After the joints on one side of {TAIL ~ the board} pass through {HEAD ~ the hot gas}, the board 13 is flipped over and the steps of FIGS 7 and 8 are repeated 
After the joints on one side of { TAIL ~ the board } pass through { HEAD ~ the hot gas } , the board 13 is flipped over and the steps of FIGS 7 and 8 are repeated
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH