P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL TO BE COMPLETED BY APPLICANT Name of Applicant: African Explosives Limited Actual Inventors: Solomon Gabaiphiwe Kgongoane Address for Service: A.P.T. Patent and Trade Mark Attorneys PO Box 222, Mitcham SA 5062 Invention Title: Booster Shell The following statement is a full description of this invention, including the best method of performing it known to us:- BOOSTER SHELL BACKGROUND OF THE INVENTION [0001] This invention relates to a booster shell. [0002] A booster shell is a device which contains an explosive charge and a 5 detonator which is connected to a shock tube. The device is exposed to explosive material which, typically, is positioned inside a borehole. The booster shell is lowered into the explosive material suspended from a length of the shock tube which extends from the detonator. [0003] As the booster shell is lowered to a desired position it can be become 10 snagged or fouled, for example on a projection inside a borehole, or for any other reason it may be caused to move irregularly. When this occurs it is possible for the tension on the shock tube to be reduced and this could cause the detonator to fall out of the booster shell. If this is not remedied the initiation of the main explosive material can be adversely affected. 15 [0004] The invention aims to provide a booster shell which permits the aforementioned problem to be addressed at least partly. SUMMARY OF INVENTION [0005] The invention provides a booster shell which comprises a tubular body which is moulded from a plastics material and which has an inner bore, 2 a partition inside the bore which has a first side and a second side, an open mouth at one end of the bore opposing the first side of the partition, first and second formations which respectively define first and second passages which extend inside the bore from the first side of the partition, through the partition 5 to the second side of the partition, and a projection which extends from the second side of the partition between opposing surfaces of the first and second formations and which is formed with a retaining formation. [0006] Preferably the body is integrally moulded with the first and second formations and the retaining formation. 10 [0007] The body may have any appropriate shape. Preferably though the body is circular cylindrical, with at least one open mouth and the volume is formed by a partition inside the tubular body. [0008] The partition may extend across the body to form a first volume, which comprises the explosive receiving volume, and a second volume which 15 contains the retaining formation. [0009] The first formation may define a first passage and the second formation may define a second passage. At least a part of the first passage and a part of the second passage may be located inside the first volume. [0010] The first formation and the second formation may each be cylindrical, 20 extending substantially the length of the body, and may be integral with or otherwise attached to an inner surface of the tubular body. 3 [0011] The first formation may be diametrically opposed to the second formation, viewed in cross section through the cylindrical body. [0012] The body may be formed with one or more breather holes, in its wall which bounds the second volume which contains the retaining formation. 5 [0013] The retaining formation is preferably positioned to engage frictionally, mechanically or in any other suitable way with a portion of the elongate flexible member which is between the first formation and the second formation. [0014] The retaining formation may be one of a plurality of formations. The 10 retaining formation may be of any suitable shape and form. In one embodiment of the invention the retaining formation is an undercut formation and includes a first section which may be substantially circular with a diameter which is approximately equal to a diameter of the elongate flexible member, and an entry section to the first section which includes opposed converging 15 sides which intersect a boundary of the first section at points which are spaced apart by a distance which is smaller than a transverse dimension of the first section and which define a transition between the entry section and the first section. 4 [0015] Preferably the retaining formation is an undercut formation. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The invention is further described by way of example with reference to the accompanying drawings in which: 5 Figure 1 is a perspective view from a first end of a booster shell according to the invention; Figure 2 is a perspective view of the booster shell of Figure 1 from a second end; Figure 3 is a plan view of the first end of the booster shell shown in Figure 1; 10 Figure 4 is a cross sectional view from one side of the booster shell taken on the line 4 - 4 in Figure 3; Figure 5 is a plan view of the second end of the booster shell; Figure 6 is a cross sectional side view of the booster shell at a right angle to the view in Figure 4; 15 Figure 7 is a perspective view of the booster shell in cross section, engaged with a detonator and a length of shock tube; and Figure 8 illustrates the assembly shown in Figure 7 installed in a borehole. DESCRIPTION OF PREFERRED EMBODIMENT [0017] Figures 1 to 6 illustrates different aspects of a booster shell 10 20 according to the invention. 5 [0018] The booster shell has a tubular body 12, of circular cylindrical configuration, which is integrally moulded from a suitable plastics material. The body has an inner bore 14, a first open mouth 16 at one end of the bore and a second open mouth 18 at an opposed end of the bore. 5 [0019] A partition 22 extends across the bore at an intermediate location of the body. The partition divides the bore into a first volume 24 and a second volume 26. [0020] First and second formations 30 and 32 extend inside the bore from a first side 22A of the partition, through the partition and from a second side 22B 10 of the partition. [0021] The first formation, in this example, is tubular and defines a first passage 36. Towards one end the passage has a reduced dimension formed by a step 38. [0022] The second formation 32 is also tubular and forms a second passage 15 40. [0023] The two formations are integrally formed with the body and are positioned on diametrically opposed inner surfaces of the body (viewed in transverse cross section). [0024] A projection 44, which is in the form of a thin sheet of material 20 integrally formed with the remainder of the body, extends from the second 6 side 22B of the partition inside the second volume 26 between opposing surfaces of the first and second formations. At its outermost end the projection is formed with a retaining undercut formation 48 which is shown in enlarged detail in an inset drawing to Figure 6. The undercut formation has a 5 first section 50 which is substantially circular with a diameter 52 and an entry section 54 which has converging sides 56 and 58 which terminate at points 60 and 62 respectively at a boundary of the circular section. The points 60 and 62 are spaced apart by a distance 64 which is smaller than the distance 52. [0025] Optional breather holes 66 are formed through an external wall of the 10 body which bounds the second volume 26, fairly close to the partition 22. The breather holes facilitate the circulation of air through the second volume and so help to displace moisture from the second volume. [0026] Figure 7 is a cross sectional perspective view illustrating how a detonator and shock tube are engaged with the booster shell while Figure 8 15 illustrates the assembly of the booster shell, detonator and shock tube positioned in a borehole. [0027] A detonator 68 of any suitable kind is fixed to a shock tube 70 of an appropriate length using techniques which are known in the art and which for this reason are not further described. The detonator is then inserted from the 20 second mouth 18 into the first passage 36 and is pushed home until a leading end 72 of the detonator is brought into engagement with the step 38. The shock tube 70 is threaded through the second passage 40. This process 7 produces a loop 74 of an exposed portion of the shock tube between the two passages. This loop is also adjacent the outer extremity of the projection 44. [0028] Referring to Figure 7 if the shock tube is pulled in a direction 76 then the loop 74, if initially correctly positioned between the converging walls 56 5 and 58, is decreased in size and at the same time is guided by the converging walls towards the circular section 50. The dimension 64 is slightly less than the diameter of the shock tube which, in turn, is approximately the same as the dimension 52. A slight degree of force is needed to pull the shock tube through the space between the points 60 and 62 into the circular section 50. 10 When the shock tube is fully positioned inside the circular section the portion of the shock tube which had been compressed in order to pass between the points 60 and 62 automatically expands under its own resilience with the result that the shock tube is effectively trapped inside the circular section, for it is frictionally and mechanically locked in position. In this configuration it is not 15 possible for the shock tube inadvertently to become detached from the retaining formation 48. [0029] The first volume 24 is filled with a suitable explosive charge 78. The position of the partition 22 and the cross sectional dimension of the bore 14 determine the capacity of the first volume. 20 [0030] As is shown in Figure 8 the booster shell can then be lowered into a borehole 80 from a surface location 82. This is done with the booster shell and its contents hanging from the shock tube 70. If any part of the booster shell should strike a surface or object inside the borehole which reduces 8 tension in the shock tube then this event, in itself, will not cause the shock tube to become detached from the retaining formation. In other words the detonator and shock tube remain securely coupled to the booster shell, and remain inside the first passage 36 with the detonator in proximity to the 5 explosive charge 78. [0031] Once the booster shell is correctly located in the borehole a predetermined quantity of explosive material 84 is poured into the borehole. The booster shell is thereby enclosed by the explosive material 84. The material 84 is initiated in a conventional way by means of signal which is 10 transferred from the shock tube to the detonator which then detonates the explosive charge 78 thereby igniting it and this leads to initiation of the explosive material 84. 9