dove tail the second main resting surface 7 is also arranged above the melt surface 2 in contrast the secondary resting surface 8 is arranged below the melt surface 2 the melt 1 can enter the secondary resting surface 8 and reduces thereby the durability of the secondary resting surface 8 with respect to the main resting surface 7 the secondary resting surface 8 is thus in contrast to the main resting surface 7 not in the position to maintain the operability over an extended period in time it is of course also possible to omit a support function or a guiding function for example by a corresponding arrangement of the centre of mass of the element 3 which is exchangeable during the melting operation because the melt 1 presses the element 3 which is exchangeable during the melt operation towards the outside towards the carrier element 4 due to the partial pressure of the melt 1 within the invention also lie for example a rotational or increasing or descending movement of the elements 3 which are exchangeable during the melting operation by which the elements 3 which are exchangeable during the melting operation are only for a certain amount of time in the area of the melting surface 2 as well as below and above the melt surface 2 in this way the main guidance 5 and or the main support surface 7 can also be arranged at least partially below of the melt surface.