Prepreg production processes

To fabricate continuous fiber-reinforced plastics that meet design specifications, the fibers should be uniformly distributed within the plastic matrix and, in most instances, all oriented in virtually the same direction. This section discusses several techniques (pul-trusion, filament winding, and prepreg production processes) by which useful products of these materials are manufactured. 

There is reasonable agreement with the viscosity data except that some deviations occur at long times. Use of this equation with mass- and heat-transfer equations for prepreg production is useful for optimizing processing conditions. 

In contrast to the planar reinforcement, the spatial reinforcement structures were produced in a discontinuous two-stage production process. In a first step, the fabric was coated with thermoset epoxy resin which remains in a so called and still shapeable b-stage . Afterwards, the prepreg-fabric was shaped with two moulds as shown in Fig. 6 (left). The moulds were placed in an oven and the fabrics were cured for 20 min at a temperature of about 180 C, Fig. 6 (right), resulting in an inherently stable reinforcement structure. 

Structil (Groupe SNPE), Vert le Petit, France—a subsidiary of SNPE, produces a range of prepreg products by hot melt process. Also has eight pultrusion machines. In 1998, Grafil Inc. purchased a 20% share. 

In 1968, Morgan joined a team at Courtaulds to manufacture carbon fibers and subsequently set up and managed a control laboratory to monitor production. He later became involved with production aspects relating to carbon fiber prepreg and pultrusion. Morgan took on the additional role of chief quality inspector in 1976 and gained approval for the production processes to Defence Standard 05-24, the forerunner of BS 5750. In 1980, he was appointed to Courtauld s Carbon Fibres division board as director with technical responsibilities. 

Briefly describe pultrusion, filament winding, and prepreg production fabrication processes cite the advantages and disadvantages of each. 

The reaction product of 4,4 -bismaleimidodiphenylmethane and 4,4 -diaminophenylmethane, known as Kerimide 601 [9063-71-2] is prepolymerized to such an extent that the resulting prepolymer is soluble in aprotic solvents such as /V-methy1pyrro1idinone [872-50-4] dimethylformamide [68-12-2] and the like, and therefore can be processed via solution techniques to prepreg. Kerim ide 601 is mainly used in glass fabric laminates for electrical appHcations and became the industry standard for polyimide-based printed circuit boards (32). 

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Thus, the fiber is impregnated in the partially cured resin. Depending upon the assembly the fiber is usually unidirectional, but they can also be made bidirectional or some other combination. The process of fitting the prepreg into, generally onto, the mold is called layup. Generally a number of layers of prepreg are used. The lay-up may be done by hand, called hand lay-up, or done automatically, or by a combination of automatic and hand layup. As expected, hand lay-up is more costly but is essential where one-of-a-kind products are produced. 

Evolving from efforts [22] to use the best features of trial-and-error, process model, expert system, and expert model approaches, QPA [23-25] combines KBES traits with online dielectric, pressure, and temperature data to implement autoclave curing control. QPA combines extensive sensor data with KBES rules to determine control actions. These rules determine curing progress based upon process feedback, and implement control action. QPA adjusts production parameters on-line as such—within the limits of its heuristics—QPA can accommodate batch-to-batch prepreg variations. 

The product is processed to a condition where it is either tack-free or slightly tacky to aid in application to vertical or contoured substrates. These films may be in the form of unsupported sheet, or they may be reinforced with glass fabric, paper, or another reinforcing medium. These supported films are sometimes referred to as prepreg. 

One of the most often used production procedures for fabricating a high-performance structural laminate is the Autoclave/Vacuum Degassing (AC/VD) laminating process. In this process, individual prepreg plies are laid up in a prescribed orientation to form a laminate. The laminate is laid against a smooth tool surface and covered with successive layers of glass bleeder fabric, Mylar or Teflon sheets, and finally a vacuum... 

This process is a take-off from compression molding that uses solid material male and female matching mold halves. This unique process uses a precision-made, solid shaped heated cavity and a flexible plunger that is usually made of hard rubber or TS polyurethane. This two-part system can be mounted in a press, either hydraulic or air-actuated. Rather excellent product qualities are possible at fairly low production rates. The reinforcement can be positioned in the cavity and the liquid TS resin is poured on it. Also used are prepregs, BMC, and SMC. 

Shown in Figure 10 are the rheological properties of the prepreg and the neat matrix resin after aging for 21 and 60 days at room temperature. The viscosity determinations, run at 1.5 Hz, were made using a process cycle typical of a production shop. 

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