What Does Pull-off Strength Mean?
Pull-off strength is a measure of the adhesive strength of a coating based on a pull-off test. The test involves adhering a dolly to the surface to be tested and pulling the dolly away from the surface, perpendicular to the surface. The pull-off strength is the result of this test based on the force used in pulling, the type of adhesive used with the dolly and the type of failure on the coating surface.
The pull-off strength of a coating is an important factor to consider when selecting an appropriate coating to protect surfaces made of metal, plastic, wood, concrete and glass. The failure to test a coating system for adhesion may increase the risk of coating delamination and exposing the underlying surface.
Corrosionpedia Explains Pull-off Strength
Even when a manufacturer's specifications for a particular coating system has the required adhesive properties it is possible that factors during the application will reduce the adhesive qualities. As such, pull-of strength testing provides cheap insurance to determine if the coating system will adhere as desired. The amount of pull-off strength to test for depends on the application and can be configured by modifying the parts of the testing equipment. The radius and surface area of the dolly, or bonded probe, can be modified to increase the maximum pull-off strength that can be tested. This dolly is glued to the surface to be tested with a resin, usually an epoxy.
While a convenient measure, it is difficult to determine the pull-off strength in a consistent and accurate way. Therefore, there are few industry standards and great variation exists across different specification sheets. Nevertheless, the use of pull-off strength adhesion evaluations has proved to be critical in preventing the costs to repair poorly adhered surface coatings in large-scale applications.