3 challenges in plastics testing: melt flow, heat deflection temperature, & impact
TRANSCRIPT
The 3 Challenges in Plastics Testing
Melt Flow, HDT & Impact
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Agenda Overview
• Testing Standard • Changes and Trends in Key Standards
• Melt Flow
• HDT & Vicat Tests
• Challenges • Factors that Influence Results and Solutions
• Melt Flow
• HDT & Vicat Tests
• Impact
• Increasing Lab Efficiency and Throughput • HDT & Vicat Tests
• Impact
3
Melt Flow Index
Polymer
Melt
Extrudate
MFI = MFR = Fluidity = Inverse of Viscosity
Ability of material melt to flow under pressure
• ISO 1133
• ASTM D1238
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ISO 1133-1,2
• Latest Revision in 2011
• Reference for most local standards on melt flow tests worldwide
• Similar to ASTM D1238, but differs in technical content
What’s Changed?
Testing Standards Reviewed – Melt Flow
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2005 2011
TEMPERATURE
ACCURACY
TEMPERATURE
VERIFICATION /
CALIBRATION
PISTON
GEOMETRY
Max absolute deviation,
defined for all materials and
as a function of different
temperature ranges
One simple procedure
required for all applications
Head diameter defined by
difference from barrel
diameter, sharp lower edge
Evolution of ISO 1133
Max absolute deviation + relative
distribution along the barrel (for
sensitive materials) over the entire
temperature range
More complex procedure added
for sensitive materials (part 2)
Absolute tolerance on head
diameter, rounded lower edge
= Significant
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Temperature Tolerance Specified by 2011 Revision of Standard
Temperature Tolerances ISO 1133-1:
• Maximum deviation at 10 mm above die surface:
± 1°C (all temperatures)
• Maximum deviation between 10 - 70 mm above
die surface : ± 2°C to ± 3°C (depending on
temperature)
• No maximum relative distribution specified
Temperature Tolerances ISO 1133-2:
For all temperatures, between 0 - 70 mm above
die surface:
• Maximum deviation from set temperature: ±
1°C
• Maximum relative distribution of the
temperature: ± 0.3°C
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TEMPERATURE
ACCURACY
TEMPERATURE
VERIFICATION /
CALIBRATION
PISTON
GEOMETRY
RESULTS
METHOD
EFFICIENCY
PRODUCT Changes
How Will These Changes Impact You?
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Heat Deflection Temperature Test
• A stress is applied on a sample in a 3-point bending mode while
temperature is raised at uniform rate
HDT value for the material
under test
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Vicat Softening Temperature
• A standard indenter penetrates into the surface of a plastic test specimen
when the temperature is raised at a uniform rate
VST value for the material
under test
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Testing Standards Reviewed – HDT & Vicat
• ISO 75-1,2
• ISO 75-3
• ASTM D648
• JIS K7207
• ISO 306
• ASTM D1525
• JIS K7206
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ISO 75-1,2
• The most common plastics Heat Deflection Temperature (HDT)
standard worldwide
• Latest revision in 2013
• Not technically equivalent to ASTM D648
What’s Changed?
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ISO 75-1, 2
Both flatwise with 64 mm
span or edgewise with 100
mm span
Only one mercury-in-glass
thermometer
Between 20 - 23°C
SPECIMEN
POSITION AND
SPAN
INITIAL
TEMPERATURE
TEMPERATURE-
MEASURING
HEATING
EQUIPMENT
Practically only oil bath
were available
Any suitably calibrated
temperature-measuring device is
allowed
(A device for each station is
recommended)
64 mm span no longer allowed for
edgewise tests
Liquid bath, fluidized bed or an air-
oven systems
Below 27°C
ISO 75:1974 (1st edition)
1987
(2nd edition) 2004 2013
1993/Split Part 1, 2 and (3) = Significant
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How Will These Changes Impact You?
HEATING
EQUIPMENT
SPECIMEN POSITION
AND SPAN
TEMPERATURE
MEASURING
INITIAL
TEMPERATURE
RESULTS
METHOD
EFFICIENCY
PRODUCT
Changes
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ISO 306
• The most common plastics Vicat Softening Temperature (VST)
standard worldwide
• Latest revision in 2013
• Equivalent to ASTM D1525
What’s Changed?
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ISO 306
Mercury-in-glass
thermometer
Between 20 - 23°C Initial
Temperature
Temperature-
measuring
Heating
Equipment
Practically only oil bath
were available
Load applied after
preconditioning
(5 minutes) phase
Test
Procedure
Any suitably calibrated
temperature-measuring device.
One per station, as close as
possible to both the indenting tip
and specimen
Liquid bath, direct-contact or
fluidized bed systems
Below 25°C
Load applied before
pre-conditioning (5 minutes) phase
1974
(1st edition) 1987 1994 2004 2013
= Significant
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How Will These Changes Impact You?
HEATING
EQUIPMENT
TEST PROCEDURE
TEMPERATURE
MEASURING
INITIAL
TEMPERATURE
RESULTS
METHOD
EFFICIENCY
PRODUCT
Changes
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Other Standards
• ASTM D648
• 2000, 2001, 2004, 2006 and 2007 (latest)
• No significant changes observed
• Current ballot to incorporate fluidized bed as
alternative heat transfer medium
• ASTM D1525
• 1987, 2000, 2006, 2007, 2009 (latest)
• From 2009 it is including fluidized powder as heat
transfer medium
• Technically equivalent to ISO 306
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Why are my results
inconsistent or
incorrect?
What influences results?
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Factors That Influence Results MFI
Temperature Accuracy
Preparation of Sample
(Moisture)
Sample Compacting
Method Parameters
Temperature Stability
Choice of Procedure
Encoder Accuracy
Extrudate Cutting
Precision
Melt Density Value
Manual Operations within Test
Maintenance of Die & Piston
Cleaning Procedures
= Most common
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Manual vs. Automatic
• Controlled Compacting
• Better reproducibility and less scattering of results
• No physical effort required by operator
(reduces risk of injury)
• Post-test automatic purging
• Reduces total test time
• Operator is ready to run next test more quickly
• Cleaning
• Thorough cleaning extends life of equipment
and helps to maintain consistent results
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Material
• Has the material been pre-conditioned according to procedure?
• Hygroscopic materials give unreliable test results if they are not dried
in consistent manner
• Moisture tends to generate bubbles and trigger degradation of sample
• Temperature and length of drying time must be consistent
• Is the melt density being used in the MFR calculations correct?
• Is the amount of material being tested consistent?
• Was the material compacted properly (or were there air bubbles)?
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Factors That Influence Results HDT/Vicat
Temperature Accuracy
LVDT Measurement
Accuracy
Specimen Dimensions –
Wrong Weights (HDT)
Span (HDT)
Oil Not Properly Selected
System Cooling Between Tests
Pre-Conditioning
Material Residual into
the Bath
Stress Applied (HDT)
Method Parameters
Unstable Temperature Rate Control
Oil Degradation
= most common sources of issues
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Oil Selection & Degradation
• Selection of the right oils helps obtain
more consistent results
• Oil that is intended for testing at higher
temperatures will be too viscous for
sufficient circulation at lower temps
• Extending the life of your oil:
• Nitrogen valve can be activated to prevent
oil contact with oxygen and prevent
premature degradation
• Specimen cages reduce oil degradation
due to materials into bath
• Bonus: saves operator time
How Much Time Can You Gain?
Increasing Laboratory Efficiency
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Solutions to Improve Throughput
6 stations
system
Automation
Manual
3 stations
system
Co
st
Effectiveness
Water Chiller
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Manual vs. Automated Test Time
6 stations
Automatic
Chiller
6.5 minutes
5 minutes
180 minutes
45 minutes
Preheating
cooling
Station preparation
up to specimens in bath
Test time
(example up to 300°C)
Ideal Setup
Total Cycle Time: 235 minutes
Total Cycle Time: 270 minutes
6 stations
Manual
tap water
cooled
180 minutes
5 minutes
9.5 minutes
75 minutes
Manual Setup
Cycle time
reduced by
about 30
minutes
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Factors That Influence Results Impact
Specimen Notching Method
Micrometers - Dimensional
Measurement
Accuracy of Equipment
Hammer Capacity
Environmental Losses
Specimen Notching Speed
Hammer Design Frame Design
Method Parameters
Indirect Verification
Calipers – Dimensional
Measurement
Specimen Conditioning
= most common sources of issues
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Bad Notch Affecting Impact Results?
• At what speed are you notching specimens?
• What is the depth of every pass?
• Are you using a linear notching knife?
• Is your knife profile within tolerance?
• When did you last change the notching knife?
40
30
20
10
0
0.25 0.5 1 2 4 8 16 32
PVC
Nylon
POM
ABS
PMMA
Notch Tip Radius (mm)
Impact
Str
ength
(kJ/m
2)
Good Notch
Bad Notch
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Bad Notch Affecting Impact Results?
Linear
Cutter
Rotary
Cutter
0.224
0.235
0.221
0.26 0.26 0.26
0.19
0.2
0.21
0.22
0.23
0.24
0.25
0.26
0.27
0.28
0.29
0.3
0.31
0 1 2 3 4
No
tch
Ba
se
Ra
diu
s (
mm
)
Number of specimens
Notch Radius Tolerance = 0.25 +/- 0.05 mm Linear cutter
Rotary cutter
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Specimen Conditioning
• Are you impacting the specimen within 5 seconds after taking it out of
the refrigerator/ Cryodispenser /cooling unit?
• Are you handling the specimen with conditioned tongs and gloves?
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Izod Vice Clamping
• Some plastics are sensitive to clamping pressure
• Differences in clamping pressure between tests and/or
operators will reduce results repeatability
Manual
Tightening Tightening with a Lever
Pneumatic Tightening
Increasing Laboratory Efficiency
How Much Time Can You Gain?
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Types of Setups
IDEAL TYPICAL
Motorized Impactor
• Integrated micrometer
• Automatic hammer release
• Automatic positioning of
hammer
Manual Impactor
• Non-integrated Micrometer
• Manual release of hammer
• Manual positioning of
hammer
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1. Measure specimen
dimensions
2. Enter specimen
dimensions
3. Place specimen on
the vice
4. Close the safety door
5. Release hammer
manually
6. Brake the test
7. Open the safety door
8. Reposition the
hammer manually
1. Place specimen
under micrometer
(Dimensions are
automatically sent
to the machine)
2. Place specimen on
the vice
3. Close the safety
door
4. Release hammer
pneumatically with
a click (Hammer is
repositioned
automatically)
SPECIMEN
HANDLING AND
MEASUREMENT
INITIATION OF
TEST
PREPARATION
FOR NEXT TEST
INCREASED USER INTERACTION MINIMIZED USER INTERACTION
The Differences
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Cycle Times
Minutes 1 2 3
50s 30s
15s
40s
20s
40s
Test Time with
Hammer Release/Reposition
Test Preparation Specimen
Measurement
IDEAL
SETUP
TYPICAL
SETUP
> 32%
FASTER! Total Cycle Time: 75 seconds
Total Cycle Time: 110 seconds
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