Machine Shot Capacity: Refers to the maximum volume of thermoplastic resin which can be displaced or injected by the injection ram in a single stroke.

Mar Resistance: The resistance of glossy plastic surfaces to abrasive action. Masterbatch: A concentration of a substance (an additive, pigment, filler, etc.) in a base polymer.

Material Safety Data Sheets: Documentation regarding the toxicity or hazards associated with contact with some substances. The manufacturer of the plastic prepares these data sheets.

Mechanical Property: Properties of plastics which are classified as mechanical include abrasion resistance, creep, ductility, friction resistance, elasticity hardness, impact resistance, stiffness, and strength.

Melt Flow Rate: A measure of the molten viscosity of a polymer determined by the weight of polymer extruded through an orifice under specified conditions of pressure and temperature. Particular conditions are dependent upon the type of polymer being tested.

Melt Flow: Rate of extrusion of molten resin through a die of specified length and diameter. The conditions of the test (e.g. temperature and load) should be given. Frequently, however, the manufacturer’s data lists only the value, not the condition as well.

Melt Index: The amount of a thermoplastic resin, measured in grams, which can be forced through a specified orifice within ten minutes when subjected to a specified force. (ASTM D-1238) Melt Strength: The strength of the plastic while in the molten state. This is a pertinent factor in extrusion, blow molding and drawing of molten resin from a die.

Memory: The tendency of a plastic article to revert in dimension to a size previously existing at some stage in its manufacture.

Metallizing: A term covering all processes by which plastics are coated with metal.

Migration (also know as Bloom): An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article caused by the exudation of a compounding ingredient such as a lubricant, stabilizer pigment, plasticizer, etc.

Mineral Reinforcements: Inorganic substances used as filler for plastics. Some common examples are clay, mica, talc.

Minimum Specifications: The minimum values, usually of mechanical properties, that a compound must meet by Quality Assurance prior to shipment.

Modulus in Compression: The ratio of compressive stress to strain within elastic limits of the material.

Modulus in Flexure: The ratio of the flexure stress to strain, within elastic limits of the material.

Modulus in Shear: The ratio of shear stress to strain within the elastic limits of the material. Modulus of Elasticity: The ratio of stress to corresponding strain below the proportional limit of a material in tensile testing.

Modulus of Resilience: The energy that can be absorbed per unit volume without creating a permanent distortion.

Modulus: Derived from the Latin word meaning “small measure”, the modulus is the ratio of stress to strain in the linear region of the s-e curve.

Moisture Absorption: The pickup of moisture from the environment by a material.

Mold (n): A hollow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article.

Mold (v): To impart shape to a plastic mass by means of a confining cavity or matrix.

Mold Changer: An automated device for removing one mold from a machine and replacing it with another mold.

Mold Frame: A series of steel plates which contain mold components, including cavities, cores, runner system, cooling system, ejection system, etc.

Mold Release Problems: Excess use of mold release may leave parts oily and weaken the material.

Mold Release: In injection molding, a lubricant used to coat the surface of the mold to enhance ejection of the molded article or prevent it from sticking to the tool.

Mold Temperature: the temperature at which the mold is maintained. Often the most important benefit of raising mold temperature is that it allows a slower injection rate without the plastic getting too cold.

Moldability: The characteristics of being easy to mold without rupturing or developing flaws due to the movement of the polymer during gelation.

Molding Cycle: The period of time occupied by the complete sequence of operations on a molding press requisite for the production of one set of molded articles.

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 sensitivity: the variability of the pressure to fill the cavity and temperature of the melt at the part as influenced by changes in injection time and barrel melt temperature.

Molding window: the range of molding conditions under which a part can be successfully molded.

Mold-Temperature-Control Unit: Auxiliary equipment used to control mold temperature. Some units can both heat and cool the mold. Others, called chillers, only cool the mold.

Molecular Weight: The sum of the atomic weights of all atoms in a molecule. Especially in plastics, an average molecular weight is reported.

Molecule: The smallest unit quantity of matter which can exist by itself and retain all of the properties of the original substance.

Monomer: A relatively simple molecular structure, usually containing carbon and of low molecular weight, which can react to form a polymer by combination with itself or with other molecules and energy.

Moving Platen: The platen of an injection molding machine that is moved by a hydraulic ram or mechanical toggle.

Multi-Cavity Mold: A mold having two or more impressions for forming finished items in one machine cycle.

Multidirectional flow: flow direction changes during filling resulting in orientation in different directions which can cause flow marks, stresses, and warping.

Multiple cavity molds: produces more that one identical part with each cycle.

Multi-Shot Molding: The injection of two-or-three materials, in sequence, into a single mold during a single molding cycle. The injection molding machine is equipped with two-or-three plasticators. (See also co-injection)

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