URETHANE INDUSTRY GLOSSARY - H

The chemical symbol used to represent water.

See blowing agent and water blown foam.

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.

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 Batch Mixing it can also be 'the time between completion of mixing and pouring into the mold.' See cream time.

A term which refers to the firm high density areas formed in a molded object when packing is excessive or poor distribution occurs. This firm area or hard spot is normally caused by a localized collapse, filled in again by excess foam from the surrounding area.

The smoke or fumes released from the foaming mass under normal conditions of continuous slab processing, particularly at peak rise or just after. Under exceptional atmospheric conditions, the smoke or haze may obscure the surface of a large area of the conveyor.

A shortened form of the word mixing head, used to describe devices ranging in complexity from simple manifolds to complex diverting valves having attached mixing chambers, impellers, drive motors, etc.

A mixing head drive motor that is mounted adjacent to the mixing head and is directly connected by framework to it. See flexible shaft mixer drive and remote drive.

Little bubbles popping up through the top skin of a continuous flexible slab or free rise flexible foam pour just past peak rise. From the very first days of the industry this was recognized as a sign that the resultant foam would be open celled and generally of good quality. The word is a direct translation from the German phrase brought to the USA with early technology. The bubbles do not have to be present to make good foam but their presence does no harm and is psychologically reassuring,

The temperature at which a sample of foam will begin to change dimensions under specified conditions of loading and environment. The Test Method is described in ASTM D 794-49, but the temperatures and times used are varied to suit the end use.

A heat exchanger for either heating or cooling one of the chemical components that does not have sufficient capacity to bring that component to the desired temperature in a single journey or pass through, but rather requires multiple recirculations of the component to condition the material properly.

A heat exchanger combined into a single unit with its source of heating or cooling. An example would be a scraped surface heat exchanger with an attached refrigeration compressor that can be reverse cycled to provide both heating and cooling. heat exchanger, scraped surface-a heat exchanger so constructed that the heat conductive surface is continually scraped to remove the temperature conditioned material. This type is normally used for cooling those materials that tend to increase in viscosity enough to stick to chilled surfaces, interfering with the efficiency of the unit.

A heat exchanger for either heating or cooling one of the chemical components that has sufficient capacity and control instrumentation to bring that component to the desired temperature in one journey or passage through.

A heat exchanger constructed of a bundle of tubes inside an outer casing or shell. This type is used for either heating or cooling of those components having low enough viscosity not to interfere seriously with the efficiency of the heat exchange surface. The chemicals to be conditioned may be circulated either through the tube or through the shell portion.

See exotherm.

The liquids or gases used to convey heat to or from a heat exchange surface. See cooling media.

A method of joining plastic films by simultaneous Application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically.

Is the condition in free rise or molded articles of having a very thick, high density, outer skin. This is generally undesirable economically in flexible slab foam and can be caused by a defect in the formulation or in the environment. It is highly desirable in some molded articles, both flexible and rigid. Self skinning or integral skin.

More properly termed 'stator helix mixing', a term used to describe the practice of mixing the chemicals by means of turbulent flow conditions created by injecting a high velocity gas stream into a helically spiraled pathway simultaneously with the individual chemicals. The developmental work on this type mixing was performed by the duPont Company in an effort to create a light weight low cost froth dispenser. The stator helix can be used for frothing when a gas such as fluorocarbon 12 is used as the high velocity gas stream or it can be used for conventional foaming if compressed air or nitrogen is used as the mixing gas. This is a useful system where quality requirements are average and the product is confined in a metal or plastic envelope.

A term describing the mixer used with the helical spiral mixing technique. The phrase is somewhat ambiguous since many of the rotating impellers are machined into a helical spiral shape. In order to avoid confusion it should be specified as a stator or non-rotating helix.

See vertical pour.

A mixer blade or impeller of the general type that mixes primarily by smearing multiple thin films of chemicals together in a high-speed close tolerance device. Generally associated with this type is a high mixer drive motor power loss and the transfer of a large amount of mechanical energy to the chemicals in the form of heat.

A term sometimes used to describe storage tank(s) in which stable premixes are made and then held until the material is required to be transferred to the "run" tanks on the machine.

The actual volume of chemicals in passage or in transit through the mixing chamber during mixing operations. This is usually not the total volume of open space in the mixing chamber, since centrifugal force generally keeps the center area open. Any built-in pumping features of the impeller will slow or speed the passage of the material through. Hold-up can only be increased if the mixing chamber is partially empty to begin with. With pumping type impellors, hold-up is rarely increased significantly by reducing the diameter of the discharge orifice.

The practice of cutting foam when the cutting portion of the blade of the saw is in a plane parallel to the horizon. Special rotary bandsaw mechanisms are most commonly used for this purpose, although hot wire cutting devices are also used.

The practice of pouring large panels of urethane foam (particularly rigid foam) when the mold or void to be filled has its two largest dimensions form a horizontal plane. This has the advantage, when anisotropy is present, of having the greatest compressive strength of the material in a direction that supports the external skins.

The practice of cutting foam by means of an electrically heated wire held taut between two posts with the help of a spring tensioning device. This has the advantage of eliminating dust and can be installed in multiple levels so that an entire Block can be cut in one passage. Disadvantages are the tendency towards rather slow production rates, the variability of response of different types of foam requiring critical adjustments, the possibility of unpleasant odors, and the ever-present possibility of fire. (The wire is maintained at 1200° F.)

An accelerated aging test under conditions of high humidity and temperature. The Test Method is described in ASTM D 1564-63T under steam autoclave test.

A system in which energy is transferred from one place to another by means of compression and flow of fluid (e.g.. water, oil).

A hydraulic drive motor for the mixing head in which the motor segment is head mounted and the power unit is remotely located in order to decrease the total weight of the mixing head installation. This also provides variable speed adjustment.

A spreading device of the type that can be used on continuous slab production lines, utilizing a hydraulic drive mechanism.

A mixing device in which the primary cause of mixing is the turbulence created by the interference of the streams of liquid components with each other as they are introduced into the mixing area. This is also called a fluid jet impingement mixer.

A term which refers to the ability of the foam product to withstand hydrolysis or dissociation by water under conditions of constant exposure. The humid aging Test Method was developed in an attempt to measure this.

Water repellent.

An affinity for water. Hydrophilic foams are more absorptive and generally make better sponges.

The combined oxygen and hydrogen radical that forms the reactive group on polyols.

See OH number.

in the sense used in the foam industry, a term which refers to the decay in strength properties under continuously applied load. A typical example of this would be in the determination of RMA values where the test specifies that the reading must be taken at an exact time interval after the application of the load in order to assist in obtaining a reproducible value, since the values drop continuously.