CA1298972C - Detonator - Google Patents

Abstract

ABSTRACT
A detonator which does not utilize the traditional styphnate/azide primer and which does not require heavy and expensive confinement comprises a loose mixture of a high explosive and a finely-divided metal, the metal being present in the mixture to the extent of from 1%-5% by weight. The preferred high explosive is PETN and the preferred metal is paint-fine aluminium. The detonators may utilize the same shells as conventional styphnate/azide detonators and are as effective, but are safer to handle.

Description

12~8972 l)ETONATOR

This invention relates to novel detonators for use with explosives.
S A detonator for use in detonating explosives typically comprises the following elements; a fuse head, an initiating composition and a base charge, all of these being in a single metal case. Thus, when the detonator is triggered, the fusehead ignite~ the initiating composition which then detonate~ the base charge which in turn detonates the explosive.
The most commonly used initiating compositions have been primary explosive compositions, usually a mixture of lead azide and lead styphnate. Thi~
mixture performs very well - it detonates with considerable force and this property makes the detonators in which it i8 incorporated highly effective.
However, it also has considerable drawbacks1 it i8 relatively unstable and ha~ been known to detonate when sub~ected to excessive shock or friction, or when exposed to static electricity. Moreover, the need for care in the handling of the material and the facilities which this reguires add considerably to the 39~2 cost of manufacturing such detonators.
The attractions of a detonator which utilises something other than an initiatinq composition of the type described above are evident and there have been attempts to produce such a detonator. One line of development has been the use of the ~DDT" (deflagration detonation transition) mechanism, wherein an explosive substance is ignited by a fusehead and this deflagration progresses rapidly to detonation. This approach has been tried with loosely packed PETN, but it has been found that in order to confine the deflagrating PETN
for a sufficient time to allow the transition to detonation, the detonator casing must be of steel.
This renders such detonators prohibitively expensive.
I have now found that it is possible to make a primerless detonator which gives excellent results without the need for expensive confinement. I therefore provide, according to the present invention, a detonator comprising an initiating composition and a base charge, the initiating composition comprising a loose mixture of high explosive and finely divided metal, the metal being present to the extent of from about 1% - 5% by weight of the mixture. I
have found that when such a mixture is used, only a simple sealer element need be used to provide sufficient confinement in a conventional detonator casing. The base charge is a conventional base charge, that is, a charge of high explosive which has been compressed at 70 Kg/cm2 or more. The initiating composition must, however, be a loose mixture.
By "loose mixture~, I mean that the high explosive (in powdered or granular form) is mixed with the finely-divided metal and the resulting mixture loaded into the detonator under no pressure or only the relatively low pressure exerted by any art-lZ~89~

recognised means of confining the mixture in thedetonator. I have found that in order to work effectively, the mixture used in the initiating composition of my invention should not be compressed to any great extent. One part of this mixture is high explosive. The term ~high explosive" defines a well-known group of explosives in the art, some members of which group are pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HDX). The preferred material is PETN.
The finely-divided metal can be selected from any such material known to the art. Such materials include copper, aluminium and iron. An especially good material is ~paint fine" (PF) aluminium, a pigment used in automotive and refinish metallic-effect coatings, and this is my preferred material.
The finely-divided metal may be present to the extent of about 1~-5% by weight of the mixture. I
have found that in some cases it is possible to formulate a working mixture just outside these limits - it depends very much on the nature and packing of the ingredients - but as a general rule mixtures lying outside this range do not work satisfactorily.
~ rhe mixture is relatively stable and can be easily and inexpensively loaded into detonators.
The detonators themselves can have aluminium or copper casings which again reduces prices. Detonators according to this invention may incorporate all of the features known to the art to be useful in detonators. They may, for example, be electric or nonelectric, and they may be instantaneous or they may comprise pyrotechnic or electronic delays.

1~9~9 . 2 The invention is now further described with reference to the drawing which depicts a part longitudinal cross-section of a preferred detonator according to the invention.
The detonator comprises an aluminium housing 1, a crimped starter element 2, an initiating composition 3 and a base charge 4.
The detonator is ignited by means of a shock wave propogated through a shock tube 5 which is sealed lQ into the detonator.
The invention is further described with reference to the following examples in which all parts are expressed by weight.

Example Detonators were prepared by loading 5.33 cm.
aluminium detonator shells each with a charge of 0.8 9 PETN which was pressed at 232 kg/cm2. To each shell was then added 0.12 9 of a loose mixture of PETN and paint fine aluminium, the aluminium comprising 2~ by weight of the mixture. This mixture was sealed in place by the fitting of standard crimped type ~H~ sealer elements. Finally there was attached to each detonator shell thereby sealing them, one metre of ~Nonel~ (trade mark) shock tubing.
The detonators were tested by firing the shock tube, and it was found that the base PETN charge was fired.

Claims (3)

1. A detonator comprising an initiating composition and a base charge, the initiating composition comprising a loose mixture of high explosive and finely divided metal, the metal being present to the extent of from about 1%-5% by weight of the mixture.

2. A detonator according to Claim 1, wherein the high explosive is PETN.

3. A detonator according to Claim 1 or Claim 2, wherein the finely divided metal is paint-fine aluminium.