Abstract: Vertical, parallel palisades (3) are distributed around the perimeter of a circle, spaced apart by gaps, surrounding the melt. An annular plate (4) supports the palisades (3), the palisades being provided with cavities through which a coolant flows. An induction coil (20) surrounds the palisades (3) on the outside, an alternating current flowing through the coil. The plate (4) is provided with support surfaces (4a, 4b), equal in number to the number of palisades (3), their shape conforming to the base surfaces of the palisades (3). Seen in the circumferential direction, every second support surface (4a) is covered by an electrically insulating film (7). All of the palisades (3) together are surrounded by a ring (18) of electrically insulating material, which holds the palisades (3) on the plate (4).