what does a vacum bag system do?
check the archives. theres an awesome thread in there. probably the best one on all of swaylocks
It is basically a type of clamping that sucks all the air out and harnesses the atmospheric pressure. When you incase something in a bag and set it under vacuum, the air is drawn out and the exterior atmosphere presses against what ever is under vac, with, I think, nearly 15 lbs per square inch.
If you are trying to “form” something from a composite of several layers/pieces the vac bag will hold them in place while the bonding agent cures. There are other benefits to vac bagging, but that is the general purpose.
By removing air and applying pressure a vac system does the following:
Removes air from the laminate, air bubbles in a laminate are source of weakness.
Increases the fibre to resin ratio, top quality laminates are 60% fibre content, providing there is sufficient wet-out the higher this number the better.
In multiply/sandwich laminates the bond between plys and core materials is greatly improved, interlamina sheer strength (ILS) and peel strength is the weak point for most laminated products.
Basically a vacuumed laminate is lighter and/or stronger.
The downside is that a vac laminate will also be more expensive, extra time, but also consummables in the form of peel ply (which stops the bag sticking to the laminate), bleed fabric (which soaks up excess resin), breather fabric (which prevents the bag getting sucked too hard to the laminate allowing the vacuum to work evenly over the moulding), and the bag itself won’t last forever.
The next level up from vac systems is an autoclave, this is a pressure vessel that applies additional force to the laminate and usually controls heat as well.
Hope this helps,