US3011883A - Dynamite composition - Google Patents

Description

United States Patent The present invention relates to an improved dynamite composition. More particularly, the present invention relates to a dynamite composition especially suited for use in underground operations.

Conventional dynamite containing nitroglycerin as the principal sensitive explosive ingredient is widely used, particularly in underground operations such as mining, because of its excellent sensitivity, even in small diameter; its stability; its uniformity of action; and its favorable oxygen balance. However, one main disadvantage of conventional dynamite is that its nitroglycerin component causes severe headaches to the persons coming in contact with it or inhaling its vapors, for example, because of leakage of the nitroglycerin from the dynamite cartridge or because of unreacted nitroglycerin in the debris from the blast. This physiological property is not peculiar to nitroglycerin alone but also to all other liquid aliphatic nitric esters. v

In attempts made to eliminate this headache problem, other sensitive explosive ingredients have been substituted for the nitroglycerin in dynamite formulations. However, the resultant formulations have not been entirely satisfactory from the standpoint of performance or cost. For example, when the nitroglycerin was replaced by PETN in conventional formulations, their sensitivity, as evidenced by their ability to propagate the detonation over an air gap, was decreased to a substantial degree. Underground boreholes frequently are horizontal or inclined slightly from the horizontal direction. The explosive cartridges must be pushed and tamped into the borehole one at a time. Because of dirt and loose material from the borehole walls, as well as failure on the part of the loader to insert fully each cartridge, gaps between individual cartridges are common. Compositions of low sensitiveness are not satisfactory for .this type of shooting because of the likelihood that all of the load in the borehole will not fire if a gap does exist. Because of the foregoing, conventional formulations based on PETN have not met with commercial success.

In order to increase the air-gap sensitiveness of PETN formulations, special measures have been taken in preparing these compositions. As an example, Johnson and Lewis (US Pat. 1,972,938, September 11, 1934) improved the sensitiveness to some extent and to a variable degree by coating the PETN onto the ammonium nitrate particles prior to their incorporation into the final formulation. However, the dynamites prepared by this special procedure still lacked sufficient sensitiveness and dependability of action for commercial acceptance.

More recently, a dynamite formulation free of nitroglycerin and having acceptable sensitiveness was developed. In this composition, which is described in US. Patent 2,499,321 (Lyte, February 28, 1950), the sensitive explosive component is pentolite, a mixture of PETN and trinitrotoluene. Although the presence of the latter compound in conjunction with the 'PETN increases sensitiveness to a satisfactory level, it also results in the production of noxious fumes common to TNT- containing compositions. Such fumes of course are highly undesirable in underground workings, and operations must be delayed after the blast, sometimes for substantial intervals, until the fumes and smoke have dissipated. For this reason, fume-producing compositions have been discriminated against in these underground operations and recourse has been necessary at times and has been made reluctantly to the headache-causing nitroglycerin-based explosives.

More recently, a PETN-sensitized composition was developed which had satisfactory air-gap sensitiveness, does not cause undesirable fumes, and has no headachecausing propensities. In this composition, which is described in detail in copending application Serial No. 741,- 004', filed June 10, 1958, by H. H. Fassnacht and D. L. Sagers and assigned to the present assignee, the desired sensitiveness is obtained by careful regulation of the particle size ratio of the oxidant and the PETN. Although this composition exhibits the necessary explosive properties, it suffers somewhat on an economic basis because its content of PETN must be maintained relatively high to obtain the desired sensitiveness, thus increasing manufacturing costs and ultimately the selling price of the composition. the explosives industry, even minor savings in manufacturing costs are of importance. Thus, the availability of a PETN-sensitized composition which has the required explosive properties and at the same time contains comparatively minor proportions of expensive ingredients would be of great value to the art.

Accordingly, an object of the present invention is the provision of a dynamite composition free of headachecausing components. Another object of the present invention is the provision of such a dynamite which does not cause undesirable fumes and thus is suitable for use in underground operation. A further object of the present invention is the provision of such a dynamite which has a low content of high-cost explosive sensitizer. Other objects will become apparent as the invention is further described. a

I havefound that the aforementioned objects may be achieved when I provide a dynamite containing 27% of PETN, the particles of which have a maximum dimension within the range of 0.1 and 10 microns, the average maximum particle dimension being within the range of 0.1 and 2 microns, as the sole organic explosive component, 0.32.0% of pigment-grade flaked aluminum, 6288.S% of ammonium nitrate, 411.5% of a combustible, and O-25% of sodium nitrate.

The following examples serve to illustrate specific embodiments of the present invention. However, they will be understood to be illustrative only and not as limiting the invention in any manner. Unless otherwise designated, the parts in the examples are parts by weight. In all examples, the ammonium nitrate used was a standard blend which passes through an S-mesh Tyler screen and is substantially held on a 325-mesh screen, and the combustibles were those conventionally used in dynamites.

EXAMPLE 1 In order to determine the effect on sensitivity of the inclusion of PETN and aluminum in an ammonium nitrate-combustible formulation, a series of mixings were made in which PETN of the afore-specified particle size was included, a standard grade of flaked pigment-grade aluminum was included, and a combination of these two components was included. In all cases, the mixtures were packed in standard 1% x 8 inch paper shells and tested Patented Dec. 5, 1961 In view of the intense competition within travels to initiate the other half-cartridge, the receptor, is determined by a trail and error" method by adjusting the gap between half-cartridges in a series of trials, similar to the method employed in the drop test. The air gap 4 max.; through IOU-mesh, 2.0% max). The resultant formulation had a stick count of 142, an oxygen balance of +6.0 (exclusive of Wrapper), and a half-cartridge airgap sensitiveness of only A inch (50% detonation over which the detonation of the primer propagates to ini- 5 d M th t tiate the receptor in 50% of the trails is termed the 50% 1 althfl'ugh alumlmlm Content Was 011 e a detonations point. The compositions and their propof the previous mix. erties are summarized in the following table.

Table 1 Ingredients (Percent by Wt.) Properties N C mbustbl Mix O l 6 Oxygen Stick Detonation Half-Otg. AmGap NH4NO3 PETN Al Balance Count 3 Velocity sensitiveness Apricot Treated (rm/sec.) 50% Point (111.) Pit Meal Starch Starch 1 1.0 4.0 4.0 +6.0 20 8 5 34. J2 -33. 2.0 5.0 4.0 +5.2 128 Could not be initiated, even with Std. No. 8 cap. 3 86.0 5.0 2.0 2.0 1.0 4.0 +6.5 120 2, 420 14%.

! Finely divided gclatinized starch powder.

1 Exclusive of paper Wrapper; formulations when packaged in the combustible paper shell are essentially oxygen balanced. 3 Standard measure of density as expressed in number of cartridges per 50-pound case.

EXAMPLE 2 In order to illustrate the influence on sensitiveness of the nature of the powdered aluminum, a formulation (86% NH NO 5% of the aforespecified PETN, 2% Al, 3% of treated starch, 1% of apricot pit meal, and 3% of starch) essentially identical to Mix No. 3 was prepared. In this formulation, however, the aluminum was a standard grade of atomized aluminum. This mixing was packaged in standard 1%. inch by 8 inch paper shells. Although this formulation was satisfactory from the point of view of oxygen balance (+6.5 exclusive of wrapper), stick count (119), and detonation velocity (2185 meters per second), its air-gap sensitiveness as determined in the previously defined test was so low 4 inch) as to preclude its acceptability.

When another formulation was prepared so as to contain 5.0% of the specified PETN, 84.5 of ammonium nitrate, 2.5% of combustible, and a greatly increased amount (8%) of the atomized aluminum, its half-cartridge air-gap sensitiveness" was still unacceptably low (4-inch 50% detonations point).

EXAMPLE 3 Into a standard mixer for granular explosive compositions were charged 2040 parts (68% by weight of the mix) of ammonium nitrate, 450 parts (15%) of sodium nitrate passing through 8-mesh Tyler screen and held on 200-mesh, 150 parts (5%) of PETN having a maximum particle dimension within the range of 0.1 and 10 microns, the average maximum particle dimension being within the range of 0.1 and 2 microns, parts (0.5%) of the standard flaked pigment-grade aluminum, parts (1%) of wood pulp, 165 parts (5.5%) of apricot pit meal, and 150 parts (5%) of finely divided gclatinized starch powder. The ingredients were mixed at ambient temperature for about 10 minutes, and then the mix was packed into standard 1% x 8 inch paper shells. The oxygen balance of the composition exclusive of shell was +5.9, the stick count being 145. In the standard half-cartridge airgap sensitiveness test, the 50% detonations point was 8 inches, and the detonation velocity was 1830 meters per second.

Another formulation was prepared and packaged in accordance with the above procedure with the exception that a commercial blend of coarse PETN was substituted for the fine PETN and the aluminum content was increased to 1% while the apricot pit meal content was decreased to 5.0%. The PETN used was the so-called cap-grade (standard Tyler Screen analysis: on 14-mesh, 0.0%; on 20-mesh, 5.0% max.; accumulated on 65-mesh, 85%

EXAMPLE 4 Three formulations were prepared containing 7% by Weight of PETN. In two formulations (Mixes A and B) the PETN had a maximum particle dimension within the range of 0.1 and 10 microns, the average maximum particle dimension being 0.1 to 2 microns, and in the other mixing (Mix C) the PETN was the afore-defined cap The properties of mixes, determined and specified as previously described, were:

Mix A:

Oxygen balance (no wrapper) +6.5 Stick count 127 Detonation velocity (m./sec.) 2040 Air-gap sensitiveness (50% point) in 10 Mix B:

Oxygen balance (no wrapper) +4.9 Stick count 127 Detonation velocity (m./sec.) 2365 Air-gap sensitiveness (50% point) in 13 Mix C:

Oxygen balance (no wrapper) +6.7 Stick count 131 Detonation velocity (m./sec.) 1870 Air-gap sensitiveness (50% point) in 3 EXAMPLE 5 When a formulation consisting of, on a weight basis, 2.0% of PETN having a maximum particle dimension of 0.1 to 10 microns (average, 0.1 to 2 microns), 1.0% of the standard flaked pigment-grade aluminum, 88.0% of ammonium nitrate, 4.0% of finely divided gclatinized starch powder, and 5.0% of apricot pit meal was packaged in the standard paper shells (1% by 8) and then tested in accordance with the specified procedures, its properties were determined to be as follows:

Oxygen balance (no wrapper) +5.7

Stick count 131 Detonation velocity (m./sec.) 1525 Air-gap sensitiveness (50% point) in 12 EXAMPLE 6 Two additional formulations were prepared and packaged in l fii-inch by 8-inch paper shells, and their properties were determined, the compositions and properties being tabulated as follows:

6 cally impractical, inasmuch as adequate sensitivity is obtained when 27% of PETN is present and increases in the content of this ingredient naturally increase manufac turing costs and, thus, selling price.

The aluminum also must be of a specific type, which Table 11 Ingredients (Wt. Percent) Properties M No Detonation Air-Gap PETN 1 Al 2 N H NO NaNO; Combus- Ethylene Oxygen Stick Velocity Sensitivetible 3 Glycol Balance Count- (m./see.) ness (50% Point). in. I

I 4. 2 0. 8 62.0 25. O 8.0 +6.1 131 1, 485 12 II 4. 2 0. 8 72. 5 l5. 0 7. 0 0. 5 +7. 9 121 not detd. 13

1 Standard flaked pigment-grade.

3 Mix I: Bagasse pith impregnated with hydrocarbon resin (50/50 wt. proportions).

divided gelatinized starch powder and 2% of gum rosin.

As illustrated by the examples, low-velocity (1500- 2500 meters per second) dynamites having not only satisfactory oap-sensitiveness but also acceptable air-gap sensitiveness and yet containing only minor proportions of the expensive organic explosive, PETN, may be readily prepared in accordance with the present invention.

Although both PETN and aluminum have been employed in explosive compositions, I believe that I am the first to discover that a combination of minor proportions of these ingredients in a simple mechanical mixture act synergistically to exert a favorable influence upon the ability of the composition to propagate its detonation across an air gip, which ability is not only desirable but necessary for commercial acceptance of the explosive. This effect of the synergistic combination in contrast to the effects of either component alone are obvious in the experiments reported in Example 1. Although PETN alone under carefully regulated conditions has been found to sensitize dynamite to the extent that the dynamite has acceptable air-gap sensitiveness, the necessary sensitiveness is imparted to the dynamite only when the PETN content is high, at least 7% and preferably greater. The use of lesser quantities e.g. the 5% of Mix No. 1, Table II, results in inadequate air-gap sensitiveness. As is well known in the art, aluminum is generally added to explosive compositions to increase their strength and capsensitiveness, generally this ingredient having only slight, if any, effect on air-gap sensitiveness except when the compositions are specially prepared by undesirably cumbersome incorporation procedures. For example, the aluminum-containing Mix No. 2 (Table I) did not even possess adequate cap-sensitiveness even though the aluminum content was relatively high with respect to the content of the component generally incorporated into explosive compositions. Only by using a combination of these ingredients in economically desirable amounts was an acceptable formulation obtained.

In order that the PETN-aluminum combination effect the required sensitization, specific and restricted types of both ingredients must be used. As shown, conventional PETN grades are unsuited to the instant composition, the desired results being obtained only when the PETN used has a maximum particle dimension within the range of 0.1 and 2 microns. The PETN is employed in the amount of 27% by weight of the total composition. The use of lesser amounts results in inadequacy of sensitivity, whereas the use of greateramounts is economi- Mix II: 5% of finely Applied Chemistry, vol. I, p. 278 (N.Y., Longmans, Green, & Co., 1937). The specifications on this pigmentgrade aluminum powder are given in ASTM-D692-49 available in 1955 Book of ASTM Standards, Part 4, pp. 125-126 (American Society for Testing Materials, Philadelphia). As has been shown other types of finely divided aluminum powder such as that type commercially termed atomized, even when present in large amounts, i.e. 8% by weight, are unsatisfactory.

The pigment-grade aluminum is included in the forrnulation in the amount of 0.3-2%. Although the use of 2% is completely acceptable, I prefer to use generally a maximum of 1% because this quantity of the relatively high-priced aluminum gives entirely satisfactory results and offers economical advantages over the use of greater amounts.

The ammonium nitrate is used in the amount of 62- 89% by weight of the composition, and any one of the commercial grades of ammonium nitrate conventionally employed in dynamite formulations is suitable for use in the instant formulation. Sodium nitrate in an amount of up to 25% by weight may also be incorporated in the interests of facilitating the establishment of an oxygenbalanced composition and the regulation of density. The oxidizing salt or salts used may be coated with any of the conventional anti-setting agents, used to protect these hydroscopic materials from moisture, without effecting deleterious results with respect to performance of the formulation. Such anti-setting agent include zinc oxide, kieselguhr, gypsum, calcium or aluminum stearate, and the like.

The combustible, or fuel, is present in the amount of 4-1l.5% by weight, the exact amount used being that required to provide the necessary oxygen balance. Suitable fuels include such carbonaceous materials as the exemplified gum rosin, starch, wood pulp, apricot pit meal, resin-impregnated bagasse pith, and finely divided gelatinized starch powder and also corn flour, ivory nut meal, soybean meal, wheat flour, brewers flakes, oat or rice hulls, walnut meal,- ground cork, bagasse pith, barcereals, wool pulp, and ground cork effecting lower densities.

The formulation may also contain, in addition to the previously discussed anti-setting agents, those additives conventionally used in small quantities to modify the formulations. Such additives are flame-suppressants and also antacids, for example zinc oxide which functions also as an anti-setting agent and calcium carbonate. Conventional additives include paste-formers such as guar flour or bentonite, materials which swell or form gels in the presence of water and thus prevent contact of the water with the hygroscopic salts of the formulations. Furthermore, in view of the dusty nature of both the PETN and aluminum powder, such materials may also be present which tend to allay the dust and thus facilitate mixing. These materials include the exemplified ethylene glycol among many others. When the additive also functions as a combustible, the amount of combustible used in the formulation must be adjusted accordingly.

The dynamite compositions of the present invention have a moisture content (as made) of less than 1%, and an oxygen-balance, exclusive of wrapper, of +514. The paper wrappers conventionally used have a negative influence upon the oxygen balance, and, therefore, the explosive cartridge comprising the composition within a paper Wrapper will have an oxygen balance of approximately zero. As previously stated, the compositions have an air-gap sensitiveness" of at least 6 inches (50% detonations point), even in small-diameter (1% inch) dynamite sticks. The compositions also have a relatively low detonation velocity, i.e. 1500-2500 meters per second, which characteristic is considered to be very valuable in the art when blasting to displace certain types of burden.

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. An explosive composition having an oxygen-balance of +5 :4 and a half-cartridge air-gap sensitiveness of at least 6 inches as expressed by the 50% detonations point which consists essentially of 27% by weight of pentaerythritol tetranitrate as the sole organic explosive component, the maximum particle dimension of said pentaerythritol tetranitrate being within the range of 0.1 and 10 microns, the average thereof being within the range of 0.1 and 2 microns, O.32% by weight of pigmentgrade flaked aluminum, 62-89% by weight of ammonium nitrate, 025% by Weight of sodium nitrate, and 411.5% by weight of particulate solid carbonaceous fuel.

2. An explosive composition according to claim 1, wherein the combustible is selected from the group consisting of wood pulp, starch, apricot pit meal, gum rosin, hydrocarbon resin-impregnated bagasse pith, and their mixtures.

3. An explosive composition according to claim 1, wherein 0.5% by weight of ethylene glycol is present.

References Cited in the file of this patent UNITED STATES PATENTS 1,992,217 Kirst et a1. Feb. 26, 1935 2,033,196 Johnson et al Mar. 10, 1936 2,043,050 Baker July 21, 1936 2,063,572 VVoodbury et 'al Dec. 8, 1936 2,409,919 Whetstone Oct. 22, 1946 2,499,321 Lyte Feb. 28, 1950 OTHER REFERENCES Gregory: Uses and Applications of Chemicals and Related Materials, 1939, Ethylene Glycol, pp, 275-276. (T? 9 G 79. Copy in Scientific Library.)

Claims (1)

1. AN EXPLOSIVE COMPOSITION HAVING AN OXYGEN-BALANCE OF +5$4 AND A HALF-CARTRIGE AIR-GAP SENSITIVENESS OF AT LEAST 6 INCHES AS EXPRESSED BY THE 50% DETONATIONS POINT WHICH CONSISTS ESSENTIALLY OF 2-7% BY WEIGHT OF PENTAERYTHRITOL TETRANITRATE AS THE SOLE ORGANIC EXPLOSIVE COMPONENT, THE MAXIMUM PARTICLE DIMENSION OF SAID PENTAERYTHRITOL TETRANITRATE BEING WITHIN THE RANGE OF 0.1 AND 10 MICRONS, THE AVERAGE THEREOF BEING WITHIN THE RANGE OF 0.1 AND 2 MOCRONS, 0.3-2% BY WEIGHT OF PIGMENT GRADE FLAKED ALUMINUM, 62-89% BY WEIGHT OF AMMONIUM NITRATE, 0-25% BY WEIGHT OF SODIUM NITRATE, AND 4-11.5% BY WEIGHT OF PARTICULATE SOLID CARBONACEOUS FUEL.