Manifold - A term used mainly with reference to blow molding and sometimes with injection molding equipment. It refers to the distribution or piping system which takes the single channel flow output of the extruder or injection cylinder and divides it to feed several blow molding heads or injection nozzles.

Masterbatch - A plastics compound which includes a high concentration of an additive or additives. Masterbatches are designed for use in appropriate quantities with the basic resin or mix so that the correct end concentration is achieved. For example, color masterbatches for a variety of plastics are extensively used as they provide a clean and convenient method of obtaining accurate color shades.

Mat - A randomly distributed felt of glass fibers used in reinforced plastics lay-up molding.

Melamine Plastics - Thermosetting plastics made from melamine and formaldehyde resins.

Melt Flow - The flow rate obtained from extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238.

Melt Fracture - An instability in the melt flow through a die starting at the entry to the die. It leads to surface irregularities on the finished article like a regular helix or irregularly-spaced ripples.

Melt Index - The amount, in grams, of a thermoplastic resin which can be forced through a 0.0825 inch orifice when subjected to 2160 grams. forced in 10 minutes at 190 degrees C.

Melt Strength - The strength of the plastic while in the molten state.

Melt Temperature - The temperature of the molten plastic just prior to entering the mold or extruded through the die.

Melting Point - The temperature at which solid and liquid forms of a substance are in equilibrium. In common usage the melting point is taken as the temperature at which the liquid first forms in a small sample as its temperature is increased gradually.

Meniscus - The free surface of a liquid in a container, for example, water in contact with air confined in a capillary tube.

Mer - The repeating structural unit in any high polymer.

Metallizing - Applying a thin coating of metal to a non-metallic surface. May be done by chemical deposition or by exposing the surface to vaporized metal in a vacuum chamber.

Metering Screw - An extrusion screw which has a shallow constant depth, and constant pitch section over, usually, the last 3 to 4 flights.

Modified - Containing ingredients such as fillers, pigments or other additives, that help to vary the physical properties of a plastics material. An example is oil modified resin.

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 - (v.) To shape plastic parts or finished articles by heat and pressure. (n.) (1) The cavity or matrix into which the plastic composition is placed and from which it takes its form. (2) The assembly of all the parts that function collectively in the molding process.

Molding Cycle - (1) The period of time occupied by the complete sequence of operations on a molding press requisite for the production of one set of moldings. (2) The operations necessary to produce a set of moldings without reference to the time taken.

Molding Pressure - The pressure applied to the ram of an injection machine or press to force the softened plastic completely to fill the mold cavities.

Molding Shrinkage - The difference in dimensions, expressed in inches per inch, between a molding and the mold cavity in which it was molded, both the mold and the molding being at normal room temperature when measured.

Molecular Weight Distribution - The ratio of the weight average molecular weight to the number average molecular weight gives an indication of the distribution.

Monomer - A relatively simple compound which can react to form a polymer. See also Polymer.

Mounting Plate - The part of the blow molding unit to which the mold is attached.

Movable Platen - The large back platen of an injection molding machine to which the back half of the mold is secured during operation. This platen is moved either by a hydraulic ram or a toggle mechanism.

Multi-cavity mold - A mold with two or more mold impressions, i.e., a mold which produces more than one molding per molding cycle.

Multiple Head Machine - A (blow molding) machine in which the plastic melt prepared by the extruder is divided into a multiplicity of separate streams (parisons) each giving ultimately a finished item.