US2358384A - Detonating explosive - Google Patents

Description

E. I. du Pont de Nemours & Company, We'- ton, Dela a corporation of Delaware No Drawing. Application January 31, 1941, Serial No. $36,842

This invention relates to a detonating explosive in granular form, and more particularly to an explosive of this nature having a relatively high ammonium nitrate content and capable of efiective use in the presence of water.

Free-flowing explosives ofier a number of advantages'in use, particularly with respect to loading, since they can be poured into the borehole and made to fill it completely, without the necessity of cartridging or tamping. Black powder and various explosives containing high ammonium nitrate contents are examples of freefiowing explosives of the prior art. Such compositions have been satisfactory from the viewpoint of loading properties under dry conditions, but have been out of the question when the bore holes contained, or were filled with, water. Because of the high content of water-soluble salts in such explosives, notably sodium nitrate or ammonium nitrate, or both, such compositions not only lost much of their content by leaching but ceased to be capable of functioning as explosives under the wet conditions.

The object of the present invention is a high .art overcome, when I prepare compressed aggre- 35 gates or granules of flowable size by balanced blends of oxidizable materials, particularly carbonaceous combustibles, and at least one inor- 'ganic oxidizing agent. Such grains are given the desired degree of v absorbency by suitable choice of carbonaceous ingredients and are then mixed with not less than of an explosive liquid nitric ester, calculated on the total weight of grain and liquid explosive. Under the conditions of my invention, the liquid explosive becomes substantially completely absorbed within the grains so that these latter retain their freeflowing characteristics, yet are capable of pronegating the explosion, when this has once been initiated.

While I preferably employ ammonium nitrate as the inorganic oxidizing agent because of the additional strength imparted by its use, this salt may be replaced in part or completely by other oxygen-supplying salts such as sodium nitrate,

potassium nitrate, various perchlorates, and the like.

explosive nitric ester'has been foundto be prefd erable in order to assure detonating properties in the explosivetafter immersion in water. Preferably, I employ no more than 30% of said liquid sensitizer. tizer, though explosive equivalents such as ethyllii ene glycol dinitrate, tetranitrodiglycerin, and

other, freezing point depressants may be dissolved in the nitroglycerin. In fact, nitroglycerin may be substiuted entirely or in part by other explosive materials (although a sensitizing agent in 15 liquid form and having a nitric ester base is preferred). Thus, other suitable sensitizers include both explosives per se, such as nitrocellulose,

smokeless powder, nitrostarch, PE'IN, TNT, and

the like, and certain non-explosive sensitizers in- 20 eluding hydrocarbons, e. g., parafln, certain nitrated hydrocarbons, e. g., dinitrotoluene, and certain forms of carbon, such as'coal and the like. Various compositions of thesetypes are disclosed and claimed in copending application Serial No. 387,919, filed April 10, 1941.

36 final explosive by nitroglycerin would be undesirable also because of the unduly high degree of sensltiveness to shock that ,would then' be present; In order to assure the desired, degree of absorptive power for the granules for nitroglycerin, control of the density of the grain as prepared is necessary, as well as proper selection of carbonaceous combustible ingredients. I have found that the apparent density of the grains or aggregates initially prepared preferably should 0 lie between 1.05 and 1.35. If a grain of density lower than 1.05 is used, the aggregate is not sufiiciently compact to hold togethr satisfactorily under the leaching effect of the water on the considerable percentage of soluble salts. If, on

4 the other hand, the density is above 1.35, the

grain is not sufliciently absorbent. When grains of the foregoing intial densities are used and mixed with nitroglycerin, the latter is absorbed without substantial chang in the volume of the grain. Hence, a final detonable grain is obtained of a preferred density range between 1.25 and 1.6.

an additional ingredient for the assurance of sufiicient absorptive power in the granular; ag- 'gregates is the presence of a minimum amount of a fibrous carbonaceous material, which pre- The presence of'not less than 15% of a liquid Nitroglycerin is the preferred sensisumably functions by binding the aggregate together, yet maintaining sumcient air spaces within the'grains to provide opportunity for absorp-' tion of the desired amount of nitroglycerin. I have found that if a liquid sensitizer is used, the, grain, as initially prepared, preferably should have a content of Woodpulp orother fibrous carbonaceous material of not less than 2%, which would mean a preferred minim-um content inthe final explosive of around 1.5%. A content of Woodpulp or the like of between 5 and 6% is suitable under many conditions, and 10% or more maybe used. While the grains described will give a suitab free-flowing explosive, I find the desired degree of compatibility with water to be best attained when an ingredient is included in the grain composition comprising a plant product capable of forming a cohesive paste on contact with'unheated water. Various ingredients of this type may be used, for example, a pregelatinized cereal product such as a flaked corn product in finely divided condition where the cereal product has been preheated to an elevated temperature or otherwise treated so that it is capable of forming a cohesive paste with cold water. Other suitable Puts-forming vegetable products are rye flour, barley flour, oat flour, spelt meal, linseed meal, and the like. Preferably,

I employ linseed meal or' barley flour, since these tend to cause a contractive effect on wetting with water and formation of the cohesive protective paste. The formation of this paste at the initial penetration of water into the explosive tends to keep the interior of the explosive from being leached out. Pulverulent explosives containing such ingredients are claimedin the copending application of Winning. Serial No. 288,131, filed August 3, 1939. I find it preferable to use the linseed meal or barley fiour, or other paste-forming material, in an amount between 2.5 and 10% of the entire composition.

The following will serve as examples or methods of carrying out my invention and obtainin the desired free-flowing, water-compatible explosive: Example 1 The ingredients for the initial grain were weighed and introduced under heavy, revolving wheels, the following relative amounts being used:

All the above ingredients, with the ,exception of thefiaked corn product, were first wheeled after the addition of about 4% of water. The corn product was added towardthe end of the mixing and stirred in. The intimate wheel cake mixture 1 was then pressed and dried at around 140 F. The

dried cake was broken up and granulated, grains being retained that were of such size that they passed a B-mesh screen and were held on 16-mesh..

The grains were then placed in a dynamite mixer and nitroglycerinwa's slowly added, the grain nitroglycerin ratio being such asto give a 20% nitroglycerin content in the final product. The grains and liquid explosive were mixed for 5 to 7 minutes. The grains, prior to mixing, with nitroglycerin, had a density of 1.18' and, after incorpropertiesafter 1 day.

. hours and 7 days.

3 hours, and 7 days.

poration of the liquid explasive, about 1.47. The grains were free flowing, as shown by their ability to flow through a or funnel. The ability of the above explosive to function after prolonged immersion in water was shown by filling a 2 x 8" tin tube with water, then pouring in the granular explosive until it reached the top of the tube. at which time th water present amounted to about 33%% of the total content by weight. Atter exposure to water for 3 hours, four successive detonations of the explosive were obtained with four diii'erent tin tubes, similarly loaded. The detonability of the explosive was tested by placing the tube on a leadblock and priming it with a half-cartridge of 40% straight dynamite. The bulk density of the explosive, as poured into the receptacle, was 0.78 and the volume occupied by it in water indicated it there to have an apparent density of about 0.66.

Example 2 A mixing (75 lbs.) was made in a dynamite mixing bowl of the following materials:

Y The above ingredients, with the exception of the) rye flour, were'mixed for about 20 minutes, with the bowl heated to 140 F, and with enough water added to give a 4 content. The rye fiour was then added and mixed for a short time, giving co- .hesiveness to'the whole. The freshly mixed material was pressed into cakes having adensity of 1.35. The cake was then broken into pieces about 1 square and dried at 140 F. for 12 hours, or to a high degree of hardness. The material was then granulated and screened, and that portion was retainedwhich passed a 6-mesh and wa held 'on a 16-mesh screen. The grains were then mixed with nitroglycerin, the relative proportions of grains and nitroglycerin being -20. The bulkdensity of the dry powderwas 0.715 and 0.85 after immersion in water. Using a half-stick of 40% straight dynamite as primer, detonations resulted on successive tests after immersions of 15 minutes,

Example 3 iA grain was formed in similar manner from th following materials:

, Per cent [Ammonium nitrate 81.5 Sodium nitr 10.0 Sulfur 2.0 Woodpulp 8.0 Chalk 0.5

The above mix in the form of blended aggregates of the desired size was blended with nitroglycerin in an 80-20 proportion." Excellent absorption of nitroglycerin by the grains was obtained. The finished grains. showed satisfactory free-flowing when immersed in an amount of water comprising 33%% of its weight, detonations in all trials. were ,obtained after 8 The apparent density of the grain, previous to. addition of the nitroglycerin,

v plosive.

2,358,384. was ,327. The bulk density of the dry final ex- Dlosive .was 0.78, and between 0.73 and 0.76 after;

nitrate, having the following composition:

Per cent Sodium nitrate 76.5

Sulfur 10.0

Woodpulp 6.0 Flaked corn'product 7.0

Chalk 1 0.5

The above material, after compacting into aggregates, was mixed with, nitroglycerin in an 80-20 proportion. The material had a bulk density, of 0.79, and 0.71 after immersion in water. Detonations wereobtained after humersion in water, though the sensitiveness was not uniform and was less than with ammonium nitrate compositions.

From the foregoing description of the explosive of my invention, it will be appreciated that said explosive possesses remarkable properties. In its ability to give satisfactory blasting execution after immersion inwater for several hours, it is equalled only by the gelatin dynamites or ammonium nitrate explosives completely enclosed in metal or other waterproof containers. No other free-flowing explosive can approach it in this respect. ?referably, I employ compositions containing'more than 50% ammonium nitrate, and lower-strength explosives are obtained when the above salt is replaced partly or entirely by sodium nitrate. Increased velocity may be obtained, if desired, by increasing the nitroglycerin content, for example to 30%. r

In carrying out the manufacturing operations, various methods and forms of apparatus may be- ,employed. In preparing the grain, for example, If find it satisfactory to incorporate the materials under wheels, as is the practice with black powder, the successive operations of wheeling, pressing, and coming being performed, if desired. Mixing may be carried out also in any type of dynamite mixingapparatus, or otherwise. Press-- ing may take place under revolving wheels or between rolls, or in any desired manner.-

When the explosive of my invention is poured into water, the grains quickly become. wet and sink rapidly to the bottom. While aportion of;

Q that nitroglycerin is commonly used as the liquid explosive nitric ester, which sensitizes the ex- By the term nitroglycerin, I intend to designate not only that compound itself but nitroglycerin containing dissolved materials which function as freezing point depressants. Likewise, many other departures may be made from the details of operations and compositions cited without departure from the scope of the invention. I intend therefore to be limited only by the following patent claims:

I claim:

1. A free-flowing granular detonating explosive comprising blended aggregates of a carbonaceous combustible materialand an inorganic oxidizing agent, and at least 15% of a liquid explosive nia parent density between 1.05 and1.35 and the combustible content being sufliciently absorbent that the liquid explosive is absorbed within said aggregates, the-completed grain having a dry surface.

2. A free-flowing granular detonating explosive comprising blended aggregates of a carbonaceous combustible material and ammonium nitrate, and at least 15% of a liquid explosive nitric ester, said aggregates having an initial apparent density between 1.05 and 1.35 and the combustible content being sufficiently absorbent that the liquid explosive is absorbed within said aggregates, the completed" grain having a dry surface.

3. A free-flowing detonating explosive in granular form and capable of functioning effectively after immersion irr'water, said. grains having densities between 1.25 and 1.6 which is sufilclerit to cause them to sink in water and comprising blended aggregates of combustible material and ammonium nitrate, and a liquid explosivenitric ester substantially absorbed within said blended aggregates, said combustible material comprising a fibrous carbonaceous ingredient and a plant product capable of forming a cohesive paste on contact with unheated water.

a. The explosive of claim 3, in which the paste forming material is present in an amount between 2.5 and 10% of the total composition.

5. llhe explosive of claim 3, in which the pasteforming material comprises a p'regelatinized ce-' real product.

'6. The explosive of claim 3, in which the paste forming material comprises barley flour.

7. The explosive of clainf 3, in which the pasteforming material comprises rye flour.

8. A free-flowing detonating explosive in granular form and capable of functioning effectively after immersion in water, said grains having an apparent density between. 1.25 and 1.6 and comprising blended aggregates of oxidizable material and ammonium nitrate, and not less than 15% of nitroglycerin substantially absorbed within said blended aggregates and dispersed therethrough, said oxidizable material comprising a fibrous carbonaceous ingredient and .a plant product capable of forming a'cohesive paste on contact with unheated water.

- 9. The explosive of claim 8, in which the blended aggregates are of such size that they will pass substantially a 4-mesh screen but are held material and ammonium nitrate, said grains trio ester, said aggregates having an initial apcomprising over 50% ammonium nitrate, more than 1.5% of a fibrous carbonaceous ingredient, between 2.5 and 10% of a plant product capable of forming a cohesive paste on contact with water, and between 15 and 30% nitroglycerin 1 substantially absorbed within said blended aggregates and dispersed therethrough.

11. The method of preparinga granular explosive which comprises preparing aggregates of explosive nitric ester of not less than 0! the total weight of grains and liquid explosive, causing said liquid nitric ester to become substantially absorbed in and dispersed through said aggregates, thereby producing a free-flowing,

' granular, detonable explosive.

' plosive.

13. The method of preparing a granular explosive capable of functioning effectively after 15. The method of claim 13, in which the pasteicrming material comprises a pregelatinised cereal product. a

18. The method of claim 13, in which the pasteforming material comprises barley flour.

17. The method of claim ,13, in which the pastefcrming material comprises rye flour.

18. The method of preparing a granular explosive which comprises mixing intimately carbonaceous combustible materials and ammonium nitrate said. carbonaceous combustible material comprising a fibrous ingredient, compressing the blended mixture into aggregates having apparent densities for the individual aggregates of between 1.05 and 1.35, admixing said granular aggregates with an amount 01' nitroglycerin suiiicient to bring about densities for said aggregates of between 1.25 and 1.6, causing said liquid e!- plosive to become substantially absorbed in and dispersed through 'saidaggregates, thereby producing a tree-flowing, =granular, detonable explosive.

immersion in water, which comprises preparing aggregates of intimate mixtures of carbonaceous combustible maierial'and at least one inorganic oxidizing agent, including as said combustible material a fibrous carbonaceous ingredient and a plant product capable of forming a cohesive paste on contact with unheated water, compressing said aggregates to apparent densities for the individual aggregates of between 1.05 and 1.35, admixing said granular aggregates with an amount of liquid explosive nitric ester or not less than 15% of the total weight of grains and liquid explosive, causing'said liquid explosive to become substantially absorbed in and dispersed through said aggregates, thereby producing a free-flowing, granular, detonable explosive.

14. The method of claim 13, in which the paste-forming material is used in an amount between 2.5 and 10%.oi the total composition.

19. The method of preparing a granular explosive capable of functioning eflectively after immersion in water, which comprises mixing intimateiy carbonaceous combustible materials and ammonium nitrate, including-as said combustible material a fibrous carbonaceous ingredient and a plant product capable of forming a cohesive paste on'contac't with unheated water and in an amount between 2.5 and 10% of the finished explosive, compressing the blended mixture into aggregates having apparent densities for the individual aggregates of between 1.05 and 1.30, ad-

mixing said granular aggregates with an amount 01' nitroglycerin of between 15 and 30% of the plosive.

CLYDE OLIVER. DAVIS.