US2460375A

US2460375A - Granular or powder explosives and their manufacture

Info

Publication number: US2460375A
Application number: US458992A
Authority: US
Inventors: Whetstone John
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1941-09-15
Filing date: 1942-09-19
Publication date: 1949-02-01
Anticipated expiration: 1966-02-01

Description

Patented Feb. 1, 1949 TENT OFFICE GRANULAR R POWDER EXPLOSIVES AND THEIR MANUFACTURE John Whetstone, West Kilbride, Scotland, as-

signor to Imperial Chemical Industries Limited, a corporation of Great Britain ber 15, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires September 15, 19.61

The present invention relates to granular detonating explosive compositions of the kind in which the granules individually comprise ammonium nitrate and an easily fusible organic explosive compound in a state of intimate admixture. The invention also relates to an improved or simplified process for the production of such explosive compositions.

Explosives made in accordance with the invention are of improved sensitiveness to initiation and the granules are of an unusually robust character, as a result of which these explosives maintain well on transport and storage the bulk density at which they are packaged and consequently also maintain their sensitiveness well. The explosives made according to the present invention include not only coarsely granular products but also those in which the granules are small, and which may be described as powder explosives. They may be used for quarrying or mining or for demolition purposes, and can be initiated directly I by the impulse of commercial detonators.

Blasting explosive powders containing ammonium nitrate and organic explosive compounds are usually manufactured by grinding the solid ammonium nitrate and the organic explosive together, even when, as in the case of fusible aromatic nitro-compounds such as trinitrotoluene, the organic explosive compound is easily fusible. An additional ingredients of the composition are introduced during or subsequent to the grinding operation. Prolonged grinding is required in order to produce an explosive satisfactorily sensitive to initiation by a commercial detonator.

Military explosives containing ammonium nitrate and aromatic nitro-compounds can be made by coating solid ammonium nitrate with the fused aromatic nitro-compound, the explosive compositions so obtained being compressed, or cast, or cast and compressed, into the ammunition in which they are to be used. They are, however, not sensitive to initiation by ordinary detonators, and in eifecting their detonation it is necessary to employ an intermediate primer or booster whereby the detonating impulse transmitted from the detonator is enhanced. The density of such charges usually exceeds 1.4 and their velocity of detonation and their negative oxygen balance are-usually higher than is desirable for commercial blasting purposes.

The fusion temperature of ammonium nitrate is too high to enable it to be safely melted with fusible organic explosive compounds, but it can be reduced by the inclusion of additional materials such as salts having water of crystallisa- 9 Claims. (Cl. 52-21) that form eutectic mixtures with it. In the man ufacture of cast explosive charges, such materials usuall of an oxidising or reducing character, have been included in melts comprising ammonium nitrate and fused organic explosive compounds, with the object of minimising the content of the organic explosive compound required to yield a composition that is sufficiently fluid to be conveniently loaded. These compositions, which contain ammonium nitrate in a more or less completely fused condition, however, suffer from the defect that the liquified inorganic salts and the molten organic explosive constitute two immiscible liquids that can only be coarsely dispersed by agitation of the melt, so that the resulting mixture segregates rapidly before it solidifies, and the resulting cast explosive charges are of lower sensitiveness to initiation than those made by coating the solid oxidising salts with molten organic explosive, and may fail to propagate their detonation properly.

In the preparation of cast explosive charges such as are used for filling containers, for example shells or other projectiles, grenades, mines and the like, it has been proposed with the aid of an emulsifying agent to emulsify a highly explosive organic compound or compounds in a melt of an oxidising salt or salts, for instance ammonium nitrate, with or without metallic nitrates. According to this proposal, the emulsifying agent may be a colloidal substance soluble or swellable by water and capable of increasing the viscosity of the melt, and the formation of the saline melt into which the high explosive organic compound, for instance trinitrotoluene, is incorporated, may be assisted by the presence of hydrated salt, an organic amide or a small proportion of water, the resulting emulsified explosives being characterised by improved sensitiveness to detonation and other advantages as compared with similar compositions made by a fusion process or partial fusion process Without the use of the emulsifying agent. One of these advantages is that compositions of sufiicient fluidity for loading into ammunition may be obtained at safe working temperatures e. g. to C. with a reduced proportion of. the fusible high explosive compound. Massive cast explosive charges produced according to the method of the aforementioned proposal, however, are insufiiciently sensitive to be initiated by an ordinary commercial detonator, and are unsuitable for commercial blasting purposes.

According to the present invention, in the mancooling atmosphere.

3 ufacture of detonating explosives suitable for commercial blasting purposes, amolten easily fusible organic high explosive compound is first emulsified with the assistance of an emulsifying agent in a melt, comprising ammonium nitrate and a non-volatile compound adapted to lower the melting point of the ammonium nitrate, that congeals to form a solid-mass when cooled 4 there may be used water and anhydrous or less fully hydrated forms of the hydrated salt. The saltsemployed are advantageously of oxidizing character, and-metal nitrates and hydrated metal nitrates such as calcium nitrate, tetrahydrate, lead nitrate, alkali ,metal nitrates, magnesium nitrate hexanitrate or the like may conveniently "*by' use'd.

to a temperature higher than those at which'explosives are customarily tested for climatic storage, andthe resulting emulsion is congealed and granulated.

According to one form of the invention the granulation is commenced beiere'the'emulsion has cooled sufiiciently to become substantially congealed, for instance by congealing the emu1-,

after broken up into granules by mechanical action.

If theemulsion is granulated by first converting it into a thin sheet, this may be carried out by picking it up on a cooled rotating drum; and in this case also it may be necessary thatthe ammonium nitrate in the hot-emulsion should be completely liquified to allow it-to run somewhat on thedrum. The granulationmay be carried out breakingup the congealed coating into flakes or The method ofgranulating' a" a coarse powder. congealing cake of the emulsion, however, does not necessitate the use of anemul'sion in which the ammonium nitrate has been completely liquified. The congealed cake is frequently easier to crush while it is still warm or even hot than when it has cooled to ordinary atmospheric temperature, and if it is allowed to coolcompletely its crushing is facilitated by warming it.

On the other hand whenthe emulsion is congealed in the'iorm' of thin sheets it can easily be broken up "into flaky granules even at room temperature.

When the sheet or cake has been broken Tup, the product may be screened to remove any particles that are too large or too small, andthewaste from the screening operation may, if desired, be employed in forminganother batch -of emulsified material. The size of the granules may be controlled by varying the intensity ofthe mechanical action in breaking up the congealed cake, and it will be understood that the invention includes not only explosive compositions of coarsely granular form but also explosive compositions in which the granules are small, and,

which may be described as powders.

For the purpose of the presentinvention, there may be used as non-volatile compounds adapted to lower the melting point of ammonium nitrate anhydrous compounds capable of forming low or in addition, there may be employed hydrated;

salts that maintain their water of crystallization at temperatures at which explosives are cus tomarily tested for climatic storage, and it will be understood that instead'of such hydra'ted'salts When non-volatile compounds adapted to assist the fusion of ammonium nitrate which are not of an oxidising character are employed, for instance anhydrous sodium acetate, sodium benzene sulphonate, sucrose, acetamide, urea or dicyandiamide, 'it is usually desirable to employ oxidising "salts alongwi'ththem. Theamount of the substance or substances adapted to lower the melting poin't'oi the ammonium nitrate should be slim y cierit to render themelt sufficiently fluid to enable the emulsification to be carried out at a temperature sufficiently low to avoid any danger of un-,- controllable decomposition, and preferably at-a I temperature below1O0 'C., but it is not necessary that'the whole of the ammonium nitrate'should,

be liquifi'ed'so long as the emulsio n is suihciently Y employed colloidalsubst'ances soluble or sw'ellable' melting eutectic mixtures with it. Alternatively,

1 scopic nature.

fluid to manipulate. -If desired, the-emulsification may beassisted by the addition'of an amount of-w-ater in excess of that'which Will-becombined in the form of a crystalline hydrate when'the emulsion is cooled, but in this'case itis'desirable that the =excess water should-be substantiaily evaporated away 'beforethe emulsion-solidifies.

As explosive-c-ompounds*there may advantageously be employed' solid high explosiv'e'c'ompounds melting at temperatures-"not appreciably in excess of "the boiling'p'oint of waten but'whi'ch will. remain solid under oidinary -hot-* sto'rage conditions,-for instance trinitrotoluene 'or tetra-' nitroanisol, but there 'may also be employed mixtures' containing high "explosives 'othigher melting points, for example;nexamtrbdipnnylamine, pentaerythrite' tetrariitrate; polyi'iitrophthaler'ies or the like, with'easily' fusible 'or even'lidiiid 'explosiv'e com ounds in 'sflit'abl'e 1r)1opt)iti'orfs'. to" yield mixturesmat-mitts solidat hot' storage temper'atures' but l iquify at temperatures not *sub stanti'ally above the b'oiling point of water. It is usually convenient to carryout theemulsification at a temperature between C. and C.

Asemulsifying agents there are-advantageously by water and capable'ofinoreasing the viscosity of the hotaqueousammoniunfinitrate solution,

for instance agar-agar, carageen moss'extract; flour, de'xtrin, sodiumicellulose'glycollate, starch and various gums, e. g. gum arable; gum 'trag'aca'nth, "or gum tragon.

tween 0.3 per cent. and 0.7 per 'centl'of th"d1-Y Weight of theemulsion.

If desired; other ingredients of various types commonly employed in the manufacture'ofexplo'sivec'onipositions"may be introduced into the composition of the emulsionor mixed with-the granules. These are desirablybf a- -non-hyg-ro- Examples of such materials inelude, for instance; oxidisable ingredients suchas metal powders or carbonaceous ingredientscooling or'fiarne quenching ingredients, waterproofing agents and so forth. The composition -of--the final explosive should be so adjusted that-it has a desirable oxygen balance taking-intoaccou-nt any wrapping 1 or packing" material that will -"be included in; the blasting charge.

The sensitiveness to the initiating of an exp10-- The quantityfof the emulsifying agent require'd will usually lie"besive of any given composition made in accordance with our invention, and also its velocity of detonation, may be controlled to a considerable extent by the bulk density at which it is packed; and this in turn depends largely in the size of the granules, but, in general, explosives sufiiciently sensitive to be initiated directly by commercial detonators are obtained even at unusually high packing densities in relation to those customarily used for ammonium nitrate powder explosives.

The invention is further illustrated by the following examples, in which the parts are parts by weight.

Example 1 A mixture of 8.4 parts calcium nitrate tetrahydrate and 5.6 parts sodium nitrate are fused together and 65.6 parts ammonium nitrate and 0.4 part agar-agar are introduced in portions into the melt, which is heated in a steam jacketed vessel until no more of the ammonium nitrate dissolves. 20 parts molten trinitrotoluene are then stirred into the mixture, which is kept at a temperature of at least 90 during the emulsification. The emulsion is then poured out to form a slab about one quarter inch in thickness, which is allowed to solidify, and is crushed when it has cooled to about 40 C. by means of a roller until it has been broken up into granules. The granules passing a 20 mesh British Standard Specification screen and those retained by a mesh B. S. S. screen are sent for remelting. The granules passing a 15 mesh and retained by a mesh B. S. S. sieve when packed under a pressure of 75 lbs. per square inch yield a granular explosive composition of bulk density about 0.9 capable of direct initiation by a No. 2 mercury fulminatepotassium chlorate detonator. It has a power amounting to about 78 per cent. of that of blasting gelatine.

Ewample 2 The procedure is the same as in Example 1, except that the slab of the congealed emulsion is further crushed and only the particles retained by a mesh British Standard Specification screen are sent for remelting. When packed under a pressure of 75 lbs. per square inch the resulting powder explosive has a bulk density of about 1.15, and is sensitive to initiation by a. No. 3 mercury fulminate-potassium chlorate detonator. In a test in which two 1%" x 3" freshly made cartridges of the same explosive packed in waxed paper wrappers at the aforesaid bulk density are placed in line at varying distances in a common paper wrapper, the second cartridge is detonated by the first at a distance of 2" but not at 3". Under the impulse of a No. 6 mercury fulminatepotassium chlorate detonator it detonates at a velocity of about 3,810 metres per second.

Example 3 7.2 parts calcium nitrate tetrahydrate and 4.8 parts sodium nitrate are fused together, 55.6 parts ammonium nitrate and 0.4 part agar-agar are introduced into the melt, and 17 parts trinitrotoluene are emulsified in the mixture at a temperature of 90 C. by the method as described in Example 1. 15 parts of aluminium powder are then stirred into the mixture, which is poured out and allowed to congeal in the form of a A" slab. The slab is then crushed under a roller at C. and only the particles retained by a 20 mesh B. S. S. sieve sent for remelting. The resulting powder explosive is packed in waxed paper containers under a pressure of '75 lbs. per square inch, and has a bulk density of about 1.07. When initiated by a No. 6 mercury fulminate-potassium chlorate detonator it detonates at a velocity of about 3,600 metres persecond, and in the aforementioned double cartridge test the second cartridge is detonatedby the first at 3" but not at 4". This explosive can also be initiated by a No. 2 mercury fulminate-potassium chlorate detonator. The explosive has a power amounting to about per cent. of that of blasting gelatine.

Example 4 toluene are emulsified therein, as described in,

Example 1, except that the emulsification temperature is at least C. The emulsion is further heated to about 105 C. and poured out so as to congeal into the form of a A" slab and is then crushed at a temperature of 40 C., only the particles retained on a 16 mesh B. S. S. sieve being sent for remelting. When packed in waxed paper containers under a pressure of 50 lbs. per square inch the resulting granular explosive has a bulk density of about 1.05. When freshly made cartridges of this explosive are tested in the aforesaid double cartridge test, the second cartridge is initiated by the first at 4" but not at 5", and after the cartridges have been stored for one month the second cartridge is initiated by the first at a distance of 5" but not at 6". This explosive has a power amounting to about 82 per cent. of that of blasting gelatine, and when initiated by a No. 6 mercury fulminate-potassium chlorate detonator, the freshly made explosive detonates with a velocity of about 3,400 metres per second. This explosive can also be initiated by a No. 2. mercury fulminate-potassium chlorate detonator.

Example 5 A mixture of 7 parts anhydrous sodium acetate, 13 parts sodium nitrate and 20 parts ammonium nitrate is fused together and a further 39.5 parts ammonium nitrate and 0.5 part agar-agar are gradually introduced into the melt, which is heated on the steam bath, until no more of the ammonium nitrate present will dissolve. 20 parts molten trinitrotoluene are then stirred into the mixture at a temperature of at least 95 C. until it has been emulsified. The emulsion is then poured out and allowed to solidify in the form of a A slab, which is crushed at a temperature of 46 C. The material passing a 16 mesh B. S. S. sieve is then packed in waxed paper containers under a pressure of 75 lbs. per square inch. Its sensitiveness does not difier markedly from that of the explosives described in the preceding examples.

Example 6 A mixture of 57.6 parts ammonium nitrate, 7.7 parts sodium nitrate and 3.8 parts sodium chloride is heated until partly fused, and 5.6 parts nitroguanidine, 4.8 parts guanidine nitrate and 0.5 agar-agar are then introduced and the mixture is further heated at a temperature of C. until completely fused. 20 parts molten trinitrotoluene are then stirred into the mixture until it has been emulsified and the fused emulsion is then spread out into a thin layer and allowed to congeal in that form. It is then flaked. The resulting explosive is then packed in a tin-plate contai n'er. Its sensitiveness do'es 'notdiffermarkedlyi nitrate and-at least one compoundnonvolatile at the temperature of the -me1t- 'and adapted to' lower the melting point ofithe ammonium nitrate, to give a resulting emulsion which congeals'at a temperature above 46- C; and Mini-Q1118 free'f-rom uncombined water, and congealingandgranulating' the resulting emulsion.

' 2. A process as-claimed in claim 1 wherein the emulsion is formedat a temperature DetWeen'SO" C; and 110 C.

' 3. A process as claimed in claim 1 whereinit'he;

high -explosive is trinitrotoluene.

4; A process as claimed in claim l Whereinthe non-volatile compound adapted to lower the melting point of the ammonium nitrate comprises an anhydrous compound forming a low melting eutectic mixture with it.

' 5. A processas claimed in claim '1 whereinjt'he non-volatile compound adapted to lower the meltingrpoint of ammonium nitrate comprises a hydrated salt.

6. A process as claimed in claim 1 whereinlthe non-Volatile. compound comprises a :metallic nitrate.

-7;' A' process as claimed in-claim 1 wherein the non volatile compound is: an oxidizing salt.

1 8. A process a-s cla'imed: in claim 1 wherein the emulsi-iyingil agenti comprises-agar-agar.

9-"; A processias-clal med-in claim 1 wherein the granulation-:-isncommenced before the emulsion has; ceoled:=sufficiently to become substantially congealed.

= JOHN WHETSTONE.

i RE -Enemies CITED "The 'following'references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date- 51,242,900 ifvl'lini ng Oct. 9, 1917 1;?973213 -Marin- Mar; 11,1919 1;6'Z1,'7,92 Stoops 1 'May 29, "1928 20; F1 ,-908';569 'stoopscnu May 9, 1933 lg9261438 --Spaeth Aug. 1,1933 =1,'968,I58 I "Nadum July 31; 1-934 211635 72 "Wcbdbury 1 'Dec. 8,- 1936 2539;712- Cairns Sept. 20; 1938 25. 2,199,218 GU01; "Apr.'30, 1940 25353 5147 Y Cook 1 July -11, "19% 2309 2919 'vlhetstone .1 Oct. 22, 1946 Number country I Date "384,966 Great-Britain i "Dec. 15, 1933 53E579, GreatnBritain June 27, 1941 #552,645 Great-Britain Apr.:19', 1943