Urethane and Polyurethane Industry Glossary

An abbreviation used to refer to the Society of Plastic Engineers. This is a national organization of engineers working in the plastics industry. The executive office is located at 65 Prospect Street, Stamford, Connecticut 06902. many regional chapters cover The SPE Journal is the official

SPI

An abbreviation used to refer to the Society of the Plastics Industry. This is a national organization of companies and individuals in the plastics industry that is oriented towards developing industry standards and test methods, their Applications, and promotion of plastics as well as maintaining the proper public image.

Sack Factor

See IFD (65/25) Index.

Sag Factor

See IFD (65/25) Index.

Sandwich Panel

A composite structure intended to serve as a structural building panel for walls, roof, floors, etc., posed of at least three pieces, a low density case (a rigid foam) and two outer skins or surfaces. The major portion of the load bearing is intended to be accomplished by the two outer surfaces, while the inner core serves primarily to maintain the outer surfaces completely in parallel. schematic diagram-a drawing that illustrates the design and relationships of a machine, circuit or process in an abstract or symbolic manner bearing no relationship to its physical appearance or size.

Scoop Cutting

The technique of producing special cut shapes from Blocks or sheets of flexible urethane foam by variably compressing certain areas of a foam Block and cutting the foam while it is deformed. Foam soap dishes and variously shaped cavities that are used as shipping containers for light bulbs, glasses, TV tubes, etc., are among the many that can be made in this manner.

Scrap

A term which normally refers to waste from a urethane foam manufacturing process that cannot be used. This term is often used to describe usable trim cuttings also. See trim. scraped surface heat exchanger-See heat exchanger, scraped surface.

Scraper Unit

A shortened form of scraped surface heat exchanger package unit.

Sealed Mixing Heads

A mixing head' with a built-in rotary seal on the impeller drive shaft and possibly an '0' ring seal around the mixer housing so that mixing under pressure, such as in frothing, may be accomplished without leaking the mixed materials into the bearing housing or other areas. For best results, rotary seals must be lubricated. The best arrangement appears to be a DOP circulation system. Another system, primarily useful in continuous processing, is the polyol lubricated seal.

Sealers

Devices used to heat-seal sheets of foam together so that the 1000 to 2000 yd. rolls used by the laminated fabric industry can be built up, The sealers are usually mounted on the frame of the peeler between the cutting bar and the wind-up roll. Sealing is usually accomplished by a combination of pressure and a heated resistance wire.

Seat Cushions

Blocks of foam used for padding in chairs on which a person sits. They may be separate from the main frame of the chair or sofa or form an integral part of it. A Back Cushion, on the other hand, is leaned on rather than sat on.

Seat Pillow

A term used in Europe with the same meaning that 'seat cushion' has in the USA.

Secondary Alcohol Groups

Are reactive alcohol groups (CHOH), present in most polyol molecules. They are less reactive than primary alcohol groups. See primary alcohol groups.

Self Cleaning

The ability of a mixing device to so completely expel the mixed materials after an 'on' cycle that repetitive cycles can be accomplished without any clogging. In actual practice this is difficult to attain on an absolute basis since it is influenced by the cream time of the formulation, the length of the 'on' time, the length of the 'off' time, etc. Because of this some form of solvent flush is normally required either after each cycle or as long as after every four hours of use.

Self Extinguishing

The ability of a foam to stop burning after it has been started burning in a controlled manner. One of the tests used to determine this is Test Method ASTM D 1692. Caution must be used in applying the results of this test to actual Applications, since the sample is unconfined during the test, and flammable decomposition products are free to escape.

Self Skinning Foam

See integral skin foam.

Semi-Prepolymer

See partial prepolymer.

Sensitivity

A term which refers to the relative ease of the daily manufacture of foam using a specific formulation. If all operating conditions must be exactly controlled in a very narrow band in order to make acceptable quality foam, the formulation is said to be sensitive or critical. If acceptable foam can be made day after day with only average control over the variables, the formulation is said to be tolerant.

Settling

The normal loss in height of the continuous flexible slab foam at a point just past peak rise. This loss of height occurs as the cell walls rupture and is a sign that the foam will be open celled. If the loss of height is excessive, splits may occur. If the loss of height does not occur the foam will normally be closed cell.

Shaping Saws

Cutting devices that can produce almost any special shape desired from a Block or sheet of foam. Some examples of this type saw are shoulder pad cutters, scoop cutters, convoluting cutters, breast pad or hip pad cutters, circular cutters and bolster cutters. sharp cut-off-a term which describes the ability of a mixing head to stop the flow of mixed liquids abruptly as soon as the valving mechanism cuts the flow of the chemicals into the mixing chamber. 'No After Drip' also describes the same condition. This condition is greatly dependent on the material viscosity and is almost impossible to achieve with low viscosity formulations.

Shear Resistance

The ability of a flexible foam to resist laterally applied forces (applied parallel to the foam surface). This has a bearing on the comfortability of the foam when used as a cushion and its abrasion resistance.

Shear Strength

The ability of a rigid foam to resist deformation when subjected to laterally applied forces (parallel to the foam surface). This is of interest particularly in sandwich panel work. The Test Method is described in ASTM C 273-61.

Shiners

An ambiguous word used sometimes to describe cratering and sometimes to describe windows.

Shiny Foam

Foam with a high proportion of cell membranes (windows) that glitter from reflected light.

Short Recycle

Short (re) cycle valving-the valves or valving device used to recirculate the separate components on a short recycle system. They are usually similar to the valves used for full recirculation, but not always. See recirculation system.

Shot

The total amount of mixed liquid dispensed from an 'on-off' mixer during an 'on' cycle.

Shot Accuracy

A term which refers to the reproducibility of the total quantity delivered by an 'on-off' mixer in a specified time interval. An Accuracy of plus or minus 0.25% can be achieved with good quality equipment, depending on the formula and the size of the shot. As a general rule the shorter the time 'on', the greater the Accuracy problem.

Shot Cycle

A term which describes the total time spent 'on' and 'off' in a single unit of operation. Usually the time 'on' and the time 'off' are both identified. For example, 5 seconds 'on' and 10 seconds 'off' would completely describe a shot cycle.

Shot Cycle Timer

A timing device used for automatic control of a shot cycle. See shot size timer.

Shot Size Timer

A timing device used to control the duration of the 'on' time only. It has to be manually actuated for each 'on' cycle and has no control over the 'off cycle. The term is often used interchangeably with shot cycle timer.

Shot Timer

A term normally used as a synonym for shot size timer.

Shredder

A mechanical device used to tear or rip foam trim pieces into very small pieces which can be used for filling dolls, pillows, etc., or for rebonding into cushioning products. They are also called grinders, hammer mills, etc. See crumb.

Shrinking (Shrinkage)

A term which describes the loss in size that occurs occasionally with foam products. Exothermic temperatures encountered in the interior of many foam products is often between 250° to 300° F. At this temperature the gas in the bubbles is exerting a higher pressure than it would at room temperature. In order to withstand this loss in pressure the cell walls must break, in the case of flexible foam, or the cell walls and structure must be rigid enough, in the case of rigid foam, to accept the pressure difference without collapsing. If a flexible foam has closed cells, it will shrink when it cools. If a rigid foam does not quite reach a truly rigid structure before cooling, the cell walls will either rupture, or, if the material is somewhat plastic, the foam will shrink in size. It is sometimes used as a synonym for settling in a flexible slab process.

Side Conveyors

Conveyors that are used as moving sidewalls on a continuous slab process conveyor. This is particularly applicable to rigid slab manufacture when the formulation has a tendency to gel prematurely and as a result exert sufficient pressure on non-moving sidewalls to lock the slab in place.

Side Cracks

Definite cracks in the foam with widely separated edges.

Side Splits

Horizontal tears or rips in the side of the foam Block. These splits are either horizontal to the plane of the foam conveyor or slightly angled. They may appear intermittently or continuously along the side of the slab. The edges of the tear are not separated to any large extent, and consequently the tears are often difficult to see. Two common causes are an excessive speed of the blowing reaction in relation to the gelation reaction and too steep an angle of rise.

Silicones

Complex chemicals formed from a combination of silicon and organic groups to form polymers that exhibit surface active properties when used in urethane foam formulations. In general these compounds add stability to the liquid foaming mixture so that drainage (collapse of bubbles due to extreme loss of bubble wall thickness) is retarded and flow ability of the mass is increased. There are many different varieties that can be used; some contribute to fine uniform cell structure, while others increase the irregularity of the cell structure (for sponges).

Simulated Chamber Pressure

See pre-pressurization.

Skin

A term which describes the higher density outer surface of a foam article. See integral skin foam. The skin usually is the result of surface cooling. It can be eliminated by maintaining the outer surface of the part at the proper temperature.

Slab Foam

Foam made by the continuous pouring of mixed liquids on a conveyor generating a continuous loaf of foam for as long as the machine is operating. This type of foam would generally be classed as free rise or unconfined, although fixed side guides give the loaf a generally rectangular cross section with a slightly rounded top. A few installations have a top conveyor to aid in flattening the top surface so that a more nearly rectangular cross section is produced.

Sleeping Pillow

A term which in the USA refers to the separate, generally soft and fluffy, cushion used to place under the head while sleeping, In other countries very hard pillows may be used for this purpose.

Slumping

A term used in rigid foam spraying to refer to the sagging of the foaming mixture that sometimes occurs during spraying of a vertical surface. Among the many causes of this are slow gelation, excessive buildup, lack of proper temperature control of the chemical components or the target surface, etc.

Smoke

Solid Elastomer

A term used to refer to rubber like compounds that have no internal cavities or gas bubbles.

Solid Filler

An insoluble Additive to a urethane foam formulation that remains a finely divided solid even after blending into the mixture. It is often used to add weight to a formula while reducing the formula cost, to add firmness to the foam or greater viscosity to the liquid mixture. Generally tensile strength is reduced by this type filler.

Solvent

A substance, usually liquid, used to dissolve another substance.

Solvent Blown Foam

See blowing agent. Many different types of low boiling chemicals have been used as blowing agents in urethane foam, most of them normally classed as solvents.

Solvent Flush

A term which refers either to the rinsing of the mixing chamber with a solvent or to the equipment required. This can be accomplished by many methods ranging from a plastic squeeze bottle, through manual valving to completely automatic types. In some cases an air flush or purge follows the solvent flush to ensure that no solvent remains in the mixing chamber when the next mix cycle is initiated. Methylene chloride is the most commonly used cleaning solvent.

Solvent Flush Cycle

A term used to describe a solvent flush, air flush cycle (or solvent cycle only), and indicates the time of each. For example, a typical solvent flush cycle might be 5 seconds of solvent followed by 10 seconds of air. The cycle may be initiated by push button and controlled by timers so that it automatically shuts off and resets for the next push button actuated cycle; it may be automatically initiated by timers or manually initiated by opening a valve. The timers are normally adjustable so that more or less air or solvent can be forced through the mixing chamber as required.

Solvent Flush Timers

Timers used to control the quantities of solvent and air dispensed during a solvent flush cycle by controlling the duration of the 'on' cycle of a valving device or pumping mechanism.

Solvent Resistance (Solvent Swell)

A term which refers to the durability of material exposed to solvent. It is usually measured by determining the percentage weight increase after a specified number of hours of immersion in the solvent. A 10 to 15% increase in weight is usually not too objectionable.

Sparkling

Specific Gravity

The density of any material divided by that of water at a standard temperature, usually 4' C. Since water's density is nearly 1.00 g./cc., density in g./cc. and specific gravity are numerically nearly equal.

Splashing

A splattering which sometimes occurs when the mixed liquid is poured into a mold or onto a conveyor. The spattering or splashing may cause the formation of large bubbles which can be trapped in the rising foam, showing up as large cavities or voids in the foam during cutting.

Splits

A general term. See side splits, side cracks, top splits or flaps, flak, top cracks, and pocket blows or blows.

Sponge

A rather ambiguous term used to describe many different foam products. It is most often used to describe 'Blown Elastomers', particularly those with high load bearing and higher densities (8 pounds per cubic foot and higher). It sometimes is used to refer to an open celled product, and sometimes to a completely closed cell product.

Spray Mixing Head

A mixing head in which the primary cause of mixing is the atomization and turbulence created in the mixing zone by one or more high velocity air jets. Mixing may be external to the nozzle and completely dependent on the air turbulence for mixing, or internal and partially dependent on impingement onto the interior walls of the mixing chamber. See external mix.

Spreader

A device to assist in placing a uniformly distributed layer of mixed foam components into a mold or onto a conveyor prior to foaming in an effort to minimize flow of the expanding mass during foaming. A typical device of this type consists of a horizontal track supported at each end on which a moving carriage rides. The mixing head is mounted on the carriage, and the carriage is driven back and forth by a drive mechanism. The drive mechanism can be linear or rotary pneumatic, hydraulic, mechanical or electrical.

Stabilizer

A term normally used to refer to those Additives that assist in maintaining the quality of the foam in use such as anti-oxidants, ultraviolet absorbers, acid absorbers, etc. Occasionally it is used to refer to foam stabilizing Additives such as the silicone compounds that add stability to the semi liquid expanding mass. stannous octoate-one of the more commonly used organotin catalysts, particularly for flexible one shot foam. One of the major reasons for its preferential use is that it is usually destroyed or converted to a less active form by the exothermic heat of the reaction, minimizing degradation in the final foam product.

Stannous Oleate

An organotin catalyst of the stannous octoate type. It is approximately 1/2 as active, by weight.

Static Fatigue

A term which describes the loss in load-bearing properties of a foam sample under constant compression.

Stator Blade

A term sometimes used to refer to non-rotating or non-moving baffles that assist in mixing foam components by forcing the liquids to follow a labyrinth like path through the mixing chamber. See labyrinth mixing and helical spiral mixing.

Steel Rule Die

A device used for stamping pr 'clicking' out intricate or simple shapes from sheets of foam or other soft material. They are manufactured by imbedding narrow bands of sharp edged steel into a wooden back plate in the pattern desired. The sharp edge of the die is placed against the surface to be cut; the die is then hit a sharp blow with a mallet or with the platen of a 'clicking' press which drives the die through the material and cuts out the desired pattern. See 'clicking'.

Step Throughput

The practice of interconnecting drive motors and pumps with a multi path gear box so that several different 'fixed or 'step' outputs or throughputs are available rather than the more usual infinite variation between fixed upper and lower limits.

Stoichiometry

A term which refers to the relationship of the various combining weights of several interacting chemicals. For example, it takes approximately 10 grams of TDI to completely react with 100 grams of standard flexible foam type polyol and approximately 1 gram of water to completely react with 10 grams of TDI. A stoichiometrical balance is achieved when 100% of all the chemicals used in the reaction are consumed in the reaction. In the urethane industry this stoichiometric balance is termed 'having an index of 100.' See index.

Straight Sided Impellers

Mixing blades or impellers that have parallel sides or cylindrical shape as opposed to tapered sides or cone shape.

Stream

A term which sometimes is used to describe the flow of liquid of one of the components in the formula or the circuit through which it flows. For example, the flow of TDI from the nozzle during metering may be called the 'TDI stream'. Also in slab foam terminology 'upstream' would be 'against' the flow of foam, and 'downstream' would be 'with' the flow of foam.

Streamers

Lines and/or streaks of cream colored liquid extending upstream from the cream line into the clear liquid dispensed from the mixer during the slab foam process. They may be from 0 to 24 inches or more in length but are generally kept between 2 and 6 inches long by careful regulation of the angle of rise, the conveyor speed, the flow rate, the catalyst quantity or balance, etc. Streamers are an important guide to quality control, and if all variables are properly controlled, will always appear the exact same distance downstream from the mixing head with the same formula . Different formulas may have different distances. Excessively long streamers will generally forecast the presence of splits; excessively short or non existent streamers will forecast undercutting and the presence of flow lines and/or side and top cracking.

Stress Relaxation

Due to the viscoelastic nature of plastics, the amount of force or stress necessary to produce a given amount of deformation gradually decreases during the time the stress is applied. This decay of stress at a constant deformation is called stress relaxation.

Striations

String Time

With rigid foams the time between pouring the mixed liquids into the container and the time that long 'strings' of tacky material can be pulled away from the surface of the foam when the surface is touched with a wooden spatula or even with the fingers.

Substrate

A term generally used with spray foam Applications to describe the surface on which the foam is applied.

Super Foot

A European term usually synonymous with the American 'board foot' which is 12 inches x 12 inches x 1 inch. This measurement of volume is used as a convenient frame of reference for pricing both rigid and flexible foam stock (cut slab foam).

Surface Active Agent

An Additive to the formulation that either helps or hinders the formation of a fine, uniform cell structure in the resultant foam.

Surface To Volume Ratio

A means of differentiating between cavities with the same volume but vastly different shapes. For example, a cube with a volume of 1 cubic foot would have a surface area of less than 1000 square inches. The same volume, distributed so that the cavity was only 1inch thick. would have a surface area of over 3000 square inches. The two different shapes of cavities require different techniques and formulations in order to exactly fill them with equal amounts of foam.

Surfactant

A commonly used contracted or shortened form of ' surface active agent'. See silicones.

Surge

The momentary increase in relative flow rate that occurs in a fluid metering system when the pressure drops from a previously higher but stable level to a lower and again stable level. With 'on-off' mixing heads, this can occur at the instant of diversion of flow from recycle to mix if the operating pressures under both conditions have not previously been balanced. Theoretically the surge would not be of significant quantity if the metering system had no flexible hoses or places in which air or gas could be trapped, but unfortunately it is usually necessary to carefully balance the pressure to avoid off ratio foam spots in the product.

Swivel Adapter

A special hose to pipe fitting or adapter that is so constructed that one permanently attached end freely rotates, permitting easy assembly and disassembly of parts. Occasionally swivel adapter and fitting are used interchangeably. See swivel fitting.

Swivel Fitting

A special hose or pipe fitting that is so constructed that one permanently attached end freely rotates, permitting easy assembly and disassembly of parts. See swivel adapter.

Synergism (Synergistic)

The property exhibited by a blend of some materials, having a greater effectiveness or chemical activity as a mixture than would ordinarily be expected from the sum of their independent abilities or activity levels. Some combinations of urethane foam catalysts would appear to have this property.

System

A rather ambiguous term used to describe almost any combination of mechanical parts or chemicals that have some relationship to each other. For example, the metering mechanism is often described as the 'metering system' which includes just the mechanical parts. A 'froth system', on the other hand, usually includes the chemicals within its scope and might even refer to the chemicals by themselves. A 'complete system' is sometimes used interchangeably with 'complete package' to indicate everything needed. to produce foam (machine, chemicals, process know how, etc.).

URETHANE INDUSTRY GLOSSARY - S

SPE

SPI