Adhesion testing is considered as an important procedure to figure out how well paints and coatings are attached to the substrate. For coatings to perform acceptably, they should adhere to the substrates on which they are applied. A variety of recognized methods can be utilized to decide how well a coating is attached to the substrate. The commonly used measuring technique is performed with a knife or with a pull-off adhesion tester. After any test, it is important to record if the attachment failure was adhesive (failure at the coating/substrate interface) or strong (failure inside the coating film or the substrate).
This basic test requires the utilization of a utility knife to pick at the coating. It sets up whether the adhesion of a covering to a substrate or to another coating (in multi-coat systems) is at a generally satisfactory level. Execution depends on both the level of difficulty to remove the coating from the substrate and the size of the removed coating.
Utilizing the knife and cutting guide, two cuts are made into the covering with a 30 – 45 degree angle among legs and down to the substrate which converges to shape a “X”. At the highest point of vertex, the motive behind the knife is used to bring up the coating from the substrate or the coating underneath.
This is an exceptionally subjective test and its value relies on the auditor’s experience. A coating which has a high level of cohesive strength may seem to have worse adhesive than one which is fragile and henceforth cracks easily when tested. There is no known relationship to other adhesion test methods. A standard method for the application and execution of this test is available in ASTM D6677.
PULL OFF TEST
A progressively quantitative test for adhesion is the pull-off test where a loading fixture, commonly called a dolly or stub, is connected by an adhesive to a coating. By the use of a portable pull-off adhesion tester, a load is progressively applied to the surface until the dolly is pulled off. The force required to pull the dolly off, yields the elasticity in pounds per square inch (psi) or uber Pascals (MPa). Failure will happen along the most vulnerable plane inside the system containing the dolly, adhesive, coating system, and substrate, and will be exposed by the fracture surface.
This test technique amplifies tensile stress as compared with the sheer pressure applied by different methods, for example, scrape or knife adhesion, and results may not be comparable. Further, pull-off strength measurement relies on the instrument utilized in the test. Results obtained using various gadgets or results for similar coatings on substrates having diverse stiffness may not be practically identical.
Testers work using either mechanical (twist by hand), hydraulic (oil) or pneumatic (air)tension. They are categorized as being fixed adjusted or self-adjusting relying on their capacity to guarantee a vertical pull-off power. Best repeatability is gotten when the pull-off force acts opposite to the surface being tried.
Positest pull-off adhesion tester by Defelsko is the best brand of paint testing equipment supplier. They measure adhesion of coatings to metal, wood, concrete, and other rigid substrates. This device is also weatherproof, dustproof and shockproof which meets IP65 standards.
If you are looking for a supplier of Defelsko Positest pull-off adhesion testers, you can go visit H.J. Unkel. They are one of the suppliers for this device in Malaysia.