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  PosiTest®  Pull-Off Adhesion Tester
Measures adhesion of coatings to metal, wood, concrete and other substrates
PosiTest AT - Overview  PosiTest AT - Two Models  PosiTest AT - Rugged Features  PosiTest AT - Technical Data  PosiTest AT - Optional Accessories  PosiTest AT - Q&A  PosiTestAT - Download Literature  Application Assistance Request Form

 

Q & A

 

Are there different models of PosiTest Adhesion Tester to choose from?
Yes, there are two models to choose from. The PosiTest AT-A features an automatic hydraulic pump while the PosiTest AT-M comes with a manual hydraulic pump.

 

What are the differences between the current PosiTest AT-M Manual and the PosiTest AT-A Automatic?
The PosiTest AT-A is an automatic version of the popular PosiTest AT-M Manual Adhesion Tester. The electronically controlled hydraulic pump automatically applies smooth and continuous pull-off pressure at a user-specified rate.

New features include...

  • Test with the simple push of a button. No twisting, pumping or cranking. No valves to close, needles to reset, or scales to adjust
  • User-selectable pull rates ensure compliance with international test methods for a variety of industries including metal, wood and concrete
  • Built-in rechargeable batteries perform over 200 tests per charge. Continue testing with AC power while batteries recharge. Supplied with universal AC Adapter

Aside from a few functional differences, the PosiTest AT-A Automatic Adhesion Tester is comparable to the PosiTest AT-M Manual Adhesion Tester in all respects but the pump.

 

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

 

What are the benefits of the optional PosiSoft 3.0 desktop software?
All PosiTest Adhesion Testers have memory for storing data on 200 pulls. This includes maximum pull-off pressure, rate of pull, test duration and dolly size. PosiSoft 3.0 downloads this information to a PC or Mac.

 

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 Loctite 907 to cure?

Complete cure is obtained after 24 hours at room temperature. HYSOL 907 will achieve handling strength in 3-4 hours at 77°F (note: this can vary with different bond configurations). Hysol 907 can also be fully cured with heat such as 2 hours at a 140°F or 1 hour at 180°F. See Product Description 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 adhesive 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 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:

  • Adhesion failure - defined as a failure between two distinct paint layers or between the substrate and the first layer of paint.
  • Cohesion failure - defined as a failure or break within one coat of paint (the coating breaks within itself).
  • Glue failure - coating bond exceeds the glue strength, and may require re-gluing.

 


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