ramics.org/lAGS Glass Fiber-Reinforced Composit Forehearth Water spray WIlIIApplicat Traverse Direct-draw oppe Direct chopped strand forming. These parameters will be discussed in depth in S-glass fibers are available across the full range, but the following section, along with another important fac- finer filament diameters are favored for applications tor mentioned briefly earlier: sizing. Sizing, also known requiring the highest tensile strength as a binder or finish, is the chemistry applied to the Finer filaments- made in production into multi glass to give compatibility with the resin matrix in filament strands show higher strengths than their is critical to the performance of the finished com- comes a lower likelihood of failure-inducing law ri c it will be used. Like filament diameter and tex, coarser counterparts because with their lower volum ensure consistent sizing composition Ppl posite, so it is equally critical that glass fiber producers fibers, especially of high-performance, high-melt viscos ity formulations, are significantly more difficult to form for this same reason Solid inclusions, whether from the refractory that lines the furnace, from devitrified glass Filament diameter arising from a cool spot in the forehearth, from con- amination, or from an inhomogeneity in the batch, Filament diameter is set and monitored by winder can cause filament breakage that cascades across th ed or pull rate. It is also verified periodically by bushing. Larger filaments can tolerate lar microscopy. Filament diameter of continuous glass inclusions, thus making the forming process is some fibers typically ranges from 9 to 24 um, although it what more forgiving and easier can be as low as 3 um. For conventional E- or E-CR glass, as described in Table I, diameters are usually at 'This is not true for pristine fibers; as discussed in the previous artide, filament diameter the higher end of this range. High-performance R oes not affect pristine fber tensile strength.forming. These parameters will be discussed in depth in the following section, along with another important factor mentioned briefly earlier: sizing. Sizing, also known as a binder or finish, is the chemistry applied to the glass to give compatibility with the resin matrix in which it will be used. Like filament diameter and tex, sizing is critical to the performance of the finished composite, so it is equally critical that glass fiber producers ensure consistent sizing composition and application. Filament Diameter Filament diameter is set and monitored by winder speed or pull rate. It is also verified periodically by microscopy. Filament diameter of continuous glass fibers typically ranges from 9 to 24 µm, although it can be as low as 3 µm. For conventional E- or E-CRglass, as described in Table I, diameters are usually at the higher end of this range. High-performance R- or S-glass fibers are available across the full range, but finer filament diameters are favored for applications requiring the highest tensile strength. Finer filaments — made in production into multi- filament strands — show higher strengths than their coarser counterparts because with their lower volume comes a lower likelihood of failure-inducing flaw.§ Fine fibers, especially of high-performance, high-melt viscosity formulations, are significantly more difficult to form for this same reason. Solid inclusions, whether from the refractory that lines the furnace, from devitrified glass arising from a cool spot in the forehearth, from contamination, or from an inhomogeneity in the batch, can cause filament breakage that cascades across the entire bushing.3 Larger filaments can tolerate larger inclusions, thus making the forming process is somewhat more forgiving and easier. Fig. 4. Fiberglass forming process.2 § This is not true for pristine fibers; as discussed in the previous article, filament diameter does not affect pristine fiber tensile strength. www.ceramics.org/IJAGS Glass Fiber-Reinforced Composites 125