A PADLOCK SUITABLE FOR USE IN HAZARDOUS ENVIRONMENTS BACKGROUND The present invention relates to padlocks that are suitable for use in hazardous 5 environments, and in particular to padlocks that are suitable for use in environments where electrical conduction and sparking poses a significant safety risk. These environments include, for example, electrical power supply and generation environments where there is a significant risk of electrocution, and also mining, mineral processing, oil and gas extraction and processing environments where there is 10 a significant danger of sparks igniting combustible materials and causing fires or explosions. Those skilled in the art will appreciate that there are also a wide range of other hazardous environments in which the padlock of the present invention would be suitable for use. 15 In many countries, there is an increasing trend for industry standards to include provisions to address and minimise the abovementioned dangers. For example, the Australia Standard relating to safety requirements for electrical equipment (AS61010.1-2003) specifies that "any accessible part must not become HAZARDOUS LIVE in normal use or in a SINGLE FAULT CONDITION". In the standard, HAZARDOUS 20 LIVE means "capable of rendering an electric shock or electric burn in normal use or in a SINGLE FAULT CONDITION". SINGLE FAULT CONDITION means "a condition in which one means for protection against a hazard is defective or one fault is present which could cause a hazard". 25 When used on high-voltage equipment or in an environment where there is a significant risk of electrocution, a padlock used on or secured to a piece of electrical equipment would usually constitute an "accessible part" within the meaning of the above-mentioned standard. However, conventional padlocks are typically made entirely (or at least mostly) of metal and are therefore highly conductive, meaning that 30 they could become HAZARDOUS LIVE in normal use or in a SINGLE FAULT CONDITION. Hence, conventional metal padlocks do not meet this standard and are often unsuitable for use in these environments. Nevertheless, there is a definite need for padlocks which can be used in these environments, for example to secure dangerous or 2 expensive equipment against unauthorised use, unintentional misuse, and to act as a deterrent to tampering. In the mining, mineral processing and petrochemical industries there is a general 5 requirement for tools and other devices to be "non-sparking" to minimise the risk of ignition which can lead to fire or explosion. Also, in the environments commonly experienced in these industries there is a problem that safety/deterrent devices such as conventional metal padlocks can rapidly corrode due to the extreme conditions (e.g. the extreme corrosive salt water conditions of offshore oil platforms). 10 "Plastic padlocks" and similar devices have previously been proposed. However, in the majority of these, the U-shaped shackle (or equivalent component) is still made of metal, often metal wire. Devices such as these are unsuitable, particularly in the kinds of environments described above where there is a risk of sparks leading to explosions 15 or fires, because the metal surface of the shackle has an inherent propensity to spark. For example, sparking from the metal shackle may occur if a sufficiently large potential drop (voltage) exists between the shackle and an unconnected nearby conductive object, or if the metal shackle impacts against or grazes past another hard object giving off sparks. Also, many of the existing "plastic padlocks" incorporate 20 metal components as part of their internal mechanisms and these metal components provide a conductive path via which electricity could flow into the metal shackle and through the padlock. There therefore remains a significant risk of electrocution with many of these existing "plastic padlocks". 25 One reason why existing devices such as the "plastic padlocks" discussed above continue to use shackles and other components made from metal is because it has not been possible to simply replace the existing metal components with identically shaped and configured non-metal components without significantly impacting on the strength and performance of the padlock/device. Even making such identically shaped and 30 configured plastic components can pose significant manufacturing difficulties. Therefore, in coming to the present invention, a number of significant design modifications and improvements have been made compared with traditional metal padlocks to enable non-metal components to be used and to increase ease of assembly.
3 It will be clearly appreciated that any reference herein to background material or a prior publication does not constitute an acknowledgement or admission that any background material, prior publication or combination thereof formed part of the 5 common general knowledge in the field or is otherwise admissible prior art, whether in Australia or any other country. DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a padlock that may at least partially 10 ameliorate one or more of the above-mentioned problems, or which may provide consumers with a useful or commercial choice. According to a first aspect, the present invention resides in a padlock wherein there is no path through which dangerously large electrical currents can be conducted through 15 the padlock. The padlock in accordance with this aspect of the invention therefore eliminates or at least significantly reduces the risk of electrocution due to electrical conduction through the padlock. In one particular form of the first aspect, the padlock may have a shackle wherein all 20 contactable surfaces of the shackle comprise a substantially non-conductive material, a body wherein all contactable surfaces of the body comprise a substantially non conductive material, a metal key cylinder for unlocking the padlock, and one or more key cylinder receiving components wherein all contactable surfaces of each key cylinder receiving component comprise a substantially non-conductive material, 25 whereby the one or more key cylinder receiving components engage with the key cylinder and the body to mount the key cylinder within the body when the padlock is assembled, the metal key cylinder is substantially electrically insulated by the components with the substantially non-conductive surfaces when the padlock is assembled, and at least one of the key cylinder receiving components is provided with 30 body mounting means, and the key cylinder and key cylinder receiving component(s), when mutually engaged, are mountable within the body without the use of any threaded fasteners by way of the mounting means. The term "contactable surfaces" as used herein refers to any surface, face or other external part of the padlock component in questions (or of the padlock itself) which can be touched or physically contacted in 4a any other way, whether by other components of the padlock or by a user or by other solid objects, in the use of the padlock. The terms "substantially non-conductive" and "substantially insulated" indicate that electrical conduction will not occur through the component or surfaces in question even when the padlock is subject to an imposed 5 voltage or current of the order likely to be encountered in the normal operation of the equipment to which the padlock is attached. In a second aspect, the present invention resides in a padlock wherein the contactable surfaces of the padlock are formed from a non-sparking material. The padlock in 10 accordance with this aspect of the invention therefore significantly minimises the risk of sparking and the associated dangers that this can create in environments that have a high explosion or fire risk. In one particular form of the second aspect, the padlock may have a shackle wherein 15 all contactable surfaces of the shackle comprise a substantially non-conductive material, a body wherein all contactable surfaces of the body comprise a substantially non-conductive material, and a conventional key cylinder for unlocking the padlock, whereby the padlock is configured so that any exposed conductive part(s) of the padlock cannot come into direct contact with the device or implement to which the 20 padlock is secured in use or when the padlock is being applied to the device or implement. This prevents sparking in the event that the padlock impacts against or grazes past the device or implement. In a third aspect, the present invention resides in a padlock having a body and a 25 shackle, and a mechanism for unlocking the padlock using a key, whereby the mechanism can be mounted to the padlock body without the use of threaded fasteners. The ability to securely mount the key operated mechanism to the padlock body without the need for threaded fasteners such as screws, bolts and the like (which in padlocks can be very small and "fiddly") significantly increases the ease and speed 30 with which the padlock can be assembled. The ability to assemble the padlock without threaded fasteners may also have advantages in preventing conduction through the padlock because such fasteners are usually made of metal and therefore their omission eliminates at least some metal components that could otherwise assist an electric current to pass through the padlock.
4b In one particular form of the third aspect, the padlock may comprise a shackle, a body, a conventional key cylinder for unlocking the padlock, and one or more key 5 cylinder receiving components at least one of which is provided with body mounting means, whereby the one or more key cylinder receiving components engage with the key cylinder, and the mutually engaged key cylinder and key cylinder receiving component(s) are mountable within the body, without the use of any threaded 5 fasteners, by way of the mounting means. Various preferred features of the invention are described below. It will be appreciated that unless the context otherwise implies, the preferred features described below are applicable to any of the aspects of the invention. 10 Like all padlocks, the padlock of the present invention has a shackle. Preferably, the shackle may be a rigid member or a plurality of rigid members rigidly connected or otherwise linked together. Alternatively, the shackle may comprise a robust flexible member (for instance in the general form of a robust cable or chain) that is securable 15 to the body. In any event, no particular limitation is meant in relation to the shape or configuration of the shackle. However, the construction of the shackle will preferably be such that at least the contactable surfaces of the shackle comprise a substantially electrically non-conductive and non-sparking material. In some embodiments, the entire shackle may be made from a non-conductive and non-sparking material. A 20 range of materials that are non-conductive, non-sparking and sufficiently strong to be suitable for use in the shackle of the present invention will be known to those skilled in the art. High-strength and non-conductive engineering polymers and fibre reinforced polymer/fibre composites are examples of materials that may be suitable. In preferred embodiments, the shackle may comprise the typical rigid "U-shape" 25 common to the shackles of conventional padlocks, and the invention will be described primarily with respect to shackles of this shape. The shackle may be pivotably attached, or pivotably attachable, to the body. For shackles having the "U-shape" of conventional padlock shackles, this pivotable 30 attachment of the shackle to the body is quite common and allows the shackle to pivot with respect to the body when the padlock is open. However, other forms of shackle may also be pivotably attached or attachable to the body, and such shackles may take a wide range of forms such as pivoting levers, catches, clips, gates, and the like.
6 In order to provide security, the shackle is preferably lockably securable to the body when the padlock is closed. The shackle may be releasable (allowing the padlock to be unlocked) by way of a key operated mechanism. The key operated mechanism will generally comprise a conventional "pin-tumbler" type key cylinder. Conventional key 5 cylinders are typically made from metal due to the intricacies of their design and their high wear resistance requirements etc. However, no particular limitation is meant thereby and any other material may be used in the construction of the key cylinder if desired. Furthermore, non-conventional key operated mechanisms may also be used. Nevertheless, it is envisaged that conventional metal key cylinders will be used most 10 often. The body of the padlock may be of any size and shape, although it is envisaged that the body may generally be sized such that the padlock is easily operable by hand and so that it will not interfere with the device to which it is secured or create an undue 15 obstruction. Therefore, the size of the body may be similar to that of conventional padlocks. The body of the padlock should be constructed so that at least the contactable surfaces of the body (both inside and out) comprise a substantially non conductive and non-sparking material. Alternatively, the entire body may be made from a substantially non-conducted and non-sparking material. In any event, similar 20 high-strength, non-conductive and non-sparking materials may be used for the contactable surfaces of the body (or for the entire body) as described above in relation to the shackle. In embodiments where the shackle has one or more legs or extended portions (such as 25 the parallel legs of "U-shaped" shackles), the body may be provided with apertures or bores adapted to receive each leg or extended portion of the shackle, and the legs or extended portions may be lockable in the apertures. If the body is generally block shaped as in conventional padlocks, the body may therefore have an upper surface or surfaces forming the top of the body, and the upper surface or surfaces may contain 30 the said apertures. The apertures may be in the form of bores extending downwardly into the body of the padlock, and it is envisaged that each bore may have a cross sectional shape corresponding to the cross-sectional shape of the portion of the shackle which it is adapted to receive.
7 The body may be provided with shackle support means for providing additional support to the shackle. This may be particularly beneficial in any embodiments where the substantially non-conductive material used in the shackle (or at least the contactable surfaces thereof) results in the shackle having somewhat reduced strength 5 and robustness compared with conventional metal padlock shackles. In preferred embodiments, the shackle support means may comprise a "built up" portion of the body at the location where a portion of the shackle inserts into the body (typically near the top of the body). This "built-up" portion may therefore surround and provide support for a greater proportion of the insertable part of the shackle. Put another way, 10 the "built up" shackle support means may reduce the length of the portion of the shackle that extends unsupported out of the body. This reduces the effective "lever arm" length of the unsupported portion of the shackle, thereby reducing the possible bending stresses and the like which can be applied to the unsupported portion of the shackle. Hence, the chance of shackle failure may be reduced. 15 Where the shackle has the "U-shape" of conventional padlock shackles, the shackle support means may comprise a built up portion of the body around the location where one or both of the legs of the shackle insert into the padlock body. Preferably, the body may be built up around where the long leg of the "U-shaped" shackle inserts into 20 the body, but the region where the short leg inserts into the body may remain un-built up. This may help to prevent the built-up portion of the body from impeding the rotation of the shackle about the long leg when the padlock is open. Those skilled in the art will recognise that it is common for the shackles of padlocks to be rotatable when the padlock is open (i.e. when the short leg is retracted out of the padlock body). 25 In general, the long leg is pivotably mounted within the body so that the short leg and the arcuate portion of the U-shaped shackle can rotate about the long leg when the shackle is open. By providing shackle support means in the form of a built-up portion of the body around the region where the long leg inserts into the body, but not around the region where the short leg inserts, it may be possible to provide additional support 30 the padlock shackle without impeding the rotation of the shackle when the padlock is open. The insertable portion of each leg of the shackle may have an aperture therein adapted to receive a locking element. These apertures will hereinafter be referred to as 8 locking apertures. Preferably each locking aperture may be in the form of a notch (a locking notch) extending in a direction substantially transverse to the longitudinal axis of the leg, the notch being sufficiently large and deep so that when a locking element is inserted into the aperture it may be retained therein to thereby prevent the leg form 5 moving axially within the aperture in the body. Even more preferably each notch may have a substantially semi-tubular shape wherein the longitudinal axis of the notch is oriented substantially transversely to the longitudinal axis of the corresponding leg, and offset therefrom. This semi-tubular shape is particularly suitable when the locking elements comprise balls resembling ball bearings which are commonly used 10 for this purpose in padlocks. Furthermore, in embodiments having parallel legs, and particularly in embodiments where the shackle is "U" shaped, the locking recesses may be located on the respective legs so that they open substantially inwardly towards each other. However, the locking apertures may alternatively take other forms and they may be positioned elsewhere on the legs, so no particular limitation is meant in 15 relation to the shape, form or location of the locking apertures. No limitation is meant with regard to the kind of locking elements that can be used either. As is alluded to above, in embodiments where the shackle is U-shaped, one of the parallel legs may be longer than the other. The leg that is longer than the other may 20 have a further aperture therein (hereinafter referred to as a retaining aperture). The retaining aperture may be located below the locking aperture of the long leg on the inner side. More particularly, the retaining aperture may be in the form of a flat recess extending downwardly from a lower edge of the locking aperture. The retaining aperture may be indented into the long leg substantially less deeply than the 25 locking aperture. The long leg may also have a substantially circumferential groove therein. The groove may be recessed into the leg approximately the same amount as the retaining aperture, and the groove may be positioned on the leg such that the bottom of the retaining aperture connects with an upper edge of the groove. Hence, the two may blend smoothly together. The long leg may also have a bottom portion 30 extending from the lower edge of the groove to the bottom end of the long leg. The bottom portion may have substantially the same cylindrical diameter as the other portions of the long leg.
9 The padlock may further comprise a locking means for moving the locking elements mentioned above into engagement with the locking apertures in the legs. Preferably, the locking means may comprise a camming member, and the locking elements may be in the form of the solid metal spheres or "balls" mentioned above. The balls may 5 be opposedly positioned on respective sides of the camming member and the camming member may have an opposed pair of camming surfaces each of which may engage with a respective ball. The camming surfaces may be suitably curved to provide camming engagement with the balls. 10 The camming member (or at least the contactable surfaces thereof) may be made from a rigid, non-conductive and non-sparking material similar to that described with reference to the shackle and the body above. Therefore, even though there may be direct contact between the metal balls and the camming member, conduction of dangerous electrical currents between the balls and the camming member may be 15 prevented by the non-conductive properties of (at least) the surfaces of the camming member. The camming member may be rotatable between a locking position and an unlocking position. Rotation of the camming member into the locking position may cause each 20 of the camming surfaces to engage the corresponding ball thereby pushing the balls outwardly. If the legs are inserted into the body, the outward movement of the balls may cause the balls to engage with the locking apertures in the legs. The engagement of the balls with the locking apertures may prevent the legs from being retracted out of the body, thus locking the padlock. The camming member may be biased towards 25 the locking position so that upon insertion of the legs, the padlock automatically locks. The camming member may also have an opposed pair of cavities adapted to receive the balls. The cavities may be interposed between the camming surfaces. Therefore, 30 rotation of the camming member into the unlocked position may allow the balls to retreat inwardly into the cavities and out of engagement with the locking apertures in the legs. Upon disengagement of the balls with respect to the locking apertures, the legs may be thereby released enabling each leg (and therefore the shackle) to move upwardly with respect to the body. More specifically, the legs may be released by the 10 retraction of the balls into the cavities because this may allow the lower edge of each of the locking apertures to move upwardly past the balls. This upward movement of the shackle may allow the short leg to retract out of the body thus opening the padlock. 5 As described above, when the camming member is rotated into the unlocked position causing the balls to retreat into the cavities, this may allow the lower edges of the respective locking apertures to move upwardly past the balls. In the case of the short leg this may allow the short leg to be retracted out of the body of the padlock. 10 However, it will be recalled that the long leg may have a retaining aperture extending downwardly from the lower edge of the locking aperture, and it may also have a groove positioned substantially near the bottom of the retaining aperture which extends circumferentially around the long leg. The retaining aperture and the groove may be substantially less deep than the locking aperture in the long leg. Therefore, 15 even though retraction of the ball into the cavity in the camming member may disengage the ball from the locking aperture in the long leg, nevertheless the ball may still extend outwardly sufficiently to engage with the retaining aperture and the groove. This engagement of the ball with the retaining aperture and the groove, and in particular the engagement of the ball with a bottom edge of the groove which may 20 form a lip, may prevent the long leg from being retracted out of the padlock body, although the circumferential shape of the groove may allow the long leg to rotate in the body. The engagement between the ball, the retaining aperture and the groove may also prevent the camming member from rotating back into the lock position. This is because the retaining aperture and the groove may push the ball into the cavity 25 in the camming member. Therefore the camming member may only be able to rotate back into the locked position when the legs are reinserted into the padlock to lock the padlock. Reinsertion of the legs into the body may bring the locking apertures in the legs back into alignment with the balls, thereby allowing the balls to move outwardly into the locking apertures thus allowing the camming member to rotate back into the 30 locked position. The padlock may comprise an entraining member operatively associated with the key cylinder so that rotation of the key cylinder imparts corresponding rotation to the entraining member. The entraining member may comprise a part or extension of the 1 cylinder, or a separate component attachable to the cylinder, although no particular limitation is meant thereby. The entraining member will typically be made of metal, although a range of other rigid materials may also be used. Preferably the entraining member may be adapted to operatively connect the key cylinder with the locking 5 means so that rotation of the cylinder in the normal manner to unlock the padlock causes disengagement of the locking elements from the locking aperture in the legs. Even more preferably, the locking means may comprise a camming member as described above and the entraining member may be adapted to cooperate with the camming member so that rotation of the cylinder (and the entraining member) thereby 10 causes rotation of the camming member from the locked position to the unlocked position. To achieve this, the entraining member may be provided with one or more protrusions that cooperate with corresponding protrusions on the camming member. In 15 particularly preferred embodiments, the protrusions on the entraining member may comprise a pair of upwardly extending entraining posts. The protrusions on the camming member may take any form suitable to cooperate with the entraining posts, but for convenience the protrusions in the camming member will be referred to as the cam blocks. 20 The entraining posts may be positioned such that rotation of the entraining member (caused by rotation of the cylinder) in one direction causes the entraining posts to come into contact with the cam blocks, whilst rotation of the entraining member in the other direction causes the entraining posts to separate from the cam blocks. Hence, 25 the entraining member may be able to rotate somewhat independently of the camming member. Even though there may be direct contact between the entraining member (which may be made of metal) and the camming member in some positions of those components 30 during the operation of the padlock, nevertheless conduction of dangerous electric currents between the camming member and the entraining member (even if the entraining member is made of metal) may be prevented by the non-conductive properties of (at least) the surfaces of the camming member.
12 As explained above, the camming member may only be able to rotate from the unlocked position back into the locked position when the legs are reinserted into the padlock to lock the padlock. Therefore, when the padlock is opened by operating the cylinder which in turn rotates the entraining member and the camming member, the 5 camming member may then be retained in the unlocked position until the legs are reinserted. Meanwhile (i.e. while the camming member is retained in the unlocked position), the entraining member and the cylinder mechanism may be able to rotate freely. If the entraining member and the cylinder mechanism are able to rotate freely, it may therefore be possible to return the cylinder to the position where the key can be 10 extracted. The body of the padlock may have a main opening to accommodate the key cylinder and the one or more key cylinder receiving components. It is envisaged that the main opening will often comprise an opening in or through the base of the padlock body. 15 The padlock may be provided with one or more key cylinder receiving components which engage with the key cylinder and the body to mount the key cylinder within the body when the padlock is assembled. Preferably, the key cylinder receiving components may be shaped so as to "marry" with or snugly mate against the key 20 cylinder, and preferably also with the inside of the padlock body. One or more or all of the key cylinder receiving components (or at least the contactable surfaces thereof) may be made from a rigid non-conductive and non sparking material similar to that described with reference to the shackle and the body 25 above. Therefore, even though there may be direct contact between the key cylinder (which may be made of metal) and one or more of the key cylinder receiving components, conduction of dangerous electrical currents therebetween may be prevented by the non-conductive properties of (at least) the surface of the one or more receiving components. Also, there should preferably be no openings left between the 30 key cylinder and the cylinder receiving components, and the body. Hence, there should preferably be no gaps or openings that may expose the inner workings of the padlock to unauthorised tampering etc through the main opening or otherwise when the padlock is locked.
13 In particularly preferred embodiments, the key cylinder receiving components may comprise a key cylinder receiving insert and a key cylinder cover. During assembly, the key cylinder receiving insert may first be inserted into the padlock body through the main opening. Some or all of the peripheral surfaces of the key cylinder receiving 5 insert may be shaped in a manner that conforms to the internal shape of the padlock body, or at least to a portion of the inside of the body. The key cylinder receiving insert may also have a part or surface that is shaped in a manner that conforms to the shape of at least a portion of the key cylinder. 10 Like the key cylinder receiving insert, some or all of the peripheral surfaces of the key cylinder cover may be shaped in a manner that conforms to the internal shape of the padlock body, or at least to a portion of the inside of the body. A part or surface of the key cylinder cover may also be shaped in a manner that conforms to the shape of at least a portion of the key cylinder. Therefore, before they are inserted into the 15 padlock body, the key cylinder and the key cylinder cover may be assembled together so that the said part or surface of the key cylinder cover marries against a portion of the key cylinder. When assembled in this way, the key cylinder and the key cylinder cover form, in effect, a single component that may be inserted into the body of the padlock. When they are so inserted (as one), a side of the key cylinder may marry 20 closely against the abovementioned part or surface of the key cylinder receiving insert and the peripheral surface of the key cylinder cover may conform to the internal shape of the padlock body, or at least to a portion of the inside of the body. Hence, the insert, the key cylinder and the cover can be inserted to be snugly received 25 and mounted within the padlock body without leaving any gaps in or around the main opening. As mentioned above, one or more of the key cylinder receiving components may be provided with body mounting means for mounting the key cylinder and the key 30 cylinder receiving components within the padlock body. The mounting means may comprise any form or combination of physically engaging mechanisms, snap fit arrangements, inter-engaging teeth, clips, mutually engaging protrusions and recesses and the like that those skilled in the art would recognise as being suitable for 14 physically retaining the key cylinder and the cylinder receiving components in the body. In preferred embodiments such as those described above where the key cylinder 5 receiving components comprise a key cylinder receiving insert and a key cylinder cover, the mounting means may comprise one or more ridges and/or recesses on an outer surface of the insert and/or the cover which engages with one or more corresponding recesses and/or ridges on the internal surface of the padlock body. Preferably, the ridges and recesses may be substantially elongate and oriented 10 perpendicular to the direction in which the insert and cover are inserted through the main opening into the body. Therefore, the engagement of the one or more ridges/recesses on the insert or cover with the corresponding recesses/ridges on the inside of the body may retain the key cylinder receiving components, and hence the key cylinder, inside the body. Preferably, a number of such corresponding 15 ridges/recesses may be provided on the insert/cover and the body. The inside of the body may also comprise whatever other forms of internal shaping, sculpting or other features as may be necessary to house, interrelate and interoperate with the various components of the padlock in use or assembly of the padlock. 20 The padlock may further be provided with release means which may be used to disengage at least one of the key cylinder receiving components (and hence the key cylinder as well) from the padlock body. The release means should be accessible from the outside the padlock body so that the at least one cylinder receiving 25 component and the key cylinder can be removed if necessary. One reason why this might be necessary is to "re-key" the padlock by replacing the key cylinder with an alternative cylinder that operates with a different key. Preferably, the release means may comprise one or more protrusions which snap or 30 click into place in one or more corresponding apertures in the body when the key cylinder receiving components are inserted into the body. Hence, the engagement of each protrusion with the corresponding aperture may further help to retain the key cylinder receiving components within the body. However, at least one of the one or more apertures in the body into which the one or more protrusions may be received 15 should preferably extend all the way through the body so that at least one of the one or more protrusions is accessible from outside the body through that aperture. The at least one accessible protrusion may therefore be depressed by inserting a thin object into the corresponding aperture to depress the protrusion thereby disengaging that 5 protrusion from its aperture. If this is done, the cylinder receiving components, or one or some thereof, may become disengaged allowing it/them to be extracted along with the key cylinder. BRIEF DESCRIPTION OF THE DRAWINGS 10 One particular embodiment of the invention is described below with reference to the drawings. However, it will be clearly appreciated that this description is provided to assist in understanding the invention only, and the invention is not limited to or by this embodiment. 15 Figure 1 shows a perspective view of a padlock in accordance with the embodiment of the invention presently described; Figure 2 shows a perspective view of the padlock of Figure 1 from the reverse side; 20 Figure 3 shows an exploded perspective view of the components of the padlock; and Figure 4 shows a partially sectional view of the assembled padlock. DETAILED DESCRIPTION OF THE DRAWINGS 25 With reference to Figure 3, there is shown a padlock assembly 10 in accordance with one embodiment of the present invention comprising a padlock body 12 and a shackle 14. Shackle 14 comprises a long leg 16 and short leg 18. Also, from Figure 4 it can be seen that long leg 16 is adapted to be insertable into a long leg bore 20 in body 12, and short leg 18 is adapted to be insertable into a short leg bore 22. 30 The general shape of shackle 14 is similar to that of an inverted "U". Therefore, the two parallel portions of the U form long leg 16 and short leg 18, and the upper end of the respective legs are integrally connected by an arcuate member 24 corresponding to the curved portion of the U. More specifically, in the embodiment shown, long leg 16 16 and short leg 18 are both substantially cylindrical (i.e. having a substantially circular cross-section) of equal diameter, and long leg 16 is substantially longer than short leg 18 so that the lower end of long leg 16 extends substantially below the lower end of short leg 18. Because the respective legs are substantially cylindrical, therefore 5 arcuate member 24 (which is integrally formed with the legs) has a substantially semi toroidal shape connecting the tops of the two legs and having approximately the same cross-section as the legs. In this embodiment, both body 12 and shackle 14 are made of a high-strength, non 10 conductive engineering polymer plastic. Because of this plastic construction, the strength of the shackle 12 is somewhat reduced compared with traditional metal padlock shackles. To compensate for this, the body 12 is provided with built-up portion 17 which provides additional support to the long leg 16 by reducing the length of leg 16 which is exposed and thus reducing the possible bending stresses that could 15 be applied to leg 16. However, it will be noted that built-up portion 17 does not extend to the region where short leg 18 inserts into the body and so the shackle can pivot as described below. Long leg 16 and short leg 18 both have a locking notch therein. The notches in long 20 leg 16 and short leg 18 are indicated by reference numerals 26 and 28 respectively. Notches 26, 28 comprise substantially semi-tubular cutouts in the inner side of the respective legs, the cutouts being oriented such that the longitudinal axis of each semi-tubular cutout is substantially perpendicular to the longitudinal axis of the respective legs and offset inwardly thereof. Notch 28 is located towards the lower end 25 of short leg 18, and notch 26 is located roughly two thirds of the way down the length of long leg 16. Consequently, both notches are located at substantially the same level, thus effectively making each notch a mirror image of the other. Long leg 16 further comprises a groove 30 (shown in Figure 3), a retaining aperture in 30 the form of inner flat 32 (shown in Figure 4) and a bottom portion 34. Groove 30, located towards the lower end of long leg 16, has a roughly semicircular cross-section and extends all the way around long leg 16. Thus, groove 30 forms a substantially circumferential cutout around the lower end of long leg 16. Importantly, the maximum depth to which groove 30 is recessed into long leg 16 is substantially less 17 than the maximum depth to which notches 26, 28 are indented into the respective legs. The reason for this will be explained below. Inner flat 32 comprises a substantially flat surface extending down the inner side of 5 long leg 16 from the lower edge of notch 26 to groove 30. Inner flat 32 is also slightly indented into long leg 16 and it therefore forms a slightly recessed flat surface. The depth to which inner flat 32 is recessed into long leg 16 is approximately the same as the depth of groove 30. Therefore, inner flat 32 effectively blends smoothly into groove 30 at the point where the two meet, and there is no distinct 10 ridge, edge or other delineation between the two. Bottom portion 34 is the portion of long leg 16 extending downwardly below groove 30. The bottom portion 34 has the full diameter of long leg 16. The edge where groove 30 meets bottom portion 34 forms a lip 37. 15 From Figure 3, it can be seen that padlock assembly 10 has a number of components that form an internal locking mechanism for locking and unlocking the padlock. The locking mechanism comprises a conventional metal key barrel 40, a plastic barrel cover 41, a metal entraining member 42, a plastic calming member 44, metal locking 20 balls 46 and 48, a metal spacer 43, a metal retainer plate 45 and a metal cam spring 47. Key barrel 40 has a conventional metal pin-tumbler construction that will be well known to those skilled in the art. Hence, it will be understood that a key may be 25 inserted into key barrel 40 (as illustrated for example in Figures 1-2) and that, if the key is the correct key for the key barrel, the key can then be rotated thereby rotating the inner workings of the key barrel. It will also be understood that rotation of the key and key barrel mechanism causes the end of the key barrel, or a portion thereof, or a pin or other abutment, to rotate accordingly. This causes rotation to be imparted into 30 the other components of locking mechanism to operate the padlock as explained in greater detail below. It can be seen that plastic camming member 44 comprises a pair of convex camming surfaces 56 located on opposite sides thereof, and a pair of concave cavities 58 also 18 located on opposed sides thereof and interposed between the camming services 56. The metal locking balls 46 and 48 are positioned one on either side of camming member 44. Camming member 44 is pivotable between a locked position and an unlocked position. Figures 3-4 show camming member 44 in the locked position 5 wherein the camming surfaces 56 contact with the balls 46 and 48, thereby pushing ball 46 into engagement with notch 26 in long leg 16 and pushing ball 48 into engagement with notch 28 in short leg 18. It will be clearly understood that the diameter of each of the balls 46 and 48 is such that balls 46 and 48 fit snugly and sufficiently deeply into notches 26 and 28 so as to prevent vertical movement of the 10 respective legs within the body. Thus, when camming member 44 is in the locked position and the legs of the shackle are inserted into their respective bores in body 12, the legs are retained within body 12 by engagement of the balls 46 and 48, and the padlock is locked. 15 Camming member 44 can be pivoted from the locked position into the unlocked position by rotating camming member 44. This is done by operating key barrel 40, as explained in greater detail below. When camming member 44 is pivoted into the unlocked position, locking balls 46 and 20 48 are no longer in engagement with camming surfaces 56 and therefore they are not being pushed into engagement with the notches 26 and 28 in the legs. Instead, locking balls 46 and 48 are allowed to retreat into the cavities 58 in camming member 44. It will be understood that cavities 58 are sufficiently deep, and that locking balls 46 and 48 can retreat sufficiently far into cavities 58, such that the bottom edges of the 25 respective notches 26 and 28 can move upwardly within the padlock body 12 past balls 46 and 48. Hence, rotation of camming member 44 into the unlocked position (which is achieved by operating the key barrel) allows legs 16 and 18 of the shackle to move upwardly within the body 12. In particular, it allows short leg 18 to be retracted entirely out of short leg bore 22, thus opening the padlock. The shackle 14 moves 30 upwards within the body under the bias of helical metal spring 19 which is mounted below long leg 16 as shown in Figure 4. However, it will also be understood that, even when balls 46 and 48 are retracted into recesses 58, they are not retracted entirely within the cavities. Therefore, balls 46 and 19 48 extend outwardly to some extent even when they are retracted into cavities 58, albeit to a lesser extent than they do when they are pushed into engagement with notches 26 and 28 by camming surfaces 56. This is particularly important in relation to ball 46. It will be recalled that inner flat 32 (which is recessed slightly into long leg 5 16 but less deeply than notch 26) extends down the inside of long leg 16 between the lower edge of notch 26 and groove 30. Therefore, even though ball 46 retracts out of notch 26 when the balls are retracted into cavity 58, nevertheless ball 26 still extends outwardly sufficiently to engage with inner flat 32. It will also be recalled that the lower edge of groove 30 forms a lip 37. Therefore, even when ball 46 is retracted into 10 cavity 58 and the short leg 18 is retracted out of short leg bore 22 so that the padlock is open, nevertheless the engagement of ball 46 with inner flat 32 and lip 37 prevents long leg 16 from being retracted out of long leg bore 20. The circumferential shape of groove 30 allows long leg 16 to rotate within long leg 15 bore 20 (i.e. shackle 14 can be rotated about long leg 16) when the padlock is open. Groove 30 effectively creates a track within which ball 46 can roll as shackle 14 rotates. Figures 3-4 show that metal entraining member 42 comprises a substantially disk 20 shaped member having approximately the same diameter as key barrel 40. It can also be seen from Figure 3 that entraining member 42 is secured to the top of the key barrel 40, coaxially therewith. Hence, rotation of key barrel 40 by a key in the manner described above causes corresponding rotation of entraining member 42. Entraining member 42 also has a pair of entraining posts 54. The respective 25 entraining posts 54 are positioned directly opposite each other on the upper surface of entraining member 42, towards the outer edge thereof, and they extend vertically upwards. Figure 3 also shows that plastic camming member 44 has a pair of cam blocks 60 30 protruding downwardly from its base. Together the cam blocks 60 extend across substantially the entire width of camming member 44. When the padlock assembly 10 is assembled, cam blocks 60 reside between the respective entraining posts 54 of entraining member 42. Hence, rotation of entraining member 44 (caused by rotation of the key in key barrel 40) causes entraining posts 54 to come into contact with cam 20 blocks 60. Therefore, rotation of key barrel 40 causes camming member 44 to rotate between the locked and unlocked position in which it respectively locks and unlocks the padlock by interacting with the balls 46 and 48 as described above. However, it will be appreciated from the above description, and from Figures 3-4, that camming 5 member 44 can rotate from the unlocked position back into the locked position only when the legs 16 and 18 are reinserted into bores 20 and 22 to lock the padlock. When the legs are reinserted, the camming member rotates back into the locked position under the bias of metal cam spring 47, thus moving the balls to lock the padlock as described above. 10 Referring again to Figure 3, it will be seen that the padlock assembly comprises a key cylinder receiving insert 39. Insert 39 is a plastic component. Together, insert 39 and plastic barrel cover 41 comprise the key cylinder receiving components in this embodiment of the invention. Insert 39 has an elongate concave receiving cavity 62 15 of corresponding shape to the convex cylindrical surface of key barrel 40. Hence, the convex cylindrical surface of key barrel 40 is able to be received snugly in concave receiving cavity 62 when the padlock is assembled. Similarly, barrel cover 41 is shaped to snugly fit over the blocklike portion of key barrel 40 which houses the split pins. The outer surfaces of insert 39 and cover 41 both have a shape that corresponds 20 with the internal surface shape of the padlock body 12. . In order to assemble the padlock, the insert 39 is first inserted into the body as can be seen in Figure 4. Then, while the key barrel 40 and cover 41 are separate from the padlock, the cover 41 is slotted onto the blocklike portion of the key barrel 40. 25 Together the key barrel 40 and the cover 41 are then inserted into the body. It will be appreciated that entraining member 42, camming member 44, locking balls 46 and 48, spacer 43, retainer plate 45 and cam spring 47 will all have been assembled on top of the key barrel 40, or alternatively in the padlock body, in the manner shown in Figure 4, before the key barrel 40 and the cover 41 are inserted. 30 From Figure 3, it can be seen that the outer surfaces of the insert 39 and the cover 41 each also have an arcuate ridge 63 near their respective bases. Insert 39 and cover 41 further have an arcuate indent 64 on their respective outer surfaces near the top. Each arcuate ridge 63 has a corresponding indent 65 in the padlock body and each indent 64 21 has a corresponding ridge 66 in the body. Therefore, when the insert 39 is inserted into the padlock body, and similarly when the key barrel 40 and cover 41 are inserted, the ridges 63 engage with the indents 65, and that indents 64 engage with the ridges 66. This maintains the insert 39, and the key barrel 40 and cover 41, within the body 5 as shown in Figure 4. Figure 2 further illustrates that insert 39 and cover 41 are each provided with a tongue 70. Each tongue 70 extends into an aperture in the padlock body as shown when the respective insert 39, and the cover 41 and key barrel 40, are inserted into the body as 10 described above. Because the tongues 70 are accessible from the outside of the padlock body it is possible to use these to remove the key barrel 40 and cover 41 if desired. This is done by inserting a small "pointy" object to depress the tongue 70 on the cover 41 inwardly into the padlock. When the tongue on the cover 41 has been depressed sufficiently deeply so that it clears the lower edges of the aperture in which 15 it is received, a downward force may then disengage the ridges/indents 63, 64 on the cover from the indent/ridges 65, 66 on the inside surface of the body, thereby allowing the cover 41 and key barrel 40 to be extracted through the base of the padlock body. It is also possible to extract insert 39 in a similar manner after the cover 41 and key barrel 40 have been removed, although this may not ordinarily be 20 necessary as all that is normally required to "re-key" the padlock is to remove the key barrel 40. Referring now to Figure 4, it should be re-emphasised that the following components are made from plastic and metal respectively. 25 Plastic components Metal components Body 12 Key barrel 40 Shackle 14 Helical spring 19 Camming member 44 Spacer 43 Insert 39 Cam spring 47 Cylinder cover 41 Metal retainer plate 45 Locking balls 46, 48 22 Therefore, as a consequence of the way these components are configured as shown in Figure 4, all of the metal components (they are all associated with the operation of the key barrel 40 and they may therefore be collectively considered as a key barrel mechanism) are electrically insulated by the plastic components, meaning that there is 5 no path through which electricity can flow through the padlock. Also, it can be seen from Figures 1-2 that the only metal component which is exposed when the padlock is assembled is the base of key cylinder 40. However, because of the shape of the padlock, it is highly unlikely that this metal portion which protrudes 10 very little (if at all) from the base could come into contact with another hard object when the padlock is applied to secure a device in use. This is particularly so because the metal portion is in the base and not the more exposed sides of the padlock. Therefore, the padlock of this embodiment of the invention is configured so that the risk of sparking due to impact of any exposed metal portion of the padlock with 15 another hard object is minimised (it being appreciated that all of the other exposed surfaces of the padlock a formed from a non-conducted and non-sparking material). It should be appreciated that various other changes and modifications can be made to the embodiment described without departing from the spirit and scope of the 20 invention. The term 'comprise' and variants of the term such as 'comprises' or 'comprising' are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any other integer or any other integers, unless in the context or usage an 25 exclusive interpretation of the term is required.