GB2255160A

GB2255160A - Low energy fuse

Info

Publication number: GB2255160A
Application number: GB9208392A
Authority: GB
Inventors: Vernon Parker
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1991-04-24
Filing date: 1992-04-16
Publication date: 1992-10-28
Anticipated expiration: 2012-04-16
Also published as: AU1510392A; GB9208392D0; GB9108753D0; GB2255160B; AU649324B2; ZA922909B; CA2066850A1

Abstract

A non-electric low energy fuse comprises plastics tubing 1 having a core loading 2 of mixed particles which are reactive or detonable to provide for signal transmission wherein the plastics tubing has a shellac resin as an outer skin 3 to thereby enhance the oil resistance of the fuse. <IMAGE>

Description

LOW ENERGY FUSE This invention relates to non-electric low-energy fuses, that is to say, transmission devices in the form of elongate plastics tubing housing reactive or detonable particulate substances at a core loading sufficiently low for there to be no cross-initiation of a similar tube placed alongside (or lateral direct initiation of a surrounding commercial emulsion blasting explosive) when such a device is fired. Ordinarily the core material detonates but in some types rapid deflagration or pyrotechnic reaction suffices as when the tubing is connected to a detonator within which a deflagration to detonation transaction occurs. The signal transmission tubing is itself initiated by an electric cap, a nonelectric detonator, an electric discharge device or indeed by any other means capable of initiating the required self-sustaining reaction or detonation of the core material.A favoured type of low energy fuse is the so-called shock tube or signal tube as described in, and cross-referenced in, European Patent Specification No 327219 (ICI). Another distinct class of low-energy fuse is that described in US Patent Specification No 4290366 (Atlas Powder Company). The contents of these prior Specifications and their references are incorporated by reference herein, in their entirety.

The mining, quarrying and construction industries are the principal users of commercial explosives and accessories and are continually extending the frontiers of their operations into new situations that challenge the reliability of current accessories. Of present relevance is the trend towards increasing use of emulsion explosives and ANFO and heavy ANFO blasting agents, the deployment of non-electric low-energy fuse initiation down-hole as well as on the surface as inter-hole linkups, coupled with long sleep times (that is the periods of time when the fuse is in contact with the explosive before firing). Commonly the hydrocarbon fuel phase of such explosives is an oil or a petroleum fraction such as diesel, and invariably the plastics from which transmission tubes have been formed have been wholly or mainly of polyethylene (e.g.LLDPE) or a related (co)polymer in which the back-bone chain is a polyethylene and the chain carries side substituents which may be hydrocarbyl or functional groups such as carboxyl and its salt and ester derivatives (e.g.

'Surlyns'). All such polymers are prone to ingress of hydrocarbons of the explosive's fuel oil phase when in prolonged contact therewith. This is so to a greater or lesser extent depending upon the nature of those hydrocarbons, the chemical and physical structure of the polymer of the transmission tubing, and the temperature of the fuel phase (as when an emulsion explosive is loaded hot). Even surface transmission tubing may be in prolonged contact with oil where there is spillage of emulsion explosive or engine oils, and this too may become hot in many of the inhospitable environments in which blasting operations take place.

The Applicants have contrived mis-fires of nonelectric transmission devices of the types abovedescribed attributable to penetration of deleterious amounts of hydrocarbons into the interior core of the transmission tubing after prolonged contact.

This invention provides a plastics transmission tubing for a low-energy fuse of which the plastic is wholly or predominantly a polyolefine or derivitised polyolefine of the kinds hereinbefore described or another oil absorbing plastics material e.g a condensation polymer such as polyamide or polyester, and which contains in its central core a detonable or reactive signal transmitting particulate substance (such as loose, consolidated, bound and/or thread/filament carried material) characterised in that the oil permeable plastic tubing is coated with a skin of shellac resin as a barrier to penetration of hydrocarbon fuels of the kinds used as the components of emulsion explosives.

Preferably such a low energy fuse would be formed from an extrudable blend of about 80% linear low density polyethylene, about 10% ethylene-acrylic acid copolymer and about 10% ethylene vinyl acetate copolymer into a tube in which there is provided a core loading of from 15 to 25 mum 1, more preferably about 20 mum~1 of a reactive/detonable mixture comprising HMX explosive and aluminium particles, and having an outer skin of de-waxed shellac resin to enhance the oil resistance of the fuse.

Shellac is the only known commercial resin of animal origin (in fact from the insect Kerria lacca). The forms, components (so far as known) and properties of shellac are described in Kirk Othmer 3rd Edition, Volume 20 at pages 737 to 747; this disclosure is incorporated herein by reference.

Shellac resin may be the sole resin component of the barrier skin (applied, say, as a concentrated solution of a de-waxed shellac in, for example, alcohol). However the presence of other resins or polymers, either as mixtures with shellac resin or coupled to the shellac resin species by chemical "cross-linking" is allowed especially when adequate barrier properties are retained with enhancement in skin adherence, toughness, or abrasion resistance. The Kirk Othmer article contains references to chemically modified shellac resins.

Barrier skins based on, containing or derived from dewaxed shellac resin are preferred.

Adherence of the shellac resin skin to the underlying tube surface may be enhanced by chemical, thermal, flame or plasma treatments of the tube surface or by application of a suitable priming coating or a combination of pre-treatment and priming coating.

Applicant has found that chromic acid cleaning of shock tube formed with a polyethylene based tubing of the kind exemplified in EP-A-327 219 followed by rinsing, drying, application of a de-waxed shellac resin coating and a final warm air drying to remove alcohol solvent resulted in the shock tube still reliably firing after immersion in hot (500C) emulsion fuel phase (Shell RTN Derv fuel oil) after more than 300 hours, very much longer than was the case with unprotected shock tube from the same stock. Of course, one may optionally overcoat the shellac-protected tube to provide further protection against abrasion and de-lamination etc.

In the attached single figure a transverse section through a non-electric low energy fuse of the invention shows a plastics tubing 1 carrying a thinly distributed inner deposit of reactive or energetic material and an outer coating 3 of shellac resin.

The invention also extends to low-energy fuse assemblies comprising delay elements and/or detonators connected to one or both ends of the transmission tubing as aforesaid.

Claims

1. A non-electric low energy fuse formed from plastics tubing having a core loading of mixed particles which are reactive or detonable to provide for signal transmission wherein the plastics tubing has a outer skin of a shellac resin to enhance the oil resistance of the fuse.

2. A non-electric low energy fuse according to claim 1 wherein the plastics tubing is extruded from a condensation polymer or copolymer.

3. A non-electric low energy fuse according to claim 2 wherein the condensation polymer or copolymer comprises polyamide or polyester.

4. A non-electric low energy fuse according to claim 1 wherein the plastics tubing is extruded from an addition polymer or copolymer.

5. A non-electric low energy fuse according to claim 4 wherein the addition polymer or copolymer comprises polyolefin(s) or derivatives thereof.

6. A non-electric low energy fuse according to any one of claims 1 to 5 wherein the shellac resin is selected from dewaxed shellac, mixtures of shellac resin with other resins or polymers, shellac resin chemically linked with other resins or polymers and chemically modified shellac resins.

7. A non-electric low energy fuse according to any one of claims 1 to 6 wherein a compatible adhesion promoter is present between the shellac skin and the plastics tubing.

8. A non-electric low energy fuse according to any one of claims 1 to 7 wherein the core loading comprises particles provided in the tubing as loose, consolidated, bound or thread/filament carried material.

9. A non-electric low energy fuse according to any one of claims 1 to 8 wherein a core loading of from 15 to 25 mum 1 is provided in the tubing.

10. A non-electric low energy fuse formed from an extrudable blend of 80% linear low density polyethylene, abut 106 ethylene-acrylic acid copolymer and 10% ethylene vinyl acetate copolymer into a tube in which there is provided a core loading of about 20 mg/m of a reactive/detonable mixture comprising HMX explosive and aluminium particles, and having an outer skin of shellac to enhance the oil resistance of the fuse.

11. A non-electric low energy fuse substantially as hereinbefore described.

12. A method of manufacturing a signal transmission tubing for use as a low energy fuse, the method comprising extruding a plastics tubing from a melt and applying an outer skin of a shellac resin thereto to enhance the oil resistance of the fuse.

13. A method according to claim 12 wherein the plastics tubing is heat treated prior to application of the shellac.

14. A method according to claim 13 wherein the plastics tubing is heated to at least 1200C or the softening point of the plastics tubing.

15. A method according to claim 12 wherein the plastics tubing has the exterior surface thereof chemically treated prior to application of the shellac.

16. A method according to claim 15 wherein the plastics tubing has the exterior surface thereof treated with chromic acid.

17. A method according to claim 12 wherein the plastics tubing has a compatible adhesion promoter applied to the exterior surface thereof prior to application of the shellac.

18. A method of extending the operational life of a signal transmission tubing for use as a low energy fuse in contact with hot fuel oil, the method comprising forming a plastics tubing having a core loading of a reactive particulate substance for use in signal transmission and applying a shellac resin as an outer skin to thereby enhance the oil resistance of the fuse.