1. Purpose of the Invention To provide a means of initiating insensitive explosives by means of detonating cord wherein the end of the detonating cord is aligned with a booster charge of secondary explosive contained within a rigid tube.

2. Background to the Invention

An explosive booster is a sensitive explosive charge that acts as a bridge between a (relatively weak) conventional detonator and a low-sensitivity (but typically high- energy) explosive such as TNT. By itself, the initiating detonator would not deliver sufficient energy to set off the low-sensitivity charge. However, it detonates the primary charge (the booster), which then delivers an explosive Shockwave that is sufficient to detonate the secondary, main, high-energy charge.

Detonating cord consists of a train of finely powdered high explosive constituting the core of a cord in which it is wrapped by such materials as a strip of paper and two or more helically wound plastics threads or strip. This assembly is usually coated with water- proofing wax or a seamless flexible layer of water and abrasion-proof flexible plastics.

The explosive most commonly used for this purpose is pentaerythritol tetranitrate (PETN) but cyclic- trimethylenetrinitramine (RDX) is sometimes used for the

I imparting of greater thermal stability. The explosive load usually ranges from approximately l .5g a metre to 200g a metre. Detonating cord most commonly employed in military usage contains 10 or I 2g a metre. One of the main applications of detonating cords with light or medium explosive loads is the transmission of a detonation wave from the point of initiation to a multiplicity of explosive main charges either in very rapid succession or simultaneously on the scale of the overall event. Whereas a light load of explosive in the detonation cord suffices for the reliable transmission of the detonation to each of the secondary charges, for reason of safety the main charges which it is required to initiate by its means are almost invariably in both military and non-military applications too insensitive to be initiated by mere contact with the outer sheath or the severed end of the detonating cord.

Detonation cord will initiate most commercial high explosives (dynamite, gelignite, sensitised gels, etc.) but will not initiate less sensitive blasting agents like ANFO on its own. 25 to 50 grain/foot (5.3 to 10.6 g/m) detonation cord has approximately the same initiating power as a #8 blasting cap in every 2 to 4 inches (5 to 10 cm) along its entire length. A small charge of PETN, TNT, or other explosive booster is normally required to bridge between the cord and a charge of insensitive blasting agent like ANFO or most water gels.

To enable the detonating cord reliably to initiate the secondary, or main, charge or charges it is therefore necessary to use an intermediate charge, which is smaller than the main charge, to convey the detonation from the detonating cord to the main charge. Such a charge is referred to as a booster. A booster charge is more sensitive to initiation than the main charge and is of such shape and size as enables it to be abutted against the end of an elongate main charge or to be inserted in a cavity provided in the end, or at another convenient point, in the secondary charge.

A primary explosive is an explosive that is extremely sensitive to stimuli such as impact, friction, heat, static electricity, or electromagnetic radiation. Some primary explosives are also known as contact explosives. A relatively small amount of energy is required for initiation. As a very general rule, primary explosives are considered to be those compounds that are more sensitive than PETN. As a practical measure, primary explosives are sufficiently sensitive that they can be reliably initiated with a blow from a hammer; however, PETN can also usually be initiated in this manner, so this is only a very broad guideline. Additionally, several compounds, such as nitrogen triiodide, are so sensitive that they cannot even be handled without detonating. Nitrogen triiodide is so sensitive that it can be reliably detonated by exposure to alpha radiation; it is the only explosive for which this is true.

Primary explosives are often used in detonators or to trigger larger charges of less sensitive secondary explosives. Primary explosives are commonly used in blasting caps and percussion caps to translate a physical shock signal. In other situations, different signals such as electrical/physical shock, or, in the case of laser detonation systems, light, are used to initiate an action, i.e., an explosion. A small quantity, usually milligrams, is sufficient to initiate a larger charge of explosive that is usually safer to handle. A secondary explosive is less sensitive than a primary explosive and requires substantially more energy to be initiated. Because they are less sensitive, they are usable in a wider variety of applications and are safer to handle and store. Secondary explosives are used in larger quantities in an explosive train and are usually initiated by a smaller quantity of a primary explosive. Examples of secondary explosives include TNT and RDX.

Tertiary explosives, also called blasting agents, are so insensitive to shock that they cannot be reliably detonated by practical quantities of primary explosive, and instead require an intermediate explosive booster of secondary explosive. These are often used for safety and the typically lower costs of material and handling. The largest consumers are large-scale mining and construction operations. ANFO is an example of a tertiary explosive.

3. The Forms of Some Existing Boosters - Slip on Booster

The Slip on Booster (SOB) consists of a length of extruded tubular PETN-based plastic-bonded explosive with a slightly elastic consistency which, having an internal diameter of approximately 7mm, accommodates usual sizes of electric and plain detonators as well as detonating cord used in demolition operations. It is approximately 17mm in outside diameter. It can easily be cut to a requisite length [see Fig. I A, I B, 8A and 8B]. - Detonating Cord Booster

The Detonating Cord Booster (DCB) consists of a conventional detonator tube which has a base charge of highly consolidated PETN with a succession of layers of PETN pressed upon it at progressively diminished pressures. A plastic clip is provided with an integral barrel which is crimped into the metal tube. The two jaws of the clip are such as to receive and grip a length of detonating cord inserted in a direction at right angles to the metal tube. The end of the barrel where it is attached to the clip is provided with s thin end wall. Initiation of the detonating cord shears the end wall and projects it along the barrel and towards the surface of the PETN which it strikes at a velocity high enough to cause detonation [see Fig. 2 and Fig. 9].

- Knotted Detonating Cord

The simplest form of booster is constituted by a bulky knot tied in the end of a length of detonating cord. This is commonly used for the initiation of a main charge of plastic explosive which can be squeezed into the interstices of the knot and moulded around it. To facilitate subsequent handling, a film of stretchable plastics such as is used more commonly for the containment and protection of foodstuffs may be advantageously stretched round the assembly and held in place by plastics insulating tape. Initiation of the main charge in this case is favoured by the amount of explosive contained in the detonating cord constituting the knot as well as the occurrence of multiple Shockwave collisions occurring within the compass of the know each of which constitutes a concentration of shock waves at various points in the mass of plastic explosive. This constitutes a simple and quickly formed booster where nothing more than an omnidirectional blast is required of the main charge: it is useless if initiation of the main charge by a specific point source is required [see Fig.3 and Fig. 10]. - Detonating Cord Loop Initiator

The Detonating Cord Loop Initiator consists of a loop formed at the terminal end of a length of detonating cord by bending this end back on itself and securing it in this position, thereby defining a loop with a profile approximately in the shape of a teardrop. This elongate space is filled with plastic explosive. Constraining the detonating cord in a suitably proportioned loop can be achieved either by taping the ends together for a short distance immediately before the cusp of the loop or by inserting the loop into a cavity in, for example, a plastic moulding which constrains the loop and prevents expansion [see Fig.4 and Fig. I I ].

When detonation running along the cord approaches this loop two possible modes of behaviour are possible. The first mode results from immediate initiation of the returning tail of the cord by the advancing primary detonation front then progress with approximate symmetry along each limb. As these diverge and approach each other at the middle of the loop, the two shock waves travel through the plastic explosive between them and collide along the longitudinal mid-plane of the plastic explosive. Finally the two detonation waves collide at the approximate mid-point of the loop, thereby generating an enhanced shock in the plastic explosive. This is believed to be the most favourable initiation pattern.

The alternative pattern occurs if detonation is not transferred directly across from the first initiated strand to the parallel strand before the strands diverge. In this instance there will be no immediate collision of Shock waves detonation wave fronts within the plastic explosive. It is probable, however, that subjection of the plastic explosive to two successive shocks generated first by one, then the other, side of the loop bring about the initiation of the plastic explosive.

Such a configuration provides a reliable means of initiation particularly in applications in which it can be applied to the surface of the main explosive charge or can be surrounded by plastic explosive. It suffers the disadvantage, however, that its profile prevents applications in which it is necessary to insert and hold the initiator in a tubular holder designed to receiving a conventional elongate detonator. 4 The Present Invention

The present invention provides an explosive booster comprising a generally tubular elongate housing which provides confinement in order to cause initiation, at one end of the housing a length of detonating cord is inserted so as to extend into the housing, and the housing contains secondary explosive material, the end of the cord is retained in or by the housing so as to be adjacent (e.g. immediately adjacent; touching/in physical contact with) the explosive material or inserted therein, the interface between the cord end and the material is confined by the housing so that the explosive material can be initiated directly by the cord.

The secondary explosive material may comprise plastic explosive. The cord may be crimped into the end of the housing. The detonating cord may extend into the housing beyond the crimp i.e. the interface between the explosive material of the detonating cord and the secondary material (main charge) is "downstream" of the crimped zone. The tube may be formed, for example, from aluminium or copper.

The booster may further comprise a supporting sleeve for surrounding the cord within the housing in order to constrain it concentrically. The booster may further comprise a protective end cap.

The booster may comprise a blind-ended tube (similar to that of a detonator), or a detonator tube with a hole drilled in it. The present invention also provides an explosive booster charge comprising a rigid tube which is open at both ends, at one end of the tube detonating cord is inserted and terminates with a cord end, the tube contains detonating cord insensitive explosive material, the cord end abuts against the explosive material and is held in position so that the interface between the cord end and the explosive material is confined by the tube whereby initiation of the material can be driven by the cord.

The present invention also provides a system for conveying detonation from a length of detonating cord to a main charge without the need of an intermediate charge of primary explosive, comprising a housing which is open at both ends, at one end of the housing detonating cord is inserted and terminates with a cord end, the housing receives detonating cord insensitive explosive material, in use the cord end abuts against the explosive material and is held in position so that the interface between the cord end and the explosive material is confined by the housing whereby initiation of the material can be driven by the cord, the housing having an external configuration such as can fit into a tubular holder designed for receiving an retaining a conventional elongate detonator.

The present invention may also include the use of a Plain Detonator Adaptor (PDA) crimped on the end of a tube with a short length of detcord itself going into the secondary (plastic) explosive. The PDA (shown in Figure 7) replicates the shape of the Detonating Cord Booster (DCB) - see Fig. 2.

The Plain Detonator Adaptor, produced by the applicant, is an ingenious solution to the old problem of connecting multiple charges into a ring main reliably. When using bulk explosive charges, a knot of detcord in the charge tied onto a ring main will work fine, but when using more precise charges, such as a shaped charge, that is a good way of messing up the performance of the charge. The best initiator of this type of charge is a detonator, but until now there have not been good ways of connecting everything together.

The PDA is a small, plastic moulding that can be fitted and crimped into the end of a standard plain detonator. The PDA has a plastic U-shaped cradle designed to accept detonating cord which can be pushed into place anywhere on a line of detcord. The position of the charge can be adjusted but once engaged it cannot be removed from the ring main. When the detcord is initiated it punches out a small disc of plastic which is shot down the tube of the PDA straight into the primary composition of the detonator which is reliably initiated on impact.

Different aspects and embodiments of the invention may be used separately or together.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combination other than those explicitly set out in the claims.

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings.

Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

The terminology used herein to describe embodiments is not intended to limit the scope. The articles "a," "an," and "the" are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including," when used herein, specify the presence of stated features, items, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealised or overly formal sense unless expressly so defined herein.

In the following description, all orientational terms, such as upper and lower are used in relation to the drawings and should not be interpreted as limiting on the invention.

I I It is the purpose of the present invention to provide a means of conveying detonation from a length of detonating cord to a main charge without the need of an intermediate charge of primary explosive and having an external configuration such as can fit into a tubular holder designed for receiving and retaining a conventional elongate detonator.

The invention consists most typically of an open ended length of metal tubing 10 of similar dimensions to those of an ordinary detonator. Aluminium or copper are the preferred metals. A length of detonating cord 15 is crimped into one end of the tube 10. The detonating cord 15 extends several millimetres along the inside of the tube beyond the crimp 20, the inserted end 17 of the cord 15 being cut transversely (i.e. a straight cut at approximately 90 degrees to the length of the cord) and care being taken that little or no explosive 18 spills from the cord. A suitable secondary explosive fills the remaining part of the tube; that is, between the severed end 17 of the detonating cord and the open end of the tube. Plastic explosive 25 is tamped incrementally into the remainder of the tube. If the booster is not to be used at once, then protection of the tube contends by means of a rubber, plastics or metal end-cap 27or foil is desirable [see Fig.5 and Fig. 12].

In an alternative form of the invention the plastic explosive is replaced by a factory- filled with a suitably sensitive plastic bonded explosive. Either the manufacturer or the user then needs only to insert the initiating length of detonating cord so that it abuts against the plastic charge and to crimp it in place.

Yet another form of the invention is of similar construction except that the detonating cord is also crimped into the tube as part of the manufacturing process. If a detonation cord is employed of which the diameter is significantly less than the inside diameter of the metal tube then a supporting sleeve 1 30 may surround that part of the detonating cord which is within the metal tube in order to constrain it concentrically within the tube and thus prevent such deformation as may cause displacement of some of its explosive content and partial obturation of the explosive path by collapse of the plastic and paper wall components of the cord [see Fig. 6].

It will be understood that:

I . The invention contains no primary explosive so does not need to be stored and transported with detonators and other flame and percussion-sensitive devices but may reasonably be considered as to require storage and transportation limitations proper to secondary explosives. 2. A multiplicity of charges may be assembled and fired using a single detonator attached to a single length of detonating cord or to an array of interconnected lengths of detonating cord of which the configuration causes an array of main charges to be initiated simultaneously, in rapid succession or in groups. The array need be is sensitised for initiation only when all the charges have been placed and interconnected. This is a possibility which renders very much safer such operations as the destruction of randomly scattered, touch sensitive sub-munitions or the orderly demolition of structures comprising steel joists in which small arrays of charges, such as may be employed to sever steel joists, must be fired simultaneously but individual arrays in rapid sequence. 3. The charges may be used under water.

4. If factory-filled, the charges may be assembled in closed ended tubes. 5. If factory filled, the base charges of the devices may consist of compressed powdered explosive, press either in a homogeneous column or in a series of increments which are pressed to a sequentially diminishing pressure, thereby combining relatively easy and reliable initiation leading to maximum pressure output at the distal end.