PROCESSING OF FIBERGLASS
In typical fiberglass insulation production the reaction and melting of the batch raw materials are carried out at 1400 °C to 1500 °C either in a gas-fired furnace or a submerged-electrode “cold-top” furnace. The batch ingredients, ground minerals such as silica sand, limestone, soda-ash, borax, and, increasingly, crushed post-consumer bottle and plate glass, are weighed, premixed, and fed into the furnace by a belt conveyor or a screw-feeder (see Fig. 2). Firing arrangements in the furnace coupled with stirring using bubblers and appropriate dwell times create a homogenous melt which is cooled to close to the working temperature in a fore hearth channel before being drawn off as a glass stream. The primary division of this glass stream occurs while it is at a viscosity of about 1000 poise; the glass flows through several thousand holes in the vertical wall of a rotating bowl called a spinner (see inset in Fig. 2). The thousands of coarse primary fibers so produced are immediately attenuated further to the desired fineness by an annular external burner and/or a high-velocity turbulent gas stream which surrounds the spinner; typical final nominal fiber diameters range from 4 μm to 15 μm. A furnace may supply glass to as many as 10 spinners, with the throughput of each spinner being 450 Kgh−1 or more. The spinners operate at temperatures as high as 1050 °C and have to withstand hoop stresses of about 27 MPa with minimal distortion or creep in a severely corrosive environment.
The fibers produced by the above process are sometimes used as-made but are more commonly bonded together en masse by being sprayed with a water-based resin binder, typically phenol–formaldehyde (PF) based, which is subsequently dried and cured in an oven to give coherence to the fibrous material to allow for handleability. Continuous slitting and high-speed guillotining cuts the moving pack into appropriate dimensions for in-line compression packaging as rolls or batts. The importance of compression packaging, for economy in storing and shipping, may be appreciated when it is realized that approximately 98% of the volume of a typical uncompressed insulation batt is air space.
A specialty fibrous wool product of some technical significance, which is used for aircraft insulation and filtration, is produced by a flame-blowing technique. For this, marbles that have been produced by a furnace melting system similar to that described earlier are remelted in a platinum bushing and drawn into coarse filaments about 1 mm in diameter which are fed into a horizontally directed, high-energy gas burner. The extremely fine fibers produced in the turbulent gas jet are collected on a sloping conveyor.
Mar 09, 2021