therein one or more apertures via which a user may operate a said actuator member.
8. A releasable lock according to any preceding claim including an aperture passing through the locking member to permit the actuator member to protrude from the locking member in order to effect radial movement of the locking member relative to the annulus.
9. A releasable lock according to any preceding claim wherein the or each said actuator member includes a screw that is threadedly received in the aperture that is threaded in a corresponding manner to the screw.
10. A releasable lock according to any preceding claim wherein the mutually engageable chamfers include mating surfaces of the locking member and the first member respectively that are aligned to cause radial movement of the locking member on operation of the one or more actuators.
11. A releasable lock according to Claim 10 wherein at least one of the mating surfaces includes formed thereon one or more bind-promoting features that promote binding with the other said surface.
12. A releasable lock according to Claim 11 wherein a said bind-promoting feature includes a pattern of grooves formed in the said mating surface.
13. A releasable lock according to any preceding claim wherein the recess in the annulus and the locking member include at least one pair of mutually engageable formations cooperable with one another to drive the mutually engageabie chamfers of the locking member and the first component into further engagement with one another on rotational movement of the annulus in an undesired direction.
14. A releasable lock according to Claim 13 wherein the rotational movement of the annulus in an undesired direction arises from unthreading of the second component from the first component.
15. A releasable lock according to Claim 13 or Claim 14 wherein the recess includes first and second pairs of mutually engageable formations separated from one another by a detent formation.
16. A releasable lock generally as herein described, with reference to and/or as illustrated in the accompanying drawings