GB2192627A

GB2192627A - Explosive

Info

Publication number: GB2192627A
Application number: GB08713944A
Authority: GB
Inventors: Neil William Munro
Original assignee: AECI Ltd
Current assignee: AECI Ltd
Priority date: 1986-07-14
Filing date: 1987-06-15
Publication date: 1988-01-20
Also published as: GB8713944D0; NO872905L; GB2192627B; AU597680B2; NO872905D0; AU7506487A; MW4987A1; BR8703586A; CA1298973C

Abstract

The invention provides an ammonium nitrate/fuel oil (ANFO-type) explosive in which the ammonium nitrate comprises ammonium nitrate prills and ammonium nitrate powder. The prills form at least 30% by mass of the ammonium nitrate, the powder forms at least 20% by mass of the ammonium nitrate, and the average particle size of the prills is at least 5 times greater than the average particle size of the powder.

Description

SPECIFICATION Explosive This invention relates to an ammonium nitrate/fuel oil explosive, ie a so-called ANFO-type explosive.

According to the invention there is provided an ammonium nitrate/fuel oil explosive which comprises particulate ammonium nitrate and a liquid hydrocarbon fuel, the ammonium nitrate comprising ammonium nitrate prills and ammonium nitrate powder, the prills forming at least 30% by mass of the ammonium nitrate, the powder forming at least 20% by mass of the ammonium nitrate and the prills having an average particle size which is at least 5 times greater than the average particle size of the powder.

The average particle size of the prills may be 5-15 times greater than the average particle size of the powder, the major proportion by mass of the prills having a particle size in the range 1,0-2,8 mm, the major proportion by mass of the powder having a particle size in the range 0,1-0,35 mm, the prills preferably forming at least 50% by mass of the ammonium nitrate and the powder preferably forming at least 30% by mass of the ammonium nitrate.

The prills are thus substantially larger than the particles of the powder which acts at least partially to fill the voids between the prills. Ideally, the proportion of powder present is sufficient substantially to fill the voids between the prills, without any excess powder. This has been found, depending on the average particle size and particle size distribution of the prills and powder, typically to occur with the proportions by mass of the prills and powder in the ranges specified above, eg for prills whose major proportion is in the size range 1,0-2,8 mm and powder particles whose major proportion is in the size range 0,1-0,35 mm, a prill:powder mass ratio of 6:4 has been found to be suitable.

The hydrocarbon fuel may be any suitable fuel of the type conventionally or usually employed for ANPO-type explosives, and may be present in the usual proportions. Thus, the hydrocarbon fuel may be a hydrocarbon oil such as diesel oil, forming 2-6% by mass of the explosive.

The explosive may contain a substance which swells on contact with water, ie a so-called water-swellable or water-blocking agent. This substance may form from 1-5% by mass of the explosive and is optionally a member of the group consisting of guar gum, locust bean gum, carboxymethyl cellulose and mixtures thereof. An effective amount of this substance will typically be used, and although it may be present as less than 1% by mass or more than 5% by mass of the explosive, it will usually form 1-3% by mass thereof.

The explosive may further contain a water-repellant substance. The water-repellant substance may form 1-4% by mass of the explosive and is optionally a member of the group consisting of calcium stearate, magnesium stearate, polyvinyl chloride and mixtures thereof. Once again an effective amount of this substance will typically be used, and although it may be present as less than 1% by mass or more than 4% by mass of the explosive, it will usually form 1-3% by mass thereof.

The prills may be porous, with the particles of the powder being solidor porous, ie the prills may be so-called porous prills, with the powder particles being non-porous, eg dense ammonium nitrate fines, or porous, eg milled porous ammonium nitrate prills.

Without being bound by theory, the Applicant believes that the particles of the powder act at least partially to fill the voids between the prills in the explosive, thereby resisting the ingress of water between the prills when the explosive is exposed to water, and acting to improve the water-resistance of the explosive when compared eg with an explosive which has only prills and no powder, and resisting degradation of the explosive on contact with water.

To formulate the explosive, the ammonium nitrate (prills and powder) are preferably mixed together to form a homogeneous mixture, followed by the hydrocarbon fuei, which is admixed into the ammonium nitrate. The other constituents may then be admixed therein. Instead, all the constituents may be added together simultaneously and mixed until homogeneous.

The explosive will in use be loaded into boreholes, and detonated, eg by means of a suitable booster. in use, the explosive can, within limits, be exposed to water, and can be loaded into a wet borehole provided the borehole has been de-watered, preferably immediately before loading, the explosive then resisting the entry of further water into the borehole to at least a limited degree.

The invention will now be described, by way of illustration, with reference to the following non-limiting Example: EXAMPLE A homogeneous mixture was prepared of porous ammonium nitrate prills and solid ammonium nitrate powder, the mass ratio of prills to powder being 60:40 and the prills and powder having the following particle size distributions: Prills % by mass retained on a screen having 2,8 mm openings: 2% % by mass passing through a screen having 1,0 mm openings: 10% % by mass passing through a screen having 0,71 mm openings: 1% Powder % by mass retained on a screen having 380 micron openings: 5% % by mass retained on a screen having 180 micron openings: 40-70% % by mass passing through a screen having 105 micron openings: 20% Diesel oil (fuel) was then admixed into the mixture of prills and powder until homogeneous, and into this ANFO mixture were then admixed a guar gum water-blocking agent and calcium stearate water-repellant substance, until homogeneous.

The proportions of constituents were as follows: Constituent % by mass Ammonium Nitrate (prills:powder 60:40) 92,5 Diesel Fuel Oil 3,5 Guar Gum 2,0 Calcium Stearate 2,0 Total 100,0.

The water-resistant ANFO-type explosive so produced was found, when a charge thereof was loaded into a 70 mm internal diameter street pipe, to be capable of detonation by means of a 150 g pentolite booster, and was found to have a velocity of detonation of 2500 m/sec.

In similar explosives containing ammonium nitrate prills, diesel fuel, a water-blocking agent such as guar gum and a water-repellant substance such as calcium stearate, the bulk of the explosive is in the form of a granular mass, the prills having between them, empty voids and channels forming a porous interconnected network of spaces in the interior of the explosive.

Water in or entering a borehole containing the charge of explosive, can move by capiliary action into these spaces, adversely affecting the explosive properties of the explosive. In contrast, as the voids between the prills of the explosive of the present invention are in substance filled with powder, ingress of water is resisted and/or retarded and the amount of water which can enter the voids is reduced, thereby reducing or at least retarding deterioration of the explosive on exposure to water.

Claims

1. An ammonium nitrate/fuel oil explosive which comprises particulate ammonium nitrate and a liquid hydrocarbon fuel, the ammonium nitrate comprising ammonium nitrate prills and ammonium nitrate powder, the prills forming at least 30% by mass of the ammonium nitrate, the powder forming at least 20% by mass of the ammonium nitrate and the prills having an average particle size which is. at least 5 times greater than the average particle size of the powder.

2. An explosive as claimed in claim 1, in which the average particle size of the prills is 5-15 times greater than the average particle size of the powder having a particle size in the range 1.0-2,8 mm, the major proportion by mass of'the powder having a particle size in the range 0,1-0,35 mm, the prills forming at least 50% by mass of the ammonium nitrate and the powder forming at least 30% by mass of the ammonium nitrate.

3. An explosive as claimed in claim 1 or claim 2, in which the hydrocarbon fuel is a hydrocarbon oil and forms 2-6% by mass of the explosive.

4. An explosive as claimed in any one of the preceding claims, which contains a substance which swells on contact with water.

5. An explosive as claimed in claim 4, in which said substance which swells on contact with water forms from 1-5% by mass of the explosive and is a member of the group consisting of guar gum, locust bean gum, carboxymethyl cellulose and mixtures thereof.

6. An explosive as claimed in any one of the preceding claims which contains a waterrepellant substance.

7. An explosive as claimed in claim 6, in which the water-repellant substance forms 1-4% by mass of the explosive and is a member of the group consisting of calcium stearate, magnesium stearate, polyvinyl chloride and mixtures thereof.

8. An explosive as claimed in any one of the preceding claims, in which the prills are porous and the particles of the powder are solid or porous.

9. An explosive substantially as described and as illustrated herein.