Abstract: The melting tub for producing the molten mass from a mixture of raw material is associated with an additional melting unit by means of which a recycled molten mass is obtained from mineral wool waste largely corresponding to the molten mass obtained from the mixture of raw materials in quality and composition. The recycled molten mass is supplied to the molten mass in the melting tub through a suitable introduction device. The recycling exhaust gas from the additional melting unit is fed to the tub exhaust gas, and the mixture of exhaust gas is utilised for pre-heating combustion air and mixture of raw materials.

Abstract: A swivel chair of the type comprising a seat which is supported at an elevated position above a base for swiveling motion relative to the base, and which has a foot support disposed between the base and seat for aiding a user of the chair to ascend to the elevated seat, is provided with clamping elements that are responsive to foot pressure applied to the foot support for preventing swiveling motion of the seat relative to the base when such foot pressure in excess of a predetermined amount is applied. The clamping elements preferably comprise an inclined surface on a bracket that pivotally supports the foot support, and a wedge-shaped element that is disposed between the inclined surface and the pillar of the swivel chair for axial displacement in response to pivotal motion of the foot support resulting from the application of foot pressure thereto.