CA1326403C - Primer - Google Patents

Abstract

ABSTRACT
A primer for an explosive charge which is to be initiated by a fuse cord is sensitized 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 which protrudes from the base of a mould in which the primer will be cast and which establishes a channel for a fuse cord. The primers of this invention have more sensitivity and robustness than known primers, and require fuse cords of lower charge weight.

Description

`-` 1 326403 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 mean~ of a primer, that i8, a sm~ll charge of soIid explosive which i~ initiated by means of a detonatlng cord. The reli~ble initlation of the primer explosive has required detonatlng cords of relatively high charge weight, that is, having a high weight of high e~plosive for a given length of cord. A cord of sufflci~nt charge weight to ignite a primer reliably has undesirable side effect~, such as side initiation ~the compression of the m~in charge in the immed~ate vicinity of the cord with resultant 1088 of sen3itivity) wherea~ a cord havlng a charge weiqht low enough to avoid these ~ide effects will not reli~bly initiate the primer.
Cne mean~ of overcoming this problem has been the incorporation in th~ pr$mer charqe of a small charge of high explo~ive to sens$tlse the primer charge. ~ .

This i8 generallv done during the manufactuxe of the primer. Primers are usually made by casting molten solid explosive ln moulds, the molten primer charge being then allowed to set. It i8 common to have protruding from such mould~ a cylindr~cal 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 8110w for the tying of the detonator cords or for detonator priming. The balloon containing the sensitisinq charge i8 wedged between the~e rods and moved into po~ition prior to the casting of the primer. A detonating cord inserted in the resultant solid charge will thu~ contact the b~lloon.
This type of primer has been succes~ful 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 permeability of balloons to oil and water, especially under pressure ~for example, at the bottom of a charge of explosive)~ Iwo further disadvantages are the expense of filling the balloona and the fact that the sensiti~ing explosive is packed tightly ln the balloons, which reduces sensitivity.
It has now been found that these disadvantages ~ay be eliminated or substantlally reduced by the prlmers of the present invention.
There is therefore provided, according to the present invention, a primer for an e~plos~ve ch~rge, adapted to be fired by ~ detonating cord, the primer comprising a charge of explosive substantlnlly completely surrounding a sensitising charge of high explosive, tle sen~itising charge being enclosed within an impermeable rigid container wh~se external shape is adapted to at least partially ~urround the S circumference of the detonating cord.
The primer charge may be selected from any suitable material. It may be, for example, a solid explosive BUCh as TNT, RDX, Tetryl and PE~N and mixtures thereof. For the purpose~ of this invention, it i8 preferred that the explosive of the primer charge be solid. However, it i8 pos~ible and permissible to use liquid explo~ives in the working of thi~ invention. Particularly useful liquid explosives for the purposes of this invention are the emulsion explosive~ 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 i8, ths primer either comprises a detonating cord integral therewith as a result of the process of production, or it has provision for the incorporation of ~uch a cord ~uch as a hole produced, for example, by mean~ of n rod in a mould as hereinabove described. The detonating cord may be selected from any ~uitable detonating cord known to the art.
The ~ensitising 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 riqid and impe D able. By ~rigid~ is meant that the container i8 constructQd such that it sub~tantially retains its shape under conditions of use, and by ~impermeable~ is meant that the container will not permit the entry thereinto of any external ~ubstance under conditions o~ use. The container may be made from any ~uitable material such as plastics and metal~, plastics being p3rticularly ~uitable materials for the containers as they can ea~ily and cheaply be moulded into any desired shape. An important feature of this container i8 that its external shape ia 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 with the external surface of the detonating cord thus allowing close contact. It is possible to mould container3 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 CQntainer may be mated to a cord and this placed in a container and primer explosive cast or poured around it. In the case of fiolid or very viscous explosives, it is preferred, however, to U8Q the method known to the art and described hereinabove, that i8~ the use of a mould having at least one rod, at least one of which provides a cylindr$cal hole completely through the primer. The invention therefore ~180 prov$des a method of manufacture of a primer by casting molten primer explo~ive in a mould, the mould having at least one rod at least one of which is 80 dimensioned as to provide in the primer a cylindrical hole extending completely therethrough, there being placed in the mould prior to casting a sen~itising charge, the 8en8iti81ng charge being enclosed in ~ rigid imperm~able contalner whose external shape is such that it at least partially surrounds a hole-providing rod and is supported thereby.

It is preferred to use a mould having at least two parallel rods - such 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 i~ 80 dimensioned that these depressions mate with the two rods snd locate the container in place in the mould.
The rod which creates the cylindrical hole extending through the finished primer has ~ub~tantially She same diameter as a detonating cord which is to be used with the primer. This means of course th~t a detonating cord inserted into the hole will contact the container with the sensitising charge.
The sensitising charge should be substantially completely surrounded by the primer charge, and th$s can be assured by providing on the container at least one leg which prevents the main body of the container from touching the bottom of the mould. Such legs are easily incorporated, especially in pl~tics containers, and in a preferred embodiment a single leg extends from the bottom of the container in a direction parallel to the axis of the rod.
The sensitising charge is easily loaded to ~
container of the type described hereinabove and the container may be closed by any suitable mean~ ~uch as a stopper. The closing means must of course perform properly in the environment in whlch the primer will be used. It must, for example, be impermeable, and it may need to have other characteri~tic~ ~uch as resist~nce to pressure.
Those skilled in the art will readily be able to select appropriate clo~ing mean~ ~nd neck configuration~ to meet any circumst~nce~. An L
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especially useful, convenient and cheap closing means i:3 a sphere of siliconQ rubber which i8 80 sized a'i to fit into a neck of the container.
An especially valuable feature of thi~
invention i~ the fact that the sensitising charge may be ~Idded loosely to the container and it w~ll remain thus. This confers greater sensitivity on the gensitising charge and permlt8 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 draw;ngs which depict a preferred embodiment.
Figure 1 $~ a side elevationsl ~iew of a container for a sen~itising charge.
Figure 2 i8 a plsn 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 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 a neck portlon 1, a body portion 2 and a leg 3 protruding from the bottom of the body portion 2.
The neck is stoppered ~fter the bottle has received its sen~itising charge with a plug 4 which i8 typically a ball of sillcone rubber. The body portion 2 has lncorporated into its shape two elongate concave depressions 5 which are on opposite sides of the bottle and whose longitudinal axes p~rallel that of the bottle itself.

Figure 3 shows the container of Figure 1 in place in a mould. The mould comprises a circular ~ase 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 i8 that when the mould i8 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 ~ame diameter as a detonating cord which will be used with the primer.
A container for a sensitising charge 10 fits between the rods 8 and 9, the container being 80 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 supports the container clear of the baseplate and ~llows the molten explosive to substant~ally completely surround the sensitising charge.

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Claims (14)

1. A primer for an explosive charge, which primer is initiated by a detonating cord, the primer comprising a charge of explosive substantially complete surrounding a sensitizing charge of high explosive, the sensitising charge being enclosed within an impermeable rigid container whose external shape at least partially surrounds the circumference of the detonating cord.

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

3. A primer according to claim 1, wherein the explosive of the primer is a liquid.

4. A primer according to claim 1, wherein the explosive of the primer is an emulsion explosive.

5. A primer according to any one of claims 1-4, wherein the primer comprises an integral detonating cord.

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

7. A primer according to any one of claims 1-4, wherein the container is made from a plastics material or a metal.

8. A primer according to any one of claims 1-4, wherein the container comprises two concave elongate depressions in opposite sides thereof.

9. A primer according to any one of claims 1 to 4, wherein the container comprises at least one leg extending from the bottom thereof to the surface of the primer.

10. 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.

11. A method of manufacture of a primer according 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 claim 10 or claim 11, 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.