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2 3,379,585 In order to make a comparative study of the effect CAST EXPLOSIVES COMPRISING CYCLO- on crack resistance of various additives, a severe thermal TRIMETHYLENE TRINITRAMINE AND shock cycle has standardized for use on the cast explosives NITROTOLUENES and an index was formulated for evaluating the results. Ciiflord L. W@ier, @s Aiam6s, N. Mex., and Joseph L. 5 The following index was used: Stark, St. Paul, Mmri.;’,,a@gnors to the United States of Ame~ca as represented by the United States Atomic Erie@ Commbion No Drawfng. Filed Jan. 12, 1951, Ser. No. 205,834 3 chink. (Ci. 149—18) This invention relates to a process for making crack- 10 Where I is the index number, W is a function of the width resistant cast explosives; more particularly it relates to a of the crack, L the length of the crack in centimeters, At process for making trinitrotoluene+ontaining explosives the range of the temperature cycle and f(n) is a function wlrich are highly resistant to cracking under thermal of the number of cyclesl Three classes of cracks were de- —. shock. The invention also relates to the products formed fined as foilows: wide open cracks, medium cracks and by the above process. 15 very fine cracks with assigned width factors of 5, 3 and Trinitrotoiuene (TNT) has been known for many years 1.5 .respectiveiy. The cracks showing de~ite clqavage to possess properties that niake it well suited for use in were selected as the wide open cracks, those appearing making cast explosives. It is highly stable over long as fine lines or checks were generally considered the very periods of storage, is relatively insensitive to shock or fine cracks and those more clearly defined than the fine blows, and forms no sensitive explosive compounds by 20 cracks and not showing any visible fracture or cleavage reaction with metals. Furthermore, it melts at a relative- were selected as the medium cracks. Al was arbitrarily ly low temperature, so that it is well adapted for forming raised to the one-half power to approximate its effect cast explosive charges, since fusion can be brought about on cracking. This was necessary because several different by use of hot water or low pressure steam. thermal cycles were used before all the testing was com- While TNT has the foregoing favorrrble properties for 25 pleted. While the magnitude of the values in this empirical employment as the explosive for cast charges, it has the formulation might not be absolute, they give a satisf- serious disadvantage that cast explosives containing it actory relative evacuation. are highly susceptible to cracking under thermal shock. Intentionally severe and abrupt thermal shock cycles Inasmuch as large changes in temperature are unavoida- of 65” C.+ O“ C.+650 C. for composition B and 65” ble in manufacturing and handling of cast explosives, 30 C.+ 20° C.+ 65° C. for Baratoi were used and all cast- elaborate precautions must be taken in order to obtain ings in a particular batch were cycled together. The com- sound castings, position B cycle consisted of heating the charges in a 65” r ‘, ., It is generally believed that cast explosives crack be- C. industrial type oven for eighteen hours, removing to cause of excessive stresses and strains set up in the charge an agitated ice-water bath for six hours and then reheat- during freezing and subsequent thermal cycling. It is 35 ing in the oven for eighteen hours. They are then removed believed that these stresses and strains sometimes exceed from the oven, allowed to cool, the cracks measured and the physical strength of the explosive: fracture or crack- the index computed. Thereafter they were sectioned and ing is produced. The use of various additives to increase examined for internal cracking. The Baratol cycle con- the physical strength of the explosive to the point where sisted of heating the charges in an oven at 65” C. for it will withstand all normal stresses and strains has been 40 eighteen hours, then placing them in a deep freeze unit suggested. However, no additive has been found prior for 18 hours after which they were again heated in the to this invention which substantiality reduces the cracking 650 C. oven for eighteen hours; after the forty-four hour of cast explosives and does not prohibitively interfere cycle the chanrges were allowed to cool to room tem- with such requisite propaties as dimensional stability, perature before the cracks were evaluated. In general, it impact sensitivity, casting properties and others. 45 was found that internal cracking was proportional to ex- It is, therefore, an object of this invention to provide ternal cracking. a prwess for making trirritrotoluene-containing cast ex- In making the tests to determine the effectiveness of the plosives which are highly resistant to cracking. va~iom additives the castings vmre made from own kel- It has been found that the above and other objects tle melts and the melting procedure and pouring tempera- are accomplished by the incorporation of proportionate- 50 ture were standardized. A medium sized shaped charge ly small amounts of a mixture comprising orthonitro- was used and a standard Oastig procedure waa adopted tohrene (ONT) and paranitrotoluene (PNT) into a molten which resulted in a charge free from all stress and feeding mixture of trinitrotoluene-containing explosive, thorough- cracks. The top contours on all charges we~e machined ly mixing the ingredients and casting the meit into the to approximately a 9.25 inch radius contour in order to desired shape. 55 insure charge uniformity and to obtain a snmoth ~p sur- The surprising results obtained by the use of the above face for examining the cracks. In order to get a reliable mixture are due to the effect of a ternary eutectic mixture statistical evaluation of the effect of the additives on crack formed by the para-, ortho-, and trinitrotoiuene. In com- prevention a number of charges were used to test eadh ad- position B, an explosive mixture of about 60 pereent ditive and these were taken from the same melt, cast with RDX (cyclotrimetbylene tnnitramine) and 40 percent 60 a standard cooling procedure and thermally shocked si- TNT, the eutectic formed has a composition of 65.5 per- multaneously. cent ONT, 19.5 percent PNT and 15 percent TNT, and Following is a tabulation of the results obtained in com- has a meiting point of – 19.5° C. Aithough the exact pesiticm B and Baratol (about 76 percent barium nitrate mechanism of crack prevention by the eutectic is not and 24 percent TNT) using the above procedures and in- known, one possible explanation may be that the low 65 dex. The index values are the average of a batch of a P. melting eutectic formed with TNT tends preferentially to number of castings. It will be noted that the average of redissolve the strained crystals since these crystals possess the values obtained without additives is 25. This value can a higher free energy than an unstrained crystal. The dis- be used as a standard for comparing the effect of the van- solved material is then re-deposited in the form of stress ous additives on crack ~esistanco. All index numbers are free crystals. Further, since the tutectic is acting on the 70 romrded off to the nearest whole integer. Amounts are crystals, there is a definite surface lubrication effeet that shown as percentages of composition B or Baratol and the adds to the stress relief. ONT-PNT mixtrrre is in the ratio of 1 to 1.

-=%...... , .,, . 3;379,585,: , : ~:, “,”’-:,’:: 3 COMPOSITION B consisting of about 60 percent RDX and 40 percent TNT .. were melted in a steam kettle and held at a temperature “ -~~ Additive Amount of Average I Aver- . Additive of Batch age 1 of 85 to 88° C. To the molten mixture formed 0.7 pmrrds = ...... - ...... of a mixture of equal amounts of PNT and ONT were “ None ...... ~ 31 Do- ...... 24 25 5 added ’slotvly with rnoderat~ sttirittg. i4fter”stirrin,g for 15 Do ...... -...... i...... 20 } mimttes the resulting mtiture Was poured idto molds OAT, ...... > ...... =...... 21 PANT ...... 4 18 and cast. The same procedure was f~p~ate’d using 175 ONT-PNT ...... 4 pounds of Baratol, and 0.10 pounds M the ONTAPNT ON T- PNT ...... 4 ,: }’ ONT-PNT Cetyl-Pabitate ...... 45 ...... mixture. After removal from the mold the chargei were ONT-PNT Iso Butyleno Glycal . . . . .45 17 ...... machined and subjected to the respective thefthal shwk 12 ...... - 10 ONT-PNT H-Hexadecane:...... ,45 cycles described above. BARATOL The cast explosives were found to have a crack index of 6 and 7 for the composition B and Baratol products respectively and in general were of higher quality than 15 explosives cast by former processes. The use of oNT-PNT additive was found to have no detrimental effect on such The cbmlbinati~ns comprising the last three additivw properties of the cast explosive as dimensional stability, in the first table were used to determine the effectiveness impact sensitivity, detonation velocity and theological of tctria@ additives. The third additive was one which characteristics. It was found that the use of the above showed some promise by itself and it was felt that it 20 additive improves the casting properties of both composi- might contribute something beneficial whaaddedwith the tion B and Baratol in that it permits faster cooling proce- ONT and PNT; .05 qertent by weight of the third additive dures and the casting of certain type charges which form- was added to the ONT-PNT mixture. erly could not be successfully cast. The results graphically demonstrate the effectiveness of It is thus seen that the process of the invention pro- tbe ONT-PNT mixture for composition B and Baratol. 25 vides a means of producing cast trinitrotoluene-contain- It is essential that the ONT and PNT be added in the fcmrn ing explosives which are highly resistant to trackhrg and of a mixture as the addition of either of these cotnpunds are superior in other characteristics to cast explosives alone dtis not produce the de-sired result. The optimum made by prior methods. ratio of ONT to PNT in the mixture is about 1 40 1 but While there have been described what are considered may vary slightly either way. 30 to be preferred embodiments of the present invention, it Experience has shown that the most convenient methcd is to be understood that the invention of this application of handIing the additives has been to weigh out separate- is not limited to the specific examples herein recited but ly the aniimnts of ONT and PNT r6qiiired and make a that numerous modifications and variations thereof may stckk sblution by dismlving the pafamitnbtuluene in the be made without departing from the scope of the inven- orthwlitfotohterte. The required amount of the mixtwre 35 tion as set forth in the appended claims. for any given size melt can then be measured either vol- Whatis claimed is: -, umetrically or gravimetrically. 1. A process of preparing a cast explosive composition ‘- The additiv~ should be added to the melt about ten to which is resistant to thermal cracking which consists in fifteen mimttes pfior ~ pouring and at a melt tempera- heatinga composition consisting of 60% cyclotnmethyl- ture below 90° C. Iri the case of vacuum melts, the addi- 40 ene trinitramine and 40% trinitrotoluene to a molten tion can be made after breaking the vacuum on the melt. condition !but not in excess of about 90” C., adding thereto Following is a tabulation of tisults of tests made to de- a mixture consisting of orthonitrotoluene and paranitro- termine the optitnum amount of ONT–PNT additive for toluene, said added mixture being in an amount equal to compo&ition B and Baratol. Weights are given as percent- about .75~0 to 1!% of the trinitrotohrene present in the composition, mixing the composition and added mixture, ages of the weight of cornp@ition B or Baratol in the 45 charge as the ca$e may be. and casting the resuhing melt into a desired shape. 2. A process of preparing a cast explnsive composition Composition B which is resistant to thermal cracking tvhich consists in Percent additive ONT-PNT I heating a composition consisting of 60% cyclotnmethyl- 0.20=0.20 .-.--. --_. _=e------6 50 enetrinitramine and40!Zo trirritrotoluene to tl molten con- 0.20=0.20 ------7 dition but not in excess of about 90° C., adding thereto 0.344.10 ------7 a mixture consisting of equal parts of orthonitrotoluene 0.14=0.04 ------~ =------13 and paranitrotohrene, said added mixture being in an 0.03–0.01 ------21 amount equal to about 1?40of the trinitrotohretre present O.lwo.lo ---=--=---s ------14 55 in the composition, mixing the composition and added ,, 0.50-0.15 ---:------8 mixture, and casting the resulting melt into a desired 0.21~0.07 ------12 shape. 0.20-0.10 ------9 3. A cast explosive composition comprisittg approxi- BaTatol mately 60% cyclotrirnethylerie trinitramine and 40% tri- 60 nitrotoluene to which has been added a mixture of equal .12-.12 =--=------=------12 amounts of ot-thonitrotoluene and paranitrotoluene, said .06-.06 ---~-ti ------11 mixture being present in an amount equal tb about l% :04+04 ------10 of the trinitrotoluene in the composition. .03-.03 ------.-=----- 7 .02-.02 .-.-.---=..------.-4=---=- 12 65 References Cited It wiibe notied frorn:he above table that theoptihibm UNITED STATES PATENTS arnmmtofthe ONT–PNT mikturehating equal amounts 829,362 8/1906 Barthelemy ------52—20X ofeachingretfient @:4pticerit forcornposition B and .06- P¢ fti BWatof. This t@ounts to between .75~0 and FOREIGN PATENTS -’7., 17. of additive based orithe weight of ~Tin composi- 70 17,128 1913 Great Britain. .,1;. - tion B. The followihg sp5cific examples are given to illustrate CARL-D. QUARFORTH, Primary Exam”iner. .prefemed embodiments of the pi-esent inventimr but are SAMUEL BOYD, WILLIAM WILES, l?x-anriner$. in no way intended to limit the scope thereof. One hundred seventy-five pounds of composition B 75, A. P. KENT, L. A. SEBASTIAN, Assistant Examiners.