Vacuum Bagging, as it suggests, is the process of utilizing a bagging apparatus and a vacuum to apply pressure on a laminate to eliminate air between layers and maximize the fiber to resin ratio, creating the strongest and lightest bond possible, laminate.
The maximizing of the fiber to resin ratio will maximize the physical properties of the fiber and resin. Vacuum Bagging applies up to one (1) Atmosphere (14 psi or 30 inches of mercury) of pressure to compress the laminate and push out any excess resin, thus achieving the best possible ratio of fiber and resin.
You can setup a Vacuum Bagging system a number of ways. The first is through a flange located on the outside of your mold. During mold construction, create an 8” flange going all the way around your mold. This flange will be used to attach the vacuum bag, with mastic tape, and is extra wide to enable room for excess resin, which the breather fabric did not soak up, to not reach your seal.
The second way is to place the entire mold and part in a vacuum bag. This method does not use the mold as a vacuum service but instead uses the enclosed bag to create the vacuum. The final way uses bagging to repair a mold or part. Here you want to attach the vacuum bag around your repair leaving enough space between your repair and seal to account for any possibility of resin reaching the seals. Whichever method you choose, the layers of material to achieve a Vacuum Bagging system remain the same.
The layers added to a mold or repair for a Vacuum system to fully work are as follows and in this order.
- The laminate for the part or repair you are trying to fabricate.
- A layer of Peel Ply to ensure the remaining layers do not stick to your part or repair.
- Breather Cloth to both soak up excess resin and to act as an applicator for the vacuum, ensuring it distributes evenly.
- Bagging Film to seal the part and ensure vacuum.
- Mastic Tape – This is sealed around your repair, or mold, and should be checked thoroughly to ensure there are no leaks.
The vacuum should then be attached through the bag using the desired fitting. It is very important that your vacuum setup is correct to minimize the waste of ruined parts. A good vacuum pump is a necessity for your project to work correctly.
Some tricks to vacuum bagging can aid in the learning curve.
- If you use a vacuum gauge, attach it directly through the bag at the opposite end of the vacuum pump. You want to know the vacuum level as far away from where you are pulling vacuum.
- Use more than one layer of Breather Fabric in the middle of your setup or use 1/4” PVC tube under the bag or enka (to add additional air channels to ensure even and complete distribution of vacuum across the part.
- If you have a complex part you are trying to fabricate, ensure that all of the reinforcing layers are formed tight to the mold. Make sure the bag is loose enough so that it will form tight in the indentation of the molded part. If the bag spans the indentation, it will not put pressure on the laminate and thus creates a puddle of resin.