Getting a grip on tensile adhesion testing

Posted by Tom Swan on Mar 25th 2020

Getting a grip on tensile adhesion testing

06/27/2016 17:39:38

EXTRACT

These testing options work for several different PSI ranges.

ARTICLE CONTENT

You have a coated surface, and need to know the level of the bonding between the coatings and the substrate. You may have to do tensile adhesion testing, and you have several choices of test units. The final chapter in our Coating Inspectors Handbook explores this form of testing and which tester types have the highest level of pull.

There are 5 categories of adhesion testers defined by ASTM D4541. All five categories have different features which can cause the testers to measure the same coating system differently. That's all the more reason to be careful as you shop for the right meter. Operator knowledge may also affect how well any of these tests work.

Here are the specifics of each type and an appropriate tester to go along with them. These are based on ASTM D4541, "Standard Method for Pull-Off Strength of Coatings using Portable Adhesion Testers" which uses the terms Methods B-F (Method A or Type 1 was previously used but retired.):

Type 2
These meters are mechanical testers that are operated manually, turning the top wheel or wrench by hand. The tester is designed for field use. Users will be able to see the results on the scale on the side of the meter .

The benefits of this tester is its portability and relatively easy means of use and you don't need power to use it. It is also one of the least expensive adhesion testers on the market.

On the Down side the accuracy is horrible (±40), the repeatability and the results depend on the operator using the unit, and it is only designed for 1 size of dolly.

"Each Type of tester can produce a wildly different result. That's all the more reason to be careful to choose the correct model."

Type 3

These are Hydraulic Adhesion TEsters (HATE) and the HATE tester provides a concentrated use of force within the dolly, leading to a smoother, better pull. Unlike the other adhesion testers, it uses a piston to push the dolly off the surface. This is often required on specification originating out of Europe. It pulls higher than a Type one tester but also suffers from manually turning a knob to push off the dolly.

Pricewise and performance wise this one is in the middle on both.

Type 4
For this type, we sell the P.A.T.T.I. meter, an automatic system that operates via gas pressure. If you're used to the manual option, switching to this one could offer a significant benifets. While most units are not as portable as the above testers , it does work for PSI ranges as high as 17,400. Its primary advantage is accuracy: It's the most precise tester on the market and gives the best pull. Where with most meters, you vary the size of the dolly to increase the pull strength, with the PATTI, it is the piston size that you change. Depending on what you test, you may need to have more than one size piston.

P.A.T.T.I. makes several models and has a new model suitable for field use. Units range rom $999 to about $5,000. Units come with one piston so others may need to be purchased if you need to pull dollies over a wider range.

Type 5
The Defelsko Adhesion Tester comes with various sizes of dollies and gives accurate and repeatable measurements. The automatic unit offers a steady pull at a push of the button and will be more accurate and repeatable than the manual unit. Its PSI range is up to 10,000 PSI with a 10 mm dolly. For substrates such as concrete it offers 50 mm dollies.

For most situations this is the first choice for and adhesion tester. The automatic unit is $2,595.00 and is good for lab or field use.

The DFD adhesion tester have a self-aligning head to ensure perpendicular pulls. While they have excellent features, they are manual and suffer from inconsistencies due to operators. Also, they are very expensive but do fill a niche in the market. It is the only commercial tester I am aware of that can be adapted to ASTM C-633, “Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings”

Don’t get lost in the numbers. It can be more important how the coating fails than the pull rate that the different units measure, We will leave that topic for a future blog.

Browse our store or read our Coating Inspectors Handbook to learn more about the right tensile adhesion test for you.

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