In addition to the amount, form and resin, the end-use properties and durability of fiberglass products are influenced by the processing and fabrication method. Various fabrication methods are used in the fiberglass industry to meet technological and mechanical property needs as well as produce components effectively and efficiently.
“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 uses a two-sided mold set or takes 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 quickly produce highly complex parts. 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 thermoplastic (LFT) technology, which enables molders to compound in-line with the injection process, is also used to make a range of structural and semi-structural parts. TUFROV® LFT
fiber glass roving 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. With maximum wet out and excellent fatigue performance, HYBON® direct draw single-end rovings are well suited to filament winding.
Long Fiber Thermoplastic (LFT)
Using LFT reinforcements in the thermoplastic composite process enables molders to produce structural and semi-structural parts, compounding the fiber glass in line with injection or compression molding techniques.
Granular Long Fiber Thermoplastic (G-LFT)
G-LFT are compounds that are obtained by impregnating continuous glass fiber rovings with thermoplastic resin, cooling then cutting it into rod-like pellets (generally 6-25 mm). These pellets are then injection molded into parts. The benefits of G-LFT include enhanced mechanical properties, improved fatigue performance and high impact performance. This process accommodates industrial, automotive, health-care and consumer applications.
Direct Long Fiber Thermoplastic (D-LFT)
In-line or direct compounding of LFT enables processors to take advantage of a “one-step” process in which the resin, fiberglass and additives are directly integrated into the molding or part-extrusion process. D-LFT compounds eliminate the stage of pellet production. 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® LFT fiberglass rovings offer optimum processing and performance for D-LFT processes.
Continuous Long Fiber Thermoplastic (C-LFT)
Tape – Tape is created by impregnating the unidirectional continuous fibers and forming a thin, wide and long geometry tape. Continuous fiber composite tapes are usually 0.005” to 0.030” thick, 0.063” to several feet wide and up to several thousand feet long. Wide spools of tape are usually slit down to narrower widths for final processing.
Organo Sheet – Organo sheets are woven glass fiber material utilizing continuous fiber composite tape for weave. Organo-sheet weaves include 0/90 and 0/45/90.
Glass Mat Thermoplastic (GMT)
GMTs are composites that are consolidated sheets containing thermoplastic matrices (common matrix polymer is polypropylene) reinforced with unidirectional, randomly oriented, long chopped and/or continuous fiberglass mats. The melt impregnation process consists of combining glass mat along with a polymer sheet under pressure and temperature through a double belt system. The material is cooled and slit and sheared into specific sizes for subsequent part molding via compression molding. Prior to the final molding, the sheets are heated again in an infrared oven above the melting point of the resin matrix, then transferred hot into a cold compression mold to form the finished part.
Non-crimp fabric (NCF) composites are reinforced with mats of straight (non-crimped) fibers, giving them advantages of strength, ease of handling and low manufacturing costs. NCF fabrics are distinguished by their stretched fibers inside the individual layers that absorb pressure and tension.
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 an open molding process.
In the pultrusion process, glass fibers are pulled from spools through a device that coats them with a resin. They are then heat treated and cut to length. Pultrusions can be made in a variety of shapes or cross-sections. The word pultrusion describes the method of moving the fibers through the machinery. Typically, it is pulled by way of a continuous roller method. This is opposed to an extrusion method which pushes the material through the dies.
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. Pultrusion yields continuous lengths of material with high unidirectional strengths. PPG Fiber Glass products used for pultrusion include HYBON® direct draw rovings, multi-end rovings and 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 because it can fill tight die radii to provide maximum die fill.
Roving fabrics are weaved using three types of techniques:
Woven Roving – Continuous rovings woven into a heavy, coarse, but drapable fabric—typically a plain weave pattern.
Multi-Axial/Non-Crimp Fabric (MAX/NCF) – As the name implies, rovings are weaved into a fabric using multiple stitch bond angle constructions.
Three Dimensional (3D) – In contrast to 2D woven fabrics, such as woven roving and MAX/NCF, 3D fabrics consist of three basic parts: 0° and 90° oriented rovings and through thickness fibers, called Z-fibers.