SE1651094A1 - A method of and a cartridge for disarming an unexploded blasting charge in a drill hole - Google Patents

Abstract

A method of disarming an unexploded blasting charge (101) in a drill hole (100), comprising:- providing a non-exploding cartridge (1) containing- a pyrotechnic composition (6) able to generate a high temperature fire, and - a blasting cap (10) for igniting the pyrotechnic composition (6); and- igniting the pyrotechnic composition (6) in the non-exploding cartridge (1) to burn away the blasting charge (101).The pyrotechnic composition (6) in the non-exploding cartridge (1) preferably is thermite.

Description

A METHOD OF AND A CARTRIDGE FOR DISARMING AN UNEXPLODEDBLASTING CHARGE IN A DRILL HOLE TECHNICAL FIELD The present invention relates to a method of disarrning an unexploded blasting charge ina drill hole.

It also relates to a cartridge for disarrning an unexploded blasting charge in a drill hole, comprising: - a substantially cylindrical outer sleeve With an end Wall in a first end; - a plug, Which, enclosing said outer sleeve, is inserted into and secured in an oppositesecond end of the outer sleeve; - a main chamber in the outer sleeve between said end Wall and said plug, Which mainchamber is filled With a pyrotechnic composition; - an opening in one of said plug and/or end Wall for receiving an igniting deviceincluding an igniting charge arranged to ignite said pyrotechnic composition,said pyrotechnic composition including a metal poWder fuel and a metal oxideserving as an oxidizer, said composition upon ignition undergoing an exothermic reduction-oxidation (redox) reaction arranged to burn away said blasting charge.

BACKGROUND ART Dynamite is usually sold in the form of cardboard cylinders about 20 cm (8 in) long andabout 3.2 cm (1 .25 in) in diameter, With a Weight of about 190 grams. It consists of amixture of nitroglycerine, an absorbent, and possible additives, like a stabilizer, afreezing point depressant, and a brisance improver. Dynamite Will not detonate by heatand is moderately sensitive to shock. Shock resistance tests are usually carried out Witha drop-hammer: about 100 mg of explosive is placed on an anvil, upon Which a Weightof between 0.5 and 10 kg is dropped from different heights until detonation is achieved.With a hammer of 2 kg, mercury fulminate detonates With a drop distance of 1 to 2 cm,nitroglycerin With 4 to 5 cm, dynamite With 15 to 30 cm, and ammoniacal explosivesWith 40 to 50 cm.

When blasting rock With dynamite, e.g. for a building site, there are often used multiplecharges, i.e. a plurality of drilled holes provided With dynamite. Not too rarely one ormore of the charges do not ignite, but stay undetonated in the hole. This may causedeath, if later an excavator unluckily hits and detonates the undetonated dynamite charge. Today specially trained dogs are used to find such undetonated charges to make it possible to remove them before starting excavating. However, the methods of todayfor removal of an undetonated dynamite charge from deep in a hole in the rock, i.e. digging it out, is very time consuming and dangerous.

US 6,765,l2l B2 discloses a method and an apparatus for neutralization of the explo sive content of mines and unexploded ordnance ("UXO"). Such ordnance includesnot only unexploded shells, rockets, and fuses, but also ordnance that is designed toexplode on contact or is triggered to explode by another activation mechanism, such asa detonator, such as a land, underwater, or shallow water mine. There exist manysources of UXO which must be destroyed. The idea is to essentially completelyconsume the explosive charge by combustion or decomposition before any explosion OCCUTS.

The method comprises reacting, on or near the surface of the mine or UXO, a charge ofa compound that reacts with an extremely high heat-release rate. The intense exotherrnicreaction generates high temperature combustion products that will melt, bum, orotherwise disrupt, a metal plastic, composite, or wooden casing, thus leading to combustion or decomposition of the explosive.

In an altemative embodiment, the high temperature in the casing decomposes thecontent thereof, causing the pressure in the casing to rise, fracturing the casing beforethe explosive detonates. In either case, the disrupted casing enables ignition of a largearea of the explosive charge and provides easy access for atmospheric air to support active bumout of the explosive.

WO 2009/ 120139 discloses a powder charged rock cracker cartridge of the kind statedin the second paragraph above. The pyrotechnic composition is gun powder, and thecracker cartridge satisfies the requirements of lowest explosive classification, whichallows transportation and storing without those rigorous safety rules that apply forhigher explosive classifications. Further, the cracker cartridge is easy to manufactureand easy to use, including easy to prime as well as to unprime safely on the working place.

SUMMARY OF THE INVENTIONThe object of the present invention is to provide a method of and a cartridge for disarrning an unexploded blasting charge in a drill hole.

In a first aspect of the invention, this object is achieved in that the method comprises the steps of: - providing a non-exploding cartridge containing a pyrotechnic composition able togenerate a high temperature fire, and an igniting device for igniting the pyrotechniccomposition; and,introducing the non-exploding cartridge into a drill hole containing said unexplodedblasting charge, and,igniting the pyrotechnic composition in the non-exploding cartridge to burn away the blasting charge.

Thereby, the unexploded blasting charge will be disarrned by combustion ordecomposition without any risk of detonation. Thanks to the invention a much moreefficient procedure is achieved, e.g. providing significantly less labor and beingsignificantly quicker. Further the invention may result in reduced costs, especially as inthe preferred case a cartridge is used that already exist on the market. Moreover, theinvention may result in increased safety, especially as in the most preferred case a specific extra safe cartridge is used that already exist on the market.

Preferably, the pyrotechnic composition contains therrnite. Therrnite is a pyrotechniccomposition of metal powder fuel, e. g. aluminum (Al), and metal oxide, e.g. FezOs orFesO4. When ignited by heat, therrnite undergoes an exotherrnic reduction-oxidation (redox) reaction, e. g.

F62Û3 "l" 2 Al -> 2 Fe + AlgÛg The reaction is used in therrnite welding, e. g. to join rail tracks, and in demo lition ofmunitions, and occurs, because aluminum forms stronger, more stable, bonds withoxygen than iron. The same reaction applies to other metal powder fuels and other metaloxides, but as aluminum has a high boiling point and a low melting point, so that thereaction can occur mainly in the liquid phase, and both aluminum and red iron(III) oxide are inexpensive, a mixture of aluminum and red iron(III) oxide is preferred.

In a second aspect of the invention, the object stated above is achieved in that thepyrotechnic composition referred to in the second paragraph above includes a metalpowder fuel and a metal oxide serving as an oxidizer, said composition upon ignition undergoing an exotherrnic reduction-oxidation (redox) reaction. Thereby, the unexploded blasting charge Will be disarrned by combustion or decomposition Without any risk of detonation.

Preferably, the pyrotechnic composition includes therrnite. As explained above,therrnite is a pyrotechnic composition of metal powder fuel, eg. aluminum (Al), andmetal oxide, eg. FezOs or Fe3O4. When ignited by heat, therrnite undergoes anexothermic reduction-oxidation (redox) reaction, and the unexploded blasting charge Will be disarrned by combustion or decomposition Without any risk of detonation.

Suitably the metal fiael is selected from the group consisting of aluminum, magnesium,titanium, zinc, silicon, and boron. In principle, any reactive metal could be used insteadof aluminum. This is rarely done, because the properties of aluminum are nearly idealfor this reaction: - It is by far the cheapest of the highly reactive metals. For example, in Dec 2014, tinWas 19,830 USD/metric ton, zinc Was 2,180 USD/ton and aluminum Was 1,910USD/ton.

- It forms a passivation layer making it safer to handle than many other reactivemetals.

- Its relatively low melting point (660 °C) means that it is easy to melt the metal, sothat the reaction can occur mainly in the liquid phase and thus proceeds fairlyquickly.

- Its high boiling point (2519 °C) enables the reaction to reach very hightemperatures, since several processes tend to limit the maximum temperature to justbeloW the boiling point. Such a high boiling point is common among transitionmetals (e.g., iron and copper boil at 2887 °C and 2582 °C respectively), but isespecially unusual among the highly reactive metals (cf. magnesium and sodium,Which boil at 1090 °C and 883 °C respectively).

It is also suitable that the oxidizer is selected from the group consisting of iron (III)oxide, iron (II, III) oxide, manganese (IV) oxide, chromium (III) oxide, silicon (IV)oxide, copper (II) oxide, bismuth (III) oxide, boron (III) oxide, and lead (II, IV) oxide.Similarly, hematite or red iron (III) oxide (FegOg) is most preferred, but magnetite oriron (II, III) oxide (Fe3O4) also Works satisfactorily. Other oxides are occasionally usedfor special purposes but are not preferred in the present application, such as MnOg inmanganese therrnite, CrgOg in chromium therrnite, quartz in silicon therrnite, or copper(II) oxide (CuO) in copper therrnite. In special applications, fluoropolymers may be substituted for the metal oxides, PTFE With magnesium or aluminum being a relatively common example. Fluoropolymer containing pyrotechnic compositions are usuallycalled "pyrolants", but the word "thermite" is used interchangeably with, and more commonly than, "pyrolant".

Even though many different forms of igniting devices may be used to ignite thecomposition, e. g. fuse wire, NONEL, blasting caps, etc. Blasting caps may be preferredin many situations. The blasting cap may be a non-electric cap or a fuse cap. In mostsituations it preferably is an electric cap, e. g. an electrically triggered detonator, i.e.containing an easy-to-ignite primary eXplosive that provides the initial activation energyto start the detonation in the main charge. Preferably the igniting device is storedseparately and not inserted into the main explo sive charge until just before use, keeping the main charge safe.

BRIEF DESCRIPTION OF THE DRAWINGSIn the following, a preferred embodiment of the invention will be described in more detail with reference to preferred embodiments and the appended drawings.

Fig. 1 shows a preferred embodiment of a cartridge in a cross sectional side view, suitable for disarrning an unexploded blasting cartridge according to the invention, Fig. 2 shows, at a larger scale, a preferred embodiment of an insert unit, which in Fig. 1 is shown inserted in the upper end of the cartridge, and Fig. 3 is longitudinal cross section through the primed cartridge of Fig. 1 and 2 inserted in a drill hole, where there is an unexploded blasting charge.

MODE(S) FOR CARRYING OUT THE INVENTION In figs. 1 and 2 there are shown a preferred embodiment of a cartridge suitable fordisarrning an unexploded blasting cartridge according to the invention. As is evident forthe skilled person various designs of blasting devices 10, e.g. blasting caps may be used to fulf1ll the object of the invention.

In the following the invention will be described in more detail by referring to saidpreferred cartridge 1. The cartridge 1 may be seen to comprise basically two parts; anouter plastic sleeve 2 and an insert unit 25, which in tum comprises a plug 4 and an inner sleeve 7.

The plug 4 and the inner sleeve 7 may, according to a preferred embodiment, be madeof an acetal plastic material, more specif1cally of an acetal (POM) copolymer and are molded j ointly to forrn an integrated unit.

The outer sleeve 2 may preferably be made of so called ABS plastic and has the shapeof an elongated circular-cylindrical tube, preferably with a flat end wall 3. The interiorof the outer sleeve 2 forms a main chamber 5 which is filled with a non-explodingpyrotechnic composition charge 6. The plug 4 has a circular-cylindrical outer wall l9, apreferably flat, annular end wall 20, which faces the main chamber 6 and appliedagainst the powder charge 6, and a tubular portion 2l, which def1nes a through hole 8that is coaxial with the outer sleeve 2. Radial supporting beams 24 may be arranged toimprove strength, preferably extending between the tubular portion 2l and thecylindrical wall. Wedge-shaped, material saving recesses 23 are preferably arranged between the beams 24. An upper flange is designated 22.

The inner sleeve 7, which is coaxial with the outer sleeve 2, extends from the end wall20 of the plug 4 into the non-exploding pyrotechnic composition charge 6 in the outersleeve to a suff1cient depth in the non-exploding pyrotechnic composition charge 6 as isillustrated in Fig. 3. The inner sleeve 7 preferably has a very thin wall l3. It mayoptionally be provided with longitudinal, extemal stiffening protrusions l4 in order toincrease its strength. Its cylindrical inside surface is preferably completely smooth. Itsnose portion l2 may be tapered. More specif1cally, the nose portion l2 is preferably tapered at an acute angle according to the disclosed embodiment.

The plug 4 is pressed into the mouth section of the outer sleeve 2 so far that the flange22 abuts the upper edge of the outer sleeve 2 and the end wall 20 of the plug with somepressure contacts the pyrotechnic composition charge 6. When entering the insert unit25, the inner sleeve 7 will be pressed into the non-exploding pyrotechnic compositioncharge 6, which is facilitated by its pointed nose portion l2. The amount of powder ofthe non-exploding pyrotechnic composition charge 6 is adapted to the space which shallaccommodate the powder, e.g. such that the non-exploding pyrotechnic compositioncharge 6 will be compacted to some degree, which may be advantageous because thatprevents the powder from moving to any essential degree during transportation, and italso guarantees a good contact between the outer surface of the inner sleeve 7 and thepowder. On the other hand, the pressure exerted by the insert unit 25 may not beexaggerated such that the thin wall l3 of the inner sleeve 7 is damaged or pressed together to any significant degree.

In the thus assembled cartridge 1, the interior inner sleeVe forrns a direct continuation ofthe through hole 8 in the plug 4 and it also has the same cross section shape and area asthe hole 8. This means that the hole 8 and the space in the inner sleeVe 7 in combinationform an integrated chamber, denominated priming chamber 9. In the priming chamber9, that section of the priming chamber which is defined by the inner sleeVe 7 is referred to as igniting chamber 11 in this context.

When priming the cartridge 1, which is carried out on the blasting site, a blasting cap 10may be entered into the priming chamber 9. The blasting cap 10 may contain an ignitingcharge which can be ignited electrically, for example, and if desired also a delayelement, all of which may be enclosed in a cylindrical capsule 15, e. g. of aluminum.When the blasting cap 10 is an electric one, it has two fuse wire leads 17, 18 (Fig. 3).Their outer ends are to be connected to an apparatus generally called a blasting machine26. When the cartridge 1 is primed, it is inserted in a drill hole 100 in a surface ofexposed rock 102 until it makes contact with the unexploded blasting charge 101 asshown in Fig. 3. The inner ends of the fuse wire leads 17, 18 are connected to each otherby a thin bridge wire in direct contact with the igniting charge. When the blasting cap 10 is entered into the priming chamber 9, Fig. 3, at least that part of the capsule 15which contains the igniting charge is in direct contact with the inside surface of theinner sleeVe 7 in the igniting chamber 11. When the igniting charge is ignited by anelectric spark, it develops such a high pressure and such a violent flame of fire that thethin-walled inner sleeve 7 will be tom to pieces and the non-exploding pyrotechniccomposition charge 6 will be ignited and start buming at suff1ciently high temperatureto bum away the unexploded blasting charge 101.

The non-exploding pyrotechnic composition 6 includes a metal powder fuel and a metaloxide serVing as an oxidizer. Upon ignition, the composition undergoes an exotherrnicreduction-oxidation (redox) reaction producing a suff1ciently high temperature.Thereby, the unexploded blasting charge 101 will be disarrned by combustion ordecomposition without any risk of detonation.

Preferably, the non-exploding pyrotechnic composition 6 includes therrnite. Asexplained above, therrnite is a pyrotechnic composition of metal powder fuel, e.g.aluminum (Al), and metal oxide, e.g. FezOs or Fe3O4. When ignited by heat, therrnite undergoes an exotherrnic reduction-oxidation (redox) reaction, and the unexploded blasting charge will be disarrned by combustion or decomposition without any risk of detonation.

Although the reactants are stable at room temperature, they burn with an extremelyintense exotherrnic reaction when they are heated to ignition temperature. The productsemerge as liquids due to the high temperatures reached (up to 2500 °C with iron(III)oxide) - although the actual temperature reached depends on how quickly heat canescape to the surrounding environment. Therrnite contains its own supply of oxygen anddoes not require any extemal source of air. Consequently, it cannot be smothered andmay ignite in any environment, given suff1cient initial heat. It will bum well while wetand cannot be easily extinguished with water, although enough water will remove heatand may stop the reaction. Small amounts of water will boil before reaching thereaction. Even so, therrnite is used for welding underwater. Consequently, even if theunexploded blasting charge 101 in a drill hole 100 is covered by rainwater, for example,the cartridge 1 of the present invention can be used to bum away the unexploded blasting charge 101.

The therrnites 6 are characterized by almost complete absence of gas production duringbuming, high reaction temperature, and production of mo lten slag. The fuel should havehigh heat of combustion and produce oxides with low melting point and high boilingpoint. The oxidizer should contain at least 25% oxygen, have high density, low heat offormation, and produce metal with low melting and high boiling point (so the energyreleased is not consumed in evaporation of reaction products). Organic binders can beadded to the composition to improve its mechanical properties, however they tend toproduce endotherrnic decomposition products, causing some loss of reaction heat and production of gases.

Suitably the metal fi1el is selected from the group consisting of aluminum, magnesium,titanium, zinc, silicon, and boron. In principle, any reactive metal could be used insteadof aluminum. This is rarely done, because the properties of aluminum are nearly idealfor this reaction: - It is by far the cheapest of the highly reactive metals. For example, in Dec 2014, tinwas 19,830 USD/metric ton, zinc was 2,180 USD/ton and aluminum was 1,910USD/ton.

- It forms a passivation layer making it safer to handle than many other reactive metals.

- Its relatively low melting point (660 °C) means that it is easy to melt the metal, sothat the reaction can occur mainly in the liquid phase and thus proceeds fairlyquickly.

- Its high boiling point (2519 °C) enables the reaction to reach very hightemperatures, since several processes tend to limit the maximum temperature to justbelow the boiling point. Such a high boiling point is common among transitionmetals (e.g., iron and copper boil at 2887 °C and 2582 °C respectively), but isespecially unusual among the highly reactive metals (cf. magnesium and sodium,which boil at 1090 °C and 883 °C respectively).

It is also suitable that the oxidizer is selected from the group consisting of iron (III)oxide, iron (II, III) oxide, manganese (IV) oxide, chromium (III) oxide, silicon (IV)oxide, copper (II) oxide, bismuth (III) oxide, boron (III) oxide, and lead (II, IV) oxide.Similarly, hematite or red iron (III) oxide (FegOg) is most preferred, but magnetite oriron (II, III) oxide (Fe3O4) also works satisfactorily. Other oxides are occasionally usedfor special purposes but are not preferred in the present application, such as MnOg inmanganese therrnite, CrgOg in chromium therrnite, quartz in silicon therrnite, or copper(II) oxide (CuO) in copper therrnite. In special applications, fluoropolymers may besubstituted for the metal oxides, PTFE with magnesium or aluminum being a relativelycommon example. Fluoropolymer containing pyrotechnic compositions are usuallycalled "pyrolants", but the word "thermite" is used interchangeably with, and more commonly than, "pyrolant".

The temperature achieved during the reaction is dependent on the availability ofoxygen. For example, the type of metal oxide has dramatic influence to the amount ofenergy produced; the higher the oxide, the higher the amount of energy produced. Agood example is the difference between manganese (IV) oxide (MnOz) and manganese(II) oxide (MnO), where the former produces a very high temperature and the latter isbarely able to sustain combustion; to achieve good results a mixture with proper ratio ofboth oxides should be used.

The reaction rate can be also tuned with particle sizes; coarser particles bum slower thanf1ner particles. The effect is more pronounced with the particles requiring being heatedto higher temperature to start reacting. This effect is pushed to the extreme with nano- therrnites.

Even though ignition device 10 may be of various kinds a conventional blasting capmay be preferred. The blasting cap 10 may be a non-electric cap or a fuse cap, itpreferably is an electric cap, more precisely an electrically triggered detonator. Ablasting cap contains an easy-to-ignite primary eXplosive that provides the initialactivation energy to start the detonation in the main charge. Explosives commonly usedin blasting caps include mercury (II) fialminate (Hg(CNO)2), lead azide (Pb(N3)2), leadstyphnate (lead 2,4,6-trinitroresorcinate CóHNsOsPb) and tetryl (2,4,6-tri11itrophenylmethylnitramine C7H5N5Og) and DDNP (diazodinitrophenol C6H2N4O5).

The cartridge 1 of the invention may advantageously be manufactured in a number ofdifferent standard lengths, corresponding to diameters and lengths of the blastingcharges. Dynamite is usually sold in the form of cardboard cylinders about 20 cm (8 in)long and about 3.2 cm (1 .25 in) in diameter, With a Weight of about 190 grams (1/2 troypound). A stick of dynamite thus produced contains roughly 1 MJ of energy. Other sizes also exist.

INDUSTRIAL APPLICABILITYThe method of and a cartridge of the present invention are applicable for disarrning anunexploded blasting charge in a drill hole by buming away the charge.

Claims (11)

1. A method of disarrning an unexploded blasting charge (101) in a drill hole (100), comprising: - providing a non-exploding cartridge (1) containing - a pyrotechnic composition (6) able to generate a high temperature fire, and - a blasting device (10) for igniting the pyrotechnic composition (6); and - introducing the non-exploding cartridge (1) into a drill hole (100) containingsaid unexploded blasting charge (101), - igniting the pyrotechnic composition (6) in the non-exploding cartridge (1) toburn away the blasting charge (101).

2. A method as claimed in claim 1, wherein the pyrotechnic composition (6) contains acomposition that will generate a temperature within the range of 600C° to 5000C°,preferably 700-2500C°. .

3. A method as claimed in claim 2, wherein the pyrotechnic composition (6) contains therrnite .

4. A method as claimed in any of claims 1-3, wherein said non-exploding cartridge (1)is produced by using an on the market existing non-exploding cartridge device (1)and f1lling said non-exploding cartridge device (1) with said pyrotechnic composition (6). .

5. A cartridge for disarrning an unexploded blasting charge (101) in a drill hole (100), comprising: - a substantially cylindrical outer sleeve (2) with an end wall in a first end (3); - a plug (4) which, enclosing said outer sleeve, is inserted into and secured in anopposite second end of the outer sleeve (2); - a main chamber (5) in the outer sleeve (2) between said end wall (3) and saidplug (4), which main chamber (5) is filled with a pyrotechnic composition (6), - an opening (8) in one of said plug (4) and/or end wall (3) for receiving anigniting device (10) including an igniting charge arranged to ignite saidpyrotechnic composition (6), - said pyrotechnic composition (6) including a metal powder fuel and a metaloxide serving as an oxidizer, said composition upon ignition undergoing anexothermic reduction-oxidation (redox) reaction arranged to bum away saidblasting charge (101). 12

6. A cartridge as claimed in claim 5, further comprising, - a substantially cylindrical inner sleeve (7), Which is coaxial With the outer sleeve(2), and connected to said plug (4), and extending into the pyrotechniccomposition (6) in the main Chamber (5); - a central through hole (8) in said plug (4), Which communicates With the innersleeve (7) that is closed at its inner end, Which plug (4) is inserted into thepyrotechnic composition (6); - the inner sleeve (7) and the hole (8) in the plug (4) in combination forming apriming chamber (9) for receiving said igniting device (10) including an ignitingcharge, said priming chamber (9) having a shape corresponding to an outershape of the blasting cap (10).

7. A cartridge as claimed in claim 6, further comprising,- said inner sleeve (7) having an inner Wall (13) arranged to be penetrated by theflame of fire that is formed When the igniting charge of the blasting cap (10) isignited, thereby igniting the pyrotechnic composition (6);

8. A cartridge as claimed in any of claims 5-7, Wherein the pyrotechnic composition(6) includes therrnite.

9. A cartridge as claimed in any of claims 5-8, Wherein the metal fiael is selected from the group consisting of aluminum, magnesium, titanium, zinc, silicon, and boron.

10. A cartridge as claimed in any one of any of claims 5-9, Wherein the oxidizer isselected from the group consisting of iron (III) oxide, iron (II, III) oxide, manganese(IV) oxide, chromium (III) oxide, silicon (IV) oxide, copper (II) oxide, bismuth (III)oxide, boron (III) oxide, and lead (II, IV) oxide.

11. A cartridge as claimed in any one of claims 5-10, Wherein the igniting device is a blasting cap (10), preferably an electrically triggered blasting cap (10).