Abstract: A method and apparatus for melting low-cost raw materials such as blast furnace slag, basalt, feldspar or electrophos slag in the formation of high temperature mineral wool insulation. The low-cost mineral stock material is fed in particulate form continuously to a preheater in which it is elevated to a temperature range of between 1500.degree. F. and 2000.degree. F. by forcing hot combustion gases through a vertical column of the particulate stock material. Volatiles such as water and carbon dioxide are thus removed from the stock material. The preheated stock material is distributed to the top of an electric melting furnace which is essentially sealed from atmosphere. A substantially homogenous, low viscosity liquid glass melt is continuously discharged from the furnace.

Abstract: A melting furnace for the production of mineral wool insulation in the nature of a receptacle closed by a cover or crown through which spaced carbon electrodes extend from an external support and also through which particulate stock material is introduced over a substantial area of a melt contained in the receptacle. The receptacle of the furnace is defined by a substantially sealed external shell having an inner lining of carbon brick covering the floor and extending upwardly on the sidewalls thereof to an upper limit or edge defined by the plane of the top surface of liquid melt maintained in the furnace. An outer lining of carbon paste is sandwiched between the inner brick lining and the outer sealed shell. The inner lining is capped with a ring of refractory and a water cooling conduit is embedded in the outer lining at the plane of the liquid level to develop a fused or solidified glass lining only at the juncture of the refractory ring and the inner lining of carbon brick.