US2513531A

US2513531A - Safety sheathed blasting explosive cartridge

Info

Publication number: US2513531A
Application number: US617695A
Authority: US
Inventors: Taylor James; Phillips Alec Harold
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1944-11-15
Filing date: 1945-09-20
Publication date: 1950-07-04
Anticipated expiration: 1967-07-04
Also published as: GB585848A; DE840222C; LU27796A1; FR916789A; NL67304C; BE461166A

Description

July 4, 1950 J. TAYLOR EIAL SAFETY SHEATHED BLASTING EXPLOSIVE CARTRIDGE Filed Sept. 20, 1945 FIG.

F/GZ.

J G F 5 s mi T NO MUD mAm SH C E L A ATTORNEY Patented July 1950 UNITE sure SAFETY sans-man nrns'rmd EXPLOSIVE CARTRIDGE Britain Application September 20, 1945, Serial No. 617,695 In Great Britain November 15, 1944 1 Claims. 1

The present invention relates to the provision of new or improved safety sheathed blasting explosive cartridges by which we mean a cartridge of a detonating explosive, made from a composition including a suitable proportion of ingredients adapted to minimise its capacity for igniting flredamp air mixtures or coal dust air mixtures when it detonates, is further provided along its cylindrical surface with an external safety sheath that also comprises flame quenching or cooling ingredients. More particularly the invention has reference to the composition of the safety sheaths in such cartridges, and has for an object to provide safety sheathed blastin cartridges that can be more advantageously manufactured or are superior in service to the hitherto known cartridges of the kind described.

In safety sheathed detonating explosive cartridges the explosive composition customarily includes ammonium nitrate as one of its power producing ingredients, and one or more. compounds capable of vap'orisation, fusion, or thermal decomposition with absorption of heat as a flame quenching or coolin ingredient, and the safety sheath also comprises one or more compounds of the latter description. In this country it is also the practice for the explosive cartridge proper to be provided with aewaterproofed paper wrapper and for this portion of the sheathed cartridge to comply with the oflicial gallery tests for Permited Explosives.

The .blanketing efiect of carbon dioxide on the flame of the explosive and its innocuous character render it a particularly desirable gas to be generated by the sheathing material when the detonation takes place. Sheathing materials consisting essentially of various more or less insoluble metal carbonates have been tried with varying results. Of the carbonates sodium bicarbonate is the most effective and is the compound generally employed in practice in this country, notwithstanding the fact that it is slightly soluble in water and must .be carefully separated by a waterproof wrapping from the explosive cartridge, since it would otherwise react with the ammonium salt present in the explosive, to produce ammonium bicarbonate which gives rise to loss of ammonia and carbon dioxide.

We have now found that the'flame quenching or cooling efiiciency of the metallic carbonate is substantially increased or other advantages are obtained by employing the metallic carbonate in admixture with a suitable proportion of hydrated alumina.

According to the present invention the safety z sheath of a safety sheathed blasting explosive cartridge of the kind described comprises a mixture of one molar part of a metal carbonate not freely soluble in water and 0.33 to 2.0 molar parts of a dry hydrated form of alumina.

As alumina, even in hydrated condition, has little or no more effect as a safety sheathing ingredient than calcium carbonate, it is surprising that mixtures of a metallic carbonate and hydrated alumina in suitable proportions should be more effective than either ingredient, and the effectiveness of such mixtures may be attributed to the ready occurrence when the cartridge detonates of a heat absorbing reaction between the carbonate and hydrated alumina resulting in the formation of a metallic aluminate, water and carbon dioxide. In the case of a bicarbonate, such as sodium bicarbonate, this reaction would further liberate more carbon dioxide-than could be obtained from simple thermal decomposition of the bicarbonate. although such thermal decomposition occurs much more readily in the case of normal carbonates.

While artificial forms of hydrated alumina, obtained by precipitation from aluminium salt solutions, may advantageously be used, there are also available natural forms of hydrated alumina that can be easily brought to a suitable state of division desirably free from grittiness. These can accordingly be applied for sheathing the cartridges without appreciable hazard of explosion resulting from friction, should for any reason the separation of the explosive ingredients from the sheathing material be incomplete. Such forms of natural hydrated alumina include for instance amorphous natural hydrated alumina, bauxite and gibbsite.

As the metal carbonate not freely soluble in water there may be employed for instance sodium bicarbonate. or a metal carbonate substantially insoluble in water; and in the latter case naturally occurring forms either hydrated or anhydrous, are frequently available; thus com minuted limestone, chalk, calcareous shell, dolomite, or magnesite, may be used. The metal'carbonate should not .be more soluble in water than sodium bicarbonate.

The hydrated alumina and the metallic carbonate are advantageously both used in a fine state of division. If desired, other flame quenchin or cooling ingredients may be added to the mixture in minor proportions.

The drawing illustrates three alternative methods of utilizing this invention. Figure 1 illustrates a shell having the explosive charge I enclosed by a paramned paper wrapper 2, a second paper wrapper 4 completely surrounding the wrapped charge, and the annular space 8 between the two wrappers filled with the powder mixture of the invention. Figure 2 illustrates a rigid cylindrical sheath 5 formed by binding the powder mixture of .the invention with a binder such as platser of Paris, theexplosive charge I being then loaded into the cylinder. Figure 3 illustrates an explosive charge I wrapped with a flexible sheet 6 made by incorporating a flexible binder with the powder mixture of hydrated alumina and metallic carbonate.

British Specification No. 416,586 discloses inter alia a flexible safety sheathing material for blasting explosives comprising in sheet form a uniform mixture of a fibrous bonding material and a preponderating proportion of a cooling salt or mixtures of cooling salts.

British Specification No. 424,784 discloses inter alia a method of forming materials suitable for use as cooling sheaths for safety blasting explosives wherein one or more cooling salts are mixed into a paste with an aqueous solution of a suitable organic binding agent such as gelatine and a hydroscopic polyhydric alcohol such as glycerine, the paste formed into any desired shape and dried.

The invention is illustrated by the following example:

Example Waxed paper covered cartridges of overall diameter 1%" containing explosive Polar Dynobel No. 2 are held centrally in a paper shell of 1 diameter closed 'in at one end. A mixture containing 61 per cent of commercial trihydrate of alumina of which 99 per cent passes a 100 mesh and 90 per cent passes a 150 mesh British Standard Sieve, and 39 per cent of ground chalk, of which the whole passes a 150 mesh British Standard Sieve is poured into the annulus between the waxed paper cartridge and the outer paper shell. The mixture is consolidated by tapping and the filling and tapping operations are repeated until the whole length of the cartridge is embedded in the mixture, care being taken to prevent accumulation of the mixture on the ends of the cartridge. The weight of the flame quenching mixture amounts to 45 per cent of the weight of the explosive.

A charge consisting of flve cartridges (30 em. in all) each containing 6 oz. of Polar Dynobel No. 2 sheathed in the above manner fired suspended freely in a 9 per cent methane-air mixture did not cause an ignition of the gas when initiated by a No. 6 electric detonator. Under similar conditions, the same explosive unsheathed gave a gas ignition at 6 oz. and sheathed with either chalk alone or hydrated alumina alone gave gas ignitions with 10 oz. charges.

4 The Polar Dynobel No. 2 contained:

Per Cent Nitrated mixture of glycerine and ethylene glycol (:20) 13.0 Ammonium nitrate 67 Sodium chloride 12.5 Woodmeal 5.0 Paraflln wax 1.0 China. clay 1.5

We claim:

1. A safety sheathed blasting explosive cartridge wherein the safety sheath comprises a mixture of one molar part of a metal carbonate not freely soluble in water and 0.33 to 2.0 molar parts of a dry hydrated form of alumina.

2. A safety sheathed blasting explosive cartridge as claimed in claim 1 wherein the dry hydrated form of alumina is an artificial form obtained by precipitation from an aluminium salt solution.

3. A safety sheathed blasting explosive cartridge as claimed in claim 1 wherein the dry hydrated form of alumina is a natural form brought to a suitable state of subdivision.

4. A safety sheathed blasting explosive cartridge as claimed in claim 1 wherein the metal carbonate is sodium bicarbonate.

5. A safety sheathed blasting explosive cartridge as claimed in claim 1 wherein the metal carbonate and dry hydrated form of alumina are in a fine state of division.

6. A safety sheathed blasting explosive cartridge as claimed in claim 1. wherein the metal carbonate is calcium carbonate.

7. A safety sheathed blasting explosive cartridge as claimed in claim 1, wherein the metal carbonate is magnesium carbonate.

JAMES TAYLOR. ALEC HAROLD PHILLIPS.

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

UNITED STATES PATENTS OTHER REFERENCES United States Dept. of Agriculture Circular No. 466, March 1938, A Weather-Resistant Fireproofing Treatment for Cotton Fabrics" by M. Leatherman. Copy in Division 38.