The American Society for Testing and Materials (ASTM) standard “ASTM F22-13 Standard Test Method for Hydrophobic Surface Films by Water Break Test” describes a test method for detecting the presence of hydrophobic (non-wetting) films on surfaces and the presence of hydrophobic organic substances in processing environments. When properly performed, this method enables the detection of molecular layers of hydrophobic organic contaminants. On very rough or porous surfaces, the sensitivity of the test may be significantly reduced.
The water break testing described in this test method is rapid, non-destructive, and can be used to control and evaluate processes for the removal of hydrophobic contaminants. The water break “free” test is typically used for in-process verification of the absence of surface contaminants on metal surfaces that could interfere with subsequent surface treatments such as priming, conversion coating, anodizing, plating, or adhesive bonding.
This test method is non-quantitative and is generally limited to applications where a satisfactory or non-satisfactory assessment of cleanliness will be sufficient.
This test method can also be used to detect and control hydrophobic contaminants in processing environments. For this application, a witness surface, free of hydrophobic films, is exposed to the medium and then tested. The sensitivity of this test varies with the level of contaminant in the air and the duration of exposure of the witness surface.
For quantitative measurement of surface wetting, test methods that measure the contact angle of a stationary drop of water or other test liquid can be used in some applications. Measurement methods based on contact angle are included in the following standards:
Instruments are available for in situ measurement of contact angle. These instruments are limited to a small surface area and may not reflect the cleanliness of a larger surface. For larger surface areas, localized contact angle measurement in conjunction with water break testing or other quantitative studies may be useful.
For surfaces that cannot be immersed or wetted with water, or where such immersion or wetting is impractical, such as large parts or assemblies that have been previously coated, prior to the application of paints, primers, or other organic coatings, “ASTM F21-65 (2002) Standard test method for hydrophobic surface films by atomizer testing” may be more appropriate than this test method for evaluating surface cleanliness.
This test method is not suitable for mounted equipment where line-of-sight assessment is not possible or where there is a risk that water will become trapped in moving surfaces or complex structures and cannot be effectively removed.
In short, the water refraction test is a simple method for checking whether a metal surface is clean. A few drops of distilled water are placed on the surface, or alternatively, the sample can be taken from a water bath. If the water does not separate into droplets, the surface is free of contamination. The fact that the metal is evenly wetted by the water indicates that it will also be evenly wetted by the adhesive.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the standard “ASTM F22-13 Standard test method for hydrophobic surface films with water breaking test” with its trained and expert staff and advanced technological equipment.
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