Adhesion of a single coating or a multi-coat system of paint, varnish or related products is assessed by measuring the minimum tensile stress necessary to detach or rupture the coating in a direction perpendicular to the substrate. This method maximizes tensile stress as compared to the shear stress put by other methods such as scratch adhesion and results may not be comparable. The test is performed by securing a loading fixture (dolly) perpendicular to the surface of the coating with an adhesive. After the adhesive is cured, a testing apparatus is attached to the loading fixture and aligned to put tension perpendicular to the test surface. The force put is gradually increased and monitored until either a plug of coating material is detached, or a specified value is reached.
Digital pull-off adhesion tester is a portable, hand-operated instrument which is used to measure the force required to pull a specified test diameter of coating away from its substrate using hydraulic pressure.
The pressure is displayed on a digital LCD and represents the coatings strength of adhesion to the substrate.
It evaluates the adhesion (pull-offstrength) of a coating by determining the greatest tensile pull-off force that it can bear before detaching. Breaking points, demonstrated by fractured surfaces,occur along the weakest plane within the system consisting of dolly, adhesive,coating layers and substrate.
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