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Railcar manufacturers are on track for more extensive use of composites due to the greater demand for weight reduction and aerodynamics and composite front ends, or noses, are relatively simple to fabricate by comparison to their metal counterparts. Composites are also the principal material for air inlets on high-speed trains because of the complex shapes and curvatures needed to alleviate noise. Composites are also a cost effective way to repair corrosion-prone systems particularly in the oil and gas industry, and in fortification of bridge pilings. Repairing or Replacing corrosion-damaged piping and industrial equipment is estimated in the hundreds of billions. 

Corrosion resistant composites are increasingly finding their way into these markets for their long-term repair strategies.

Part design criteria

When developing a new part, designers of composites choose from a wide variety of fiber reinforcements and resin systems. Knowledge of material properties is a prerequisite to satisfactory product design, but cost is a major factor, as well. Over-designed composites cannot compete with lower-cost, established material systems. The well-designed part not only employs the right materials and processes to meet application requirements, but, many times, is commercially competitive with other materials, when installation, maintenance and lifecycle costs are factored into the total equation.

Fiber reinforcements provide mechanical properties such as stiffness and strength, and resin matrices provide physical characteristics, including toughness and resistance to impact, weather, fire, ultraviolet light and corrosive chemicals.

A significant design consideration is fiber-to-matrix ratio, which a determining factor in the ultimate weight and cost of the component and governs the extent to which performance properties inherent in the fiber reinforcement can be optimized in the part. Fiber-to-resin ratio can range from 20:80 for low-cost, nonstructural components as high as 70:30 in some high-end pultrusion applications for structural use. A 60:40 or higher ratio is common in advanced composites.

Three additional factors must be considered when designing with fiber: fiber type, form and orientation or architecture. Orientation refers to fiber direction relation to the longest part dimension. Typically, fiber architecture is tailored in the direction of the primary loads placed on a structure, a design principle comparable to what civil engineers use to orient steel reinforcing bars a concrete structure. Common orientations are parallel (0degrees ), circumferential (9O°) and helical (usually ±33° to ±45°). However, fiber direction can vary extensively. For example, a 54degrees winding angle satisfies both the circumferential (hoop) and longitudinal (axial) strength requirements of most pipes and pressure vests, usually manufactured by the filament winding process. However, if more stress is placed on the pipe in the axial direction, as is the case with an unsupported span, a ±20degrees /±70° fiber orientation will provide a stiffer bending modulus for increased axial strength.

Composites, by nature, allow designers to tailor fiber architecture to match the performance requirements for a specific part. Laminates may be designed to be isotropic or anisotropic, balanced or unbalanced, symmetric or asymmetric - depending on the in-use forces a component must withstand. Varied fiber orientation allows a range of wall-thickness variations, making it possible to develop lightweight, complex shapes and to produce large parts with integral reinforcing members.

An understanding of layered or laminate structural behavior is vital to effective composite component design. Adhesion between laminate layers (called plies) is critical; poor adhesion can result in de-lamination under stress, strain, impact and load conditions. Ply lay-up designers must consider mechanical stresses/loads, adhesion, weight, stiffness, operating temperature and toughness requirements, as well as variables such as electromagnetic transparency and radiation resistance. Additionally, composite component design must encompass surface finish, fatigue life, overall part configuration and scrap or rework potential, to name just a few of the many applicable factors.

The intended fabrication method also will influence design. For instance, manufacturers of filament-wound or tape-layed structures use different reinforcement forms and build-up patterns than those used either for laminate panels layered up by hand or for vacuum bag-cured prepreg parts. Resin transfer molding (RTM) accommodates three dimensional preforms more easily than do some other manufacturing techniques. The varying benefits and limitations of these fabrication techniques provide designers a very flexible set of options, in their efforts to achieve optimum performance and economies.

A common type of composite structure - sandwich construction - combines a lightweight core material with laminated composite skins (face sheets), similar to the construction of corrugated cardboard. These very lightweight panels have the highest stiffness-to-weight and strength-to-weight performance of all composite structures and are extremely resistant to bending and buckling. Suitable core materials include closed-cell foams, balsa wood and celled honeycomb in a variety of forms (aluminum, paper or plastic). Some foam cores are syntactic (i.e., containing hollow microspheres) for lighter weight. Sandwich construction is used extensively on modern aircraft and boats as well as in applications such as cargo containers and modular buildings.

Fabrication methods

The most basic fabrication method for composites is hand layup, which typically consists of laying dry plies or prepreg plies by hand onto a tool to form a laminate stack. Resin is applied to the dry plies after layup is complete (e.g. by means of resin infusion) or, in a variation known as wet layup, each ply is coated with resin and "debulked" or compacted before the next ply is placed. Several curing methods are available. The most basic is simply to allow cure to occur at room temperature. Cure can be accelerated, however, by applying heat, typically with an oven, and pressure, by means of a vacuum. For the latter, a vacuum bag, with breather assemblies, is placed over the layup and attached to the tool, then evacuated before cure. The vacuum bagging process consolidates the plies of material and significantly reduces voids or off-gassing that occur as the matrix progresses through its chemical curing stages.

Many high-performance parts require both heat and high consolidation pressure to cure, conditions that require the use of an autoclave. Autoclaves, generally, are expensive to buy and operate. Manufacturers equipped with autoclaves usually cure a number of parts simultaneously. Computer systems often monitor and control autoclave temperatures, pressure, vacuum and inert atmosphere, which allows for unattended and/or remote supervision of the cure process and maximizes efficient use of the technique.

When heat is required for cure, the part temperature is "ramped up" in small increments, maintained at cure level for a specified period of time, then "ramped down" to room temperature, to avoid part distortion or warp caused by uneven expansion and contraction. When this curing cycle is complete and after parts are demolded, some parts go through a secondary freestanding post cure, during which they are subjected for a specific period of time to a temperature higher than that of the initial cure, to enhance crosslink density.

Electron-beam (e-beam) curing holds promise as an efficient curing method for thin laminates. In e-beam curing, the composite layup is exposed to a stream of electrons that provide ionizing radiation, causing polymerization and crosslinking in radiation-sensitive resins. X-ray and microwave curing technologies work in a similar manner. A fourth alternative, ultraviolet (UV) curing, involves the use of UV radiation to activate a photoinitiator added to a thermoset resin, which, when activated, sets off a crosslinking reaction. UV curing requires a light-permeable resin and reinforcements.

Open molding

Open contact molding in one-sided molds is a low-cost, common process for making fiberglass composite products. Typically used for boat hulls and decks, RV components, truck cabs and fenders, spas, bathtubs, shower stalls and other relatively large, noncomplex shapes, open molding involves either sprayup or hand layup. In an open-mold sprayup application, the mold is first treated with mold release. If a gel coat is used, it is typically sprayed into the mold after the mold release has been applied. The gel coat is then cured and the mold is ready for fabrication to begin. In the sprayup process, catalyzed resin (viscosity from 500 to 1,000 cps) and glass fiber are sprayed into the mold using a chopper gun, which chops continuous fiber into short lengths, then blows the short fibers directly into the sprayed resin stream so that both materials are applied simultaneously. To reduce volatile organic compounds (VOC) emissions, piston-pump-activated, non-atomizing spray guns and fluid impingement spray heads can be used to dispense gel coats and resins in larger droplets at low pressure. Another option. is roller impregnators, which pump resin into a roller similar to a paint roller.

In the final steps of the spray up process, workers compact the laminate by hand with rollers. Wood, foam or other core material may then be added, and a second spray up layer imbeds the core between the laminate skins. The part is then cured, cooled and de-molded.

Hand lay up and spray up methods are often used in tandem to reduce labor. For example, fabric might first be placed in an area exposed to high stress; then, a spray gun might be used to apply chopped glass and resin to build up the rest of the laminate. Balsa or foam cores may be inserted between an the laminate layers in either process. Typical glass fiber volume is 15 percent with spray up and 25 percent with hand lay up

Resin transfer molding processes

Ever-increasing demand for faster production rates has pressed the industry to replace hand lay up with alternative fabrication processes and has encouraged fabricators to automate those processes wherever possible.

A common alternative is resin transfer molding (RTM), sometimes referred to as liquid molding. RTM is a fairly simple process: It begins with a two-part, matched, closed mold, made of metal or composite material. Dry reinforcement - a preform - is placed into the mold, and the mold is closed. Resin and catalyst are metered and mixed in dispenser equipment, then pumped into the mold under low pressure through injection ports, following predesigned paths through the preform. Extremely low-viscosity resin is used in RTM applications for thick parts, to permeate preforms quickly and evenly before cure. Both mold and resin can be heated, as necessary, for particular applications. RTM produces parts that do not need to be autoclaved. However, once cured and de-molded., a part destined for a high temperature application usually undergoes post cure. Most RTM applications use a two-part epoxy formulation. The two parts are mixed just before they are injected into the preform. Bismaleimide and polyamide resins also are available in RTM formulations.

The benefits of RTM are impressive. Generally, dry preforms for RTM are less expensive than prepreg material and can be stored at room temperature. The process can produce thick, near net shaped parts, eliminating most post-fabrication work. It also yields dimensionally accurate complex parts with good surface detail and delivers a smooth surface finish on all exposed surfaces. It is possible to place inserts inside the preform before the mold is closed, allowing the RTM process to accommodate core materials and integrate "molded in" fittings and other hardware into the part structure during the molding process. Moreover, void content on RTM'd parts is very low, measuring in the 0 to 2 percent range. Finally, RTM significantly cuts manufacturing cycle times and can be adapted for use as one stage in an automated, repeatable manufacturing process for even greater efficiency, reducing cycle time from what can be several days required for hand lay up to just hours - or even minutes.

In contrast to RTM, where resin and catalyst are premixed prior to injection into the mold, reaction injection molding (RIM) injects a rapid-cure resin and a catalyst into the mold in two separate streams; mixing and the resultant chemical reaction both occur in the mold instead of in the dispensing head. The automotive industry is increasingly combining structural RIM (SRlM) with rapid pre-forming methods to fabricate structural parts that don't require a Class A finish. Where, previously, continuous or chopped-strand mat reinforcements were hand layed into the mold before injection of a polyurethane resin, recent developments have eliminated the labor intensive manual placement of mat. Programmable robots spray a chopped fiberglass/binder combination onto a vacuum-equipped preform screen or mold. Robotic spray up can be directed to control fiber orientation. General Motors successfully adapted this type of pre-forming and SRIM technology several years ago, to manufacture a 2m/6.5' long composite pickup bed box as an optional replacement for the steel box on its full-size 2001 Chevrolet Silverado truck. The box was molded of 50 percent glass-filled polyurethane, using robotic spray up of a single, directed fiber preform and a heat-activated polyester thermoset binder material.

A related technology, dry fiber placement, combines stitched preform and RTM. Fiber volumes of up to 68 percent are possible, and automated controls ensure low voids and consistent preform reproduction, without the need for trimming.

Vacuum-assisted resin transfer molding (VARTM) refers to a variety of related processes, which represent the fastest growing new molding technology. VARTM-type processes and standard RTM differ in that VARTM draws resin into a preform through use of a vacuum rather than positive pressure. VARTM does not require high heat or pressure. For that reason, VARTM operates with low-cost tooling, making it possible to inexpensively produce large, complex parts in one shot.

In the VARTM process, fiber reinforcements are placed in a one-sided mold, and a cover (rigid or flexible) is placed over the top to form a vacuum-tight seal. The resin typically enters the structure through strategically placed ports. It is drawn by vacuum through the reinforcements by means of a series of designed-in channels that facilitate "wetout" of the fibers. Fiber content in the finished part can run as high as 70 percent. Current applications include marine, ground transportation and infrastructure parts. Resin film infusion (RFI) is a hybrid process in which a dry preform is placed in a mold on top of a layer or layers of high-viscosity resin film. Under applied heat, vacuum and pressure, the resin is drawn up through the thickness of the preform in one direction, resulting in uniform resin distribution, even with high-viscosity, toughened resins.

High-volume molding methods

Compression molding is a high-volume process that employs expensive but very durable steel dies. It is an appropriate choice when production quantities exceed 10,000 parts. As many as 200,000 parts can be turned out on a set of forged steel dies, using sheet molding compound (SMC), a composite sheet material made by sandwiching chopped fiberglass between two layers of thick resin paste. To form the sheet, the resin paste transfers from a metering device onto a moving film carrier. Chopped glass fibers drop onto the paste, and a second film carrier places another layer of resin on top of the glass. Rollers compact the sheet to saturate the glass with resin and squeeze out entrapped air. The resin paste initially is the consistency of molasses (between 20,000 and 40,000 cps); over a three- to five-day period, its viscosity increases and the sheet becomes leather-like (about 25 million cps), ideal for molding.

When the SMC is ready for molding, it is cut into smaller sheets and the charge pattern (ply schedule) is assembled on a heated mold (121degrees C to 262degrees C/250degrees F to 325degrees F). The mold is closed and clamped, and 500 to 2,500 psi pressure is applied. Material viscosity drops and the SMC flows to fill the mold cavity. After cure, the mold is opened and the part is removed manually or by integral ejector pins.

A typical low-profile (less than 0.05 percent shrinkage) SMC formulation for a Class A finish consists, by weight, of 25 percent polyester resin, 25 percent chopped glass, 45 percent fillers and 5 percent additives. Fiberglass thermoset SMC cures in 30 to 150 seconds and overall cycle time can be as low as 60 seconds. Other grades of SMC include low-density, flexible and pigmented formulations. Major SMC markets worldwide include the high-volume electrical and transportation industries. Low pressure SMC formulations now on the market offer open molders a low-capital investment entry into closed mold processing with near-zero VOC emissions and the potential for very high-quality surface finish. Automakers are exploring carbon-fiber-reinforced SMC, hoping to take advantage of carbon's high strength and stiffness-to-weight ratio in exterior body panels and other parts. Newer, toughened SMC formulations help prevent micro cracking, a phenomenon that can lead to paint "pops" during the painting process (surface craters caused by "outgassing", the release of gasses trapped in the micro cracks during oven cure).

Injection molding is a fast, high-volume, low-pressure, closed process using, most commonly, filled thermoplastics, such as nylon with chopped glass fiber. In the past 20 years, however, automated injection molding of bulk molding compound (BMC) has taken over some markets previously held by thermoplastic and metal casting manufacturers. They include electrical and automotive components, appliance housings and motor housings, to name a few. BMC is a low-profile (nearly zero shrinkage) formulation of a thermoset resin mix, containing between 15 percent and 20 percent chopped fiberglass. After initial mixing, BMC is about the consistency of sticky bread dough, but it loses viscosity and liquefies when heated to near its curing temperature, allowing it to be injection molded. The use of BMC must be justified by production volume, because the cost of the molds and presses is relatively high.

A ram- or screw-type plunger forces a metered shot through a heated barrel and injects it (at 5,000 to 12,000 psi) into a closed, heated mold. In the mold, the liquefied BMC flows easily along runner channels and into the forming cavities. Heat build-up is carefully controlled to minimize curing time. After cure and ejection, parts need only minimal finishing. Injection speeds are typically one to five seconds, and nearly 2,000 small parts can be produced per hour in a multiple-cavity mold.

Parts with thick cross sections can be compression-molded or transfer-molded. Transfer molding is a closed-mold process wherein a measured charge of BMC is placed in a pot with runners leading to the mold cavities. A plunger forces the material into the cavities, where the product cures under heat and pressure.

Filament winding

Filament winding is a continuous fabrication method that can be highly automated and repeatable with relatively low material costs. A long, cylindrical tool called a mandrel is suspended horizontally between end supports, while the "head" - the fiber application instrument - moves back and forth along the length of a rotating mandrel, placing fiber onto the tool in a predetermined configuration. Computer-controlled filament winding machines are available, equipped with from 2 to 12 axes of motion.

In most applications, the filament winding apparatus passes the fiber material through a resin "bath," just before the material touches the mandrel. This is called "wet winding." Tow preg - continuous fiber pre-impregnated with resin also can be wound, eliminating the need for an on-site resin bath. In a slightly different process, fiber is wound without resin ("dry winding"). The dry shape is then removed and used as a preform in another molding process, such as resin transfer molding (RTM).

Following oven or autoclave curing, the mandrel may remain in place as part of the wound component or it may be removed. One-piece cylindrical or tapered mandrels, usually of simple shape, are pulled out of the part with mandrel extraction equipment. Some mandrels, particularly in more complex parts, are made of soluble material that can be washed out of the part. Others are collapsible or built from several parts that allow it to be disassembled and removed in smaller pieces. Filament winding manufacturers often "tweak" or slightly modify off-the-shelf resin to meet application requirements, and some develop their own resins.

In thermoplastics winding, material is prepregged, therefore a resin bath is unnecessary. Material is heated as it is wound onto the mandrel - a process known as curing "on the fly" or "in situ consolidation." The heated prepreg is layed down, compacted, consolidated and cooled in a continuous operation. Thermoplastic prepregs eliminate autoclave curing (cutting costs and size limitations), reduce raw material costs and can be reprocessed to correct flaws.

Filament winding yields parts with exceptional circumferential or "hoop" strength. The highest-volume application of filament winding is golf club shafts. Fishing rods, pipe, pressure vessels and other cylindrical parts comprise the bulk of the remaining business.

Pultrusion

Pultrusion has been used for decades with glass fiber and polyester resins, but in the last ten years the process also has found applications in the advanced composites industry. In this relatively simple, low-cost, continuous process, the reinforcing fiber (usually roving, tow or continuous mat) is typically pulled through a heated resin bath, then formed into specific shapes as it passes through one or more forming guides or bushings. The material then moves through a lengthy heated die, where it takes its net shape and cures. Further downstream, after cooling, the resulting profile is cut to desired length. Pultrusion yields smooth finished parts that do not require post-processing.

A wide range of solid and hollow profiles are pultruded, and the process can be custom-tailored to fit specific applications. Pultruders are currently developing ways to create variable cross-sectional shapes by manipulating resin chemistry temperature and die characteristics. New pultrusion resins, such as polyurethanes are yielding tougher parts.

Tube rolling

Tube rolling is a long-standing composites manufacturing process for producing finite-length tubes and rods. It is particularly applicable to small-diameter cylindrical or tapered tubes in lengths up to 6m/20 ft. Tubing diameters as large as 165 mm/6 inches can be rolled efficiently. Typically, a tacky prepreg fabric or unidirectional tape is used depending on the part. The material is precut in patterns designed to achieve the requisite ply schedule and fiber architecture for the application. The pattern pieces are laid out on a flat surface and a mandrel is rolled over each one under applied pressure, which compacts and debulks the material. When rolling a tapered mandrel - for a fishing rod, as an example - only the first row of longitudinal fibers falls on the true 0degrees axis. To impart bending strength to the tube, the fibers must be continuously reoriented by repositioning the pattern pieces at regular intervals.

Fiber placement and tape laying

The fiber placement process automatically places multiple individual pre-impregnated tows onto a mandrel at high speed, using a numerically controlled placement head to dispense, clamp, cut and restart each tow during placement. Minimum cut length (the shortest tow length a machine can lay down) is the essential ply-shape determinant. The fiber placement heads can be attached to a 5-axis gantry or retrofitted to a filament winder or delivered as a turnkey custom system. Machines are available with dual mandrel stations to increase productivity. Advantages of fiber place~ ment fabrication include speed, reduced material scrap and labor costs, parts consolidation and improved part-to-part uniformity. The process is employed when producing large thermoset parts with complex shapes.

Tape laying is an even speedier auto~ mated process in which prepregged tape, rather than single tows, is laid down con~ continuously to form parts. It is often used for parts with highly complex contours or angles. Tape lay up is versatile, allowing breaks in the process and easy direction changes. Capital expenditures for computer-driven, automated equipment can be significant, however. Suitable for both simple and complex parts, tape laying is the current method of choice for wing skin panels on the F-22 Raptor fighter jet.

Centrifugal casting

Centrifugal casting of pipe from 25 mm to 355 mm (1 inch to 14 inches) in diameter is an alternative to filament winding for high-performance, corrosion-resistant service. In cast pipe, 0degrees /90degrees woven fiberglass provides both longitudinal and hoop strength throughout the pipe wall and yields greater strength at equal wall thickness compared to multi axial, fiberglass-wound pipe. In the casting process, epoxy or vinyl ester resin is injected into a cylindrical mold that is spinning at 150 Gs of centrifugal force, causing the resin to permeate woven fabric pre-placed on the mold's interior surface. The force concentrates resin near the mold surface, creating a smooth finish on the pipe exterior, and excess resin pumped into the mold creates a resin-rich corrosion and abrasion-resistant interior liner.

Extrusion

Fiber-reinforced thermoplastic shapes are now being extruded, as well. Breakthrough materials and process technologies have been developed featuring long-fiber glass-reinforced thermoplastic (ABS, PVC or polypropylene) composites. The processes provide profiles that offer a tough, low-cost alternative to wood, metal and injection-molded plastic parts used in office furniture, appliances, semi-trailers and sporting goods. A huge emerging market is extruded thermoplastic/wood flour composites, used to make look-alike replacements for traditional wood decking, siding, fencing and window and door frames.

Tooling considerations

The molds used for forming composites, also known as tools, can be made from virtually any material. For parts cured at ambient or low temperature, or for prototyping, where tight control of dimensional accuracy isn't required, materials such as fiberglass, high-density foams, machinable epoxy "boards" or even clay and wood/plaster models are often suitable. Tooling costs and complexity increase as part performance requirements and production numbers go up. High-rate production tools are generally made of robust metals that can stand up to repeated cycles and maintain good finish and dimensional accuracy.

Molds for high-performance composite parts can be made from carbon fiber/epoxy, monolithic graphite, castable graphite, ceramics or metals. Each material offers unique capabilities and drawbacks. Sometimes called "hard" tooling, ceramic and metal molds are relatively heavy but able to withstand many thousands of production cycles. Composite, or "soft," tooling is I more vulnerable to wear and typically finds service in low-volume production.

Steel and aluminum are less expensive and more readily available than high-performance metal alloys, but during autoclave cure, the mismatch in coefficient of thermal expansion (CTE) often is too extreme for compatibility with most advanced composite parts. Higher-priced metal alloys such as Invar offer closer CTE matches.

Composite tools made from traditional tooling prepregs offer several advantages, among them a CTE close to the part CTE, which maintains dimensional integrity during cure. Plus, the cost of several tools made with composite materials can be less than the cost of a single hard tool, for relatively short-run applications. As with other high-temperature composite forms, composite tools can be cured in an autoclave or oven, or by integral heating, in which individual heating elements are placed inside the tool.

Commercialized tooling design software is reducing the time it takes to model and manufacture a tool including back-up structure - in some cases, by 80 percent. New inspection systems give tooling suppliers and fabricators a way to verify a tool's dimensional accuracy prior to and during production. In recent years, a variety of low-cost modeling materials that maintain dimensional stability at higher temperatures have made inroads into traditional tool making.

Airtech International (Huntington Beach, Calf., U.s.A.) recently introduced a combination of fabrics and resins called Tool fusion, for vacuum-assisted resill transfer molded (VARTM) tools for aero space-grade parts, with service temperatures in the > 150degrees C/300degrees F range.

Rigid carbon foams made from petroleum-based mesophase pitch or carbonization of polymer materials, also provide a cost-effective alternative to traditional tool structures. For example Touchstone Research Laboratory Ltd's (Triadelphia, W. Va., U.S.A.) CFOAM has sufficient strength to endure autoclave pressures and retains dimensional stability even at temperatures in excess of 260degrees C/500degrees F.

SprayShape 2055 from CASS Polymers (Madison Heights, MI, U.S.A.) is a new material suitable for models, plugs or low-temperature prototyping molds. The epoxy-based paste has the same chemistry and characteristics as CASS' TCC solid tooling planks, but can be sprayed up to 12.7-mm/O.50-inch thick on vertical surfaces, without sag. Coastal Enterprises (Orange, CA, U.S.A.) offers Precision Board High Temp (PBHT), a new higher-temperature urethane tooling board with a CTE similar to aluminum, based on autoclave testing at 163degrees C/325degrees F and 100 psi. Castable TEPIC high-temperature, high strength modified polyisocyanurate foam distributed by Scion Industries (Ft. Collins, CO., U.S.A.) can produce one-piece tools that retain strength and dimensional accuracy in an autoclave up to 204degrees C/400degrees F and 100 psi.

No matter what the tooling material, the importance of mold release agents cannot be over emphasized. Releases create a barrier between the mold and the part, preventing part/mold adhesion and facilitating part removal. For open molding, most releases today are waxes or they are based on polymer chemistry. Most of the latter are polymers in solvent-based carrier solutions, such as an aliphatic hydrocarbon blend. Some manufacturers prefer naptha-based releases, which have longer shelf life and faster evaporation rates and are considered to be less damaging to composite tool surfaces. Increasingly strict environmental regulations have encouraged development of water-based release agents, which do not emit volatile organic compounds (VOC's) and clean up more easily with less skin irritation.

Semi-permanent polymer mold release systems enable multiple parts to be molded and released with a single application, in contrast to traditional paste waxes that must be reapplied for each part. Semi permanents have been specifically formulated to meet the needs of resin transfer molding (RTM) and other closed mold processes, which are preferred for better control over VOC emissions. Internal release agents, added to the resin or gel coat and used instead of or in addition to external agents on the mold surface, further reduce emissions, and have negligible effects on a part's physical properties and surface finish.

Internal release formulations are required for pultrusion processing, because the the part is pulled continuously through the die, allowing no opportunity for intermittent application of external releases to the die surface.

Safety/environmental concerns

Fabricators and OEMs must address health, safety and environmental concerns when using composite materials. Their methods for maintaining a safe workplace include periodic training, adherence to detailed handling procedures, maintenance of current toxicity information, use of protective equipment (gloves, aprons, dust-control systems and respirators) and development of company monitoring policies. Both suppliers and OEMs are working to reduce emissions of highly volatile organic compounds (VOC's) by reformulating resins and prepregs and switching to water-dispersible cleaning agents.

The U.S. Environmental Protection Agency (EPA) has continued to strengthen its requirements to meet the mandates of the Clean Air Act Amendments, passed by Congress in 1990. Specifically, the agency's goal is to reduce the emission of hazardous air pollutants (HAPs), approximately 180 volatile chemicals considered to pose health risks. Some of the compounds used in resins and released during cure contain HAPs. In early 2003, the EPA enacted regulations specifically for the reinforced plastic composites industry, which require emission controls using maximum achievable control technology, or MACT.

Repair considerations

As more composite materials find a place on aircraft, boats, bridges and hundreds of other applications where part replacement is difficult and expensive, OEM engineers are considering the reparability of structural and secondary composite components during the initial design phase. On Boeing's 777 passenger aircraft, for example, engineers originally planned a 15m/49-ft-Iong, single-piece flap but chose instead a segmented flap that facilitates autoclave repair by incorporating shorter, more easily handled components. Designers often pre design thicker laminate in areas where damage typically occurs to permit later bolted repairs.

Standardization of repair materials and procedures is reducing repair materials inventory and cost, ensuring consistent quality, and bringing down the high cost of qualifying and testing materials for particular aircraft programs, as well. The Commercial Aircraft Composite Repair Committee (CACRC), founded in 1991, is a joint-action group of airframes, operators and fabricators dedicated to the creation of global standards for composite repair procedures, training and materials. Administered by the Society of Automotive Engineers' (SAE) Aerospace Materials Div., the group has sought since 1997 to standardize specifications for standard- and intermediate-modulus carbon fibers in structural aerospace applications.

Other composite components that require repair include heavy truck front ends and other automotive and marine products. Whether damage is minor or extensive, training and specific repair materials are available. A number of materials suppliers provide kits containing low- or room-temperature curing adhesives and potting compounds formulated for onsite repair, along with dry fiber or prepreg and vacuum-bagging materials. At least a dozen private U.S. training companies offer from one- to ten-day courses in composite repair.

Future composites engineers

Building a composite part to the same specifications provided for an existing wood or metal is rarely successful. In recognition of this reality, an increasing number of colleges and universities offer composite materials and design courses with significant curricula within mechanical, chemical and civil engineering degree programs. Educators have networked progressively with suppliers and OEMs, co-sponsoring projects that give students hands-on experience in materials evaluation and procurement as well as part design and fabrication. These efforts include student design competitions that provide real-world experience with traditional and alternative materials. Aspiring engineers thus are encouraged to view composites as viable material choices.

A multitude of markets

The outlook for the composites industry remains healthy over the long term, with suppliers expressing cautious optimism about the next 12 months. According to figures compiled by the Freedonia Group Inc. (Cleveland, OH.), demand for reinforced plastics in the U.S., for example, will increase at an annual rate of 2.5 percent (down half a percentage point from its prediction last year) to more than 4 billion lb by the year 2007, a market value of $6.5 billion (USD). During that period, manufacturers of composites are expected to consume 2.8 billion lb of resin and 1.3 billion lb of reinforcements. However, resin prices increased significantly throughout 2004, as manufacturers sought to relieve pressures from an unprecedented spike in the price of crude oil. Throughout 2004, however, economies around the world picked up steam, and the composites industry was a direct beneficiary.

Boat building - Durable fiberglass composites continue to replace wood and aluminum in boat hulls and superstructures, and the overall U.S. marine market picked up again in for 2004, promising, in the near term, a generally stable market. Open molding will continue to give way to emission-reducing processes such as vacuum-assisted resin transfer molding (VARTM). Further, today's prefabricated FRP stringers and complete boat "kits" comprised of structural sandwich panels represent not only environmentally sound building approaches, but significant labor/cost reductions, as well.

Automotive and transportation - Composites continue to be attractive replacements for steel in automotive body panels, structural components and under-the-hood parts, in part because sheet molding compound (SMC) compounders and their resin suppliers recently formulated tougher paint "pop-free" SMC. Compounders also an developing SMC formulations compatible with powder-coat finishes, which are under consideration by some automakers as a more environmentally friendly alternative to the oven-baked paints currently in use.

While automakers are expected to make even greater use of SMC and other glass-reinforced and filled polymers to meet increasing demand for fuel economy, carbon fiber composites have become a real selling point in the high-end sports car and aftermarket segments. Most notably, a carbon fiber hood on the 2004 Chevrolet Corvette ZO6 Commemorative Edition became the first carbon fiber outer body panel to appear on a North American production automobile. The Porsche Carrera GT and Mercedes SLR McLaren have incorporated considerable quantities of carbon not only in the body panels, but also in the structure. In the Carrera GT, carbon composite structural members include the cockpit and engine cradle.

In 2004, the automotive aftermarket's retail value was estimated by the Specialty Equipment Market Ass. (SEMA) at nearly $30 billion (USD), driven, in part, by predominately youthful auto enthusiasts in the burgeoning "tuner" market. The composite material range in aftermarket parts is enormous, from filled thermoplastics to carbon/epoxy prepregs, as hundreds of small to medium-sized composite fabricators turn out composite hoods, spoilers, air dams, bumpers, fenders, side skirts, step-assists, grilles, dashboards and tonneau covers (see CT August 2004, p. 38). Despite carbon's cost, parts reinforced with carbon fabrics (many sold unpainted to display the eye-catching "look" of the reinforcement fabric) have been hot items.

Corrosion-resistant applications - The direct cost of metallic corrosion in the U.S. alone is estimated at $300 billion (USD) per year by CC Technologies Laboratories Inc. (Dublin, OH) with support from NACE International (National Association of Corrosion Engineers). Every sector of the economy has significant corrosion costs, including water and sewer piping systems, highways and bridges, electrical utilities and industrial plants. Composite materials are ideally suited to replace metallic structures, because of their excellent corrosion resistance. Composite piping, tanks, scrubbers and pressure vessels have expanded into industrial sectors, including the pulp/paper and electronics industries, because of their virtually maintenance-free performance.

Cured-in-place pipe (CIPP) rehabilitation technology is a burgeoning market that eliminates the disruptive digging that is otherwise required to repair underground water/wastewater piping. Currently several CIPP processes use non woven glass/polyester mat that, when wet out with resin, bond with the inside surface of existing pipe, forming a tough, seamless, corrosion-resistant liner.

Corrosion-resistant composites are making significant inroads into the huge and growing global water and wastewater market, estimated at more than $45 billion a year. Equipment used in water and wastewater treatment plants must withstand sustained exposure to highly corrosive chemicals, combined with high heat, humidity and sunlight. Composite equipment has been in continuous service for more than 30 years, meeting rigorous wastewater processing requirements throughout the world and holding great promise for initial installations in developing nations.

Construction - Composite materials continue to play an increasingly significant role in construction, primarily in residential housing applications. The housing market remained strong in 2004, indicating continued business for the solid surface and bath ware composite segments of the industry. A huge growing market, estimated to reach $2 billion (USD) by 2007, is wood-filled thermoplastic lumber, used for outdoor decking, house siding, fencing and window and door frames, among other products.

Civil infrastructure - More than 250,000 deficient or obsolete structures, such as bridges and parking garages, need repair, retrofit or replacement in the U.S. alone. Glass, glass/aramid hybrids and carbon fibers, used with epoxy resin, continue to find application as cost-effective column-wrapping and jacketing systems for seismic and structural upgrading. Fiberglass composites are finding niche applications in areas such as stay-in-place concrete forms, reinforcing rebar, bridge decks, wind fairing and enclosures, as well as entire bridges. Exhibiting corrosion resistance, light weight (approximately one-fifth the weight of steel), high strength and ease of installation, composite materials are gradually being accepted as alternative to traditional materials to reduce dead load and extend structure life.

Governments and engineering associations worldwide are cooperating to standardize workable international design parameters, and the composites industry is forging critical alliances with the civil engineering community and associations such as the American Concrete Institute (ACI) and CERF (Civil Engineering Research Foundation). Standards development continues for civil composites applications.

Corrosion in marine environments has opened opportunities for composites in waterfront applications, such as marine fenders, pilings and outfall structures. The U.S. Army Corps of Engineer estimates that about $2 billion is spent each year maintaining wooden pilings damaged by corrosion, termites and marine organisms. Several types of composite applications now address this problem, including large mono piles made with vacuum-assisted resin transfer molding (VARTM), hybrid glass/carbon pilings and supports for large outfalls, and pultruded composite sheet piling for marine construction.

Oil and gas - The vast offshore oil and gas industry is increasingly receptive to the use of both fiberglass and advanced composites. Miles of piping and other composite components are already in place on platforms and rigs, for fire water, gratings, housing modules and other topside facilities service. Several manufacturers are working with major oil companies to develop composite production systems, including riser pipe for deepwater exploration and production.

Sports and recreation - Composites are now found in products used for seven of the ten most popular outdoor sports and recreational activities. Glass reinforced composites continue to replace wood and metal in fishing rods, tennis racquets, spars/shafts for kayak paddles, windsurfing masts, hockey sticks, kites and bicycle handlebars, as well as in niche applications such as fairings for recumbent bikes. Sporting goods consume at least 11 million pounds of carbon fiber annually, worldwide, according to one carbon fiber producer. Golf shaft makers in particular represent a large segment of the market, producing roll-wrapped and filament-wound shafts with tailored properties for their "tuned" club sets.

Aerospace - Military and commercial airplane manufacturers are the major end-users of advanced composite materials. Beginning in 2004, the market for materials surged as production began on Airbus Industries' (Toulouse, France) double-decked, 555-passenger A380 jetliner. By mid-October 2004, Airbus had secured firm orders for 129 A380 aircraft, from 11 customers. Airbus has started production of the first articles of the jumbo dual-aisle, triple deck airplane, scheduled for flight testing in early 2005, and entry into service in 2006. In addition, Jet Blue Airways recently ordered 123 new Airbus A320 aircraft, with options for 50 more. Now close on its heels, The Boeing Co's smaller, 225-seat 7E7 Dream liner, expected to take to the air for the first time as early as 2008, was formally launched in June 2004, with a firm order for 50 of the planes from All Nippon Airways (Japan). Both planes make greater use of composites than any previous commercial aircraft. Existing projections call for nearly 50 percent of the 7E7's total airframe weight to be composite - compared to about 25 percent for the A380.

Wind and power - Wind power is the world's fasted growing energy source and the composites industry's fastest growing fiber-reinforced polymer (FRP) application. The European Union still leads the way in this market, with the U.S. running a distant second. Together they accounted for 88 percent of the new capacity in 2003. Petroleum poor European Union nations, having long embraced the concept of "green energy," have installed 67 percent of the world's new wind turbines. Germany leads the 15 European nations, producing 10 percent of its total electrical power from wind farms that generate almost 15,000 MW, the highest of any nation in the world. Though smaller in megawatts of power output, Denmark generates over 15 percent of its electricity with wind power. In the U.S., total wind power capacity reached 6,374 MW in January 2004 The U.S. operates large-scale turbines in wind farms located in 25 states, with projects in the works in several others. While U.S. efforts stalled later in 2004, due to the Dec. 31, 2003 expiration of a U.S. Congress' Wind Energy Tax Credit, the credit's extension in September 2004 (through 2005) is now expected by the American Wind Energy Ass. (A WEA) to enable about $2 billion (USD) in wind energy projects to proceed to completion. The most significant area of new growth, however, is expected in India. That nation installed 408 MW in 2003, the largest expansion of any nation outside the EU and the U.S., with an estimated 45,000 MW of potential wind energy generating capacity. The World Energy Council has estimated that wind energy capacity worldwide may total as much as 474,000 MW by the year 2020, and the A WEA is lobbying for 100,000 MW in the U.S. by 2020.

Wind turbines, onshore and offshore, convert wind energy to electrical power with the aid of giant rotors, constructed with composite blades that, until recently, were manufactured almost exclusively from glass-reinforced composites. To reduce the cost of energy from wind turbines to levels competitive with coal- and gas-fired electricity production, producers have raised tower height to place turbines in stronger winds and lengthened blades to capture more wind. To date, the largest installed rotor is 80m/262.5 ft in diameter. As this strategy reaches the upper limits of practicality, designers are now exploring the use of carbon fiber as a means to further push the design envelope and decrease the cost of energy. Compared to conventional all-fiberglass designs, composites that replace some of the glass with carbon fiber reinforcements can produce the same blade using less fiber and resin, while increasing blade stiffness, improving aerodynamics and decreasing the loads imposed by the blades on the tower and hub. A design that incorporates carbon fiber also can make power input from the blades more predictable: Two teams are currently studying non symmetric carbon fiber reinforced laminates with anisotropic properties that enable the blade to twist along its longitudinal axis in high winds, giving the blade a lower angle of attack into the wind, which, in turn, reduces the bending load.

Fuel Cells - Fuel cell technologies of several types offer a "clean" means to convert hydrogen to electric power systems. Due to the conductivity, corrosion resistance, dimensional stability and flame retardant, vinyl-ester-based bulk molding compounds with carbon fiber reinforcement have already been selected in at least one commercially available stationary unit.

Other Markets - space satellite and related communications industries, propellant tanks, heat sinks, optical benches, armor systems, luggage containers, cargo containers, cockpit doors, UAV's and more.

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