. "2 Manufacturing Processes, Chemical Composition, and Classification." Review of the U.S. Navy's Exposure Standard for Manufactured Vitreous Fibers. Washington, DC: The National Academies Press, 2000.
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Review of the U.S. Navy's Exposure Standard for Manufactured Vitreous Fibers
personnel but do not apply to Navy contractors, which are regulated by the Occupational Safety and Health Administration or applicable state regulatory agencies.
The Navy does present an overview of the chemical composition of the fiber classes. Table 2-1 shows the chemical composition of various classes of fibers, expressed as percentages. From Table 2-1, it is evident that all MVF contain silica (SiO2), but they vary widely in their other components, both between and within classes of fibers. It should be noted that although the Navy refers briefly to the use of special purpose fibers, it does not include any information on their composition or sizes or on what distinguishes them from other MVF. The manufacturing processes for and composition of each fiber type are discussed below.
The primary ingredient in glass fibers is naturally occurring silicon dioxide; it also contains small amounts of other minerals. Permutations are made by adding other substances, such as oxides of aluminum, titanium, and zinc as stabilizers and oxides of magnesium, lithium, barium, calcium, sodium, and potassium as modifiers. By varying the amounts and types of stabilizers and modifiers, one can alter the physical properties of glass fibers. Stabilizers contribute to chemical durability; the intended use determines the amount of stabilizer added.
Glass fibers are produced by mixing and melting the raw materials in high temperature furnaces and then processing them with various methods that depend on the end product. A continuous filament process is used for textile fibers, a rotary spray process for glass wool, and a flame attenuation process for making special purpose glass fibers.
In the manufacture of textile fibers, molten glass is continuously drawn from the melting pot through bushings. This process allows for little variation in the preset average fiber diameter, which typically ranges from 3 to 25 µm. These continuous glass filaments are used in various applications, including textiles, and as reinforcements for plastic composites, such as boat hulls and automobile body parts.
Glass wool is manufactured with a rotary process that consists of pouring the molten glass through a spinner that fiberizes the glass into discontinuous fibers. Fiber diameters vary widely: some are as small as