The water break test is a common way for manufacturers to test the surface cleanliness of metals. Compared to other legacy cleanliness tests, it is relatively simple to perform, however, the results rely almost entirely on the subjective eye of the person performing the test.
Hydrophobic contaminants can be detrimental to adhesion — water break tests allow users to test for the presence of these contaminants. Although this test is nondestructive, because it only uses water, the test has significant limitations. The test lacks the ability to detect surfactants or other hydrophilic substances on the surface. As the test does not require purified water, and as purified water can contain contaminants, the water can introduce contaminants to the surface and can lead to inaccurate test results.
Highly engineered materials are becoming the norm in complex manufacturing environments. Manufacturers now rely on a wide array of raw materials including custom designed metals, polymers and an extensive variety of advanced composites. Advances in part molding technology have led to the development of parts with increasingly complex geometries. Water break tests are not effective in this increasingly sophisticated manufacturing environment. Although, historically, water break tests were effective for large, flat surfaces, this test is becoming obsolete as manufacturers embrace new technologies for highly sophisticated power production.
IoT and leveraging the power of data is transforming the way manufacturers collect and analyze test results. Water break tests are not well suited for manufacturers who are seeking to gain actionable, traceable and quantitative test results about surface quality. Data-driven process control requires sophisticated testing methodologies that can seamlessly capture all relevant surface analytics data.
The ASTM-F22 Handbook sets the standard for water break tests. To perform a test, a material is dipped into water and withdrawn vertically. In some instances, the water is sprayed or poured onto the surface. The technician performing the test visually evaluates the behavior of the water on the surface. The technician’s analysis is subjective.
For strong, reliable adhesion, a material needs to have a high surface energy in order to be chemically attractive to the adhesion, paint, ink or other coating that will be applied to it. A clean surface generally has high energy and, in the case of the water break test, should result in the water sliding off the surface in an unbroken sheet. If the surface is clean the water will spread out due to its attraction to the surface. The reaction of the water to the surface can strongly correlate to adhesion ability. Water is an excellent indicator of surface energy but when applied in a subjective, difficult to control manner, as it is in the water break test, the results aren’t suitable for process control in the modern manufacturing process.
Water break tests are used primarily for metals to identify the presence of contaminants on incoming raw materials or after surface processes, such as etching, anodizing, painting, priming, coating, grit-blasting, or sanding, have occurred. These tests, however, can be messy and frequently result in unintended contaminating from impure water.
Drying time is another constraint of the water break test. A significant amount of time needs to be allocated for the part to dry after the test. This can include a manual wipe of the part or a baking process — either process can transfer contaminants or alter the surface chemistry of the part in an unintended way.
A Critical Control Point (CCP) represents any specific opportunity throughout the manufacturing process when a material surface has the potential to inadvertently change. A nondestructive methodology that can precisely capture surface quality at any point in the production process is required to validate process control over CCPs. The water break test does not hold up to these challenges because the testing methods themselves can be a source of contamination.
Although technicians can be trained regarding how to conduct a water break test, there are no definitive pass/fail standards for the water break test. This leaves test results vulnerable to inconsistent standards both within a company and throughout specific industries. This highly subjective test does not support the rigorous accuracy needs required in tightly controlled manufacturing industries.
A lack of test sensitivity is another weakness of the water break test. Although a surface may appear clean visually, it could actually be contaminated. Multiple tests on the same surface can yield conflicting results. False positives, that indicate the surface is clean when it is actually contaminated, are quite common with this test.
Maintaining objectivity and capturing consistently accurate results can be achieved with the appropriate processes and equipment. The Surface Analyst™ is a contact angle measurement system that is sensitive to the top 2-3 molecular layers of a surface where adhesion occurs. The Surface Analyst™ deposits a single drop of highly purified water on a surface to accurately predict adhesion success. This reliable and quantitative surface quality measurement is completely nondestructive and poses no threat to the measurement surface.
The Surface Analyst has the ability to measure any surface or surface orientation, regardless of shape, size, geometry or roughness. Unlike a water break test that requires a part to be removed from production in order to test surface adhesion readiness, the Surface Analyst can perform measurements on actual parts during the manufacturing process.
Results of the water contact angle measurement are available instantly so action can be taken immediately if contamination is detected. The automatic calculation of contact angle removes operator subjectivity. The Surface Analyst measures on a cleanliness scale as opposed to a binary go/no go result. Measurements taken with the Surface Analyst can more closely map out a surface's characteristics. Manufacturers can know precise contamination levels and contamination locations.
To find out more about an alternative to the water break test, download the "Manufacturer's Roadmap to Eliminating Adhesion Issues in Production" eBook. This guide gives clear insight into eliminating guesswork around adhesion so manufacturers can achieve consistent and successful results.