The study carried out so far on the application of ethylene-propylene diene rubber (EPDM) in the field of insulation of case bonded solid rocket motors has been reviewed. The various studies by the authors (unpublished work) have also been reported. All these findings bring out the excellent potential of EPDM as insulator in view of its ageing resistance, low-temperature flexibility, low erosion rate, and low specific gravity.Keywords: Solid rocket motors, insulation, ethylene-propylene diene rubber, ablation resistance, EPDM, case-bonded solid rocket motors
. INTRODUCTIONCertain elastomers find use as thermal insulators for case-bonded solid rocket motors (SRMs) 1 . Insulators, by forming the inner lining of rocket motors, prevent their exposure to the extremely high temperature gases of the propellant during combustion and help the integrity of motor without failure during operation. Selection of an insulation system for solid propellant motor applications involves considerations such as design function, material bonding, compounding and fabrication costs, fabrication techniques, storage, handling, environmental exposures, etc 2 .Apart from general requirements like superior thermal resistance etc, the insulator should be lightweight with low thermal conductivity and good mechanical properties. The insulation must remain intact and fully functional throughout propellant combustion and there should be no migration of its components to or from adjacent interfacial surfaces. It should also retain its elastomeric characteristics to avoid brittleness over operational temperature range for required duration of time to avoid catastrophic failure of the entire mission 3 .Nitrile rubbers, PDMS (polydimethyl siloxane), polyisoprene are few of the various elastomers used as insulators in solid rocket motors 4 . Nitrile/ rubber 5 -based insulation system is being currently used in Indian space programme. Skolnik 6 , et al. have reported the efforts made for replacement of nitrile-rubber based insulation by ethylene-propylene diene rubber (EPDM)-based non-asbestos insulation for Tomahawk booster motor.The technology for the manufacture of casebonded motors 7-8 and insulation laying of nitrile rubber has been well established. But nitrile rubberbased insulation suffers from the disadvantages such as limited shelf life, higher density, inferior low temperature properties etc. The evaluation of elastomers like EPDM 9-14 to replace nitrile rubber in Indian space and missile programme is in progress.
REVIEW PAPER309 310 DEF SCI J, VOL. 56, NO. 3, JULY 2006 The use of EPDM as an insulator for case-bonded solid rocket motors was evaluated more than a decade ago 15 and found feasible. Being a material with a low specific gravity 16,17 , EPDM has emerged as a novel material for manifold applications including insulation for solid rocket motors.The main attributes of EPDM rubber are its outstanding resistance to oxidation, ozonisation, and weathering effects. The most important properties from defence application point of...