Using vacuum on a bag constructed of film is not an optimal method to
compress completely around a male core evenly. Here's why...
Atmospheric pressure is only able to compress the layup perpendicular to the film surface. When you lay 2 pieces of film on either side of a male core, they form a seam where the film must transition away from the core surface. At that seam, the atmosphere is not able to apply force radially to the section... or perpendicular to the surface. See the drawing, the film can't compress "down" or "up" on the core.
If the core were placed in a seamless bag, like inside a balloon, then yes it could compress evenly around the section. The seam is the problem.
Elastic banding offers an advantage because it is able to apply perpendicular compression all the way around the layup and radially against the core surface.
The caveat with the banding is that the compression comes from the tension, so it doesn't apply appreciable pressure to a flat section, and it won't apply any to a concave section.
Atmospheric pressure is only able to compress the layup perpendicular to the film surface. When you lay 2 pieces of film on either side of a male core, they form a seam where the film must transition away from the core surface. At that seam, the atmosphere is not able to apply force radially to the section... or perpendicular to the surface. See the drawing, the film can't compress "down" or "up" on the core.
If the core were placed in a seamless bag, like inside a balloon, then yes it could compress evenly around the section. The seam is the problem.
Elastic banding offers an advantage because it is able to apply perpendicular compression all the way around the layup and radially against the core surface.
The caveat with the banding is that the compression comes from the tension, so it doesn't apply appreciable pressure to a flat section, and it won't apply any to a concave section.
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