AU2021313307A1 - Conductor for use with a detonator and detonator assembly - Google Patents

Abstract

A detonator which includes a tube which is open at one end and closed at an opposing end, an explosive and a printed circuit board with electronic components on the board, a conductor with exposed wires which extend through the open end and which are kept in electrical engagement with contacts on the board, and a sealing member which is engaged with the open end and the conductor.

Description

CONDUCTOR FOR USE WITH A DETONATOR AND DETONATOR ASSEMBLY

BACKGROUND OF THE INVENTION

[0001] This invention relates to a detonator.

[0002] In a typical detonator production process two conductive wires of a conductor are fixed by means of solder to contacts on a printed circuit board of the detonator. Thereafter the detonator with an attached length of the conductor is shipped to a user. As the detonator is classified as “dangerous goods” the detonator and the attendant conductor are jointly classed as “dangerous goods”. As a consequence, due to the presence of the conductor, transport and security costs are increased. [0003] The soldering of the wires to the contacts can be a tedious exercise. Also the strengths of the bonds between the wires and the contacts should be such that inadvertent breaking of the bonds is avoided. Steel wires and, to a lesser extent, copper wires transmit forces which are exerted on the wires to the detonator. These forces act on the soldered connections between the wires and the contacts and such connections can thereby be broken. Also, in a two-wire system, the force in one wire might not be the same as the force in the other wire. This can lead to a twisting force being exerted on the printed circuit board, and result in negative consequences.

[0004] Prior art documents which are partly relevant to the aforementioned situation are US9004933 and US8069789. In the former case a wedge is used to hold wires in contact with contact pads on a printed circuit board. In the second case use is made of a bridge element which extends through a plug. Opposed ends of the bridge element are engaged with a conductor and with components of the detonator respectively.

[0005] An object of the present invention is to provide a detonator arrangement which can lower security and transport costs and which allows a user to assemble an operative detonator on site.

SUMMARY OF THE INVENTION

[0006] The invention provides a detonator assembly which includes a tube with a closed end and an open end, a printed circuit board inside the tube, the printed circuit board including an inner end, an outer end and conductive contacts at the outer end, and a plug which is sealingly and removably engaged with the open end of the tube and which abuts the outer end of the printed circuit board.

[0007] No conductive wires extend from the tube.

[0008] The plug may include a formation with which the outer end of the printed circuit board is engaged. The formation may be a recess into which the outer end of the printed circuit board is inserted.

[0009] The printed circuit board contains electronic components and, as is known in the art, an explosive composition is loaded into the detonator tube.

[0010] The plug may be regarded as a transit or transport plug and is used to seal the interior of the tube until such time as a detonator is to be constructed from the detonator assembly. [0011] The plug may include a formation or a marking which is related to the orientation of the printed circuit board inside the tube. In one embodiment the plug includes a projection which is visible to a user and which is such that the position of the projection relative to the tube allows the user to establish the position or orientation of the recess which is engaged with the printed circuit board.

[0012] The plug, typically, is a disposable component made from an appropriate material e.g. a plastics material.

[0013] The interior of the tube may contain an inert gas, e.g. argon or nitrogen, which is sealed inside the tube when the plug is engaged with the tube. The inert gas helps to guard against damage to the electronic components on the printed circuit board e.g. due to corrosion, the ingress of moisture, and the like.

[0014] The invention also provides a conductor for use with a detonator, wherein the conductor includes at least two electrically conductive wires, a sheath of insulating material which encases portions of the wires and which spaces the portions of the wires apart from each other, wherein each wire includes a respective exposed section which is not encased in the insulating material and which projects from an end of the sheath, and a holder which is made from an insulating material and which is positioned adjacent said end of the sheath and which is engaged with the two exposed wire sections, and wherein ends of the wire sections are exposed. [0015] The conductive wires may be side-by-side.

[0016] The exposed ends of the wire sections may extend or project from the holder. [0017] In one embodiment of the invention the exposed ends of the wire sections are curved slightly.

[0018] The holder may include a first part and a second part which is engaged with the first part, with portions of the two exposed wire sections located between the two parts. [0019] Opposing surfaces of the two parts may be shaped to form cavities or hollows in which respective portions of the wire sections are positioned. This enhances frictional engagement of the holder with the wire sections.

[0020] Each wire section may include a respective retention formation which is engaged with a complementary formation in the holder. Each retention formation may include one or more bends. The retention formation may for example define a serpentine shape, a zig-zag or a sinusoidal shape.

[0021] The holder may include an internal cavity which, in use, is positioned adjacent the retention formation of each wire section.

[0022] The conductor may include a seal member within which the holder and a part of the sheath are positioned.

[0023] The invention also provides a detonator which includes a detonator assembly of the aforementioned kind wherein the plug is removed from the open end of the tube, and a conductor of the aforementioned kind, and wherein the holder and a part of the seal member extend through the open end of the tube and are thereby located inside the tube with the exposed ends of the wire sections in electrical engagement with the conductive contacts at the outer end of the printed circuit board.

[0024] It is possible for the exposed ends of the wire sections to be soldered to the contacts in the printed circuit board. However, in a preferred embodiment, electrical connectivity is established through frictional engagement of the exposed ends of the wire sections with the contacts on the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is further described by way of examples with reference to the accompanying drawings in which : Figure 1 is a side view in section of a detonator assembly according to one form of the invention,

Figure 2 shows the detonator assembly of Figure 1 engaged with a conductor, according to a first form of the invention, from one side and in cross section,

Figure 3 depicts in cross section and from one side, one end of a conductor according to a second form of the invention, and

Figure 4, which is similar to Figure 2, shows the conductor of Figure 3 engaged with a detonator assembly to make up a functional detonator.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] Figure 1 of the accompanying drawings illustrates from one side and in cross section a detonator assembly 10 according to one form of the invention. [0027] The detonator assembly 10 includes a detonator tube 12 which has a closed end 14 and an open end 16.

[0028] A printed circuit board 18 of generally conventional construction is positioned and held inside the detonator tube 12 using techniques which are known in the industry and which are therefore not described herein. The printed circuit board carries an ignition element 22 which is exposed to an explosive charge 24 inside the tube at the closed end 14. As is known in the art if the ignition element 22 is fired the explosive charge 24 is initiated. This aspect is conventional and therefore is not further described herein.

[0029] The printed circuit board 18 carries electronic components 28 of a nature known in the art. This aspect is not further described for it is not important to an understanding of the invention. These components are however sensitive and should be protected against damage, an aspect which is addressed hereinafter.

[0030] The printed circuit board 18 has an inner end 18A and an outer end 18B.

[0031] At the outer end 18B the printed circuit board carries conductive contacts 30. Typically there are two contacts which are side-by-side. In the side view in Figure 1 only one contact 30 is visible.

[0032] A transit plug 34 which is made from a relatively soft plastics material is inserted into the open end 16 of the tube 12. The plug 34 carries an orientation projection 36 at a protruding end of the plug. At an opposed end 38 the plug has a recess 40 which has a predetermined orientation relative to the direction in which the projection 36 extends. It is thus possible for a user to insert the plug 34 into the open end 16 and then to position the plug 34 so that the recess 40 at the inner end 38 of the plug can engage with the outer end 18B of the printed circuit board which is inserted into the recess 40.

[0033] In an alternative approach the printed circuit board 18 is engaged with the transit plug 34 before the two components are inserted into the detonator tube 12. This technique automatically eliminates the requirement to orientate the plug correctly relative to the printed circuit board which has previously been placed into the tube 12.

[0034] Prior to the engagement of the transit plug 34 with the tube 12, an inert gas e.g. argon or nitrogen, may be flushed into the tube. The plug 34 ensures the gas remains in the tube. The gas helps to prevent oxidation of the electronic components 28, the ingress into the tube of moisture which could affect the components 28, and other possible factors which could adversely affect the electronic components 28 or the explosive charge 24.

[0035] The fabrication of the detonator assembly 10, as shown in Figure 1 , is carried out under factory conditions. At this stage no wires extend from the detonator tube 12. The detonator assembly 10 is compact and a number of similar detonator assemblies can be shipped in a cost-effective manner, ex-factory to a site of intended use.

[0036] In order to fabricate a fully functional detonator using the detonator assembly 10, the transit plug 34 is removed from the open end 16 of the tube 12. An end 50 of a conductor 52 is then engaged with the open end 16, as is shown in Figure 2. The conductor 52 includes two side-by-side conductive wires 54 (only one is visible in Figure 2) and a sheath 56 of electrical insulating material which encases the wires 54 and which holds them side-by-side as is known in the art. Each wire 54 includes a respective exposed section 58 which extends from an end 60 of the sheath 56. Each section 58 is formed with a respective retention formation 64 in the shape of two bends, and thus has a zig-zag or a serpentine appearance. A holder 68 is engaged with the retention formations 64 of both sections 58. The holder 68 is made from two parts 68A and 68B which are clipped together around the retention formations 64 so that the formations 64 are located in custom-designed recesses formed in opposing surfaces of the parts 68A and 68B. In this way the wire sections 58 are mechanically and frictionally anchored to the holder 68.

[0037] Ends 72 of the wire sections 58 are curved slightly and, when the holder 68 is pushed into the open end 16 of the tube 12, these curved sections are brought into firm frictional engagement with the contacts 30 on the outer end of the printed circuit board 18. In this way a sound electrical connection is made between the wires 54 and the printed circuit board. The curved ends 72 abut, on one side, a surface of the holder 68, the arrangement being such that the ends are urged by the holder into close engagement with the contacts 30.

[0038] Additional inert gas e.g. argon or nitrogen, may be flushed into the tube 12 when the holder 68 is pushed into the open end 16 of the tube 12. The inert gas, once sealed inside the tube 12, assists in the prevention of oxidation of the ends 72 of the wire sections 58, the contacts 30 and the electrical components 28 on the printed circuit board 18. The inert gas displaces atmospheric air, which contains oxygen, and so helps to ensure that a good electrical contact is maintained for an extended period at the frictional interface between the ends 72 and the contacts 30.

[0039] A seal member 74 is engaged with the end 50 of the conductor 52 and abuts the holder 68. The seal member 74 has an enlarged section 76 which abuts a rim of the open end 16 of the tube 12. A remaining portion 78 of the seal member 74 extends into the detonator tube 12 and is then crimped in position by means of a suitable tool (not shown) which deforms the tube 12. Crimping formations 80 which are produced by the crimping tool ensure that the seal member 74 is firmly fixed mechanically and in a sealing configuration to the detonator tube 12.

[0040] The seal member 74 has a mating and retention formation 82 which engages with a complementary formation 84 on the holder 68 thereby to lock the holder 68 to the member 74. [0041] When the crimping takes place a portion of the seal member 74 is urged to the right

(in Figure 2) i.e. towards the printed circuit board 18 by the crimping force and a force is thereby exerted on the holder 68 which urges the wire sections 58 to the right. This enhances the electrical connection which is established between the curved ends and the contacts. A small cavity 85 in the holder 68 facilitates this type of movement for it creates a volume into which some of the deformed material from the holder can expand.

[0042] The parts 68A and 68B are made from a material e.g. a hard plastics material which is rigid compared to the seal member 74 which is made from a compliant, flexible and compressible rubber-like material. The different material characteristics help to facilitate the aforementioned assembly process. [0043] Figure 3 of the accompanying drawings illustrates an end of a conductor 86 according to another form of the invention. The conductor 86 includes two side-by-side electrically conductive wires 88 and 90 respectively which are encased in a sheath 92 of insulating material which holds the wires 88 and 90 side-by-side and spaced from each other as is known in the art. Ends of the wires 88 and 90 have exposed sections 96 and 98 respectively and project from an end 100 of the sheath 92. Parts of the sections 96 and 98 are engaged with a holder 104. [0044] A seal member 108 encloses a part of the sheath 92 adjacent the end 100, the holder 104, and protruding ends 96A and 98A of the wire sections 96 and 98. The seal member 108 has a large diameter end part 110 and a smaller diameter part 112 which is longer than the end part 110. [0045] Figure 4 shows the conductor 86 in cross section and from one side engaged with a detonator assembly 10A which is generally of the kind described in connection with Figures 1 and 2. The exposed sections 96 and 98 of the wires 88 and 90 are formed with retentive formations 118 which, in this instance, comprise a number of bends which impart to each of the sections a serpentine or sinusoidal shape. The holder 104 is made in two parts 104A and 104B respectively and opposing surfaces of these parts are formed with recessed formations which are complementary to the shapes of the retentive formations 118.

[0046] The formations 118 are snugly located within the recessed formations inside the holder parts 104A and 104B which are then clipped together to ensure that the retention formations are securely locked to the holder 104. Thereafter the holder 104 is positioned inside the seal member 108.

[0047] In Figure 4 shaped leading ends 96A and 98A of the exposed wire sections 96 and 98 are shown in electrical connection with the contacts 30 on the outer end of the printed circuit board 18. The small diameter part 112 of the seal member 108 is fully inserted into the open end 16 of the detonator tube 12 which is then crimped, generally in the manner shown in Figure 2 but not shown in Figure 4, so that the seal member 108 and the enclosed components are securely locked to the detonator tube 12.

[0048] The resulting detonator, assembled in the manner shown in Figure 4, is then ready for use. [0049] The detonator assembly 10A without wires extending from the detonator tube, is produced under factory conditions and can then be shipped with other, similar assemblies in a cost-effective manner, but classified as dangerous goods, to an intended location of use. The conductors which are to be used with the detonator assemblies are separately shipped. When an installation is to be done a detonator assembly is selected and the respective transit plug is detached from the detonator tube. Insulating material is stripped from the sheath of a conductor which is to be used with the detonator assembly. The exposed wire sections e.g. the sections 96 and 98 shown in Figure 3, are shaped using a custom-designed press forming tool (not shown) and thereafter are secured to the holder 104 which, as stated, is made from the parts 104A and 104B which clip together and thereby are firmly secured to the retentive formations 118. The holder 104 has internal channels that follow the contours of the formations 118 and thus prevent stress and strain forces which act externally on the wires 88 and 90 from altering the formed shapes of the sections 96 and 98.

[0050] In the assembled configuration shown in Figure 4 (once crimped together) the ends of the wire sections which are brought into electrical connection with the contacts 30 are unable to move relative thereto for such movement is effectively eliminated. The ends of the sections 96 and 98 are kept electrically connected to the contacts 30 by means of frictional forces but the use of solder or crimping components to enhance this type of connection is not discarded.

[0051] The correct orientation of the seal member 74 relative to the printed circuit board 18 inside the detonator tube 12 is facilitated by means of a marking on the detonator tube 12 which coincides with the projection 36 on the plug 34 shown in Figure 1. An inert gas can at this stage be directed into the tube 12 in order to prevent corrosion of the electrical connections created by the components 30, 96 and 98, for an extended period. Once the transit plug 34 has been removed from the tube 12 by an operator, the orientation of the tube 12 is maintained and an end 120 of the conductor 86 can be engaged with the tube thereby to make an electrical connection between the leading ends of the wire sections and the contacts. This aspect can be enhanced, as is shown in Figure 4, by providing a recess 122 in a leading end 124 of the part 112. A portion of the outer end 18B of the printed circuit board 18 can be inserted into this recess 122 once the components are correctly orientated relative to each other. This ensures that the ends of the sections 96 and 98 are readily brought into electrical connection with the contacts 30.

[0052] It is relatively easy to form the projecting ends of the wire sections, under field conditions, using a custom-designed tool. Thereafter the conductor and the detonator assembly can be interconnected. This option substantially reduces the logistical problem of having numerous custom lengths of wires connected to various detonators which are kept in magazines and which are transported in bulk as dangerous goods. Detonator assemblies without wires but with explosives and electronics (as per the illustration in Figure 1) are manufactured and then transported and stored in a cost-effective manner. The transit plug 34 ensures that the interior of a detonator tube, preferably filled with an inert gas, is sealed.

[0053] The seal member (74,108) which extends into the open end of the detonator tube is relatively soft and if tensile force is applied to the conductor, to the left of the seal member (Figure 2 and Figure 4), the holder (68, 104) compresses material of the seal member, in one direction.

[0054] An alternative assembly technique (applicable to each embodiment) involves preassembling the printed circuit board 18 so that it is connected to the conductor (52, 86), the seal member (74, 108) which, as noted, acts as a crimp plug, and the holder (68, 104). Thereafter the resulting assembly is inserted into a detonator tube 12 into which an explosive charge 24 has previously been placed. An inert gas is then preferably injected into the tube. Thereafter through the use of a suitable tool the tube 12 is deformed to produce crimping formations similar to those marked 80 in Figure 2. [0055] In each embodiment the compressed material of the seal member (74, 108) tends to expand in a transverse direction - a characteristic which enhances the mechanical bond between the seal member and the detonator tube 12. This is in addition to the retentive force obtained by means of the crimping process. The seal member also acts as a reinforcing means which helps to strengthen the tube against collapse due to impacting shock waves during a blast.

Claims (16)

1. A detonator assembly (10) which includes a tube (12) with a closed end (14) and an open end (16), a printed circuit board (18) inside the tube (12), the printed circuit board (18) including an inner end (18A), an outer end (18B) and conductive contacts (30) at the outer end (18B), and a plug (34) which is sealingly and removably engaged with the open end (16) of the tube (12) and which abuts the outer end (18B) of the printed circuit board (18).

2. A detonator assembly (10) according to claim 1 wherein no conductive wires extend from the tube (12).

3. A detonator assembly (10) according to claim 1 wherein the the plug (34) includes a formation with which the outer end (18B) of the printed circuit board (18) is engaged.

4. A detonator assembly (10) according to claim 3 wherein the formation is a recess (40) into which the outer end (18B) of the printed circuit board (18) is inserted.

5. A detonator assembly (10) according to claim 1 wherein the printed circuit board (18) contains electronic components (28), and an explosive composition (24) is loaded into the tube (12).

6. A detonator assembly (10) according to claim 4 wherein the plug (34) includes a formation (36) or a marking which is related to the orientation of the printed circuit board (18) inside the tube (12), and wherein the formation (36) is a projection (36) which is visible to a user and the position of the projection (36) relative to the tube (12) allows the user to establish the orientation of the recess (40) into which the outer end (18B) of the printed circuit board (18) is inserted.

7. A detonator assembly (10) according to claim 1 wherein an interior of the tube contains an inert gas which is sealed inside the tube (12) when the plug (34) is engaged with the tube (12).

8. A conductor (52; 86) for use with a detonator, wherein the conductor (52; 86) includes at least two electrically conductive wires (54; 88, 90), a sheath (56; 92) of insulating material which encases the wires (54; 88, 90) and which spaces the wires (54; 88, 90) apart from each other, wherein each wire (54; 88, 90) includes a respective exposed section (58; 96, 98) which projects from an end (60; 100) of the sheath (56, 92), and a holder (68;

104) which is made from an insulating material and which is positioned adjacent said end (60; 100) of the sheath (56; 92) and which is engaged with the two wire sections (58; 96, 98), and wherein ends (72; 96A, 98A) of the wire sections (58, 96; 98) are exposed.

9. A conductor (52; 86) according to claim 8 wherein the ends (72; 96A, 98A) of the wire sections (58; 96, 98) extend from the holder (68; 104) and are slightly curved.

10. A conductor (52; 86) according to claim 8 wherein the holder (68; 104) includes a first part (68A; 104A) and a second part (68B; 104B) which is engaged with the first part (68A; 104A), with portions of the two wire sections (58, 96, 98) located between and engaged with the two parts (68A, 68B; 104A, 104B).

11. A detonator which includes a detonator assembly (10A) according to claim 1 wherein the plug (34) is removed from the open end of the tube (12), a conductor (52, 86) according to claim 8, wherein the holder (68; 104) extends through the open end (16) of the tube (12) and is thereby located inside the tube (12) with exposed ends (72; 96A, 98A) of the wire sections (58; 96, 98) in electrical engagement with the conductive contacts (30) at the outer end (18B) of the printed circuit board (18), and a seal member (74) which is sealingly engaged with the open end (16).

12. A detonator according to claim 11 wherein the ends (72; 96A, 98A) of the wire sections (58; 96, 98) are soldered to the contacts (30).

13. A detonator according to claim 11 wherein said electrical engagement is established through frictional engagement of the ends (72; 96A, 98A) of the wire sections (58; 96, 98) with the contacts (30).

14. A detonator according to claim 11 wherein the tube (12) is flushed with an inert gas prior to engagement of the seal member (74) with the open end (16).

15. A detonator which includes a tube (12) with a closed end (14) and an open end (16), a printed circuit board (18) inside the tube (12), the printed circuit board (18) including an inner end (18A), an outer end (18B) and conductive contacts (30) at the outer end (18B) and a conductor (52, 86) according to claim 8, wherein the conductive wires (54, 88, 90) extend through the open end (16) into the tube (12) and said ends (72, 96A, 98A) are connected to said conductive contacts (30).

16. A detonator according to claim 15 which includes an inert gas inside the tube (12).