Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781118799499
Скачать книгу
0.5 106 K/s for a typical commercial fiber‐forming process. Stable drawing processes require adequate control of the fiber cooling rate, which is managed through a combination of process controls, including appropriate bushing design, cooling manifolds (commonly known as fin coolers), cooling air flow, and water spray. In addition, one optimizes the fiber drawing and cooling rates by tuning the oxidation state of iron (either from raw material impurities or intentionally added) in the glass, specifically the concentration of ferrous ion (Fe2+).

      The oxidation–reduction of iron in the melt is affected by glass chemistry and oxygen partial pressure ([16, 17], Chapter 5.6)

      (3)equation

      and by the presence of other multivalent species either from additives or impurities,

      (4)equation

      In general, drawing processes for making finer or smaller diameter fibers (and typically smaller bushings also) require glasses with a relatively lower concentration of Fe2+ (hence, slower cooling rate) than coarse fibers made from larger bushings (hence, higher cooling rate). The control of the iron oxidation state (or ferrous ion concentration in glass) is directly related to the amount of fining agent in the batch and the total iron in the batch, both of which are adjustable variables to maintain process stability. The ferrous ion concentration in glass is routinely monitored in production with a colorimetric method through acid digestion of a glass powder sample or with a calibrated UV‐VIS spectroscopic method on an optically polished glass disk.

      In commercial production, glass fibers are drawn at a temperature TF where melt viscosity is near 100 Pa∙s (Figure 4). Stable melt viscosity at the tip plate is critical for an efficient fiber‐forming process. If melt viscosity at the tip plate is too low (i.e. too high temperature at the tip plate), spreading of the glass melt across multiple tips on the tip plate results in flooding and disruption. If melt viscosity is too high (i.e. too low temperature at the tip plate), fiber drawing tension increases and the stable forming cone at the tip exit begins to fail, causing fiber breakage [3]. In addition, the actual forming temperature must be greater than the glass liquidus temperature, Tliq, by at least 50 oC to reduce the risk of devitrification. Microcrystals formed in colder spots along a primary canal or forehearth (Figure 2a), no matter how small, can lead to significant fiber breakage in the drawing process and hence, adversely impact productivity.

      In making commercial glass fiber products for reinforcements, various processes are used to provide the desired end form. Direct draw or single end winding, direct chopped fibers, and numerous downstream secondary processes may be employed. Depending on the product needs, the types of bushings vary in dimension, number of tips, and tip diameters. In addition to the glass and process elements necessary to produce commercial glass fibers, the surface of the fiber must be treated to provide optimum compatibility of the inorganic glass fiber with the organic resins used in the reinforcements industry. This leads naturally into a discussion on the role of sizing chemistry.

      3.4 The Role of Sizing/Binder in Glass Fiber Products

      The long history of growth in both volume and breadth of glass‐fiber commercial successes has been driven by unique combinations of strength, stiffness, weight, and cost attributes that can be achieved through glass chemistry. However, to realize fully the value of the glass fiber in a reinforced composite, a means must be provided to facilitate the effective interactions between the inorganic fiber and the organic polymer that together make up a reinforced composite material. One maximizes this interaction by designing an interface that synergistically combines the material properties of each element. A design that provides for effective load transfer between the constituents transforms an inherently heterogeneous material into one that behaves as a homogeneous structure.

Classification Functionality
Coupling agents Adhesion promoters that bond or couple the glass surface with specific matrix resin systems; may also provide excellent filament protection and increased dry breaking strength.
Film formers Hold filaments together and provide protection to the fiberglass strand.
Film modifiers Modify the film formation to increase strength, flexibility, and tackiness.
External lubricants Provide resistance to abrasion damage at external contact points such as strand guides in downstream processes.
Internal lubricants Reduce the filament‐to‐filament abrasion within the fiberglass strand.
Emulsifiers/Surfactants Form stable suspensions or emulsions of immiscible ingredients, generally in water‐based systems.
Other process aids May be used as required to control foam, wetting, static behavior, biological activity, and any other special requirements by a particular end‐use or internal processing need.