Vacuum Bagging

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In conventional construction the layers of fiberglass are laid in a mold and soaked with resin. The resin is then worked in and the combined layers are allowed to cure until hard. If the laminate were pressed together, the layers would bond better. And if the excess resin were squeezed out, strength would be increased, weight reduced, and air voids eliminated.

The best way to press the laminate is with vacuum bagging. Here the layers are placed in the mold, then covered with a plastic sheet that is sealed along the mold's edge. The air between the sheet and laminate is sucked out, drawing the sheet tightly against the laminate, while compressing the laminate with 6 to 12 psi. This process also squeezes out resin to help achieve a stronger 60-to-40 fiber-to-resin ratio, rather than a conventional layup's 40-to-60 ratio.

One type of vacuum bagging is resin infusion. Dry fiberglass is put in the mold and the vacuum draws resin through it. There are several patented versions of this that give uniformly high-quality laminates. One is SCRIMP (Seemann Composite Resin Infusion Molding Process), which claims a 70-to-30 fiber-to-resin ratio and has been used by Hinckley, Sabre, and Wellcraft.