Present investigation reports the results  of systematic studies on the use of bimodal RDX in low-vulnerability  ammunition (LOVA) gun propellants. Several formulations based on bimodal  RDX as oxidiser, cellulose acetate as binder, and diocty1 phthalate or  triacetin as plasticizer were processed with different proportions of 5  micrometer and 20 micrometer particle size of RDX samples in the range  100:0 to 60:40 ratios. The effect of varying the proportion of fine RDX  of the two particle sizes on propellant burning behaviour was found to  be quite significant. The study concluded that by using bimodal RDX, it  is possible to modify burning behaviour without sacrificing  low-vulnerability aspects of LOVA propellants

Dayanandan, C. R.

Gandhe, B. R.

Joshi, M. M.

Karir, J. S.

Pillai, A.G.S.

English

Defence Science Journal

Defence Science Journal, Vo148. No 3. July 1998, pp. 317-321@ 1998, DESIDOCRole of Bimodal RDX in LOV A Gun Propellant CombustionM.M. Joshi, C.R. Dayanandan, A.G.S. Pillai, B.R. Gandhe andJ.S. KarirHigh Energy Materials Research Laboratory, Pune -411 021.ABSTRACTPresent investigation reports the results of systematic studies on the use of bimodal RDX inlow-Vulnerability ammunition (LOV A) gun propellants. Several formulations based on bimodal RDXas oxidiser, cellulose acetate as binder, aild dioctyl phthalate or triacetin as plasticizer were processedwith different proportioris of 5 ~ and 20 ~ particle size ofRDX samples in the r3l1ge 100:0 to 60:40ratios. The effect of varying tile proportion of fine RDX of the two particle sizes on propellant bunungbehaviour was found to be quite signifiC3l1t. The study concluded that by using biInodal RDX, it ispossible to mOOify burning behaviour witlIout sacrificing low-vulnerability aspects of LOV Apropellat1ts.gun propellants reported earlier appears to be quiterelevanr-4. These propellants use nitraminedispersed into inert or energetic polymericbinder-plasticizer matrix. Propellants based on suchformulations have realised higher ignitiontemperatures and less sensitivity to impact andfriction as compared to the conventionalpropellantss. Their ballistic performance andchemical stability are found to be superior to thenitrate .ester-based propellants in use currently.The energy level of LOVA gun propellantsdepends mainly on the percentage of nitramine.Because of its easy availability and comparativelylow-cost, RDX has been preferred to HMX in manycompositions reported earlier. It is known that theburning behaviour of nitramine propellant dependsupon the particle size of nitramine used in thepropellant. However, a few studies have dealt withthe effect of particle size of RDX on the burningbehaviour of the propellant. Pillai6, et al. havereported that increase in particle size of RDXincreased the burning rate as well. as the pressureNOMENCLATURECA Cellulose acetateCAB Celluose acetate butyrateDOP Dioctyl phthalateGAP Glycidyl azide polymerT A TriacetinCV Closed vesselF Force constanta Pressure exponentJ31 Linear burning rate coefficientdpld, Rate of rise in pressure w.r.t. timer Burning rate1. INTRODUCTIONThe conventional nitrate ester-based gunpropellants are quite satisfactory as far as theirballistic performance is concerned. The maj~rdisadvantage with these propellants is their highsensitivity to heat, impact and friction. Theliterature on low-vulnerability ammunition (LOVA)Received 31 March 1997. revised 08 December 1997317DEF SCI J. VOL 48. NO 3. JULY 1998Table 1 (a). Effects or variation or bimodal fine RDX ratioon burning behaviour or LOV A gun propenantsbased on RDX/CA/NC/fA system (CV test vesselcapacity: 700 cc, loading density: 0.2 g/cc)Composition I II III IV VProportion of 5 ~ to 100:0 90: 10 80:20 70:30 60:4020 ~ RDXPercentage of 20 J.Lm 0 7.7 15.4 23.1 30.8RDX in propellantcompositionForceconstant 1047 1050 1059 1051 1055(JIg)Linear burning rate 0.06 0.088 0.13 0.14 0.16coefficient (131)(cmls/MPa)Pressure exponent 0.74 0.844 0.96 1.02 1.05(a)(dpldt) max 33.54 44.76 57.51 61.12 65.32(MPa/ms)Burningrate(r)cmls 13.75 17.86 23.00 23.32 26.53at 154 MPaAverage vivacity 0.597 0.798 1.036 1.071 1.195(10-3) (Mpa x ms)exr onent of the nitramine gun propellant.JUilasZ and Rocchio1 have reported the use ofbimodal HMX or RDX with polyurethane orpolybutadiene as binder and observed that the useof bimodal nitramine system helped in minimisingwell-known slope break effects ofnitramine. Mackowiak7 has studied the effect ofgrain size of RDX on the performance of thepropellant based on RDX/GAP, RDX/CAB andRDX/polybutadiene that are using unimodal RDXsystems only. Lu Anfang and Liao Xin8 havereported the effect of RDX particle size on theerrosivity of the propellants, but this work dealtwith only unimodal systems, where particle sizevariation was from 4.86 to 25.5 ~m. Lussier,9 eta/.also used bimodal RDX in their studies, but theirobjective was to study the effects of grain length,igniter type, and conditioning temperature on theburning behaviour of the propellant. Thus, theliterature survey clearly indicated that nosystematic studies were carried out on theformulations based on bimodal RDX with respect tovariation in the proportion of two particle sizes in agiven system.In the present investigation, systematic studieshave been carried out on the effects of varying theproportion of 5 ~m and 20 J1In fine RDX in bimodalform on the burning behaviour of LOVA gun)ropellant as well as on different binder-plasticizercombinations.2. EXPERIMENTAL PROCEDURETwo series of LOVA gun propellantformulations based on RDX/CA/NC/DOP andRDX/CA/NC/TA compositions, with varyingproportion of 5 ~ to 20 ~m RDX from 100:0 to60:40 but keeping overall quantity of RDX in allformulations at constant level (77 per cent wlw)were processed. The percentages by weight of eachingredient in all the formulations were:Bimodal RDX 77 %CA 13 %TA or DOP 6 %NC (N2 : 12.2 %) 4 %The batch size in each case was about 2 kg. Asigma blade incorporator (5 1) was used forpropellant processing by solvent method. Thepropellant dough was extruded into heptatubularstrands with the help of a vertical hydraulic pressusing a suitable die-pin assembly. The strands afterdrying were cut into grains of suitable sizelength-to-diameter ratio (2.3) and the propellantfo~ulations were subjected to closed vessel (CV)firing test and determination of vulnerability.3. RESULTS & DISCUSSIONAll propellant formulations were processedunder identical conditions with grains having samegeome:try (heptatubular) and lengih-to-diameterratio (2.3 :t 0.2). The replacement of 5 ~m RDXwith certain percentage of20 ~m RDX did not makeany significant change in the process conditions,especially during the extrusion stage. The extrusionpressure during all experiments remained in therange 60-70 kg/cm2, as normally observed. TheCV firing data were obtained using same igniterpowder in all cases and the propellant samplesconditioned at room temperature (27 °C) were usedin all experiments. Thus, except the proportion ofJ318DEF SCI J, VOL 48, NO 3, JULY 19983ind ~ates that low-vulnerability aspects have notbeen sacrificed at all while replacing unimodalRDX by bimodal RDX in a LOVA composition.Bimodal RDX-based propellants reported here arealso found to be less vulnerable to heat, impact andfriction than the conventional propellant like NQ.4.4. CONCLUSIONLOVA propellant fonnulations using fine RDX(5 ~m) may give better processibility, but lead tolo,v burning rates. On the other hand, thecomposition ,vith 20 ~m RDX alone hasundesirable burning behaviour (high a. values). Thepresent study indicates that the use of bimodalRDX-based composition with appropriateproportion of the two particle sizes was found to bequite useful to achieve desired burning behaviourand low-vulnerability aspects for LOVA gunpropellants, without sacrificing energy level.Between the two series of propellants studiedhere, the bimodal RDX/CA/NC/TA-basedcompositions were found to be superior to bimodalRDX/CA/NC/DOP-based compositions, for gunapplications.Wise, S. & Rocchio, 1.1. A development processfor low-vulnerab~lity propellant. Paper presentedat the International Annual Conference ofFraunhofer Institute fur CheIriische Technologie(IC1), on use of Plastic Materials for Propellantsand Explosives, 30 June-2 July 1982, Karlsruhe,Federal Republic of Gennany, 1982. pp.539-44.Mezger, M.; Strauss, B.; Moy, S.; Prezelski, I. &Lu, P. The development of insensitive explosives.Paper presented at the Joint InternationalSymposium on Compatibility of Plastics andother Materials with Explosives, Propellants,pyrotechnics & Processing of Explosives andIngredients, 18-20 April, 1988. New Orleans,USA. American Defence PreparednessAssociation, Arlington, Virginia, 1988. pp. 2-8.5,6.7,ACKNOWLEDGEMENTThe authors wish to thank Dr Haridwar Singh,Director, High Energy Materials ResearchLaboratof)', Pune, for his keen interest and valuablesuggestions during this study.8Kirshenbaum, M.S.; Avrami, L. & Strauss, B.Sensitivity characterisation of low-vulnerability(LOV A) propellant, 1ournal of BallL\'fics, 1983,7(2),1701-40.Pillai, A.G.S.; Dayanandan, C.R.; JOS~, M.M.;Patgaonkar, S.S; & Karir, J.S. Studies on theeffects of RDX particle size on the burning rate ofgun propellants. Det Sc. 1.,1996,46(2),83-86.Mackowiak, H.P. Recent investigations on gunpropellant formulations for LOV A. Proceedingsof the Joint International Symposium onCompatibility of Plastics and other Materials withExplosives, Propellants and pyrotechnics. andprocessing of Explosives, Propellants and)ngredients. 22-24 April 1991, San Diego.California. American Defence l>reparednessAssociation. C.alifornia. pp. 136-143.Anfang, Lu & Xin, Liao. Investigation of theproperties of LOV A propellants. Paper presentedat the 24th International Annual Conference ofFraunhofer Institute Fur Chemische Technologie,(ICT). on Energetic Materials-lnsensitivity andEnvironmental Awareness. 29 June -2 July 1993Karlsruhe, Federal Republic of Germany, 1993.pp. 86-1 -86-11.Lussier, L.S.; Lavigne. J.; Boily, G &Archambault. P. Preliminary study of LOV Acombustion in closed vessel. Proceedings of 11thInternational Symposium on Ballistics. Vol 1,Brussel, May1989, pp.225-35.9.REFERENCES1. Juhasz, A.A. & Rocchio, J.J. Combustionproperties of LOV A propellallt. Paper presentedat the International Annual Conference ofFraunhofer Institute fur Chemische Technologie(ICT), on use of Plastic Materials for Propellantsand Explosives, 30 June-2 July 1982, Karlsruhe,Federal Republic ofGermany, 1982. pp.545-61.2. Wise, S. & Law, H. The low-vulnerabilityan1ffiunition progranmle. Army Res. Develop.ACqld. Mag., September-October 1983,22-23.320JOSHL et al: BIMODAL RDX IN LOVA GUN PROPELLANT ~OMBUSTIONContributorsMr MM Joshi obtained his MSc (Organic Chemistry) from the University of Poona in 1976. Hejoined DRDO at the High Energy Materials Research Laboratory (HEMRL), Pune, in 1978 and sincethen, he has been working in the field of solid gun propellants. Currently, he is engaged in thedevelopment of low-vulnerability ammunition (LOVA) propellants.Mr CR Dayanandan obtained his MSc (Organic Chemistry) from the University of Poona. Hejoined DRDO at HEMRL in 1967. Since 1971, he has been working in the field of solid gunpropellants. Currently, he is engaged in the development of solid gun propellants for LOVAapplications.Mr AGS Pillai, Scientist, has been working in the field of solid gun propellants processing andevaluation at HEMRL, for more than 27 years. Currently, he is engaged in the developmen~ ofnitramine-based solid gun propellants for LOVA applications.Dr BR Gandhe obtained his PhD (Chemistry) from University of Poona in 1974. He joined DRDOin 1975. Since then, he has been working on various R&D projects of Defence interest, such asdetection techniques for hazardous chemicals, polymer degradation, LOVA, high energy fuel fortorpedoes, etc. He has published more than 25 papers in national/international journals. At present,he is working as Scientist F and heading the Quality Assurance & Reliability Division at HEMRL,Pune.Mr JS Karir obtained his BE (Chemical Engg) from University of Delhi in 1964. He is Scientist atHEMRL, Pune. Since 1918, he has been working as Head, Gun Propellant Division. He is anassociate member of the Indian Institute of Chemical Engineers, Calcutta.321

Role of Bimodal RDX in LOVA Gun Propellant Combustion

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Role of Bimodal RDX in LOVA Gun Propellant Combustion

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