Preimpregnated tape

Applications. Boron fibers are used as unidirectional reinforcement for epoxy composites in the form of preimpregnated tape. The material is used extensively, mostly in fixed and rotary wing military aircrafts for horizontal and vertical stabilizers, mdders, longerons, wing doublers, and rotors. They are also used in sporting goods. Another application is as reinforcement for metal matrix composites, in the form of an array of fibers pressed between metal foils, the metal being aluminum in most applications. 

In fiber placement, a moving head is mounted to a multidegree of fieedom carriage. The fiber placement head is designed to cut and place each tow individually. The head may also include a controlled heat source and compaction roller for in situ consolidation. Tow placement with in situ consolidation has made it possible to place preimpregnated tape along nongeodesic paths, manufacture parts with concave sections, and to locate ply dropoffs precisely. 

The ability to form complex shapes with low-pressure laminates has been utilized in fabricating helium dewars to the optimum shape for specific applications, A typical example is the cryostat assembly of Fig. 6, which is intended for use as an airborne geophysical exploration device.Experience has shown that leakage problems are minimized when a wet layup is used with glass-cloth reinforcement of the epoxy. Attempts to fabricate dewars from preimpregnated tape with an autoclave cure have been less successful, probably because of the many internal joints that provide potential leak paths. 

The thermoplastics, PPS (polyphenylene sulphide) and PAS (polyaryl sulphone), are both manufactured by Phillips Petroleum. The reinforcement is an unspecified E-glass. Manufacture was achieved by layirig-up preimpregnated tape. 

To overcome the drawbacks of preimpregnated tape or film stacking, intermediate fibers for continuous fiber-reinforced thermoplastic composites have been developed. Intermediate fibers have flexibility and are developed for textile appH-cations. As shown in Figure 10.14, the powder-impregnated yarn contains fibers impregnated with fine thermoplastic particles [12-16]. The incorporation of the matrix powder into the reinforcement yarn is performed by the fluidized-bed... 

Process in whicli continuous strands of roving or roving tape are wound, at a specified pitch and tension, onto the outside surface of a mandrel. Roving is saturated with liquid resin or is preimpregnated with partially cured resin. Application of heat may be required to promote polymerization. 

Engineering thermoplastics have also been used in preimpregnated constructions. The thermoplastic is thoroughly dispersed as a continuous phase in glass, other resins, carbon fibers (qv), or other reinforcement. Articles can be produced from these constructions using thermoforming techniques. For example, the aerospace industry uses polyetheretherketone (PEEK) in woven carbon-fiber tapes (26). Experimental uses of other composite constructions have been reported (27) (see also COMPOSITE MATERIALS, POLYMER-MATRIX). 

The PEEK resin is marketed as neat or filled pellets for injection molding, as powder for coatings, or as preimpregnated fiber sheet and tapes. Applications include parts that are exposed to high temperature, radiation, or aggressive chemical environments. Aerospace and military uses are prominent. At present, polyamideimide (PAI) resin and poly(arylene sulfides) are the main competitors for applications requiring service temperatures of 280°C. At lower temperatures, polyethersulfones, amorphous nylons, and polyetherimides (PEI) can be considered. 

Fiber placement is basically a hybrid of filament winding and tape laying and is a continuous process for fabricating composite shapes, by laying thermoset or thermoplastic preimpregnated tows (in tow or slit tape form) onto a mandrel or tool having concave or convex surfaces. There is no limit to the fiber angle and tows can be added or removed as and when necessary. 

In addition to wet systems, where reinforcements are resin-coated during the process, more convenient prepregs are available that can be used for many applications. Suppliers assist in the selection of preimpregnated materials, which are available as unidirectional, woven, and nonwoven tape, tow, mat, and so forth. 

Nonreactive thermoplastic pultrusion utilizes completely polymerized plastics in various preprocessed states such as powder, granulates, filaments, or solutions. The use of preimpregnated fibers is advised due to short flow paths. These preimpregnated fibers can be fed into the pultruder as commingled yarns, thermoplastically coated yarns or tapes. Since impregnation is already done, no impregnation device is needed. Instead, due to the low thermal conductivity of the matrix material and its limited deterioration temperature. 

The basic structure of a tape-layer is a multi-axis gantry system holding and guiding the layer head, which can move up to 30 m/min. A tape-la5rlng machine can have up to ten axes [49]. The lay-up process is performed with preimpregnated rovings or tapes (normally... 

Filament Winding. Pipe is produced by machine-winding, under controlled tension and in predetermined patterns, of glass reinforcement— which may consist of continuous-filament strands, woven roving, or roving tape—onto the outside of a mandrel. The reinforcement may be saturated with a hquid resin or preimpregnated with partially cured resin. After the pipe has been formed and cured, the mandrel is removed. The dimension of the inside diameter is set by the mandrel that of the outside diameter by the thickness of the wall. 

Prepreg is the composite industry s term for continuous-fiber reinforcement preimpregnated with a polymer resin that is only partially cured. This material is delivered in tape form to the manufacturer, which then directly molds and fully cures the product without having to add any resin. It is probably the composite material form most widely used for structural applications. 

The insulation of the coil sides is built up as continuous tape isolation, i.e., both the straight sections of the coil and the core ends are wound with tape. The insulation consists of epoxy-impregnated mica glass-tape. Both the preimpregnated MICAREX system and the vacuum-pressme impregnated MICAPACT system satisfy the requirements for temperature class F (155°C). The insulation systems used are described in more detail in separate brochures. 

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