US2752848A - Blasting explosive - Google Patents

Description

nited States Patent Cfiice 2,752,848 Patented July 3, 1956 BLASTING nmmosrvn Application February 19, 1953, Serial No. 337,888

3 Claims. (Cl. 102-24) No Drawing.

The present invention relates to a novel explosive blasting cartridge, and to its manufacture.

At the present time, substantially all of the underground blasting operations, such as in the mining industry, are carried out with conventional dynamite cartridges having a diameter of from to 1 /2 inches, and a length of 8 inches. The dynamite compositions are based on nitroglycerin, which is present in a ratio of from 25 to 15% of the entire explosive. For special purpose blasting, cartridges as long as 12 or 16 inches have been manufactured, but the 8 inch length constitutes the usual cartridge size. The 1% inch diameter represents the largest diameter considered practicable by the industries using underground blasting because of the expense in producing larger diameter boreholes, and the necessity of holes properly spaced for good fragmentation. This diameter limitation has heretofore precluded the use of nitroglycerin-free explosives, since the high-density charges of diameters under two inches would not propagate the detonation throughout the borehole. When the density was decreased, detonation could be obtained with the small diameters, but the loss of strength rendered the charge unsuitable for underground work.

There are several serious objections to the nitroglycerin dynamites which make a replacement thereof highly desirable. In loading long boreholes, it is frequently necessary to split the cartridge and tamp the composition into the hole. The operating personnel thus subjected to nitroglycerin liquid and vapor sufier from the severe headaches produced by nitroglycerin. The loading of the relatively soft dynamite composition into the borehole presents difficulties since it is essential that the explosive extend to the end of the borehole, and be present throughout in sufficient density for proper blasting action. Since many boreholes present rough sides, and are angled in various directions from the point of loading, the tamping operation requires skill and careful supervision. The short length of the individual cartridge requires repeated withdrawals and replacement of the tamping rod or stick in the borehole.

It is an object of the present invention to provide a small diameter explosive blasting cartridge which does not contain a nitroglycerin composition. A further object is to provide rigid, high-density blasting explosive cartridges in small diameters. A still further object is to provide a method for manufacturing rigid, high-density blasting explosive cartridges free from nitroglycerin which have the requisite sensitivity in small diameters. Additional objects will become apparent as the invention is further described.

We have found that the foregoing objects are attained, and an explosivecartridge of the desired characteristics and dimensions obtained when we package a composition containing at least 60% by weight of a mixture of ammonium nitrate and sodium nitrate, wherein the ammonium nitrate constitutes from 30 to of the weight of the mixture, 10 to 30% of a blend of dinitrotoluene and trinitrotoluene wherein the dinitrotoluene constitutes from 1 to 50% of the weight of the mixture and not more than 10% of the weight of the entire composition, and from 0.5 to 10% by weight of a finely divided metallic fuel.

The ammonium nitrate has a fineness such that at least 40% will pass through a mesh screen. The bulk density of the entire amount of ammonium nitrate present must be less than 0.95 gram per cubic centimeter. While the fineness of the sodium nitrate is not as critical as that of the ammonium nitrate, it is preferred that at least 50% pass a 48 mesh screen.

The cartridge is manufactured by first forming a blend of the substances in the proportions set forth above at a temperature of at least about 160 F., then slowly cooling, with constant stirring, the blend thus formed to a temperature between F. and F., and immediately packing at the latter temperature to form a substantially cylindrical cartridge having a diameter of from 1 to 2 inches. The cartridge thus produced is rigid when cooled to ambient temperatures and has a density of from 1.3 to 1.5 grams per cubic centimeter.

The cartridge may be made several feet in length, if desired, and packaged in a shell of waterproof material such as paraffined paper, synthetic film, etc. The preferred procedure is to pack the heated composition directly into the shell. However, the invention is not limited with respect to the packaging material or to packing the composition directly into a waterproof shell.

The cartridge prepared as described above is a highvelocity, high-strength blasting explosive completely free from nitroglycerin which can be initiated by a cap-sensitive primer and will propagate the detonation along a column within a borehole, in diameters as small as from 1 to 2 inches. The high density of the cartridge provides a sufficient quantity of explosive composition per unit length of the borehole to approximately equal the blasting strength of an equivalent length of tamped dynamite.

The composition of the charge may be varied over a considerable range provided the high density, high velocity, and adequate sensitivity are, maintained.

The effects obtained by varying the proportions of the ingredients and by the omission or substitution of ingredients is illustrated in Table 1, wherein the ingredients are listed as per cent by weight of the final composition. The density is measured as grams per cubic centimeter and the velocity as meters per second. In Examples 1 to 11 inclusive, the sensitivity was measured with full cartridges placed end to end, while in Examples 12 to 18 inclusive, the cartridges were cut in half and the distance the primer would consistently initiate the receptor was measured. In Examples 19 to 23 inclusive, the cartridges were again end to end, but the ends were closed with metal foil. In all of the examples, the cartridges had a diameter of 1% inches and a length of from 18 to 24 inches.

The cartridges were prepared by mixing the ammonium nitrate and sodium nitrate in a ribbon-type mixer at about 150 F., adding the ferrosilicon and raising the temperature of the mixture to F. At this point, the melted trinitrotoluene-dinitrotoluene blend was added, and the ingredients mixed for 10 minutes at F. The mixture was slowly cooled with constant mixing to between 120 F. and 140 F. and packed at this tempera ture into the shells to the density shown. The packing was done by hand, the composition being tamped to the desired density.

TABLE I Dinitrotoluene Trinitrotoluene #3 Ammonium Nitrate #2 Ammonium Nitrate Example nium #4 Ammo- Nitrate Sensitivity Calcium Stearate Ferrosilicon Sodium Nitrate Density Velocity #mhwmmwwwoamww-mm es s wwweeew ewoomm wwesm OQ'IUIUIQILAQOOOOOUIOOOOOOOOOO Propagation over an air gap. #1 Ammonium Nitrate:

On 20 mesh sereen1025%.

On 35 mesh sereen80%.

Through 65 mesh screen-5%.

#2 Ammonium Nitrate:

On 35 mesh sereen5%.

On 65 mesh sereen0-10%.

Tllloclgll 100 mesh screen55100%; bulk density-less than 0.90

From the foregoing table, the following conclusions can be drawn:

1) Mixtures having 10% or less of the mixture of trinitrotoluene and dinitrotoluene as illustrated in Examples l to 4 are not adequately sensitive, and the absence of dinitrotoluene (Example 5) causes the density of the packed charge to be below the desired level. However, where the dinitrotoluene is present in an amount exceeding of the total weight of the composition (Example 17), the resultant product will be insensitive and will not propagate. Any of the commercial grades of trinitrotoluene and dinitrotoluene may be used.

(2) The physical characteristics of the ammonium nitrate are of importance in determining the properties of the explosive. Example 21, utilizing only coarse ammonium nitrate, illustrates that such composition will not propagate the detonation. Example 20, using a finer ammonium nitrate than that of Example 21 shows some improvement, but is still not sufficiently sensitive. When an ammonium nitrate of fine, regular grains, and a correspondingly higher density than 0.93 gram per cubic centimeter, is used, as in Example 19, the sensitivity is still not adequate. The fine, irregularly shaped grains of ammonium nitrate designated as ammonium nitrate #2, either in admixture with a coarse ammonium nitrate as in Examples 6 and 10, or with sodium nitrate as in Examples 11, 18, 22 and 23, produces the desired characteristics of density, sensitivity and high velocity.

The effect of density on propagation and also the desirability of using metal closures on the ends is illustrated in Table 2, wherein the air gap was measured with the cartridges in an end-to-end relationship.

A cartridge having a density below 1.3 grams per cubic #3 Ammonium Nitrate:

On 35 mesh screen1520%. Through mesh screen1535%. #4 Ammonium Nitrate:

On 35 mesh screen05%. On 65 mesh sereen0-10%. Thr/ough 100 mesh sereen55100%; bulk density-more than 0.93

g. cc.

centimeter can be prepared from the present compositions, but such low-density explosive cartridges are not suitable for underground blasting, and are therefore outside the scope of the present invention.

By the ballistic mortar test, the preferred composition, illustrated in Examples 11 and 22, is rated about 94% as strong as trinitrotoluene. In actual field trials in hard granite rock, the same composition was found to be equal to an ammonia semi-gelatin dynamite having a ballistic mortar rating of in comparison with TNT.

The packing density of the composition is a function of the packing temperature. When packed at temperatures over 150 F., the density of the cartridge exceeds 1.5, while when packed at temperatures below F., densities as high as 1.3 could not be consistently obtained.

The explosive cartridges of the present invention are thus substantially equal in strength to the nitroglycerin dynamites and have the distinctive advantage over the nitroglycerin dynamites of being rigid and free from toxic effects on the users. An additional advantage is that the present cartridges are much safer to handle since they are much less sensitive to shock than the conventional dynamites. Because of the safety features of this explosive, methods of packing the cartridges are not so limited as in the case of nitroglycerin-containing compositions and cartridges can be made in long lengths for example, 36 to 48 inches, without difficulty, and, due to their rigidity, used to tamp the preceding cartridges into the borehole. Thus, for long borehole shooting, they are much easier and safer to load.

While only ferrosilicon has been used in the examples, conventional metallic fuels such as aluminum, magnesium-aluminum alloys, and magnesium silicide can be used just as satisfactorily. The ferrosilicon will preferably contain at least 40% silicon. The following example illustrates the use of aluminum in the present composmon Example 24 The procedure described in connection with the examples listed in Table 1 was followed, using the following ingredients:

20 parts trinitrotoluene, 4 parts dinitrotoluene, 30.2 parts #2 ammonium nitrate, 42.7 parts of sodium nitrate, 2.0 parts of finely divided aluminum, and 0.5 part of calcium stearate.

The composition had a velocity of 4165 meters per second at a density of 1.3 grams per cubic centimeter. The sensitivity, measured by the air-gap test, was 1 /2 inches with plain ends and over 7 inches with metal covered ends.

The invention has been described in detail in the foregoing. Many variations and modifications may be made without departing from the scope of this invention. Therefore, we intend to be limited only by the following claims.

We claim:

1. A blasting cartridge comprising a substantially cylindrical charge having at least 60% by weight of a mixture of ammonium nitrate and sodium nitrate, the proportion of ammonium nitrate in said mixture being from to 85% and the ammonium nitrate having a bulk density of less than 0.95 gram per cubic centimeter and at least thereof passing a 100 mesh screen, over 10% and up to 30% by weight of a blend of dinitrotoluene and trinitrotoluene, the proportion of dinitrotoluene in the blend being from 1 to but not exceeding 10% by weight of the entire charge, and from 0.5 to 10% by weight of a finely divided metallic fuel, said charge having a diameter of from 1 to 2 inches and a density of from 1.3 to 1.5 grams per cubic centimeter.

2. A blasting cartridge as claimed in claim 1 wherein the finely divided metallic fuel is a ferrosilicon having at least 40% silicon.

3. A method for the cartridging of a detonating explo sive composition containing at least by weight of a mixture of ammonium nitrate and sodium nitrate, the proportion of ammonium nitrate by weight in said mixture being from 30 to and the ammonium nitrate having a bulk density of less than 0.95 gram per cubic centimeter and at least 40% thereof passing a mesh screen, over 10% and up to 30% by weight of a blend of trinitrotoluene and dinitrotoluene, the proportion of dinitrotoluene being from 1 to 50% but not exceeding 10% of the weight of the entire charge, and from 0.5 to 10% by weight of a finely divided metallic fuel, which comprises heating said composition to a temperature of at least 160 F., cooling said charge slowly and with constant stirring to a temperature of between and F., and packing at this temperature into a substantially cylindrical form having a diameter of from 1 to 2 inches to a density of from 1.3 to 1.5 grams per cubic centimeter.

References Cited in the file of this patent UNITED STATES PATENTS 393,634 Favier Nov. 27, 1888 1,992,217 Kirst et al. Feb. 26, 1935 2,069,612 Kirst et a1 Feb. 2, 1937 2,087,285 Handforth et al. July 20, 1937 2,168,562 Davis Aug. 8, 1939 2,602,732 Farr July 8, 1952

Claims (1)

1. A BLASTING CARTRIDGE COMPRISING A SUBSTANTIALLY CYLINDRICAL CHARGE HAVING AT LEAST 60% BY WEIGHT OF A MIXTURE OF AMMONIUM NITRATE AND SODIUM NITRATE, THE PROPORTION OF AMMONIUM NITRATE IN SAID MIXTURE BEING FROM 30 TO 85% AND THE AMMONIUM NITRATE HAVING A BULK DENSITY OF LESS THAN 0.95 GRAM PER CUBIC CENTIMETER AND AT LEAST 40% THEREOF PASSING A 100 MESH SCREEN, OVER 10% AND UP TO 30% BY WEIGHT OF A BLEND OF DINITROTOLUENE AND TRINTROTOLUENE, THE PROPORTION OF DINITROTOLUENE AND BLEND BEING FROM 1 TO 5% BUT NOT EXCEEDING 10% BY WEIGHT OF THE ENTIRE CHARGE, AND FROM 0.5 TO 10% BY WEIGHT OF A FINELY DIVIDED METALLIC FUEL, SAID CHARGE HAVING A DIAMETER OF FROM 1 TO 2 INCHES AND A DENSITY OF FROM 1.3 TO 1.5 GRAMS PER CUBIC CENTIMETER.