The Cure Cycle

Benzoyl peroxide is most commonly used for elevated temperature curing. The peroxide is generally supplied as a paste (-50%) in a liquid such as dimethyl phthalate to reduce explosion hazards and to facilitate mixing. The curing cycle in pressure moulding processes is normally less than five minutes. 

Pressure bag molding This is a take-of to vacuum bag molding where the bag and mold is placed in a closed system and is subjected to pressure during the curing cycle. 

The application of instrumentation to the automatic control of a sequence of operations, e.g., injection moulding processes. Once the mould has been loaded with inserts (assuming a rubber to metal bonded part) into the press, the operation of a push-button starts the controller which closes the press, injects the rubber, controls the cure cycle, recharges the injection unit, opens the press, operates the ejectors and presents the mould for cleaning and loading of inserts. 

A development of slush moulding used for the production of hollow articles from plastisols. The moulds are continuously rotated in two directions during the curing cycle. 

Epoxy film specimens of two different weight/weight ratios of TGDDM/DDS were evaluated (73/27 and 80/20). The films were cast between teflon sheets using a spacer. The cure cycle was 1 hr at... 

The Impedance Analyzer was controlled by a 9836 Hewlett-Packard computer which also controlled the time-tempe ture of the press. Measurements at frequencies from 5 to 5 x 10 Hz were taken at regular Intervals during the cure cycle and converted to the complex permittivity. Further details of the experimental procedure has been given elsewhere [10]. 

Materials Description. Three CIBA-GEIGY epoxy/hardener systems were studied Araldite 6010/906, Araldite 6010/HY 917 and Araldite 6010/972 with stoichiometries 100/80, 100/80 and 100/27, respectively. Araldite 6010 was a DGEBA epoxy resin. The hardeners 906, HY 917 and 972 were, respectively, methyl nadic anhydride (MNA), methyltetrahydro phthalic anhydride (MTPHA) and methylene dianiline (MDA). These systems were investigated previously for the matrix controlled fracture in composites (6-8). The curing cycles used can be found in (6). The ideal chemical structures of the systems are shown in Table I. Neat resins were thoroughly degassed and cast into 1.27 cm thick plates for preparation of test specimens. 

The mold and sample were placed in the press also preheated to 185°C and the cure cycle started immediately. Press temperature and pressure were microprocessor-controlled for consistent cure cycles. The cure cycle consisted of an initial 30 minute hold at 185°C with 1300 psi of pressure followed by 45 minutes at 221°C with 850 psi pressure and finally 15 minutes at 260°C with 300 psi pressure. The mold was removed from the press immediately following the completion of the final step and the sample removed from the mold while still hot. 

Cured specimens were a transparent golden brown color. DSC indicated less than lOX residual exotherm. Following the cure cycle described above the specimens ware postcured for 1 hour at 300°C in nitrogen. The extent of cure was determined by DSC to be greater than 95% following postcure. The cure cycle and postcure described above have been used in the fabrication of all cured BCB specimens. 

The formulated RTV silicone is usually cured at room temperature for 16 hours and then at 120°C for 4 hours to ensure the complete removal of organic solvent. A rubbery and non-tacky elastomer is usually obtained after the curing cycle. 

It is fundamental, therefore, to control the rate of heat absorption and temperature variations during the cure cycle [33,34]. The cure cycle depends on the part geometry, thermal... 

For pure water voids, void nucleation is instantaneous. For air-water voids, air void nucleation or entrapment has already occurred during lay-up or at the beginning of the cure cycle. 

If zero initial void diameter is assumed, then no void growth occurs while Oat = Q,. The time increment from the start of the cure cycle to the moment when Qat — Coo is denoted as tBEGIN ar d is given by ... 

Using the input information described earlier, void behavior was examined during the various stages of the cure cycle shown in Figure 6.2. The specific stages are as follows ... 

It is also noteworthy that after the initial period of growth, the higher density of the air-water vapor mixture produces a void that is slightly smaller than the pure water vapor void produced under identical conditions. The air-water void, however, cannot completely dissolve during the cure cycle, whereas the water void is capable of complete dissolution. 

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