US2861875A - Explosive composition - Google Patents

Description

EXPLOSIVE COMPOSITION Cyril James Breza, Thorofare, N. J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 1, 1957 Serial No. 637,628

1 Claim. (Cl. 52-6) The present invention relates to an improved blasting explosive composition. More particularly, this invention relates to a novel explosive composition characterized by unusually high bulk strength or strength per unit of volume.

In all quarry and shipping operations of substantial size, explosives in large quantities are used to release the rock or ore from its bed and to fragment the material so that it can be removed and further processed. much as the cost of the explosive and of the operations required to effect a blast represent a substantial proportion of the cost of the material thus obtained, much time and effort has been spent to reduce such costs. Up to the present, however, the major effort has been in the direction of replacing higher cost materials in the explosive composition and with improving the mechanical means of preparing for blasting operations. Relatively little attention has been given to increasing the bulk strength of the explosive composition. Fewer boreholes or boreholes of smaller diameter can be used if an explosive composition is available which will provide more energy per unit volume of explosive. The only explosives known up to the present time which possessed very high strength per unit volume are either undesirably sensitive to initiation for satisfactory field use in the large quantities required, for example, liquid nitroglycerin and blasting gelatin, or are far too expensive, for example, RDX, HMX, and the like. V

Accordingly, an object of the present invention is to provide a low-cost explosive composition having a very high strength-per unit volume. A further object is to provide such explosive composition further characterized by favorable sensitivity properties. Additional objects will become apparent as this invention is more fully defined.

The foregoing objects are achieved by providing as an explosive charge a cast homogeneous composition consisting of very specific proportions of fine ammonium nitrate, coarse sodium nitrate, TNT, dinitrotoluene, finely divided ferrosilicon, and, preferably, stearic acid, the composition thus cast having a cross-sectional area of at least 3 square inches. r

In order to fully illustrate the present invention, reference is now made to the following example.

Example 1 Twenty-seven parts of fine ammoniumnitrate (atleast 90% passing through a 65 mesh screen and at least 60% passing through a 100 mesh screen), 72 parts of coarse sodium nitrate (98% through mesh screen and 90% held on 20 mesh screen) 24 parts of ferrosilicon (45-65% passing through 200 mesh screen),,and 0.5 part of stearic acid, were mixed and heated in a steam-jacketed mixer to a temperature of about 165 F. To the heated mix was added a molten blend of 23.2 parts of TNT and 3.3

Inas-.

ited States Patent 2,861,875 Patented Nov. 25, 1958 parts of DNT, and mixing and heating were continued until a temperature of about 175 F. was obtained. The mixture, now a thick fluid mass, was poured while at 175180 F. into metal cans 5 inches in diameter by 24 inches in length and allowed to solidify.

The composition thus produced had the following ingredient content by weight:

Percent TNT 15.45 Dinitrotoluene 2.2 Stearic acid 0.35 Ferrosilicon 16.0 Sodium nitrate 48.0 Ammonium nitrate 18.0

The cast density of the mixture was 1.82 grams per cubic centimeter, and the detonation rate was about 4000-4500 meters per second. The propagation sensitiveness was such that detonation could be propagated from the end of one can to the end of the next can over an air gap of at least 4 inches. The cast composition could not be initiated by a No. 8 commercial blasting cap, but was readily initiated by a primer cartridge manufactured for the purpose. Satisfactory propagation of the detonation, however, required a minimum cross-sectional area of at least 3 square-inches.

The bulk strength, i. e., the strength per unit volume, of the above composition in comparison with well known blasting explosive compositions is shown by the following table. To establish a basis for comparison, amatol (21% by weight TNT, 79% by weight ammonium nitrate) was assigned a weight and bulk strength factor of 100.

Density, Weight Bulk Explosive g. Ice. Strength Strength Factor Factor Amatol l. 47 100 100 Ammonium Nitrate-Fuel (93% NH4NO3, 7% Carbon) 1.0 78 54 Nitroglycerin (100%) 1. 60 149 162 Blasting Gelatin (93% NG, 7% nitrocotton) 1. 55 154 162 Example Composition 1. 82 133 165 the nitroglycerin is replaced by ammonium nitrate-fuel mixtures have strengthfactors lying between those of the individual compositions. Thus, the present composition is superior in bulk strength to even the highly sensitive explosive compositions, yet possesses all the handling advantages of the low-strength, relatively insensitive compositions.

Obviously, a closely-controlled ingredient proportioning and selection is essential for the preparation of the present explosive composition. Experimental mixings have shown that the required density and propagating characteristics can be obtained only by a blend of fine ammonium nitrate of such particle size that at least 90% will pass through a mesh screen and at least 60% will pass through a 100 mesh screen, sodium nitrate of such particle-size that at least 98% will pass through a 10 mesh screen and at least will be held on a 20 mesh screen, and ferrosilicon of such size that at least 45% will pass a 200 mesh screen and at least 95% will pass through an 80 mesh screen. If the particle size of the ammonium nitrate exceeds that of the above limits, the composition will not have the propagating characteristics necessary to.insure detonation of the entire column, particularly if individual charges are not in exact alignment and in tight contact with each other. If the particle size of the sodium nitrate exceeds that which will pass a 10 mesh screen, incomplete reaction, with consequent re duction in strength, will result. On the other hand if the particle size is less than that held on a 20 mesh screen, density is decreased because the optimum blending can not be obtained. If the ferro-silicon is not very finely divided, incomplete reaction will result, again causingdecreased strength. a

The quantity of the-TNT-DNT blend used is the minimum required-to provide a mobile mass while the nitrocompoundsare molten-and ahomogeneous continuous solid when-the nitrocompounds -are solidified, andto provide the required sensitizing action. The use of up to 0.35% by weight of stearic acids provides increased mobility to the hot mixture, thus permitting the use of slightly less nitrobody than isrequired in the absence of the stearic acid.

The ingredients must be present in the following proportions by weight:

Percent Ammonium nitrate 15-20 Sodium nitrate 45-55 Ferrosilicon 15-20 TNT 12-17 Dinitrotoluene 2-5 Stearic acid -0.35

The presence of any carbohydrate material is deleterious to both the density of the composition and to the manufacturing safety. Under the conditions of mixing, any carbohydrate material present would represent a serious fire hazard. Oxidation of the carbohydrate material at the casting temperature produces gaseous decomposition products which decreases the density of the finished casting.

The effectiveness of the described composition is illustrated by the following examples in which the explosivecomposition used was identical to that previously described.

Example 2 The present explosive was compared to a conventional explosivein shooting a limestone quarry in West Virginia. The dolomitic limestone in this location is recognized as a material difficult to break.

In the shot, a total. of 16 holes 6 /2 inches in diameter and approximately 52 feet in depth were drilled parallel to the face of the quarry. Each hole was charged with from 12 to 15 cans of explosive, the cans being 5 /2 inches in diameter by 24 inches in length, and two cans of conventional primer. In 7 of the holes, the cans contained the commercial explosive, Nitramex No. 2, a cast charge containing 30% ammonium nitrate, 40% sodium nitrate, 21.65% TNT-DNT blend, 8% ferrosilicon, and 0.35% stearic acid, the composition having a'density of- 1466'grams per cubic centimeter. Each can contained 35 pounds of this composition. Thi composition represents the highest density explosive available prior to the present invention. 5

The cans in the remaining 9 holes contained the'presently described composition, each can weighing '38 pounds. The individual charge per hole consisted of essentially the same number of units as'used in the first 7 holes.

After'thech'argeswere'sh'ot, the ditference'in result was veryjnoticeable. The fragmentation of the limestone broken in frontof'the holes loaded with the presently claimed composition was greatly superior to that broken in front of the conventional explosive. The portion blasted by the present explosive produced a lower pile because of the greater throw of the limestone fragments, thus providing greater safety. and accessibility for shovel operation.

Example 3 The present explosive wascompared also to a conventional explosive in shooting a taconite-type ore in New York. The material is extremely hard to drill; the drill bit having to be resharpened after only about 10 feet of drilling.

Using Nitramex No. 2, the conventional explosive described in Example 2, the drilling pattern employed was 6 /2 inchdiameter holes feet in depth having a 12 foot burden and spaced 12 to 13 feet apart. Each hole was loaded with 9 cans of 5 inches x 24 inches (29 lbs. per can) and 9 cans of 4 /2 inches x 24 inches (22 lbs. per can) of the Nitramex No. 2, 3 cans of 4 inches x 24 inches 14.5 lbs. per can) of primer and from about 50 to pounds ofpellet'ed TNT (Pelletol No. l), a total explosivesweight of between 550 and 575 lbs. The breakage ,obtainedwas satisfactory for loading.

When the present composition, as described in Example 1, was used in place of the Nitramex No. 2 on a can for can basis, the total ex losive weight per hole was increased to from 600' to 625 pounds. Accordingly, the holes were drilled on a 15 foot spacing, thus requiring 20% fewer holes along the face. The breakage was exceptional.

From the foregoing examples, the improvement in blasting efficiency provided by the availability of the present high bulk strength explosive is apparent. In one case, the same explosive loading on a volume basis provided considerably better breakage. In the other case, the high strength of the present explosive permitted the use of wider'spacings, and therefore fewer boreholes, to accomplish the desired results. Both types of effect are of definite economic advantage.

Throughout'this description, the term dinitrotoluene has been'used'to refer to the commercially available mixture of the dinitrotoluene isomers. However, since the dinitrotoluene' is blended with trinitrotoluene at a temperature near to the melting-temperature of trinitrotoluene, the exact isomercomposition of the dinitrotoluene is not critical. The term ferrosilicon is used to refer to the commercial electric furnace product consisting by weight of approximately 50% silicon and 50% iron. As previously indicated, the material is used in very finely divided form.

The explosive ofthis invention isprepared by thoroughly mixing theingredients-to produce a homogeneous mass while'theiTNT and'dinitrotoluene are in liquid form. This mass is then cast into the desired container, which may be of metal as in theexamples, or of any other rigid,

water-impervious packaging material, and allowed to solidify. The'proportion of liquid to solid is such that no segregation of the ingredients can occur during solidification of the molten nitrocompounds. The composition thus cast will have a density of at least 1.8 grams per cubic centimeter. Obviously, the cast composition will be used in its cast form, since granulationwould produce a material havinga' lower bulk density.

The invention h'as been fully described in the foregoing. I intend, therefore, to be limited only by the following claim.

I claim:

A high-density blasting explosive comprising a cast composition having a cross-sectional areaof' at least 3 square inches and consisting by weight of from 15 to 20% of'ammonium nitrate of such fineness that at least will pass through a 65 mesh screenand at least 60% will pass through a l00 mesh screen, from 45 to 55% of sodium nitrate of such coarseness that atleast 98% will pass throught a- 10 meshscreen and at least 90% will be held on a 20 mesh screen, from l5' to 20% of ferrosilicon 6 References Cited in the file of this patent UNITED STATES PATENTS 2,602,732 Farr July 8, 1952 2,733,139 Winning Jan. 31, 1956 2,752,848 Davis July 2, 1956