AU642574B2 - Pyrotechnic delay composition - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Int. Class Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: be r Name of Applicant: Imperial Chemical Industries PLC Actual Tnventor(s): Moira Logan Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: PYROTECHNIC DELAY COMPOSITION Our Ref 243077 POF Code: 1453/1453 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- 6006 r PYROTECHNIC DELAY COMPOSITION This invention relates to a novel pyrotechnic delay composition characterised by uniform burn rate, moisture resistance and low toxicity and to ignition delay elements or devices containing the said composition. The composition is useful in the range of intermediate to slow-burning delay period. This is considered to mean a burning time period of from about 400 to about 3200 milliseconds per centimetre length of the delay element. With respect to electrically initiated systems, the delay time is regarded as the time between application of the initiating electric impulse to the pyrotechnic composition of the delay element and the subsequent detonation of the explosive charge of an associated detonator.

Delayed action detonators, both non-electric and electric are widely employed in mining, quarrying and other blasting operations in order to permit sequential initiation of explosive charges in a pattern of boreholes. Delay or sequential initiation of shotholes is effective in controlling the 2fragmentation and throw of the rock being blasted and in addition provides a reduction in ground vibration and in airblast noise.

Modern commercial delay detonators, whether non-electric or electric, comprise a metallic shell closed at one end which shell contains in sequence from the closed end a base charge of a detonating high explosive, such as for example, PETN and an above adjacent, primer charge of a heat-sensitive detonable material, such as for example, lead azide. Adjacent the heat-sensitive material is an amount of deflagrating or burning composition of sufficient quantity to provide a desired delay time in the manner of a fuse. Above the delay composition is an ignition charge adapted to be ignited by an electrically heated bridge wire, or alternatively, by the heat and flame of a low energy detonating cord or shock wave conductor retained in the open end of the metallic shell. Such a delay detonator may serve as an in-line delay as when coupled to a detonating cord or shock wave conductor. However, a delay device need not also be capable of serving as a detonator in order, for example, to initiate a shock wave conductor. An ignition charge in close proximity-to the end of the shock wave conductor instead of a base charge of detonating high explosive, will suffice.

A large number of burning delay compositions comprising mixtures of fuels and oxidisers aLe known in the art. Many are substantially gasless compositions; that is, they burn without evolving large amounts of gaseous by--products which would interfere with the functioning of a delay detonator. In addition to an essential gasless requirement, delay compositions are also required to be safe to handle, from both an explosive and health viewpoint, they must be resistant to moisture and not deteriorate S" over periods of storage and hence change in burning characteristics, and they must be adaptable for use in a wide *range of delay units within the limitations of space available o. 15 inside a standard detonator shell. The numerous delay ee compositions of the prior art have met with varying degrees of success in use and application.

One such prior class of delay composition which has been well-received is that described in GB-A-2 089 336 (incorporated herein by reference), which composition comprises silicon and barium sulphate and optionally includes a proportion of red lead oxide. The present invention also relates to silicon/oxidant delay compositions and to delay devices and detonators containing a column of such a composition. Although the delay composition could be loaded directly into a detonator casing, it is customary for the composition to be contained in an open-ended tubular metal element e.g. a drawn lead element which is snugly fitted into the detonr ,or shell.

There is a desire in the explosive industry to phase out all needless use of lead either as the metal Crawn-lead elements) or as compounds in delay composition, e.g. red lead oxide as described above. The alternatives to drawn-lead tubular containment of delay compositions are drawn elements r< another metal, such as aluminium, and the so-called rigid element. A rigid element is a pre-formed tube of the required dimensions made of a metal such as zinc, which does not present an environmental problem, into which the desired particulate mixture of delay composition ingredients is pressed to provide delay elements which afford the desired delay period.

An object of this invention is to provide further delay compositions and delay devices containing same for use in ignition delay trains. A further object is to provide a delay composition which burns at a reproducible speed when compacted in rigid metal elements.

Accordingly this invention provides a pyrotechnic delay composition for uce in delay devices or detonators comprising from about 20 to 40% particulate silicon (by mass), preferably from about 25 to about 35%, with the balance being pw;.iculate ferric oxide. The silicon ferric oxide (Si/Fe20 3 composition preferably comprises silicon and ferric oxide in a ratio of go•• 15 40:60 to 60:40 by volume a substantially 50:50 mixture by volume being the most preferred. The advantage of such a composition is that being essentially a binary system, it provides for more reliable mixing especially if utilising a composition based on about 30% (by mass) Si with about 70% (by mass) Fe 2 03 which generally achieves the preferred 50:50 mixture by volume. This is a very desirable ratio from a mixing/particle packing point of view, which is very important considering the method of loading the delay devices and detonators used in the art. Other advantages are that ferric oxide is, of courseinsoluble in 25 water and should be storage stable against moisture in the locus of storage or arising from environmental conditions. The Si/Fe 2 03 mixture is considered to be of the lowest possible toxicity in comparison with commercially available compositions such as those containing dichromates. It also appears to be very safe when tested by typical impact, friction and static tests GB-A-2 089 336) and its ignition temperature appears to be in the region of 1000 0

C.

The silicon preferably has a specific surface of 5 to KM.2/g and the ferric oxide preferably has a specific surface of 3 to 1 The invention also includes an ignition delay element comprising the above mentioned pyrotechnic delay composition and a delay device or a detonator comprising the said ignition delay element or the said composition. From a further aspect the invention consists in the use of a composition comprising 20 to by mass of silicon, the balance being ferric oxide as the delay burning composition providing a delay period in the ignition train of a delayed action ignition device or detonator.

The invention is further illustrated by the following examples.

The compositions described in the Examples were formulated from particulate silicon having a specific surface of 5.4m 2 g-1 and ferric oxide having a specific surface of 4.3m 2 g-l. The ingredients were mixed as an aqueous slurry, dried, and sieved •to obtain a relatively free-flowing powder which was 15 subsequently consolidated to a density of about 2.5g/cm 3 in an open-ended tubular zinc element of internal diameter 3.1mm and outside diameter of 6.4mm.

Example 1 A delay composition containing silicon and ferric oxide in the mass ratio 30:70 was prepared and consolidated in a 22mm long zinc element as described above. The delay element was encased in a delay detonator containing a high explosive base charge which was capable of being initiated to detonation by the delay :....composition. The delay composition was ignited at the end remote from the high explosive base charge by means of an electric fusehead. A sample of 20 such detonators were prepared and fired successfully with a mean delay time of 3.583 0.031 seconds i.e. a delay burning rate of 6.15mm/s.

Example 2 Delay detonators similar to those of Example 1 except that a fast burning incendiary sealer composition consisting of 62% by weight of ]ead dioxide and 38% silicon was consolidated in a 2mm length at the end of the zinc element adjacent to the initiator means and the initiation means was a length of shock wave conductor tube (EXEL, Registered Trade Mark). A sample of detonators fired with a mean delay time of 3.329 0.071 seconds i.e. a burning rate of 6.01 mm/s.

*Example 3 Detonators were prepared as described in Example 2 except that the zinc element was 10mm long and contained an 8mm length of delay composition and 2mm length of the fast burning incendiary composition sealing the end adjacent to the shock wave conductor tube.

A sample of 20 detonators initiated with a length of EXEL tube fired with a mean delay time of 806 23 milliseconds i.e. a burning rate of 9.9 mm/s.

Example 4 Detonators were prepared as described in Example 3, except that the delay composition contained silicon and ferric oxide in the mass ratio of 25 75. The detonators fired with a mean delay time of 1.100 0.036 seconds i.e. a delay burning rate of 7.28mm/s.

Example Detonators were prepared as described in Example 3, except that the delay composition contained silicon and ferric oxide in the mass ratio of 15:85. The detonators fired with a mean delay time of 2.342 0.204 seconds i.e. a delay burning rate of 3.41mm/s.

Example 6 Detonators were prepared as described in Example 3, except that the delay composition contained silicon and ferric oxide in the mass ratio of 35:65. The detonators fired with an average delay time of 1.067 0.245 seconds i.e. a delay burning rate of The Examples show that the delay compositions of this invention burn at a reproducible speed with low variation between samples for a given physical arrangement and initiation system.

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Claims (12)

1. A pyrotechnic delay composition for use in delay devices or detonators comprising from about 20 to 40% (by mass) particulate silicon and from about 60 to 80% (by mass) ferric oxide.

2. A pyrotechnic delay composition according to Claim 1 comprising from about 25 to 35% (by mass) particulate silicon and from about 65 to 75% (by mass) ferric oxide.

3. A pyrotechnic delay composition according to Claim 2 consisting of 30% by mass of silicon and 70% by mass of ferric oxide.

4. A pyrotechnic delay composition according to any of claims 1 to 3 inclusive comprising silicon and ferric oxide in the volume ratio of 60:40 to 40:60. *0 a A pyrotechnic delay composition according to Claim 4 which is a substantially 50:50 mixture by volume of silicon and ferric oxide.

6. A pyrotechnic delay composition according to any of claims 1 to 5 inclusive wherein the silicon has a specific surface area of from 5 to 6 m 2 /g and the ferric oxide has a specific surface area of from 3 to 5 m 2 /g.

7. A pyrotechnic delay composition substantially as hereinbefore described with reference to any one of the Examples.

8. An ignition delay element comprising a delay composition according to any one of claims 1 to 7 inclusive compacted into a tubular metal element.

9. An ignition delay element according to claim 8 wherein the tubular metal element is a rigid element. An ignition delay element according to Claim 9 wherein the tubular metal element is a zinc element.

11. An ignition delay element substantially as hereinbefore described with reference to any one of the Examples.

12. A delay ignition device or detonator characterised by a pyrotechnic delay composition comprising an intimate mixture of particulate silicon and ferric oxide, according to any one of claims 1 to 7 inclusive.

13. A delay ignition device or detonator comprising an ignition delay element according to any one of claims 8 to 11 inclusive.

14. Use of a pyrotechnic composition according to any one of claims 1 to 7 inclusive as the delay burning composition providing a delay period in the ignition train of a delayed action ignition device or detonator. Use of a Si/Fe20 3 composition comprising from about 20 to 40% (by mass) particulate silicon having a specific surface area of from 5 to 6 m 2 /g and from about 60 to 80% (by mass) ferric oxide having a specific surface area of from 3 to 5 m 2 /g in a delay device or detonator. lI. Use of a Si/Fe20 3 composition comprising from about 25 to (by mass) particulate silicon having a specific surface area of from 5 to 6 m 2 /g and from about 65 to 75% (by mass) ferric oxide having a specific surface area of from 3 to 5 m 2 /g in a delay device or detonator. DATED: 30 JANUARY 1992 PHILLIPS ORMONDE FITZPATRICK Attorneys for: IMPERIAL CHEMICAL INDUSTRIES PLC