URETHANE INDUSTRY GLOSSARY - N

The chemical symbol for nitrogen. Nitrogen is often used as an inert, dry gas blanket over the chemicals in the otherwise sealed chemical tanks in order to avoid problems with moisture contained in atmospheric air.

The chemical symbol for the isocyanate reactive radical or group.

Is the ratio between the available isocyanate groups and the available hydroxyl group in a foam formulation. When referring to a complete foam formula , the term index is more commonly used. The isocyanate index is the NCO/OH ratio x 100. When referring to a prepolymer formula , it is more common to refer to the NCO/OH ratio.

The chemical abbreviation for n-ethyl morpholine, an Amine catalyst used in foam formulations.

The chemical abbreviation for n-methyl morpholine, an Amine catalyst used in foam formulations. It is slightly more volatile than NEM.

See N₂.

A term used by foam machine manufacturers to indicate a throughput or flow rate capacity that a particular machine was designed to handle with 'normal' formulations. Because of the extreme variability in the type of chemicals that can be used to make urethane foam, not all formulations process the same way on the same machines so that a machine capable of metering and mixing 30 pounds per minute of a 1000 cp viscosity material might only be capable of metering and mixing 10 pounds a minute of a 20,000 cp viscosity material.

A rather ambiguous term permitted to be applied to certain formulations of foam fulfilling certain conditions of test outlined in Test Method ASTM D 1692. In actual use particularly in confined areas, some, but not all, of the foams with this label may burn quite rapidly; therefore, if a foam is required that will not contribute fuel to a fire under any circumstances, a different method of test must be used. Since the term is misleading, it should not be used without precise statement as to the conditions involved.

A term generally used to describe a nozzle or mixer that does not become plugged in use. The term, when used by itself, should be taken to mean non-clogging 'in normal use with a normal formulation'. Non-clogging under any condition of use has not been demonstrated as yet by any device.

A metering system in which the metered chemical flow goes directly to the mixing head and out. During off periods, the flow of chemicals is stopped. The term is primarily used to describe those systems in which the metering pump itself is stopped, although it is occasionally applied to systems in which a valve is used to stop the flow to the mixing head and a pressure relief valve bypasses the flow to another location until the valve is reopened. See recirculate system.

See helix mixing.

A term used in working with 'on-off' mixing heads to describe those components introduced to the mixing zone through a port that is not controlled by the 'on-off' valve. For example, a 3 component mixing head of the 'on-off' type would normally have 3 valved ports that were simultaneously switched plus 2 additional non-valved openings that would normally be used for solvent and air but could be used for other components such as fluorocarbon 11and colors.

A very general term used to describe the discharge opening or tip of the mixing head or spray gun. It is occasionally applied to the entire mixing head, particularly if the device is hand-portable.

A term used to describe assistance applied toward the generation of many small, uniform bubbles as opposed to the formation of a few large bubbles in the same volume of space. As currently understood under chemically pure conditions it requires more energy to create a new bubble than it does to make an existing bubble larger, consequently without assistance foams would try to form the largest possible bubbles. The assistance normally given, as described by the term nucleation, may involve the addition of special molecules, small rough particles, dissolving high vapor pressure gas in the liquid, forming tiny gas bubbles mechanically throughout the liquid, or may even involve a shortening of the time interval during which bubble formation occurs in order to minimize migration of gas molecules toward existing bubbles.

Is a rather ambiguous term used to indicate the number of separate fluid streams that enter the final mixing zone. It should normally be qualified in use to avoid confusion. For example, a 4 component 'on-off' mixing heads would normally be expected to have 4 openings into the mixing chamber that are controlled by the 'on-off' valving when, in actual fact, many mixing heads have 2 additional openings that are not controlled by the valve. Contrarily, a 4 component continuous mixing head may have just the 4 openings with no additional ports.