Title of Invention

"A PROCESS FOR PREPARATION OF LOW VULNERABILITY GUN PROPELLANT"

Abstract

This invention relates to a process for preparation of low vulnerability (LOVA) gun propellant. According to the process RDX or HMX is mixed with inert plasticiser in ethyl alcohol. A mixture of inert binder and an energetic binder is added and the combined mixture is kneaded thoroughly. The kneaded mixture is dried using hot air and the dried mixture is incorporated in a solvent mixture of acetone and ethyl alcohol. A stabilizer is added therein and the mixture is extruded followed by the steps of cutting, drying, blending, graphiting etc. as for other propellants.

Full Text

FIELD OF INVENTION The present invention relates to a process for the preparation of Low Vulnerability (LOVA) gun propellant. PRIOR ART The conventional nitrocellulose-nitro-glycerine based gun propellants are highly prone to accidental initiation as a result of an external stimulation such as fire, Shockwave and impact. Due to this sensitive nature of conventional gun propellants, there is always risk of accidental loss of not only the stored ammunition but also of crew and vehicle in which, the ammunition may be stored. To reduce this risk of accidental initiation, the low vulnaribility(LOVA) ammunition propellant are used. The LOVA gun propellant formulations incorporate an inert binder due to which these formulations have higher ignition threshold and reduced burning rates at low pressures and less sensitivity to impact and, therefore offer significant reduction in vulnerability to ignition and impact. LOVA gun propellants basically consist of an inert binder Cellulose Acetate (CA) and an energetic crystalline material such as cyclo trimethylene trinitramine (RDX) or cyclo tetramethylene tetranitramine (HMX) as oxidiser. Small percentage of Nitrocellulose (NC) is also incorporated as energetic binder from the ballistic point of view. A suitable plasticizer and stabilizer are the other ingredients in the formulation. Since major protion of the binder is constituted by inert material, crystalline oxidiser material is required to be incorporated in very high percentage 7 0 to 8 0 -depending upon the energy requirement. Such a high percentage of Nitramine (RDX or HMX) in the propellant formulation requires sufficient desensitisation of nitramine before processing. This is normally achieved by coating or the plasticizer before use. For ballistic reasons RDX with HMX in fine particulate form having about 0.5 microns particle diameter is preferred for LOVA gun propellant. Particle size of RDX or HMX has great influence on ballistics of gun propellants. In one of the process known in the art for preparation of LOVA gun propellant, a mixture of 12% of cellulose acetate butyrate (CAB),4% of nitrocellulose(NC), 76% of RDX, 7.. 6% of tributyl citrate (TBC) and 0.4% of ethylcentralite (carbamite) are heated with water saturated methyl ethyl ketone to about 70°C under agitation and pressurisation by nitrogen gas (one atmosphere) to form a solution. The mixture is then fed to the ejector at a flow rate of 3kg per minute and at a vapour pressure of approximately 3kg/cm . The precipitated products obtained are washed, dried and fed into a twin screw extruder and kneaded with solvent mixture of ethyl acetate and ethyl alcohol and then extruded into desired shapes. One of the disadvantage of the above process is that during the process of solutioning and precipitation, the fine RDX particle size increases which adversely affects the ballistics of the propellent. Another disadvantage of the above process is that the final product obtained by screw extrusion is not homogenous. Further disadvantage of the above process is that the process involves use of highly costly equipment due to which the process is not cost-effective. In another process known in the art for preparation of LOVA gun propellant, wet fine RDX is dehydrated by stirring with five times its weight with ethyl alcohol. The dehydrated RDX obtained by filteration is coated with a plasticiser triacetin and air dried. Vacuum dried cellulose acetate as inert binder and nitrocellulose as energetic binder are gelatinised with the help of a solvent mixture of acetone and alcohol. The plasticised fine RDX is then incorporated into the gelatinised binder matrix followed by addition of stabilizer carbamite. The resulting dough is extruded into the required size and shape using suitable die—pin assembly in vertical hydraulic press at an extrusion pressure of 150--17(3 kg /cm , The extruded strands are then granulated by cutting to the required length/diameter (L/0) ratio followed by drying at 4(3- o 45 C till volatile matter is not more than 0„5%. A disadvantage of the above process is that large quantity of the solvent ethyl alcohol is required during dehydration of wet fine RDX„ Another disadvantage of the above process is that due to partial solubility of RDX in ethyl alcohol,, variation in particle size of RDX takes place during dehydration which in turn affects the ballistic properties of the finished propel 1 ant. Further disadvantage of the above process is that the propellant obtained has higher chances of batch to batch variation,. OBJECTS OF PRESENI INVENTION The primary object of the present invention is to propose an improved process for the preparation of Low vulnerability iLOVA) gun propellant. Another obiect of the? present invention is to propose process for the preparation of Low Vulnerabi1itv (LOVA) gun propellant which eliminates the step of dehydration of wet RDX fine particles by treatment with ethyl alcohol which practice is followed in existing processes whereby the problem of increase in the size of RDX fine particles experienced in the existing processes is overcome« A further object of the present invention is to propose a process for the preparation of Low yu.lnerabil.itv (t.OVA) gun propel 1 ant which avoids the route of solutionisinq, precipitation, desensitising arid hot-air drying followed in existing process thereby ovesrcoming the problem of agglomeration of desensitised fine RDX during hot. air drying experienced in the existing processes. Still another object of the present invention is to propose a process for the preparation of Lew Vulnerability (LOVA) gun propellant which leads to a ballistically unmiform o roduct. Further object of the present; invention is to propose a process for preparation of LOVA gun propel 1 ant which is a cost—effective as it does not involve use of any expensive processing equipment. Still further object of the present invention is to propose a process for preparation of LOVA gun propellant which is a relatively safer process as is eliminates use of dry explosive materia].., Yet further object of the present invention is to propose a process for preparation of LOVA gun propellant which involves use of only conventional equipment and facilities. Sophisiticated and costly equipment such as twin screw extruder and its accessories are totally dispensed with. DESCRIPTION OF INVENTION According to this invention there is provided a process for preparation of Low Vulnerability (LOVA) gun propellant characterised by the step of: a) mixing 70-80% of RDX or HMX with 2 to 8% of inert plasticiser for example triacetine (TA) or acetyl triethyl citrate (ATEC) or tributyl citrate (TBC) or tri-ethyl citrate (TEC) in ethyl alcohol. b) Adding mixture of 10 to 12% by weight of inert binder for example cellulose acetate (CA) or ethyl cellulose (EC) or cellulose acetate butyrate (CAB) and 10 to 11% by weight of an energetic binder for example nitrocellulose (NC) and throughly kneading the combined mixture; c) Hot air drying and incorporating the dry mixture in a solvent mixture comprising of acetene and ethyl alcohol in the range of 80: 20 to 60: 40 ratio preferably in 17: 30 ratio; d) Adding 0.2 to 0.5% stabilizer such as ethyl centralite (Carbanite); e) Extruding by hydraulic press followed by cutting, drying, blending, graphiting etc. as for other propellants. In accordance with the present invention the process comprises in the step of preparing a mixture of 70 to 80 preferably 70 to 73% of energetic crystalline material such as cycio trimetbylene trinitramine (RDX) or eye. lo tetra methylene tetrani.tr amine ( HMX ) in particle size of for example about 5 microns with 2 to 3% preferably 3 to 7.57. of inert plasticiser such as triacetine (FA) acetyl triethyl citrate (ATEC), tr.ibuty'J citrate (TBC) or triethyl citrate (TEC) as a solution in ethyl alcohol. The mixture is loaded into a siqma blade mixer and kneaded for 1 to 2 hours. A mixture is separately prepared of about 13% preferably 10 to 11% of energetic binder such as nitrocellulose? and 8 to 167. preferably 10 to 12% of inert binder such as cellulose acetate (CA)„ ethyl cellulose (EC), or cellulose acetate butyrate (CAB),. Such a mixture is added to the mixture in the siqma blade? mixer and kneaded for another' .1. to 2 hours. The mixture is unleaded and subjected to hot o air drying at 40 to 45 C. Drying, is con tin Lied at 40 •! o o 45 C till the content, of volatile matter comes down to :i to 2% The dry mix is added to a solvent mixture comprising of acetone and ethyl alcohol mixture in t»ie range of 80:20 to 60:40 ratio preferably in 17:38 ratio. The next step consists in adding 0.2 to 0.5% oreferably 0.5% of stabiliser like ethyl centralite (car bamite ) and small quantity 1 to 7 . 8% preferably 7% of energetic plasticiser like clinitro-toluene (DNT) or qiycidvl azide polymer (GAP'S, preferably DMT. The propel 1 ant dough as formed hereinabove after about 6 hours of incorporation is subjected to the process of extrusion by hydraulic press followed by Cutting, drying , b1endinq, graphA tingotc . as i n the case o f other prope11an ts . The process of the present invention will now be illustrated with a working example which is intended to be a typical example to illustrate the working of the invention and is not intended to be taken restrictive]v to imply and limitation on the scope of the present invention. WORKING EXAMPLE-I. 4.3.27 kg of water wet fine RDX of parti c te size of about 5 microns and with water content of 27 „ 9%, and 0.2320 kq of triacetine as solution in 0.11.60 kg of ethyl alcohol were loaded in 10 litre capacity siqma blade mixer and kneaded for one hour 0.5005 kq of cellulose acetate having moisture content 4.1% and 0.2457 kq of water wet nitrocellulose (water content. 34.9%) were premised and loaded into the mixer,, T he kneading was continued for another one and half hour". The wet mix was unloaded and dried by hot air blowing at 40—45 (0 till the moisture content came down to 1-2%. : y : Weighed quantity of dry mix on volatile matter free basis was loaded in a sigma mixer and incorporated with 18 to 19% solvent mixture of acetone and alcohol to form homogenous dough. 0.2% of carbamite was also added at this stage. Period of incorporation was maintained for six hours at a temperature of 36-40°C at one atmospheric pressure. The propellant dough so formed was then extruded in heptatubular geometry using suitable die-pin assembly in a vertical hydraulic press. Extrusion pressure was maintained between 150-170 kg/cm2. The propellant strands were cut to 2.1 - 2.5 (length to diameter) ratio with the help of a rotary cutting machine. The cut propellant was dried by hot air blowing at 40-45°C at ambient pressure. WORKING EXAMPLE-2 5.081 kg of water wet fine RDX of particle size of about 5 micron and with water content of 28.17%, 0.100 kg of dinitro toluene (DNT) and 0.240 kg of triacetin solution in 0.120 kg of ethyl alcohol were loaded in a 10 litre capacity sigma blade mixer and kneaded for one hour. 0.5108 kg of cellulose acetate having moisture content of 2.13% and 0.735 kg of water wet nitrocellulose (water content. 32.0%) were premixed and loaded into the mixer. The kneading was continued for another one and half hour. The wet mix was unloaded and dried by hot air blowing at 40 - 45°C till the moisture content came down to 1 to 2%. Weighed quantity of dry mix on volatile matter free basis was loaded in a sigma mixer and incorporated with 18 to 19% solvent mixture, acetone and alcohol to form a homogenous dough. 0.2% of carbamite was added at this stage. The period of incorporation was 6 hours at a temperature of 3 6 to 4 0°C at one atmospheric pressure. The propellant dough so formed was extruded in heptatubular geometry using suitable die-pin assembly in a vertical hydrualic press. Extrusion pressure was maintained between 150 to 170 kg/cm2. The propellant strands were cut to 2.1 to 2.5 (length : diameter ratio) with the help of rocary cutting machine. The cut propellant was dried by hot air blowing at 40 to 45°C at ambient pressure. WORKING EXAMPLE-3 2.300 kg of water wet fine RDX of particle size about 5 micron and with water content of 22.83%, 0.1375 kg of triacetin in 0.06875 kg of ethyl alcohol were loaded in 5 litre capacity sigma blade mixer and kneaded for one hour. 0.255kg of cellulose acetate having moisture content of 2.01% and 0.437 kg of water wet nitrocellulose (water content 37.01%) were premixed and loaded into the mixer. The kneading was continued for another one and half hour. The wet mix was unloaded and dried by hot air blowing at 40-45°C till the moisture content comes down to 1 to 2%. Weighed quantity of dry mix on volatile matter free basis was loaded in a sigma mixer (5 litre capacity) and incorporated with 2% dinitr toluene (DNT) and 18 to 19% solvent mixture of acetone and alcohol to form a homogenous dough. 0.5% of carbamite and 1% of potassium nitrate (passing 150 BSS sieve) was also added at this stage. The period of incorporation was 6 hours at a temperature of 3 6 to 40° at one atmospheric pressure. The propellant dough so formed was extruded in heptatubular geometry using suitable die-pin assembly in a vertical hydraulic press. Extrusion pressure was maintained between 150 to 170 kg/cm'. The propellant strands were cut to 2.1 to 2.5 (length diameter ratio) with the help of rotary cutting machine. The cut propel lant was dried by hot air blowing at 40 to 4 5°C and ambient pressure. LOVA gun propellant having composition CA 12%, NC 4%, RDX 78%, TA 5.8% and Carbamite 0.2% prepared as per working example-1 above, in heptatubular geometry, and by the existing process were evaluated for ballistic aspects by closed vessel (700 cm ) technique at 0.2 g/cm3 loading density. The results obtained in four experiments are as shown in Table-I. TABLE-I (Table Removed) Results from the above table ahow that the linear burning rate co-efficient of propellants processed by the existing process recorded higher value as compared to that of the propellant processed by the process of the present invention. Also the pressure exponent of the propellant by existing process recorded higher value as compared to that of the propellant from the process of present invention. Higher value of linear burning rate co-efficient: ( -ß) } and pressure exponent ( CK, ) are the indications for increase in particle size of fine RDX during the processing. Higher value of linear burning rate co-efficient and pressure exponent are undesirable for gun ammunition ballistic performance. This clearly indicates that the process of present invention is superior to the existing process and yields finished propellant of consistant and superior ballistic performance. It is to be understood that the process of the present invention is susceptible to adaptations, changes, modifications. Such adaptations, changes, modifications are intended to be within the scope of the present invention which is set forth by the following claims:- WE CLAIM: 1. A process for preparation of Low Vulnerability (LOVA) gun propellant characterised by the step of: a) mixing 70-80% of RDX or HMX with 2 to 8% of inert plasticiser for example triacetine (TA) or acetyl triethyl citrate (ATEC) or tributyl citrate (TBC) or tri-ethyl citrate (TEC) in ethyl alcohol. b) Adding mixture of 10 to 12% by weight of inert binder for example cellulose acetate (CA) or ethyl cellulose (EC) or cellulose acetate butyrate (CAB) and 10 to 11% by weight of an energetic binder for example nitrocellulose (NC) and throughly kneading the combined mixture; c) Hot air drying and incorporating the dry mixture in a solvent mixture comprising of acetene and ethyl alcohol in the range of 80: 20 to 60: 40 ratio preferably in 17: 30 ratio; d) Adding 0.2 to 0.5% stabilizer such as ethyl centralite (Carbanite); e) Extruding by hydraulic press followed by cutting, drying, blending, graphiting etc. as for other propellants. 2. A process for the preparation of Low Vulnerability (LOVA) gun propellant as claimed in claim 1 wherein RDX or HMX is present in an amount of preferably 70-73% by weight of the mixture. 3. A process for the preparation of Low Vulnerability (LOVA) gun propellant as claimed in claim 1 wherein the inert plasticiser is preferably triacetine in 3 to 7.5% of the weight of mixture. 4. A process for the preparation of Low Vulnerability (LOVA) gun propellant as claimed in claim 1 wherein the energetic plasticiser is preferably DNT. 5. A process for the preparation of Low Vulnerability (LOVA) gun propellant as claimed in claim 1 wherein the energetic plasticiser is 2% of the weight of the mixture. 6. A process for the preparation of Low Vulnerability (LOVA) gun propellant as claimed in claim 1 wherein inert binder is preferably cellulose acetate. 7. A process for the preparation of Low Vulnerability (LOVA) gun propellant substantially as herein described and exemplified in the example.

Documents:

82-del-1999-abstract.pdf

82-del-1999-claims.pdf

82-del-1999-correspondence-others.pdf

82-del-1999-correspondence-po.pdf

82-del-1999-description (complete).pdf

82-del-1999-form-1.pdf

82-del-1999-form-19.pdf

82-del-1999-form-2.pdf

82-del-1999-form-3.pdf

82-del-1999-pa.pdf