US2218563A - Manufacture of explosive compositions or blasting charges - Google Patents

Description

Patented Oct. 22, 1940 UNITED STATES PATENT OFFICE MANUFACTURE OF EXPLOSIVE'. COMPOSI- TIONS OR BLASTING CHARGES James Taylor, Saltcoats, and Vernon Harcourt Williams, Ardrossan, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application April 18, 1938, Serial No. 202,805. In Great Britain April 26, 1937 Claims.

The present invention relates to new or improved methods for preparing explosive compositions or blasting charges containing ammonium nitrate and carbonaceous ingredients, and to improved explosive compositions or blasting charges the normal vegetable cellular carbonaceous ingredients, in addition to the other ingredients usually present in explosive compositions in which nitric esters are used as sensitizing ingredients. Ammonium nitrate is a common ingredient of such explosives.

As is well known, mixtures of ammonium nitrate and the usual vegetable cellular carbonaceous ingredients are generally difficult to detonate.

The sensitiveness to initiation of a mixture of a given carbonaceous ingredient with ammonium nitrate is relatively high when the composition of the mixture is such that the mixture is highly oxygen-positive, and falls considerably as the proportion of the carbonaceous ingredient is increased up to and beyond the point at which the composition becomes oxygen-balanced. Introduction of the flame-quenching ingredients used in permitted explosives causes a further decrease in sensitiveness. The ammonium nitrate explosives of commerce, which are preferably approximately oxygen-balanced and when adapted for use in fiery mines safe in gassy atmospheres, ac cordingly contain a proportion of a nitric ester as sensitising ingredient.

5 not segregate during transport nor suiier inconvenient deformation while being handled and loaded into the borehole. Whereas ordinary powder explosives are cartridged under various pressures such that their bulk densities range from '50 about 0.9 gram per 0. c. upwards, the low-density explosives are cartridged only under a' gentle pressure, and are characterised by bulk densities lower than about 0.75 gram per c. c.

This invention has as an object to provide a 55 low-density explosive composition which can be easily detonated in the absence of a sensitiser. A further object is to devise a. method of manufacturing such an explosive composition.

Further objects will appear hereinafter.

Strongly oxygen positive ammonium nitrate compositions give rise to a concentration of nitrous fume that may be objectionable in certain situations; this is especially the case in underground mines.

Although the sensitiveness of mixtures of ammonium nitrate and carbonaceous material de- 7 creases as the quantity of carbonaceous material is increased beyond a certain proportion at which the mixture is strongly oxygen positive, we have discovered that to a remarkable extent the decrease in sensitiveness may be ofiset by reducing the bulk density of the composition. Powders of very low bulk density, however, are usually liable to pack considerably on storage and transport. We have discovered that explosive compositions, not containing sensitising ingredients such as nitroglycerine and the like, and having a desirable oxygen balance may be produced in a state sufficiently sensitive, even after the ordinary incidents of storage and transport, to en- 25 able them to be employed, at least under slight confinement, provided we use vegetable cellular carbonaceous materials of sufliciently low inherent bulk density. According to the invention we are therefore able to manufacture without selfexplosive sensitising ingredients explosive powders which have the desirableblasting characteristics of low density explosives, and are capable or detonation under conditions of slight confinement or in some cases even unconfined by means of commercial detonators for instance a detonator not stronger than a No. '7 mercury fulminatechlorate detonator; which require no additional primer. This we achieve by incorporating ammonium nitrate with a vegetable carbonaceous ingredient of inherently low density together with other ingredients such as flame-quenching ingredients and heavier carbonaceous material, as may be desired, the quantity of the low-density material and the grist being so adjusted that the bulk density of the final product is less than 0.65 gram per 0. c.

Some vegetable cellular carbonaceous ingredients are known that have a particularly low bulk density on account of their irregular or extended particle form; but such materials are not necessarily the best for the purpose of the present invention, as on the one hand they may too' readily lose their extremely low density characteristics under very slight compression, and on the other hand their structural nature may be detrimental to the sensitiveness of mixtures of the type in question. Such materials, however, may in some cases be usefully employed as a minor proportion of the total carbonaceous ingredients in order to control the reduction of density brought about by the use of vegetable cellular carbonaceous materials intrinsically more suitable for the purposes of the present invention. The low-density explosive compositions of the present invention differ from the customary low-density explosive compositions sensitised with nitric esters, in that their sensitiveness to initiation depends upon the maintenance of their low-density characteristics.

For the purposes of the present invention ,there must be used as the principal carbonaceous ingredient a vegetable cellular carbonaceous ingredient characterised even when in a fairly fine state of division by low bulk density and by possession of a substantial degree of resistance to permanent deformation under pressure. Woods, barks, and piths, of low density even when in a relatively fine state of division, are specially suitable for the purpose of the invention, and may be employed in the form of meals; cork is an example of such a material, and may be used in the proportion of 10-15 parts per 100 parts ammonium nitrate.

In putting the invention into effect we may obtain suitable compositions by simple admixture of powdered ammonium nitrate with the carbonaceous ingredient or ingredients in the state of a low-density meal; this may be accomplished for instance by lightly milling the mixture for a short time, or by mixing it in machines such as are used for mixing powder explosives. erate degree of pressure is not objectionable in this operation.

Any starch or flour or the like high-density vegetable carbonaceous cellular material intended for use may be introduced during this stage; but if any portion of the low-density material is to consist of a material incapable while in a state of a meal of maintaining its low density under slight pressure, it should be very lightly mixed into the mixture of the other ingredients. Cooling materials, which should not have a particle size small in comparison with the voids between the particles of the remainder of the mixture; may also be introduced in similar fashion.

The invention is furtherillustrated by the following examples, in which the parts are parts by weight. The cork used is a: meal, containing,6% natural moisture, of which 83% passes a 36 mesh B. S. S. sieve, and 52% passes a 60 mesh sieve.

Example 1 12 parts cork, 100 parts pulverised ammonium nitrate and 5 parts maize starch are subjected to the action of a mechanical mortar for .ten minutes and then 12 partawater are added and the mixing is continued for another five minutes. The material is spread out into a quarter-inch layer and is dried at 70 to 80C., the cake so .sure not exceeding lbs. per sq. in. whereby its bulk density is increased to about 0.35 to 0.42. This density is well maintained on storage. The

A modmaterial is sufliciently sensitive to be initiated by a No. 4 detonator.

Example 2 To the wet mixture prepared according to Example 1 from 100 parts of ammonium nitrate, 5

parts starch, 12 parts cork and 12 parts water, is

A mixture of ammonium nitrate, starch and cork in the proportions 100:9:6 is subjected to the action of a mechanical mortar for 20-30 minutes and is then mixed with 2 parts of peat and 2 per cent. of its weight of common salt; this being lightly'mixed in. The product is heated from to 65 C. during one and a half hours and is sieved through a 6 mesh sieve after the cake has been broken up: The bulk density of the lightly tapped material is about 0.65, and it is then sensitive to a No. 6 detonator when confined in a tin canister.

Example 4 A mixture of 100 parts ammonium nitrate, 17 parts cork prepared by subjecting these materials to the action of a mechanical mortar for a period of ten minutes, is further mixed with 16 parts of a sodium silicate solution in presence of a little water, and the product is rapidly dried in a thin layer and the cake is broken up and passed through a 6 mesh sieve. It is filled into a 1 /2" waxed paper cartridge case and gently tapped into position, under which circumstances it has a bulk density of 0.37 approximately. The cartridge can be initiated by means oi. a No. 5 detonator.

Example 5 A composition containing 100 parts ammonium nitrate, 12 parts of cork meal and 5 parts of starch is granulated by the process described in Example 1. The granular composition is loaded into a 28 gauge 1%" diameter tin canister and plugged in with plaster of Paris. Similar charged canisters are produced from a granulated composition containing the same ingredients with the addition of 70 parts limestone chips (LO-30 mesh) per 100 parts ammoniumnitrate.

Canisters charged with each composition are suspended in a 9%-methane-in-air mixture and detonated with N0. 8 detonators. The charge limit for .the composition without cooling material is 2 oz.; and the charge limit with cooling ma-. terial is 6 oz., equivalent to nearly 4 oz. of the initial explosive composition.

Example 6 12 parts cork, 100 parts pulverised ammonium nitrate and 5 parts maize starch are subjected .to the action of a mechanical mortar for ten minutes; then 12 parts water are added and the mixing is continued for five minutes. The material is then dried at 65-70" C. without any preliminary caking, and packed as loosely as possible. It' is broken up lightly and passed through a 20' mesh sieve; then showing a density of 0.5 when filled under moderate pressure into waxed manila paper cases of 1 diameter. The material is sufiiciently sensitive when cartridged in this way to be initiated by means of a No. 5 detonator.

Example 7 A mixture of 100 parts ammonium nitrate, 10 parts cork meal, 4 parts starch, 10 parts water and 30 parts limestone b'roken to .30-60 mesh are mixed as described in Example 6, dried and granulated to pass a 20 mesh sieve. When cartridged at a bulk density of 0.5 in waxed manila paper cases 1 in diameter, the mixture can be initiated by a No. 5 detonator.

A No. 7 detonator is a detonator containing a charge of 1.5 gram 80:20 fulminate-chlorate composition pressed in a copper tube 5.92 mm. diameter ,under a pressure of about 4,130 lbs, per' sq. inch. The other detonators mentioned in this specification are similar, except that they contain Instead of, or in part substitution for, the cork used in the above examples, we could have used other low-density vegetable cellular carbonaceous ingredients, such, for instance, as bagasse. Part of the low-density vegetable cellular carbonaceous ingredient may also be substituted by a proportion of peat. Moreover, the carbonaceous vegetable material need not consist exclusively of low-density cellular ingredient; and in mixtures of ammonium nitrate and carbonaceous ingredients that are already of a low bulk density, the

presence of a minor proportion of starch, dextrin, flour, or similar relatively dense carbonaceous material in a finely divided form does not unduly affect the bulk density of the mixture. For example, 4-5 parts of starch per parts of ammonium nitrate may be used.

When cooling or flame-quenching ingredients are included in the, composition, they should not be so finely divided that they fill the voids between the particles of the other ingredients or of the mixture.

In some cases, particularly where an approximately oxygen-balanced mixture is required, it may be desirable to eifect a further reduction in bulk density than can conveniently be obtained by the simple process of admixture described above, While still maintaining a sufliciently high degree of permanence of bulk density under ordinary conditions of transport and handling.

A slight reduction in bulk density of a mixture of ammonium nitrate and carbonaceous materials prepared in the manner described above may be achieved by heating the mixture to a temperature above the transition point of ammonium nitrate, and driving oil the moisture normally present in the carbonaceous ingredients; after which the material may be sieved through a coarse sieve to remove lumps. If cooling ingredients are being'used, they may conveniently be introduced at this stage.

By a modification of the above method a great er reduction in' bulk density may be obtained, which depends on the low packing-density of granules each consisting of the same mixture of ingredients. For this purpose the ammonium nitrate, the low-density cellular carbonaceous ingredient meal, and if desired other carbonaceous ingredients, are mixed ..-with sufiicient water to form a paste with the ammonium nitrate. Any

safety or flame-quenching ingredients to be used, which in this case should be of an insoluble nature, as for instance ground limestone, coarse iron filings, or the like, may be introducedinto the wet paste. As already indicated, these ingredients should not be so finely divided that they occupy the voids between the particles of the other ingredients in the paste. The wet material is then spread out and dried at raised temperature, and the dried cake so produced is broken up 10 by light mechanical treatment and sieved through a coarse, e. g., 6-30 mesh sieve. If desired, further quantities of coarse cooling or flame-quenching ingredients may then be admixed.

For a given bulk density the mixtures prepared 15 according to this modification may not be so sensitive'to initiation as those prepared by dry admixture, but it is possible to achieve in this way a lower bulk-density that is still capable of being maintained under a slight cartridging pres- 20 sure; and this more than ofi'sets the slight loss in initial sensitiveness.

In cartridging the explosive compositions manufactured according to our invention, due regard must be paid to the possibility of a slight settle- 25 ment and increase of bulk density during transport and handling, and it is therefore'desirable to cartridge them at a density sufiiciently low to provide a good margin as regards sensitiveness to initiation; and for the same reasonif they 30 are packed in canisters these should be well tapped. If desired, they may be packed under a slight pressure, as in the case of. the low-density explosives of commerce. I

This invention is a valuable advance in the 35 art, as the explosive or highly-inflammable nitric esters which are usually employed .as sensitisers introduce a large factor of danger during manufacture and handling. By using the process of this invention this factor of danger is eliminated, besides providing a more economical method of manufacturing these low-density explosive compounds. All the explosives covered by this invention can be detonated by a detonator of size No. 7

or smaller, if they are confined in a 30-gauge 45 tinplate canister, while many can be detonated in less confinement. If confinement is used it is more important that the explosive should be confined laterally than longitudinally.

. As many apparently widely different embodi ments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as 55 defined in the appended claims. i

We claim: V

1. A detonating blasting explosive free from self-explosive sensitizers, comprising particles of ammonium nitrate and a vegetable cellular car bonaceous ingredient bound together in the form of granular agglomerates and broken up. through a sieve having at least six meshes to the inch, saidagglomerates having a bulk densityless than being characterized by a low bulk density even when in a fine state of division, and said exploporating in the absence of self-explosive sensisive being capable of initiation by means of a No. 7 detonator.

3. The blasting explosive of claim 2 wherein the low density vegetable carbonaceous ingredient comprises cork meal.

4. A detonating blasting explosive free from self-explosive sensitizers, comprising one hundred parts ammonium nitrate, ten to fifteen parts cork meal, four to five parts starch, and flamequenching ingredients, bound together in the form of granular agglomerates and broken up through a sieve having at least six meshes to the inch, said agglomerates having a bulk density less than 0.65 gram per cc.

5. A process for the manufacture of a detonating blasting explosive, which comprises incortizers, ammonium nitrate and a vegetable carbonaceous ingredient with sufficient water to form a paste, drying said paste and granulating' the same through a screen having at least six meshes to the inch to form agglomerates con-' taining both said ammonium nitrate and said carbonaceous ingredients, and incorporating in said granular product a-water-insoluble flamequenching ingredient, the grist of which is such that it does not collect in the voids between the granules of the mixture, said vegetable carbonaceous ingredient being of such a density that the final product has a density of less than 0.65 gram per cc.

JAMES TAYLOR.

VERNON HARCOURT WILLIAMS.