vacuum bag molding
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TRANSCRIPT
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Vacuum bag molding
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• Vacuum bag molding
• Also known as vacuum bagging.
• Open mold techniques for thermoset composites.
• Hand lay-up: The application of reinforcement along with a polyester or epoxy resin by hand.
• Vacuum bagging: The use of a vacuum bag to apply an even pressure over the composite to consolidate the material.
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Hand layup
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Hand Layup
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Hand Layup
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What is vacuum bagging?•Vacuum bagging (or vacuum bag laminating) is a clamping method that uses atmospheric pressure to hold the adhesive or resin-coated components of a lamination in place until the adhesive cures.
•(When discussing composites, “resin” generally refers to the resin system— mixed or cured resin.)
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Vacuum Bagging - Advantages
• Even Clamping pressure
• Control of resin content
• Custom shapes
• Efficient laminating
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Vacuum bagging -Equipment
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Vacuum Bagging - Materials
• Release fabric
• Perforated film
• Breather Material
• Vacuum bag
• Mastic sealant
• Plumbing system
• Mold release
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Release fabric:•Smooth woven fabric – not bond to epoxy.
•Used to separate breather and laminate.
•Excess epoxy can wick through release fabric.
Perforated film:•Used in conjunction with release fabric.
•This film helps to hold the resin in laminate, when high vacuum pressure is used with slow curing resin system (or) thin laminates.
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Breather material:•(or) bleeder cloth.
•Allows air from all parts of the envelope – to be drawn to a port (or) manifold by providing slight air space between the bag and laminate.
Vacuum bag:•If vacuum pressure less than 5psi(10 hg) at room temperature – 6mil polyethylene plastic can be used.
•Clear plastic material is preferable as compared to opaque - for easy inspection
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• For high pressure and temperature applications – specially manufactured vacuum bags can be used.
• Vacuum bag should always larger than mould.
Mastic sealant:• Provide a continuous air tight sealant between bag
and mold.
• Also used to seal the point where the manifold enters the bag and to repair leaks in the bag.
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Plumbing system:•Provides an airtight passage from vacuum envelope to vacuum pump – allowing pump to remove air.
•A basic system consists of flexible (or) rigid hose pipe, a trap, a port that connects pipe to the envelope.
•Vacuum hose designed specially for this.
•Vacuum port connects the exhaust tubing to vacuum bag.
•Control valve – control of airflow at the envelope.
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• Trap incorporated into the line as close as possible to the envelope.
• Vacuum gauge – is necessary to monitor the level.
The reading of negative pressure inside the bag is equal to the net pressure of the atmospheric pressing on the outside of the bag.
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Mold release:
•Necessary to prevent epoxy from sticking.
•Three types of mold release:
1.Carnauba based paste wax
•(usually 5 layers for new mold and atleast one layer before each new part is molded)
•Also use PVA in wax.
•Fine detail gloss level obtained by the use of wax.
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2. Semi permanent formulation:
•Liquid release system.
•Fine detail and gloss level are obtained as well as texture.
3. General contaminant variety:
•Grease, vaseline, toilet bowl wax, hair spray, hair gel.
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Example: Step 1
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Step 2:
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Step 3:
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Step 4:
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Step 5:
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Step 6:
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Step 7:
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Step 8:
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Challenges:
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Example 2: Step 1
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Step 2:
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Step 3:
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Step 4:
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Step 5:
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Step 6:
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Step 7: