A hand lay-up process in which the lay-up is cured under pressure generated by applying air or steam pressure up to 50 psi between a tailored bag placed over the lay-up and a pressure plate placed over the top of the mold.
This process is related to vacuum bag moulding in exactly the same way as it sounds. A solid female mould is used along with a flexible male mould. The reinforcement is place inside the female mould with just enough resin to allow the fabric to stick in place. A measured amount of resin is then liberally brushed indiscriminately into the mould and the mould is then clamped to a machine that contains the male flexible mould. The flexible male membrane is then inflated with heated compressed air or possibly steam. The female mould can also be heated. Excess resin is forced out along with trapped air. This process is extensively used in the production of composite helmets due to the lower cost of unskilled labor. Cycle times for a helmet bag moulding machine vary from 20 to 45 minutes, but the finished shells require no further curing if the moulds are heated.
Pressure bag molding is similar to the vacuum bag molding method except that air pressure, usually 30 to 50 psi, is applied to a rubber bag, or sheet that covers the laid up composite to force out entrapped air and excess resin. Pressurized steam may be used instead, to accelerate the cure. Cores and inserts can be used with the process, and undercuts are practical, but only female and split molds can be used to make items such as tanks, containers, and wind turbine blades.
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