Title of Invention	A VULCANIZABLE RUBBER BASED INSULATOR COMPOSITION
Abstract	This invention relates to a vulcanizable rubber composition useful as insulators.The composition consists of masticated rubber,hydroxy terminated polybutadiene resin,dibenzo thiazole disulphide,tetra methyl thiruam disulphide and known fillers and extradients.

Full Text

This invention relates to a vulcanizable rubber based insulator composition. Reactive insulator compositions are suitable for applications in Solid Propellant Rocket motor (SRM) system, where, the solid propellant is of the composite type based on Hydroxy Terminated Polybutadiene (HTPB) or polyurethane or polyol as binders. This composite propellant contains apart from binder. Aluminum as fuel, Ammonium perchlorate as oxidizer and other additives. Reactive insulator is applicable to composite propellant formulations containing binder resins with hydroxyl groups. Solid propellant Rocket Motor (SRM) cases may be either metallic or non metallic composite types and are protected from hot combustion gases during burning of propellants by insulation system. The insulation system is usually based on organic or inorganic rubbers. If not properly designed, mission failure can happen by chamber failure due to burn through of hot gases, during the combustion process of the propellant, in the range of 1700-3000^K. In the conventional process, apart from insulation of the chamber, a layer of elastomeric material termed as liner is also applied to the insulator to ensure bonding between the insulator and cast composite propellant. Hence there are two distinctive polymeric systems namely liner and insulator in SRM. The present invention envisages that future SRM will do away with the liner system. The reactive insulator is formulated to have good interfacial bonding between the insulator and propellant. This reactive Insulator system will reduce process time for propellant manufacture. Use of the reactive insulator will improve reliability and reproducibility of SRM, since one of the systems, namely the liner, is eliminated from SRM processing. The major advantages of reactive insulator are (1) ease of application to rocket motor (2) reduction in process time (3) improved reliability and reproducibility and (4) cost effectiveness. This invention relates to a potential insulator composition for the composite solid propellant eliminating the use of a liner. It utilizes the reactive sites available in the form of hydroxyl group in the binder matrix with the active NCO linkages available with composite propellant. Toluene di-isocynate Reactive insulator composition is a rubber based product. The rubber can be nitride or Ethylene Propylene Diane Monomer (EPDM). This rubber based compound is made reactive and bondable with the propellant by the addition of hydroxy terminated poly butadiene (HTPB) resin in the rubber matrix during compounding of the rubber by judicious mixing sequence. The reactive insulator compositions are given in table - lA & IB. It has good interfacial properties and thermal properties to function as a good insulator. The inter facial properties, mechanical properties and thermal properties are given in table 2. Reactive insulator was successfully proved in subscale composite propellant rocket motors having propellant weight of 20 kgs and 30 seconds of burning duration. Accordingly, the present invention provides / a vulcanizable rubber based insulator composition comprising masticated rubber, hydroxy terminated polybutadiene resin, dibenzo thiazolate, disulphide, tetramethyl theorem disulphide known fillers and anti oxidants. The compounding ingredients are weighed separately according to the proportions specified in table lA or IB and are packed in separate containers/packets for compounding. The rubber is masticated thoroughly in a double roll mill for 10-15 mts. Water is circulated through the mill rolls till the end of mixing process. Antioxidant is added and mixed for another 5 mts. Then Zinc oxide, Satiric acid, Capolyte and Sulphuric are added in the order of sequence. Each of the Ingredients is milled for 5 mts. Then the filler, pre-o-sil, is added in installments and the compounding operation is continued till a uniformly filled recipe is obtained. This operation will take about 20 mts for completion. The compounded recipe is allowed to cool to room temperature. The compounding operation is continued with the addition of HTPB resin, acrylonitrile, carbon black, MBTS & TMTD in the order of sequence. Every item is mixed thoroughly giving a compounding time of 5-10 mts each. After the addition of TMTD, the last ingredient, the composition is mixed for about 15 mts. The recipe is taken out in the form of rubber sheet through the mill roller and is cooled to room temperature by keeping on a table with out wrinkes/foldings. The sheet can also be rolled over a pipe with a layer of cloth in between successive layers. Vulcanisation of the sheet is carried out by heating in hot air circulated oven at 120*^C for 3 1/2 hours. The sheet is spread (unrolled) on the floor of the oven on a platform trolley. The vulcanized sheet is allowed to cool down in the oven. Thereafter it is rolled on a pipe and stored. The sheets can be applied to the motor case before or after the vulcanization as desired by the end user. The two roll mill used is a standard rubber compounding equipment driven by a heavy duty electric motor through a reduction gear mechanism. The gap between the two rolls is adjusted as desired by the compounding and sheeting operations. The hot air oven used for the vulcanization of the reactive insulator sheets is a standard electrically heated process equipment with an inbuilt air circulator/blower to ensure uniform distribution of temperature inside the oven. The insulator sheets are cut to the desired size and one of the sides is abraded with grinding stone wheel/wire brush. It is then brushed, cleaned with solvent (dichloro methane, DCM) and is dried in oven for 2 hrs. at ll0 C before casting the propellant. For evaluation of interface properties the propellant is cast in cartons. The propellant is cast on to the abraded side of the insulator and is cured. The insulator is bonded to the motor case with suitable adhesive for casting case bonded grains for static firings or flight test. Abrading, cleaning and drying are also done before casting the propellant in the chamber. Static tests Static testing of two types of rocket motors insulated with reactive insulator were conducted. The first type was a standared 2kg motor with a radial burning mode of shorter burning time. The second type was a subsale motor in the end burning mode with a burning time of more than 30 seconds. Thermocouples were suitably positioned on the surface of the motor case and the temperatures were constantly measured through out the test. The results were compared with the static test data of motors insulated with standared insulator. In all these tests, the composition of the propellant, weight and length of the propellant grain, insulation thickness and nozzle throat diameter were kept identical and the motors were similar to one another, so that the results could be compared realistically. In order to prove the efficiency of the reactive insulator system during long duration firing, subsale motor in end burning mode was cast using standard propellant composition and the thickness of the insulation was kept at 6 mm. The burning time was designed to be more than 30 seoonds. The thermocouples, one near the head end, one near the nozzle end and the third at the middle of the motor were postitioned. One reference identical in all respects using the standard insulator was also cast. The motors were successfully static tested and their performance were similar. The temperature rise on the skin of the motor in all the three locations were similar. Figures 1 and 2 show the temperature profiles vs. time of 2 kg. motors firings. WE CLAIM: 1. A vulcanizable rubber based insulator composition comprising masticated rubber, hydroxy terminated polybutadiene resin, dibenzo diazole disulphide, tetramethyl thiuram disulphide, known fillers and anti oxidants. 2. The composition as claimed in claim 1 wherein said rubber is a nitride rubber or ethylene propylene diene monomer. 3. The composition as claimed in claims 1 and 2 wherein said composition optionally contains zinc oxide, sulphuric, acrylonitrile stearic acid and carbon black. 4. The composition as claimed in claims 1-3, capable of being vulcanizable at 110-130 0 and at ambient pressure. 5. A vulcanizable rubber based insulator composition substantially as herein described.

Documents:

0450-mas-1999 abstract-duplicate.pdf

0450-mas-1999 abstract.pdf

0450-mas-1999 claims-duplicate.pdf

0450-mas-1999 claims.pdf

0450-mas-1999 correspondence-others.pdf

0450-mas-1999 correspondence-po.pdf

0450-mas-1999 description(complete).pdf

0450-mas-1999 description(complte)-duplicate.pdf

0450-mas-1999 drawings-duplicate.pdf

0450-mas-1999 drawings.pdf

0450-mas-1999 form-1.pdf

0450-mas-1999 form-19.pdf

0450-mas-1999 form-26.pdf

0450-mas-1999 form-8.pdf