Abstract: A process of using a thermally insulating board, made of a homogeneous mixture of expanded perlite particles and cellulosic and/or mineral and/or ceramic fibers, bonded together, comprising placing on the surface of a molten steel mass, in direct contact with the surface, so as to cover substantially all the surface. According to a preferred embodiment, the board consists of 51 to 80% by weight of expanded perlite particles, 15 to 39% by weight of cellulosic and/or mineral fibers and 5 to 10% by weight of binder.

Abstract: The ingot mould comprises a hot-top positioned inside the upper part of the mould and comprising an inner wall formed by at least one plate of a material capable of withstanding contact with a molten metal poured into the ingot mould, without being melted or fused. The thickness of the inner wall is less than that of the wall of the mould, at least one recess is provided inside the upper part of the mould wall and the inner wall of the hot-top is placed in the recess, with its surface essentially flush and aligned with the inner surface of the mould, so as to form a closure wall separating the interior of the recess from the interior of the mould.