URETHANE INDUSTRY GLOSSARY - L

A process similar to helix mixing, except the mixing zone is irregularly baffled instead of spiraled.

A term which refers to the delay or reduction in flow that occurs when a restriction in the flow circuit causes a build-up in pressure. This delay is particularly severe in flow systems that may have trapped air or gas in some portion of the circuit or in those systems that use accumulators or flexible hoses. When using 'on-off' mixing heads the pressure must be balanced between recirculation and mix or a surge or lag may occur.

The process of adhering 2 or more thin sheets of the same or different materials together to form a thicker product with possibly different properties. In the flexible foam industry in particular, it refers to the process of adhering thin sheets of flexible foam and fabric together. Two processes are in common use, flame lamination and Adhesive Lamination. A paper or foil covered rigid foam insulation board may be made by self-lamination of the chemical to the skins. Laminates are also made of rigid foams and plastics, metals, wood, and other substrates.

A term used to describe the problem of non-uniform or off ratio flows at the instant of starting or stopping the mix cycle in 'on-off' mixers. When complete control over flow conditions is not obtained, one material may 'lead or lag' the other material (s). The most common cause of trouble is a lack of proper pressure balance in the flow circuit between the mix cycle and the recirculate part of the cycle. Uneven velocities of discharge from the orifices may also cause trouble, as will one of the liquid streams being directed away from the impeller shaft while the other is directed towards the shaft.

A term occasionally used on flexible slab production lines to describe the distance between the mixer and the cream line. See cream line.

The device, used in frothing, that provides the transition zone between the higher pressure in the mixing chamber and atmospheric pressure. It can vary in design from the readily adjustable (by pneumatic pressure) rubber sleeve type valve to a short length of hose that is squeezed by a C clamp. The object is to keep the mixture as a liquid as far down the nozzle as possible so that shearing of the bubbles is minimized. The discharge tip of the nozzle should be designed to minimize air turbulence so that a smooth 'rope' of froth is produced.

That portion of a let-down nozzle that can be classified as a controllable valve. A let-down valve is usually employed in the production of froth foam.

The ability of a plastics material to resist fading after exposure to sunlight or ultraviolet light. Nearly all plastics tend to darken under these conditions.

A long chain molecule as contrasted to one having many side chains or branches.

See diluent.

The technique of introducing the least reactive material, usually the polyol, into the mixing chamber at a point just below the mechanical seal, so as to lubricate the mechanical seal and act as a buffer to prevent direct contact of the seal with isocyanates. This is most useful with continuous mixers, it being difficult to maintain the liquid seal and ratio balance during rapid 'on-off' cycling.

See Block.

A term used to describe a long narrow Block of foam that is to be 'peeled'. See peeler.

A phenomenon in molding in which the skin of the molded article is a loose intact film. This is normally caused by excessive movement or flow of the foam after gelation is too far advanced.

In general, laminates molded and cured in the range of pressures from 400 psi down to and including pressures obtained by the contact of the plies.

A mixing technique whereby the liquid components are mixed primarily by rolling and stirring the chemicals in a mixing chamber of relatively large volume. Power loss and mechanical energy transfer in the form of heat are generally quite low. The pin type mixer is generally described as a low shear mixer. See high shear mixing.

See fluorocarbon and fluorocarbon blown foam. Although the term generally refers to the fluorocarbon family, there are other materials that may be used such as methylene chloride, etc.

A device installed in an air line feeding a pneumatic device (air motor or piston), requiring small amounts of lubricant for best performance and service. The device meters the required amount of lubricant into the air as it passes through on the way to the air motor or piston.