China Suppliers of Heat-Shrinkable Bags - Quality Industrial Packaging from Trusted Factory
Core functions and how they work
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1
Create a closed vacuum environment
Wrap the vacuum bag tightly on a mold lined with reinforced fibers (such as carbon fiber, glass fiber) and resin flow media.
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2
Apply uniform pressure
Air is pumped by a real air pump to create a negative pressure in the bag (usually -0.95 bar or higher). This negative pressure will generate a uniform pressure up to nearly 1 atmosphere, which will act on the workpiece.
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3
Resin immersion and compaction
- Compacting fibres: Under vacuum pressure, multiple layers of fiber material are compacted to remove between layers of air to achieve the desired fiber volume content.
- Drive resin flow: Under negative pressure, the resin is inhaled from the inlet, so that it completely saturates the dry fiber-reinforced material and expels bubbles.
- Controlling resin content: The retention ratio of the resin is precisely controlled by vacuum pressure.
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4
Form a smooth surface
The vacuum bag is pressed against the surface of the workpiece, which can reproduce the smoothness of the mold surface (the side of the mold contacting) or form a smooth "bag surface" (the side that contacts the vacuum bag).
Main components (vacuum bag system)
A complete industrial vacuum bag system typically includes:
The core material. It requires high ductility, high toughness, resistance to puncture and resistance to a certain temperature. Commonly used nylon (PA) film (such as PA6). For high temperature curing (such as epoxy resin above 120 ° C), high temperature polyamide or polyimide films are used.
A highly viscous, creamy sealing grease used to form airtight seals at the edges of the mold so that vacuum bag membranes can adhere to them.
Laid between the workpiece and the vacuum bag to prevent the resin from sticking to the vacuum bags or the flow network, facilitating de-molding. Usually porous polytetrafluoroethylene (PTFE) or silicone-coated glass cloth.
Laid above the workpiece to provide a fast channel for the resin to flow under the vacuum bag to ensure that the resin is uniformly soaked.
Absorbs excess resin and ensures the opening of the vacuum channel so that air and volatile gases can be effectively pumped out.
Include spiral pipes, fast joints, vacuum meters, and three-way valves to connect vacuum pumps to inner bags.
Provides a stable and continuous vacuum source.
Key features and requirements
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1
Excellent physical performance
- High tensile strength and elongation: it can cover complex shapes of molds without rupturing and can withstand volume changes and pressure during curing.
- Anti-piercing: prevents puncture by mold edges or fibers.
- Uniform thickness: Typically the thickness is between 50-150 microns to ensure that the pressure is uniform.
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2
Stable chemical and thermal properties
- Temperature resistance: must be able to withstand the highest temperature of the resin curing cycle (from room temperature to 180 ° C or higher).
- Low permeability: Very low permeability for air and volatile organic compounds to maintain a stable vacuum.
- Chemical resistance: does not react with resins or depolymerizers.
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3
Process suitability
It has good fit and can be laid manually or automatically.
Main application industries
Aerospace: Manufacturing large composite components such as aircraft wings, fuselage parts, radar shields, interior panels and so on.
Wind energy: Manufacturing wind turbine blades (this is the largest application area of the vacuum filling process).
Ship yachts: Manufacture hulls, decks, superstructures, etc., to achieve large-scale integrated molding.
Automotive industry: Body parts, chassis parts, etc. for high-performance sports cars, racing cars, and new energy vehicles.
Sports equipment: Manufactures high-performance bicycle racks, rowing boats, paddle boards, helmets, fishing rods, etc.
Industrial products: Such as storage tanks, pipes, building reinforcing panels, etc.
Frequently Asked Questions
What is the primary function of a vacuum bag film?
The primary function of a vacuum bag film is to create a completely sealed, negative-pressure environment over the mold. This allows atmospheric pressure to exert uniform force, compacting the fiber layers and driving resin flow while removing trapped air bubbles.
What materials are typical vacuum bag films made of?
They are commonly made of high-elongation nylon (PA) film, such as PA6. For high-temperature curing processes (exceeding 120°C), specialized high-temperature polyamide or polyimide films are used to prevent degradation.
Why is elongation capacity important for vacuum bag systems?
High elongation (stretchability) allows the film to fit tightly into complex mold geometries, deep recesses, and sharp corners without bridging or puncturing under vacuum pressure, ensuring uniform consolidation.
What is the difference between a de-molding cloth and a ducting net?
A de-molding cloth (or release film) is placed directly against the composite to prevent the resin from sticking to outer bagging layers. A ducting net (or distribution medium) is laid on top to create flow channels that help resin spread evenly across the workpiece.
Which industries benefit most from vacuum bag molding?
This process is widely used in high-performance industries including Aerospace (fuselages, wings), Wind Energy (large rotor blades), Marine (yacht hulls), Automotive (chassis and body panels), and Sports Equipment (carbon fiber frames, helmets).