Vacuum Bagging of molded HPV parts

Vacuum Bagging 101

By Garrie Hill

This page explains the basics of vacuum bagging. Vacuum bagging is used to remove the voids and air pockets from a multilayer composite layup, and to remove the excess epoxy. This technique helps to ensure a strong and lightweight finished product. In the drawing below, the nylon bleeder fabric allows the epoxy resin to soak into the breather fabric when the layup is vacuumed together. The part is bagged and sealed, and the vacuum pump is run at least until the part has partially cured. Heating the part to around 100 degrees F will accelerate the curing. The nylon fabric, also known as "peel ply" peels easily off of the molded part after curing. care must be taken to keep the epoxy out of the vacuum pump.

These materials are available through many on-line businesses specializing in composite construction. See below for tips for finding alternative vacuum bagging materials:

Nylon peel ply notes:
Peel ply is nylon cloth.
1) Do not use light colored rip stop nylon. Often, in processing, the nylon has been chemically "scoured" or etched. Epoxy can stick to the nylon surface. This is A Bad Thing

2). Test the nylon fabric before purchase. Stretch some tightly across your mouth and blow through it. You should just barely be able to blow through the fabric.

3). You will be purchasing this rip stop nylon in a fabric store. These stores are predominantly populated by persons of the female persuasion. If you do not happen to be of similar design, be prepared for concerned/questioning/perplexed/antagonistic stares. Do not be concerned when asked what you plan to do with all of this rip stop nylon. Just smile brightly and say, "I am going to throw it away". Then give the clerk your 15% off discount coupon ;-)

Breather ply notes:
Breather ply is polyester matt, generally around 1/2" thick. . You can also find polyester matt/filler at fabric stores or even Wal-Mart.

Vacuum bag notes:
Vacuum bags can be made from a variety of materials. Generally its best to have clear bags so you can see your layup and make sure everything stayed where you put it. Plastic sheet can be used, or large and heavy duty garbage bags.

Sealing your vacuum bags:
The vacuum that your pump can pull is mostly reliant on how well you can seal your bag. Gorilla tape is good for sealing the bag to the mold or around the vacuum hose. Double sided tape or a thick sealant like Lexel can be used to seal the ends of the bag or edges of a folded flat sheet of plastic.


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