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
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