Re-usable Vacuum Bags
The primary reason for having a re-useable system is to save time, and the savings can be substantial. Its not uncommon for a conformal bag to take less than one-fourth the time it takes to carefully pleat and seal a nylon/sealant tape vacuum bag. With labor and overhead factored in, this could save more money on the final part cost than by any other process improvement.
See our list of standard size envelop or "BOA" bags
Why use latex?
Before Piercan, USA developed this high temperature latex it has not been a candidate for many bagging operations. Piercan, USA High Temperature (HT) Latex now, with service temperature capabilities of 250° F to 350° F. With it's high elongation, HT latex offers the following advantages:
- Latex is one of the lowest cost elastomeric materials. The cost is low enough for short production runs, and in some cases, as a disposable conformal bagging system.
- Latex is the easiest and cheapest to mold of any other bagging material. It can be formed around a mandrel in a dipping process, or cast in a temporary plaster mold.
- Latex has very high elongation, up to 900%. Many parts can be bagged without pleating, reducing the risk of bridging.
- Latex is tough, it has high tear resistance. A latex bag can be thinner, easier to handle, and more compliant than a bag made of cast or fabricated silicone.
- Latex is easy to handle with common composite shop techniques. It works with sealant tape, clamping, rubber adhesive, and various mechanical seals and vacuum fittings. It can be cut and fabricated easily.
- Latex is relatively free of possible contaminates and safe for bonded surfaces. Latex can usually be used directly against the uncured laminate surface, and if any rubber particles are left on a part, they can be easily cleaned off.
Latex Temperature and Compatibility
LTI latex is compatible with most epoxy and polyester resin systems, and some phenolic and cyanate ester systems. It is always advisable to test the material first. Service temperatures for LTI HT Latex are about 25-30 hours at 250° F and about an hour at 350° F.
Considerations for Using Latex Vacuum Bags
Envelope (Boa) Bags Our Boa bags are made by dipping mandrels that are basically sheets of aluminum with rounded edges. The standard sizes range up to 100" with widths up to 30". Larger sizes can be fabricated by adhesive bonding sections together. Boa bags can be sealed at the open end by simply rolling and clamping, or with regular sealant tape.
Latex Sheet Sheet sizes are up to 30" x 100", or 60" x 53"without seams. If seams are acceptable, large sizes can be fabricated.
Conformal Bags We can mold just about any shape in latex for a wrinkle free bag that fits the part exactly. They are a great time saver for complex shapes, and can be quite inexpensive. We have two methods of producing them, by dipping mandrels and by casting in plaster molds. Each process has it's own advantages, but in general the plaster casting method is best for larger vacuum bags. We keep the mandrels or casts at our facility and produce the bags to order.
Examples
This is an example of a conformal vacuum bag. It fits quickly and easily over the lay-up and leaves a smooth surface.
The part above is being de-bulked in one of our envelope or "Boa" bags. Photo courtesy of Compositek, Boulder, CO. Note "clamping" method for closing the open end. Spring clamps are used for oven cures.
Latex sheeting is used to bond a foam core to the inside of a small boat hull. The stretch eliminates pleats and bag wrinkles. It is sealed to the mold flange with common vacuum sealant tape.
A Boa bag is used to vacuum bag a helmet mold. The latex is pushed into the cavity as the vacuum draws out the air and the stretch of the material eliminates bridging.
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