Transcript Slide 1

inspection equipment
Adhesion Testing for
Protective Coatings
Understanding Cross Hatch and Pull-Off Adhesion Testing
© Elcometer Limited 2011
60 years of excellence
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Adhesion Testing for
Protective Coatings
inspection equipment
A presentation for MECC 2012
Author: John Fletcher
ASTM D01 Committee Chairman
Technical Support Manager, Elcometer
Presenter: Craig Woolhouse
Sales Manager, Elcometer
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Contents
Introduction
Cross Cut Adhesion Testing
Pull-Off Adhesion Testing
Types of Pull-Off Adhesion Testers
Inspection Areas and Test Frequency
Interpretation and Expression of the ASTM Comparison Test Results
Issues arising from the ASTM Tests
Conclusions
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Introduction
Clarifying the current Adhesion Testing options available in
the market
Different Standards exist
Many types of Adhesion Testers exist
How do they work?
How do we compare results?
What do the ASTM and ISO Standards mean?
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Introduction
Why test for adhesion?
It is not always simply to meet a standard
Also to ensure that the following processes have been done correctly
Surface Profile
Surface Cleanliness
Application Conditions
Dry Film Thickness
What is an adhesion test?
A test designed to assess whether the coating will adhere to the
substrate during its service life
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Introduction
Two Field Methods For Adhesion Testing
The Cross-Cut and X-Cut Methods – Comparison Method
The Pull-Off Method – Value Method
Two key Standards
ASTM D4541
ISO 16276 Parts 1 and 2
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The Cross-Cut Method
ISO16276 Part 2
Summarised by ISO 16276 Part 2:
Cutting the coating, applying specific adhesive tape to remove non-adhered
coating followed by comparison tests against pictorial standards
Cross-Cut (Cross Hatch)
X-Cut (St Andrews Cross)
References ISO 2409 and ASTM D3359
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The Cross-Cut Method
Typical Cross-Cut Adhesion Test Kit
Cutter Blades
Multi-blade Cutter with brush, magnifier and tape
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The Cross-Cut Method
Using the specialised self adhesive tape
Pulling the tape
Use on hard substrates only.
Test method and
tape
ISO 2409
BS 3900-E6
BS 6496
BS 6497
ASTM D3359
Time to complete
the test
Less than 5
minutes
Less than 5
minutes
90  30 seconds
Angle of pull
60°
90°
180°
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The Cross-Cut Method
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X-Cut Method
Use a sharp blade to create a X-Cut in the coating
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Pull-Off Adhesion Testing
ISO 16276 Part 1 and ASTM D4541
Determination of coating adhesion or coating fracture strength by
mechanically pulling adhered ‘dollies’ and the coating from the substrate
For clarity this review concentrates
on adherence to ASTM D4341
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Pull-Off Adhesion Testing
ASTM D4541
Five Types of Portable Adhesion Testers (Type II to Type VI)
20 mm diameter dollies
Force Application Rate – 1 MPa/s or less to complete test over full
range within 100 s or less
Force applied in a continuous and smooth manner
Cutting round the dolly – or not!
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Types of Pull-Off Testers
Fixed Alignment Adhesion Tester – Type II
Mechanically load applied by
Compressed Spring
Mechanically load applied by
Compressed Washers
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Types of Pull-Off Testers
Self-Alignment Adhesion Tester – Type III
Operated by manually applied Hydraulic Pressure
Often called Push-Off Testers or HATE Testers
Curved Dolly Options
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Types of Pull-Off Testers
Self-Alignment Adhesion Tester – Type IV
Operated by pneumatically applied Pressure
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Types of Pull-Off Testers
Self-Alignment Adhesion Tester – Type V
Operated by manually or automatically applied hydraulic pressure
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Types of Pull-Off Testers
Self-Alignment Adhesion Tester – Type VI
Operated by manually applied Hydraulic Pressure
Feature ‘self- aligning’ legs
Often called PAT Testers
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Inspection Areas - How often
should we test?
ISO 16276 Part1 and ASTM D4541
Normally defined by project specification
If not defined then whole area of structure is the inspection area – one
failure fails the whole job!
Random measurements according to size of inspection area
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Inspection Areas - How often
should we test?
Inspection Area (m²)
Number of valid measurements
< 1,000
3 for each 250 m² area
or part thereof
> 1,000
12 plus 1 for each additional
1,000m² area or part thereof
Subdivision into smaller inspection areas is recommended
Examples
3 areas of 900 m² is equivalent to four areas of 250 m². 16
valid measurements for each area. Total = 48 measurements
1 area of 2,700 m² is equivalent to three areas of 1,000 m².
12 valid measurements plus 2. Total = 14 measurements
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Interpretation & Expression of Results
Type of failure
Glue failure is not a valid test unless the force applied
exceeds the specified value
Inspect the face of the dolly after the coating has failed
The Coating must cover a minimum of 80% of the
area of the dolly face to be considered as a valid test
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Interpretation & Expression of Results
Adhesive and Cohesive failure modes
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Interpretation & Expression of Results
Test Acceptance or Rejection Criteria
For the acceptance of an inspection area, the following three criteria
must be fulfilled:
The fracture strength values for substrate/primer (A/B) adhesive failures shall be
equal or greater than the specified value
When 10 or more measurements are made in a single inspection area, not more
than one-tenth of fracture strength values shall be between 20% and 60% of the
specified value
Two-thirds of the fracture strength values shall be equal or greater than the
specified value, with the additional requirement that the remaining one-third of the
values are equal or greater than 60% of the specified value
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Testing Issues – Adhesive choice
Two-pack Epoxy Adhesive
Easy to mix, tolerant of surface contamination and mix.
Long cure time
Cyanoacrylate (super glue) Adhesive
Single component, need clean surfaces, can damage some
types of coating. Quicker cure time
Be aware of cure time and ambient temperature issues
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ASTM Comparison Test
ASTM D4541 Tester Type ‘Round Robin’ Testing 2007
Six coatings to cover high and low adhesion values
Seven operatives, four tests per coating
6 mm thick hot-rolled steel coated test plates
Coating A and F – adhesion performance exceeded range of adhesion
testers used and so were eliminated from analysis
ASTM deemed that the failure methods for each test type are different hence
the results are not comparable
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Testing Issues
D4541 Summary of Reproducibility (R & r Test Data)
Adhesion Tester
Type
Test Method
Maximum
Recommended
Difference (%)
Type II
B
64.7
Type III
C
33.8
Type IV
D
14.8
Type V
E
27.8
Type VI
F
17.5
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give numerical values in force per unit area
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
ISO 16276-1 references D4541 and defines inspection areas, sampling
plans and acceptance rejection criteria.
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
ISO 16276-1 references D4541 and defines inspection areas, sampling
plans and acceptance rejection criteria.
Choice of adhesive is important as the adhesive must damage the coating
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
ISO 16276-1 references D4541 and defines inspection areas, sampling
plans and acceptance rejection criteria.
Choice of adhesive is important as the adhesive must not damage the
coating
The gluing process should minimise glue failures
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
ISO 16276-1 references D4541 and defines inspection areas, sampling
plans and acceptance rejection criteria.
Choice of adhesive is important as the adhesive must not damage the
coating
The gluing process should minimise glue failures
Cutting round the dolly depends on the type of coating and the risk of
damage to the coating under the dolly – user to be consistent in choice
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Conclusions
Cross-Cut and X-Cut tests compare the adhesion of a coating
Pull-Off Adhesion tests give values in force per unit area
ASTM D4541 describes five different types of apparatus and five different
methods
ISO 16276-1 references D4541 and defines inspection areas, sampling
plans and acceptance rejection criteria.
Choice of adhesive is important as the adhesive must not damage the
coating
The gluing process should minimise glue failures
Cutting round the dolly depends on the type of coating and the risk of
damage to the coating under the dolly – user to be consistent in choice
ASTM conclude load values using different test methods can’t be compared
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inspection equipment
Adhesion testing for
Protective Coatings
Standards for Cross Hatch and Pull-Off Testing
Questions?
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