Bushing
- 1. Glass Fibers Frederick T. Wallenberger, James C. Watson, and Hong Li, PPG Industries, Inc. GLASS FIBERS are among the most versatile highlighted wherever appropriate but not dis- sion of compositions, melt properties, fiber prop- industrial materials known today. They are read- cussed in full. Additional details about fiber erties (Ref 12), methods of manufacture, and sig- ily produced from raw materials, which are forming are provided in the section “Glass Melt- nificant product types. An in-depth discussion of available in virtually unlimited supply (Ref 1). ing and Fiber Forming” in this article. composite applications can be found in other ar- All glass fibers described in this article are de- Sizes and Binders. Glass filaments are highly ticles in this Volume. rived from compositions containing silica. They abrasive to each other (Ref 4). ’Size’ coatings or Glass fibers and fabrics are used in ever in- exhibit useful bulk properties such as hardness, binders are therefore applied before the strand is creasing varieties for a wide range of applica- transparency, resistance to chemical attack, sta- gathered to minimize degradation of filament tions (Ref 13). A data book is available (Ref 14) bility, and inertness, as well as desirable fiber strength that would otherwise be caused by fil- that covers all commercially available E-glass fi- properties such as strength, flexibility, and stiff- ament-to-filament abrasion. Binders provide lu- bers, whether employed for reinforcement, filtra- ness (Ref 2). Glass fibers are used in the manu- brication, protection, and/or coupling. The size tion, insulation, or other applications. It lists all facture of structural composites, printed circuit may be temporary, as in the form of a starch-oil manufacturers, their sales offices, agents, subsid- boards and a wide range of special-purpose prod- emulsion that is subsequently removed by heat- iaries, and affiliates, complete with addresses, ucts (Ref 3). ing and replaced with a glass-to-resin coupling and telephone and fax numbers. And it tabulates Fiber Forming Processes. Glass melts are agent known as a finish. On the other hand, the key properties and relevant supply details of all made by fusing (co-melting) silica with miner- size may be a compatible treatment that performs E-glass fiber grades, that are available in the als, which contain the oxides needed to form a several necessary functions during the subse- market today. given composition. The molten mass is rapidly quent forming operation and which, during im- Special-Purpose Glass Fibers. S-glass, D- cooled to prevent crystallization and formed into pregnation, acts as a coupling agent to the resin glass, A-glass, ECR-glass, ultrapure silica fibers, glass fibers by a process also known as fiberi- being reinforced. hollow fibers, and trilobal fibers are special-pur- zation. pose glass fibers. Selected special-purpose glass Nearly all continuous glass fibers are made by fibers are discussed in the subsequent section of a direct draw process and formed by extruding Glass Fiber Types this article. That section reviews compositions, molten glass through a platinum alloy bushing manufacture, properties, and applications to an that may contain up to several thousand individ- extent commensurate with their commercial use Glass fibers fall into two categories, low-cost ual orifices, each being 0.793 to 3.175 mm (Ref 15). general-purpose fibers and premium special-pur- (0.0312 to 0.125 in.) in diameter (Ref 1). While A companion data book (Ref 16) is available pose fibers. Over 90% of all glass fibers are gen- still highly viscous, the resulting fibers are rap- that covers all commercially available high- eral-purpose products. These fibers are known idly drawn to a fine diameter and solidify. Typ- strength glass fibers including S-glass and, all by the designation E-glass and are subject to ical fiber diameters range from 3 to 20 lm (118 silica or quartz glass fibers, including Astro- ASTM specifications (Ref 5). The remaining to 787 lin.). Individual filaments are combined quartz and Quartzel. It also lists a wide range of glass fibers are premium special-purpose prod- into multifilament strands, which are pulled by woven fabrics, that are commercially available ucts. Many, like E-glass, have letter designations mechanical winders at velocities of up to 61 m/ in the market of today, ranging from S-glass/ar- implying special properties (Ref 6). Some have s (200 ft/s) and wound onto tubes or forming amid, S-glass/carbon, silica/aramid, and silica/ tradenames, but not all are subject to ASTM packages. This is the only process that is de- carbon yarns to silica/boron yarns. In addition, specifications. Specifically: scribed in detail subsequently in the present ar- it covers all commercially available carbon, ce- ticle. ramic, boron, and high-temperature polymer fi- The marble melt process can be used to form Letter designation Property or characteristic bers and yarns. This data book also lists all yarn special-purpose, for example, high-strength fi- E, electrical Low electrical conductivity counts, fabric constructions, fabric weights, and bers. In this process, the raw materials are S, strength High strength commercial sources. C, chemical High chemical durability melted, and solid glass marbles, usually 2 to 3 M, modulus High stiffness ASTM Test Methods. ASTM has published cm (0.8 to 1.2 in.) in diameter, are formed from A, alkali High alkali or soda lime glass standard test methods for glass density (Ref 17), the melt. The marbles are remelted (at the same D, dielectric Low dielectric constant alternating current loss characteristics and di- or at a different location) and formed into glass electric constant (Ref 18), direct current conduc- fibers. Glass fibers can also be down drawn from tance of insulating materials (Ref 19), dielectric the surface of solid preforms. Although this is Table 1 gives compositions and Table 2 gives breakdown voltage and dielectric strength (Ref the only process used for manufacturing optical physical and mechanical properties of commer- 20), softening point of glass (Ref 21), annealing fibers, which are not discussed in this Volume, it cial glass fibers. point and strain point of glass by fiber elongation is a specialty process for manufacturing struc- General-purpose glass fibers (E-glass vari- (Ref 22), annealing point and strain point of tural glass fibers such as silica or quartz glass ants) are discussed in the following section of glass by beam bending (Ref 23), viscosity (Ref fibers. These and other specialty processes are this article, which provides an in-depth discus- 24), liquidus temperature (Ref 25), and coeffi-
- 2. 2 / Constituent Materials Table 1 Compositions of commercial glass fibers Composition, wt% Fiber Ref SiO2 B2O3 Al2O3 CaO MgO ZnO TiO2 Zr2O3 Na2O K2O Li2O Fe2O3 F2 General-purpose fibers Boron-containing E-glass 1, 2 52–56 4–6 12–15 21–23 0.4–4 ... 0.2–0.5 ... 0–1 Trace ... 0.2–0.4 0.2–0.7 Boron-free E-glass 7 59.0 ... 12.1 22.6 3.4 ... 1.5 ... 0.9 ... ... 0.2 ... 8 60.1 ... 13.2 22.1 3.0 ... 0.5 ... 0.6 0.2 ... 0.2 0.1 Special-purpose fibers ECR-glass 1, 2 58.2 ... 11.6 21.7 2.0 2.9 2.5 ... 1.0 0.2 ... 0.1 Trace D-glass 1, 2 74.5 22.0 0.3 0.5 ... ... ... ... 1.0 Ͻ1.3 ... ... ... 2 55.7 26.5 13.7 2.8 1.0 ... ... ... 0.1 0.1 0.1 ... ... S-, R-, and Te-glass 1, 2 60–65.5 ... 23–25 0–9 6–11 ... ... 0–1 0–0.1 ... ... 0–0.1 ... Silica/quartz 1, 2 99.9999 ... ... ... ... ... ... ... ... ... ... ... ... cient of linear thermal expansion of plastics (Ref to eliminate boron from the off-gases of boron- ASTM standards for E-glass (Ref 5) cover all 26). containing melts. Alternatively, the use of envi- three commercial E-glass variants, distinguish- Some fiber properties (Ref 4), such as tensile ronmentally friendly boron-free E-glass is re- ing E-glasses by end use. Compositions contain- strength, modulus, and chemical durability, are quired. These melts do not contain, and therefore ing 5 to 10 wt% by weight of boron oxide are measured on the fibers directly. Other proper- do not emit, boron into the environment during certified for printed circuit board and aerospace ties, such as relative permittivity, dissipation processing. As a result, a boron-free E-glass applications. Compositions containing 0 to 10 factor, dielectric strength, volume/surface resis- product was recently introduced into the market wt% by weight of boron oxide are certified for tivities, and thermal expansion, are measured on by Fiberglas (Owens Corning Corp., Toledo, general applications. According to these stan- glass that has been formed into a bulk patty or OH) under the trademark Advantex. dards, E-glass compositions for either type of ap- block sample and annealed (heat treated) to re- Commercial boron-containing E-glass comes plication may also contain 0 to 2 wt% alkali ox- lieve forming stresses. Properties such as den- in two variants. One commercial variant is de- ide and 0 to 1 wt% fluoride. The more recent sity and refractive index are measured on both rived from the quaternary SiO2-Al2O3-CaO- boron-free E-glass variants may also be fluorine- fibers and bulk samples, in annealed or unan- MgO (Ref 2, 4, 6, 27), and the other is derived free. nealed form. from the ternary Oxide Compositions. E-glasses of any type SiO2-Al2O3-CaO phase diagram (Ref 2, 4, 6, are general-purpose fibers because they offer 28). Commercial E-glasses in the ternary SiO2- useful strength at low cost. Table 1 presents the General-Purpose Glass Fibers Al2O3-CaO system contain a small amount oxide components and their ranges for the two (Ͻ0.6 wt%) of MgO that is not deliberately types of E-glass fibers that are currently being Types. Two generic types of E-glass (Ref 6) added but obtained as by-product (or tramp) produced and used in composites. A range is are known in the market today. The incumbent from other ingredients. On the other hand, com- given for each with regard to its oxide compo- E-glass contains 5 to 6 wt% of boron oxide. mercially available boron-free E-glass is derived nents because each manufacturer, and even dif- Stringent environmental regulations require the from the quaternary SiO2-Al2O3-CaO-MgO ferent manufacturing plants of the same com- addition of costly emission abatement systems phase diagram (Ref 2, 7, 8, 29). pany, may use slightly different compositions for Table 2 Physical and mechanical properties of commercial glass fibers Annealing Straining Log 3 forming temperature(a) Liquidus temperature Softening temperature temperature temperature Bulk density, Fiber ЊC ЊF ЊC ЊF ЊC ЊF ЊC ЊF ЊC ЊF annealed glass, g/cm3 General-purpose fibers Boron-containing E-glass 1160–1196 2120–2185 1065–1077 1950–1970 830–860 1525–1580 657 1215 616 1140 2.54–2.55 Boron-free E-glass 1260 2300 1200 2190 916 1680 736 1355 691 1275 2.62 Special-purpose fibers ECR-glass 1213 2215 1159 2120 880 1615 728 1342 691 1275 2.66–2.68 D-glass ... ... ... ... 770 1420 ... ... 475 885 2.16 S-glass 1565 2850 1500 2730 1056 1935 ... ... 760 1400 2.48–2.49 Silica/quartz Ͼ2300 Ͼ4170 1670 3038 ... ... ... ... ... ... 2.15 Dielectric Volume Coefficient constant resistivity Weight of linear Specific at room Dielectric at room Refractive loss in 24 h Tensile strength Filament expansion, heat, temperature strength, temperature index in 10% at 23 ЊC (73 ЊF) Young’s modulus elongation Fiber 10–6/ЊC cal/g/ЊC and 1 MHz kV/cm log10 (X cm) (bulk) H2SO4, % MPa ksi GPa 6 10 psi at break, % General-purpose fibers Boron-containing E-glass 4.9–6.0 0.192 5.86–6.6 103 22.7–28.6 1.547 ϳ41 3100–3800 450–551 76–78 11.0–11.3 4.5–4.9 Boron-free E-glass 6.0 ... 7.0 102 28.1 1.560 ϳ6 3100–3800 450–551 80–81 11.6–11.7 4.6 Special-purpose fibers ECR-glass 5.9 ... ... ... ... 1.576 5 3100–3800 450–551 80–81 11.6–11.7 4.5–4.9 D-glass 3.1 0.175 3.56–3.62 ... ... 1.47 ... 2410 349 ... ... ... S-glass 2.9 0.176 4.53–4.6 130 ... 1.523 ... 4380–4590 635–666 88–91 12.8–13.2 5.4–5.8 Silica/quartz 0.54 ... 3.78 ... ... 1.4585 ... 3400 493 69 10.0 5 (a) The log 3 forming temperature is the temperature of a melt at a reference viscosity of 100 Pa • s (1000 P). Source: Ref 2, 7–10, 11
- 3. Glass Fibers / 3 the same glass. These variations result mainly and boron-containing E-glasses. Elastic modulus acid resistance and short-term alkali resistance from differences in the available glass batch (raw (or fiber stiffness) of boron-free E-glasses is (Ref 27). materials). Tight control is maintained within a about 5% higher than that of boron-containing The addition of high levels of ZnO and TiO2 given production facility to optimize composi- E-glasses, while pristine, virgin, or single-fila- to the boron-free quaternary E-glass system fur- tional consistency and maximize production ef- ment tensile strength is said to be about the same ther enhances the corrosion resistance of the re- ficiencies. for both types of E-glasses when both are tested sulting ECR glass fibers while at the same time As shown in Table 1, commercial, boron-con- at room temperature (Ref 8, 9). reducing the log 3 forming temperature. The taining E-glass compositions (Ref 1, 2, 4, 6, 12, Physical Properties. In addition, Table 2 product and process advantage are obtained at a 24) differ substantially from boron-free E-glass compares the physical properties of the boron- cost penalty. About 2% ZnO and two additional compositions. The silica content for commercial free and boron-containing E-glasses. Most im- percent TiO2 are required, and both materials are boron-containing E-glasses ranges from 52 to 56 portantly, the corrosion resistance of boron-free known to be costly batch ingredients. wt% by weight, and for commercial boron-free E-glasses was found to be seven times higher S-Glass, R-Glass, and Te-Glass. The tensile E-glasses from 59 to 61 wt%. The alumina con- than that of boron-containing E-glasses when strength of glass fibers is determined by the tent generally ranges from 12 to 15 wt% for these tested at room temperature for 24 h in 10% sul- structure connectivity of the silicate network, no- boron-containing E-glasses and from 12 to 13.5 furic acid. It approaches that of ECR glass fibers tably, by the absence of alkali oxides, which are wt% for these boron-free E-glasses. The calcia (Ref 9, 10). not readily integrated into the structure. The content ranges from 21 to 23 wt% for these com- Boron-free E-glasses have a slightly higher structure of boron oxide, though being a part of mercial boron-containing E-glasses and from 22 density (2.62 g/cm3) than boron-containing E- the network, is weaker than that of silicon oxide, to 23 wt% for these boron-free E-glasses. glasses (2.55 g/cm3), but the density of both fi- and therefore, boron oxide serves as a flux. Sev- For commercial, boron-containing, ternary or bers is lower than that of ECR glass (2.66 to 2.68 eral high-strength glass fibers are known, includ- quaternary E-glasses, the magnesia content g/cm3), a corrosion-resistant special-purpose fi- ing S-glass, Te-glass, and R-glass (Ref 2). All ranges from 0.4 wt% (tramp only) to greater ber. Boron-free E-glasses have a higher refrac- offer 10 to 15% higher strength than E-glass at amounts if magnesia (dolomite) is deliberately tive index and linear expansion coefficient than room temperature, but their real value is their added. For commercial boron-free E-glasses, it boron-containing E-glass fibers. The refractive ability to withstand higher in-use temperatures ranges from 3.1 to 3.4 wt% (see Table 1). The index of both E-glasses is lower than that of ECR than E-glass. These fibers are used in military boron oxide content ranges from 5 to 6% for glass. The linear expansion coefficient of ECR applications. Stringent quality-control proce- commercial boron-containing E-glasses, and it is glass fibers is midway between that of the two dures are necessary to meet military specifica- zero for boron-free E-glasses. The titania content E-glasses. tions. ranges from 0.4 to 0.6 wt% for commercial bo- Boron-free E-glasses have a slightly higher di- S-glass and Te-glass are derivatives of the ter- ron-containing E-glasses. For boron-free E- electric constant (7.0) than boron-containing E- nary SiO2-Al2O3-CaO system. R-glass is a de- glasses, it ranges from 0.5 wt% (Ref 8) to 1.5 glasses (5.9 to 6.6) when measured at room tem- rivative of the quaternary SiO2-Al2O3-CaO- wt% (Ref 7) (see also Table 1). perature and at a frequency of 1 MHz. As a MgO system. S-glass and S-2 glass fibers, a Environmentally friendly E-glass melts are result, boron-containing, but not boron-free, E- product variant, have the same glass composition boron-free and fluorine-free. However, the log 3 glass fibers are needed for electronic circuit (Ref 2) but different coatings. While internal fiber forming or fiberization temperature (TF) of boards and aerospace applications. On the other structural uniformity (high strength) is achieved boron-free E-glass melts may be as much as 100 hand, boron-free and boron-containing E-glass with these boron-free and alkali-free composi- to 110 ЊC (180 to 200 ЊF) higher than that of fibers are used in structural composites where the tions, their forming temperatures are higher than boron-containing E-glass melts (Fig. 1). The log dielectric constant is of no concern. Composite that of E-glass. Attainment of high in-use tem- 3 forming temperature is the temperature of a and laminate uses of all glass fibers are discussed peratures is a definite product advantage, but melt at a reference viscosity of 100 Pa • s (1000 in other articles in this Volume. P). In addition, the softening point of boron-free E-glass is 60 to 90 ЊC (110 to 160 ЊF) higher also Temperature, °F than that of a boron-containing E-glass. The Special-Purpose Glass Fibers higher process temperature requires more pro- 5.5 1800 2000 2200 2400 2600 cess energy, but the higher softening point fa- Types. Special-purpose fibers, which are of cilitates higher use temperatures. commercial significance in the market today, in- Melt Properties. According to Table 2, the clude glass fibers with high corrosion resistance 5.0 log 3 forming temperature, TF, of boron-contain- (ECR-glass), high strength (S-, R-, and Te- ing E-glasses ranges from 1140 to 1185 ЊC (2085 glass), with low dielectric constants (D-glass), 4.5 Boron-free E-glass to 2165 ЊF). The liquidus temperature (TL) is the high strength fibers, and pure silica or quartz fi- temperature below which solid (crystals) will bers, which can be used at ultrahigh tempera- Viscosity, log poise 4.0 form. It ranges form 1050 to 1064 ЊC (1920 to tures. These fibers will be discussed in the fol- 1945 ЊF). The difference between forming and lowing paragraphs. Others special-purpose fibers 3.5 liquidus temperature (DT) ranges from 81 to 90 include A-glass, C-glass, hollow fibers, bicom- ЊC (146 to 162 ЊF). In contrast, the log 3 fiber ponent fibers, and trilobal fibers. These special- forming temperature of boron-free E-glasses purpose glass fibers have recently been reviewed 3.0 ranges from 1250 to 1264 ЊC (2280 to 2307 ЊF), in detail (Ref 2). the liquidus temperature from 1146 to 1180 ЊC ECR-Glass. The corrosion resistance of glass 2.5 (2095 to 2155 ЊF), and the difference between fibers is determined by their chemical structure. forming and liquidus temperature (DT) from 86 It has already been noted in the preceding sec- 2.0 Boron-containing E-glass to 104 ЊC (155 to 187 ЊF) (Ref 7–10). Finally, tion on general-purpose glass fibers that boron- the softening point of boron-containing E- free E-glass fibers derived from the quaternary 1.5 glasses ranges from 830 to 860 ЊC (1525 to 1580 SiO2-Al2O3-CaO-MgO phase diagram have 900 1000 1100 1200 1300 1400 1500 ЊF); that of boron-free E-glasses is about 916 ЊC higher acid resistance than E-glass fibers that Temperature, °C (1680 ЊF). are derived from the ternary SiO2-Al2O3-CaO Mechanical Properties. Table 2 also com- phase diagram but have high boron levels. The Fig. 1 Viscosity of boron-free and boron-containing E- pares the mechanical properties of the boron-free ECR glass fibers offer enhanced long-term glass
- 4. 4 / Constituent Materials higher melt temperatures, more process energy, high-temperature fibers have lower dielectric glass, ultrapure silica fibers, and D-glass (see and more costly bushing alloys are required. constants than solid E-glass. They, too, can and Ref 2). Silica/Quartz Fibers. Glass fibers with in- are being used to reinforce printed circuit board Batch Mixing and Melting. The glass melt- creasing SiO2 levels can be used in applications (PCB) laminates. However, silica fibers have a ing process begins with the weighing and blend- requiring increasingly high in-use temperatures. low modulus and are, therefore, less effective as ing of selected raw materials. In modern fiber- High-silica fibers (95% SiO2) are amorphous reinforcing fibers. Hollow fibers, although ini- glass plants, this process is highly automated, glass fibers. They are obtained by acid leaching tially effective because of their low dielectric with computerized weighing units and enclosed of borosilicate E-glass fabrics, which are, in turn, constant, lose their dielectric properties if mois- material transport systems. The individual com- used as insulation blankets at temperatures up to ture can seep into the laminate structure. ponents are weighed and delivered to a blending 1040 ЊC (1900 ЊF). Pure silica fibers (99% SiO2) station where the batch ingredients are thor- are made by dry spinning from aqueous water- oughly mixed before being transported to the glass solutions. They are known by the traden- Glass Melting and Fiber Forming furnace. ame “Silfa” and mostly are used as yarns, for Fiberglass furnaces generally are divided into example, for wire insulation at temperatures up A glass is an amorphous solid obtained by three distinct sections (Fig. 2). Batch is delivered to 1090 ЊC (1990 ЊF). For details see Ref 2. They cooling a melt (i.e., liquid phase) sufficiently fast into the furnace section for melting, removal of are not used in composite applications and are that crystallization (devitrification) cannot occur. gaseous inclusions, and homogenization. Then, therefore not shown in Table 2. When the melt is cooled slowly, crystallization the molten glass flows into the refiner section, Ultrapure silica glass fibers or quartz fibers can occur at the liquidus temperature, TL, where where the temperature of the glass is lowered (99.99% SiO2), which are down-drawn from pre- crystals and melt are in equilibrium, or below. from 1370 ЊC (2500 ЊF) to about 1260 ЊC (2300 forms (Ref 2) in a containerless process, are also Glass fibers are therefore obtained at high cool- ЊF). The molten glass next goes to the forehearth amorphous, despite the fact that the trivial name ing rates. Chemically, a glass consists of a silica section located directly above the fiber-forming “quartz” or trade names Quartzel and Astro- network. Other oxides facilitate melting, homog- stations. The temperatures throughout this pro- quartz would imply the presence of the hexag- enizing, removal of gaseous inclusions, and fiber cess are prescribed by the viscosity characteris- onal crystal structure of quartz. Ultrapure silica formation at optimum temperatures. This section tics of the particular glass. In addition, the physi- (quartz) fibers combine superior high-tempera- addresses the generic glass-melting and fiber- cal layout of the furnace can vary widely, ture resistance with superior transparency to ul- forming process, including the viscosity versus depending on the space constraints of the plant. traviolet (UV) and longer wavelength radiation. temperature profile that is required for general- Fiberizing and Sizing. The conversion of For example, in a composite radome on the nose purpose E-glass glass fibers and, more specifi- molten glass in the forehearth into continuous of an aircraft, they protect delicate radar equip- cally, for E-glass fibers containing 5 to 6% boron glass fibers is basically an attenuation process ment from flying objects, lightning and static oxide (see Ref 1 for details). (Fig. 3). The molten glass flows through a plat- discharge (Ref 30). The purest of all commercial Depending on fiber diameter, optimum fiber inum-rhodium alloy bushing with a large num- silica glass or quartz fibers (99.999% SiO2) are formation is achieved with melts having a vis- ber of holes or tips (400 to 8000, in typical pro- obtained by dry-spinning of a reagent grade te- cosity ranging from log 2.5 to log 3 P. The ge- duction). The bushing is heated electrically, and traethylorthosilicate sol-gel (Ref 2). neric melting and forming process that is re- the heat is controlled very precisely to maintain All ultrapure silica glass or quartz fibers are quired for boron-free E-glass is the same as that a constant glass viscosity. The fibers are drawn used in yarn and in composite applications and required for boron-containing E-glass, but the down and cooled rapidly as they exit the bush- are, therefore, shown in Table 2. Ultrapure and viscosity/temperature profile differs. The relative ing. pure silica yarns and fabrics can be used at tem- forming temperatures can be deduced from the A sizing is then applied to the surface of the peratures up to 1090 ЊC (1990 ЊF), high silica Fulcher curves shown in Fig. 1. They will be fibers by passing them over an applicator that fabrics at up to 1040 ЊC (1900 ЊF), and S-glass, proportionately higher for boron-free E-glass at continually rotates through the sizing bath to Te-glass, and R-glass yarns and fabrics at up to equal melt viscosities between log 2.5 to log 3.0 maintain a thin film through which the glass fil- 815 ЊC (1500 ЊF) (for process and product details P. This section does not address the glass melting aments pass. It is this step, in addition to the see Ref 2). and fiber forming processes required for the spe- original glass composition, which primarily dif- D-Glass. The electrical properties of glass fi- cial-purpose glass fibers, that is, ECR-glass, S- ferentiates one fiberglass product from another. bers are determined by their volume resistivity, surface conductivity, dielectric constant and loss tangent (Ref 2). E-glass with its relatively high dielectric constant is the major reinforcing fiber for printed circuit board (PCB) laminates in the market today, but miniaturization drives the in- dustry toward specialty fibers with lower dielec- tric constants and lower dielectric loss tangents. Several low D-glass variants are known. All have very high B2O3 levels (20 to 26%) and, therefore, much lower dielectric constants than E-glass (4.10 to 3.56 versus 6.86 to 7.00). Those D-glass variants having low dielectric loss tan- gents as well (Ref 8) are said to offer the highest value in-use when used to reinforce PCB lami- nates. Because of their high cost, however, any D-glass version will remain a low volume spe- cialty fiber. The very high boron-oxide levels, which are needed and in part emitted from the melt, may require an entirely different specialty process (see Ref 2 for details). For very different reasons, ultrapure silica fi- bers, hollow E-glass fibers, S-glass, and other Fig. 2 Furnace for glass melting
- 5. Glass Fibers / 5 The components of the sizing impart strand in- trolled by the take-up device. Fiber diameter is specific fabrication area for conversion into the tegrity, lubricity, resin compatibility, and adhe- also affected by bushing temperature, glass vis- finished fiberglass roving, mat, chopped strand, sion properties to the final product, thus tailoring cosity, and the pressure head over the bushing. or other product. the fiber properties to the specific end-use re- The most widely used take-up device is the In recent years, processes have been devel- quirements. After applying the sizing, the fila- forming winder, which employs a rotating collet oped to produce finished roving or chopped ments are gathered into a strand before ap- and a traverse mechanism to distribute the strand products directly during forming, thus leading to proaching the take-up device. If small bundles in a random manner as the forming package the term direct draw roving or direct chopped of filaments (split strands) are needed, multiple grows in diameter. This facilitates strand re- strand. Special winders and choppers designed gathering devices (often called shoes) are used. moval from the package in subsequent process- to perform in the wet-forming environment are Fiber Diameters. The attenuation rate, and ing steps, such as roving or chopping. The form- used in these cases (Fig. 4). therefore the final filament diameter, is con- ing packages are dried and transferred to the Yarn Nomenclature. It is standard practice in the fiberglass industry to refer to a specific filament diameter by a specific alphabet desig- nation, as listed in Table 3. Fine fibers, which are used in textile applications, range from D through G. One reason for using fine fibers is to provide enough flexibility to the yarn to enable it to be processed in high-speed twisting and weaving operations. Conventional plastics rein- forcement, however, uses filament diameters that range from G to T. Important Commercial Products Once the continuous glass fibers have been produced they must be converted into a suitable product form for their intended composite ap- plication. The major finished forms for E-glass fibers are continuous roving, woven roving, fi- berglass mat, chopped strand, and yarns for tex- tile applications. Fiberglass roving is produced by collecting a bundle of strands into a single large strand, which is wound into a stable, cylindrical pack- age. This is called a multiend roving process. The process begins by placing a number of oven- dried forming packages into a creel. The ends are then gathered together under tension and col- lected on a precision roving winder that has a constant traverse-to-winding ratio, and is called Fig. 3 Fiberglass forming process the waywind. This ratio has a significant effect on package stability, strand characteristics, and ease of payout in subsequent operations. The yield (meter per kilogram, or yard per pound) of the finished roving is determined by the number of input ends and the yield of the input strand or sliver. Final package weight and dimensions can be made to vary widely, depending upon the re- quired end-use. Figure 4 shows the entire pro- cess. Rovings are used in many applications. When used in a spray-up fabrication process, the roving is chopped with an air-powered gun that propels the chopped-glass strands to a mold while si- multaneously applying resin and catalyst in the compact ratio. This process is commonly used for bath tubs, shower stalls, and many marine applications. In another important process, the production of sheet molding compound (SMC), the roving is chopped onto a bed of formulated polyester resin and compacted into a sheet, which thickens with time. This sheet is then placed in a press and molded into parts. Many fiber-reinforced plastic (FRP) automotive body Fig. 4 Multiend roving process production panels are made by this process.
- 6. 6 / Constituent Materials Filament winding and pultrusion are processes from low to high, depending on the application. area where they are dried, screened, and pack- that use single-end rovings in continuous form. For example, hand lay-up processes used to aged. The direct-chop process has provided the Applications include pipes, tanks, leaf springs, moderate corrosion-resistant liners or boat hulls industry with a wide variety of chopped rein- and many other structural composites. In these require high solubility, whereas closed-mold forcements for compounding with resins. processes the roving is passed through a liquid processes such as cold press or compression Chopped glass is widely used as a reinforce- resin bath and then shaped into a part by winding molding require low solubility to prevent wash- ment in the injection molding industry. The glass the resin-impregnated roving onto a mandrel or ing in the mold during curing. and resin may be dry blended or extrusion com- by pulling it through a heated die. Because of a Continuous-strand mat is formed in a similar pounded in a preliminary step before molding, property called catenary (the presence of some manner but without chopping, and, usually, less or the glass may be fed directly into the molding strands that have a tendency to sag within a bun- binder is required because of increased mechan- machine with the plastic resin. Hundreds of dif- dle of strands), multiend rovings sometimes do ical entanglement, which provides some inherent ferent parts for many applications are made in not process efficiently. Catenary is caused by un- integrity. Continuous-strand mat may be used in this manner. Chopped glass may also be used as even tension in the roving process that results in closed mold processes and as a supplemental a reinforcement in some thermosetting applica- poor strand integrity. product in unidirectional processes such as pul- tions, such as bulk molding compounds. While providing desirable entanglement for trusion, where some transverse strength is re- Milled fibers are prepared by hammer milling transverse strength in pultrusion, the looser ends quired. A number of specialty mats are also pro- chopped or sawed continuous strand glass fibers, in the roving may eventually cause loops and duced. Surfacing veil made with C-glass is used followed by chemically sizing for some specific breakouts in close-tolerance orifices, making re- to make corrosion-resistant liners for pipes and applications and by screening to length. Fiber inforced plastics processing difficult. Conse- tanks. Surfacing veils made from other glass lengths typically vary from particulates to screen quently, the process of direct forming single-end compositions are used to provide a smooth fin- opening dimensions for the reported nominal 1 1 rovings was developed by using very large bush- ished surface in some applications. Glass tissue length (0.79 to 6.4 mm, or 32 to 4 in.). As ings and a precision winder specially designed is used in some vinyl flooring products. such, milled fibers have a relatively low aspect to operate in the severe forming environment. Combinations of a mat and woven roving ratio (length to diameter). They provide some No subsequent step other than drying is required. have been developed for specific products in re- increased stiffness and dimensional stability to Single-end rovings have become the preferred cent years. In many lay-up processes the lami- plastics but minimal strength. Their use is pri- product for many filament-winding and pultru- nate is constructed from alternate layers of fi- marily in phenolics, reaction-injection molded sion applications. berglass mat and woven roving. Fiberglass urethanes, fluorocarbons, and potting com- Woven roving is produced by weaving fiber- producers thus began to provide products that pounds. glass rovings into a fabric form. This yields a make this process more efficient. The appropri- Fiberglass paper is the reinforcing element coarse product that is used in many hand lay-up ate weights of fiberglass mat (usually chopped- for fiberglass roofing shingles. Chopped strands and panel molding processes to produce FRPs. strand mat) and woven roving are either bound of 25 to 50 mm (1 to 2 in.) length are usually Many weave configurations are available, de- together with a chemical binder or mechanically used in making fiberglass paper or a thin fiber- pending on the requirements of the laminate. knit or stitched together. This product can then glass mat. In this process, chopped fibers are dis- Plain or twill weaves provide strength in both be used as a significant labor saver by the fab- persed in water to form a dilute solution. The directions, while a unidirectionally stitched or ricators. fiberglass strands filamentize during the mixing knitted fabric provides strength primarily in one Chopped strand products are produced by and dispersion process. The solution is pumped dimension. Many novel fabrics are currently two major processes. In the first process, dried onto a continuously moving chain, where most available, including biaxial, double-bias, and tri- forming packages are used as a glass source. A of the water is removed by vacuum, leaving be- axial weaves for special applications. number of strand ends are fed into a chopper, hind a uniformly distributed, thin fiberglass mat. Fiberglass mats may be produced as either which chops them into the correct length, typi- A binding resin is added on-line, followed by 1 1 continuous- or chopped-strand mats. A chopped- cally 3.2 to 12.7 mm ( 8 to 2 in.). The product drying and curing, to form the fiberglass paper. strand mat is formed by randomly depositing is then screened to remove fuzz and contami- This paper is then combined with the appropriate chopped fibers onto a belt or chain and binding nation and boxed for shipment (Fig. 5). The sec- resin system to form roofing shingles. them with a chemical binder, usually a thermo- ond process, used in recent years to produce Textile yarns are fine-fiber strands of yarn plastic resin with a styrene solubility ranging many chopped-strand products, is the direct- from the forming operation that are air dried on chop process. In this process, large bushings are the forming tubes to provide sufficient integrity Table 3 Filament diameter nomenclature used in forming, and the strands are chopped in to undergo a twisting operation. Twist provides a wet state directly after sizing is applied. The additional integrity to yarn before it is subjected Filament diameter wet, chopped strands are then transported to an to the weaving process, a typical twist consisting Alphabet lm 10–4 in. AA 0.8–1.2 0.3–0.5 A 1.2–2.5 0.5–1.0 B 2.5–3.8 1.0–1.5 C 3.8–5.0 1.5–2.0 D 5.0–6.4 2.0–2.5 E 6.4–7.6 2.5–3.0 F 7.6–9.0 3.0–3.5 G 9.0–10.2 3.5–4.0 H 10.2–11.4 4.0–4.5 J 11.4–12.7 4.5–5.0 K 12.7–14.0 5.0–5.5 L 14.0–15.2 5.5–6.0 M 15.2–16.5 6.0–6.5 N 16.5–17.8 6.5–7.0 P 17.8–19.0 7.0–7.5 Q 19.0–20.3 7.5–8.0 R 20.3–21.6 8.0–8.5 S 21.6–22.9 8.5–9.0 T 22.9–24.1 9.0–9.5 U 24.1–25.4 9.5–10 Fig. 5 Chopped-strand production
- 7. Glass Fibers / 7 of up to one turn per inch. The twisting operation ● The first letter specifies the glass composi- The product brochures from various weavers as is shown in Fig 6. In many instances, heavier tion, in this case, E-glass. well as to Ref 4 should be consulted for details yarns are needed for the weaving operation. This ● The second letter specifies the filament type on commercially available fabrics. The Glass- is normally accomplished by twisting together (staple, continuous, texturized) (in the case, Fibre Dictionary and Databook (Ref 14) should two or more single strands, followed by a plying of ECG 75 2/4, continuous). be consulted for even greater detail and/or for a operation. Plying essentially involves retwisting ● The third letter specifies the filament diameter summary of all commercially available yarns. the twisted strands in the opposite direction from (in this case, G). Fiberglass Fabric. Fiberglass yarns are con- the original twist. The two types of twist nor- ● The next series of numbers represents the ba- verted to fabric form by conventional weaving 1 mally used are known as S and Z, which indicate sic strand yield in terms of 100 th of the operations. Looms of various kinds are used in the direction in which the twisting is done. Usu- yield (in this case, 75 means 7500 yd/lb). the industry, but the air jet loom is the most pop- ally, two or more strands twisted together with ● The fraction represents the number of strands ular. The major characteristics of a fabric include an S twist are plied with a Z twist in order to twisted together (numerator) to form a single its style or weave pattern, fabric count, and the give a balanced yarn. Thus, the yarn properties, end and the number of such ends plied to- construction of warp yarn and fill yarn. Together, such as strength, bundle diameter, and yield, can gether (denominator) to form the final yarn. these characteristics determine fabric properties be manipulated by the twisting and plying opera- In the above case, 2/4 means two basic such as drapability and performance in the final tions. strands are twisted together to form a single composite. The fabric count identifies the num- The yarn nomenclature for fiberglass yarns end, and four such ends are plied together ber of warp and fill yarns per inch. Warp yarns consists of both letters of the alphabet and num- (usually in the opposite direction) to form the run parallel to the machine direction, and fill bers. For instance, in ECG 75 2/4: final yarn. yarns are perpendicular. There are basically four weave patterns: plain, basket, twill, and satin. Plain weave is the sim- plest form, in which one warp yarn interlaces over and under one fill yarn. Basket weave has two or more warp yarns interlacing over and un- der two or more fill yarns. Twill weave has one or more warp yarns floating over at least two fill yarns. Satin weave (crowfoot) consists of one warp yarn interfacing over three and under one fill yarn to give an irregular pattern in the fabric. The eight-harness satin weave is a special case, in which one warp yarn interlaces over seven and under one fill yarn to give an irregular pattern. In fabricating a composite part, the satin weave gives the best conformity to complex contours, followed in descending order by twill, basket, and plain weaves. Texturized Yarn. Texturizing is a process in which the textile yarn is subjected to an air jet that impinges on its surface to make the yarn ’fluffy’’ (Fig. 7). The air jet causes the surface filaments to break at random, giving the yarn a bulkier appearance. The extent to which this oc- curs can be controlled by the velocity of the air jet and the yarn feed rate. The texturzing process Fig. 6 Twisting allows the resin-to-glass ratio to be increased in the final composite. One of the major applica- tions of texturized yarns is as an asbestos re- placement. Carded Glass Fibers. Carding is a process that makes a staple fiberglass yarn from contin- uous yarn. The continuous yarn is chopped into 38 to 50 mm (1.5 to 2.0 in.) lengths, and then aligned in one direction in a mat form. It is fi- nally converted to a staple yarn. The yarn pro- duced by this process can absorb much more resin than texturized yarn. Carded glass fibers are also used as an asbestos replacement in friction applications, such as automotive brake linings. REFERENCES 1. K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, 3rd revised ed., Elsevier, 1993 2. F.T. Wallenberger, Structural Silicate and Fig. 7 Texturizing Silica Glass Fibers, in Advanced Inorganic
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