US2613146A - Unsheathed safety explosive composition - Google Patents

Description

of a flame-quenching solid material.

Patented Oct. 7, 1952 UNSHEATHED SAFETY EXPLOSIVE COMPOSITION Arthur J. Lowe, West Kilbride, Scotland, assignor to Imperial Chemical Industries poration of Great Britain Limited, a cor- No Drawing. Application March 26, 1951, Serial No. 217,677. In Great Britain May 5, 1950 Thepresent invention relates to the production of nitroglycerine-free ammonium nitrate/trinitrotoluene compositions particularly suitable for use in the production of unsheathed safety explosive cartridges.

The object of the present invention is to provide nitroglycerine-free ammonium nitrate/trinitrotoluene compositions particularly suitable for use in the production of unsheathed safety explosive cartridges which at least substantially approach in explosive character and in safety sheathed explosive cartridges of nitroglycerinefree type containing ammonium nitrate and trinitrotoluene and common salt.

It is known that an exceptionally high degree of freedom from danger of ignition of fiery and dusty atmospheres is attained by the use of the so-called safety sheathed explosives, in which 7 Claims. (01. 52-7) the cylindrical surface of the wrapped explosive cartridge is provided with an exterior covering Although the sheathing of explosive cartridges with flame quenching materials renders it possible to employ as the flame-quenching medium certain very effective materials that cannot normally be incorporated into the explosive composition itself and more generally facilitates the production of blasting cartridges having a desirable combination of safety, sensitiveness to initiations and power, the provision of an external sheath of such material and the handling and employment of the resulting blasting cartridges entail a certain amount of inconvenience. Thus in the manufacture of safety sheathed explosive cartridges it is necessary to accommodate the flame-quenching material either in powder form in an outer annular receptacle formed between the normal wrapping of the explosive cartridge and an external container of paper, or in the form of a more or less stiff structure made with the aid of some binding or bonding medium, which can be applied by rolling or otherwise around the normal wrapped explosive cartridge and protected by an additional outer layer of paper. It follows that safety sheathed explosive cartridges are of greater diameter than the actual cartridges of explosive embodied in them and consequently necessitates the drilling of correspondingly wider bore-holes. Moreover, care must be taken to obviate the possibility that some of the flame-quenching material still finds its way in pulverulent form between the end of the normal explosive wrapper and the terminal portion of the outer wrapper of the explosive cartridge, which might prevent end-to-end propagation of detonation when such cartridges are arranged in file in the bore-hole. It is accordingly desirable to provide unsheathed explosive cartridges of satisfactory sensitiveness and safety characteristics comparable with those of sheathed explosive cartridges of the same power; or to provide unsheathed explosive cartridges of the same degree of safety, as indicated for instance by an unstemmed test in a gallery containing a 9% methane/air mixture of comparable effective power to those of sheathed explosives.

It is well-known for example that unsheathed nitro-glycerine-free ammonium nitrate/trinitrotoluene explosive cartridges made for instance from Douglas powder containing 15% trinitrotoluene, 69% ammonium nitrate and 16% sodium chloride, have a power equivalent to of that of blasting gelatine as observed in the ballistic pendulum and are in themselves safety explosives, and that when such explosive cartridges are sheathed so that the sheathed cartridges have in effect a power of about 43% of that of blasting gelatine they exhibit that greater degree of safety which may be called for in many mining operations.

We have now found that it is possible to make nitroglycerine-free ammonium nitrate/trinitrotoluene compositions particularly suitable for the production of unsheathed explosive cartridges having a degree of safety at least approaching that of said sheathed explosive cartridges made from Douglas powder and likewise having a power in the region of 43% of that of blasting gelatine if said compositions include as additional major constituents both sodium chloride and sodium nitrate and if the four major constituents, trinitrotoluene, ammonium nitrate, sodium nitrate and sodium chloride lie within certain ascertained gravimetric limits.

According to the present invention safety explosive compositions consisting of a mixture of trinitrotoluene, ammonium nitrate, sodium nitrate, and sodium chloride as major ingredients. having abulk density of 0.90 to 1.05 gm./co. at 25 lbs. pressure per sq. in., and having a calculated oxygen balance between -0.5 and +3 gms. oxygen per gms. of the composition are characterised in that the percentage by weight of trinitrotoluene is between 11 and 22%, of ammonium nitrate is between 22 and 36%, of sodium nitrate is between 12 and 27% and of sodium chloride is between 29 and 35%.

If desired the safety explosive compositions of the present invention can include up to 3% of oxidizable organic materials as for example vegetable tissue materials, preferably of low density, for instance balsa woodmeal or ground cork; such materials as organic dyestuffs of sulphonated character, for instance Acid Magenta and salts of tri-sulphonated New Magenta which may be present in very small quantities on the surface of the ammonium nitrate as an antisetting agent, or incorporated into the explosive composition as such may also be reckoned as an oxidizable organic material for this purpose, as may other organic ingredients which are not of vegetable tissue nature but which may be present as minor constituents.

For the compositions of the present invention to have the bulk density specified they can be prepared in known manner by mixing the ingredients by dry milling with attrition and thereafter moistening sufliciently to give the mixture a moisture content of approximately 1% and drying without mechanical agitation at a temperature exceeding the transition point of ammonium nitrate at 32.2 0., allowing the mixture thus produced to cool and finally screening the resulting pulverulent material.

In adjusting the oxygen balance for any proposed explosive composition the oxygen requirements of the various organic constituents may be calculated if necessary after performing an elementary analysis of the material on the basis that the carbon is to be oxidized to carbon dioxide and the hydrogen to water and any nitrogen is to be liberated as elementary nitrogen, due allowance being made for any water content in the original material.

In putting the invention into effect any lumps of the final material retained on the screen may be broken down mechanically by light pressure into powder. A relatively coarse screen may be used for this purpose although the product is a relatively fine powder, which when packed into pre-formed paper cartridge cases in known man ner has a density of approximately 1 gram per 00., tending to be a little higher than this figure in the absence of low density vegetable tissue material and a little lower when such material is included. It may be noted that the explosives provided according to the present invention need not contain any ingredients that are difficult to obtain in a satisfactory condition from the point of view of the thermal stability of the explosive composition as indicated by the Abel heat test.

We have found that if explosive compositions consisting of a mixture tof trinitrotoluene, ammonium nitrate, sodium nitrate and sodium chloride as major ingredients, have these ingredients in quantities outside the limits specified for the compositions of the present invention although having the bulk density and oxygen value ing or are not as safe as the safety sheathed explosive cartridges of the nitroglycerine-free type containing ammonium nitrate, trinitrotoluene and common salt.

We have also found that it is necessary to adhere to the limits specified for the bulk density of the compositions of the present invention in order that the said compositions should have the required degree of sensitivity to initiation and propagation.

Furthermore it is well-known in order that safety explosive compositions consisting of a mixture of trinitrotoluene, ammonium nitrate, and sodium chloride should not give off poisonous fumes on initiation that these compositions should have a calculated oxygen balance between -0.5 and +3 gms. oxygen per gms. of the composition.

It is also often desirable to include in such compositions up to 3% of fibre in order to lower the bulk density of the compositions.

From the stipulated oxygen balance of 0.5 to +3 gms. oxygen per 100 gms. of the composition it can be deduced that the percentage, by weight of trinitrotoluene must be between 11 and 22% and having regard to the total quantity of flame-quenching ingredients of a sheathed explosive of the non-nitroglycerine trinitrotoluene/ammonium nitrate type, it can be assumed that the sodium chloride content should be in the region of 33%.

In view of the high proportion of common salt which it may thus be possible to include, it becomes impossible to obtain the required oxygen balance with ammonium nitrate as the only oxygen giving salt. It thus becomes necessary to include a salt yielding more oxygen per; unit weight than ammonium nitrate, and for -commercial reasons sodium nitrate is the salt chosen for this purpose. From general considerations it is deducible that the sodium nitrate content should be between 14 and 25%. From this it can be easily deduced that the ammonium nitrate content is to be between 20 and 42%. It can also be deduced by calculation that if a composition containing as major ingredients trinitrotoluene, ammonium nitrate, sodium nitrate, and common salt, is to approach in power 43% of that of blasting gelatine the ammonium content must be not less than 22% and not more than 42%.

The following table embodies experimental data which indicate that the limits specified for the major ingredients of the compositions of the present invention are essential if these compositions are to satisfy the requirements of safety, power, and oxygen value. I

A positive sign indicates that the gas test has been passed with respect to safety. A negative sign indicates that the gas test has not been passed with respect to safety.

Experimental examples Composition No. l 2 3 4 5 6 7 3 9 'lrinitrotoluene, percent l8 l7. 5 l8 l3 18 20 15 15 15 Ammonium nitrate 20 25 30 35 28 24 39 41 34 Sodium nitrate. 30 20 20 20 22 25 10 12 18 Common salt. 30 36 32 29 30 30 35 3 23 Balsa 2 1. 5 3 2 1 1 2 3 Power (actual). 35. 9 35. 3 40. 6 40. 4 40. 4 41. l 41. 4 45. 8 43. 6 Bulk density l- 03 1. 02 1. 05 0. 92 1. 04 1.10 l. 04 0. 98 0.99 Oxygen value +2- 3 -0. 5 +2. 1 +3. 0 +0. 1 -o. 5 +0. 8 2 5 Safety in gas test specified for the compositions of the invention, they are either too weak for practical coal min- In the above table those compositions having a power less than 36% of blasting gelatine are unsuitable as they are not sufliciently powerful for practical coal mining.

If the compositions numbered 3 to are made so that they have a bulk density greater than 1.05 at 25 lbs. per sq. in., they have experimentally been found to be unsafe in accordance with the gas test. The lower limit of 0.90 at 25 lbs. per sq. in., for the bulk density of the compositions of the present invention is one which is known to be the lowest obtainable under manufacturing conditions.

' Compositions in accordance with the invention are illustrated by the following examples, in which the parts and percentages mentioned are by weight.

Example 1 18 parts flake TNT and 18 parts dried ammonium nitrate are milled together in a suspended steel edge-runner mill until the discrete particles of TNT are no longer visible to the naked eye. A further parts dried ammonium nitrate and 22 parts sodium nitrate and thereafter in successive stages, 30 parts sodium chloride and 2 parts balsa woodmeal are introduced, the milling being continued for a period sufficient to ensure that the TNT and the inorganic nitrates are reduced to a fine powder and thoroughly incorporated in known manner. It is desirable to add the balsa wood meal at a late stage of the incorporation. Thereafter, sumcient water is added to bring the moisture content to 1% and the water is dispersed through the composition by continuing the milling for a short period. The thus moistened powder is shovelled on to aluminium trays, which are carried to a drying room in which they are exposed to a current of warm air, the ambient temperature in the room being about 50 C. When the material, which constitutes a powder, is thoroughly dry it is screened through a mesh British Standard Specification screen and any remaining lumps are subjected to light impact on the screen with wooden balls,

- which causes them to fall to a fine powder which will join that which has already passed through the screen.

The explosive powder so obtained is fed under very light pressure into pre-formed paper cases of 1%," or 1 diameter giving cartridges of weight from 2-8 ozs. as may be required. The oxygen value of the composition is +0.1. Its density at 25 lbs. pressure is 1.04 grams per cubic centimetre.

A No. 2 mercury fulminate/potassium chlorate detonator is found to be sufilcient to initiate the fresh dry explosive cartridge of 1%" diameter, but in service it will be understood a No. 6 or No. 8 detonator, which may conveniently be a lead azide/lead styphnate/tetryl detonator having a copper alloy casing, is normally employed.

The power of the explosive is 40.4% of that of blasting gelatine as measured by the ballistic pendulum. In a double cartridge test in which two cartridges each of 1%" diameter and 3" length are disposed in an empty paper tube in alignment along their longitudinal axis with their ends separated by an air gap, and one of the cartridges is initiated from its remote end by a No. 8 detonator, it is found that the second cartridge detonates satisfactorily when the gap'is 1" but fails when it is 1.5" long. The velocity of detonation measured in a cartridge of 1 diameter and 8" length is 1950 metres per second. In an unstemmed test in an explosive gallery with inverse initiation in a 9% methane/air atmosphere (by volume) unsheathed cartridges of the explosive of 1%" diameter are found to have a charge limit between 16 and 20 ozs.

The charge limit in a similar test of a normally made exposive composition not in accordance with the invention known as Douglas powder and containing 15% TNT, 69% ammonium nitrate and 16% sodium chloride sheathed with 30% sodium bicarbonate powder is between 12 and 16 ozs. of explosive. This Douglas powder gives a power in its sheathed condition equivalent to 43% of that of blasting gelatine as observed in the ballistic pendulum, and with unsheathed gives a power equivalent to 65% of that of blasting gelatine. Its velocity of detonation is 3,500 metres per second.

Example 2 The ingredients of the explosive composition are as follows:

Per cent TNT 18 Ammonium nitrate 30 Sodium nitrate 20 Sodium chloride 32 The manner of mixing the explosive is similar to that in Example 1 and it is cartridged in the same way. The resulting explosive has an oxygen value of +2.1 grams per grams explosive and its density is 1.05 gram-s per cc. Its power is 40.6% of that of blasting gelatine. The dried explosive freshly made can be initiated by a No. 1 detonator. Its velocity of detonation is 2,200 metres per second, and in the double cartridge test the second of the cartridges detonates when separated from the first by a gap of 1 /2" but fails to do so when the gap is 2". In the gallery test referred to in Example 1 the charge limit is between 10 and 12 ozs.

Example 3 The ingredients of the explosive composition are as follows:

Per cent TNT 13 Ammonium nitrate 35 Sodium nitrate 20 Sodium chloride 29 Balsa woodmeal 3 The oxygen value of the resulting explosive powder, which is made after the fashion described in Example 1, is +3.0 grams oxygen per 100 grams explosive and its density is 0.92 grams per cc. Its power as measured in the ballistic mortar is 40.4% of that of blasting gelatine and in the double cartridge it gives the same figures as the explosive of Example 1. The explosive when freshly made and dried is sensitive to a No. 2 detonator. Its velocity of detonation is 2,150 metres per second and in the gallery test referred to in Example 1 the charge limit of a 11%" diameter unsheathed cartridge is not less than 18 ozs.

What I claim is:

1. Safety explosive compositions consisting of a mixture of trinitrotoluene, ammonium nitrate, sodium nitrate, and sodium chloride as major ingredients, having a bulk density of 0.90 to 1.05 gram per cc. at 25 lbs. pressure per sq. in., and having a calculated oxygen balance between 0.5 and +3 grams oxygen per 100 grams of the composition characterized in that the percentage by weight of trinitrotoluene is between 11 and 22%, of ammonium nitrate is between 22 and 36%, of Sodium nitrate is between 12 and. 27%, and of sodium chloride is between 29 and 35%.

'2 Safety explosive compositions as claimed in claim 1 which include up to 3% of oxidizable organic materials.

3. Safety explosive compositions as claimed in claim 2 wherein the oxidizable organic materials are vegetable tissue materials.

4. Safety explosive compositions as claimed in claim 3 wherein the vegetable tissue materials are of low density.

5. Safety explosive compositions as claimed in claim 4 wherein the vegetable tissue material'of low density is balsa woodmeal.

6. Safety explosive compositions as claimed in 15 claim 4 wherein the vegetable tissue material is ground cork.

8 V 7; Safety. explosive compositions as claimed in claim 2 wherein the oxidizable organic materials are sulfonated organic dyestuffs.

ARTHUR J. LOWE. 4

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

Claims (1)

1. SAFETY EXPLOSIVE COMPOSITIONS CONSISTING OF A MIXTURE OF TRINITROTOLUENE, AMMONIUM NITRATE, SODIUM NITRATE, AND SODIUM CHLORIDE AS MAJOR INGREDIENTS, HAVING A BULK DENSITY OF 0.90 TO 1.05 GRAM PER CC. AT 25 LBS. PRESSURE PER SQ. IN., AND HAVING A CALCULATED OXYGEN BALANCE BETWEEN -0.5 AND +3 GRAMS OXYGEN PER 100 GRAMS OF THE COMPOSITION CHARACTERIZED IN THAT THE PERCENTAGE BY WEIGHT OF TRINTROTOLUENE IS BETWEEN 11 AND 22%, OF AMMONIUM NITRATE IS BETWEEN 22 AND 36%, OF SODIUM NITRATE IS BETWEEN 12 AND 27% AND OF SODIUM CHLORIDE IS BETWEEN 29 AND 35%.