US2333637A - Explosive composition - Google Patents

Description

Patented Nov. 9, 1943 UNITED STATES PATENT OFFICE EXPLOSIVE COMPOSITION Claude H. ,Carey, Wilmington, Del., assignor to Atlas Powder Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application August 3, 1940, Serial No. 351,212

4 Claims.

.sive com osition-wharacterL csii lrelaiw 10W detonating velocity and :whlchmaybe sensitized to propa a s ns e es with...-a mna. tively small amount of-.a nitric-,estensuch asrnitrogylcerine, Other objects of the invention will hereinafter more fully appear.

Ammonium nitrate;explosivemixtures havin low-velocity ot detonatlon' are well known infithe art; In pro uc na-the e Pee er el -.1- siderationzwas given-to the physical character? sensitizing agent, such as nitroglycerine; they were not consistently capable-of detonation, being entirelyinefiective when used in cartridges of less than 1% inches in diameter. Simple mefer to carry-out this mixing operation at a temperature above 80 F. in order to facilitate thor' ough incorporation of the ingredients. The plastic mass so produced is then passed through a screen or the like to form-grains or vermicelii which is dried at least sufficiently to case harden the particles. The case hardened particles art then fragmented, preferably by rubbing them through a screen of finer mesh than that of the-screen. employed to form:the. grains or ver n'i'celli from .the.plastic mass.- Of the frag chanical mixtures of -water soluble nitrateand starch have also been proposed for the purpose of producing a-low detonating velocity explosive. These mixtures;,however, have been very unsatisfactory since their sensitivity is too low for practical-purposes. I m

Explosive compositions of colloidal starch and soluble nitrates have been previously proposed. While such compositions are more sensitive than simple mechanical mixtures-of the in redients and may be sensitized with secondary compo nents such as nitroglycerine, I have found that mented product so produced. I employv as the explosive composition of the present invention any on alr-of that portionsubstantially all of which passes .an 8 mesh sieveand is retained on afl30 mesh sieve. While I found-that .the entire ram Pas$ ne a8n shsie nd r ine o a 3 0 mesh sieve ise xce11ently suited for use in various explosives, it is to be understood that smaller portions as,,. f o r exa mple,. that passing all) mesh sieve and held on a 20 ,mesh sieve may be,used to thereby control the density and other characteristics of the ultimate explosive in a manner well-known to those skilled in the art.

"'"Wliile'the theoryoi theresults which I have obtained cannot be precisely defined and I.do not want to be bound by any theoretical concept. the greatly increased sensitiveness of the exploslve composition of the present invention is probably caused by the existence of exposed minute crystals of the water soluble nitrate. The crystals of water soluble nitrate are in intimate contact with the oxidizable starch in microscopical or even molecular dimensions which offers an ideal combination for rapid decomposition o i the constituents when subjected to flame and shock such as the result from a blasting cap. Grained compositions, by means of agitation and drying; cause comparatively large crystals to be formed without exposed angular. surfaces. In accordance with the present invention the crystals are minute ,and in intimate contact with the starch and the fragmentation of the case hardened granules or vermicelli exposes the minute crystals and allows maximum contact to the propagating Wave and flame by outcropping crystals at the surface of the fracture. Moreoverythe dried fractured granules present surfaces from the interior which are highly irregular due to the fact that the granules being case hardened before much of the moisture has been removed only permit shrinkage to take place in the in terior of the hardened granule shell by the formation of voids which were occupied by the concentrated solutionsof the soluble salts. As a --cooled;-and partially dried-vermioelliwere-broken up, and forcedthroughthe'screenby means of fingers and plcughs on'r'evolvmg ""'Th" result of the more porous structure of the interior of the granule than the surface, the faces of the fractured particles offer more minute proieetions and undulations which are sensitive to detonation.

In order to more clearly point out the invention, the following illustrative examples are given in which all parts are parts by weight.

EXAMPLE 1 147 parts of ammonium nitrate coated with 0.3% of a mixture of 75% petrolatum and 25% paraffin, and parts of corn starch containing 12.3% moisture were thoroughly mixed ina jacketed dough mixer, and 61.5 parts of a solution of ammonium nitrate containing 64.4% of NH4N03 were added and kneading and mixing continued. with hot water in the jacket, until the mixture had become of a dough-like consistency, and attained a temperature of 120 F. The dough was removed from the mixer and forced through a fiat iron screen by means of revolving paddles set at angles less than 90 to the screen. The screen was of the square mesh steel wire type. having openings 0.104 inch x 0.104 inch, and the diameter of the wires 0.063 inch. Thedough came through the screen in the-form of strings or vermioelli, and approximately 45 minutes were required for this operation during which time the shredded dough was exposed to a current of air at 74" which cooled andease hardened the vermioelli. This material was then transferred to the grainer provided with a steel wire screen having square openings of 0.093 inch, and wires by 0.032 inch in diameter. The case'hardened.

moisture content of the material atthis stepof the process was between 7 and.8%. The granules passing through the screen were placed in drying. trays to a depth of 1 ,5 to 2 inches and dried'for 2-0 hours at a temperature of 135' F. During the drying the material became caked. and upon removal from the dry house it was broken up in the same graining machine, using a screen having square openings of 0.102 inch. which allowed a of grained material to pass through. The final treatment was the screening of the granular i 1. -fiowing mass through a standard 8 mesh on and over a 30 mesh screen. The moisture content was 0.31%.

EXAMPLE 2 65.5 parts of a solution containing 43.23 parts of ammonium nitrate were put into a jacketed dough mixture, and 23 parts of coated ammonium nitrate added with the mixer in operation and hot water in the heating jacket until the temperature of the mixer contents was 150 F. At this stage 120 parts more of ammonium nitrate and 5 parts of corn starch, containing 12.7% moiste. were added with continued mixing and heatuntil the temperature of the dough was 120 F. The dough was then forced through a steel wire screen having 0.102 x 0.102 inch square o enings. and 0.041 inch diameter wires. During operation which required 45 minutes the ai 'ial was blown with air at 88 F.. and an 91101181 period of one hour for case hardening. This operation was followed by treating the vermicelli on a graining machine equipped with a wire screen having square openings of 0.093 inch, and wire 0.032 inch in diameter. The rained granular material was put in drying trays and allowed to stand at room temperature for l? hours, and then blown in a container for 4 hours with air at F. The dried product was passed over a U. 8. Std. 30 mesh sieve.

EXAMPLE 3 70 parts of coarse ammonium nitrate, 97% passing through a standard 14 mesh sieve and 13% through a 40 mesh, coated with 0.3% of a mixture of 75% petrolatum and 25% paraflin, and 4:1 parts of corn starch, containing 12.2% moistme, were placed in a warm jacketed dough mixer and thoroughly mixed. 4.5 parts of water were added with continued kneading. followed by the addition of 12.3 parts of fine ammonium nitrate of such a fineness that 68% passed through a 100 mesh standard sieve, and 22.5 parts of line material passing a standard 30 mesh sieve, obtained by screening the dried grained product having a similar composition and method of preparation as now being described. The total time of the mixing required about 3 minutes. 2.0 parts more of water were added with continued mixing for 1 to 2 minutes. The temperature of the mixture at this stage was 86 F. The moistened mass was rubbed through a flat screen having 0.132 inch square openings, and 0.035 inch diameter wires. The resulting granular mass was placed in drying trays to a. depth of 1% to 2 inches and dried at 160 F. for 10 hours. The dried porous cakes composed of granules were rubbed through a screen having 0.093 inch squareopeningsand 9.032 inch diameter-wires.- "This prddlict was-lpassed' 6ver'a vibratingscreen nsvmgmoaze-mcno enmg and 0.023inch1iiam" 6W partsof thgdw product' remained on the 'screenfand lrparts passed' tho 'u'gli'which' womd'be usd in}; subsequent batch. a

EXAMPLE 4 4250 parts of coarse ammonium nitrate similar to that used in Example 3 and 300 parts of corn starch. containing 12.2% moisture, were thorthen 300 parts of water added with continued kneading, followed by the addition of parts of fine ammonium nitrate 68% passing a 100 mesh standard sieve, and 1200 parts of fine material passing a 30 mesh sieve, obtained by screening the dried grained product having a similar composition and method of preparation as now being described. Heat was applied to the batch by means of the steam jacket of the mixer, and the temperature of the charge raised to 90 F. in 7 minutes with kneading. 200 parts of water were added at this stage and the kneading continued for 10 minutes. The final temperature of the batch was 93 F. The soft moist batch was rubbed through a screen having 0.130 inch square openings and 0.035 inch diameter wires. The resulting granular product was put on trays to a depth of from 1% to 2 inches and dried in a dry house for 5 hours at F. The porous cake made up of granules, after cooling, was broken up and passed through a screen having 0.113 inch square openings, and 0.054 inch diameter wires. This product was screened over a sieve having 0.0326 inch openings. 4767 parts of the desired coarse granular product were obtained and 1186 parts of fine material which was used in a subsequent batch.

In each of the foregoing examples, the starch was present in the ultimate composition in a small Uri.

EAFLUOWL, r

proportion insufiicient in amount to combine with all of the oxygen capable of being liberated by the water soluble nitrate but suflicient in amount to bind the ammonium nitrate granules together. The relatively coarse ammonium nitrate granules retained their identity in the finished product. The starch and the fine ammonium nitrate (or the ammonium nitrate of the ammonium nitrate solution) formed a binder for the coarse ammonium nitrate granules, the final product being in the form of fragmented agglomerates consisting essentially of water soluble ni- Table I Example Passed U. S. std. sieve: Per cent S-mesh 100.0

22. 4 None 0.65

Percent Percent Percent 81. 56. 0 28. 0 None 0. 67

Apparent density The apparent density was determined by placing the material in a 1%" diameter cylinder and applying pressure of pounds per square inch on each 2 inch increment (depth) of material filled into the cylinder until a column 10" high was produced. The weight of the charge was then divided by the weight of an equal volume of water at 16 C.

The explosive composition of the'present invention gives great reliability due to its sensitiveness when used per se as an explosive fired by a booster. However, I have found that its greatest applicability is for the replacement of water soluble nitrates in permissibles and the like in which case the composition of the present invention is used with other ingredients commonly employed as, for example, oxygen consuming ingredients, oxygen suppliers, sensitizers, etc., as will be apparent to those skilled in the art.

Having described my invention what I claim is as follows:

1. The process of preparing starch-water soluble nitrate explosive compositions which comprises mixing starch and granular water soluble nitrate consisting of at least 60% ammonium nitrate, in the presence of water to a plastic consistency, the starch being present in a small proportion insufficient in amount to combine with all the oxygen capable of being liberated by the water liiUliS ti tiiltiilitllit soluble nitrate but sufficient in amount to bind the ammonium nitrate granules together, drying a relatively large surface area of the plastic mixture so produced at least sufiiciently to case harden the same and to form agglomerates consisting essentially of water soluble nitrate granules bound together by a starch-water soluble nitrate binder, and fragmenting the case hardened mixture.

2. The process of preparing starch-water soluble nitrate explosive compositions which comprises mixing starch and granular Water soluble nitrate consisting of at least 60% ammonium nitrate, in the presence of water to a plastic consistency, the starch being present in a small proportion insufficient in amount to combine with all the oxygen capable of being liberated by the water soluble nitrate but sufiicient in amount to.

bind the ammonium nitrate granules together, passing theplastic mixture so produced through a sieve to provide grains, drying masses of the said grains at a temperature of at least F. to provide porous cakes consisting essentially of agglomerates of water soluble nitrate granules bound together by a starch-water soluble nitrate binder. 3. A starch-water soluble nitrate explosive composition wherein the water soluble nitrate consists of at least 60% by weight of ammonium nitrate and the starch is present in a small proportioninsufficient in amount to combine with all the oxygen capable of being liberated by the water soluble nitrate but sufiicient in amount to bind the ammonium nitrate granules together, said composition being in the form of fragmented irregular agglomerates consisting essentially of water soluble nitrate granules bound together by a starch-Water soluble nitrate binder, said agglomerates being of such size as to pass an 8-mesh sieve and be retained on a 30-mesh sieve and having an apparent density no greater than .71.

4. A starch-water soluble nitrate explosive composition wherein the water soluble nitrate consists of at least 60% by weight of ammonium nitrate and the starch is present in a small proportion insufficient in amount to combine with all the oxygen capable of being liberated by the water soluble nitrate but sufficient in amount to bind the ammonium nitrate granules together, said composition being in the form of fragmented irregular agglomerates consisting essentially of preformed water soluble nitrate granules of a size that would be held on a IO-mesh sieve, said granules being bound together by a starch-water soluble nitrate binder, said agglomerates being of such size as to pass an 8-mesh sieve and be retained on a 30-mesh sieve and having an apparent density no greater than .71.

CLAUDE H. CAREY.

search 00!! CERTIFICATE OF combmron. Patent 30.- 2,555,657. November 9, 191

CLAUDE 11. cm.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, sec- 0nd column, line 8, for "art' read --are--; page 5, second column, line 26, claim 2, after "binder" and before the period insert and mgnentin the cakes to pass an 8-mesh sieve-; end that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case the Patent Office.

Signed and sealed this 25th day of January, A. 191m.

Henry Van Arsdale, (3 1) Acting Commissioner of Patents.