HISTORY OF OZONE CRACKING IN BUNA-S RUBBER WING II INTERNAL INSULATION - WEAPON SYSTEM 133A,

In the normal assembly sequence of Rocket Motor M-57E1, Spiralloy cas wound upon a Buna-S rubber internal insulator. In October 1962, the internal insulators of several motors were found to contain surface cracks. Two inspec tion programs were initiated to examine each case and categorize the magnitude of cracking. About 46 of the cases examined were cracked to depths ranging to a maximum of 0.060 in. Analysis of these results showed that the cracks occurred in areas of residual rubber stress and were a form of deterioration caused by normal exposure of the insulator to the atmosphere over a period of time. Effects of ozone cracking were then evaluated. Case bond strength was determined in one series of tests. In another test series, erosion rates of ozone cracked specimens were compared to that of control samples in test firings of hundred-pound-charge motors. Results of these tests indicated that ozone cracking has no effect on case bond strength or erosion rate of the Buna-S rubber internal insulators. Author