URETHANE INDUSTRY GLOSSARY - E

A mixing head capable of being used for conventional or froth pours with no modifications other than the substitution of metering ports or 'mixer housings'.

A term used to describe the resistance of some fluids to flowing under certain conditions of shear and applied force. Under these conditions the liquid may behave more like a rubber than a water-like fluid, See dilantic.

See elastic component of viscosity.

The point of deformation beyond which a material will permanently deform rather than elastically recover. See yield point. The Method of Test for this is described in ASTM E 6-61.

A ratio between the force applied to cause the deformation and the resistance to that force by the material being deformed. It can be determined for samples in tension as well as compression. Where a straight line graph is not produced, a tangent line to the largest part of the curve is used to express the ratio. The modulus must be determined below the point at which the elastic limit is reached.

A rubber-like material not necessarily made from what we conventionally think of as rubber. In the urethane industry, elastomers are ordinarily thought of as the solid or non-foamed materials, but there are exceptions known as "blown elastomers" which have been foamed by methods conventionally used for expanding rubber rather than the methods used to make urethane foam.

The percent of its original length to which a specially shaped sample will stretch before breaking. The Test Method is described in ASTM D 1564-63T.

Are Additives to a formulation that aid in stabilizing a mixture, between the time it is mixed and poured and the time it starts to foam, by the formation of an emulsion. This becomes important at times as not all the isocyanate materials are readily miscible with all polyols or resins creating a tendency to separate quickly after the mixing of the components .

A suspension of fine droplets of one liquid in another.

Is the molecular weight of a chemical divided by the number of reactive (functional) groups. For example, the molecular weight of pure TDI is 174, the number of reactive groups is two (it is a diisocyanate) so the equivalent weight is 174/2 or 87. In a formulation, the number of equivalents of TDI must be balanced against the number of equivalents of water and polyol in order to achieve stoichiometry. The equivalent weight of isocyanate materials is often determined by the Amine equivalent test method and consequently the equivalent weight of the material may be called the 'Amine equivalents'.

The heat liberated by some of the chemical reactions occurring in the foaming mass. Urethane foam reactions fall in the general class of exothermic reactions, which have heat as a by-product. Under some conditions this heat becomes excessive and can damage the foam. Large pours or high density formulations are particularly critical in this respect because of the excellent insulating ability of the foam.

The final mixing of the liquid ingredients outside the final discharge nozzle on the way to the target surface. This is normally accomplished by turbulence created by air jets, and thus the mechanism or device is usually classed as a spray gun. An advantage of this type mixer is that a solvent flush is theoretically not required.

A slang expression meaning to adjust as closely as possible to the desired instrument setting by visual means or by sense of touch or feel without making mechanical cross-checks.