A slag conditioner containing MgO, carbon or a filler and a binder is mixed and formed under pressure to produce aggregates which can have the form of a briquette. A heat pipe that has been extrusion-sealed includes a circular tubular body with two free ends connected to conical shrunk tubular portions. The cord includes a first and a second wire, inner ends of which are extended into the hollow tubular body below the inner annular section.