According to {HEAD ~ a first, preferred embodiment} of the invention, shown in FIGS 1 and 2 and also partially illustrated by FIG 6, the contact member or members 111, 111′; 411, 411′ is/are arranged for being in physical contact with the shell surface 103; 403 during the heating and for maintaining the third distance 112; 412 substantially constant along the shell surface 103; 403 in the direction of the shell axis 102; 402 in {TAIL ~ cooperation} with the suspension attachment 107; 407 
According to { HEAD ~ a first , preferred embodiment } of the invention , shown in FIGS 1 and 2 and also partially illustrated by FIG 6 , the contact member or members 111 , 111′ ; 411 , 411′ is / are arranged for being in physical contact with the shell surface 103 ; 403 during the heating and for maintaining the third distance 112 ; 412 substantially constant along the shell surface 103 ; 403 in the direction of the shell axis 102 ; 402 in { TAIL ~ cooperation } with the suspension attachment 107 ; 407
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