Adhesion Testers

Adhesion Testing Guide

Pull-off adhesion testing is used to measure the resistance of a coating to separation from a substrate when a perpendicular tensile force is applied. Coated substrates typically include metals, plastics, concrete, wood and glass. Coatings, finishes and linings vary greatly and include paint films, powder coatings, UV cured, ceramics, epoxies, bitumens (tar enamel, asphalt mastics), thermoplastic resins (polyethylene, vinyl and plastisols), laminates, lacquers, varnishes, specialty resins (urethanes, fluorocarbons, phenolics and polyesters), elastomerics, and inorganics (glass, zinc, and lead).

There are very few industry or application specific pass/fail criteria defined in standards. Expected adhesion testing results are often predetermined by the parties concerned. Dependent on the accuracy and repeatability of equipment involved, large variations have been noted between various equipment and manufacturers. To minimize these undesired variations, it is critical to utilize an adhesion tester that minimizes shear forces (forces acting parallel as opposed to perpendicular to the coating). The PosiTest AT series is specifically designed for this purpose. It possesses a self-aligning feature that utilizes a spherical articulating dolly head so that it is always pulled vertically by a ring of small bearings in the actuator.

Adhesion testing may be performed for quality control purposes, but is more typically undertaken to adhere to industry standards and customer specifications. Dependent on the application, the specific need for maintaining strong adhesion may vary. Coating applications may range from consumer products to large scale construction projects, but a common factor is that premature adhesion failures can have a significant cost.

Even in established coating application processes, many factors can influence the adhesive strength of a coating. Seemingly minor variations in process parameters may have significant impacts on the resulting adhesion strength between the coating and the substrate. Markets for adhesion testing range from Research and Development Labs that develop and test coating and application processes, through to the Contractors, Coaters, Finishers and Inspectors involved in applying and testing the actual applied coatings.