• Different types of pull-off adhesion-testers can produce a substantialy different adhesion-value

Different types of pull-off adhesion-testers can produce a substantialy different adhesion-value

Pull-off adhesion tests as per ISO 4624 or ASTM D4541 are classic tests through which the adhesion of a paint or coating can be determined.
The test results not only supply a quantitative adhesion value (expressed in MPa, kg/m², N/mm², PSI, ...) but also provide a visual image of the "weak link" in a coating system, making it the perfect test procedure for comparing different coating-systems when it comes to their adhesive properties.

However, you may want to consider the following flaw within the involved standards!

There are currently different models in the market available to execute such testing:

  • Mechanical pull-off adhesion testers (fixed alignment)
  • Manual hydraulic pull-off adhesion testers (self-aligning)
  • Automatic hydraulic pull-off adhesion-testers (self-aligning + automatic & constant increase of pull-off load)

Experience has shown that the hydraulic pull-off testers are far more reliable than the mechanical testers, which is mainly related to the self-aligning characteristics of the hydraulic testers, ensuring an optimal perpendicular pull (which can sometimes be compromised with mechanical testers resulting in a shear-force, rather than a pull-off adhesion).
Pay attention however to the fact that the test results obtained through different types of adhesion testers CANNOT be compared with one another!  Notwithstanding the fact that they all operate according to the same (above-mentioned) standards, they can produce substantially different test results.  See also the attached graph showing the test results of a comparative study we performed where the pull-off adhesion of a coating in its curing phase was tested using 3 different pull-off adhesion testers, clearly showing the difference in pull-off adhesion values obtained with different types of instruments (on the same coating, on the same panel, at the same time).
So, for a true comparison of the adhesion of multiple coating systems, a comparative test should be run using the SAME test instrument.
And whenever specifying a minimum pull-off adhesion value in a coating specification, one should also specify the type of instrument that needs to be used for the required test.
For further information, feel free to contact us back at any of the coordinates listed on our website.

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