DEFELSKO POSITEST AT - Automatic & Manual Adhesion TesterS in accordance with ISO 4624

In a nutshell: 

The PosiTest AT-M is a manual Pull-Off Adhesion Tester with hydraulic pump that stores up to 200 test data and is ideal for occasional testing. 

The PosiTest AT-A offers automated hydraulics, reduces user influence, stores up to 100,000 results and supports Bluetooth for integration with the PosiTector app. Both models comply with ASTM D4541, ISO 4624 and other standards.

In more detail, there are differences between the PosiTest AT-M (manual) and the PosiTest AT-A (automatic) in terms of operation, data management capability and integration of advanced technologies:

The PosiTest AT-M is a manual adhesion tester developed by DeFelsko. It is used to measure the adhesion strength of coatings on various substrates such as metal, wood and concrete. 

Here are some of the key features and applications of the device:

Main features of the PosiTest AT-M

• Manual hydraulic pump: The device has a manual hydraulic pump that applies uniform and continuous pressure with a single stroke.

• Pull rate indicator: It provides a pull rate indicator for manual monitoring and adjustment of the pull rate.

• Internal memory: The internal memory can store up to 200 test results.

• USB port: The measured values can be transferred to a computer via a USB port for further processing with the PosiSoft software.

The PosiTest AT-A is an automatic Pull-Off Adhesion Tester from DeFelsko designed for measuring the adhesion strength of coatings to various substrates such as metal, wood, concrete and other solid materials. 

Key features of the PosiTest AT-A

Electronically controlled hydraulic pump: This provides an even and continuous peel pressure that is adjustable by the user. The pump reduces operator effort and provides precise control over the testing process.

Touchscreen display: The device has a shock and scratch resistant color touchscreen that can be operated even when wearing gloves. It enables easy navigation through the menus and the display of test results.

• Storage capacity: The PosiTest AT-A can store up to 100,000 test results in 1,000 blocks, allowing for extensive documentation of test results.

• Bluetooth interface: The results can be transferred wirelessly to the PosiTector app to add notes, images and other details. This facilitates the creation of professional reports.

• Versatility: The device is compatible with different dolly sizes, making it suitable for a wide range of applications. Customized dollies are also available as an option.

Technical details

• Dolly sizes: The most common dolly sizes are 10 mm, 14 mm, 20 mm and 50 mm. Each size is suitable for specific adhesive strength ranges.

• Battery: The rechargeable battery allows up to 200 tests per charge. The battery can be recharged during use to continue operation.

• Protection from weather conditions: The device is weatherproof, dustproof and shockproof, making it suitable for use in various environments.

All PosiTest AT tensile adhesion testers are supplied pre-calibrated and are ready for immediate use and measurement. A calibration certificate in long form, which is traceable to NIST or PTB, is included in the scope of delivery. It documents the actual measurement values measured by the device in our calibration laboratory to standards traceable to a national institute for standardization. Tip: Beware of supposed “certificates” or “certificates of conformity” offered by some competitors. As a rule, these do not contain any actual measured values of the device and are often not sufficient to meet the necessary quality requirements.

Recalibration is recommended annually or after 500 tests, depending on the intensity of use.

Yes, they are both portable and suitable for outdoor use. With an IP65 environmentally protected metal housing, a high performance hydraulic pump and a high quality industrial pressure sensor, both the manual PosiTest AT-M and the automatic PosiTest AT-A are designed for exceptional durability and a long service life, following our guiding principle of maximum sustainability. All devices are weatherproof, dustproof and shockproof and can be used indoors and outdoors in all weather conditions (they meet or exceed the requirements of protection class IP 65).

The automatic PosiTest AT-A models also feature a practical shoulder strap and rubberized handles.

Yes, the dollies are included in the scope of delivery. PosiTest AT-M with 20 mm and PosiTest AT-M with 50 mm are supplied with self-aligning dollies that are precision machined from a robust but lightweight aluminum alloy (6061-T6). They offer a cost-effective alternative to steel dollies.

The PosiTest AT-M 50T 50 x 50 mm and PosiTest AT-M 50C 50 mm models in accordance with ASTM C1583, ZTV-ING and DIN EN 1542 are supplied with self-aligning steel dollies that are precisely manufactured in accordance with the relevant standards.

mtv messtechnik offers all accessories, including steel and aluminum dollies, in the webshop as consumables. These are perfect for permanent visual documentation of tests.

The dolly size (e.g. dollies with diameters of 20 mm, 14 mm, 10 mm) depends on the expected adhesive strength and the respective substrate properties. Smaller dollies are suitable for high-strength coatings, larger ones for weaker adhesion or rough surfaces. The selection is based on the manufacturer's recommendations and test standards and norms.

The 50 mm dolly is typically recommended for concrete, mineral materials, wood and composites and measures coatings with expected adhesion values between 50 psi and 560 psi for automatic PosiTest AT-A (50 - 500 psi for manual PosiTest AT-M models). 

The 20 mm dolly is recommended for testing coatings applied to metals or where the expected adhesion values are above 500 psi.

The certified accuracy of both PosiTest AT model series AT Automatic and PosiTest AT Manual is +/- 1%. 

However, the fully automatic design of the PosiTest AT-A ensures greater consistency of measurements, as incorrect operation or user influence on the test process is ruled out.

No, no training is required. Our measuring and testing devices are easy to operate and have intuitively structured menus. In addition, we provide our customers with detailed operating instructions for each of our products and provide them with numerous helpful videos that clearly show how the measuring devices from mtv messtechnik and DeFelsko work. Instead of demonstration models, we offer our customers expert technical support by phone or e-mail.

Yes, this is possible for diameters over 200 mm. Feedback from our customers has shown that the PosiTest AT gauges are suitable for testing most internal or external applications on pipes with a diameter of more than 200 mm.  In such cases, the maximum bonding gap between the surface of the 20 mm dolly and the coating of the pipe is 0.5 mm. For smaller pipe diameters, a 10 mm or 14 mm dolly can be used depending on the expected peel strength of the coating. The outer diameters of the 10 mm and 14 mm dollies can be reduced to a maximum of 50 mm and 100 mm respectively.

DeFelsko does not supply bent dollies for the adhesion test and does not recommend them. Not only do they affect the surface used to calculate the pull-off force and the direction of the lines of force (causing unwanted shear forces), but most adhesion test standards specifically require the use of flat dollies.

The replaceable rechargeable battery in the PosiTest AT-A enables over 200 pull-off adhesion tests on a single charge. 

Very practical: thanks to the mains adapter supplied, you can continue testing while the battery is charging.

When used with a 50 mm diameter dolly, the PosiTest AT is in a priming state until a priming pressure of 16 psi (0.110316 MPa) is reached. As soon as the suction pressure is reached, the device starts the calculation and displays the pull rate.

The manual PosiTest AT-M model allows readings to be obtained below this suction pressure, whereas the automatic PosiTest AT-A model does not allow the suction pressure to build up so slowly, making the PosiTest AT-A unsuitable for use below this suction pressure.

Note that all adhesion values given (including those obtained below the suction pressure) are subject to the accuracy of the PosiTest AT tensile adhesion meter of ± 1% (± 30 psi, AT-M; ± 35 psi, AT-A).

The epoxy adhesive ResinLab EP11HT included with the PosiTest AT is easy to use and is suitable for testing a wide range of coatings. In special cases, special coatings require a different adhesive.

Certified, fast-curing, two-component epoxy adhesives should be used to ensure a reliable bond between the dolly and the coating. Incompatible adhesives can lead to incorrect measurements.

The epoxy adhesive supplied with the PosiTest AT cures completely within 24 to 48 hours. Users who require faster curing, i.e. a shorter curing time, should check other adhesives for compatibility with the coating to be tested and our aluminum test dolly. Cyanoacrylate adhesives (“super glues”) are often sufficient for lower pull-off forces.

PosiTest AT hat strength testers are designed for use on rigid, fixed substrates. A flexible substrate can negatively affect the accuracy and repeatability of the test. In addition, using the PosiTest AT to measure the adhesion of coatings applied to a brittle substrate would typically result in the destruction of the substrate material, making it difficult to quantify the adhesion strength of the coating to the substrate.

Interpretation of fracture patterns in the tensile adhesion test

The interpretation of the fracture pattern after a tensile adhesion test is crucial to understanding the properties of the coating and its adhesion to the substrate. 

The interpretation of fracture patterns is an important step in material testing and failure analysis.

Here are the most important aspects of interpreting fracture patterns:

Macroscopic observation

First, a macroscopic examination of the fracture surface is carried out with the naked eye or under low magnification1. This analysis enables a rough distinction to be made between the causes of fracture based on the type of fracture and the presence of strand marks.

Microscopic examination

A more detailed examination is carried out by microscopic observation, in which the structure of the fracture surface is analyzed using optical microscopes or scanning electron microscopes (SEM). Specific features such as indentations and striation patterns are recorded.

Here are the most important fracture pattern types and their interpretations:

Cohesive fracture in the coating material: the coating fractures within the material itself without touching the interface with the substrate surface.

Interpretation: This shows that the adhesive strength of the coating is higher than the strength of the coating material itself. As a rule, this is a good sign of a strong coating, as the adhesion is difficult to overcome.

Adhesive fracture at the interface: The fracture occurs exactly at the interface between the coating and the substrate, with no part of the coating remaining on the substrate.

Interpretation: This indicates weak adhesion between the coating and the substrate. It may indicate inadequate surface preparation, the wrong coating material or incorrect application

Mixed fracture: The fracture is both cohesive (in the coating material) and adhesive (at the interface). 

Interpretation: Mixed fractures indicate that both the substrate-coating interface and the coating material are weak. This could indicate a combination of material properties and surface defects.

Break from substrate: Description: The break occurs partially or completely in the substrate itself, e.g. in the case of concrete or wood.

Interpretation: This means that the bond strength is greater than the strength of the substrate. In such cases, the coating is well anchored, but the substrate itself could be in need of improvement.

When interpreting these fracture patterns, it is important to consider the specific requirements and standards of the project, as well as the conditions of the test, such as temperature, humidity and age of the coating. This information helps to evaluate the quality of the coating and substrate preparation.

1. dolly preparation

Problem: Insufficient cleaning or uneven sanding of the dolly surface.

Solution: Clean dollies thoroughly with solvent and sand evenly to ensure optimum adhesion.

2. adhesive selection and application

Problem: Unsuitable adhesive or incorrect application.

Solution: Use only recommended, fast-curing two-component epoxy resin adhesives and apply evenly.

3. curing time

Problem: Insufficient curing of the adhesive.

Solution: Allow at least 24 hours curing time at room temperature or follow manufacturer's instructions.

4 Alignment of the device

Problem: Not pulling vertically during the test.

Solution: Use the PosiTest AT's self-aligning actuator to ensure vertical force application.

5. environmental conditions

Problem: Extreme temperatures or humidity can affect adhesive curing and measurement.

Solution: If possible, carry out tests under controlled ambient conditions.

6 Substrate condition

Problem: Inhomogeneous or contaminated test surface.

Solution: Select and prepare representative, clean test areas.

7. calibration of the devices

Problem: Outdated calibration can lead to inaccurate measurements.

Solution: Perform regular calibration according to manufacturer's recommendations.

8. user error

Problem: Incorrect settings or operation of the device.

Solution: Thoroughly familiarize yourself with the operating instructions.

9. dolly size selection

Problem: Unsuitable dolly size for the specific application.

Solution: Select dolly size according to expected bond strength and substrate condition.

10. cutting process

Problem: Incomplete or incorrect cutting around the dolly.

Solution: Ensure careful and complete cutting down to the substrate with a suitable tool.

By observing these points, you can significantly improve the reliability and accuracy of your tensile adhesion tests with the PosiTest AT.

If a tensile adhesion test with the PosiTest AT has to be terminated prematurely, there are several aspects to consider:

With the PosiTest AT-M (manual model):

Stop manual pumping immediately.

The maximum pressure reached up to this point is shown on the display.

Make a note of this value if it is relevant for your documentation.

With the PosiTest AT-A (automatic model):

Press the “Stop” button on the device.

The device stops the pressure increase immediately.

The maximum pressure reached up to that point is saved and displayed.

For both models:

Carefully relieve the pressure in the system.

Check the dolly and the test surface for any damage.

Data handling:

Decide whether the aborted test should be kept in your records or deleted.

If required, you can add a note to the aborted test.

Preparation for the next test:

Carefully remove the dolly if it is still attached.

Clean the test area and the device for the next test.

Analyze the aborted test:

Investigate the reasons for the test abort (e.g. errors in preparation, unexpected behavior of the coating).

Use these findings to improve future tests.

Documentation:

Make a note of the reason for the test abort in your test log. This can be important for quality assurance and subsequent analysis.

By carefully handling an aborted test, you can retain valuable information and improve the efficiency of your testing processes.

Before sending your gage in for repair, please go through the troubleshooting steps in the instructions. If this does not help, a member of our technical support team will of course be happy to help you on +49 (0) 2235 987170 or send us an e-mail to info@mtv-messtechnik.de