MATERIALS AND MOLDING METHODS 



4-17 



Heat Cure 



Fiberglass reinforcement and properly catalyzed resin can be cured to a hard structural 

 laminate by the application of heat to initiate the reaction (21). Steam or electrically heated 

 molds are used to develop heat cured laminates with superior physical properties at rapid 

 production cycles. Open molds can be heated by a bank of infra-red heat lamps or resistance 

 heaters. Heat cure during molding, or subsequent heat cure, can produce superior laminates. 



Room Temperature Cure 



Room temperature cure does not require a heated mold. The addition of an accelerator 

 and catalyst to the resin will cause the necessary reaction which produces sufficient heat to 

 cure the laminate without the application of external heat (7, 21). Room temperature cure is 

 extremely useful for producing very large lay ups as boat hulls because they allow extended 

 cure time and are difficult to heat. This slow cure cycle limits the rate of production for 

 any individual mold. 



Contact Molding 



The contact molding method, as illustrated in Figs. 4-16 and 4-17, is simply the lay- 

 ing up of plies of resin impregnated fiberglass reinforcement to the required thickness on an 

 open female or male mold of the desired hull form and allowing the laminate to cure at room 

 or elevated temperature (14). After the cure is completed, the boat hull is removed from the 

 mold and the process is repeated. For extremely large size hulls, the molds may be made 

 in two halves for ease in lay up and removal of the molded hull. It is easier to lay up the 

 plies of reinforcement over a male mold although an uneven outer surface results. Addi- 

 tional finishing operations are usually required to obtain a smooth outer surface and good 

 appearance. Since a smooth outer surface is desirable in boat hulls, the female mold is 

 generally preferred. 



Fig. 4-16. Molding of hull of sailboat in female 

 mold. Resin mix being sprayed on reinforcement 

 (Courtesy American Carbide Corporation) 



