Methods and apparatus for producing mineral fibers such as glass fibers generally include a first step of melting mineral material in a large gas-fired and electrically heated tank. Smaller melters having dual heating elements are also used and generally include a cold top batch blanket. Electric melters having cold top batch blankets generally have a short life due to thermal stress and consumption of electrodes by corrosive elements of the molten mineral bath.
The manufacture of mineral fibers by a rotary fiberizing method is well known as exemplified by the disclosure of U.S. Pat. No. 4,511,383 to Bhatti.
It has been proposed to manufacture fibers with gaseous occlusions in several prior art patents. For example, U.S Pat. No. 4,526,597 to Olinger et al, a method and apparatus for forming fibers, including a rotary spinner having a porous member positioned adjacent fiber forming ports is disclosed. Gas is supplied under pressure during the fiber forming operation to cause the introduction of gas into the molten mineral material. One of the stated purposes of this method is to provide means for adding a last minute chemical additive treatment or to control the turbulent fiberizing environment. Another stated purpose is to permit the manufacture of hollow or partially hollow fibers thereby enabling weight reduction and potentially improving the thermal resistance of insulation products. The proposal disclosed in Olinger required costly modifications of the fiberizing spinner.
When stir-melting was initially developed, it was with a view to manufacturing quality glass having a minimum number of gaseous occlusions and seeds. In fact, considerable developments were directed to elimination of gaseous occlusions and seeds as disclosed in U.S. Pat. No. 3,951,635 to Rough. In that patent, it was proposed to use a centrifuge to eliminate seeds and gaseous occlusions in the molten mineral material. Seeds are considered to be undesirable in the prior glass processing techniques because they reduce optical clarity.
It has long been an object in the mineral fiberizing field to provide a rapid and flexible method of producing molten glass fibers. Rapid glass melting can result in considerable energy savings. Large, static glass tanks used in fiberglass production are generally maintained at elevated temperatures continuously due to the long period of time required for melting glass batch. In addition, repeated heating and cooling of glass melters creates stress and wear, which reduce the effective life of the equipment.