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A B C D E F G H I J
K L M N O P Q
R S T U V W X
Y Z
Acceptable runner/cavity ratio
-
runner systems designed for high pressure drops to minimize material usage and increase frictional
heating in the runner.
Amorphous -
non-crystalline. Material assumes more random molecular structure when cooling.
Artificially balanced runner system
-
balancing a runner system by adjusting the pressure drop of a long large diameter runner against
a short small diameter runner. Since pressure drop over the small diameter runner will be much
more affected by heat loss than the large diameter runner, an artificially balanced runner system
will work with a set range of molding conditions. The width of this range of molding conditions
determines the stability of the molding.
Backflow -
the melt flows back out of the mold, returning to the runners.
Cavity -
the interior opening in the mold where the part is formed.
Commonly Used Conversions
KPa x 0.145 = psi
MPa x 145 = psi
°C x 1.8 + 32 = °F
Liters/min x 0.2642 = Gal/min
Inches x 25.4 = mm
Flow rate = ((# of cavities) x (volume per cavity))/(injection time)
Constant pressure gradient
-
pressure drop per unit length. The constant pressure gradient principle says that the most efficient
filling pattern is when the pressure gradient is constant along the flow path.
Controlled frictional heating
-
runners designed to deliver a higher melt temperature to the cavity. This results in lower stress
levels in the part without causing material degradation due to long exposure to elevated temperatures.
Cooling time -
the elapsed time required for the melt to reach its Vicat softening temperature.
Crystalline -
material assuming fixed internal forms. Slow cooling areas have high crystallinity and shrinkage.
Cycle -
complete, repeating sequence of operations for injection molding a part.
Cycle time -
elapsed time between a certain point in one cycle and the same point in the next cycle.
Differential cooling -
occurs when one area of the part cools at a different rate or when the mold surfaces are at different
temperatures. Warping results from differential cooling.
Dimensional stability -
retention of the precise shape of the cavity.
Dominant flow -
at the juncture of two confronting flows the dominant flow will reverse the direction of the other.
Draft -
degree of taper of the cavity side walls, allowing the part to be removed easily from the mold.
Edge gate -
entrance to the part from the runner located on the parting line.
Element -
a triangle defined by three nodes, creating the basis for the finite element analysis.
End of flow -
the melt is just touching the last part of the mold to be filled and the pressure at that point
is zero.
Ejector pin -
part kick-out mechanism.
Family mold -
a mold which produces non-identical parts simultaneously.
Filler -
material added to the molding material to reduce cost and/or improve mechanical properties.
Fill pattern -
the contours of the advance of the material as the cavity fills. (See flow pattern)
Fill pressure -
the pressure required to fill the cavity.
Finite element analysis -
the solution of simultaneous equations for each element (triangle) with resulting pressure, temperature
and elapsed time at each node and the direction and speed of the material (at the instant of fill).
Flash -
excess material retained by the part along the parting line.
Flow balancing -
modifying flow paths, particularly runner sections, so that all flow paths within a mold fill
in equal time with equal pressure.
Flow deflector -
local reduction in thickness to divert flow.
Flow leader -
local increase in thickness to encourage flow in a particular direction.
Flow pattern -
the contour the melt takes sequentially as it fills the cavity. The mold should fill with a straight
flow front with no changes in direction throughout filling.
Flow rate -
the volume of material passing a fixed point per unit time.
Freeze off -
the temperature of the material is reduced to the point that it blocks an area it would fill if
it were hotter.
Frictional heating -
heat generated by the friction of the chains of molecules slipping past each other.
Gate -
the narrowed link between the runner and the cavity.
Glass transition -
change in an amorphous polymer from viscous to hard and relatively brittle.
Hesitation effect -
occurs in parts of varied thicknesses. The flow moves preferentially into a thicker area causing
an adjacent thin area to freeze off while the thicker area fills. Gates should be positioned as
far as possible from where the flow divides into thick and thin flow paths.
Hygroscopic -
readily absorbs moisture.
Injection or fill time -
time required to fill the cavity or mold.
Insert -
a removable part of the mold imparting increased resistance to wear or heat transferability to
that area of the mold.
Isobar -
a line of equal pressure. In MOLDFLOW graphic output, any point along an isobar sees the same
cavity pressure as any other point along the same isobar.
Isochrone -
a line of equal time. In MOLDFLOW graphic output, any point along an isochrone is filled at the
same time as any other point along the same isochrone.
Isotherm
a line of equal temperature. In MOLDFLOW graphic output, any point along an isotherm is at the
same temperature as any other point along the same isotherm.
Land -
gate dimension parallel to the direction of melt flow.
Material database -
the file of the information on each material acceptably tested for use in MOLDFLOW analyses.
Maximum shear stress -
the critical level for the material.
Meld line -
the juncture of two flow fronts moving in the same direction rather than in opposite directions.
Meld lines should be positioned in least sensitive areas.
Melt -
the molten material which will fill the mold cavity to form the part.
Mesh -
the finite elements.
Mold -
the blocks containing the cavity, runners and sprue.
Molding conditions -
the temperature of the mold and melt and the time required to fill the mold.
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.
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.
Molding window -
the range of molding conditions under which a part can be successfully molded.
Multidirectional flow -
flow direction changes during filling resulting in orientation in different directions which can
cause flow marks, stresses and warping.
Multiple cavity mold -
produces more that one identical part with each cycle.
Naturally balanced runner system
-
each succession of runner is identical to the runners in the same succession in all other flows
in the mold.
Node -
defined by x, y, z coordinates which in turn defines one point of an element (triangle).
Nozzle -
hollow metal hose screwed into the extrusion end of the heating cylinder of an injection machine
designed to form a seal under pressure between the cylinder and the mold.
Orientation -
the arrangement of the molecules of the melt. If the molecules are orientated, they are aligned
with each other; if non-orientated they are not in alignment. In general, orientated material
shrinks more than non-orientated material.
Orifice -
opening.
Out-of-round -
failure to remain round.
Overpack -
melt will fill the easiest flow path first and will continue to pack this area while material
reaches the other areas. This is a cause of warping created by unbalanced flow.
Part -
the payload formed in the cavity.
Partially-balanced runner system
-
composed of both naturally and artificially balanced runners.
Parting line -
mark on the part indicating where the two halves of the mold met in closing.
Part quality -
minimal residual stress level, avoiding both warpage and sink marks.
Plots
graphical representations of analysis results.
Pressure drop -
the amount of pressure required to fill that section. Adding up the pressure drops over every
section in a flow path totals the pressure required to fill the mold.
Racetrack effect -
thicker area in flow cross section speeds up the flow.
Regrind -
previously molded material re-entering the processing cycle.
Reinforced plastics -
high strength fillers imbedded in the part.
Release agent -
a material sprayed on the mold which facilitates removing the part.
Rib -
a reinforcing section of the part.
Runner design -
using the runner as a flow control device (positioning the gate and using the size of the runner
to control the filling pattern within the cavity) in addition to getting the melt into the cavity.
Runner balancing -
developing a runner system which delivers the required amount of melt to each cavity with the
correct pressure to finish filling all the cavities simultaneously at the correct temperature
for the part.
Runners -
channels cut interior to the mold which transport the melt from the entrance to the mold to the
entrance to the cavity.
Scrap -
any output of a mold that is not usable as the primary product.
Shear rate -
the rate at which a layer of melt slides over the layer below. Shear rate is velocity-related
rather than force- related.
Shear stress -
the shearing force divided by the area. It is always a maximum at the outside of the flow channel.
As it is force-related, it depends on the viscosity of the material, which in turn depends on
the material and molding conditions. The maximum allowable stress level is usually taken as 1%
of the tensile strength of the material. High shear stress is unimportant at gates, and in sprues
and runners.
Short shots -
sequential views of the flow front through the cavity.
Shrinkage -
contraction upon cooling of all or areas of the part. Shrinkage occurs less is disorientated material
and more across chains of molecules than along their lengths. Lower pack area have lower areas
of orientation and shrinkage.
Single cavity mold -
produces one part with each cycle.
Sink marks -
an indentation on the surface of the part as a result of significant local change in wall section.
The mark will occur in the thicker area.
Skin -
a relatively dense layer at the surface of the material.
Slide -
projection in the mold used to form the geometry of the part, which is not in the direction of
the closing of the mold and must be withdrawn before the part can be ejected.
Splay -
area of abnormal racing of the melt in the mold causing surface blemish. Oil in the mold is one
cause.
Sprue -
the entrance to the mold interior into which the melt is injected.
Stress Concentrators -
abrupt changes in geometry of the part serve as the focus of high stresses. Various means can
be devised to relieve the abruptness of the geometric changes and thus the stresses.
Structural strength -
reduction in melt quality or distressed melt flow due to welding, melding, etc. during molding
reduce the structural integrity of the part, lowering longevity in use.
Subgate -
entrance to the part from the runner located below the parting line. On ejection the part breaks
away from the subgate.
Submolding -
break up of a full molding into component areas.
Surface appearance -
distressed melt flow due to welding, melding, splay, etc. will appear as surface imperfections.
Tabgate -
edge-gating or sub-gating into a tab added to the part for gating purposes only.
Thermal conductivity -
ability of a material to conduct heat.
Thermal degradation -
deterioration of the material by heat, characterized by molecular scission.
Thermal shut-off -
material freezes causing blockage.
Thermoplastic -
material that will repeatedly soften when heated and harden when cooled.
Thermoset -
material that has undergone a chemical reaction so that it remains hardened, even when reheated.
Thickness -
depth of the material and contributory to pressure requirements; thickening reduces the pressure
required to fill the part.
Time scan -
effects of mold and melt temperature and injection time changes on pressure, stress and temperature
at the end of flow.
Undercut -
a protuberance or indentation that impedes withdrawal from a mold.
Underflow -
the dominant flow of two confronting flows, over the other. The lesser flow reverses direction
giving poor surface appearance and structural strength. Underflow should be avoided by positioning
gates so that the flow fronts meet at the end of filling.
Unidirectional flow pattern
-
plastic flowing in one direction with a straight flow front throughout filling.
Uniform cooling time -
cooling time the same throughout the part to avoid warping.
Vicat softening point -
the temperature at which a flat ended needle will penetrate a specimen under a specified load
using a uniform rate of temperature rise.
Virgin material -
never processed other than that required for initial pellet manufacture.
Viscosity -
resistance to flow of a liquid.
Void -
an unfilled space within a solid material.
Warping -
acquired contortion of the part due to differential shrinking of the material.
Weld line -
the intersection of two confronting flow fronts creating areas of local weakness. Weld lines should
be positioned in the least sensitive areas.
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