Vacuum Bagging Materials

Vacuum bagging process, also just known as ‘bag moulding’ is a process where the laminate is enclosed in an airtight bag and a vacuum is drawn from the inside of the bagged enclosure. Atmospheric pressure on the outside then presses the bag or vacuum membrane uniformly against the wet lay-up or pre-preg. Atmospheric pressure is equal in all directions, so the part enclosed in the bag is pressed or squashed equally from the top, bottom and sides. The level of vacuum drawn will depend on the desired result wanted. Atmospheric pressure, at sea level, at 23°C is equal to 1 Bar pressure. (1 Bar pressure = 10,000 kg force per square metre). Should more than 1 Bar pressure be required (typically when processing pre-pregs), the mould with the vacuum bag in place, is placed in an autoclave, and then more pressure and heat is applied. Many applications only require a partial vacuum, then the level of vacuum should be controlled via the vacuum pump or by other means. We at Aerontec will be glad to assist you with the correct materials for your particular application.

Vacuum Bagging Films

These films are traditionally made from “nylon” and or nylon derivatives. Temperature capabilities vary from as low as 80°C to as high as 425°C. Certain types of resin systems, like phenolics, could have a negative effect on nylon films. If using phenolic resin systems, choose bagging films that are compatible with the resin system.

There are many sizes of bagging film from 75mm tube, up to 12m wide sheet.

Release Films

There are many types of release films, and like vacuum bagging films, vary in their capabilities. Release films are traditionally the most expensive part of the vacuum bagging stack. Release films are available in different perforation styles, depending on the application. P3 perforation is the most common.

Sealant (Tacky) Tape

Sealant tapes are a sticky type of butyl tape that ensures a good seal between the bagging film and the tool / mould surface. There are many types, but traditionally are classified according to the temperature rating. Good quality sealant tapes should stick well, hold the seal during the curing cycle, and then be able to be removed without leaving residue.

Peelply Fabrics

Peelply fabrics are normally a smooth, tightly woven nylon or polyester fabric. Other fibres like glass and Aramid are also used, but only for certain applications. If phenolic resins are used, it is advisable not to use nylon, but rather a polyester type peelply. It is important to remove the peelply fabric before the part / mould goes into operation. Peelply fabrics are there to impose a clean, uncontaminated surface ready for bonding or painting.

Breather / Bleeder Fabrics

Breather fabrics are normally a type of uncompressed felt, also called spun-bonded, needled felt. Various types and thicknesses are available depending on the temperature, pressure and resin type. The breather aids in removing air and volatiles from the laminate, and transports them across the surface to the vacuum port, as well as allowing the vacuum to be dispersed all over the bag area.

Bleeder (to bleed out excess resin) is fundamentally the same thing, but separated from the breather by a solid release film. It is most common to use 1 fabric to do both functions.

Vacuum Infusion Materials

Vacuum Infusion is a term used to laminate the part dry, and then allow the resin to flow into the dry fibres.

These materials are generally normal vacuum materials, with a few differences. There is no requirement for a breather or release film, but an infusion mesh that transports the resin inside the bag to the dry fibres, as well a re-usable silicone infusion track that disperses the resin. This is a simple process once you get the gist of it, but there are very definite considerations when laminating with core for example.

We will gladly assist in the planning of the infusion process and the placing of the various materials.

Vacuum Valves and Vacuum Lines / Pipes

As with the vacuum film itself, there are many variations and careful consideration is required when choosing the correct equipment. Autoclave heat and pressure will collapse a pipe that is not constructed from the correct materials, as will normal vacuum at room temperature collapse an unsuitable one. Most vacuum pipes have a wire spiral either inside the tube wall or a separate one inside the tube. The ends require fittings that fit to the vacuum pump and to the bag.

Special quick couplers keep the vacuum “pressure” when separated on both sides of the coupling. These work very well with the “401 C” vacuum fittings (as shown in sketch), as well as vacuum gauges.

With infusion, we need cheap disposable lines (and no quick couples) as they will be filled with cured resin and be disposed of.

Vacuum pumps and Resin Traps

Again there are many types of vacuum pumps. Vane pumps can work dry, in oil or in water with electric motors. There are also venturi pumps that work with water or compressed air.

All pumps need some protection from excess resin entering the vacuum lines and into the pump. The danger of this is much larger in the resin infusion process, where a trap collects the excess resin in a bucket. The trap also has a vacuum gauge and plumbing that helps with the setup of the infusion process.

Vacuum Leak Detectors

There are two types of leak detectors that are available. One is a simple visual indicator, and the other is an ultrasonic noise detector that is converted to a noise that we can hear through a set of earphones.