AU592690B2 - Primer - Google Patents

Description

PATENTAUSTRALCT 1952-1973 PATENTS ACT 1952-1973 AUS 1345 2 °9 0 Form COMPLETE

SPECIFICATION

Class: Int. CI: *,Application Number: Lodged: O0 .Complete Specification-Lodged: Accepted: Published: Priority: Related Art Related Art: l 1iri""

(ORIGINAL)

FOR OFFICE USE This document contains the amendments made under Section 49 and is correct for printing.

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PATENT OFFICE LODGED Ai SUBO-FFICE 01 1 8 DEC 987 Vi&QiiB&s~wf Fi|iL 5 5* TO BE COMPLETED BY APPLICANT Name of Applicant: ICI AUSTRALIA OPERATIONS PROPRIETARY LIMITED Address of Applicant: Industrial Property Section ICI Australia Operations Proprietary Limited 1 Nicholson Street Melbourne 3001 Victoria Australia Actual Inventor: Richard DOWING Jolanta PAULL David VINCE Address for Service: Industrial Property Section ICI Australia Operations Proprietary Limited GPO Box 4311 Melbourne 3001 Victoria Australia Complete Specification for the invention entitled:

"PRIMER"

The following statement is a full description of this invention, including the best method of performing it known to me:- *Note: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

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PRIMER

This invention relates to a primer for the detonation of an explosive charge.

A well-known means of detonating a main charge of explosive for the breaking of rock and ore is by means of a primer, that is, a small charge of solid explosive which is initiated by means of a detonating cord. The reliable initiation of the primer explosive has required detonating cords of 10 relatively high charge weight, that is, having a high weight of high explosive for a given length of cord. A cord of sufficient charge weight to ignite a primer reliably has undesirable side effects, such as side initiation (the compression of the main charge in the immediate vicinity of the cord with resultant loss of sensitivity) whereas a cord having a charge weight low enough to avoid these side effects will not reliably initiate the primer.

One means of overcoming this problem has been the incorporation in the primer charge of a small charge of high explosive to sensitise the primer charge.

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.i ir--il 2 This is generally done during the manufacture of the primer. Primers are usually made by casting molten solid explosive in moulds, the molten primer charge being then allowed to set. It is common to have protruding from such moulds a cylindrical rod of essentially the same diameter as the detonating cord, such that a suitable passage for the insertion of the cord is provided and the cord can readily be fitted to the primer charge on its removal from the mould. The sensitising charge is usually added sealed in a flexible container, commonly a balloon.

Many moulds have a second cylindrical rod which is "parallel to the first but which does not necessarily protrude from the mould, this being present to allow 15 for the tying of the detonator cords or for detonator priming. The balloon containing the sensitising charge is wedged between these rods and moved into position prior to the casting of the primer. A detonating cord inserted in the resultant 20 solid charge will thus contact the balloon.

This type of primer has been successful in practice but still suffers from drawbacks. One of these is the fragility of balloons which can break in the process of making the primer. Another is the 25 permeability of balloons to oil and water, especially under pressure (for example, at the bottom of a charge of explosive). Two further disadvantages are the expense of filling the balloons and the fact that the sensitising explosive is packed tightly in the balloons, which reduces sensitivity.

It has now been found that these disadvantages may be eliminated or substantially reduced by the primers of the present invention.

There is therefore provided, according to the present invention, a primer for an explosive charge, adapted to be fired by a detonating cord, the primer comprising a charge of explosive substantially i 3 completely surrounding a sensitising charge of high explosive, the sensitising charge being enclosed within an impermeable rigid container whose external shape is adapted to at least partially surround the circumference of the detonating cord.

The primer charge may be selected from any suitable material. It may be, for example, a solid explosive such as TNT, RDX, Tetryl and PETN and mixtures thereof. For the purposes of this invention, it is preferred that the explosive of the primer charge be solid. However, it is possible and permissible to use liquid explosives in the working .of this invention. Particularly useful liquid explosives for the purposes of this invention are 15 the emulsion explosives well known to the art.

These range in consistency from thick semi-solid pastes to reasonably free-flowing liquids.

The primer is adapted to be fired by a detonating cord, that is, the primer either *o* 20 comprises a detonating cord integral therewith as a result of the process of production, or it has provision for the incorporation of such a cord such as a hole produced, for example, by means of a rod in a mould as hereinabove described. The detonating 25 cord may be selected from any suitable detonating cord known to the art.

The sensitising explosive may be selected from the high explosives known to the art to be suitable for such a use, for example, Tetryl, PETN, RDX and mixtures thereof.

The container within which the sensitising explosive is housed is rigid and impermeable. By "rigid" is meant that the container is constructed such that ii- substantially retains its shape under conditions of use, and by "impermeable" is meant 4 that the container will not permit the entry thereinto of any external substance under conditions of use. The container may be made fror any suitable material such as plastics and metals, plastics being particularly suitable materials for the containers as they can easily and cheaply be moulded into any desired shape. An important feature of this container is that its external shape is adapted to at least partially surround the circumference of the detonating cord. In practical terms, this means that the container is so shaped as to provide an *elongate concave or cylindrical surface which mates 0* I.

S* with the external surface of the detonating cord thus allowing close contact. It is possible to 15 mould containers which will surround most or even all of the circumference of the cord.

The primers of this invention may be prepared by any convenient means. For example, a container may be mated to a cord and this placed in a 20 container and primer explosive cast or poured around it. In the case of solid or very viscous explosives, it is preferred, however, to use the 0* method known to the art and described hereinabove, that is, the use of a mould having at least one rod, 25 at least one of which provides a cylindrical hole completely through the primer. The invention therefore also provides a method of manufacture of a primer by casting molten primer explosive in a mould, the mould having at least one rod at least one of which is so dimensioned as to provide in the primer a cylindrical hole extending completely therethrough, there being placed in the mould prior to casting a sensitising charge, the sensitising charge being enclosed in a rigid impermeable container whose external shape is such that it at least partially surrounds a hole-providing rod and is supported thereby.

ug M It is preferred to use a mould having at least two parallel rods srch moulds are well known to and widely used by the art. The container for use in such a mould has two concave elongate depressions on opposite sides thereof, and the container is so dimensioned that these depressions mate with the two rods and locate the container in place in the mould.

The rod which creates the cylindrical hole extending through the finished primer has substantially the same diameter as a detonating cord o; which is to be used with the primer. This means of course that a detonating cord inserted into the hole will contact the container with the sensitising .15 charge.

o The sensitising charge should be substantially completely surrounded by the primer charge, and this can be assured by providing on the o. container at least one leg which prevents the main g [20 body of the container from touching the bottom of the mould. Such legs are easily incorporated, especially in plastics containers, and in a preferred embodiment a single leg extends from the bottom of the container in a direction parallel to s 25 the axis of the rod.

The sensitising charge is easily loaded to a container of the type described hereinabove and the container may be closed by any suitable means such as a stopper. The closing means must of course perform properly in the environment in which the primer will be used. It must, for example, be 4 impermeable, and it may need to have other I characteristics such as resistance to pressure.

Those skilled in the art will readily be able to select appropriate closing means and neck configurations to meet any circumstances. An :i

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6 especially useful, convenient and cheap closing means is a sphere of silicone rubber which is so sized as to fit into a neck of the container.

An especially valuable feature of this invention is the fact that the sensitising charge may be added loosely to the container and it will remain thus. This confers greater sensitivity on the sensitising charge and permits of the use of detonating cords of even lower sensitivity than have previously been possible to be used.

The invention will now be further illustrated with reference to the drawings which depict a preferred embodiment.

Figure 1 is a side elevational view of a 15 container for a sensitising charge.

Figure 2 is a plan view of the container of 'Figure 1.

Figure 3 is a part vertical section of a mould for the making of a primer according to the n* invention, showing a container of the type depicted in Figure 1 in place prior to the pouring of molten primer explosive.

The container depicted in Figure 1 is a bottle moulded from plastics material. It comprises 25 a neck portion 1, a body portion 2 and a leg 3 protruding from the bottom of the body portion 2.

a The neck is stoppered after the bottle has received its sensitising charge with a plug 4 which is typically a ball of silicone rubber. The body portion 2 has incorporated into its shape two elongate concave depressions 5 which are on opposite sides of the bottle and whose longitudinal axes parallel that of the bottle itself.

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S S Figure 3 shows the container of Figure 1 in place in a mould. The mould comprises a circular base plate 6 and a removable sleeve 7 which is a tight fit around the base plate. Extending vertically from the base plate are two vertical cylindrical rods 8, 9, rod 8 being taller than the sleeve and rod 9 being shorter than the sleeve; the result is that when the mould is filled with molten primer explosive, rod 8 protrudes clear of the explosive and the resulting primer will have a cylindrical hole extending along its entire length.

Rod 8 is of the same diameter as a detonating cord which will be used with the primer.

A container for a sensitising charge 10 fits 15 between the rods 8 and 9, the container being so shaped and dimensioned that the elongate concave depressions 5 mate with the rods and hold the container in a vertical position in the mould. The leg 3 protruding from the bottom of the container 20 supports the container clear of the baseplate and allows the molten explosive to substantially completely surround the sensitising charge.

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Claims (13)

1. A primer for an explosive charge, adapted to be fired by a detonating cord, the primer comprising a charge of solid explosive substantially completely surrounding a sensitising charge of high explosive, the sensitising charge being enclosed within an impermeable rigid container whose external shape is adapted to at least partially surround the circumference of the detonating cord.

2. A primer according to claim 1, wherein the explosive of the primer is a solid. 6*e

3. A primer according to claim 1, wherein the explosive of the primer is a liquid. A primer according to claim 1, wherein the explosive of the primer is an emulsion explosive. A primer according to any one of claims 1-4, wherein the primer comprises an integral detonating cord. s..

6. A primer according to claim 2, wherein there is provided in the solid explosive a hole suitable for the insertion of a detonating cord.

7. A primer according to any one of claims 1-6, wherein the container is made from a plastics material or a metal.

8. A primer according to any one of claims 1-7, j wherein the container includes two concave elongate depressions whose longitudinal axes parallel that of the container itself arid which are on opposite sides thereof. <f3\~Q n -9

9. A primer according to any one of claims 1 to 8, wherein the container comprises at least one leg extending from the bottom thereof to the surface of the primer. A method of manufacture of a primer by casting molten primer explosive in a mould, the mould having at least one rod at least one of which is so dimensioned as to provide in the primer a cylindrical hole extending completely therethrough, there being placed in the mould prior to casting a sensitising charge, the sensitising charge being enclosed in a rigid impermeable container whose external shape is such that it at least partially surrounds a hole-providing rod and is supported a Do thereby. a

11. A method of manufacture of a primer according 0 to claim 10, wherein the mould comprises two rods and the container is so shaped as at least partially to surround both rods and be supported thereby.

12. A method of manufacture of a primer according to claim 10 or claim 11, wherein the container comprises at least one leg extending from the bottom thereof and which supports the container clear of the bottom of the mould.

13. A method of manufacture of a primer according to any one of claims 10-12, wherein the container is made of plastics or metal.

14. A method of exploding an explosive charge by utilising a primer according to claim 1. 4 ~Li 10 A primer for an explosive charge substantially as described with reference to the drawings.

16. A method of manufacture of a primer substantially as described with reference to the drawings. 9~ a 6 6 646 6 66 64 6 4 6 66 6 6 66 Jo a 66 V as 6 @6 6 6 6* ma 6 664 e 44 664 Dated this day of December, 1987 64 6 6 @6 a *a 6

06646. a a 6 66 6 6 6 66 a 64*66 4 ICI AUSTRALIA OPERATIONS PROPRIETARY LIMITED Cl JAMcS CRLP1. 2 I 11 ABSTRACT I. S. I A primer for an explosive charge which is to I be initiated by a fuse cord is sensitised by a loose charge of a high explosive, this high explosive being contained in a rigid, impermeable container which is so shaped that it at least partially surrounds the fuse cord. The container is of plastics or metal and preferably comprises at least one elongated concave surface which mates with and is supported by at least one metal rod wh.ch protrudes from the base of a mould in which the °primer will be cast and which establishes a channel for a fusecord. The primers of this invention have more sensitivity and robustness than known primers, and require fusecords of lower charge weight. e L