US2320972A - Explosive composition - Google Patents

Description

l oteslted June attests exemswis oorsrosrrtois Milton Massey.

or to The Powder @omxia (lie-lo, a corooratiozo oi illliilc No Drawing.

Serial No,

(Ci. 52-===ll5i 2 Claims,

This invention is directecl to nevr'and improves explosive compositions anti is a continuation in part of my copending application, Serial No. 275,491? which discloses and claims a method of melting them. The invention is cliscloseel particclarly in relation to granular, high explosive materials suitable for blasting, mining, commercial demolition and munitions purposes.

compositions of the present invention may exhibit explosive strength from approximately to 7@%, as determined by the Pent ballistic mortar, anti may exhibit packed, volumetric densities varying from approximately (3.5 to 1.2 or higher. They are characterized icy the superior blasting qualities which they exhibit, that is, a more emcient result than heretofore obtainable with explosives of similar strength anti sensitivity. The explosives are characterized partioularly in the fact that each grain, individually,

is a completely explosive composition, in and.

.W. ate, other oxidizing agents, fuels, stabilizers, These ingredients are mechanically loleri together in a suitable mixing machine, such as a sizmainite mixer, and then sensitizing agents such as nitroglycerine, nitro starch, nitrocellulose or the l ke are added. in the finishes exelcsive compositions the respective materials remain as individual particles in admixture.

The compositions of the present invention are granular materials in which the principal errplosive ingredient is a crystalline material, such as ammonium nitrate, or m xture of ammonium nitrate and sodium nitrate, or the like. In each however, this crystalline component, in= of being admixed with the other explo eoiients such as ammonium nitrate, sodium factoring so e ll, recs, 3 14,95?

siveing elients, the cerea, fuel, stabilizers, etc, forms a crystal nucleus or embodiment in which the other ingredients are present as inclusions. Each grain is a toll and balanced explosive in and of itself, and in this respect; the compositions are distinguished from aggregates of discrete particles.

The grains also are of a porous nature and are too insensitive, in most instances, to be detonated. except icy the use of special or extraordinary detonators. To render such grains suficientiy sensitive for practical commercial usages the surfaces of them carry sensitizing agents, enabling the compositions to respond to detonating waves and be set off when the grains are collected into cartridges.

The ccm cositions made in accordance with the present invention exhibit slov; average speeds of detonation; for instance, 3000 to veto feet per second, and are highly sensitive; for example, their. sensitivity may he as high as 50 centimeters, aletermineclliy the lz'itantlarll lialvecl cartridge method (1 by 3 inch cartridges). Such results,

moreover, are obtained witoout nitro-sensitizers, such as nitroglycerineor the like, which are obectionahle because oi the headaches caused by the gases from them.

Various methods may be employed for manuthe present compositions, anti one method particularly suitable is disclosed in the aforesaid. conceding patent application of whichv this application is a continuation in part. For the purpose of assisting those skilled in the art, the disclosure of this method is repeated here.

The components entering explosive compositions, whether they be or" the detonating or deflagrating kind, may be clivirleol intotwo classes: (a) the materials of a crystalline nature which.

- are liquefied or melt under the influence of heat and (e) the materials which are of solid, amorphous' or non-liquefiable nature. Ammonium nitrate is a typical example of an explosive ingredient of the first group, while tar char, cereal, and charcoal are typical examples of the other. Other liquefiable and non-liquefiable explosive ingredients are disclosed at later points in the specification.

It is the concept of the present process first to melt or liquefy one or more of the crystallizable and liquefiable components of which an explosive is to be made. This is done preferably by placing this component part in a suitable vessel or container, and heating while stirring or agitating it until it melts or becomes of liquid or semi-viscous consistency.

Meanwhile, the remaining ingredients of the composition intended to be made, that is, the nonliquefiable components (and whatever liquefiable components that have not been melted in the preceding step) are placed in a mixer and thoroughly admixed with one another. In this operation no heat necessarily is added. Next, the melted, hot component or components, which are now in the liquid state, are added to and thoroughly incorporated with the admixed non-liquefiable components and the whole mass is stirred and agitated until all of the ingredients are thoroughly associated with each other. As a practical matter, in this operation the components preferably are associated to such a degree that they lose their individual physical identities.

The temperature or cooling is so controlled that the mass, now comprising the liquid components associated with the non-liquid components, is of a plastic nature, somewhat dough-like and tacky in consistency. Otherwise expressed, the temperature is maintained sufficiently high to avoid solidification but the temperature is below that at which the material would tend to ignite, or exothermically decompose.

In the next step the crystalline component is permitted to recrystallize, holding within it, as inclusions, the other explosive components. During such transition from the plastic to the solid state the mass is subdivided into grains. A preferred technique for accomplishing this result is to subdivide the plastic mass into particles of predetermined size by passing the mass through a screen, perforated membrane, or plate, while it still is hot.

By first melting the liquefiable components of the finished composition and then adding the non-meltable ingredients, the dangers of spontaneous ignition are avoided and the process proceeds with safety. If the fuel, oxidizing and binding agents were to be associated with the crystalline nitrate, and the whole mass then heated to liquefy the latter, spontaneous ignition would occur almost certainly; the danger, at least, would be so great as to preclude any prac-, tical usage of the idea. n the other hand, if the ammonium nitrate, or other meltable components, be first melted and then this mass be added to, and incorporatedwith, the remaining materials, the temperature at no time approaches the tempertaure at.which ignition might occur. The relatively high temperature required for melting the liquefiable materials prevails only during vthe period of safety, and decreasing or relatively low temperatures, are employed during the otherwise dangerous phase, that is, when all of the components are being admixed with one another and when a finished explosive composition is being operated upon. This safety feature is based upon the fact that the meltable compoasaaora nents used in explosives manufacture, either he i or cold, are relatively stable in and of themselve but their stability decreases as the other mate rials are admixed with them. In the presen process, the relatively increasing instability o the mass, as the materials become more inti mately associated, is offset by permitting th mass to cool and the temperature to decreas duringthis phasr Briefly, therefore, this process for making th products may be said to comprise destroying th crystalline nature of the crystalline componeni then incorporating therein particles of the othe explosive ingredients, and finally subdividing th mass and recrystallizing the crystalline compo nent so that it holds the particles of other in gredlents as inclusions.

For forming of the grains of finished ex plosive the temperature of the mass is con trolled so that it is of a plastic doughy nature To subdivide this mass into granules it is force through a screen or perforated membrane whicl serves to provide discrete, granular particles The plastic mass, before subdivision, dissipate its heat quite slowly. However, the ratio of th surface area to volume of the subdivided parti ,cles emerging from the forming membrane 1 much greater. These particles, therefore, los their plastic nature and become set in their physi cal form quite quickly. In some instances a filn or hard casing is formed upon the particles. Th rapidity with which the particles become set i dependent largely upon the temperature of th atmosphere surrounding them as they emergl from the forming screen or membrane. It particles, therefore, retain their individualit: sufiiciently to permit them to be sorted as t size, packed, or treated with surface sensitizing material without waiting for them to cool com pletely. As a matter of economy, the very fin particles and any lumps or large particles ar recovered and later admixed with the non-lique fying ingredients to which the liquefied ingredi cuts or components are to be added in the manufacture of a subsequent batch of the material.

In the present description, the material melter is termed the liquefied or meltable compound This designation is intended to include 11101881114 metallic nitrates, meltable carbohydrates havin usage in explosives manufacture, and material: of similar function. Combinations of material: which tend to form eutectic mixtures melting 8A lower temperatures than the components of then preferably are used to avoid unnecessarily higr temperatures. For instance, admixtures of ammonium nitrate, sodium nitrate, sugar, dextrlne and the like may be used, both for the purpose oi lowering the melting point of the mixture and f0] the purpose of contributing to the chemical composition and physical characteristics of the explosive itself. This term also is intended to include such materials as starches, carbonates resins and gums which function in the finished explosive compositions as stabilizers or fuels. All of these materials are characterized in that thei: use in the manufacture of explosives is recognized by those skilled in the art, and in that they, or combinations of them, melt to become fluid or viscous when heated to temperatures below the temperatures of decomposition or ignition.

In this description the term non-meltable or non-liquefiable ingredients is intended, as the term implies, to designate the materials entering the explosive composition which do not melt or liquefy under the influence of heat. Typical maof this group are coal, charcoal, cereals, oi similar strength, that more of ill go "wood pulp, starch, metallic sensitirdug addition to these solid and meltaiele materials, there is a group or materials used in exploslves manufacture which are liquid at room coal of the desired lorlnatiozi are 0 ed pound of explosive than is otherwise oocairzaiile with conventional materials. There is a sub D stautially lesser percentage of slack due to the temperature or have very low melting point. sustained heaving action exhibited by the mamirieral, vegetable and animal oils, and terlals and they are not injurious to the roofs explosive organic hitrc compounds are typical of of mines, particularly in instances Where slips s grou They are not compatible with the exist. In substance, the spread producedby ials o the melt, nor sale to heated with '10 the materials is comparable to that of his i h materials are to are powder and this result is obtained without the ,rter or as the melted and hon-meltuse of nitro explosive ingredients which give or; materials are incorporated with other. toxic gases which affect the workmen by causing previously disclosed the present explosive headaches. one ere adage-ted to he used for commer- 1.3 Mama-0m emwgives i demolition purposes we coal mirrsimilar 33111330593 W118i 8 material? A composition adapted particularly for use for the type well as materials of susmunitions purposes is as 5031mm: tai ed power are desired, and for use li'i ir'mltiohs. the examples which follow the Melting materials: are melted and the materials Ammonium nitrate are of rromiiuuefiahle nature are classed Sodium nitrate so the iollorviugheadings Dextrioe itejoreseeieiioe composttioas for general blasting gem-games X High L0 3 w re are, are hereto. strait esp sure 9 13 two cap -ave sivelqgljlded sive glgided diameter .Eaplosiees for cool mini-ogy of explosives for coal mining and case is preferably about A ,le of a permissible type high ex is as follows:

Such a composition has been accepted as permissible by the United States Bureau of Mines.

The experience gained in the field with the use of compositions of the present invention for coal mining purposes, indicates that they uniformly exhibit from 5 to more blasting efficiency than materials oithe type heretofore available ther ingredients:

Sulphur Z "Paraifine Tar char 2 Charcoal Wood pulp Aluminum it Total l 60.;

but insufficiently fluid to penetrate deeply into the grains. For making such compositions the trinitro toluene is added to the plastic mass at the time it is being subdivided and preferably before the grains have set to hard solid state. The plastic grains carrying the sensitiser are charged into the shell or cartridge and are of such plastcity that they readily conform to one another to provide the desirable high density, especially if the shells or cartridges be vibrated. Afterwards, when the explosives are permitted to cool in the cartridges each grain carr es its own sensitizer on its surface and the grains remain individually discrete so as to be readily detonatable.

In place of the wood pulp employed in the if a similar charge be fired in hard rock.

foregoing compositions ivory meal, cereals, bagasse, almond shells, corn meal, rice hulls and other carbonaceous fuels may be used. The aluminum employed in the foregoing compositions serves as'a sensitizing agent. Where control of the speed of detonation of the ultimate composition is desirous, in conjunction with the control of the sensitivity, the aluminum may be of powdered form and applied as a surface sensitizing material in accordance with Lindsley Patent No. 2,126,401, issued August 9, 1938. Otherwise, the aluminum may be incorporated directly with the other nonmeltable material; compositions similar to Ammonal may thus be prepared. In place of aluminum as a surface sensitizing agent other sensitizing ingredients also may be employed, for instance, as described in the aforesaid patent.

The sulphur, paraffine, charcoal, wood pulp and other ingredients fulfill their usual functions in the explosive compositions.

From the point of view of physical structure, each explosive grain is a relatively porous particle, with sensitizing material applied to its exterior surface. The material at the inside of the grain is relatively insensitive, that at the surface, on the contrary, is very sensitive and, therefore, responds promptly to a detonating wave. composition of the material at the surface of each grain lends todecomposition and detonation in the material at the interior grain, since the two are essentially integral with one another.

In the explosive grain, the crystalline sodium nitrate or ammonium nitrate, or a mixture of these which may be used, is a substantially continuous phase, even though it is of a porous nature, and the other explosive ingredients, the fuel, stabilizer, etc. are present in the crystalline phase as inclusions surrounded by it. The mass of each grain is, therefore, distinguished from an explosive in which the particles of the various components reside. at best, only adjacent one another, depending upon the degree of compaction and mixing employed at their preparation.

The porosity of the materials makes them adapted particularly to the reception of surface coating sensitizing substances, such as powdered aluminum or the like. Very small quantities of sensitizing material can be distributed over the surface to obtain the desired sensitivity, for instance, approximately to 2% by weight. Even with so small a quantity of sensitizer, the compositions nevertheless have a sensitivity as great as centimeters as determined by the halved cartridge method. In contrast, sensitivities of 5 to 10 centimeters have been considered good in the past for ammonium nitrate explosives.

One of the characteristics of the explosives of the present materials which is not fully explained by the present knowledge concerning explosive decompositions is the fact that the present materials respond differently according to the environment in which they are detonated. To a greater degree than has been exhibited by any of the materials heretofore available with which I have been familiar, a given explosive composition of the present invention will exert a relatively slow and sustained heaving action if detonated in a soft medium like coal, and yet detonate briIsg'sliys' believed that one reason which may account for this result is that the interior of the grains is substantially insensitive though potentially detonatable, while the surface sensitizer in and of itself may be, or otherwise forms with the explosive at the surface of the grain a very sensitive material. The response of a potentially explosive composition is determined by the chemical composition as well as the physical environment. The physical environment of an explosive, as determined by the pressure or the heat to which it is subjected, affects its sensitivity by upsetting chemical equilibrium and thereby increasing sensitivity toward detonation. Conventional explosive materials of the type heretofore available have been uniformly sensitive throughout their mass, whereas in the present compositions the insensitivity of the interior portion of each grain enables it to respond in accordance with the pressure and heat of its environment. In a hard rock pressure and heat are substantially greater than in a soft coal or friable shale; in the latter the gases escape more readily. Consequently, the insensitive nature of the grain is offset to a greater degree in hard rock blasting than in coal mining or like operations.

The grains of the explosives produced by the process may be packed immediately, as previously described, they'may be surface coated and then packed, or they may be fed into a pelleting press after which the usual procedures are followed. The granules of material also may be further sensitized by the impregnation of them with liquid nitro explosives in a process of the type employed in the manufacture of present day dynamite. When'this is done, the sensitivity is augmented, but with corresponding increase in the speed of detonation.

Most of the componentsv of the typical granular explosive compositions are poor conductors of heat. If all of the components ,of a given explosive are admixed and then heated, local portions, for instance, those adjacent the walls of the heating vessel, become overheated and initiate exothermic decomposition of the mass as a whole. By first melting the components which will liquefy under the influence of heat, in the absence of the other materials which will not liquefy, the dangers of overheating are avoided since the heat is transferred more readily throughout the mass as it becomes fluid. The liquid mass, in turn, is very easy to incorporate intimately with other materials. A recognition of this differentiation is important in the practice of the invention.

In making the melt, raw materials of commercial moisture content are used, and pre-drying of them is not necessary since the heating tends to drive 011' the moisture. In some instances the addition of a small quantity of moisture, for example, up to about 1% of the materials being melted, is employed .for the purpose of decreasing the time required to make the melt. This added quota of water serves as a conductor of heat to the interior of the mass; it is driven off as the melting proceeds, sufficiently that the finished explosive need not be subjected to the usual. drying process. Explosive grains mad by the process, but intended to be made into pellets, may contain up to about 6-8% of water; this water may be added at the time the melt is being made, but, of course, it must be removed after the pellets have been formed.

' Ammonium nitrate alone melts at a temperature of about 305 F. The addition of sodium nitrate to the ammonium nitrate decreases the temperature at which the mass melts by forming or tending to form eutectic mixtures. Material compositions are required and is disclosed as a partial equivalent to the process previously illustrated.

The foregoing details, as well as the explanation proiferedv to explain the reasons for the fuel and oxidizing agents residing within the continuous phase as inclusions, the external portions ofsaid grains being of a hard and dense nature and having metallic sensitizer intimately associated therewith to the extent of from approximately V to 2% by weight of the grains as a whole, while the interior portion of each grain is porous and permeated with cracks and fissures and is substantially insensitive, the sensitivity of th mass of grains as a whole being as high as 50 centimeters as determined by the halved cartridge method using 1% by 8 inch cartridges.

2. A detonatable explosive composition. comprised of a mass of discrete grains, each discrete grain being in and of itself a balanced explosive and having ammonium nitrate as its principal explosive component but also having fuel and oxidizing components associated therewith, the ammonium nitrat component of the grain forming a substantially continuous phase with the fuel and oxidizing components being present in the continuous phase as inclusions, with pores permeating the continuous phase but with the surface of the grain being dense and compact and having thereon a metallic sensitizing agent, the porous continuous phase of the explosive being substantially insensitive to detonation while the surface sensitizer forms with the dense compact surface of each grain an explosivecomposition sufilciently sensitive that the mass as a wholev has a sensitivity of as high as centimeters as determined by the halved cartridge method using cartridges 1% inches by 8 inches, the porosity of the grains enabling the grains to provide a relatively slow heaving action in soft stratum.

MILTON F. LINDSLEY, JR.