Significance and Use
4.1 The pull-off strength of a coating is a performance property that may be referenced in specifications. This test method serves as a means for uniformly preparing and testing coated surfaces, and evaluating and reporting the results. This test method is applicable to any portable apparatus meeting the requirements for determining the pull-off strength of a coating in this standard (see Annex A1 – Annex A5).
4.2 Variations in results with the same coating are likely when any parameter of the test is changed. This includes change in glue, load fixture size, substrate coating cure time, pull rate, environmental conditions, if the coating is scored, or using a different device. Therefore, when a series of results will be compared with one another or used for statistical analysis, the type of apparatus, substrate, test procedures, glue type, and if scoring is used should be the same for the pulls considered.4 It is recommended that these parameters and the environmental conditions allowed during the test be mutually agreed upon between the interested parties.
4.3 The purchaser or specifier shall designate a specific test method procedure; B, C, D, E, or F and test Protocol; 1, or 2, when calling out this standard. In cases where either the Protocol or a pass/fail criterion is not designated, Protocol 1 shall be used.
Scope
1.1 This test method covers a procedure for evaluating the pull-off strength (commonly referred to as adhesion) of a coating system from metal substrates. Pull-off strength of coatings from concrete is described in Test Method D7234. This test offers two test protocols. Protocol 1 (test to fracture) determines the greatest perpendicular force (in tension) that a surface area can bear before a plug of material is detached. Protocol 2 (pass/fail) determines if the coated surface remains intact at a defined load criteria. Fracture will occur along the weakest plane within the system comprised of the test fixture, glue, coating system, and substrate, and will be exposed by the fracture surface. This test method maximizes tensile stress as compared to the shear stress applied by other methods, such as scratch or knife adhesion, and results may not be comparable.
Note 1: The procedure in this standard was developed for metal substrates, but may be appropriate for other rigid substrates such as plastic and wood. Factors such as loading rate and flexibility of the substrate must be addressed by the user/specifier.
Note 2: The procedure in this standard was developed for use on flat surfaces. The results could have greater variability with lower values and averages for surfaces other than flat.
1.2 Pull-off strength measurements depend upon material, instrumentation and test parameters. Results obtained by each test method may give different results. Results should only be assessed for each test method and not be compared with other instruments. There are five instrument types, identified as Test Methods B-F. It is imperative to identify the test method used when reporting results.
Note 3: Method A, which appeared in previous versions of this standard, has been eliminated as its main use is for testing on concrete substrates (see Test Method D7234).
1.3 This test method describes a class of apparatus known as portable pull-off adhesion testers.2 They are capable of applying a concentric load and counter load to a single surface so that coatings can be tested even though only one side is accessible. Measurements are limited by the strength of adhesive bonds between the loading fixture and the specimen surface or the cohesive strengths of the glue, coating layers, and substrate.
1.4 This test can be destructive and spot repairs may be necessary.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
