• 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.
What is vacuum bagging?•Vacuum bagging (or vacuum bag laminating) is aclamping method that uses atmospheric pressure tohold the adhesive or resin-coated components of alamination in place until the adhesive cures.•(When discussing composites, “resin” generally refersto the resin system— mixed or cured resin.)
Vacuum Bagging - Advantages• Even Clamping pressure• Control of resin content• Custom shapes• Efficient laminating
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 highvacuum pressure is used with slow curing resin system(or) thin laminates.
Breather material:•(or) bleeder cloth.•Allows air from all parts of the envelope – to be drawnto a port (or) manifold by providing slight air spacebetween the bag and laminate.Vacuum bag:•If vacuum pressure less than 5psi(10 hg) at roomtemperature – 6mil polyethylene plastic can be used.•Clear plastic material is preferable as compared toopaque - for easy inspection
• 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.
Plumbing system:•Provides an airtight passage from vacuum envelope tovacuum 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 vacuumbag.•Control valve – control of airflow at the envelope.
• 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.
Mold release:•Necessary to prevent epoxy from sticking.•Three types of mold release:4.Carnauba based paste wax•(usually 5 layers for new mold and atleast one layerbefore each new part is molded)•Also use PVA in wax.•Fine detail gloss level obtained by the use of wax.
2. Semi permanent formulation: •Liquid release system. •Fine detail and gloss level are obtained aswell as texture. 3. General contaminant variety: •Grease, vaseline, toilet bowl wax, hair spray,hair gel.