3 14 materials [read-only]

7/25/2019 3 14 Materials [Read-Only]

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Copyright 2001 Moldflow Corporation

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Materials

Materials


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Searching Techniques

Searching Techniques


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Graphing data

Graphing data


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Viscosity Graph

Viscosity Graph


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Comparing materials

Comparing materials

Use search function

Set up search criteria

Sort list by clicking on

column heading Modify search criteria

as necessary

Click Details to look at

data specifically


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Properties Needed for Flow AnalysisProperties Needed for Flow Analysis

Thermal Specific heat

Thermal conductivity

Rheological Viscosity (Cross-WLF default model)

Transition temperature

PVT Melt Density

2-Domain tait PVT

Recommended Processing Mold temperature

Melt temperature

Ejection temperature


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Other PropertiesOther Properties Recommended Processing

Mold and melt minimum &maximum temperatures

Maximum shear stress &

shear rate

General

Commercial name

Manufacturer

Family abbreviation

Mechanical

Modulus

Poissons ratio

Coefficient of thermal

expansion Shrinkage

Corrected residual in-mold

stress

Filler

Type

Percentage by weight


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Types of Plastic MaterialsTypes of Plastic Materials

Amorphous

Same molecular

structure throughout

molding cycle Semi-crystalline

Compact molecular

structure when cool,

amorphous when hot


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How Plastics FlowHow Plastics Flow

Frozen Layer

Melt

Mold Wall

Mold Wall

Fountain

Flow Region


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Polymer ViscosityPolymer Viscosity

Viscosity Models

Newtonian

Power Law

Cross WLF

.


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Polymer ViscosityPolymer Viscosity Definition: Resistance to Flow

Decreases with increasingshear rate or temperature

Material Viscosity

Water 10-1

10Polymer

10,000

Glass 1020

Increasing

temperature

Shear Rate (1/s)

Viscosity(Pa-s)

Low

resistance

to flow

High

resistance

to flow


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Melt Flow RateMelt Flow Rate Test run with constant temperature and shear rate

Useful to compare difference between materialgrades within a resin family

Low MFR Material

Higher

Pressure

High MFR Material

Lower

Pressure

W W


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Lesson 10


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Material Influence on InjectionPressure and Clamp Force

Material Influence on Injection

Pressure and Clamp Force

Different materials require different injection

pressures

Different materials

exhibit a wide rangeof viscosity levels

PMMAHi Viscosity

PP

Low Viscosity

Fill Time (sec)Inj.

Pressurean

dClampForce


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Polymer Thermal PropertiesPolymer Thermal Properties

Cp - specific heat capacity

ability to hold heat

k - thermal conductivity

ability to conduct heat


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Impact of Material on Cooling TimeImpact of Material on Cooling Time

Cooling time based on the

thermal conductivity, density,

and specific heat

These combine to create the

thermal diffusivity of the

material

Density (p)

Specific

Heat (Cp)

Thermal

Conductivity (k)

Cooling TimeChange


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PVT PropertiesPVT Properties p - pressure;

v - specific volume;T - temperature

Describes how the plastic

contracts and expands with

changing pressure andtemperature

During filling and packing,

the plastic contracts due to

increased pressure

During cooling the plastic

contracts due to decreased

temperature

Pressure

Increases

Temperature

Spe

cificVolume


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Amorphous vs. Semi-CrystallineAmorphous vs. Semi-Crystalline

Crystallization occurs

when plastic moleculestake an ordered structure

forming crystal-like

patterns

Higher crystallization

means more shrinkage


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PVT Characteristics for

Amorphous Resins

PVT Characteristics for

Amorphous Resins

Increasing

Pressure

Temperature

SpecificVolum

e

p- pressure

v- specific volume

T- temperature

B

A


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Influence of Thermal PropertiesInfluence of Thermal Properties

Alpha1 (flow direction)

and alpha2 (cross-flowdirection) are linearthermal expansion

coefficients (LTEC) Describe how much a plastic

dimension changes linearly withchange in temperature

Differences in flow and cross-flow alpha values causedifferential shrinkage

Typical of semi-crystallineresins

alpha2 (mm/C)alpha1 (mm/C)


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Influence of MechanicalProperties

Influence of Mechanical

Properties Modulus values, E1 and E2 represent the flow

and cross-flow moduli, respectively

Higher and uniform E value, lower shrinkage

and less warpage in general E1 and E2 vary sometimes with semi-

crystalline resins

Glass filled resins have significant differencesbetween E1 and E2, more warpage

E1

E2


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