Prepregs fabrication

Prepreg. Fabric is impregnated with 25 percent of liquid resin and laid in the mold. To insure isotropic properties, or to maximize properties in a specific direction, successive layers of impregnated fabric are carefully oriented in different directions. The mold is closed, pressed, and heated till cured. Products made from such impregnated fabrics have much higher strength than simple random fiber reinforcements. 

Trim losses are negligible for SMC. Nonrecoverable raw material loss associated with prepreg fabrication and defective parts due mainly to poor material flow contributes about 4% and 3% respectively to the total material usage for this molding process. 

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. 

A cheaper alternative is the cold temperature hardening prepreg system. As opposed to heat-hardening prepregs, where the prepreg fabrication can take place at a different place and time than the manufacture of the ultimate component, in the cold temperature process the fabric or rovings are coated with the matrix at the point where the component itself is made. 

Courtaulds Performance Films, Runcorn UK—Courtaulds bought Fothergill Harvey in 1973. Company was previously called Fothergill-S5monds, becoming part of Courtaulds Aerospace Ltd. Manufacture prepreg fabric. CP Films are now called Solutia, a spin-off from... 

The basic fabric material characterization consists of quantifying the evolution of the shear stiffness as a function of yarn rotation and the tensile behavior. Such characterization should be done over the range of temperatures that can occur during fabric deformation when using prepreg fabrics. For dry fabrics, that is, no prepreg, the characterization can be done at room temperature. 

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). 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

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