During the mechanical cycles, the packing temperature was subjected to {HEAD ~ varying thermal cycles} repetitively between {TAIL ~ the ambient temperature} and 450° F.  
between
During the mechanical cycles , the packing temperature was subjected to { HEAD ~ varying thermal cycles } repetitively between { TAIL ~ the ambient temperature } and 450 ° F.
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH