US3090714A - Explosive - Google Patents

Description

3,090,714 Patented May 21, 1963 3,090,714 EXPLOSEVE Frank Harold Fenix, Joplin, Mo., assignor of fifty percent to Glenn Qook, Arkansas City, Kans. N Drawing. Filed June 19, 1958, Ser. No. 742,988 1 Claim. (Ql. 149-43) This invention relates to explosive compositions and more particularly, to relatively inexpensive, easily manufactured explosives containing ammonium nitrate as the principal ingredient thereof whereby the compositions are safe for use in all types of blasting and mining operations.

Although ammonium nitrate has been very extensively used in high explosives of the dynamite type, and has replaced nitroglycerine for many types of explosive uses, it has certain inherent disadvantages which tend to minimize the fact that ammonium nitrate as the principal power producing ingredient of an explosive composition possesses high explosive strength, has outstanding safety properties, and is economically attractive. The principal disadvantage of the utilization of ammonium nitrate in explosive compositions stems from the fact that ammonium nitrate is relatively insensitive to detonation and therefore, various additives must be employed in conjunction with the same in order to permit the compositions to be exploded with conventional blasting caps or similar devices which do not have extremely high power. Also, ammonium nitrate is relatively hygroscopic and therefore, the compositions containing ammonium nitrate tend to absorb water over extended periods of time during storage and thereby become hard in the presence of even small amounts of moisture. Hardening of the explosive composition brings about decreased sensitivity of the explosive and a much lesser degree of uniformity in performance. It is to be noted that the water resistance of ammonium nitrate explosives is generally low because of the presence of this relatively soluble salt.

In order to increase the sensitivity of ammonium nitrate to detonation and thereby make the same explodable with a #6 blasting cap, it has heretofore been common practice to utilize expensive, relatively dangerous, organic nitro compounds in order to increase the sensitivity of the ammonium nitrate. The most widely used sensitizing agents have been trinitro toluene, nitroglycerine or similar compositions such as dynamite in gel form. These prior compositions were unsatisfactory from many as pects, particularly because of the relatively unsafe nature of the same and the fact that nitroglycerine compounds cause persons handling such explosives to be afflicted with extreme headaches. Furthermore, the compositions containing nitro derivatives are not safe for many blasting operations, particularly those conducted beneath the ground wherein poisonous gases and dust are a major problem.

It is, of course, well known that in recent years commercial high power explosives have been formulated so as to be detonatable through utilization of a conventional #6 blasting cap or by a length of detonating fuse, which cap or fuse is fired electrically, or by safety fuse, to initiate the explosion. Inasmuch as these practices have been substantially uniformly adopted because of the relative safety of the same, it is desirable that any new explosive be susceptible to detonation with a cap of this type. Ammonium nitrate explosives may be sensitized with nitro derivatives as described above but, cost factors and the other disadvantages pointed out have operated to prevent total acceptance of ammonium nitrate explosives for all types of commercial blasting operations.

It is, therefore, the principal object of the present invention to provide an explosive composition containing ammonium nitrate as the principal power producing component therein and which may be easily detonated with a #6 blasting cap or equivalent means without the utilization of expensive and dangerous components such as trinitrotoluene, nitroglycerine and dynamite gels.

Another important object of the present invention is to provide 'a superior permissible explosive employing ammonium nitrate as the primary component thereof, which is uniform in physical characteristics and performance and which is stable under all types of weather con ditions and therefore, may be shipped over long distances within the permissible explosive category.

Also an important aim of the instant invention is to provide an explosive as described wherein all of the components are inexpensive, thereby materially lessening the cost of manufacture of the explosive composition, and which is also uniquely adapted for permitting the user to vary the strength of the same as desired without the necessity of employing expensive sensitizing agents as has heretofore been required.

Another important object is to provide an explosive as referred to wherein ammonium nitrate is employed as the principal power producing agent and which is in normally very diflicultly explodable prill form, the sensitizing agents of the instant invention permitting the prills to be detonated with a #6 blasting cap under all types of conditions encountered in the field.

A further important aim of this invention is to provide an explosive composition which is relatively free-flowing and therefore has many advantageous uses because the same may be poured into a vertical bore in a manner similar to granular black powder, with the velocity of the final explosion being equal to or exceeding many types of commercial explosives available.

Other important objects of this invention relate to the provision of an explosive composition which does not produce an obnoxious gas and only a minimum of carbon monoxide, whereby the composition may be utilized in blasting operations within mines or the like; to a blasting composition having minimum flame suppression, thereby -making the composition safe for use in coal mines; to an explosive wherein the abrasiveness of the resulting explosion may be readily varied by controlling the degree of fineness of certain components of the present composition; to an explosive which is adapted to be utilized under moist conditions and even below water if necessary, with the same uniformity of detonation and velocity being retained; to an explosive which does not require tamping during packaging of the powder nor heating or cooking of the admixture during manufacture of the composition, thus making the same much safer to produce and also limiting the dangerous characteristics of the explosive during transportation and use of the same; to a composition employing ammonium nitrate prills wherein such spheres are coated with a sensitizing agent permitting the same to be detonated with a #6 blasting cap and which also serve to prevent the ammonium nitrate from absorbing moisture from the surrounding media; to a novel process of producing an explosive as described wherein the ammonium nitrate prills are subjected to warm air currents to remove substantially all of the moisture therefrom prior to coating with the subsequent additive materials and which serve the additional function of preventing the ammonium nitrate from absorbing the defined vapors; and to other important objects and salient features of the instant invention which will become obvious or be explained more fully as the following specification progresses.

It has been determined that the foregoing objects are accomplished by admixing suitable proportions of a specific type of ammonium nitrate with additives capable of sensitizing the principal power producing ingredient and which primarily comprise powdered aluminum, carbonaceous material and a finely divided abrasive. Other materials may also be added to the composition in order to adapt the same for certain types of blasting operations and in particular it is contemplated that a dehydrating agent be employed in conjunction with the explosive admixture, as well as components for materially lessening the degree of moisture absorption of the ammonium nitrate and also serving the dual function of smoothing out and assuring a complete, maximum strength explosion for the particular combination of ingredients utilized. The instant invention contemplates two basic explosive compositions having substantially equal utility and adapted for individual uses. The first basic formulation includes preselected proportions of ammonium nitrate, powdered aluminum, activated charcoal and finely divided ground glass, while the other basic composition comprises ammonium nitrate, powdered aluminum, sulfur, high velocity powdered coal and calcium oxide dust. Extensive tests have shown that, in order to produce an explosive of sufficient sensitivity to be exploded with a #6 blasting cap, the first basic composition preferably should contain by weight, 60 to 94 parts of ammonium nitrate, 1 to 6 parts of powdered aluminum, 0.5 to 1 part of finely divided glass, and 2 to 50 parts of activated charcoal. By the same token, such empirical work has indicated that the second explosive composition should similarly contain by weight, 60 to 94- parts of ammonium nitrate, 1 to 6 parts of powdered aluminum, 0.5 to 1 part of calcium oxide, 2 to 50 parts of high velocity powdered coal, and 2 to 5 parts of sulfur.

Describing in detail the various components of the instant explosive, as well as additional additives which may be employed to improve the final product for certain specific applications, it is to be noted that the ammonium nitrate utilized as the principal power producing agent is of the type commercially prepared by various manufacturers principally in midwestern areas chiefly for fertilizer purposes. The molten ammonium nitrate is permitted to drop from a considerable height within a tower so that small spheres are thereby produced which are collected in suitable means at the bottom of such tower. The spherical particles thereby formed and which are generally termed prills vary somewhat in size but a representative sample had an average individual mean diameter of 0.075 in. 100% of the sample passed through a#6 screen, 56.3% went through #10 screen, 20.7% passed through a #12 screen, 12.4% went through a #14 screen, 8.5% passed through a #20 screen, while only 2.8% went through a #35 screen. This ammonium nitrate product is commercially available in 97% pure form with only approximately 3% consisting of inert ingredients. The chemically pure grade of ammonium nitrate comprising 99% of the pure compound may be employed if desired, but the standard commercial grade is much less expensive and gives satisfactory results under all operating conditions encountered.

The ammonium nitrate product utilized in preparation of the instant explosive is of the uncoated variety and approximately 90% of the total material is in the form of small prills, as defined above, while about 10% of the material is described as being crushed by virtue of the manner in which the same is produced, namely, falling through an extended path of travel from the top of the tower to the lower end thereof where the prills are collected. It can be recognized that a small percentage of the prills and which normally is about 10%, are broken or fragmented and it has been found that this crushed proportion of the commercial form of the ammonium nitrate materially adds to the explosive character of the instant composition and improves the overall results as Well as the uniformity of the detonation, irrespective of the time which the product is stored prior to use thereof.

The ammonium nitrate prills referred to above are relatively insensitive to detonation and therefore, it is necessary to employ certain specific sensitizing agents with such prills in order to permit the same to be exploded with a #6 blasting cap or equivalent means. Powdered aluminum has been found to properly sensitize the ammonium nitrate prills and also serves to propagate the explosion once the same has commenced. Although extra fine, powdered, atomized aluminum may be employed for the present purposes, the best results have been obtained by utilization of an admixture of preselected proportions of atomized aluminum, #40 atomized aluminum, and quantities of unatomized commercial, extra fine ground aluminum. The most uniform detonation has been obtained by maintaining the quantities of #120 and #40 aluminum powder in substantially equal proportional relationship. As used herein, the terminology #120 aluminum powder is meant to define powder sufiiciently fine to pass through a #120 sieve, while #40 aluminum powder is likewise intended to mean powder which will pass through a #40 sieve. The regular aluminum is preferably at least as fine as the #120 atomized aluminum powder.

The basic formulations set forth above indicate that various solid carbonaceous materials may be employed. It is preferred that activated charcoal be utilized in one composition because charcoal of this type is capable of absorbing many times its weight of poisonous gases, thereby making the instant explosive compositions safe for utilization in enclosed areas such as coal mines and the like, and furthermore, the activated charcoal provides the proper amount of carbon to enhance detonation and propagation of the explosion even though relatively large ammonium nitrate prills are utilized as the main power producing material of the admixture. However, in certain applications it is desirable to utilize high velocity powdered coal in lieu of the activated charcoal and in this formulation, predetermined quantities of sulfur should also be added in order to assure proper detonation and complete explosion of all of the ammonium nitrate prills.

High velocity coal as used herein is intended to designate coal having a relatively high methane content. For use in explosives, this coal is ground to a very fine form and then intimately admixed with the other materials.

It is also necessary that a finely divided abrasive be added to the explosive composition and although many materials meeting the hereinafter referred to specifications could be employed, it has been determined that the best results are obtained by ultization of finely divided ground glass and/ or calcium oxide generally termed lime dust. The ground glass, which is of the white variety, operates as a drying agent to prevent the ammonium nitrate from absorbing considerable quantities of water and also aids in triggering of the explosion of the ammonium nitrate prills because of the gritty nature of the glass. By the same token, the calcium oxide also facilitates complete detonation of the entire quantity of ammonium nitrate prills and smooths out the detonation so that maximum power is obtained from each particular formulation.

In many instances, it is desirable to incorporate a preselected proportion of lead dioxide in the explosive admixture to give additional thrust toward the latter part of the explosion and to hold vapors back during detonation. The oxygen supplied by the lead dioxide is believed to assure an even supply of the same throughout the complete explosion and thereby increase the uniformity of the explosive as well as the velocity of the same.

For certain applications of the present explosive, par ticularly under moist conditions, it has been found advantageous to incorporate a quantity of sodium chlorate admixed with nitrobenzene to the final admixture. The quantity of sodium chlorate and nitrobenzene utilized in the composition may be varied within a range to be more specifically defined hereinafter, but it is to be pointed out that the ratio of sodium chlorate to nitrobenzene should be approximately 4 to 1 in order to obtain the best results under wet blasting conditions and particularly, when the explosive is exposed to considerable water during initial detonation.

In order to improve the explosive power of the present composition and also to provide a substantially moisture resistant coating around each individual prill of ammonium nitrate, it is recommended that an admixture of toluene, nitrobenzene and glycerine be introduced into certain of the components of the present explosive during manufacture of the same, to thereby cause a relatively moisture impervious layer to be formed over each individual ammonium nitrate prill. In this connection, tests have shown that approximately 1 pint of the liquid should be added to each 100 pounds of the final admixture, and the toluene, nitrobenzene and glycerine should be present in approximately equal amounts.

In order to more clearly define the various components which may be utilized in the instant explosive as well as the most suitable proportions thereof to obtain improved results, the following ingredients may be admixed with the proportions of each being expressed as parts by weight:

Ammonium nitrate 60 to 9'4. #120 atomized aluminum 0.5 to 2.5. #40 atomized aluminum 0.5 to 2.5

Finely ground regular aluminum to 0.25. Sodium chlorate-nitrobenzene (ratio of sodium chlorate to nitrobenzene should be maintained at approximately4to 1) 0.5 to 10. Lead dioxide, approximately 0.12. Finely divided ground white glass 0.25 to 1. Toluene nitrobenzene glycerine (toluene, nitrobenzene and glycerine should be in approximately equal amounts) 1 pint for each 100 parts by weight of the total admixture.

Charcoal 2.5 to 50.

In lieu of the activated charcoal, 2.5 to 50 parts by weight of finely powdered, high velocity coal and 2 to parts of sulfur may be substituted.

Specific examples of explosive compositions include the following:

Example 1 Parts by wt. Ammonium nitrate (approximately 90% 11 mesh prills with the remaining percentage being in crushed form) 94 #120 atomized aluminum 1 #40 atomized aluminum 1.33 Finely ground regular aluminum 0.17 Finely divided ground white glass 0.5 Lime dust 0.5

Activated charcoal 2 Nitrobenzene-glycerine-toluene, equal parts suflicient to provide 1 pint of the liquid for each 100 parts by weight of the total admixture.

Example 2 Same formulation as set forth above with the exception that 2.5 parts by weight of sulfur and 2.5 parts by weight of finely powdered, high velocity coal are substituted for the activated charcoal and with 91.5 parts by Weight of ammonium nitrate being utilized.

Example 3 Same formulation as contained in either Example 1 or 2, with 1 part by weight of nitrobenzene and 4 parts by weight of sodium chlorate being introduced into the admixture.

Example 4 Formulation essentially the same as described in Examples 1, 2 and 3 with approximately 0. 125 part by weight of lead dioxide being added to the composition.

Example 5 Parts by wt. Ammonium nitrate prills (uncoated) 58 Ammonium nitrate prills (uncoated and partially crushed) 7.25 #120 atomized aluminum 0.75 Sulfur 2.5 High velocity powdered coal 30 Lime dust 0.5

Equal parts of nitrobenzene, glycerine and toluene sufiicient to provide 1 pint of liquid for each parts by weight of the total admixture.

Example 6 Partsby wt. Ammonium nitrate prills (uncoated) 84 Ammonium nitrate prills (uncoated and partially crushed) 10 atomized aluminum 1 #40 atomized aluminum 1.33 Finely ground regular aluminum 0.17 Activated charcoal 2.5 Lime dust or finely divided ground white glass 0.5

Example 7 Same formulation as listed in Example 6 with the exception that 2.5 parts by weight of powdered high velocity coal is substituted for the activated charcoal, and 1.5 parts by weight of sulfur is added, with this weight of material being removed from the ammonium nitrate prills.

In production of the instant explosive it is essential that the ammonium nitrate prills be subjected to sufiicient warm air to substantially remove all of the moisture therefrom prior to coating of the same with the sensitizing and dehydrating fraction of the explosive. Removal of the Water from the ammonium nitrate prills may be accomplished in various ways, but it is noted that a convenient and inexpensive process involves disposing the prills on a conveyor belt and then passing the same through cross or countercurrent airflow at an elevated temperature. After the ammonium nitrate prills have been thus subjected to moisture-removing currents of air, the aluminum sensitizing agents are admixed with the ammonium nitrate prills, whereupon the carbonaceous materials such as activated charcoal or high velocity coal are introduced into the mixing machine. Then the lead dioxide and sodium chlorate-nitrobenzene compositions are introduced into the mixer if the same are utilized in the particular formulation, followed by addition of the abrasive material such as ground glass and/or lime dust, with intimate admixing of the materials being continued. Finally, the liquid containing nitrobenzene, glycerine and toluene is directed into the mixer which tends to cause the various detonation initiation materials to uniformly coat the ammonium nitrate prills to thereby form a moisture resistant layer over the outermost surface of each prill. It can be recognized that the hygroscopic nature of the ammonium nitrate prills facilitates placement of the coating over the outer surfaces of the same because of the slight amount of water which is absorbed after the prills have been subjected to warm currents of air and the present explosive may thus be stored over extended periods of time without the same becoming hard and setting up.

Although the lead dioxide and nitrobenzene-sodium chlorate admixture may be omit-ted from the formulations, it is ordinarily desirable to utilize the nitrobenzenetoluene-glycerine admixture with all explosive compositions to assure coating of the individual ammonium nitrate prills with the sensitizing and detonation improvement additives. The mixing time of the various ingredients should be maintained as low as practical and 7 preferably within the range of 2 to 3 minutes. The final product is in condition for immediate packaging and may be placed in cardboard, cylindrical cartridges previously coated on the inner surface thereof with a toluene-nitrobenzene admixture and provided with a parafiin coating on the outer surface thereof to preclude entrance of moisture into the cartridge. Opposed ends of the cylinder are capped with metal covers, whereupon the cartridge is in condition for immediate detonation with a #6 blasting cap or equivalent means. Note should be taken particularly of the fact that the present composition is not packed or tamped into the cartridge but merely permitted to flow into the same. No packing or tamping is required and thus, manufacture of the product is not only made much safer but a uniform explosion is obtained because of the substantially simultaneous detonation of each of the ammonium nitrate prills.

Under certain blasting specifications, it is oftentimes advantageous to incorporate a synthetic-ally produced composition including lime dust and silica into the explosive. A product of this type is commercially available and is substantially fluffy in appearance and relative- 1y lightweight. The detonation and propagation of the explosion of ammonium nitrate when this material is introduced into the explosive admixture has been found to be more uniform and complete.

If ammonium nitrate prills are utilized in the instant explosive without the 10% of crushed prills being present as is the case in the commercially available product, it has been determined that approximately 0.5 part by weight of the total admixture of potassium nitrate assures proper detonation of the explosive with a #6 blasting cap.

Also, for certain applications it may be desirable to substitute an admixture of potassium perchlorate and nitrobenzene for the specified sodium chlorate-nitrobenzene composition. Again, the ratio of potassium perchlorate to nitrobenzene should be maintained substantially within the ratio of 4 to 1 but sodium chlorate is the preferred material from both a cost standpoint and detonation of the ammonium nitrate prills. Because of the extreme versatility of the composition as well as the explosive power to weight ratio thereof, the explosive designated in Example 4 is the preferred admixture with the same being equivalent to at least 90% dynamite. Furthermore, the explosive may be utilized in any type of mining operation regardless of the moist conditions encountered therewithin, but the use is not restricted to mining and the explosive may be employed in all types of blasting operations.

Although it has been specifically stated that the instant explosive composition is of particular utility because the same is detonatable with a #6 blasting cap and is also categorized as a permissible explosive, it is to be understood that tshe present explosive may also be detonated with other similar ignition means such as Primacord, which may be passed through the center of the cartridge substantially the entire length thereof to a point where the same may be ignited. The Primacord includes an admixture of lead styphnate, trinitrotoluene and lead azide enclosed within a flexible, plastic tube.

Another important feature of the present invention which was alluded to briefly above is the fact that the velocity of each individual charge may be changed as desired by various expedients, the simplest of which is changing the degree of fineness of the charcoal or coal utilized in the explosive. Furthermore, other additives may be introduced into the composition to lower the velocity thereof and thereby reduce the shattering produced by the explosion. Additives which may be used to lower the velocity of the composition are well known to those skilled in the art and thus, the same will not be detailed herein.

Although the explosive components giving the best results have been specifically set forth herein, it is intended toinclude all chemical equivalents of the same and therefore, the invention is limited only by the scope of the appended claim.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

An explosive consisting essentially of by Weight of the total admixture, to 94 parts of fertilizer grade, prilled, uncoated ammonium nitrate, 1 to 6 parts of powdered aluminum, 0.5 to 1 part of ground glass, 2 to 50 parts of a solid carbonaceous material selected from the group consisting of powdered coal and powdered charcoal, and approximately one pint for each pounds of said total admixture of equal proportions of nitrobenzene, glycerine and toluene.

References Cited in the file of this patent UNITED STATES PATENTS 677,722 French Dec. 18, ,1929 2,126,401 Lindsley Aug. 9, 1938 2,407,151 Glogau Sept. 3, 1946 2,410,801 Audrieth Nov. 12, 1946 2,43 6,305 Johnson Feb. 17, 1948 2,478,918 Hale et al Aug. 16, 1949 FOREIGN PATENTS 479,261 Canada Dec. 11, 1951