US3026221A - Explosive composition - Google Patents

Description

3,026,221 EXPLOSTVE (IQ-MPQEHTTQN William E. Kirst, Woodhury, N..l., assignor to E. l. (in Pont de Nemours and Company, Wilmington, Deh, a corporation of Delaware Mo Drawing. Filed .lnly 21, 1958, Ser. No. 749,632 2 Claims. (Cl. 149-39) The present invention relates to a novel blasting composition which is of high density. More particularly, the

present invention relates to a high-density blasting com- 7 position comprising low-cost ingredients.

In blasting operations, for example quarrying and stripping, the use of a high-density explosive composition is highly desirable on a theoretical basis. High-density compositions providing greater weight of explosive, and thus increased available energy, per unit volume make pos sible the use of fewer and/ or smaller diameter boreholes, equivalent blasting energy being provided by a lesser volume of high-density explosive. The savings in drilling costs resulting from reduction in number and size of the boreholes are of obvious importance. However, in practice, these theoretical considerations are complicated by several factors.

In the main, the relatively high costs of the available high-density explosives, e.g. blasting gelatin, more than counteract the economies effected by reduction in drilling costs. This factor, and also the undesirably high initiation sensitivity of blasting gelatin and the like, has led to widespread usage in blasting operations of the lowercost but low-density ammonium nitrate-type compositions.

To overcome the aforementioned deficiencies of the high-density explosives, certain cast explosives which are of high density, low cost, and satisfactory sensitivity have been developed for use in blasting operations. These cast compositions, in spite of their many advantages, are at times deficient in that their rigid nature prevents their expansion to fill the borehole volume, which naturally reduces the advantages resulting from their high density. This problem is also encountered to some extent with the high-density blasting gelatins which must be tamped to fill the borehole space. Really efiicient tamping is seldom achieved, especially in those boreholes formed by the 4 jetting technique and thus having very irregular contours. Inasmuch as the jetting method of drilling is becoming more and more prevalent, the tamping procedure, on a whole, is becoming less and less popular.

Accordingly, an object of the present invention is the such a blasting composition which is free flowing in nature and can be readily poured to fill the entire volume of the borehole.

i have found that the foregoing objects may be achieved when I provide a blasting composition comprising sodium nitrate admixed with high-density, essentially spherical trinitrotoluene (TNT) pellets relatively uniform in size. In accordance with the present invention, a metallic fuel, which influences density and detonation velocity, and/or a hydrocarbon oil, which assists in maintaining the proper intermingling of ingredients, optionally may be included in the formulation.

The following examples serve to illustrate specific embodiments and features of the present invention. However, they will be understood to be illustrative only and not as limiting the invention in any manner. Parts in the examples are parts by weight, unless otherwise designated. The TNT pellets used in the exemplified experiments were a commercially available material termed pelletol comprising free-flowing water-resistant pellets of TNT substantially spherical in form.

Example 1 Into a mixer of the type conventionally used in the preparation of explosive compositions were charged 4000 parts of the TNT pellets and 6000 parts of sodium nitrate of a commercial grade having the following fineness specifications.

Tyler standard screens:

On 10 mesh 2.0% max. On 20 mesh 14.0% max. Through 100 mesh 15-40%.

The ingredients were mixed until a uniform blend was apparent and then the free-running mixture was discharged from the mixer. A 4-inch-diameter, 24-inch-long metal can of the type conventionally used for explosives was packed with the formulation in the amount of about 6725 parts. The density of the material within the can was 1.43 grams per cubic centimeter. The explosive cartridge was submerged in water and was initiated by a standard 4-pound pentolite (TNT-PETN) primer. The charge detonated at a velocity of 3135 meters per sec- Example 2 A formulation comprising 36% by weight of the TNT pellets, 54% by weight of the sodium nitrate, and 10% by weight of ferrosilicon was prepared and packaged in accordance with the procedures of Example 1. The freerunning explosive, which was present in the metal container in the amount of 6880 parts, had a density, as packed, of 1.46 grams per cubic centimeter. Upon initiation under water by the pentolite primer, the charge detonated at a velocity of 3580 meters per second.

Example 3 Another mixing was prepared and packaged by the Example 1 procedures, the composition comprising a free-running mixture of 38% of the TNT pellets, 60% of the sodium nitrate, and 2.0% of motor oil. The filled metal container held 6330 parts of the formulation which had a density, as packed, of 1.36 gram per cubic centimeter. The charge was initiated under water by the pentolite primer and detonated at a velocity of 3970 meters per second.

Two other formulations were prepared, in one of which grained TNT was substituted for the pellets and in the other the TNT pellets were replaced by flaked TNT. Formulation A consisted of 38.5% of grained TNT, 60% of the sodium nitrate, and 1.5% of a low-viscosity mineral oil (commercially available as Bayol F), Formulation B being identical with the exception that the TNT was flaked. The 4 x 24 inch metal container held only 5780 parts of Formulation A (density, 1.22 g./cc.) and only 6020 parts of Formulation B (density, 1.27 g./cc.). When initiated by the pentolite primer, Formulations A and B detonated at velocities of 4100 and 3100 meters per second, respectively.

Example 4 A number of other free-running mixings were prepared and packaged as aforedescribed, the compositions and the properties of the mixings being summarized in the following table. In all cases, the mixes were initiated under water by 4-pound pentolite primers.

Ingredients (wt. percent) Wt. of D. of Velocity of Mix N0. Metal Fuel Compn. Compn. Detonation Bayol in car- (g./cc.) (KL/S90.) 'lNl NaNO F oil tridge Al FeSi Fe (parts) powder powder 1 Prilled sodium nitrate (coarse granules).

As has been exemplified, free-running explosive compositions of high-density and desirable sensitivity may be readily prepared by simple mechanical admixture of TNT pellets with sodium nitrate and optional modifiers. Although the other ingredients naturally exert an influence upon density, it may be seen from Example 3 that all other things being equal, the use of pelletized TNT results in greater density than does the employment of either grained or flaked TNT. To facilitate the attainment of high density, the TNT pellets should be of high density. To expedite the formation of a uniform mixture, the TNT pellets should be substantially spherical in form and relatively uniform in size, that is, their diameter should fall within the limits of narrow range. Thus, the use of TNT pellets meeting the afore-mentioned prerequisites constitutes a critical feature of the present invention. Suitable TNT pellets are readily available commercially as pelletol pelleted TNT. These pelletol pellets are free-flowing and water-resistant. The diameter of the individual pellets is inch. Their absolute density is 1.55- 1.60 grams per cubic centimeter, while their bulk density falls within the range of O.901.05 grams per cubic centimeter. Although these exemplified pellets function very satisfactorily and, thus, their use constitutes a preferred embodiment of the present invention, other TNT pellets meeting the afore-mentioned requirements may be substituted, when available, for the exemplified material.

The TNT pellets are incorporated in the mixture in the amount of at least 25% by weight, in order to insure propagation of the detonation. The most important factor determining the upper limit on the proportion of TNT used is an economic factor, the cost of the finished composition being directly proportional, on the whole, to the amount of TNT present. Inasmuch as increases in the TNT content beyond 40% increase the total cost of the composition without effecting material gains in its performance, I prefer to employ not more than 40% of TNT pellets in the composition.

To obtain the desired high density, the TNT pellets must be mixed with sodium nitrate as the oxidant, other conventional oxidants, for example ammonium nitrate, being of too low absolute density to serve the purposes of the present invention. The sodium nitrate is used in the amount of 4864%. Its granulation per se is not critical, although naturally the finer granula-tions give higher packed densities than those resulting from the employment of very coarse sodium nitrate, for example prills.

As illustrated in the foregoing examples, the novel blasting agent compositions of the present invention are characterized by a bulk density of at least about 1.4 grams per cubic centimeter.

A metallic fuel optionally may be included in the formulation in an amount of up to about 20% by Weight. The inclusion of such fuel naturally modifies density, oxygen balance, and velocity of detonation, and, thus, these factors must be considered in the selection of the specific metallic fuel and its percentage. The metallic fuel naturally should be employed in finely divided state to provide an essentially uniform commingling of ingredients.

In addition to the exemplified ferrosilicon, aluminum, and iron, suitable metallic fuels include all those conventionally incorporated into blasting compositions, for example, manganese, magnesium, ferromanganese, and magnesiumsilicon alloys, among others.

The hydrocarbon oil, for example mineral oil or motor oil, may be incorporated, if desired, in slight amounts, e.g. up to 2%, as an antisegregating agent, that is to maintain the proper intermingling of ingredients.

Due to its free-running nature, the present explosive composition may be employed in a number of ways in blasting operations. It may be packaged in conventional shells, say of paper, or in the Waterproof metal cans commonly used, the exemplified formulations being packaged in the latter manner to facilitate testing. Advantageously, the composition may be poured directly into dry boreholes to give an explosive column conforming to the borehole contours. Wet holes may be provided with a liner of plastic, e.g. polyethylene, which prevents contact of the composition with water and permits the loading of the composition in loose form into wet holes. Of course, if the hygroscopic sodium nitrate is provided with a protective waterproof coating, the composition may be used in wet holes without the employment of auxiliary waterproofing means, e.g. the plastic borehole liner or metal or other Waterproof shells, because the other components of the formulation are not seriously affected by water.

The invention has been described in detail in the foregoing. However, it Will be apparent to those skilled in the art that many variations are possible Without departure from the scope of the invention. I intend, therefore, to be limited only by the following claims.

I claim:

1. A substantially dry high-density, free-running explosive composition which consists essentially of a heterogeneous mixture of 25-40% by weight of high-density TNT pellets relatively uniform in size and substantially spherical in form admixed with 4864% by weight of sodium nitrate, 0-20% by Weight of a metallic fuel selected from the group consisting of ferrosilicon, aluminum, and iron, and 02% by weight of a hydrocarbon oil selected from the group consisting of motor oil and mineral oil, said explosive composition having a bulk density of at least about 1.4 grams per cubic centimeter.

2. An explosive composition according to claim 7, wherein said TNT pellets have a diameter within the range of A A inch, a bulk density of 0.90-1.05 grams per cubic centimeter, and an absolute density of 1.55-1.60 grams per cubic centimeter.

References (Jilted in the file of this patent UNITED STATES PATENTS 1,659,449 Snelling et al. 'Feb. 14, 1928 2,733,139 Winning Jan. 31, 1956 2,930,685 Cook et al. Mar. 29, 1960 FOREIGN PATENTS 755,695 Great Britain Aug. 22, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,026 22l March 2O 1962..

William E. Kirst It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 60, for the claim reference numeral "7" read l Signed and sealed this 24th day of July 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Amsfing Officer Commissioner of Patents

Claims (1)

1. A SUBSTANTIALLY DRY HIGH-DENSIYT, FREE-RUNNING EXPLOSIVE COMPOSITION WHICH CONSISTS ESSENTIALLY OF A HETEROGENEOUS MIXTURES OF 25-40* BY WEIGHT OF HIGH-DENSITY TNT PELLETS RELATIVELY UNIFORM IN SIZE AND SUBSTANTIALLY SPHERICAL IN FORM ADMIXED WITH 48-64% BY WEIGHT OF SODIUM NITRATE, 0-20% BY WEIGHT OF A METALLIC FUEL SELECTED FORM THE GROUP CONSISTING OF FERROSILICON, ALUMINUM, AND IRON, AND 0-2% BY WEIGHT OF A HYDROCARBON OIL SELECTED FROM THE GROUP CONSISTING OF MOTOR OIL AND MINERAL OIL, SAID EXPLOSIVE COMPOSITION HAVING A BULK DENSITY OF AT LEAST ABOUT 1.4 GRAMS PER CUBIC CENTIMETER.