According to 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 {HEAD ~ cooperation} with {TAIL ~ the suspension attachment} 107; 407 
According to 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 { HEAD ~ cooperation } with { TAIL ~ the suspension attachment } 107 ; 407
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