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Foaming

MFG 355

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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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Self-healing foams

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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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Molded foams

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Reaction Injection MoldingFoaming Agent

Foamed

Part

Mold

In-line

Mixer 

Resin

Part A

Resin

Part B

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RIM

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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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EPS beads

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EPS

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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

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Compression Set

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Thank You