Measuring Coating Adhesion to Metals, Concrete, and more with the PosiTest AT from DeFelsko- the Measure of Quality.
For any coating to perform, it is critical that it be properly adhered to the substrate. Factors such as an unstable substrate, inadequate surface preparation, surface contamination, and improper coating application can result in a coating system with poor performance.
Adhesion Testing plays a significant role in coatings inspection, whether the user is trying to adhere to industry standards, maintain quality control, or follow customer specifications.
Pull-off adhesion testing has become the industry standard for most applications, because of its repeatability, ease of use, and meaningful results.
It is done in accordance with international standards from organizations such as ISO and ASTM, which describe methods for testing various substrates and coatings.
A portable pull-off adhesion tester quantifies the perpendicular force required to pull a specified area of coating away from its substrate.
Typically, a loading fixture with a known surface area, also known as a “dolly” or “pull stub”, is glued to the coating.
An actuator attaches to the loading fixture, applying force to the loading fixture and removing the coating from the substrate.
The maximum pressure required to pull the loading fixture from the surface is measured and reported for the user.
The PosiTest AT series is DeFelsko’s simple, durable, and accurate solution for pull-off adhesion testing.
Both models are portable and require no external power source, making them ideal for use in the field or lab. They employ a patented self-aligning actuator design that ensures the loading fixture is always pulled perpendicular to the substrate, eliminating any peeling motion that could lead to an incorrect result.
Each PosiTest AT comes with everything required for testing, including the tester, loading fixtures, abrasive pads, a cutting tool, glue, and mixing sticks, all packaged in a durable hard-shell carrying case. PosiSoft software for managing measurement data and creating professional inspection reports is also included.
All PosiTest AT units undergo rigorous testing at DeFelsko’s US-based manufacturing facility, and include a NIST-traceable calibration certificate documenting actual readings from the instrument.
The PosiTest AT-M Manual Adhesion Tester features a manual hydraulic pump designed to apply smooth and continuous pressure with a single stroke, a pull rate indicator to manually monitor and adjust the rate of pull, and an internal memory that stores all the data of a pull-off test for up to 200 pulls.
The PosiTest AT-A Automatic Adhesion Tester boasts an electronically controlled hydraulic pump which automatically applies smooth and continuous pull-off pressure with a user adjustable pull rate, pull limit and hold time. It can store test data for 100,000 pulls in up to 1,000 batches. The impact and scratch resistant color touch screen and keypad is ideal for operation both with and without gloves. Using built-in Bluetooth technology, measurements can be transmitted to the PosiTector App for further annotation.
The versatile actuator design included with both the PosiTest AT-A and AT-M features a removable standoff, making the instrument compatible with a wide range of loading fixture sizes for a variety of applications.
20-millimeter kits include the common 20-millimeter loading fixtures, ideal for measuring coating adhesion on metals. This kit is also compatible with 14- and 10- millimeter loading fixtures, allowing the unit to measure adhesion strengths of up to fourteen thousand PSI or 96 megapascals.
50-millimeter kits are ideal for testing coatings with a lower bond strength applied to concrete, plastic, and wood.
The 50-millimeter C1583 kits comply with the ASTM standard for testing the strength of concrete surfaces and cementitious overlays.
Finally, the 50 by 50-millimeter tile Kits comply with standard EN 12004-2 for measuring the strength of cementitious adhesives for tiles.
Both adhesion tester versions can be configured with any of the above loading fixture options. Conversion kits are also available for using multiple different loading fixtures with one adhesion tester.
There are 5 Basic Steps to Performing a Pull-Off Adhesion Test.
First, clean and roughen the surfaces of the loading fixture and coating using the included abrasive pad. This helps the glue form a tight bond and prevents a premature glue failure.
Additional preparation such as degreasing may be required to promote bonding between the glue and coating being tested.
Next, squeeze equal amounts of the included 2-part epoxy onto the palette. Use a mixing stick in a circular motion to stir the two parts until they are combined.
Once mixed, apply a uniform coating of glue to the loading fixture, and place it on the coating.
Press straight down to squeeze out excess glue. Do not twist, rock, or slide the loading fixture, as this can create voids. Once applied, use a swab to remove any excessive glue.
If the surface is uneven, vertical, or overhead, use a piece of removable tape to hold it in place while the glue cures. At room temperature, the included glue cures in 24 to 48 hours.
Depending on the standard or test method being followed, it may be necessary to cut the coating around the loading fixture. Cutting isolates the test area from the surrounding coating, but can also create stress cracks in the coating or glue. In general, cutting isn’t necessary for thinner coatings below 20 mils or 500 microns, but is recommended for thicker, reinforced, or elastomeric coatings.
The pull-off test can now begin. The procedure varies slightly between the manual and automatic models.
To begin measuring with the PosiTest AT-M, unscrew the relief valve to release any residual pressure.
Push the actuator handle completely down into the actuator assembly. Place the actuator over the loading fixture and attach the quick coupling to the dolly by reaching through the holes in the actuator and lifting the coupling. Release the quick coupling when the dolly head is completely engaged.
Close the relief valve on the pump.
Verify that the proper loading fixture and units are selected, then press the green button to Zero the instrument.
Prime the pump slowly until the instrument begins to display a pull rate. Return the pump handle to its full upright position and then complete a single continuous stroke at the desired pull rate until a pull off occurs. Additional strokes may be necessary for high bond coatings.
Testing with the PosiTest AT-A Automatic Adhesion Tester follows a similar, simplified method.
Attach the actuator to the dolly and ensure the quick coupling head is completely engaged. Verify that the units, loading fixture size, and pull rate are properly set, then press the green button to initiate the test.
Upon completion of the priming stage, a live pressure-over-time graph will display. When a pull off occurs, the maximum pressure value will blink on the display.
Both PosiTest AT Adhesion Testers can store results into memory. For the Manual version, simply press the memory button to save that test result into memory after the test is complete.
On the Automatic model, if a memory batch is open, the results are automatically stored into memory. The PosiTest AT-A also allows the user to digitally record the nature of the fracture of each test, as required by test standards.
The PosiTest AT-A also features Bluetooth technology allowing communication with the PosiTector App for iOS and Android smart devices. After testing, results can be loaded into the app and annotated with notes, pictures, and other relevant details. Professional PDF reports can be created with ease.
For nearly 20 years, DeFelsko has been a leader in adhesion testing, manufacturing simple, durable, and accurate testers. Backed by DeFelsko’s renowned quality, customer service and exceptional two-year warranty, the PosiTest AT series is the ideal choice for measuring adhesion.