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Q & A

 

 

Are the PosiTest AT instruments rugged?
Absolutely. With an environmentally sealed, metal enclosure, heavy-duty hydraulic pump and a high grade industrial pressure sensor, both the Manual and Automatic PosiTest AT are built to last. They can be used indoors, outdoors and in all types of weather.

 

How are the Manual and Automatic PosiTest Adhesion Testers calibrated at DeFelsko?
The Manual and Automatic PosiTest Adhesion Testers are calibrated against known conditions using NIST traceable equipment. A Certificate of Calibration containing actual measurements is included with every tester.

 

How much time should be allowed for the included Resinlab EP11HT Gray to cure?

Full cure can be obtained after 24-48 hours at room temperature. Cure time can be accelerated by the application of heat. See Technical Data Sheet for full details.

 

Are curved dollies available for convex surfaces?
We do not provide or support the use of curved dollies for adhesion testing.

In addition to affecting the surface area used in calculating pull-off strengths and the direction of the force lines (creating unwanted shear forces), most adhesion testing standards specifically call for the use of flat dollies.

Feedback from our customers is that most internal or external pipe applications greater than 200 mm in diameter do not require curved dollies for satisfactory results. In such cases the maximum glue gap between the surface of the dolly and the coating is 0.5 mm.

For smaller pipe diameters, depending on the expected pull-off strength of the coating, it may be possible to use a 10 mm or 14 mm dolly. The smaller surface areas of the dollies will allow them to sit flatter on the curved surface. The height of the actuator pulling the dolly becomes the limiting factor within internal diameters. External diameters can be decreased to as low as 50 mm and 100 mm respectively.

If you have more specific information on the application it may be possible to provide a more definitive response.


Can pull-off adhesion tests be conducted underwater?
The PosiTest can be used for underwater measurement provided only the cable and actuator are placed under the surface. In such cases, the following precautions should be taken:

  • The standoff and actuator should be thoroughly dried immediately upon completion of testing.
  • Once dried, a generous amount of lubricant should be applied to discourage corrosion (rust).

Note: During measurement, the manual PosiTest AT may require more than one continuous stroke to complete the test. This differs from our recommendation in the instruction manual and operational video.

PosiTest adhesion testers can be specifically manufactured with longer pressure hoses to facilitate underwater measurement.


Where does failure occur?
Tensile adhesion pulls are evaluated in pounds per square inch (psi) or megapascals (MPa), and visually, as follows:

  • Cohesive fracture: fracture occurs within a coating layer (same coating on dolly face and coated surface).
  • Adhesive fracture: fracture occurs at the interface between layers (coating on dolly face differs from surface).
  • Glue failure: visible separation of the glue from iteself, the coating or dolly (no coating visible on the dolly face).

 

PosiTest AT-A models can record fracture information for up to five layers.

 


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