Urethane and Polyurethane Industry Glossary

MDI

An abbreviation for diphenylmethane diisocyanate. 'Crude' MDI refers to polymeric isocyanates derived from MDI.

ml

See cc.

Mn (Number-Average Molecular Weight)

The total weight of all molecules divided by the total number of molecules.

Mw (Weight-Average Molecular Weight)

The sum of the total weights and molecules of each size multiplied by their respective weights divided by the total weight of all molecules.

Machine Start-Up Service

A service provided by some machine manufacturers to start new machines in operation. The manufacturer provides an experienced technician who trains the customer's personnel in the proper operation and maintenance procedures (usually on site). Since these machines are often rather complex, the service is quite valuable. A rule of thumb often quoted is that 'proper operation is 50% of the profits'. Sometimes the service is included in the cost of the machine; at other times it is extra.

Machine Tanks

Those tanks that form a part of the operating system of a foam machine, usually mounted on the machine frame with the metering pumps either inside or directly beneath.

Manual-Automatic Selector Switch

A switch, included on the control panel by some machine manufacturers, that permits the operator to choose between automatic dispensing controlled by the timer or manual control timed by the operator.

Manual Solvent Flush-Squeeze Bottle Type

A term which refers to a plastic squeeze bottle filled with solvent such as methylene chloride, which is used to force solvent through the mixing chamber after operation.

Manual Solvent Flush, Valve Type

A term which refers to a permanently connected solvent flush system that requires manual opening and closing of a valve. The solvent may be supplied by a pump or pressure pot. A manually operated air flush may also be included.

Mass Effect

A term which refers to the influence that the total amount of chemicals poured has on the density, cure time, etc. A small pour generally requires a higher catalyst level and a much more careful control of the environment than does a larger pour in order to achieve the same properties. The 'surface to volume ratio' of the mold and the mass of the mold also has an influence on foam properties.

Masterbatch

A term sometimes used to describe the mixture resulting from premixing as many minor ingredients as possible in with the polyol' in order to reduce the final number of components ' to the lowest possible level or to have time to blend efficiently a chemical that is not very miscible with the polyol. See premix.

Master-Slave Drive System

See interlocked systems.

Materials Producer

A term used to describe the basic chemical supplier, sometimes called 'raw material supplier'.

Material Tanks

An ambiguous term sometimes used to refer to the machine tanks built into or onto the metering system and sometimes used to refer to the material storage tanks in which bulk chemicals are stored until needed.

Matrix

That material within which something originates or takes form. In the case of urethane foam the bubbles originate within a liquid matrix.

Mattress

A term used in the USA to describe the cushioning material applied to a bed in order to make it more comfortable. A single bed mattress, in the USA, generally measures approximately 39 inches wide by 72 inches long by 4 inches or more thick, although there are many variations of this. A double bed mattress, in the USA, generally measures 54 inches wide by 72 inches long by 4 or more inches thick, again with many variations. Other countries have different names and different dimensions for this article.

Mechanical Traverse Drive

A drive system for mixed liquid spreaders or traversers that takes all reversal thrust directly on gear teeth, screw threads or some other non-shock absorbent device. This type of drive system generally has a greater maintenance problem than the pneumatic or hydraulic type.

Mechanical Mixing Head

A mixing device in which the primary cause of mixing is a power driven rotor or impeller which, by its speed of rotation and configuration, imparts turbulence to the fluids as they enter the mixing zone.

Mer

The repeating structural unit of any high polymer.

Metal Belt Conveyor

A particular type of metal surfaced conveyor in which each slat interlocks with its neighbor in such a manner that a chain link is formed across the entire width of the conveyor. This type is often used for continuous slab foam manufacture.

Metal Slat Conveyor

A type of metal surfaced conveyor used in the foam industry in which the metal slats are supported at each side of the conveyor by a chain and are not themselves interconnected as in the metal Belt Conveyor described above.

Metering

See positive metering. The term is also used to describe the practice of collecting the simultaneous flows of the various components in individual cups for definite time periods in order to check the calibration of the machine.

Metering Ports

The discharge orifices through which the final components are introduced into the mixing chamber. These may or may not be replaceable to assist in balancing pressures. Pressure balancing is very important to good molding and readily replaceable tubes are very important not only for start-up but also for maintenance cleaning. See metering tubes.

Metering System

The pumping system used to accurately control the flow of the liquid plus all the hoses, valves, gauges, and piping needed to make a complete flow circuit.

Metering Tubes

The interchangeable tubes used as discharge orifices in those machines designed for ease of pressure balancing. See metering ports.

Methylene Chloride

A chlorinated hydrocarbon that is most commonly used as the cleaning solvent in the urethane foam industry. It is the most effective of the cheaper, non-flammable solvents. Many other solvents are more or less effective and can also be used. Flammable solvents should not be used.

Mill

A term which, in the rubber industry, refers to a roller type mixing device that is effective with mixing very high viscosity materials such as gum rubbers and elastomers. In the paint industry as 'Ball Mill', it refers to a rolling type mechanism that revolves a drum in which pigments and powders are dispersed into a resinous medium by means of heavy pellets also contained in the drum. A 'hammer mill' is used to produce finely divided pieces of flexible foam from flexible foam trims. See crumb.

Mixer

A mechanical device capable of mixing two or more materials together homogeneously.

Mixing Chamber

The section of a mixing head in which the final. combination of the ingredients occurs. It is usually that section contained within the impeller housing.

Mixing Chamber Port

A term occasionally used to refer to a metering port.

Mixing Head

A mechanical device capable of mixing two or more materials together homogeneously in one passage through the mixing zone, It may include valves, bearings, motor, etc. See mixer and Batch Mixer.

Mixing Head Hold-Up

See hold-up.

Mixing Head Mounted Drive

See head mounted drive.

Mixing Zone

The portion of a mixing chamber in which mixing is actually accomplished. Normally the mixing zone is around the outer perimeter of the impeller.

Modified Total Prepolymer

A total prepolymer system that has been modified by diluting the catalyst solution with plasticizers, fire retardent Additives or even a portion of the original or other polyol. This serves the purpose of changing the ratios from about 97/3 to approximately 80/20 and consequently improves the tolerance or ease of handling of the formula , particularly at very low flow-rates.

Modulus of Elasticity

The ratio of stress to strain in a material that is elastically deformed. moisture vapor transmission-the rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.

Mold Liners

Thin shaped films of plastic or treated paper that fit smoothly into the mold cavity and are used in place of mold release. The liners may or may not form the finished surface of the molded article. Vacuum formed vinyl and ABS skins are often used.

Mold Packing

A term which refers to the slight excess of the actual foam quantity poured into the mold over that actually required to fill the mold under ideal conditions, particularly for rigid foams. The excess usually is set at some point between 5% and 15% over the exact amount required. This extra material serves as a buffer to absorb slight changes in material temperatures, mold temperatures, distribution of materials, etc., and also seem to aid in reducing rejects caused by skin defects. It is also said to aid in improving load bearing properties of the foam. Flexible foam molding techniques do not generally employ packing in excess of 5% due to the formation of hard spots under excessive internal pressure conditions.

Mold Release Agent

One of many chemical compounds which, when applied to the mold surface, serve to prevent the cured foam from sticking to the mold. Because of the many variations in the formulations used in urethane foam, no one class of releases seems to have a clear advantage over others. Classes of releases that have proven useful include telomers, silicones, waxes (both synthetic and natural), and soaps of various sorts. One of the more useful. concepts used for flexible foam release involves the use of a microcrystalline wax which is a solid at the temperature of the mold during pouring, but melts during curing so that the final release coating is a liquid film.

Molding

The practice of pouring the mixed liquid foam ingredients into a shaped cavity, closing the cavity, allowing the foam to expand and cure to the handling point, and then removing the foam article from the cavity. Good molding practice usually dictates control over the temperature and quantity of the foam ingredients used, the temperature of the mold surface, the distribution of the liquid in the mold, the cure temperature, the cure time and the venting of the displaced gas from the mold.

Monitor

A term used by some continuous slab process companies to describe the individual(s) that supervise the production of the foam by direct observation of the foaming process, the instruments, the final foam, etc.

Monofluorotrichloromethane

See trichlorofluoromethane.

Moon Cratering

See cratering.

Movable

A term suggested by some to be used in the foam equipment field to describe those machines that are portable only with the use of many men or heavy lifting equipment.

Multiple Component

A term used to describe a formula or machine that requires handling two or more liquid ingredients at the point of final mixing.

Multiple Pour Technique

A technique used to overcome deficiencies of formulation or equipment in the filling of molds, particularly thin, high rise cavities. If a single pour in the mold cavity would deform the walls or would result in an uneconomically high density, the wall would preferentially be poured in layers. The foam rise in each layer is restricted to that amount associated with the best properties in the foam. Usually each layer is permitted to harden before adding the next, If the equipment does not have sufficient capacity of flow rate to fill the cavity in one pour without seriously damaging the rising foam, then the cavity must also be poured in layers. The height of each layer would then be determined by the flow rate of the machine.

URETHANE INDUSTRY GLOSSARY - M

MDI

ml