There are several different vacuum bagging methods, like single-stage vacuum generators, breather fabric, mastic, and perforated release film. Each one has its advantages and disadvantages. In this article, I’ll explain all of them in detail. In addition, there are several things you need to know to ensure the success of your vacuum bagging project. After reading this article, you will be better prepared for your next vacuum bagging project.
Breather fabric
The breather fabric allows the composite part to breathe under the vacuum bagging process, allowing the resin to bleed out. This technique also allows for excellent conformity around the part under vacuum pressure. Composites One can supply breather fabric in standard roll and slit width formats, cut shapes, and 3D stitched formats. Breather fabric is a crucial element in the vacuum bagging process.
Vacuum bagging techniques rely on several essential components, including the breather fabric, vacuum valves, and bagging film. These materials must be fixed to the vacuum bagging tool with sealant tape. Vacuum bagging techniques should also be done carefully to prevent wrinkles and bridge concave corners. Breather fabric can be made of practically any material, including t-shirts.
Mastic
Some basic vacuum bagging techniques should be followed to get quality vacuum-sealed mastic. A poor bag can result in resin leaks and voids. Among these problems are making the bag too small and skewed and stretching the sealant tape. Therefore, the pleats should be arranged in a systematic order to fix this problem. In addition to the pleats being aligned systematically, you should also be aware of the vacuum level.
The first step is to wet out the layers of the release fabric and perforated film. These components should be slightly more significant than the repaired area. Next, apply the mastic sealant around the perimeter of the repair area. Finally, fill the voids with WEST SYSTEM 105 Epoxy Resin mixed with the 206 Slow Hardener. When finished, repeat steps one and two. After the sealing, remove the breather fabric and any excess epoxy.
Perforated release film
There are several advantages to vacuum bagging with perforated release film. Firstly, it has higher elongation, which is ideal for vacuum bagging with epoxy and phenolic resin systems. It is also available in all the standard perforations, reducing the high-temperature vacuum bagging cost. Also, it can be easily applied over simple tooling and part shapes. Finally, it will not wrinkle when exposed to high temperatures.
There are two main types of release films: perforated and non-porous. The former offers a smoother finished surface, while the latter is suitable for a textured or granular surface. However, the amount of epoxy bleeding depends on the type of perforations, epoxy system, bleeder, and pressure. Therefore, release films tend to bleed off less epoxy than TCG.
Single-stage generators
Single-stage vacuum bagging generators utilize compressed air to remove large volumes of air. These devices use the Venturi effect to accelerate the air through a restrictor tube, allowing it to escape the required air volume. These generators are commonly set for the highest evacuation and flow requirements. The ratio between compressed air consumption and vacuum flow can be set to approximately 1:1 or 2:1, depending on the application’s needs.
One of the advantages of single-stage vacuum bagging generators is their small size. As a result, they are lightweight, compact, and low-cost. In addition, compared to multi-stage generators, single-stage vacuum pumps are maintenance-free. They are also ideal for packaging and other applications that require a high amount of debris-free air. Single-stage vacuum generators come in several different capacities. Moreover, the J series of vacuum generators are highly reliable and offer interchangeable performance with European brand GV pumps. The EV series models feature an auxiliary port and are made of solid aluminum.
Ultrasonic leak detectors
When you want to ensure the highest quality of finished parts, you must ensure that the vacuum pressure is maintained during the process. Losing the vacuum pressure may cause the finished piece to become porous, decreasing its physical properties. Ultrasonic leak detectors use an advanced microphone system that senses sounds generated by escaping gases from 38 to 42 kHz. Unfortunately, some low-quality acoustical leak testing equipment is limited in its frequency band, which can cause false alarms. High-quality ultrasonic leak detectors use heterodyning to convert high-frequency sounds generated by leaks into lower-frequency sounds to solve this problem. This enables the user to pinpoint the leak and quickly seal it easily.
Unlike other leak detection methods, this technique effectively assesses the amount of fluid flow within a vacuum bag. It can measure the volume of the flow to determine the amount of leakage. This information is valuable in assessing the leak’s extent and is particularly useful in preventing further damage. However, the detection range is limited due to the leakage rate. A typical leak can have a volume up to several liters per minute.
