1.5.8 VACUUM BAG PROCESSING Vacuum bag processing, Figure 1.12, uses a vacuum to eliminate entrapped ai and excess resin from a lay-up from on either a male or female mold. A non-adhering film(usually polyvinyl alcohol or nylon) is placed over the lay-up and sealed at its edges A vacuum is drawn on the bag formed by the film, and the FRP composite is cured, either at room temperature or with heat to speed the process. Compared to hand lay-up, the vacuum method provides higher reinforcement concentration and better adhesion between layers. Flexible Film Edge Bleeder 33 Heat Source Laminate vacuum FIGURE 1. 12. Vacuum Bag Processing 1.5.9 PRESSURE BAG MOLDING Pressure bag molding is similar to the vacuum bag method except that air pressure of 30 to 50 psi is applied to a rubber bag or sheet that covers the laid-up assembly to force out entrapped air and excess resin. Pressurized steam may be used instead accelerate the cure. This process is practical only with female molds. See Figure 1.13 Mold FIGURE 1. 13. Pressure Bag Molding
18 1.5.8 VACUUM BAG PROCESSING Vacuum bag processing, Figure 1.12, uses a vacuum to eliminate entrapped air and excess resin from a lay-up from on either a male or female mold. A non-adhering film (usually polyvinyl alcohol or nylon) is placed over the lay-up and sealed at its edges. A vacuum is drawn on the bag formed by the film, and the FRP composite is cured, either at room temperature or with heat to speed the process. Compared to hand lay-up, the vacuum method provides higher reinforcement concentration and better adhesion between layers. 1.5.9 PRESSURE BAG MOLDING Pressure bag molding is similar to the vacuum bag method except that air pressure of 30 to 50 psi is applied to a rubber bag or sheet that covers the laid-up assembly to force out entrapped air and excess resin. Pressurized steam may be used instead to accelerate the cure. This process is practical only with female molds. See Figure 1.13 below
.10 AUTOCLAVE MOLDING Autoclave molding is a further modification of either vacuum bag or pressure bag olding. The process produces denser, void-free composites because higher heat and ressure are used in the cure. Autoclaves, Figure 1. 14, are essentially heated pressure essels (usually equipped with vacuum systems)into which bagged lay-ups, on their lolds, are taken to be cured at pressure of 50 to 100 psi. Autoclaves are normally used to process high-performance components based on epoxy-resin systems for aircraft and aerospace applications Insulated shell Air Distribution Shroud eating Elements Air F FIGURE 1.14, autoclay 1.5.11 FILAMENT WINDING quirng unusual production methods involve specialized approaches to making parts Some frp properties or configurations such as very large size, extremely high strength, highly directional fiber orientation, unusual shape or constant cross section. In nost cases, these methods are the only ones suitable for the conditions of configuration for which they were designed. Continuous, resin-impregnated fibers or roving are wound on a rotating mandrel in a predetermined pattern, providing maximum control over fiber placement and uniformity of structure. See Figure 1. 15. In the wet method, the fiber picks up the low iscosity resin either by passing through a trough or from a metered application system In the dry method, the reinforcement is impregnated with resin prior to winding. Integral fittings and vessel closings can be wound into the structure. When sufficient layers have been applied, the FRP composite is cured on the mandrel and the mandrel is removed Filament winding is traditionally used to produce cylindrical and spherical FRP products such as chemical and fuel storage tanks and pipe, pressure vessels and rocket
19 1.5.10 AUTOCLAVE MOLDING Autoclave molding is a further modification of either vacuum bag or pressure bag molding. The process produces denser, void-free composites because higher heat and pressure are used in the cure. Autoclaves, Figure 1.14, are essentially heated pressure vessels (usually equipped with vacuum systems) into which bagged lay-ups, on their molds, are taken to be cured at pressure of 50 to 100 psi. Autoclaves are normally used to process high-performance components based on epoxy-resin systems for aircraft and aerospace applications. 1.5.11 FILAMENT WINDING Some FRP production methods involve specialized approaches to making parts requiring unusual properties or configurations such as very large size, extremely high strength, highly directional fiber orientation, unusual shape or constant cross section. In most cases, these methods are the only ones suitable for the conditions of configurations for which they were designed. Continuous, resin-impregnated fibers or roving are wound on a rotating mandrel in a predetermined pattern, providing maximum control over fiber placement and uniformity of structure. See Figure 1.15. In the wet method, the fiber picks up the low viscosity resin either by passing through a trough or from a metered application system. In the dry method, the reinforcement is impregnated with resin prior to winding. Integral fittings and vessel closings can be wound into the structure. When sufficient layers have been applied, the FRP composite is cured on the mandrel and the mandrel is removed. Filament winding is traditionally used to produce cylindrical and spherical FRP products such as chemical and fuel storage tanks and pipe, pressure vessels and rocket
motor cases. However, the te ed, and with computer controlled nding machines, other shape w being made al control can provide up to ll axes of moti single and multiple spindles. Examples are helicopter tail booms and rotor blades, rbine blades and aircraft cowls Wet Method) 彎酈 Resin Trough FIGURE 1. 15. Filament Winding 1.512 PULTRUSION Constant section-reinforced FRP shapes such as structural members (I-beams, channels, etc. ) solid rod, pipe and ladder side rails are produced in continuous lengths by pultrusion. The reinforcement, consisting of a combination of roving, mat, cloth and surfacing veil, is pulled through a resin bath to wet-out the fibers, then drawn through a forming block that sets the shape of the composite and removes excess resin, and through heated steel die to cure the resin. See Figure 1. 16. Temperature control and time in the die are critical for proper curing. The finished shape is cut to lengths by a traveling cutoff saw strengths are possible in pultruded shapes because of high fiber content d orientation parallel to the length of the FRP shape. Pultrusion is easily auto and there is no practical limit to product length manufactured by the
20 motor cases. However, the technology has been expanded, and with computer controlled winding machines, other shapes are now being made. Today, computerized numerical control can provide up to 11 axes of motion for single and multiple spindles. Examples are helicopter tail booms and rotor blades, wind turbine blades and aircraft cowls. 1.5.12 PULTRUSION Constant section-reinforced FRP shapes such as structural members (I-beams, channels, etc.), solid rod, pipe and ladder side rails are produced in continuous lengths by pultrusion. The reinforcement, consisting of a combination of roving, mat, cloth and surfacing veil, is pulled through a resin bath to wet-out the fibers, then drawn through a forming block that sets the shape of the composite and removes excess resin, and through a heated steel die to cure the resin. See Figure 1.16. Temperature control and time in the die are critical for proper curing. The finished shape is cut to lengths by a traveling cutoff saw. Very high strengths are possible in pultruded shapes because of high fiber content (to 75 percent) and orientation parallel to the length of the FRP shape. Pultrusion is easily automated, and there is no practical limit to product length manufactured by the process
Pull Rolls FIGURE 1.16. Pultrusion 1.513 CONTINUOUS LAMINATING PROCESSES Sheet FRP products such as glazing panels, flat and corrugated construction panels are made by a continuous laminating process. Glass fiber chopped rovings reinforcing mat and fabric are combined with resin and sandwiched between two carrier film sheets. The material then passes between steel rollers to eliminate entrapped air and to establish finished laminate thickness, then through a heated zone to cure the resin Wall thickness can be closely controlled ulmi v wide variety of surface finishes and textures can be applied and panel length is 1.6 Uses of Composite Material Since the publication of the first edition of this text in 1986, the use of c materials has grown enormously both in quantity and variety. In 1999 composite usage was increasing at 4%o in North America and 6%o worldwide. According to the Freedonia Group, Inc. of Cleveland, reinforced thermoset resin demand will increase at an annual rate of 3% to 2.37 billion pounds by 2001. Faster growth is predicted for thermoplastics, 3.8% to 1 44 billion pounds by 2001. They also see increasing demand for glass fibers because of automotive market growth and in construction to 2. 4 billion pounds by 2003 The shipment of U.S. composite materials, showing the growth with time, is given in Figure 1.[1
21 1.5.13 CONTINUOUS LAMINATING PROCESSES Sheet FRP products such as glazing panels, flat and corrugated construction panels are made by a continuous laminating process. Glass fiber chopped rovings, reinforcing mat and fabric are combined with resin and sandwiched between two carrier film sheets. The material then passes between steel rollers to eliminate entrapped air and to establish finished laminate thickness, then through a heated zone to cure the resin. Wall thickness can be closely controlled. A wide variety of surface finishes and textures can be applied and panel length is unlimited. Corrugations are produced by molds or by rollers just prior to the curing stage. 1.6 Uses of Composite Materials Since the publication of the first edition of this text in 1986, the use of composite materials has grown enormously both in quantity and variety. In 1999 composite usage was increasing at 4% in North America and 6% worldwide. According to the Freedonia Group, Inc. of Cleveland, reinforced thermoset resin demand will increase at an annual rate of 3% to 2.37 billion pounds by 2001. Faster growth is predicted for thermoplastics, 3.8% to 1.44 billion pounds by 2001. They also see increasing demand for glass fibers because of automotive market growth and in construction to 2.4 billion pounds by 2003. The shipment of U.S. composite materials, showing the growth with time, is given in Figure 1.17 [1]
4,500 U.S. COMPOSITE SHIPMENTS 00 Qz5.. 3,500 2.500 2,000 91.500 1,000 Shaded areas s Us recessions FIGURE 1. 17 1.6.1 AIRCRAFT The increasing use of composite materials in commercial and military aircraft are clearly seen in Figures 1. 18 and 1. 19 [1]. Advanced Composites by Commercial Aircraft Model pty structural weight) 要员a A330A310 ●A3A3 1865197019751980198519901995200020052010 FIGURE 1. 18. Composite Weight Growth in Commercial Aircraft as a Percentage of mpty Structural Weight
22 1.6.1 AIRCRAFT The increasing use of composite materials in commercial and military aircraft are clearly seen in Figures 1.18 and 1.19 [1]