Complete curing process

Fig. 27.5 The complete curing process of a moisture-curing PU system.

To make a decorated plate, the mold is opened shortly after the main charge of molding compound has been pressed iato shape, the decorative foil is laid ia the mold on top of the partially cured plate, ptinted side down, and the mold closed again to complete the curing process. The melamiae-treated foil is thus fused to the molded plate and, as with the decorative lamiaate, the overlay becomes transparent so that the ptinted design shows through yet is protected by the film of cured resia. 

At this point in the process, thermoplastic and chlorosulfonated polyethylene (CSPE) membranes are complete and are ready for packaging. In the case of ethylene—propylene—diene monomer (EPDM), the curing step occurs before the membrane is ready for packaging. The curing process is accomphshed by placing the membrane in a large vulcanizer where the material is heated under pressure to complete the cure. 

This is a resin-rich system. The stator is wound with pre-formed coils on similar lines as noted above. After thorough testing on each coil for the polarization index and dissipation factor (tan S), as discussed in Sections 9.5 and 9.6, and the impulse voltage withstand test, as discussed in Section 11.4.9, the individual coils are completely cured and toughened before inserting them into the slots. The rest of the process is as noted earlier. 

Crosslinking of epoxy resins with carboxylic acid anhydrides is catalyzed by tertiary amines thus,if 50 mg /V,/V-dimethyl aniline are added to the initial mixture in the above example, the curing process is already complete after 1 h at 120 °C. 

Figure 4.21 shows the sensor output for the smart automated sensor expert system-controlled run. The resin reached the center sensor at 37 min. The viscosity is maintained at a low value by permitting slow increases in the temperature. At 60 min, fabric impregnation was complete. The resin was advanced during a 121 °C hold to a predetermined value of degree of cure of 0.35, based on the Loos model s predictions of the extent of the exothermic effect. This value of a is clearly dependent on panel thickness. Then at 130 min, the ramp to 177°C was begun. Achievement of an acceptable complete degree of cure was determined by the sensor at 190 min. Then the cure process was shut down. 

The cure of thermoset resins involves the transformation of a liquid resin, first with an increase in viscosity to a gel state (rubber consistency), and finally to a hard solid. In chemical terms, the liquid is a mixture of molecules that reacts and successively forms a solid network polymer. In practice the resin is catalyzed and mixed before it is injected into the mold thus, the curing process will be initialized at this point. The resin cure must therefore proceed in such a way that the curing reaction is slow or inhibited in a time period that is dictated by the mold fill time plus a safety factor otherwise, the increase in viscosity will reduce the resin flow rate and prevent a successful mold fill. On completion of the mold filling the rate of cure should ideally accelerate and reach a complete cure in a short time period. There are limitations, however, on how fast the curing can proceed set by the resin itself, and by heat transfer rates to and from the composite part. 

Thermochemical submodel The thermochemical submodel provides temperature, viscosity, degree of cure (for thermosets), crystallinity (for thermoplastics), and the time required to complete the cure process. 

In order to optimize each embedding material property, complete cure of the material is essential. Various analytical methods are used to determine the complete cure of each material. Differential scanning calorimetry, Fourier transform-infrared (ftir), and micro dielectrometry provide quantitative curing processing of each material. Their methods are described below. 

Aliphatic or aromatic peroxide curing agents can also be used, by reactions with vinyl side chains or even saturated alkyl groups. Specihc peroxides are chosen on the basis of their decomposition temperatures, and the reaction products they leave behind after the curing process is complete. Some peroxides used are Mv(2,4-dichloroben-zoybperoxide, benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide.83-86... 

---