Oven-cured system

These three cure systems have in common the need for a two-step cure cycle to generate the best cured properties. The first step is the appHcation of heat and pressure in a mold to shape the article (press cure). The second step is a high temperature oven cycle at atmospheric pressure to obtain the final cured properties. 

Finally, the energy required to evaporate one pound of water from the coating at 70 F to vapor at 600 F is found to be 1296 BTU/lb. These basic parameters/relations for the curing system can now be used in analyzing the energy requirement of the curing oven. 

Instead of applying pressure in a closed mold, the mix of liquid resin and reinforcing fiber may be laid into an open mold, and optionally pressed gently at room temperature until cured. To accelerate low-temperature cure, more active catalyst systems are added. Alternatively, the assembly may be UV or oven cured. This requires less capital investment but more skilled labor, so it is useful for prototype and small production runs. It permits unlimited size, so the largest reinforced thermoset products are made in this way, for example, large tanks and whole boat hulls. 

Resin system and chopped fibers are sprayed simultaneously from two guns against a mold after spraying, layer is rolled flat with a hand roller. Either room temperature or oven cure. 

Usually these hot air ovens will be designed to operate at temperatures just sufficient to initiate cure for periods of not over one hour. The cure temperatures of modern adhesives are generally in the 250°F to 350°F range and most assemblies being bonded will tolerate exposure to these temperatures for extended periods. Thus, if trouble should occur on the oven conveyor system, the parts being bonded may not suffer damage. 

A 121°C curing, low to medium service temperature epoxy displaying good toughness and strength, and offering an outstanding surface finish with lower case vacuum bag/oven cure. The system is MIL-R-9300 approved and is self-adhesive to honeycombs and foam cores. 

RS-12C - a controlled flow, vacuum bag/oven cure formulation RS-12D - a low-tack, extremely low flow, autoclave formulation RS-12M - an extremely low flow, autoclave formulation 175 C cure, low viscosity system suitable for RTM 135°C cure, toughened system. 

Heat Cure. Oven-curable systems use an extended bake, ranging from 15 min. to several hours or longer, for the material to cure fully. Thermally activated systems require the increased temperature to start the curing process, whereas thermally accelerated systems will cure eventually at room temperature but are baked to speed up the process and improve material properties. Generally, the hotter the oven, the quicker the cure, and the harder the finished material. 

Trim Line. In the trim shop, the fresh paint surface forms the substrate for a number of bonding operations in which parts prefabricated to a greater or less extent and subsupplied parts are adhesively bonded into the painted body. Because no more bake ovens are involved, cold-curing systems (moisture or two-component systems) are employed. 

First, the materials are press cured at different times and temperatmes, depending on the size of the product, the structure of the polymer, the curing systems, and on end-use requirements (paints, O-rings, membranes, seals) [28]. Press-cure conditions vary from 4 min at temperatures approaching 200 C for thin cross sections, to 30 min at 150-170 C for thick sections [28,110]. The purpose of this step is to develop sufficient crosslinks in the sample to prevent the formation of bubbles due to the release of trapped air during the early stages of the subsequent oven cine [111]. 

The methods used are high frequency induction heating, to provide local heating normally around the periphery of an assembly, or a full oven-based system which will heat the whole assembly to the curing temperature. The latter system is of lower initial capital cost but the running costs tend to be higher and the facility occupies a larger floor area. 

Catalysis is utilized in the majority of new paper filter cure ovens as part of the oven recirculation/bumer system which is designed to keep the oven interior free of condensed resins and provide an exhaust without opacity or odor. The apphcation of catalytic fume control to the exhaust of paper-impregnation dryers permits a net fuel saving by oxidation of easy-to-bum methyl or isopropyl alcohol, or both, at adequate concentrations to achieve a 110—220°C exotherm. 

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