In underground mining operations reinforcing and/or retaining means are used in a variety of situations. In a number of instances when the reinforcing and/or retaining function has been fulfilled the reinforcing and/or retaining means must be removed. Often this involves cutting of the reinforcing and/or retaining means. For instance, wires, typically in the form of a mesh, are frequently used to support the roof and/or sidewalls of a drive (or tunnel) for the safety of personnel and equipment. Production blasting retreats along the drive, so that personnel and equipment continue to be protected in the supported drive. However, it is necessary to remove or cut the wires as production continues, or perhaps if the size or direction of a tunnel changes. Removal or cutting of the wires can be potentially hazardous, and also labour intensive and time consuming, and can thus significantly reduce the efficiency of the mining operation. It would therefore be desirable to provide means for cutting the wires quickly and effectively.

In another instance, elongate members, typically in the form of rockbolts or cables, are frequently used to support a roof itself or the aforementioned wire mesh, and as production proceeds, such members may protrude from the roof. The members need to be removed to allow safe passage of men, machinery and material. Removal of bolts or cables can be labour intensive and time consuming, primarily because they are intentionally well secured in the roof, so as to provide support. Here, too it would be desirably to provide means for cutting these (larger diameter) elongate members quickly and efficiently, in order to increase the efficiency of the mining operation.

In accordance with the present invention it has been found that cutting of elongate members typically used in mining operations may be achieved using a number of small, discrete explosive charges arranged in series along a length of detonating cord.

Accordingly, the present invention provides a device which is suitable for cutting an elongate member, which device comprises a length of detonating cord and a number of explosive charges arranged along the detonating cord, wherein each explosive charge is contained in a casing which is adapted to be attached to or positioned adjacent to the elongate member it is desired to cut.

As will be appreciated from the following, the positioning of the explosive charges along the detonating cord and the way in which the casing is adapted to be attached or positioned relative to the elongate member will depend upon the nature of the elongate member to be cut. In one embodiment described herein individual explosive charges are used to cut individual elongate members, whereas in another embodiment described a number of explosive charges are used to cut an individual elongate member.

The exact configuration of the casing will depend in part upon the type of explosive charge which is used. This will be explained in greater detail below. Typically, however, the casing comprises a hollow body which is adapted to contain an explosive charge, and which comprises an engagement means and a detonating cord receiving means. The engagement means allows the casing to be attached, or positioned adjacent, to the elongate member it is desired to cut.

The hollow body defines a chamber for the explosive charge. The size of the chamber will typically be influenced by the type of elongate member being cut and its diameter, and the strength of explosive charge used. In one embodiment the casing takes the form of a thin- walled cylinder, and the chamber is therefore also cylindrical. The walls of the casing are preferably as thin as possible whilst providing the necessary structural rigidity. The cylinder is usually closed at one end and open at the other to allow the casing to be loaded with explosive charge. The cylinder is usually closed at one end by a thin membrane extending across the diameter of the cylinder. This membrane actually separates explosive

charge contained in the chamber from the elongate member it is desired to cut.

Typical dimensions for the casing are 30-100mm, for instance 30-70mm, in length and 20- 50mm in diameter. In practice the casing will be about 50mm long and about 30mm in diameter. With these dimensions in mind, for elongate members of relatively small diameter (2-10mm), such as wires, the device is generally used in such a way that a single explosive charge is used to cut a single elongate member. This means that each casing of the device is associated with each elongate member to be cut. In contrast, for elongate members of relatively large diameter (e. g. 10-30mm), the device is generally used in such a way that a number of explosive charges are used to cut a single elongate member, i. e. more than one casing is associated with a single elongate member to be cut. The way in which the device is used may vary subject to the dimensions of the casing and thus the volume capacity of the casing for explosive charge.

In one embodiment the elongate member is a wire making up a series of wires, for example, a wire mesh. In accordance with this embodiment, in one aspect the present invention provides a device which is suitable for cutting a series of wires, which device comprises a length of detonating cord and a number of explosive charges arranged along the detonating cord at intervals corresponding to intervals between the wires it is desired to cut, wherein each explosive charge is contained in a casing which is adapted to be attached to a wire in the series and through which detonating cord runs in contact with the explosive charge. In use the casings of the device are attached to the wires it is desired to cut, and the explosive charges contained detonated using the detonating cord. In this embodiment individual explosive charges are typically used to cut individual wires in the series.

In this embodiment the casing must be attachable to a wire it is desired to cut. Thus, the casing may comprise wire engagement means which allow the casing to be attached to a wire to be cut. Preferably, the wire engagement means allows releasable attachment of the casing. The wire engagement means usually takes the form of a pair of recesses into which wire may be clipped. The opening of each recess is typically narrower than the diameter of the wire so that the wire is pushed/clipped into each recess and positively retained therein.

The recesses are generally U-shaped. The recesses are usually provided in a sleeve portion extending from the closed end of the casing. This sleeve portion may be shaped in order to arrange adjacent loaded casings in close proximity, for instance if the separation of wires to be cut is small. For instance, portions of the sleeve portion may be cut-away and usually the cut-away portions are provided diametrically opposite each other and perpendicular to the diameter at the ends of which the wire engagement means are provided. It is also preferred that when attached to a wire the explosive charge contained in the casing is spaced the optimum distance from the wire. It is also desirable to minimise the amount of explosive energy which does not contribute to cutting of the wire.

In another embodiment the explosive charge of a single casing is insufficient to cut an elongate member. For the casing dimensions quoted above, this may be the case when the elongate member has a diameter of 10-30mm, such as a bolt, reinforcing bar, hawser or cable. In accordance with this embodiment, the present invention provides a device which is suitable for cutting an elongate member, which device comprises a length of detonating cord and at least two explosive charges arranged along the detonating cord, wherein each explosive charge is contained in a casing which is adapted to be attached to or positioned adjacent the elongate member and through which detonating cord runs in contact with the explosive charge. In this embodiment a number of explosive charges are used to cut a single elongate member.

Each explosive charge is housed in a casing and in practice of this embodiment a number of casings are arranged around the elongate member it is desired to cut. Typically, the casings are cylindrical and the longitudinal axis of the casing is usually positioned perpendicular to the longitudinal axis of the elongate member. When the elongate member is circular in cross-section the casings will be positioned around a circumference of the member.

In this embodiment the length of detonating cord between each casing is the minimum required to allow the chosen number of casings to be suitably positioned around the elongate member to be cut. If the length of detonating cord is too short it will not be

possible to position the casings around the elongate member so that the longitudinal axis of each casing is essentially perpendicular to the longitudinal axis of the elongate member. If the length of detonating cord is too long, the casings may be positioned appropriately but excess cord is then used leading to wastage. The length of detonating cord between casings (or rather the interval between casings along the cord) will vary as a function of the size (diameter) of the elongate member being cut and the number of casings required for the cutting operation. The number of casings required for a given cutting application will vary as a function of the size of the casings (and thus the amount of explosive charge contained). Typically from two to six, preferably two, four, or six casings are used for cutting elongate members. The number of casings used will also dictate the number of points at which the detonating cord linking the casings should be initiated for satisfactory results. When two, four or six casings are used, the casings are usually initiated in pairs so that the linking detonating cord is initiated at one, two or three points respectively. When three or five casings are used, the linking detonating cord is usually initiated at three or five points respectively. The size and number of casings required in any given situation may be determined by trial and error and the results logged before practice of the invention in the field so that for a particular type and dimension of elongate member the most appropriate device configuration may be used. The same is true for the wire cutting application described.

When using a number of explosive charges to cut a single elongate member it is desired to either attach casings to the elongate member or to position casings adjacent to and in contact with the elongate member. One end of the casing may be suitably adapted to facilitate this. It is desirable that in use the charge contained in the casing is spaced the optimum distance form the elongate member. To enable suitable positioning relative to the elongate member one end of each casing may include engagement means which allows releasable attachment of the casing to the elongate member or positioning of the casing close to an in contact with the elongate member. The engagement means may comprise flexible arms which extend from the casing and which allow the casing to be attached to the elongate member. Alternatively, one end of the casing may be shaped to allow the casing to be positioned adjacent the elongate member. The end of the casing may thus be

shaped to match the external surface of the elongate member. The end of the casing may include an appropriately shaped sleeve portion to facilitate positioning of the casing adjacent the elongate member. It is also desirable to minimise the amount of explosive energy which does not contribute to cutting of the elongate member.

In a preferred embodiment the device which is specifically adapted for cutting a series of wires may also be used for cutting single elongate members, the device therefore having multi-functionality. The rigidity of the detonating cord may enable casings specifically adapted to the wire cutting application to be retained in positioned around an elongate member if the end of each casing is not especially adapted to allow ready attachment, or positioning, of individual casings around the elongate member. In this embodiment the interval between casings must simply be sufficient to allow suitable positioning of the casings around the elongate member.

The device used for cutting a single elongate member will take the form of a number of casings provided along a length of detonating cord, the latter having two free ends. In use, when the casings are suitably positioned around the elongate member the free ends of the cord are typically taped together, and any excess cord may be trimmed prior to, or bound in, this step. The detonating cord linking the charges may be initiated by use of a separate length of detonating cord. Preferably, the device is initiated at a number of locations along the detonating cord linking the explosive charges. Usually, the cord linking the charges is initiated at two points, typically at points diametrically opposing each other around the loop of detonating cord provided through the casings and around the elongate member.

The detonating cord used to initiate the device may be of the same or different strength as the cord used to link the explosives charges. The initiating detonating cord may be tied to the detonating cord linking the explosives charges. The intention is that each explosive charge in the loop is fired at essentially the same time (within microseconds of each other) so that the combined explosive energy which is associated with each explosive charge and which is focussed radially toward the elongate member results in cutting of the elongate member.

In general, a feature of the casing is that it must be adapted to allow detonating cord to run through it in intimate contact with the explosive charge. Thus, the device of the invention consists of a continuous length of detonating cord running through a series of casings, each casing containing an explosive charge surrounding the detonating cord. Intimate contact between detonating cord and explosive charge ensures satisfactory operation of the device such that all explosive charges of the device are detonated.

In a preferred embodiment the casing is configured such that the explosive charge is shaped, thereby enhancing the cutting efficiency of the device. More specifically, the explosive charge may be shaped such that there is a hollow space facing the elongate member it is desired to cut. This increases the directional penetration effect of the explosive charge. The shape of the explosive charge is usually controlled by the shape of the chamber in which it is contained in the device of the present invention. For example, when the casing takes the form of a thin-walled cylinder closed by a thin membrane, as described above, the membrane may be shaped in order to provide spacing between the explosive charge and the object it is desired to cut. Thus, the membrane may extend upwards into the chamber for the explosive charge. In a preferred embodiment, the membrane is roof-shaped, or conical, the apex extending into the chamber in a direction remote from the intended position of the wire. When multiple charges are used to cut an individual elongate member, the casings housing each charge are positioned adjacent the member such that on detonation the focus of the associated explosive energy is radially inwards toward the member (the detonating cord linking casings then running circumferentially around the member). In this way the explosive energy of adjacent shaped charges is combined and focussed towards the elongate member, thereby enhancing the cutting efficiency of the device.

In an alternative embodiment, the chamber for the explosive charge may be unlined or lined. When used the lining may take the form of a thin hollow metallic (e. g. Cu or Al) or glass cone. This also leads to an increase in penetration when compared to an unlined charge. When the lined chamber is displaced from the wire by some distance, penetration increases even further. The preferred configuration for the present invention is that the

membrane is roof-shaped and the chamber unlined.

The casing usually also comprises a detonating cord receiving means. This allows detonating cord to be fed through the body of the casing, and thus through the chamber for the explosive charge. In use this means that the detonating cord will be surrounded by the explosive charge. The detonating cord receiving means may take the form of two holes in opposing walls of the casing. When the casing is cylindrical the holes are diametrically opposite each other. The holes are of a size which permits the detonating cord to be threaded through them. Preferably, when the detonating cord is in place there is the minimum gap between the detonating cord and the casing, i. e. the holes are only slightly bigger than the detonating cord they are intended to receive.

In a preferred embodiment the casing comprises a pair of longitudinal grooves extending from the open end of the casing in opposing walls. If the casing is cylindrical, these grooves are provided diametrically opposite each other. The grooves are sized such that the detonating cord may be positioned at the end of the grooves. In this embodiment the casing also comprises a separate sleeve (or ring) portion which is open at both ends and which is adapted to form an interference fit with the open end of the casing. The sleeve is also provided with a pair of opposing grooves, complimentary to and oriented in the same manner as the grooves of the casing. Typically, the sleeve portion is cylindrical and either has an external diameter which is just less than the internal diameter of the casing, or an internal diameter just greater than the external diameter of the casing. Thus, the sleeve may be inserted into or fit over the casing in an interference fit. In use the detonating cord is positioned running through the grooves of the casing and the sleeve portion positioned such that the detonating cord runs through its grooves also. Thus, the sleeve portion is used to retain the cord in place and prevent it coming out of the grooves in the casing.

When in position the detonating cord may run at any direction relative to the object to be cut relative to the casing (s) when in position. Typically, however, when in position a wire or elongate cut runs at a right angle to the detonating cord when the casings are positioned prior to detonation.

The explosive charge may take a variety of forms. When the charge is a flowable powder or liquid, the casing or sleeve portion when used, may be provided with a cap to prevent escape of the explosive charge. However, in a preferred embodiment of the invention, the explosive charge is a castable explosive, such as Pentolite. In this preferred embodiment the device may be prepared by positioning the casings along a detonating cord with the desired spacing between casings. If used, the cord is retained using a sleeve portion as described. The explosive composition is then poured into the open end of the casing (or casing/sleeve portion) until the cord is completely covered with explosive composition.

The composition is then allowed to set after which the device is ready for use. The casings may be supported at the desired spacing in a tray (or former) during pouring of the explosive. After the explosive has set the casings are removed from the tray and the ends may be sealed. The device may then be packaged. Alternatively, the castable composition may be poured prior to positioning of the detonating cord. In this case the amount of explosive used should be sufficient to ensure that when in place the detonating cord is in contact with the explosive charge. Preparing the device also forms part of the present invention.

Where present, the shape of one end of the casings, may also aid orientation of individual casings during loading with detonating cord and explosive charge. For instance, the shaped end or cut-away portion of casings may be positioned around a support rod (typically cylindrical) so that a series of casings so-positioned will have the same orientation of detonating cord receiving means. This may assist insertion of the cord along a series of casing. In an embodiment of the invention the tray used to support casings during explosive loading includes a suitably oriented support rod.

The individual casings and, where used sleeve portions, may be made of any suitable materials such as plastics and cardboard. Typically, these components will be formed of an injection mouldable plastic such as polypropylene.

Individual explosive charges of the device are initiated by the detonating cord in contact with the charges. Typically the detonating cord itself is initiated at the same time or during

a main blast. For example, in the wire cutting application described the explosive charges may be initiated at the same time or during production blasting. Initiating the explosive charges in this way saves time and expense. There may also be benefits in terms of safety when compared with initiating the explosive charges post-firing of a main blast.

The detonating cord is of conventional type and may be fired by conventional techniques.

In an embodiment of the invention the end of the detonating cord may be attached to the end of the detonating cord of another such device using a clipping device. This is usually employed using the device for the wire cutting application. The clipping device is intended to allow the ends of two detonating cords to be clipped together so that one will initiate the other. The device should also prevent release of explosive powder from the end of the cords and prevent water and/or other contaminants contacting the end of the cords.

The device may also prevent filled casings sliding off the end of the detonating cord.

In an embodiment of the invention, the clipping device comprises two adjacent detonating cord receiving channels. One of these channels is capped at one end and is intended to slidably receive an end of a detonating cord. The size and shape of this channel is configured so that the detonating cord is held in place by an interference fit. The cap of the channel is intended to seal the end of the detonating cord. The other detonating cord receiving channel is open at both ends and has its longitudinal axis parallel to that of the first channel. The function of this second channel is to allow adjacent detonating cords to be clipped together. The second channel thus also includes a longitudinal opening along its length through which detonating cord may be forced into the channel where it is held in place. In practice the ends of respective cords will be capped by a clipping device, the ends overlapped and a portion of each detonating cord pushed into and retained by the remaining detonating cord receiving channel of the device associated with the adjacent cord. In this way, the ends of adjacent detonating cords are capped and the cords attached to each other in close proximity. The clipping device may also include a series of longitudinal ribs to allow the device to be gripped during use. Typically, the clipping device is made of an injection mouldable plastic such as polypropylene. Use of a clipping device in this way enables lengths of loaded casings to be connected together prior to use.

Alternatively, ends of detonating cord may be tied or taped together. In use, the individual charges are simply attached to a series of wires before being fired via the detonating cord.

The spacing of the explosive charges along the detonating cord will be determined by the nature of the object to be cut.

In another more preferred embodiment the clipping device comprises three adjacent detonating cord receiving channels, two channels being open-ended and one being capped at one end. The size and shape of this capped channel is also configured so that detonating cord is held in place by an interference fit. The capped end of one channel is intended to seal the end of the detonating cord. The other two detonating cord receiving channels are each open ended and each has a longitudinal axis parallel to that of the capped channel. At least one, but typically only one, of the open ended channels includes a longitudinal opening or slot along its length through which a detonating cord may be pushed into the channel where it is held in place (the side walls of the channel may be resiliently flexible to permit this). In use two such clipping devices are required to join the ends of two detonating cords. In practice a clipping device is attached to the end of a detonating cord in order to seal the cord, for example during the manufacturing process. Here the end of the cord is passed through one of the open-ended channels and bent back on itself and fed into the capped channel. The cord is then pulled back so that the end of the cord is locked in place in the capped channel, thereby effectively sealing the end of the cord and securing the cord in place. The cord is retained by a bending over and locking action. Prior to use the remaining open-ended channel is unused, and this remaining channel must be of the slotted type to allow insertion of another adjacent detonating cord. In use two so-capped detonating cords are secured adjacent each other by insertion of detonating cord into the slotted open-ended channel of respective clipping devices. Thus, the detonating cord of a first clipping device is slotted into the slotted channel of a second clipping device, and vice versa.

Alternatively, two detonating cords may be secured to each other at the time of use using the three channel clipping device. This may be done when the free ends of detonating cord are pre-sealed. In this case, the free end of one detonating cord is passed through one of

the open-ended detonating cord receiving channels of a first clipping device and also through one of the open-ended channels of a second adjacent clipping device. The free end of the cord is then bent back on itself and inserted into and retained in place in the capped detonating cord receiving channel of the second clipping device. In likewise fashion, the free end of a second detonating cord is passed through the open-ended cord receiving channels of the second and first clipping devices respectively and then bent back on itself and inserted into and retained by the capped cord receiving channel of the first clipping device.

Either way, in use the capped end of one clipping device will be facing and adjacent the capped end of the other clipping device. The clipping device may include a series of ribs and may be made of similar materials as described above in connection with the other embodiment of the clipping device. The clipping device may be used in a variety of applications where it is desired to join two ends of detonating cord. Typically, the clipping device is used in conjunction with the cutting device described herein.

The invention further provides a casing, and optionally, sleeve portion described herein.

The invention also provides a method of cutting using the device described herein. The method involves positioning the casings of the device on or around an elongate member as necessary and then detonating the explosive charges contained in the casings. The invention further provides use of a device as described herein for cutting an elongate member.

The invention will now be illustrated by way of example only by reference to the following non-limiting figures in which: Figures 1 and 2 represent perspective views of an unloaded device in accordance with the present invention.

Figures 3 and 4 represent perspective views of a clipping device in accordance with the present invention.

Figure 5 is a schematic representing how the kind of clipping device shown in Figures 3 and 4 would be used in practice.

Figure 6 represents a perspective view of use of a device in accordance with the present invention.

Figures 7 and 8 represent perspective views of a clipping device in accordance with the present invention.

Figure 9 is a schematic representing how the kind of clipping device shown in Figures 7 and 8 would be used in practice.

Figure 1 shows a device (1) comprising a cylindrical casing (2) and a sleeve portion (3).

The cylindrical casing (2) defines a hollow chamber (4) for an explosive charge (not shown). The casing (2) includes wire engagement means in the form of a pair of U-shaped recesses (5) (only one shown) provided at the end and across the diameter of the casing (2).

The casing (2) also includes a roof-shaped membrane (6) at its lower end which will result in separation of explosive charge present in the chamber (4) and wire when positioned in the wire engagement means. The casing (2) also comprises a pair of diametrically opposed grooves (7) adapted to receive a detonating cord (not shown). The sleeve portion (3) comprises a pair of complimentary grooves (8). The sleeve portion (3) is sized such that it engages with the upper portion of the casing (2) in an interference fit, the grooves (7,8) being aligned so that in use the detonating cord is held in place.

Figure 2 illustrates the same unloaded device as Figure 1 but from a slightly different angle. In Figure 2 it is clear that the external shape of the casing (2) is influenced by the roof-shaped membrane (not shown in Figure 2 but (6) in Figure 1).

The casing (2) and sleeve portion (3) shown in Figures 1 and 2 are especially well-suited for use with an explosive charge which is castable. In use detonating cord is retained by

grooves (7,8) and the casing/sleeve portion (2,3) filled with a castable explosive composition so that the detonating cord is immersed by the composition. After the explosive composition has solidified the casing (2) may be clipped onto wire it is desired to cut using wire engagement means (5), or arranged around an elongate member to be cut.

Figure 3 shows a clipping device (9) comprising two detonating cord receiving channels (10,11). One of these channels (10) is open at one end (12) and closed at the other (13).

The other channel (11) is open at both ends (14,15) and along a longitudinal axis of the channel (16). In the embodiment shown the channel (10) also includes a longitudinal opening along its length, but this is not essential. The longitudinal entrance to the channel (16) is such that the sides of the channel must be displaced when detonating cord (not shown) is pushed into it.

Figure 4 shows the same device as Figure 3 but from a different perspective. Figure 4 clearly shows that one of the detonating cord receiving channels is capped at one end.

Figure 5 shows how in practice the ends of two adjacent detonating cords would be clipped together using the kind of clipping device shown in Figures 3 and 4. The end of each detonating cord (18,19) is capped by insertion into the capped detonating cord receiving channel of a clipping device (1). Subsequently, the ends of the detonating cords are overlapped and a portion of each cord pushed into the detonating cord receiving channel of the device capping the other cord.

Figure 6 shows an elongate steel bar (20) having a diameter of approximately 20mm. The bar (20) is to be cut using a cutting device (21) in accordance with the present invention.

The cutting device (21) includes four cylindrical casings (22) loaded with an explosive charge. The casing is shaped and configured such that on detonation the explosive energy of each charge is focussed radially inwards towards the elongate member to be cut. Each casing (22) is provided along a length of detonating cord (23) which runs into and through the explosive charge contained. In the embodiment depicted the longitudinal axis of each casing (22) is perpendicular to the longitudinal axis of the elongate bar (20). The casings

(22) are provided equi-distant from each other around the length (loop) of detonating cord (23). The free ends of the detonating cord (23) are taped together (24), (the ends running perpendicular to the longitudinal axis of the elongate member). One end of each casing is of the same configuration as that useful in the wire cutting application as illustrated in Figures 1 and 2, although this is not essential. Separate lengths of initiating detonating cord (25) are attached to the detonating cord (23) by knots (26), at two diametrically opposite points around the loop of detonating cord (23). The detonating cord (23) is passed through and retained in position in each casing (22) in the same manner described for Figures 1 and 2. The detonating cords (25) provides run-up paths to the device (21) of equal length and would be fired initially by a non-electric detonator (27). When the cord (25) is initiated a detonation front the loop of detonating cord (23) and all of the charges containing in the casings (22) within a matter of microseconds. The combined explosive effect of the four charges directed radially cuts the elongate bar (20).

Figures 7 and 8 shows different perspective views of the same clipping device (28). The device (28) comprises three detonating cord receiving channels (29,30,31). Two of these channels (29,30) are open-ended and the third (31) capped at one end (32). The longitudinal axes of the channels (29,30,31) are parallel with each other. One of the open-ended channels (30) includes a slot into which detonating cord (not shown) may be inserted. In use, a clipping device is attached to the end of a detonating cord (not shown) by passing the end of the cord through the open-ended channel (29), bending it back on itself and feeding it into the capped channel (31). The cord is then pulled back so that the end of the cord is locked in place in the capped channel (31), thereby effectively sealing the end of the cord and securing the cord in place.

Figure 9 shows how in practice two adjacent detonating cords (33,34) would be clipped together using the kind of clipping device shown in Figures 7 and 8. The end of each detonating cord (33,34) is capped by a clipping device (28) in the manner described in connection with Figures 7 and 8. The bent portion of each cord is depicted (35).

Subsequently, a portion of one cord is pushed into the slotted detonating cord receiving channel (30) of the device capping the other cord, and vice versa.

The following non-limiting examples illustrate embodiments of the present invention.

Example 1 The present invention is applied to cut a 100mm x 100mm mesh of steel wire having a diameter of 6mm. The device used consists of 2m of detonating cord having a charge density of lOg/m with explosive casings provided every 100mm. The dimension of each casing is approximately 50mm long and 32mm in diameter, containing about 33g of explosive charge (60: 40 Pentolite). Individual casings are clipped onto the wires of the mesh by means of recesses provided at one end of the casing. The casings are positioned so that a series of adjacent parallel wires will be cut thereby severing the mesh. The detonating cord is initiated by use of a conventional detonator leading to successful wire cutting.

Example 2 In this example the invention is applied to cut an elongate steel bar having a diameter of 20mm. The device is essentially described in Example 1, a total of four casings making up the device. The casing are positioned with the longitudinal axis perpendicular to the longitudinal axis of the bar. The casings are spaced evenly around the bar and are therefore provided at a rotation of 90° to each other. The explosive charge is the same as in Example 1. The free ends of the detonating cord (5g/m) are taped together. Separate lengths of detonating cord (also 5g/m) are tied at diametrically opposite points to the detonating cord passing through the casings. These separate lengths are initiated by a detonator and in turn initiate the explosive charge in the casings. The bar was successfully cut into 2 pieces at the desired location.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word"comprise", and variations such as"comprises"and"comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.