In this age of vulcanized rubber materials and thermoplastic plastic Elastomers (TPE) there is a wide range of elastic materials used to produce foamed products.
Expanded cellular elastomers come in open-cell, referred to as sponge rubber and closed-cell referred to as expanded rubber.
An elastomer is a polymer, rubber or TPE with elastic properties.
Materials that can be foamed range from natural rubber, neoprene, EPDM, nitrile, polyurethane and silicone (almost all rubber compounds can be produced in cellular form) to TPEs ranging from PVC to polyethylene. Naturally the polymer used will influence the characteristics of the end product with natural rubber being on the most lively side and polypropylene on the slow recovery side of the spectrum.
Processes used to expand the foam range from chemical to mechanical, each introducing gas into the polymer to form the cells. Functions of the foaming process range from producing simply a high volume low cost structure, to producing a soft compliant sealing or cushioning material. Reticulated foams are used as filters, a open cell foam with very thin walls is produced and then acid etched to remove the thin walls leaving only the very open structure where cells intersect.
Foam materials can be molded, extruded or formed into buns and skived into slices of sheet material. Today molding is rare, extruding is more common but sheet goods die-cut or slit into finished parts is most common. Note that foams have a natural skin on the outside in each of the base processes that is lost when the foam is slit or punched. Thus closed cell materials will have better sealing qualities while open cell materials will have better recovery properties.
Specifying Foam
ASTM has good specifications for foam products for industrial purposes.
Tests and specifications for flexibility and density, polymer, open versus closed cell, operating temperature and chemical resistance are only some of the classification criteria. ASTM D 1056 lists the classifications and references the test procedures that apply.
We work with all types of foamed materials and processes to produce your part. We can advise you on economical selections with proper performance.
Contact Us with Your Foam Project.
By Walter Jobst
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