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Foaming Overview
• Processes to create foams
– Mechanical, Chemical, Physical, Syntactic
(hollow spheres)
• Processes to shape and solidify foams
– Molding, RIM, Foam-in-place, Extrusion,
Casting, Expanded foam molding
• Rebond materials
• Foam product characteristics
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Foaming
• Mechanical foaming
– Mix air into the resin while in a liquid state
– Plastisols, vinyl esters, urea formaldehydes,
phenolics, polyesters
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Foaming
• Mechanical foaming
– Mix air into the resin while in a liquid state
– Plastisols, vinyl esters, urea formaldehydes,
phenolics, polyesters
Polyester foamPhenolic foam
Phenolic foam
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Foaming
• Chemical foaming
– Foaming agents or blowing agents
– Chemical reaction that forms a gas/vapor
Bread (yeast foam)
Urethane foam
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Foaming
• Physical foaming
– Gas is forced into a liquid or molten resin
– Pressure is released quickly
– Foam is created
Shaving cream
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Foaming
• Syntactic foams
– Physically mix in hollow beads
– Beads are usually glass or plastic
– Wide density capability
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Foams
• Self-healing plastics – Beads filled with reactive resin
– Initiator (catalyst) mixed into
the surrounding plastic
– Beads crack under pressure of
crack growth
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Processes to Shape and Solidify
Foams
• Molding
• RIM
• Foam-in-place• Extrusion
• Casting
• Expanded foam molding (EPS)• Rebond
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Foam Molding
Foam Inlet
Expandable Mold
Liquid Resin withFoaming Agent
Fill Position
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Foam MoldingFoam Inlet
Expandable Mold
Liquid Resin with
Foaming Agent
Expanded Position
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Reaction Injection MoldingFoaming Agent
Foamed
Part
Mold
In-line
Mixer
Resin
Part A
Resin
Part B
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Foam-in-place
Refrigerator Walls
Foam
Foaming Injector Nozzle
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Extrusion Foaming
Paper
Paper
Extruder
(Resin and Foaming
Agent)
Saw
Belt Drive
Expanded Foam
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Extrusion foam line
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Casting Foams
Resin and
Foaming Agent
Expanded
Foam
Open Pan
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Casting Foams
• Skiving the Foamed Bun
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Foam Spraying
• Foaming agents mixed as they exit the
spray nozzle
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Expanded Foam Molding
• PS is the standard material used
• Can be done with PP or PE as well
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Expanded Foam Molding
Tiny BeadsExpansion
Chamber
Storage
Part
Mold
Steam or Hot Air Steam or Hot Air Unexpanded Expanded
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Rebond
• Scrap from other foaming processes
• Ground/chopped up
• Molded into sheets
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Material Considerations for
Foamed Parts
• Most thermoplastic and thermoset
materials can foamed by one or more of
the methods
• The most commonly foamed resins are
PVC, Polyurethane, PS, PE, PP, Epoxy
Phenolic, ABS, Ureaformaldehyde,
Silicone, Ionomers and Cellulose Acetates
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Foam Applications
• Strength to weight ratios
• Thermal insulation (Celestia product)
• Energy absorption
• Load bearing
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Energy Transmitted
Energy (g's)
Frequency (Hz)
Natural vibration frequency
Truck = 4-6, 12-14/ Train = 2-7, 50-70/ Ship = 2-20; Airplane = 1-3, 25-200
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Load bearing
Polyurethane foam
Natural rubber foam
Vinyl foam
Strain
Stress