| Fabrication Processes
“Braid" refers to a family of fabrics continuously woven on the bias, with a system of three or more yarns intertwined such that no two yarns are twisted around one another. Braided fiber architecture resembles a hybrid of filament winding and woven material. Like filament winding, tubular braid features seamless fiber continuity from end to end of a part. Like woven material, braided fibers are mechanically interlocked. When functioning as a composite reinforcement, braid exhibits exceptional properties because it distributes loads very efficiently.
Closed molding comprises a family of techniques for composite fabrication that either use a two-sided mold set or take place within a vacuum bag. The processes are often largely automated and include methods such as compression molding, pultrusion, reinforced reaction injection molding, resin transfer molding, vacuum bag molding, vacuum infusion processing, centrifugal casting and continuous lamination.
Compounding and Injection Molding
Injection molding is used predominantly to manufacture thermoplastic parts, and it can produce very complex parts very quickly. The mold usually comprises two sections held together by a clamp strong enough to withstand the pressure of injected molten plastic, with channels for heating, cooling and venting. Resin systems can be filled or unfilled, and using glass fibers in the resin increases the mechanical strength of the part and provides dimensional control. Typical reinforcements are chopped or milled fibers in the form of pellets.
Thermosets such as bulk molding compound are also used in compounding. Long fiber technology (LFT), which enables molders to compound in-line with the injection processes, is also used to make a range of structural and semi-structural parts. TUFROV®
Roving fiber glass by PPG provides high composite strength and offers excellent processing in compounding and injection molding operations.
Filament winding is an automated process in which continuous filament or tape is treated with resin and wound on a mandrel in a pattern that provides maximum strength in one direction. By varying relative amounts of resin and reinforcement along with the winding pattern, the strength of the filament-wound structures may be controlled to resist stresses in specific directions. After sufficient layers are wound, a structure is cured. Filament winding is used to make hollow tubular structures such as pressure vessels, pipes and storage tanks. HYBON®
Direct Roving single-end fiber glass roving by PPG is well suited to filament winding, with maximum wet-out and excellent fatigue performance.
Long Fiber Technology (LFT)
Using LFT reinforcements in the thermoplastic composite processes enables molders to produce structural or semi-structural parts, compounding the fiber glass in-line with injection or compression molding techniques.
Granular Long Fiber Technology (G-LFT)
The G-LFT process incorporates fiber glass rovings into an impregnation center with any of dozens of available base polymers. After the glass is incorporated with the resin, the compound is cooled and then pulled into a chopper that cuts it into pellets. The benefits of G-LFT include enhanced mechanical properties, improved fatigue performance and high impact resistance. This process accommodates industrial, automotive, health-care and consumer applications.
Direct Long Fiber Technology (D-LFT)
In-line or direct compounding of LFT enables processors to take advantage of a "one-step" process in which the resin, fiber glass and additives are directly integrated into the molding or part-extrusion process. D-LFT achieves cost, time and processing savings by integrating the compounding step into the final parts-molding process. The final composite then exhibits exceptional mechanical properties because fiber integrity and length are maintained better than in traditional thermoplastic processes. TUFROV
Roving fiber glass by PPG offers optimum processing and performance for D-LFT processes.
With open molding, the gel coat and laminate are exposed to the atmosphere during the fabrication process. Hand lay-up, spray-up and filament winding are examples of open mold processes.
Pultrusion is a continuous process for manufacturing composites with a uniform cross-sectional shape. A fiber reinforcement is pulled through a resin-impregnation bath and into a shaping die, where the resin is subsequently cured or set. Heating to both gel and cure the resin is accomplished within the die length. Pultrusion yields continuous lengths of material with high unidirectional strengths. PPG fiber glass products used for pultrusion include HYBON
Drirect Roving single-end and multi-end fiber glass rovings as well as MatVantage II continuous-strand fiber glass mat.
Scrim is a simple, strong, flexible, web-like product that is sometimes fire retardant. Its fibers are not crimped by weaving but joined at a greater variety of angles and chemically bonded through advanced technology. Scrim can be produced at far greater speeds than other glass-reinforced fabrics.
The texturizing process blows air into continuous fiber glass filaments, adding bulk. When a certain air pressure is reached in the process, air hitting the fiber glass causes it to break or become disoriented, resulting in a "puffed-up" appearance. Texturized yarn is often used in high-temperature applications because of its thermal tolerance, and it can fill tight die radii to provide maximum die fill.
HYBON, MatVantage and TUFROV are trademarks of PPG Industries.