US2754755A - Cored ammonium nitrate explosive cartridge - Google Patents

Description

July 17, 1956 J TH ETAL COREID AMMONIUM NITRATE EXPLOSIVE CARTRIDGE Filed Dec. 29, 1950 III/III!IIIIIIIIII'IIIIIII 1 "q I I I I I l I I I l I I I I I I I I I 1. I. a.

INVENTORS JOHN A. RUTH RALPH VINCENT WAKEFIELD BY w ATTORNEY nited States CORED AMMONIUM NITRATE EXPLOSIVE CARTRIDGE John A. Ruth, Alton, and Ralph Vincent Wakefield, East Alton, Ill., assignors to Olin Mathieson Chemical Coporation, a corporation of Virginia This invention relates to an improved blasting cartridge and more particularly to ammonium nitrate explosive assemblies of controlled detonation rate and strength.

It is recognized in the blasting art that the industry requires a family of blasting explosives which vary in detonation rate and strength over a wide range. For instance, in blasting coal an explosive of low strength and low rate is usually used. In blasting some sandstone and limestone, explosives possessing higher rates and strengths are employed, and in some strip mining operations and hard rock blasting explosives possessing still higher rates and strengths are required. Pratt in U. S. Patent 1,785,529 attempted to provide such a family of explosives to meet the above requirements by utilizing a main charge of black blasting powder with a center core of a nitroglycerine dynamite extending throughout the length of the charge. The manufacture of such an assembly is attended, however, by the disadvantage that a large variety of dynamites all containing nitroglycerine and varying in explosive characteristics must be manufactured and stored as the core material. Furthermore, the numerous well known disadvantages attending black powder and nitroglycerine dynamites such as high cost and toxicity with nitroglycerine and low moisture-proofness with black powder and hazard in handling with both nitroglycerine and black powder are obtained with such assemblies. Black powder and straight nitroglycerine explosives have in large part been supplanted in the industry with less sensitive explosives having ammonium nitrate as the principal ingredient. Many ammonium nitrate explosives of this type are relatively insensitive, particularly in small diameter charges, and the inventive efforts in the art have been in large part directed to methods and means for obtaining propagation of detonation throughout the explosive charge. Favier in U. S. Patent 393,634 attempted to solve this problem by employing a high density ammonium nitrate explosive of low sensitivity with a center core of dynamite or gun cotton. Manufacture and use of such assemblies is attended by the known disadvantages obtained with nitroglycerine dynamites and gun cotton, such as high cost, hazard in handling, and the like. Lheure in U. S. Patent 905,336 provided a blasting assembly composed of ammonium nitrate having a. central bore and a tube of trinitrotoluene or trinitrobenzine within the bore for the purpose of obtaining complete detonation of the insentitive ammonium nitrate. Such an assembly had the disadvantages that no variation in strength could be obtained regardless of the amount of core material in the assembly, and that the use of the pure ammonium nitrate made it subject to misfires and failure of propagation from one cartridge to the next in the bore holes. Various other means have been proposed for providing ammonium nitrate dynamites of various strengths and detonation rates, but, in order to supply the industry with the required variety in detonation rate and strength, the manufacturer has had to provide dynamites of widely varying composition and physical characteristics.

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It is therefore an object of this invention to provide an improved blasting assembly permitting a wide variation in detonation rate and strength without requiring the manufacture of a series of different explosive compositions. Another object of this invention is to provide a blasting assembly of novel composition and construction. Still another object of the invention is to provide a family of blasting explosives with a minimum of raw materials at reduced cost. A further object is to provide an improved ammonium nitrate explosive of the cored-type. A still further object is to provide a blasting cartridge having a novel combination of ingredients and improved explosive characteristics.

Further objects will become apparent from the following description taken in connection with the accompanying drawing in which Figure 1 is a longitudinal sectional elevation of a blasting cartridge illustrating an embodiment of this invention, and

Figure 2 is a cross-sectional view of the cartridge taken at XX of Figure 1.

The foregoing objects and advantages are accomplished in accordance with this invention by providing an explosive cartridge in which an ammonium nitrate explosive forms the base charge and which. is provided with a center core of trinitrotoluene containing substantially uniformly distributed therein granular high explosive.

Any explosive having ammonium nitrate as the principal ingredient is suitable and the particular composition of the ammonium nitrate explosive is not of great importance, it only being necessary that the ammonium nitrate explosive be sufficiently sensitive that in the presence of the core the detonation is propagated throughout the assembly. In any event, the ammonium nitrate explosive should generally have a sensitivity no less than that of a standard mixture composed of 94.5% ammonium nitrate and 5.5% paraflin with a fineness such that 25% to 40% will pass a 100 mesh screen at a density not in excess of 1.15, all as defined by Kirst and Woodbury in U. S. Patent 1,992,216 and is preferably in granular form at a density of about 0.8 to 1.2.

The core has a density of not less than about 1.4 and preferably in the range of 1.5 to 1.8, and a weight strength preferably above The core may be formed by melting the trinitrotoluene, uniformly incorporating therein the granular explosive and any other added ingredients, and then casting the composition in molds of the desired dimensions. Any granular explosive which has its explosion or ignition temperature above C., so that it can be incorporated in molten trinitrotoluene without firing, and which has a rate of detonation at a density of 1.5 in excess of about 7000 meters per second, but preferably in the range of about 7500 to 8000 meters per second may be utilized in accordance with this invention, and should be present in an amount within the range of about 20% to 80% by weight of the core. Cyclotrimethylene-trinitramine, commonly referred to as cyclonite, has been found particularly suited as the granular explosive for the purpose. Examples of other suitable granular explosives are ethylene dinitramine, pentaerythritol tetranitrate, nitrostarch, nitromannite, and the like. The granulation of such high explosive in the core is such that most or more than about 50% of it will pass through a standard U. S. 40 mesh sieve and preferably through a 200 mesh sieve.

It has been found that a family of explosives having detonation rates varying within the range from about 4000 meters per second up to about 8000 meters per second can be obtained merely by varying the length of the center core. The core should have a minimum cross sectional area in the neighborhood of about M4 square inch and in any event should be greater than 1 square inch. By varying the cross sectional area or diameter of the core the weight strength of the cartridge may be varied from about 60% to about 90%, with a resulting variation in bulk strength from about 40% to about 80%. The term weight strengt as used herein refers to the strength as compared with a similar weight of 100% nitroglycerine blasting gelatin. The term bulk strengt as used herein refers to the strength as compared with a similar volume of 100% nitroglycerine blasting gelatin. Inasmuch as certain sized charge holes are drilled in blasting operations, bulk strength is of considerable importance in evaluating an explosive. The core may extend throughout the length of the cartridge, in which instance the maximum rate of detonation is obtained. When the core length is less than the length of the cartridge the rate of detonation is correspondingly reduced.

The ammonium nitrate explosive and the core composition may be so formulated as to be either sensitive or insensitive, as desired, to detonation by means of a standard blasting cap such as the No. 6 or No. 8 cap. If both the core and explosive are insensitive to detonation by a blasting cap, the cartridge is detonated by means of a booster charge placed at the end of the cartridge. Such a booster charge preferably has at least the strength of 1000 grams of trinitrotoluene at a density of 0.95 for cartridges of about 4 /2 inches in diameter. The composition of the core and ammonium nitrate explosive therefore depends in large part on whether or not a cap sensitive cartridge is desired. Having chosen the desired compositions for core and explosive charge, it is possible in accordance with this invention to vary the rate of detonation and strength of the cartridge without having to provide a series of cores and explosives of difierent compositions, etc.

For the purpose of further clarifying the invention, following is a specific example illustrating a typical embodiment of the invention.

Referring to the drawing, Figures 1 and 2, the ammonium nitrate explosive 1 was composed of 88.5% ammonium nitrate, 7.5% TNT, 3% coal dust, 0.5% chalk dust, and 0.5% aluminum powder intimately admixed in granular form at a density of from 0.9 to 1.0 gram per cubic centimeter and having a detonation rate of about 3560 meters per second and a weight strength of about 67%. The core 2 was in cast form and composed of approximately 60% trinitrotoluene and 40% cyclonite. The cyclonite was in the form of crystals or granules having an average particle size in the range from about 100 to 200 mesh and was substantially uniformly distributed throughout the trinitrotoluene in the cast core, the core density being in the range from 1.5 to 1.6 grams per cubic centimeter and having a Weight strength of about 98%. The container 3 which was made of card board, although other suitable material may be used, was sealed with end caps 4 of similar material and had internal dimensions of 4 /2 inches in diameter and 20 inches long. The exact construction of container shown is merely illustrative and may be fashioned in any other suitable manner, for instance, instead of employing caps 4 to close the container, the rosette-type crimp formed of the end portions of the container, such as is wellknown in the industry, may be used. The core had a cross sectional area of one square inch and its length was governed by the desired rate of detonation. For

instance, the eii'cct of core length on the rate of detonation is shown in Table I below. The use of granular ammonium nitrate explosive facilitates loading of the cartridge and if desired spacers 5, formed of card board or other combustible material may be utilized to position the core accurately. Both the ammonium nitrate explosive and core were insensitive to a No. 6 cap and the cartridges were detonated by means of a capsensitive booster composed of 1000 grams of 40% ammonium Table I Detonation Rate, Meters/ Second Gore Length, Inches Table II Core per- Det.

cent by Density Rate Weight Bulk Weight of Cart. (m./ Strength Strength of Oar- (gr./cc.) sec. (percent) (percent) tridge Cores .25 Square Inch in Cross Section Length (Inches):

Cores .58 Square Inch in Cross Section Cores 1.0 Square Inch in Cross Section Length (Inches)- Cores 1.78 Square Inches in Cross Section Length (Inches):

Cores 4 Square Inches in Cross Section Length (Inches):

As may be seen from Table II, the strength varies in accordance with the amount of core material present and as the percentage of the core material increases the strength likewise increases. With cores of small cross section there is no great change in strength with increased core length. With cores of large cross section, the effect of core length on strength is more pronounced.

The method of assembling the blasting cartridges of this invention is relatively simple. For example, assuming it is desired to use a cylindrical cast core 12 inches in length in a cartridge 20 inches long, the container having its bottom end closed is first filled to a height of about 4 inches with the granular ammonium nitrate explosive, which is poured and tamped therein. The core is then inserted in the center of the container with its end resting on the ammonium nitrate explosive therein. Additional ammonium nitrate explosive is then poured and tamped in to fill the remaining space in the container and the top cap is glued in position to seal the container. With some relatively insensitive compositions and in some blasting operations where a number of cartridges are used in a bore hole there may be encountered a tendency for some of the cartridges not to detonate. It is therefore within the purview of this invention to include adjacent the ends of the container a more sensitive explosive such as a wafer of 40% ammonium nitrate-nitroglycerin dynarnite on the order of /2 inch thickness in order to provide satisfactory gap sensitivity. Such wafers are utilized only when necessary to the particular composition and operation. The cartridges in the foregoing specific embodiment may as stated hereinbefore be detonated by means of a suitable booster such as granular trinitrotoluene, or Primacord, or the like. Small amounts of additional ingredients having known beneficial effects may likewise be included in the core composition, such as ammonium nitrate and sodium nitrate to supply oxygen and thus make the mixture somewhat more efficient, other explosives, alunimum powder, and the like. For instance, a core composed of 20%75% trinitrotoluene, 20%-75% cyclonite, and %25% aluminum dust is well suited for the purpose.

Various ammonium nitrate explosives in granular form are known in the art and are suitable for use with the core of trinitrotoluene containing granular high explosive in blasting cartridges of this invention. For example, such explosives have been formed by sensitizing am monium nitrate by intimately admixing therewith powdered aluminum or other metals, trinitrotoluene, picric acid, ammonium picrate, nitrostarch, pentaerythritol tetranitrate, cyclonite, tetryl, small amounts of nitroglycerine and the like. The following compositions have been found well suited for the purpose and, when utilized with a core of composition similar to that set forth in Example I above and having a cross section of one square inch and 12 inches long in a 4 /2 inch by 20 inch cartridge, give the detonation rates respectively set forth: 91.0% ammonium nitrate, 5.0% trinitrotoluene, 3.0% coal dust, 0.5% aluminum dust, and 0.5% powdered chalk with a detonation rate of 4800 meters/second; 86.0% ammonium nitrate, 10.9% trinitrotoluene, 3.0% coal dust, 0.5% aluminum dust, 0.5% powdered chalk with a detonation rate of 5460 meters/second; 91.0% ammonium nitrate, 7.5% trinitrotoluene, 0.5% aluminum dust, 0.5% powdered chalk with a detonation rate of 5680 meters/second; and 89% ammonium nitrate, 7.5% trinitrotoluene, 3.0% coal dust, 0.5 powdered chalk with a detonation rate of 5080 meters/second, all having a Weight strength of about 67%, and, for example, a composition containing 60% ammonium nitrate, 20% trinitrotoluene, sodium nitrate, 5% coal dust, 4.5% aluminum dust and 0.5 chalk dust with a detonation rate of about 4500 meters per second and a weight strength of about 56%. Various other suitable compositions having ammonium nitrate as the major constituent and having varying strengths are set forth for example in the book entitled High Explosive by W. S. Colver published by D. Van Nostrand Company in 1918. For greatest advantage it is preferred that the ammonium nitrate explosive have a detonation rate less than about 4000 meters per second and a weight strength less than about 70%. A preferred ammonium nitrate explosive is one containing from 80% to 95% ammonium nitrate, up to as much as 10% of a sensitizer, such as trinitrotoluene, aluminum dust, or the like, and up to 5% of a carbonaceous material such as coal dust or the like. The invention is therefore applicable to various types of ammonium nitrate explosives and to various core compositions and a novel low cost blasting cartridge is provided.

While the invention has been described in considerable detail in the foregoing, it will be understood that many variations may be made in the procedure and compositions without departing from the spirit of the invention.

Having thus described the invention, what is claimed and desired to secure by Letters Patent is:

1. An explosive cartridge having a case containing granular ammonium nitrate having a sensitivity of not less than the sensitivity of an explosive composition consisting of 94.5 per cent ammonium nitrate and 5.5 per cent parafiin and having a granulation whereby from about 25 per cent to about 40 per cent will pass through the openings in an 100 mesh screen and compressed to a density of not more than about 1.15, said granular ammonium nitrate having a density within the range of about 0.8 to about 1.2, and, embedded in said granular ammonium nitrate, a core of trinitrotoluene having substantially uniformly dispersed therein crystals of a granular high explosive, said core having a density of not less than about 1.4 and being in contact with the surrounding ammonium nitrate, said cartridge having a detonation rate of about 4000 to 8000 meters per second, a weight strength of about 60 per cent to about 90 per cent and a bulk strength of from about 40 per cent to per cent.

2. An explosive cartridge having a case containing granular ammonium nitrate having a sensitivity of not less than the sensitivity of an explosive composition consisting of 94.5 per cent ammonium nitrate and 5.5 per cent paraffin and having a granulation whereby from about 25 per cent to about 40 per cent will pass through the openings in an 100 mesh screen and compressed to a density of not more than about 1.15, said granular ammonium nitrate having a density within the range of about 0.8 to about 1.2, and, embedded in said granular ammonium nitrate, a core of trinitrotoluene having substantially uniformly dispersed therein about 20 per cent to 80 per cent granular high explosive, said core having a density of not less than about 1.4 and being in contact with the surrounding ammonium nitrate, said cartridge having a detonation rate of about 4000 to 8000 meters per second, a weight strength of about 60 per cent to about per cent and a bulk strength of from about 40 per cent to 80 per cent.

3. An explosive cartridge having a case containing granular ammonium nitrate having a sensitivity of not less than the sensitivity of an explosive composition consisting of 94.5 per cent ammonium nitrate and 5.5 per cent paraffin and having a granulation whereby from about 25 per cent to about 40 per cent will pass through the openings in an mesh screen and compressed to a density of not more than about 1.15, said granular ammonium nitrate having a density within the range of about 0.8 to about 1.2, and, embedded in said granular ammonium nitrate, a core of trinitrotoluene having substantially uniformly dispersed therein crystals of a granular high explosive, said core having a density of not less than about 1.4 and being in contact with the surrounding ammonium nitrate, said cartridge having a detonation rate of about 4000 to 8000 meters per second, a weight strength of about 60 per cent to about 90 per cent and a bulk strength of from about 40 per cent to 80 per cent, and a cap sensitive booster charge disposed at the end of the cartridge.

References Cited in the file of this patent UNITED STATES PATENTS 905,336 Lheure Dec. 1, 1908 2,171,384 Young Aug. 29, 1939 2,231,043 Winning Feb. 11, 1941 OTHER REFERENCES Ohart: Elements of Ammunition, page 34 (1946), John Wiley & Sons, N. Y.

Claims (1)

1. AN EXPLOSIVE CARTRIDGE HAVING A CASE CONTAINING GRANULAR AMMONIUM NITRATE HAVING A SENSITIVITY OF NOT LESS THAN THE SENSITIVITY OF AN EXPLOSIVE COMPOSITION CONSISTING OF 94.5 PER CENT AMMONIUM NITRATE AND 5.5 PER CENT PARAFFIN AND HAVING A GRANULATION WHEREBY FROM ABOUT 25 PER CENT TO ABOUT 40 PER CENT WILL PASS THROUGH THE OPENINGS IN AN 100 MESH SCREEN AND COMPRESSED TO A DENSITY OF NOT MORE THAN ABOUT 1.15, SAID GRANULAR AMMONIUM NITRATE HAVING A DENSITY WITHIN THE RANGE OF ABOUT 0.8 TO ABOUT 1.2, AND, EMBEDDED IN SAID GRANULAR AMMONIUM NITRATE, A CORE OF TRINITROTOLUENE HAVING SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN CRYSTALS OF A GRANULAR HIGH EXPLOSIVE, SAID CORE HAVING A DENSITY OF NOT LESS THAN ABOUT 1.4 AND BEING IN CONTACT WITH THE SURROUNDING AMMONIUM NITRATE, SAID CARTRIDGE HAVING A DETONATION RATE OF ABOUT 4000 TO 8000 METERS PER SECOND, A WEIGHT STRENGTH OF ABOUT 60 PER CENT TO ABOUT 90 PER CENT AND A BULK STRENGTH OF FROM ABOUT 40 PER CENT TO 80 PER CENT.

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