Testing for Effectiveness of Aluminum Sheet Cleaning

Question:

We are currently using a dyne solution as well as water break test to determine the effectiveness of our aluminum sheet cleaning.

Can you tell me if there is any guideline for the surface tension (in dynes) that equates to a certain standard of cleanliness that is used as an industry standard for aluminum that is top coated with a primer?

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We also use a water break test that is a pass/fail and would be interested in any information on that. J.M.

Answer:

Unfortunately, there is no single answer to the question “How clean is clean." It is largely in the eye of the end user or the next person receiving that part in the manufacturing process. In your case, you have started in the right direction.

There are different ways to measure surface tension. There are laboratory instruments that measure contact angles/surface tension, although they would not be well suited to manufacturing. The water break test you mentioned could be made to be at least semi-quantitative by estimating the percentage of the surface that does not contain water breaks. In this case, 100% could be considered completely clean. You would have to set up a test procedure that would do this in a very controlled manner. Some variables to control would be time, temperature, incoming water type, and time between cleaning and test.

Another version of this would be to place a drop of water on a flat part and then measure the contact angle. The more the drop spreads, the larger the contact angle will be and the cleaner the part is. The contact angle could be viewed or photographed from the edge of the panel, and a contact angle measured. You may also want to consider measuring the diameter of spread that you get from the water drop on the surface.

Another option would be a relatively new method of measuring surface tension. We have evaluated surface tension pens in the past. These are markers that contain fluid of different surface tensions. You use a range of pens to bracket the surface tension of the material you are evaluating. You start by using pens from one range. If you start on the low end of the range, the “marker” from the pens will likely bead up. You then progress to the next highest pen number and continue until you reach a pen where the marker does not bead. The pens are usually graduated in increments of two dynes and your final result will then be between two pens (the one that beaded and the one that did not).

Even though this sounds very precise, in our evaluations of these pens, they are not quite as predictable as you would hope, and you should still use a very controlled method to apply them. We tried various cleaning methods (on aluminum) and did not see fine differences between them. Large differences were noticeable, but not small ones.