Water Break Test for Cleaning Parts

I was amazed that when I went to the Netherlands that they wash their dishes and leave the soap suds on top.  This is one reason that they the toilets with the shelves which use a lot less water than the very wasteful American toilets (two litres of good water down the drain because of a really poor design).  Where I am going with this?  If you have a plate with any soap or other oil on it is still dirty until you rinse it with a lot of water.  You will be able to see this by running some water and seeing if it has breaks in the water e.g. beads or blotches on the surface of the dish.  This is simply called the water break test and is a something you can do at home to see if the plate is properly clean.  The surface tension of water is 72.8 mN/m.

Knowledge of this test is important for two particular reasons.  The first one is beer (which the Benelux countries are particular good at making).  If you have soap or dirt on the inside of the beer glass the bubbles will stick to the glass producing less foam and give a flat beer.  So clean the glass thoroughly with water before adding beer.  The second reason this water test is important is for plating or painting surfaces.  If the paint or plating material needs to adhere to the surface a film (like soap) can prevent the adhesion.  This test can be frequently applied to freshly cleaned metals including steel, aluminum, brass, and other metals.  When totally clean these metals should be hydrophilic.  The water break test will allow a quick, easy, and non-destructive test to test for hydrophobic films.

So how do you do it?

It can be applied to large flat surfaces like sheet metal or to other surfaces with a smooth surface geometry.  You might find parts with a complex geometry difficult to do this test.  With this test you can detect oil and hydrophobic contaminants on hydrodrophilic substrates like metal or glass.  Take the part and put in a bath of clean water.  This is typically the final rinse of the cleaning process.  The surface tension on a clean surface will start to be a continuous sheet that will dry without any discontinuities or dry with a singular line that receds down the surface as the water drains off.  This can be done if the surface on a 45 degree angle or completely vertical.  Do not do it horizontally.  

How can you see contamination?

The 'sheet' of water on the part that is contaminated with any hydrophobic film will be seen in the area of the contamination.  This break is caused from the surface tension difference in the water and the difference in surface tension of the contaminated portion on the substrate (metal, glass ect).

How to interpret it?

A.  No break a well defined or no-line (CLEAN)
B. Blotches or breaks in the surface.  Sometimes you can measure the time of the breaks in seconds.  This may likely be measured in 10 seconds or so.  (Not as CLEAN)
C. Beaded.  This indicates a severely contaminated parts will bead up in various sizes.  You can try spraying water on it and seeing this. (DIRTY).



 Taken from (Posted on August 10, 2011 by John Fuchs)

With soaps and other cleaning solutions they are difficult to get off the surface of some substrates.  A seperate dip tank is important and fresh water spray.  Of course the 'fresh water' also has to be pretty clean.  If you have a good filter and if the water does not have any organic carbons in it this is always better.  Likely the hardness of the water will affect how effective the water is at getting rid of any residue (much like when you wash your hair or beer glasses in the hard water of the Netherlands.  Unfortunately, the water break test also may not detect particles that are hydrophylic in nature.  Quality of water is important. One sure fire test to see if your water is free of contaminates is to use the Kibron AquaPi.  Water will have a surface tension of 72.8 mN/m.  With any contaminate it will likely lower the surface tension of the water so it will be harder to clean.  (this instrument can also be used to make sure your Nickel and Chrome baths have the correct surface tension parameters).

You can also find nice surfactants in which to wash your parts at this trade show called Parts2Clean in Germany every year.