Urethane and Polyurethane Industry Glossary

An acronym which is a registered trademark representing one of the polymeric isocyanates that are used in the manufacture of one shot rigid foam, particularly flame resistant formulations where high char strength is desired. PSI-the abbreviation for pounds per square inch but does not indicate if the reading is by gauge or is absolute. PSIG-the abbreviation for pounds per square inch, gauge. Absolute readings at sea level would be 14.7 pounds per square inch. higher than gauge readings.

An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH7 - acid solutions being under 7 and alkaline solutions over 7. Accurate pH meters are commercially available.

Package (d) Unit

A unit that needs only to be supplied with services and filled with chemicals to make foam. The term is somewhat ambiguous, since it is used to refer to small individual metering and mixing units as well as to giant continuous slab process lines complete with all accessories required to make the final product.

Packing

A term which can refer either to mold packing or to the seal around the rotating shaft of some pumps or mixers.

Paper Handling Device

An overall description given to an apparatus on a slab foam production line that cradles one or more rolls of paper, allows the paper to unwind over a special framework at the proper tension, shapes the paper to the form desired, smoothes and flattens the paper on the conveyor, and may or may not unwind the paper from the foam slab.

Paper Shaping Device

That portion of a paper handling device that shapes the paper into the desired form and holds it there until the foam has enough strength to support it without assistance.

Paper Unwinding Device

A system of mechanically peeling the paper from the slab of foam as it moves past the unwinding station. It generally consists of a spindle at each side of the conveyor driven by a device producing constant torque rather than speed, and a roller device beneath the conveyor driven by the same or similar type drive motor. It may or may not be included under the general heading of paper handling system in a machine description.

Partial Prepolymer

Refers to a system for the preparation of urethane foam in which all of the isocyanate is prereacted with a small part of the polyol at some time prior to the introduction of the final components into the mixing chamber. This prereacted intermediate (partial prepolymer) may be prepared in a very complex manner in expensive equipment or it may just be poured together in a tank or bottle, mixed briefly and allowed to stand overnight. Foam prepared from a partial prepolymer can have superior properties to one shot foam but is usually more expensive due to the extra processing. Ratios between the two major components vary from about 50/50 to about 70/30. This is also known as a quasi-prepolymer or semi-prepolymer system.

Peak Rise Point

The point on a continuous slab foam process of maximum foam rise or height. Because of cell rupture there is usually some settling or subsidence of the foam beyond this point.

Peelable Quality

A term used to describe foam in which the cell structure is so uniform that when it is peeled or split to a thickness of as little as 1 millimeter, no noticeable variations in cell size or structure appear. To achieve this goal stringent control of all mechanical, chemical, and environmental variables is usually required.

Peeler

A term used to describe a mechanical cutting device that is capable of slitting or peeling a continuous sheet of foam, as little as 1 millimeter in thickness, from the circumference of a round log shaped piece of foam. The technique is similar to that used to peel veneer from a wooden log. The cylindrical foam logs are sometimes trimmed from long Blocks of foam, with a square cross section that have been bored to accept the mandrel of the peeler. More recently techniques of foaming continuous round sections have been developed. See pre-peelers.

Peeling Cutter

Percent Set Test

See compression set.

Permanent Set

The increase in length, expressed in a percentage of the original length, by which an elastic material fails to return to original length after being stressed for a standard period of time. In flexible foam this generally is related to loss of height of a cushion in service.

Permeability

The rate at which a liquid or gas can penetrate into or through a material, in this case foam. It is primarily of interest for water vapor or carbon dioxide gas permeability of rigid foams used in insulation Applications since either material reduces the effectiveness of the foam. See water vapor permeability.

Pillow

A somewhat ambiguous term applied, in the USA, to a wide variety of small cushions used in many different type Applications. It usually is preferable to qualify the term with a more descriptive adjective such as head or sleeping pillows for those used on beds to support heads, decorator or throw pillows for those colorful and variously shaped cushions used to decorate furniture, etc. The original definition in the USA was limited to "something that cushioned and supported the head" but recently the meaning has broadened, perhaps in response to an awareness that Europeans used the word in a much different way.

Pin Impeller

A rotating mixing blade generally characterized as having a straight, relatively sturdy, central shaft parallel to the direction of liquid flow and a series of smaller, round, square or hexagonal shaped "pins" mounted on the central shaft at right angles to the central shaft and generally perpendicular to the liquid flow. There are many variations of this involving pin mounting angles other than 90 degrees (different diameter pins, different quantity of pins, different spacing between pins, etc). It is usually classed as a low shear mixing device.

Pin Mixer

A mixing head utilizing a pin impeller.

Plastic

(n.) One of many high polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture every plastic is capable of flowing, under heat and pressure, if necessary, into the desired final shape. (a.) Made of plastic; capable of flow under pressure or tensile stress.

Plastic Deformation

A change in dimensions of an object under load that is not recovered when the load is removed; opposed to elastic deformation.

Plasticizers

Various chemicals used as Additives in a formulation that generally serve to increase the flexibility of the foam structure. In flexible foam they can be used in some formulations to give a softer, more rubbery feel to the foam. In rigid foam they can be used to overcome extreme brittleness or friability where heat distortion is not critical.

Plateau

A term used to describe the flat spot in a compression-deflection curve of a flexible foam that can be classified as 'boardy' or possessing 'boardiness'. A 'wide plateau' would indicate a very boardy foam. See IFD Index.

Pneumatic Drive

A term better known as air drive or air actuated. There are three different types classed as linear actuating pistons, vane type rotary shaft and piston type rotary shaft. Properly designed into a mechanism, air drives can be useful. As an example, pneumatic drive of a traversing mechanism provides two design features that are not present in any other type: pneumatic cushioning of the reversal to avoid metal fatiguing shock waves, and complete elimination of the heat produced by the absorption of the energy involved in reversal of the mechanism (the hot air is immediately discharged).

Pocket Blows

Tears or rips in the foam, approximately the size of a man's hand, having smooth walls that are separated from each other. They may occur in the side or the interior of the foam slab.

Poise

A measure of the specific viscosity of a fluid. It is measured by the force required to move one plate in relation to another plate when the space between is filled with the fluid. A material with a viscosity of 1 poise requires 1 gram of force to move the plate 1 centimeter in 1 second. Since most of the fluids used in urethane foam have viscosities that vary with the temperature, any statement regarding the viscosity of these fluids must be qualified with the temperature of the hid at which the data was taken. centipoise, which is 1/1OOth of a poise, is more commonly used in the foam industry particularly since water is approximately 1 centipoise at 20 degrees C and thus provides a physical comparison with which we are all familiar.

Polycone

A term used by some to describe the polyethylene cone shaped nozzles with different orifice sizes that are used to control the diameter and shape of the liquid stream being discharged from the mixing chamber of a urethane foam mixing head.

Polyester

Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized by the presence of -C-O-groups in the molecule. This type of bond is more susceptible to attack by water (hydrolysis) than is the single oxygen present in the polyether type. Polyester polyols are generally more expensive, in the USA, than polyether polyols.

Polyether

Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized as having ether groups -C-0-C-in the molecule. This type of molecular joint is less susceptible to hydrolysis than the type characteristic of polyesters. In general polyethers are less expensive than polyesters in the USA.

Poly Isocyanates

Isocyanate compounds having more than one isocyanate (NCO) group attached to the molecule. See functionality.

Polymer

A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g., polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.

Polymeric Isocyanates

Is generally used to refer to those isocyanates containing products that consist of a mixture of isocyanate compounds containing more than two isocyanate groups in the molecule. This type is being widely used in the rigid foam field where good heat resistance and high char strength is required. This type of isocyanate reacts with polyol with less heat generation than with 'pure' diisocyanates; hence there is less tendency for scorching of the foam.

Polymerization Reaction

The chemical reaction during which larger molecules are being created by the joining of smaller molecules. If polymer chains are linked by chemical bonds to form a network, a cross linked polymer results. Flexible foams possess a lightly cross linked structure while rigid foams possess a highly cross linked structure. Proper choice of the base chemicals and the formula can result in a product with any desired degree of flexibility or rigidity.

Polyol

Is a chemical compound with more than one reactive hydroxyl group attached to the molecule.

Polyol Mix

The product resulting from premixing many of the compatible minor ingredients into the polyol component. This is usually done in order to reduce the final number of components required to be metered and introduced into the mixing head and to improve the Accuracy of the compounding when some of the minor ingredients would be difficult to meter individually because of very small quantities or very high viscosity. This also allows time to mix some materials that are difficult to mix in the short length of time available in the final mixer. This product is also called 'masterbatch' and 'premix'.

Polyurethanes (Also termed Urethane Polymers)

Are a family of chemical compounds that can be prepared by the reaction of an isocyanate containing material with a hydroxyl containing material. See polymerization reaction and urethane.

Pore Diameter

A term synonymous with cell size. It is primarily used in Europe.

Portable

An ambiguous word that is defined as meaning 'easily carried'. Many advertising brochures carry descriptions of machines labeled as 'portable' that can only be 'easily carried by a fork lift truck. To avoid misunderstanding it has been suggested by some that portable be used in connection with anything that can be easily carried by one man, and that the word moveable be used for anything requiring 2 or more men.

Portable Cutters

Small, lightweight cutting machines for foam or fabric that have 8 inch to 24 inch long high speed reciprocating blade(s). These machines are usually quite versatile and are convenient to use in cutting out complex shapes that have been ordered in quantities too low for economical die cutting.

Positive Displacement

A term which refers to those pumps that are so designed that substantially all of the material displaced from the suction side of the pump is delivered to the outlet side of the pump. In other words internal recirculation is at a minimum and what little there is, is constant over a fairly wide range of conditions. In normal practice some limitation in use is necessary. Under some conditions, a pump that is positive metering with a 1000 cps material, may slip rather badly with 100 cps material. Under other conditions, a pump that is designed to be positive metering with a 1 cps material may transfer enormous quantities of energy in the form of heat to material of 1000 cps.

Positive Metering

The ability to control the flow rate of a particular fluid to an Accuracy of approximately 1% of the total flow regardless of temperature or pressure fluctuations downstream from the metering device. This is difficult to achieve in normal practice at all times under any conditions. It can be achieved economically if certain design rules and limitations of use are practiced. There is a certain amount of ambiguity in the term since many piston pumps can be classified as positive metering for total quantity delivered, while the amount delivered per second may vary, and many gear or vane pumps can be positive metering both for total quantity delivered and for quantity per second delivered.

Positive Proportioning

A term which refers to the condition in which two or more fluid streams are positively metered with respect to an absolute standard and are maintained in an exact ratio with each other continuously.

Positive Tracking

A term used to describe the condition existing when the flow rate is changed in two or more fluid circuits simultaneously while still maintaining positive proportioning. For Accuracy positive tracking is normally stated as a plus or minus variation from a standard flow level and for a specific viscosity material.

Post-Cure

A term normally applied to the period of curing after the foam product has been handled by removal from the mold or conveyor. In some cases accelerated curing (usually oven heating) is practiced in order to achieve some predetermined level of physical properties. Depending on the formula and the final product desired, this may be accelerated post-cure in an oven at temperatures between 250° and 300° F. or a room temperature post-cure over a period of several days. The term sometimes is used ambiguously to cover what is otherwise called 'After-Cure'. See pre-cure and After-Cure. post-cure oven-an oven in which post-curing is accomplished. To be completely effective the product to be post-cured in an oven must be placed in the oven with as little temperature loss as possible while in transit from the manufacturing area.

Post-Forming

A term applied to the practice of reshaping a piece of foam by the Application of a combination of heat and pressure after it has been cut to the proper dimensions. It is usually performed on flexible slab foam when pleasing or intricate curves are desired, and the investment in foam molding equipment would not be practical.

Potting

The process of encapsulating or imbedding a device by pouring a casting compound into a cavity in which the device has been fixed and curing the compound in place, As a result the device is imbedded completely in a plastic polymer, either solid or foamed. The compounds are usually thermosetting and vacuum may be used with the solid polymers in order to avoid entrapped gases.

Pour-In-Place

A term referring to the practice of pouring a liquid into a cavity and having it foam, fill the cavity, harden and cure without having to remove it from the cavity and without having to shape the product by cutting or sawing. The term is sometimes used interchangeably with potting, but potting is used more to refer to the solid or non-foamed pour-in-place.

Pour Pattern

The pattern formed by a liquid steam being deposited in a mold, in a cavity or on a conveyor. This is often quite critical.

Pouring Head

A mixing head designed only to dispense liquid mixtures.

Pouring Point

The position at which the mixed liquid is deposited on the conveyor in a slab process system.

Powered Conveyor

A conveyor having the moving surface powered by a drive motor. The term is used to differentiate between this type of conveyor and other non-powered types, such as roller conveyor and skate wheel conveyor.

Pre-cure (pre-curing)

A term normally applied to the time interval between pouring the chemicals into a mold and the time the product can be removed from that mold without damage to the product or the mold. This is also sometimes called 'stripping time' or "handling time'.

Pre-Cure Oven

An oven in which pre-curing is accomplished. This can be supplied with heat from any source that will raise the temperature of the mold quickly without damaging the foam product or the mold. This is a critical part of molding process and is usually the limiting factor in molded foam production rates. Types of ovens in use range from hot air circulating heat, powered by steam, gas, oil or electricity, to microwave powered units. Some are equipped with powerful 'fast heat' radiant units to increase the internal mold temperatures more rapidly.

Pre-Heat

A term normally applied to the technique of bringing molds or cavities to the desired temperature level prior to pouring. This is a fairly critical factor and must be accomplished with reasonable Accuracy and reproducibility for best quality control. Even the so-called 'cold molding' process requires some mold heat control for quality standardization.

Pre-Heat Oven

The oven in which pre-heating is accomplished.

Premix

A term often used synonymously with masterbatch or polyol mix to indicate the mixture resulting from blending many of the minor ingredients in with the polyol in an effort to reduce the final number of components or to allow more time for mixing or blending those chemicals that may not be readily miscible in the short period of exposure to the final mixing. See polyol mix.

Premix Tank

A term used to indicate tanks that are used for making batches of premix separately from the machine and also those tanks on the machine that are used in the premix flow circuit.

Pre-Peelers

Specially modified cutting devices that round off the corners of Blocks of foam that are to be peeled so that very little time of the actual peeler is wasted in this time consuming operation. Actually, the major portion of the peeling cycle is spent in installing the 'logs' of foam and attaching the first amount of peeled material to the wind-up roll. Prepeeling may reduce this wasted time by as much as 50%.

Prepolymer

A chemical intermediate used at times in the production of urethane foam. It is normally manufactured by prereacting all of the isocyanate material with part or all of the polyol. This can be carried out in a special reactor kettle or in a normal blending tank and is a means of building some properties into the final foam product that would not be there ordinarily. See total prepolymer, modified total prepolymer and partial prepolymer.

Pre-Pressurization

A technique used to secure more exact chemical metering when froth is to be produced. Usually special valves are installed between the pumps and the mixing head and the pressure generated by the pumps is increased to the value that would be present during the frothing pour by using this special valve to throttle the liquid flow. Metering or calibration of the liquid flow rates and ratios is accomplished while the pressure is at the artificially high level in order to minimize the effects of internal pump slippage on calibration. The valves are left in this position during operation. Pressures of 70 to 150 psig are normally maintained in the mixing head during frothing in order to keep the fluorocarbon 12 in its liquid phase during the mixing operation.

Pressure Balance

A term used to describe the condition existing in an 'on-off' fluid metering circuit when the pressure during the 'on' cycle is exactly the same as the pressure during the 'off' cycle. This condition is normally required for best quality foam production, as most commercial foam machines have rubber hoses in the circuit plus places that could trap gas and act as accumulators. Under these circumstances if the pressure were permitted to change, a surge or lag of material could occur immediately after switching 'on' (mix cycle) which would cause an imbalance in the stoichiometric ratio of the chemicals, and poor quality foam or 'initial spot' during at least a portion of the cycle would result. Generally the shorter the 'on' time, the more critical is the pressure balance, depending on the design and capacity of the impeller and mixing chamber.

Pressure Balance Valve

A valve located somewhere in the return line between the mixer and the tank and used to help in balancing pressures. In some cases this valve is built into the mixing head, and in others it is separate and located on the tank. For some materials, particularly isocyanates, the construction of the valve is important, and it should be of a type that does not accumulate small particles. In most cases a filter is installed just prior to the valve to ensure more trouble free performance. The closer the valve is to the mixing head, the better is the performance. regulators are sometimes used for pressure balance instead of valves.

Pressure Cut-Off Switch

See overpressure cut-off switch.

Pressure Developing

A technique used to gain more positive control of metering when a water-thin (1 cp) viscosity liquid must be metered at extremely small flow rates. This situation is encountered often when total prepolymer systems are used for filling very small cavities. With this technique a special needle valve or pressure regulator is installed in the flow circuit of the catalyst system between the metering pump and the mixing head and as close to the mixing head as possible. A back-pressure (between the valve and the pump) of at least 5 psig is maintained at all times. Very small inner diameter metering tubes must be used in the mixing head to keep the system liquid full at all times, but they must not be so small as to cause the pressure to rise during the 'on' cycle.

Pressure Gauge

A device for measuring and indicating pressure. It is not safe or practical to operate a urethane foam machine without accurate pressure gauges in all flow circuits.

Pressure Introducing Device

See pre-pressurization and pressure developing.

Pressure Isolating Regulator

See isolating regulator.

Primary Alcohol Groups

Are reactive groups present in certain polyol molecules. Primary alcohol groups react faster than secondary alcohol groups. Usually, the higher the percentage of primary alcohol groups in the formulation, the less catalyst is required for curing. The term 'primary hydroxyl groups' is often used interchangeably.

Prime Mover

A term used to describe the master drive motor and speed controller used with interlocked or master-slave systems.

Process Variables

Factors in the chemicals, the machine or in the environment that could change in such a way as to affect the quality of the foam. More than 50 have been identified and labeled in the production of flexible slab foam. Among these factors are such things as the control over metering stability, temperature of the chemicals, catalyst type and level, etc.

Profiling

See convoluting cutting.

Proportional Limit

A term used by those concerned with testing work to describe the point at which an elastic modulus changes from a straight line function. This would normally indicate the elastic limit of the material beyond which permanent damage to the material structure would result. puddle-the practice of pouring all the mixed liquid material into one spot in a mold or cavity with no attempt to distribute the material.

Pumper

A term occasionally used to describe a metering unit.

Pumping Impeller

A mixing blade designed to positively move the liquids being mixed through the mixing zone and through the discharge orifice by means of the force exerted by the pumping action designed into the mixing blade itself.

URETHANE INDUSTRY GLOSSARY - P

PAPI

pH