Polyurethane Glossary

Prepared by The Edge Sweets Company, Inc.
Please visit our website: http://www.edge-sweets.com

The EDGE SWEETS Company
2887 Three Mile Road NW, Grand Rapids MI USA, 49544-1386
phone: 616.453.5458 fax: 616.453.6227

The Edge Sweets Company, Inc., ©1971 - 2005 All rights reserved. Printed in the United States of America.
Library of Congress catalog card number (FIRST PRINTING): 73-1 52730

We are the urethane industry experts. Please contact us if you require additional information or would like a hard cover copy of this glossary free of charge. You may reproduce glossary information ONLY if you provide a link to our site as the source (or reference our site in printed materials).

EDITOR'S NOTE

This glossary is an attempt to provide a firmer foundation than exists currently for the transfer of technical information or knowledge from person to person or company to company without misconceptions arising from the use or misuse of words having special meanings. Undoubtedly some of the meanings assigned here are different from those used by some individuals in the industry, but it is hoped that the meanings in broadest usage have been captured. For those readers having words or phrases that have been omitted, please feel free to forward them to us with their proper meaning(s). Some words that would not have been included for the U.S.A. alone have been included to aid in translations into other languages.

URETHANE GLOSSARY

ASTM

Initials used as an abbreviation for the American Society for Testing and Materials. An organization devoted to the establishment of standard methods and procedures of testing materials. Copies of the approved test methods for urethane foam may be secured by supplying the identifying code number of the test plus the fee.

Accelerator

Normally used in the chemical sense of being a substance used to increase the rate of a chemical reaction, often used synonymously with the term catalyst, amine catalyst, or tin catalyst.

Accuracy

In normal foam industry practice, it is required that the chemicals used be weighed, pumped and dispensed within plus or minus 0.5% of the correct amount. Capability of operation within these narrow limits is available from most machine suppliers. See also 'metering accuracy' and 'shot accuracy';.

Acid Number

The value given to trace residues of acids in the finished polyol. It is of interest because acids can react directly with NCO groups (TDI) and thus must be allowed for in formulation calculations (see index). The normal value for most polyether polyols is less than .05 parts per hundred. Most polyester polyols normally have an acid number between 0.1 and 0.5.

Activator

Adapters

Small mechanical parts that assist the joining of 2 dissimilar pieces, normally used to join pipes of different sizes or to assist in joining pipe to hose threads. Pipe threads are normally tapered while hose threads are straight.

Additive

A general term used to describe anything that may be added to the foam chemical mixture, not required in order to produce foam. It generally covers chemical classes such as plasticizers, colorants, reodorants, anti oxidants, fillers.

Adhesive Lamination

Adjustable Crossbar Height

A term used by liquid spreading device (reciprocator, traverser, spreader) manufacturers to describe the ability of machines to vary the height of the mixer discharge nozzle above the conveyor (or mold) by raising or lowering the crossbar or rails on which the mixer is riding. The adjustability may range from manually loosening bolts and lifting the crossbar into position up to automatic push button operation. Hand powered cranks turning built-in lifting screws are used for an intermediate type.

Adjustable Speed

A term used by machinery manufacturers to describe the ability of their pumps and mixers to be driven at different rates of speed. The minimum type covered by this somewhat all-inclusive term is a set screw adjusted split sheave (pulley). Other types range in complexity from manually rotated cranks or hand wheels up to automatic push button adjustment. Not all adjustable speeds are positive; thus some are not able to hold a setting after adjustment and others are not able to reset at the same markings in order to repeat the desired speed of rotation.

Adjustable Throughput

See fixed throughput and variable flow rate.

After-Cure

(See pre-cure and post-cure) a term used to refer to the period of time after all accelerated curing attempts have ceased during which maximum final physical properties are attained. Temperatures are usually maintained at 70-75° F during this period. Example: a molded flexible cushion may be pre-cured for 10 minutes at 250° F to develop enough properties to permit removal from the mold, then post-cured for 1/2 to 3 hours to reach 85% to 95% of the final properties, and then packaged and shipped during which time 'after-cure' continues until 100% of the properties are achieved. After-cure generally is not longer than 3 to 6 days with most formulations.

After-Drip

A term which describes material dripped from the discharge orifice of a self-cleaning mixing head after the continuous flow of liquid has ceased. It is usually objectionable and is influenced by mixer design, mixer wear, mixer cleanliness, material viscosity and flow characteristics, and leakage from the liquid delivery passages (metering ports). agitators-a term which usually refers to the mechanisms that mix and recirculate the various liquids within their tanks. These may be propellers, paddles, turbines, etc. Occasionally the term is used to describe the rotor or impeller that mixes the liquids together in the final mixing chamber, just prior to foaming.

Air Bleed

A term which refers to the practice of injecting very small amounts of compressed air (or other gas) into the mixing chamber or into the polyol stream prior to the mixing chamber in order to decrease the average cell diameter in the foam. A high degree of control over cell diameter can be achieved with a precision regulated air bleed system. See also 'catalyst air bleed adapter.'

Air Metering Device

A term which refers usually to a precision air bleed regulating system. Generally it includes regulators, filters, flowmeters, needle valves, check valves and also inline mixers.

Airless Spray

Method of atomizing a liquid stream for spray application purposes without using compressed air at the spray nozzle. Overspray and surface rebound are minimized.

Aliphatic

(See also Aromatic) one of the main divisions of organic compounds (those containing carbon) and particularly indicates those compounds having ab open chain molecular structure.

Ambient

An ambiguous term usually coupled with temperature and refers to the normal temperature of the particular room or environment in which the foam producing equipment or process is installed. It is often used to indicate U.S.A. house or factory temperatures of approximately 70° F.

Amine

A term which refers to a class of catalyst compounds used in the urethane foam reaction, These are characterized by having N or NH groups in the molecule and generally accelerate the 'blowing reaction' in preference to the 'gelling reaction'. The amines used as foam catalysts usually (but not necessarily) have a distinctive odor, and are miscible with water.

Amine Catalyst

Amine Equivalent

An analysis value determined for isocyanate materials to express their reactive strength, used in some methods for calculating 'stoichiometric balance' of a formula . The value secured has an inverse relationship to the strength of the chemical as the larger the value, the weaker is the reactive strength of the isocyanate per unit of weight. For example, the amine equivalent value for pure TDI is approximately 87 while that of the less reactive crude 'polymeric isocyanates' may be over 130. The method of analysis may be obtained by request to one of the major chemical companies supplying the isocyanate.

Angle of Foam Rise

A term which refers to the angle formed between the rising foam front and the moving surface from which it is rising on a continuous slab process. This is usually critical for a given formula with an excessively large angle tending to cause cracking of the foam block, while too low an angle tends to cause excessive settling and splits. Adjustments to conveyor speed, chemical flow rate or conveyor angle are usually helpful. Under extreme conditions, the catalyst balance' of the formulation or the processing temperature may have to be modified.

Anisotropic

Is used to describe foam having different properties when tested along axes in different directions, e. g. parallel to foam rise as opposed to perpendicular to the foam rise. This difference occurs under conditions causing the individual bubbles to elongate in the direction of foam rise, creating a strong columnar structure parallel to foam rise and a weaker cylindrical structure perpendicular to the foam rise.

Antioxidants

Materials which when added to a foam formulation improve the resistance of the foam to oxidative type reactions. Some of these materials retard the yellowing of flexible foam; some improve the aging characteristics of the final foam product under both dry and humid high heat conditions.

Antistatic Agents

Chemicals which impart a slight to moderate degree of electrical conductivity to plastic compounds, thus preventing the accumulation of electrostatic charges on finished articles. They may be incorporated in the materials before molding or applied to their surfaces after molding. They function either by being inherently conductive or by absorbing moisture from the air. Examples of antistatic additives are long-chain aliphatic amines and amides, phosphate esters, quaternary ammonium salts, polyethylene glycols, polyethylene glycol esters, and ethoxylated long-chain aliphatic amines.

Application

A term sometimes used as a noun in describing the practical use of a particular formulation or piece of equipment. The use of urethane foam is often described in a manner such as 'an insulating application' or a 'spray-in-place application'.

Applicator

A term used to describe an individual or company specializing in the application of foam to a surface or structure. It is often used to describe those who apply foam by spraying and thus are called 'spray applicators'.

Aromatic

A term which refers to a class of organic chemical compounds characterized by having a benzene ring type molecular structure. Tolylene diisocyanate is an example of this type chemical but other isocyanates may or may not be. See also aliphatic.

Artificial Ageing

The accelerated testing of plastics to determine their changes in properties such as dimensional stability, water resistance, resistance to chemical and solvents, light stability, and fatigue resistance.

Automatic Pressure Cut-Off

A term used to describe a control system on a metering unit in which a pressure surge or over-pressurization in the fluid circuit is sensed, actuating a relay which turns off the pump drive motor. This is an excellent safety-feature and does not affect the positive metering value of the system.

Automatic Solvent Flush

A term used to describe a solvent cleaning system for a urethane foam mixing and dispensing head. The usual system is activated by a push button which begins a cycle consisting of a timed amount of solvent, dispensed by a pressure pot or pump, injected into the solvent flush hose and then followed by a timed dispensing of compressed air blowing the solvent from the hose line into the mixing chamber and from there to the waste container. Both solvent and air timers can usually be adjusted to obtain optimum cleaning with maximum economy. A newer system termed 'fully automatic solvent flush' includes an additional timer which initiates the solvent cycle automatically if pouring has not occurred during a preset time period.

Auxiliary Blowing Agent

A term which usually describes a 'low temperature boiling solvent' type blowing agent added to a formulation deriving at least 80% of the gas required for foam expansion from the water-TDI reaction.

Back Cushion

A chair cushion that forms the back of the unit and is characterized by being leaned on rather than sat on. Generally a lower density, softer foam is used for a Back Cushion than is used for a 'seat cushion'.

Back Pressure

The higher upstream pressure developed by a restrictive valve or regulator.

Ball Rebound Test

One of several test methods for comparing various flexible foam samples for resilience (see Resilience Value). A steel ball of specified mass is dropped from a fixed height onto a foam sample, and the height of the rebound of the ball is recorded. The rebound height is divided by the original height to give a percentage. The method is a relative test rather than absolute, since the density of the foam has a strong influence on the results. The Test Method is described in ASTM D 1564-63T.

Barrier Coat

A term used to describe a clear or pigmented coating sprayed into a mold prior to foaming, which adheres to the foam and provides a base for further finishing steps. Usually used for rigid foam moldings finished to resemble wood.

Batch Mixer

A term which describes a type of mixer in which the entire amount of the formula required is poured or pumped into the mixing head and mixed for a definite period of time with multiple recirculation of the material through the mixing zone. The entire amount of the material is poured out of the mixing head at the conclusion of the mixing time period.

Batch Mixing

The process of simultaneously mixing the entire amount of the formula required in one container.

Batch Tank

A term normally used to describe the polyol or other premix tanks used in the flexible foam slab process. In this process some of the ingredients required are premixed in a Batch Tank in order to cut down on the number of components required to be metered into the final mixer or to eliminate the problems involved with metering very tiny amounts of materials into a continuously mixed stream. Also called 'machine tanks' to differentiate them from 'in-plant storage tanks'.

Belt Conveyor

A type of conveyor in which the conveying is performed by means of the movement of the top surface of the structure as a continuous ribbon or belt. The belt surfaces normally used in the urethane foam industry are metal, cloth or rubber. The commonest construction used in the flexible foam slab process is probably that of the interlocked metal belt.

Blanket Heater

A term which refers to the type heating device that is wrapped around a chemical tank to provide heat by conduction through the tank walls. Some of these heaters are equipped with variable thermostats; some are not. They are often used to supplement the in-line heaters when the chemical to be pumped has a high viscosity, creating a cavitation problem if not warmed.

Block

A term used to describe a cut-off segment of the continuously produced loaf of flexible or rigid foam being made by the slab' technique. In some cases this Block would have top, bottom, and side skins intact and have cut surfaces only on the ends. In other cases the top, bottom and side skins may be removed by in-line trimmers leaving a smooth rectangular Block.

Blowing Agent

The chemical ingredient in the formulation that provides the gas creating the expansion of the foam. This can be either a low boiling chemical that vaporizes from the heat of the reaction such as fluorocarbon 11 or a chemical such as water that reacts with the isocyanate material to produce carbon dioxide. The low boiling chemical type formulation is usually referred to as 'solvent blown foam', while the other type is commonly referred to as 'water blown foam'. blowing reaction-one of the several chemical reactions occurring in the final mixture while it is foaming. It is most often used to refer to the chemical reaction resulting in the release of carbon dioxide.

Blown Elastomer

Blows

Cavities that occur in the interior of the continuous foam slab as it is produced. Some of these cavities reach all the way to the top surface of the Block and can be seen ejecting little clouds of vapor just past the peak rise point. See flaps.

Board Foot

A standard of measurement in the foam and construction industry which refers to a square foot of material one inch in thickness. See super foot.

Boardiness

A descriptive term applied to foam that feels stiff and not flexible and yet is still in the flexible category. A typical foam of this type would require a small amount of force to cause an initial deflection in the foam and very little more force to deflect it to 50% or more of its thickness, and then a straight line increase in force is required for further deflection. See IFD (65/25) Index and plateau.

Board Stock

Sometimes used to describe the flat sheets of rigid or flexible foam cut from Blocks of foam. However, recently the term has been specifically applied to the product of a Continuous Lamination Foaming Line on which the foam is sandwiched between two skins.

Boiling

Is a phenomenon that occurs when the gas being generated is not trapped in the liquid resin to make foam. It occurs usually if the surface active agents have been omitted or are defective, or if gelation is not occurring rapidly enough in relation to the speed of the blowing reaction.

Bolster

A specially shaped Back Cushion, usually for Danish modern style couches or divans. The normal shape is a truncated wedge, although round, rectangular, and triangular are also available. The term is also used to describe a cylindrical, stiff pillow used for decorative purposes on a bed.

Bonding

A synonym for gluing, adhering, laminating or rebonding. See rebonding.

Bones

A slang term referring to the pattern of high density streaks or flow lines that occur on the bottom of a foam Block when undercutting of the rising foam front occurs, or when shearing movements occur in the rising foam mass.

Borer

A mechanical device for drilling a long straight hole through a Block of foam in order to insert the mandrel used in 'log peeling''.

Buckshotting

A term used in slightly different ways by many people but ordinarily refers to the presence of a scattering of cells 2 to 4 times larger than the uniform background cell diameter. If a thin section of the foam were cut from the Block, it would look as if a shotgun had blasted it with buckshot.

Buffered Catalyst

A catalyst, usually a very alkaline Amine, that has been partially or wholly neutralized with acid so that the reaction would not be affected by the extreme alkalinity of the catalyst. The general effect of the buffering is to slow the rate of the polymerization reaction.

Buffers

Chemicals added to the formula that decrease the sensitivity of the formula to slight changes in the alkalinity or acidity of any of the components . They are also known as buffering agents.

Bulking Agent

A material or chemical added to another chemical that increases the quantity of the mixture required without changing the chemical reactivity of the total. The term is not only used to describe solid or powdered Additives, but is also used to refer to liquid Additives. An example is the bulking or dilution of the tin catalyst that is often used to gain greater control over the metering of very small quantities. In this case the tin catalyst is often diluted or bulked-up with a portion of the polyol. Barium sulfate is a solid bulking agent often added to the polyol to increase the density of the final foam product.

Bulk Storage

A series of tanks large enough in capacity that bulk shipments of one or more of the ingredients used in the formulation can be unloaded and stored directly on the premises. Also called 'in plant storage'.

Bun

Another synonym for Block.

Burp

A term used to describe what happens when a puff of gas is released during the formation of blows.

The common abbreviation for the cubic centimeter of the metric system. For liquid measurement the abbreviation ml (milliliter is often used in place of cc. The two measurements are approximately equal.)

CD Curve

A common abbreviation for Compression-Deflection curve.

CFM

An abbreviation for cubic feet per minute.

cps

The abbreviation for centipoise.

CPS

The abbreviation for cycles per second. A recent international decision suggests the use of HERZ instead of CPS with reference to electrical wave motions. CPS is satisfactory for mechanical cycles.

C0₂

The chemical symbol for carbon dioxide.

CO₂ Blown Foam

Foam in which all of the gas for expanding or blowing is carbon dioxide, generated by the chemical reaction between water and the isocyanate material. This type foam is called 'water blown foam'.

Calibration

A synonym for metering, referring to the weighing of carefully timed amounts of chemicals from the dispensing ports of the mixing head in order to set an exact ratio of flow rates between each component or to set an exact total

Casting

A term used to describe the filling of small molds with liquid, nonfoaming formulations of urethanes or other types of polymers, sometimes called solid elastomers or casting resins. Occasionally used to describe the potting of electrical or mechanical parts in foam.

Castor Oil Based Foam

Foam made from a formula in which the major polyol ingredient is derived from castor oil.

Catalyst

Technically, a chemical that has the property of being able to change the speed of a chemical reaction without apparently taking part in the reaction. Most of the so-called catalysts of urethane form reactions do have some part in the reaction and consequently do not fall under the proper definition, although they are often referred to by that name. (See Accelerator.)

Catalyst Air Bleed Adapter

A device used to surround a catalyst metering tube with a compressed air flow in order to prevent unwanted accumulation of foam around the port that could interfere with the flow of the liquid.

Catalyst Balance

The ratio between the Amine catalyst and the organotin catalyst. See reaction balance.

Catalyst Mix

A shortened form for catalyst mixture. Most formulations require delicate balancing between the blowing and gelation reactions, and consequently blends of different types of catalysts are often used together with an inert carrier or diluent to aid in metering accuracy or in miscibility.

Catalyst Solution

A synonym for catalyst mix.

Cell

Is synonymous with bubble or pore. It refers to the cavities left in the foam structure after the bubble walls have completely polymerized and solidified or curled back and fused into the boundary joints to form a skeletal structure. Cells can be closed (intact walls) or open (skeletal ribs only). Cell shape is more like an irregular polygon than a globe.

Cell Count

The number of cells or bubbles per linear inch or per centimeter. Cell count is very important to the physical properties of foam. See cell size.

Cell Membrane

The thin intact film that forms the bubble walls in closed cells, also called windows.

Cell Size

A term which refers to the average diameter of the pores (bubbles) in the filial foam product. Although often still referred to as fine, medium or coarse, or by the diameter in microns, most workers refer to the number of cells per linear inch (cell count).

Cell Structure

(See cell size) A term often used to point out overall uniformity of foam cell diameter. Example, 'uniform cell structure' describes foam with generally equal cell diameters.

Cellular Plastic (Expanded Plastic, Foamed Plastic)

A plastic with numerous cells disposed throughout its mass. The terms cellular, expanded, and foamed plastic are used synonymously. A cellular plastic may be produced by (1) incorporating a blowing agent which decomposes to liberate a gas; (2) mechanically stirring in a fluid or gas; (3) adding a water soluble salt or a solvent extractible agent to the mix prior to foaming then leaching out the agent after foaming to leave voids; or (4) other techniques.

Centipoise

1/100th of a poise, commonly used in describing the viscosities of the various chemical components in urethane foam. Although many formula viscosities are less than 2000 centipoise, some individual components may have viscosities as high as 100,000 to 200,000 centipoise. See poise.

Chain Extension

Is the lengthening of the spine or main chain of polymer molecules by end to end attachment usually involving condensation of functional groups between two or more molecules during the chemical (polymerization) reaction. Cross linking, a side to side attachment of molecules, also occurs during polymerization. Some physical properties are enhanced more by chain extension, others by cross linking.

Channeling

A small scale or narrow undercutting of the expanding or rising foam front by a stream of the mixed clear liquid. This is usually due to wrinkles in the paper or uneven distribution of the liquid. Channeling often results in high density ridges on the bottom of the foam Block referred to by some as bones and others as striations or flow lines. Occasionally the term is used to refer to the condition arising when a heated portion of a viscous liquid is recirculated back into a tank without agitation, flowing immediately to the inlet of the pump without mixing with the cooler liquid.

Charging

A term occasionally used to describe the process of filling the machine tanks with the various quantities of chemicals.

Chemical Seals

The disks and flanges used to separate the foam ingredients from the operating mechanism, usually of a pressure gauge. The interior of the bourdon tube or bellows is filled, under vacuum conditions, with an inert fluid, up to the back side of the metal disk or diaphragm. This combination of liquid and membrane effectively isolates the mechanism without affecting Accuracy.

Chiller

A heat exchanger used for cooling the chemical materials. Scraped surface, tube and shell, and plate type exchangers are all used, with the scraped surface being the most efficient, particularly with the higher viscosity materials,

Chiller Package

A heat exchanger used for cooling the material but including the cooling source. It usually consists of a scraped surface, tube and shell, or plate type heat exchanger plus a refrigeration compressor and controls. The package unit may be a direct expansion type in which the refrigerant expands directly into the main heat exchanger or it may be of the liquid transfer type in which the refrigerant gas expands into an intermediate heat exchanger, and then a circulating liquid is used to conduct the heat from the main heat exchanger. See cooling media.

Chopper

A term sometimes used to describe the in-line type cut-off saw, and sometimes used to describe a device used to cut or chop urethane foam trims into small pieces for rebonding, stuffing toys, pillows, etc. See crumb.

Clean-Out Type Chemical Seal

A special type chemical seal permitting cleaning of the chemicals side of the disk without complete disassembly. See chemical seal.

Clickable Foam

Foam that recovers 100% from the pinching effects of clicking.

Clicking

The process of stamping out irregular shaped articles from thin sheets of foam by means of a hammering mechanism and a steel-rule die. See die cutting.

Closed Cells

Is the property of a foam of having each individual bubble completely sealed off from its neighbor so that no exchange of gas can take place except by diffusion through the walls, With rigid foams, it is usual to try for 100% closed cells to achieve maximum thermal insulating ability and minimum water pickup. With flexible foams, it is normal to try for 100% open cells for maximum flexibility, resilience, and breathability even to the extent of achieving a true skeletal foam in which even the broken membranes between cells have been removed or fused back into the ribs."

Closed Molding

The practice of molding a foam object in a cavity in which the foaming liquid is 100% contained with only gas being allowed to escape.

Coarse Cells

Very large bubbles averaging not over 20 to 30 cells per lineal inch. See cell size.

Cold Molding

The process of flexible foam molding in which the molds are maintained at temperatures between approximately 100° F and 150° F as compared with the alternate "one shot" molding technique in which temperatures of 250° F to 350° F are obtained within one minute of pouring. Flexible prepolymer molding normally has utilized temperatures in the "cold molding" range.

Collapse

The sudden or complete loss of height occurring after the foam has partially or completely expanded. Under extreme conditions, the foaming chemical mixture may not expand at all but may merely boil violently and then harden into a solid sheet. See boiling.

Colorant

A dye or pigment used to color the foam for appearance, identification, or for other sales purposes. Occasionally a necessary minor ingredient may act as a colorant.

Complete Package

A term normally used by those interested in continuous slab processing and referring to all of the equipment required to make a product. This comprehensive list generally includes the paper handling equipment, chemical handling equipment, the foam machine, the conveyors, the spreading or traversing device, curing devices or ovens, cutting equipment and packaging equipment. Testing equipment and technical service may or may not be included.

Component

A term used to describe a separately metered stream of liquid that will be directly introduced into the mixing head for the final mixing. Although as many as 11 or more chemical components may be used in a formulation, these may be preblended into as few as two components for the final formulation used in the machine. See number of components.

Compression Load Deflection (CLD)

The determination of the resistance to compression of a foam sample when the entire area of the sample is compressed. This Test Method is described in ASTM.

Compression Set

An industry expression used to describe the recovery of foam from static or fixed compression. Less than 10% compression set (which is greater than 90% recovery) is usually accepted as good. Also called 'percent set.' This Test Method is described in ASTM D 1564-63T.

Compressive Strength

A term primarily used to describe the resistance of rigid foam to compression. This test method is described in ASTM D 1621-59T.

Continuous Mixing Head (Continuous Mixer)

A mixing device capable of dispensing homogeneously mixed material continuously, without affecting the temperature or pressure of the mixture by virtue of its continuous operation. The individual components may be valved as in the 'on-off' mixing heads, but are not required to be. Instantaneous start and/or stop of all components is not essential, although desirable.

Continuous Slab

The production of a continuous, homogeneous, seamless loaf of urethane or other foam by laying down a uniformly distributed liquid film of mixed materials on a conveyor belt moving beneath the mixing head at such a rate of speed as to form a stable rising front of foam. The process may only last for a few minutes, or it may run for 24 hours per day depending on sales requirements.

Conventional System

A method of foam production in which the mixed material being discharged from the mixing head is a clear liquid. This term is used to differentiate between non- frothed (conventional) and frothed systems of production.

Converting

A term which refers to the process of cutting and shaping used to convert bread loaf shaped slab foam Blocks into saleable items.

Conveyor Belt

An endless loop of material, either metal, cloth, rubber, or paper, used to carry the expanding foam mixture in the manufacture of continuous slab foam. The types are usually further described as 'linked metal', 'slat type metal', 'rubber' (even when fabric reinforced), 'cloth', 'cotton', or 'canvas belt'.

Convoluting Cutting

The splitting of a sheet of flexible foam while it is variably compressed so that two matching pieces of foam are created, each with alternating patterns of hills and hollows on their adjacent sides. The main advantages are that the foam can be made softer and more resilient mechanically and that two pieces of foam are produced, each of which is almost as thick as the original piece.

Cooling Media

The material that carries the heat away from the chemicals. In the direct expansion type of heat exchanger, the refrigerant gas is the cooling medium; in the liquid transfer or 'brine' cooled type of heat exchanger, the 'brine' is the cooling medium for the chemicals and the refrigerant gas is the cooling medium for the 'brine'. In most modern cases, a solution of ethylene glycol permanent anti-freeze is used for the 'brine' solution rather than the salt solution. See chiller package.

Core Density

The density of the foam at the center of the foam object. In most cases, foam will form a density gradient in an object with the highest density being at the outer or skin surfaces and the lowest density being in the center or core of the object.

Cracks

Long narrow openings or cavities in the foam Block that have widely separated and relatively smooth sides. These are subdivided into side cracks, top cracks and pocket blows (internal cracks) for trouble shooting purposes. See the specific headings for more detailed descriptions.

Cratering (Moon Cratering)

The condition in which the top surface of the continuous slab of foam resembles a photograph of the surface of the moon. It is normally caused by entrapment of very large gas bubbles that may have originated in the mixer or developed from excessive lay down splashing or possibly liquid undercutting (channeling) the foam front.

Crazy Balls

Globules which may pop to the surface of the foam front under certain conditions of flexible slab foam manufacture. The balls may race madly down the slope of the rising foam front or dash erratically around on the surface or just beneath the surface of the rising foam.

Cream Line

The point on a continuous foam slab conveyor where the clear mixed liquid becomes cloudy and begins to expand. When streamers are present, they extend upstream from the cream line into the clear material. When all variables have been stabilized during a production run, the cream line will remain at a fixed distance downstream from the mixing head.

Cream Time

A time interval defined somewhat differently between a laboratory batch or hand mix and a production machine mixer. The laboratory or batch type mixing definition is usually 'the time between the start of the final mixing and the point at which the clear mixture turns creamy or cloudy and starts to expand'. With the machine mixing process the cream time is generally taken to be 'the time between the first material being poured until that material turns creamy or cloudy'. Occasional misunderstandings arise over this and over the occasional practice of labeling the time between final mixing and the start of creaming or foaming as 'cream time' for laboratory or Batch Mixing when it could more properly he termed 'liquid handling time'. The problem results from the fact that laboratory type mixing requires as much as 100 times more mixing time than machine mixing. "Frothing" masks the cream time but usually extends the overall 'handling time'.

Creep

The dimensional change with time of a material under load, following the initial instantaneous elastic deformation, Creep at room temperature is sometimes called Cold Flow.

Cross Linking

Applied to polymer molecules, the setting-up of chemical links between the molecular chains. When extensive, as in most thermosetting resins, cross-linking makes one infusible super-molecule of all the chains.

Crown

A term used by the furniture industry to describe a mattress or cushion that is thicker in the middle than it is at any edge. This is much easier to achieve with molded articles but can be achieved for slab produced articles with the use of special cutting or abrading machines.

Crude Isocyanate

Is a term sometimes used to describe an undistilled isocyanate mixture containing several different polymeric isocyanates. These mixtures are ordinarily a dark brown in color as opposed to the clear water white color of distilled TDP. Some chemical manufactures object to the description 'crude' and consequently many prefer the term 'polymeric' isocyanate or 'undistilled' isocyanate.

Crumb

A term used to describe very finely divided pieces of flexible urethane foam that have been shredded, ground, milled or torn from flexible foam trims or scraps.

Cubic Centimeter

A common metric measure of volume developed from lineal measurement. There are approximately 16.4 cubic centimeters in a cubic inch. The liter is a preferred volumetric measurement, particularly liquids. One milliliter (ml) is approximately equal to 1cc.

Cubic Foot

A common measure of volume in the English System. This is a cube with length, width and height all equal to 1 foot. There are 1,728 cubic inches in a cubic foot. See cubic centimeter.

Cubic Meter

A common measure of volume in the metric system developed from lineal measurement. This is a cube with length, width, and height all equal to 1 meter. Since there are 100 centimeters in a meter, there would be 1 million cc's in a cubic meter. There are approximately 35.3 cubic feet in a cubic meter. A meter is approximately 39.4 inches in length.

Cure

A term which refers to the completeness of the chemical reaction. At 100% completion, the foam should have 100% of the maximum physical properties attainable with that particular formulation used. Because 100% cure is not always reached in a practical length of time, some arbitrary time- temperature period is usually assigned to a particular formula to designate a practical level of cure at which testing for physical properties may be started. See cure time.

Cure Oven

The final oven into which foam articles are placed in order to achieve the desired final level of accelerated cure. The term is sometimes ambiguous in normal use and is usually qualified with a prefix or another word to make it more specific, such as pre-cure or post-cure.

Cure Time

The time required to achieve a specified level of cure. See pre-cure, post-cure and handling time.

Curtain Wall Panel

Any type of panel that is hung on the outside of a building to form the exterior skin of the building, without bearing any structural load other than that which itself generates, sandwich panels with a foam core are often used in this type application.

Cut-Off Saw

A special type of foam cutting saw that is used to make vertical cuts. The traveling cut-off saw is used to make cuts on a continuous slab line in a direction across or perpendicular to the direction of foam movement, while the foam is moving. The stationary cut-off saw is used to cut long slabs into shorter slabs while the foam slab is stationary. This type of cutter is normally a special band saw, having the blades twisted 90" from the plane of the wheel surfaces in order to avoid interference problems with the saw wheels or the other portion of the blade. Another version of this type saw is based on the vibrating bayonet type of blade.

DABCO

Is a registered trademark used for triethylenediamine, a very powerful Accelerator or catalyst of the tertiary Amine family. It is used as a highly selective blowing reaction catalyst for flexible foam and a more general catalyst for rigid foams.

DTA

See differential thermal analysis.

Day Tanks

A slang expression generally meaning either Batch Tanks or machine tanks used for one day's production run. The tanks may not have to be very large as a 'daily' production run may be only 20 minutes long for some factories.

Decorator Pillows

Small, variously shaped pillows, usually with bright colors, that are thrown onto chairs and sofas for color accent or general decoration. Also called throw pillows or occasional pillows.

Degree of Polymerization (DP)

The number of structural units or mers in the 'average' polymer molecule in a particular sample. In most plastics the DP must reach several thousand if worthwhile physical properties are to be had.

Demolding Time

The time between pouring the liquid into the mold and the removal of the foamed article from the mold. This is usually kept to the minimum possible time in which the partially cured object can be handled without damage, since it is more economical to reuse the molds as quickly as possible.

Density

The weight of a specified volume of material (foam). In some countries this is expressed as pounds per cubic foot; in others it is expressed as grams per cubic centimeter or kilograms per cubic meter.

Density Profile

The graph plotted from variations in density occurring in foam samples due to physical problems of heat loss, surface wetting, and shearing of foam during movement. Because of these factors, most foamed articles exhibit a variation in density from the outer skin into the geometrical center. When this variation is plotted on a graph, the result is a density profile shaped like the letter 'U'.

Dibutyltin Diacetate

Is a powerful catalyst of the organotin group. See organotin catalysts.

Dibutyltin Di-Ethyl Hexoate

Is a powerful catalyst of the organotin group. This is one of the best, but is, unfortunately, not destroyed by the heat of reaction. See organotin catalysts.

Dibutyltin Dilaurate

Is a powerful catalyst of the organotin group. It is sometimes used for rigid foam and for adhesives. See organotin catalysts.

Die Cutting

The process whereby shaped foam articles are stamped out of a sheet of foam by the impact of a die against the sheet of foam. This can be done by an impact device hitting a steel-rule type die on an individual basis, or by a special roller die compressing the foam sheet against a cutting bar or roller on a continuous basis. This is a low cost method of providing very unusual shapes. Another name for this process is 'clicking'. The lowest cost dies for this type work are called 'steel rule dies' and consist of specially shaped, sharp edged steel straps imbedded in a wooden backing. See also clicking and clickable foam.

Differential Thermal Analysis

Is an examination technique whereby the foam may be heated to destruction while a temperature profile recording is being taken. This test assists the developmental chemists and engineers to better understand the behavior of foams during exposure to high temperature and flames.

Diisocyanate

Is one of the major chemicals used in the manufacture of urethane foam, particularly flexible foam and rigid prepolymer intermediates. Tolylene diisocyanate (TDI), which is currently the most popular one, is an Aromatic chemical having a benzene ring type structure and two isocyanate (NCO) groups attached to two of the six possible positions. The most commonly used type of TDI is a mixture with approximately 80% of the molecules having one of the NCO groups in the ortho position and one in the para position with the other 20% of the molecules having both NCO groups in the ortho position. One of the reasons for the warning against allowing this type material to freeze is that these two isomers will selectively separate during freezing, changing final foam properties if reacted partly frozen.

Dilantic

Is a term sometimes applied to a liquid that resists being moved but is quite fluid at rest. Some of the polyols used in the manufacture of urethane foam are not Newtonian (water- like) fluids and can be described by this term. They are characterized as being very difficult to handle, particularly at higher flow rates. The phrase 'high elastic component of viscosity' is also used.

Diluent

A material used to extend or bulk up another material without changing the reactivity of the original material other than by the dilution occurring. The term is usually applied to fluids; whereas the words bulking agent, extender and filler are generally used with solids. This type material is also called 'liquid filler'.

Dimensional Stability

Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.

Dimer

A substance (comprising molecules) formed from two molecules of a monomer.

Diol

A polyol or resinous material having two reactive hydroxyl (OH) groups attached to each molecule.

Discharge Orifice

The port or opening through which the chemicals are discharged. This term is usually restricted to the final discharge of the mixed materials rather than to intermediate points opening into the mixing chamber, which are normally called metering ports or metering tubes'.

Discoloration

The gradual yellowing of urethane foam due to a photochemical reaction occurring from the effect of certain wave lengths of light. It is faster in sunlight than in artificial light, although it occurs in both. At the moment there is no inexpensive method of prevention, although several methods are in use to retard the reaction and to lessen the final extreme of discoloration. It is possible to mask the reaction through the use of colorants. Occasionally fresh foam will discolor in the center of the Block for several reasons, one of which may be an excessively high internal temperature.

Distribution Block

A term which on urethane foam equipment refers to a manifold arrangement used on continuous or non-recirculating systems for collecting the various component streams together to enter the mixing chamber. There is no valving in this type Block, although there may be valves in the feed lines.

Double Cells

A slang term used by some as a synonym for buckshotting.

Dribble Marks

Long lines of undesirable large bubbles rather close together and usually just under the top skin of Blocks of slab foam. They generally result from a combination of excessive channeling and too much air entrapped in the liquid deposited on the moving conveyor belt. The channeling tends to line up the bubbles and carry them under the foam front resulting in dribble marks. These unsightly chains of bubbles create a low tensile line at which tears or rips can easily initiate.

Dry Heat Aging

An accelerated aging test that helps to screen out formulations that may have a tendency to deteriorate too rapidly under certain climatic conditions. The foam samples are exposed to dry heat for varying periods of time as specified in ASTM Test Method D 1564-63T.

Dynamic Balance

A term sometimes used to describe the stability achieved after all operating variables are in balance on a continuous slab foam production line, and the cream line and peak rise point remain at an exact point indefinitely.

Either-Or (Combination) Mixing Head

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'.

Elastic Component of Viscosity

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.

Elastic-Fluid Behavior

See elastic component of viscosity.

Elastic Limit

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.

Elastic Modulus

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.

Elastomer

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.

Elongation

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.

Emulsifiers

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 .

Emulsion

A suspension of fine droplets of one liquid in another.

Equivalent Weight

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'.

Exotherm

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.

External Mix

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.

Eyeball In

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.

Fadeometer

An apparatus for determining the resistance of resins and other materials to fading. This apparatus accelerates the fading by subjecting the article to high intensity ultraviolet rays of approximately the same wave length as those found in sunlight.

False RMA

A term which refers to the practice of increasing the initial RMA of a foam sample by formulation techniques which give only a temporary boost in firmness that is soon lost in normal use (flexing) of the foam product. See flex fatigue.

Fast Heat

Intense heat supplied to a mold in order to raise the temperature of the mold-foam interface to 250° F. or higher within 1 or 2 minutes after the pour. This has been found to shorten the handling time, and to improve the quality of the skin and ha1 physical properties of the molded article. This is used in 'one shot' flexible foam molding.

Fast Heat Oven

An oven capable of supplying the intense heat required for the fast heat process. The most common type are those using either gas or electric radiant heat.

Filler

An inert material added to the foam formulation to change the final physical properties. Normally fillers are used to increase the density of the product without significantly adding to the cost, or they are used to assist in a cost reduction. The solid fillers often result in higher load bearing properties but lower tensile and tear strengths.

Filter

A device to remove unwanted particles of material from the liquid streams of chemicals. For trouble free operation all lines should be properly filtered.

Fine Cells

A term which is used to describe foam with a cell count of 80 or more per lineal inch, See cell size.

Fingernail

A foam industry term used to describe the reaction of foam to a point indentation such as would occur when pressing a fingernail firmly into the foam article. 'Good Fingernail' means rapid recovery with no permanent marking. 'Poor Fingernail' means slow recovery or failure to recover leaving a line or point impression in the foam. With experience this can be a useful screening test for relative comparisons between foams.

Fixed Calibration Time

The practice of metering the various fluid streams during a fixed time interval such as 6 seconds or 1 minute in order to calibrate and set the liquid streams to a desired total flow rate per minute as well as to a desired ratio with each other.

Fixed Ratio

The condition of having all components with a fixed throughput so that ratio variations are not possible. See Ratio Control.

Fixed Throughput (Fixed Flow rate)

A term used to describe a machine with one or more pumps directly connected to the drive motors so that no variation in flow rate is possible.

Fixtures

An ambiguous term used at times to describe the more permanently installed portions of the mechanical handling devices needed in order to load and unload molds and to carry them through the curing area. The term jigs is sometimes used to describe that portion of the total that aids in fastening the molds to the fixtures.

Flak

A slang term used to describe many small splits scattered widely throughout and on the top surface of a foam slab or Block. This is usually seen in flexible slab production when the gelation or polymerization reaction has been excessively retarded in relation to the blowing' reaction.

Flame Lamination

The practice of sticking together or gluing flexible foam and fabric by melting one surface of the foam with radiant heat and quickly pressing it to the fabric before the melted material resolidifies. For best results a slightly thermoplastic formulation of foam (normally classed as a thermoset) is needed. See definition of thermoset and thermoplastic.

Flame Retardent

Has several meanings according to the Test Method used. In general, it can be said that a flame retardent material imparts a certain degree of flame retardancy to a foam, i. e. the foam will burn less rapidly or lose less weight on burning.

Flammability

Describes the relative burnability of the material in a specified situation. Meanings vary according to the test method used.

Flaps

The external symptom of large internal blows or voids. These generally develop just past the peak rise point and are usually semi-circular tears in the top skin that connect with the internal voids. Under extreme conditions they may occur prior to the peak rise point.

Flashing or Sparkling

A condition in continuous slab foaming, during which there is a continual release of tiny bubbles of gas from the surface of the mixed material just after it has been poured on the conveyor. It may continue until the foam has partially expanded. Under certain conditions of light reflection, the foam appears to sparkle. It resembles boiling to some extent, but the bubbles are so tiny that no collapse occurs and foaming proceeds normally as soon as the material viscosity has increased to the point in which all gas is trapped.

Flat Blade Impeller

A mixing blade that is characterized by a generally single plane shape or flat appearance. It may be solid, perforated with various patterns, or may be irregular in contour.

Flex Fatigue

The loss of physical properties of a foam sample undergoing continuous flexing of a specified magnitude, duration and rate. The Test Method is described in ASTM D 1564-63T.

Flexible Mold Material

The rubber like material used for molding very intricate shapes and contours into rigid foam. These materials can be any elastomers but are more usually urethane or silicone based. The usual compounds are liquids which are poured over the 'master', allowed to gel, then removed and oven cured to maximum tensile strength before use.

Flexible Molds

Molds made of rubber or elastomeric plastics used for casting plastics. They can be stretched to remove cured pieces with undercuts.

Flexible Shaft Adapter

A special metal spindle that attaches to a motor shaft at one end and permits coupling of the flexible shaft to the other. These Adapters are different for each motor shaft size and for each flexible shaft size.

Flexible Shaft Mixer Drive

A long flexible coupling between the mixer drive motor and the mixing head. This type drive shaft is often used when the mixing head must be moved during operation. The drive motor is remotely located in order to cut down on the weight and inertia of the mixing head assembly. Durability of the shaft is good if properly installed and used according to the manufacturer's specifications. This arrangement is also called 'remote drive'.

Flexible Strength

The strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure. With plastics, this value is usually higher than the straight tensile strength.

Floating Lid

A term used to describe a special lid used on some flexible foam cushion molds. The lid, which has a specified weight per square inch, is suspended above the foam at a position near the desired maximum rise and is free to float on the surface of the rising foam against the gradually increasing compression of springs. The use of this type lid appears to minimize the appearance of loose skin and hard spots in the cushions.

Flow

Rate of all chemicals.

Flow Lines

A term which refers to a pattern of high density streaks or ridges radiating upward from the bottom of a Block of flexible slab foam. They are usually caused by undercutting (channeling) of the foam front or pouring freshly mixed materials on top of rising foam. See bones.

Flowmeter

A flow indicating device usually consisting of a glass tube containing a float which rises or falls in response to variations in flow of a fluid through the tube. These are usually not accurate enough to serve as anything other than 'guides' to metering.

Flow-Rate

A term which refers to the quantity of chemicals delivered to the discharge nozzle or metering port in a specified time interval, usually expressed in pounds per minute per component, in the USA. 'Total flow rate' would be the quantity of mixed liquid discharged from the mixing chamber in the required time interval (the total of all individual component flow rates).

Fluorocarbon

A term which refers to the general family of fluorinated hydrocarbons to which belong some of the most popular low temperature boiling chemicals used as blowing agents.

Fluorocarbon Blown Foam

Foam produced entirely by the gas generated from the boiling of a fluorocarbon, such as trichlorofluoromethane (R-11).

Foam

In the sense the term is used in the urethane foam industry, a product, either flexible or rigid, that has been produced by the internal generation or liberation of a gas in a fluid medium that is simultaneously polymerizing while expanding in volume, The bubbles that make up the final product may be completely interconnected (open celled) or walled off from each other (closed cell).

Foam Fatigue

The loss of physical properties of a foam article in use. Some loss is to be expected. The most noticed problem is the softening of cushions. Better quality foams would ordinarily be expected to fatigue less than poor quality foams.

Foam-in-Place

Refers to the deposition of foams and requires that the foaming machine be brought to the work which is 'in place' as opposed to bringing the work to the foaming machine.

Foam Line

See cream line (Also refers to a foam producing assembly line)

Formula

The list of ingredients and their proportions to each other which must be used to make a particular foam product.

Formulation

A term used either as a synonym for formula (the list) or used to refer to the chemicals that would be used in the preparation of a foam from a formula.

Free Rise (Unrestrained)

The unhampered expansion of a foam sample or product in a container with no top and a height of side wall not greater than twice the diameter. This is normally used in most laboratory sample screening work and is the normal condition in the slab process. The lowest possible density with a particular formula is attained under free rise conditions.

Friable (Foam)

A term used to describe rigid foam with such a low tensile strength that any wiping of the surface or jarring of the sample produces a fine powdery dust. Some formulations go through a friable stage of cure, others remain friable permanently. This is generally regarded as a highly undesirable property.

Froth (Frothing, Froth Process)

A term which refers to the practice of incorporating an unusually low boiling material into the final foam mixture (in a pressurized mixing chamber). When this liquid is discharged from the pressurized chamber, it expands instantly into a semi-liquid foam (froth). In normal practice enough of the special frothing gas is added to the mix so that this initial or pre-expansion produces approximately one third of the total expansion of foam required. The remainder of the expansion is by the normal procedure. Fluorocarbon 12 is the most common low boiling liquid used for frothing.

Froth Mixing Head

A mixing device for urethane foam that is designed for introducing the low boiling point frothing agent into the mixing chamber as a liquid and is capable of withstanding internal pressurization up to approximately 250 psig. in the mixing chamber without leakage problems.

Froth Spray

The practice of atomizing a frothed discharge from a mixer and spraying the particles of semi-expanded material onto a vertical or overhead surface. This has the advantage of practically no slump on a surface, over widely varying temperatures, and results in minimum final foam density due to self insulation from the surface on which the froth spray is applied. The final product has the disadvantage at present of a rather irregular surface.

Full Recirculation

A term applied to a urethane foam machine designed to permit all fluid components to be circulated between the tank and the mixing head during the 'idle' or non-production time. For 'full recirculation' the valve that diverts the flow to the mixing chamber should be immediately adjacent to the chamber so that stagnant areas are eliminated. See short recycle valving.

Fully Automatic Solvent Flush

The solvent flush cycle is initiated automatically by the machine.

Functionality

The number of reactive groups attached to a single molecule. A polyol with a functionality of 2 would be a diol.

Furniture Foam

Rigid urethane foam of a quality, density and appearance suitable for replacing wood products. Most of the formulations would produce foam in the 25 to 30 pound per cubic foot density range (similar to white pine) although lower density foams are available.

Gas Loss

The net weight loss of chemicals during foam production, determined by subtracting the total weight of foam produced from the total weight of chemicals used. In most cases this refers only to the carbon dioxide generated in a water blown formula . In some cases it is used to refer to evaporation and eventual loss of the fluorocarbon. To avoid confusion the type of gas loss should be specified.

Gel Coat

A thin coating of a high quality polyester plastic applied to the surface of a mold prior to filling the mold with foam. The foam adheres to the gel coat so that the part, when removed from the mold is finished.

Gel Strength

An expression of the stability of the foaming mass. This is at least partly dependent on the increasing viscosity of the liquid. A foam with high gel strength would be very stable and could withstand more shearing stresses in molding than could a formulation with low gel strength.

Gelation Rate

The speed with which the chain extension and cross linking reactions are occurring in the foaming mass. This rate of reaction must be balanced with the rate of gas generation so that gelation occurs just after peak foam rise in order to achieve the best quality product. See reaction balance.

Gelling Reaction

The increase in viscosity of the foaming mass caused by the polymerization of the liquid chemicals. See polymerization reaction.

General Purpose Foams

Foams or formulations that are capable of being used in a wide variety of Applications without modification while still attaining a reasonably high level of physical properties.

Glycol

Is the generic terms for polyols having a functionality of 2, also termed diols.

Grinder

A term used to refer to a machine used to produce small foam particles from foam trim. These devices are also called shredders, cutters and hammer mills. See crumb.

Guard Thermostat

An extra thermostat in the electrical circuit of a heating system, used as a safety control over the maximum temperature of the heating source.

H₂O

The chemical symbol used to represent water.

H₂O Blown Foam

See blowing agent and water blown foam.

Hand Batching

The practice of weighing all the ingredients of a foam formula separately into a mixing container and stirring the mixture with a spatula or paddle for the appropriate mixing period, then pouring this mixture into a mold. Although usually practiced only in laboratories, there are some commercial operations based on this method.

Handling Time

The time, in a molding process, between either the start or the completion of the pour and removal of the product from the mold without damage. In the continuous slab process it is often referred to as the time between deposition of the liquid mixture on the conveyor and the time the foamed Block containing the specified portion of chemicals can be lifted from the conveyor and handled without damage. In

A Glossary of POLYURETHANE INDUSTRY TERMS