A blasting cartridge usually comprises a blasting agent such as an emulsion explosives composition contained within a tubular plastics sleeve.

The sleeve is gathered and closed at either end with a metal or plastics clip or a knot to form a sausage-shaped cartridge. The metal or plastics clip or knot is needed to prevent the blasting agent from flowing out of the cartridge. These cartridges are packed into boxes for transportation and, in use, are conveniently loaded into bore holes with a tamping rod.

A problem experienced with blasting cartridges is that the mechanical closing of the ends of the cartridges, by clips and knotting is time consuming and requires special machinery. Furthermore, when clips are used, the clips often cause jams in the machinery, which results in wasted production time and blasting agent. Secondly, when cartridges are loaded into a bore hole, the clips or knotted ends of adjacent cartridges cause gaps between the cartridges which may lead to"decoupling"between adjacent cartridges in a bore hole. This decoupling between cartridges retards the propagation of an explosives reaction between cartridges within a borehole, on detonation.

It is an object of this invention to address these problems.

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a blasting cartridge comprising: a plastics sleeve having a first end and second end, with at least one of the ends being only crimped, preferably open; and blasting agent contained within the sleeve, wherein the blasting agent is sufficiently viscous to remain within the sleeve during normal packaging and transport without exuding from the crimped or open end or ends.

The blasting agent may be a slurry, water gel or emulsion explosives composition.

Preferably, the composition includes a rheology modifier to increase the viscosity thereof.

The rheology modifier may be a polymer or waxes.

Preferably, the polymer is formed by the reaction of a polymerizable compound and a crosslinking agent, during the preparation of the explosives composition.

Advantageously, the composition has the consistency of dough, preferably spongy rubber.

Typically, the composition is an emulsion explosives composition.

The sleeve is usually formed from at least one plastics film.

According to a second aspect of the invention there is provided a method of producing blasting cartridges containing an emulsion explosives composition, the method including the steps of: a) providing a fuel phase containing a fuel oil and an emulsifying agent; b) providing an aqueous phase containing oxidising salts ; c) mixing the fuel phase and the aqueous phase to provide an emulsion; d) pumping the emulsion into a plastics sleeve ; and e) only crimping and cutting the plastics sleeve to form blasting cartridges having the desired length.

According to a preferred embodiment of the invention, the ends of the cartridges are not crimped and are left open after cutting.

Preferably, a rheology modifier is added to the fuel phase of a composition to ensure that the composition within the sleeve, after the cutting step 5, is sufficiently viscous to remain within the sleeve during normal packaging and transport without exuding from the crimped or open ends thereof.

Advantageously, the rheology modifier is a polymer.

Typically, a polymerizable compound and cross-linking agent is added to the fuel phase at step 1 to form the polymer.

Preferably, a portion of the cross-linking agent is added to the fuel phase at step a, and the rest of the cross-linking agent is added to the emulsion formed at step c.

Conveniently, 50% of the cross-linking agent is added to the fuel phase at step a, and the rest of the cross-linking agent is added to the emulsion formed at step c. The cross-linking agent is typically a di-isocyanate such as diphenyl methane isocyanate.

The polymerizable compound is preferably a compound that has hydroxyl functional groups that are cross-linked by the di-isocyanate cross-linking agent.

The preferred polymerizable compound is a fat or fatty oil, particularly a vegetable oil such as castor oil.

The emulsifying agent may be sorbitan mono oleate, but is preferably a combination of sorbitan mono oleate and poly isobutyl succinic anhydride.

According to a third aspect of the invention, there is provided an emulsion explosives composition containing a fuel phase, an aqueous phase, an emulsifying agent, a cross-linking agent and a polymerizable compound, wherein the polymerizable compound has hydroxyl functional groups, such as a fatty oil or fat, for example a vegetable oil such as castor oil.

Preferably, the fuel phase is made up of the following ingredients: Fuel oil 19-60% Vegetable oil, such as Castor oil 9-54% Emulsifying agent 20-45% Di-isocyanate cross-linking agent 5-20%, by weight of the fuel phase.

Advantageously, the fuel phase is made up of the following ingredients: Fuel oil 35-45% Vegetable oil, such as Castor oil 18-24% Emulsifying agent 26-32% Di-isocyanate cross-linking agent 10-14%, by weight of the fuel phase.

Preferably the di-isocyanate cross-linking agent is crude di-phenyl methane isocyanate.

The emulsifying agent may be sorbitan mono oleate, but is preferably a combination of sorbitan mono oleate and poly isobutyl succinic anhydride.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a flow diagram of a process for producing blasting cartridges according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS A blasting cartridge according to the invention comprises a tubular sleeve of plastics film containing a blasting agent. The ends of the sleeve are only crimped, i. e. they are not closed with a clip or by knotting. In a preferred embodiment the ends of the sleeve are left open, i. e. they are not even crimped.

The plastics film may be a single a sheet of high density polyethylene having a thickness of about 100 microns (0. or it may be laminated (for example, a trilaminate of polyethylene or polyethylene terephthalate films). The cartridge will usually have a diameter of 25 to 50mm and a length of 30cm.

The rheology of the blasting agent is modified so that it is sufficiently viscous to be contained within the sleeve (ie. it does not exude from the crimped or open ends of the sleeve) during normal packaging and transport so that the ends thereof do not need to be closed by way of clipping or knotting.

The blasting agent may be a slurry, water gel or emulsion explosives composition, with the rheology thereof adjusted to provide the required viscosity.

A typical water gel formulation would comprise ammonium nitrate, sodium nitrate, ethylene glycol, thickeners, a sensitizer such as monomethyl ammonium nitrate, aluminium, sulphur, a density agent, and if required an emulsifier and oil or wax. The viscosity of such compositions may be increased by hydrating the composition with a hydrating polymer thickener. A cross-linking agent could also be used to further increase the viscosity of the composition.

In a preferred embodiment, an emulsion explosives composition with the required viscosity comprises an aqueous phase containing oxidizer salts and a fuel phase containing a fuel oil, an emulsifier, a polymerizable compound and cross-linking agent (optionally a catalyst) and/or waxes.

Generally speaking, the ratio of fuel phase to aqueous phase in an emulsion explosives composition is 10: 90 to 6: 94, by weight of the composition.

The oxidizer in the aqueous phase is typically a nitrate salt, such as ammonium nitrate.

The fuel oil will usually comprise 19% to 60%, typically 35% to 45%, by weight of the fuel phase. Any oil that will act as a fuel in an explosives reaction may be used as the fuel oil, the main requirement is it is compatible with the cross-linking agent employed.

A preferred cross-linking agent is a modified di-isocyanate (MDI) such as diphenylmethane isocyanate. Generally, the cross-linking agent comprises WO 01/23326 PCT/IBOO/01379 5% to 20% (typically 10% to 14%) by weight of the fuel phase. The MDI reacts with functional groups of the polymerizable compound in the fuel phase, to form a cross-linked matrix between the functional groups of the polymerizable compound and the MDI, with the aqueous phase with the droplets of the aqueous phase acting as inclusion bodies.

The polymerizable compound may be any agent that is polymerized with a cross-linking agent, to increase the viscosity of the composition. The polymerizable compound may comprise from 9% to 54% (typically 18% to 24%) by weight of the fuel phase, depending on the polymerizable compound used. Suitable polymerizable compounds are compounds having the following functional groups that may be cross-linked by an iso- cyanate cross-linking agent: hydroxyl, amine, urethan, disubstituted urea, carboxyl, sulfhydryl, imino, substituted amino, carbonamide, substituted carbonamide, sulfonamide, substituted sulfonamide, thioamide and sulferic groups.

According to a preferred embodiment of the invention the polymerizable compound is one having hydroxyl groups, such as a fatty oil or fat which has consituents having hydroxyl groups on their hydrocarbon backbone.

Other preferred compounds are propylene glycol and hydroxy-terminated polybutadiene (HTBP).

Especially preferred fatty oils are vegetable oils such as castor oil. Castor oil has the required hydroxyl groups which react with the cross-linking agent and is readily available and relatively inexpensive.

The emulsifier comprises 20% to 45% by weight of the fuel phase. The emulsifier may be selected from compounds such as SMO (Sorbitan Mono oleate), PIBSA (Poly Isobutyl Succinic Anhydride), SSO (orbital Sesqui Oleate), glycerine etc. The emulsifier used depends on the fuel oil that is used and the polymerizable compound that is used. The preferred emulsifier is a combination of SMO and PIBSA. It has been found that the use of SMO only results in a product that absorbs water. The combination of SMO and PIBSA results in a product that absorbs less water and has the required consistency. The emulsifier may comprise SMO and PIBSA in a ratio, by weight, of from 1: 1 to 9: 1, preferably about 9: 1.

Sensitizers such as microballoons or microspheres, polystyrene beads, gas bubbles or perlite may also be added to the composition to increase the sensitivity of the composition.

In addition, substances such as porous ammonium nitrate or ANFO or aluminium flakes, granules or powder may also be added to the composition to improve the"energy"of the explosives reaction.

The required viscosity may be attained by making various combinations of the above substances to produce a product that may range from a maleable to a hard product.

According to an especially preferred embodiment of the invention the blasting agent has the consistency of dough, preferably the consistency of spongy rubber. A blasting agent having the consistency of spongy rubber, when pressed with a finger, is deformed, but returns to its original shape after the pressure is removed. Usually it will take 10 to 30 seconds for the composition to return to the original shape. The consistency of spongy rubber is preferred because the cartridge can be dropped or even trodden on without breaking. Even after it has been deformed, e. g. when it is trodden on it returns to its original shape. It is also convenient to load cartridges of this viscosity into a borehole.

An emulsion explosives composition having the preferred consistency of dough or spongy rubber is produced by using the following materials and method: Materials : The ratio of the fuel phase to the aqueous phase may range from 10: 90 to 5: 95.

The fuel phase is made up of the following ingredients: fuel oil (a base mineral oil eg. GTM8) 19-60% polymerizable compound (eg. castor oil) 9-54% emulsifier (eg. SMO and PIBSA) 20-45% polyurethane cross-linker (eg. MDI) 5-20% optionally a catalyst 0.5% The aqueous phase is made up of the following ingredients: Ammonium nitrate 77-85% Urea 0-7% Sodium nitrate 10-20% The MDI used is a crude MDI which is branched. This crude MDI has been found to be advantageous over the linear form in that it is less moisture and light sensitive and easier to work with. It also reacts better with the hydroxyl groups on the castor oil to provide a 3-Dimensional cross-linked system. It has more branching points to give a better cross-linked matrix.

The ratio of the aqueous phase to fuel phase is 94% to 6% by weight of the composition.

Method Referring to the drawing, a fuel phase 10 is made by mixing the fuel oil, the polymerization agent (castor oil) and the emulsifier (SMO and PIBSA) in a mixer. WO 01/23326 PCT/IBOO/01379 The fuel phase 10 is then passed through a pipe 12 to a static mixer 14.

Before the fuel 10 reaches the static mixer 14, a cross-linking agent (MDI) 16 is added by through a metered pumping system. The cross-linking agent may be mixed into the fuel phase in the static mixer 14, by shearing.

Preferably, only half of the cross-linking agent is mixed into the fuel phase at this stage.

An aqueous phase 18 is made by dissolving ammonium nitrate, urea, and sodium nitrate into water which is heated to 60-110°C to form a super- saturated aqueous phase.

The fuel phase 10 containing cross-linking agent is heated to a temperature of 30-40°C and mixed together with the aqueous phase 18 in a mixer 20 by shearing to form an emulsion. The rest of the cross-linking agent is then added to the emulsion. The addition of the cross-linking agent in two batches slows down the curing process to ensure that the emulsion has a low enough viscosity to be pumped and cartridged. At this stage, the emulsion is at a temperature of about 95°C. The apparatus used in the invention is heated by steam tracing in a water jacket at a temperature of about 95°C to keep the emulsion at a high temperature, until it reaches cartridging apparatus 22.

The emulsion leaves the mixer 20 via a pipe 24 and a gassing agent 26, which in this case is an aqueous or emulsified sodium nitrite is then added by a metered pumping system, whereafter the emulsion enters a static mixer 28. This results in a chemical reaction which releases nitrogen bubbles into the emulsion, which serve to sensitize the product.

The emulsion is then pumped into a sleeve of cartridging material at the cartridging apparatus 22. As mentioned in the first paragraph of this specification, the sleeve of cartridging material may be a single sheet or laminated sheet of plastics material. The emulsion is fed through the cartridging apparatus at a temperature of 95°C and at a speed of 30 to 90m per minute.

If a single film of cartridging material is used, the sleeve, filled with the emulsion is sprayed briefly with cold water to reduce the temperature of the film so that the film does not stretch due to the high temperature of the emulsion. If a trilaminate film is used, this brief cooling step is not necessary.

In prior art processes, filled cartridges are cooled (for example in a cooling bath) shortly after leaving the cartridging apparatus. According to the invention, other than brief cooling for the single sheet product with a spray of water, the product is not cooled immediately, but is allowed to cool slowly at ambient temperature, or in a water bath 30 (which may be insulated or even heated) for a period of 5 to 10 minutes. This is to allow the emulsion to cure into a sufficiently viscous state for the cartridged emulsion to be cut into cartridges 32, without the emulsion exuding from the open-ends of the cartridges after cutting. Alternatively, cartridges may be formed by forming pairs of crimps and cutting between the crimps to form cartridges with crimped ends, with the emulsion being sufficiently viscous not to exude from the crimped ends which are not closed with clips.

To further facilitate the curing process, a catalyst may be added to the composition. The catalyst is added to the fuel 10 and comprises about 0.5% by weight of the fuel. Typical catalysts may include dibutylin dilaureate, stannous octate, or Thorcat 5350 which is a mercury based catalyst including a Phenyl Mercury Ester and C, o monocarboxylic acid, available from Thor Chemicals in South Africa. The Thorcat 535 catalyst has been found to be very effective as it promotes the desired polyol reaction and promotes rapid and good crosslinking. The addition of the catalyst will cut down the curing time, prior to cutting, from 10 to 5 minutes but the whole process from the preparation of the fuel to cartridging will have to be very fast (eg. under 3 minutes) to ensure that the emulsion is cartridged before the viscosity thereof increases to too great an extent and it can no longer pass through the pipes of the apparatus.

After cutting, the cartridges are allowed to cure for another 10 to 20 minutes before being packed into boxes. Typically, the cartridges are packed into a cardboard box 34 with a plastic liner. The cardboard box has a length (1) of 590mm, a width (w) of 270mm, a height (h) of 210mm and contains 166 cartridges (length of 270mm and diameter of 25mm). The total weight of the box 34 containing the 166 cartridges is approximately 25kgs and the emulsion is sufficiently viscous for it to remain within the sleeve (even in the cartridges at the bottom of box), during normal transport to a blasting site.

The advantages of the blasting cartridge according to the invention is that the ends thereof do not need to be sealed by clipping or knotting and this speeds up the process. There is less down-time as there are fewer jams and stoppages as there are no clips and the process is more cost effective.

In the case of open-ended cartridges, in use, the ends of adjacent cartridges in a borehole are contiguous and are not separated by clips or plastics material and there is better coupling of the charges and thus propagation of explosion when the explosives reaction is initiated.

Examples A-F The tables below set out the constituents of the fuel phase for compositions according to the invention. The aqueous phase is an oxidiser phase having the following constituents, by weight: Ammonium nitrate 73.30% Sodium nitrate 14.00% Urea 4.50% Thiourea 0.05% Water 8.15% Table 1-Fuel phase formulations for a 94: 6 type emulsion. Raw % in % in total % in fuel % in total % in % in total material fuel formulation phase formulation fuel formulation phase phase A A B B C C Castor oil 20.35 GTM8 38. 67 2. 32 42. 00 2. 52 42. 00 2. 52 MD@ 12.50 0.75 12.50 0.75 12.5 0.75 SMO 28. 00 1. 68 20. 67 1. 24 11. 50 0. 69 PIBSA 0 0 2. 33 0. 14 11. 50 0. 69 Table 2-Fuel phase formulations for a 92: 8 type formulation Raw % in % in total % in % in total % in % in total material fuel formulation fuel formulation fuel formulation phase phase phase D D E E F F Castor oil 20.81 GTM8 38. 62 3. 09 41. 88 3. 35 41. 88 3. 35 MDI 12.0 SMO 28. 00 2. 24 20. 75 1. 66 11. 50 0. PIBSA 0 0 2. 25 0. 18 11. 50 0. 92 GTM8 is a base mineral oil that may be obtained from Castrol SA in South Africa under the trade name Magna LF.

Emulsion compositions made from formulations A, B, D and E have the preferred spongy rubber consistency, while emulsion compositions made from formulations C and F have the consistency of dough. Emulsion compositions made from formulations A, B, D and E may be used with crimped or open-ended cartridges, while emulsion compositions made from formulations C and F are best used with crimped cartridges.

After mixing with the fuel phase to form an emulsion, the emulsion has a low enough viscosity to be poured into a plastics sleeve. The sleeve may be cut or crimped and cut 10 minutes later and cures to the required consistency for packaging and transport 30 minutes later.

Example G This example gives the detailed steps for the production of a 500 g sample of Formulation B above.

1. Preparation of oxidiser phase: 1.1 Prepare 90% ammonium nitrate solution by dissolving 345g of analytically or chemically pure ammonium nitrate in 38 grams of water and heating to 110 °C in a suitable container using a hot plate.

1.2 Add 66g sodium nitrate and 21 g urea to the ammonium nitrate solution and allow to dissolve.

1.3 Adjust temperature of this solution to 110°C.

1.4 Adjust fudge point of the solution until it is in the range 84 to 86°C by adding or boiling off water if necessary.

1.5 Check the solution pH and adjust to between 4.6 and 4.9 by adding Nitric acid or caustic soda as required.

2. Preparation of fuel phase 2.1 Weigh out 6.7g castor oil, 12.6g GTM8,6.2 g SMO and 0.7g PIBSA and mix in a suitable container.

2.3 Heat this mixture to 40 °C in an oven 3. Preparation of emulsion 3.1 Add 1. 9g of MDI to the fuel.

3.2 Mix the fuel phase for 10 seconds by agitation using a suitable high speed mixer or shearing device such as for example a bar mixer.

3.3 While continuing to agitate the fuel phase add the oxidiser phase to fuel phase over a period of one minute allowing an emulsion to form 3.4 Continue to agitate the emulsion formed for a period of 20 seconds 3.5 Add 1.9 g MDI and 1g of a 25% concentration sodium nitrite solution to the emulsion and mix in by stirring the mixture by hand for 10 seconds.

3.6 Pour the emulsion formed into a suitable plastic sleeve and allow emulsion to cure.

3.7 Product may be cut with a knife into a shorter sleeve after 10 minutes.

3.8 Product may be packaged into a box or cardboard carton after 30 minutes.

3.9 The consistency of this product is that of a resilient sponge, i. e. that of spongy rubber.