Testing water break

When a quantitative estimate of residual soil is not called for and the suitabiUty of a metal surface for further finishing needs to be assessed, the water-break test is used. The term water-break refers to the behavior of a water film on a smooth greasy surface. When the film becomes sufficiently thin by drainage, it suddenly breaks into islands or droplets between which the surface appears dry. On the other hand, when a film drains from a clean water-wettable, nongreasy surface, it becomes progressively thinner and finally disappears by evaporation without ever breaking into droplets. Such a surface is said to be free from water-break. 

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

To check the efficacy of grease removal, the alkali solution is rinsed away or neutralised by dipping in dilute acid. If, after removal from the acid, the draining metal surface remains wetted evenly all over for 30-60 s (or until it dries by evaporation), hydrophobic soils have been removed. Traces of grease cause the surface to de-wet, and surface tension draws the water into separate droplets. This is the water-break test. Traces of grease which remain when the work is plated do not prevent electrodeposition, but are detrimental to adhesion and corrosion resistance. 

Water-break test, 9 782 Water carriers, 25 327 liability of, 25 336... 

Cool the test tube in the air. Put the tube with the solidified phosphorus into a crystallizer with water. Break the tube under the water and remove the dirty surface layer from the obtained piece... 

The specific surface preparation can be checked for effectiveness by the water-break free test. After the final treating step, the substrate surface is checked for a continuous film of water that should form when deionized water droplets are placed on the surface. A surface that is uniformly wet by distilled water will likely also be wet by the adhesive since the specific surface energy of water is 72 dyn/cm and of most organic adhesives is 30 to 50 dyn/cm. However, this test tells little about weak boundary layers or other contaminants that may be present on the substrate s surface but still be capable of wetting with water. 

The steam generator is filled half full with water and then heated to produce steam. 50 to 80 grams of whole cloves are ground in a mortar and pestle and then placed in the sample flask. The clove oil then is removed by steam distillation and collected in a receiving flask. The collected material usually will be a milky white or light yellow suspension and will eventually yield a few small drops of clove oil. Five different methods then will be tested to break this emulsion. 

Methods for determining surface cleanliness are too involved for online evaluation, so that simple tests such as water break are employed. Recently, Buser reported a rapid method based on surface tension (15). Evaporative rate analysis (16) has also been used to determine surface cleanliness as well as more sophisticated methods employing scanning auger spectroscopy (17. 18). 

Effect of preconditioning on migration results. The effects of preconditioning and of migration test water were investigated using multifactor ANOVA (analysis of variance). This statistieal tool breaks the variability of data (pH, Al, Ca or K) into contributions due to various factors (preconditioning conditions and CO2 added in test water). 

The process does not produce a surface that will pass the "water-break test (see Note). Thus, for cleaning requirements that necessitate essentially complete freedom from water-soluble, solvent-soluble, and chemically combined contaminants, vapor degreasing may be followed by water rinsing to remove traces of water-soluble soils and oxidation and reduction steps to remove any oxides or sulfides, and so forth, from the surface. 

Note—The "water-break is used to detect the presence of organic contaminants on a metal surface. This test indicates a hy-drophillic surface rather than cleanliness. The surface is immersed in a beaker of overflowing deionized water (or tap water free of contaminants), removed vertically, and the draining water film observed. On a surface with organic (hydrophobic) matter, the water film will tend to break up and withdraw into wetted areas and expose areas not wetted. 

Mori et al. (56) carried out tests to break W/O emulsions in a small sample cell. Kerosene and 50 mol/m hydrochloric acid were emulsified by using Rheodol SP-OlO surfactant (equivalent to Id s Span 80). Tests were carried out at frequencies between 40 and 2000 Hz at potentials of up to 8 kV. Coalescence was found to be enhanced with increase in frequency. Taking into account power requirements, 1000 Hz was found to be the most effective operating fire-quency. Phase separation was found to be faster for a smaller initial hold up of water but, with an aqueous content of less than 40%, coagulation occurred before coalescence and this slowed the process. 

Clearly the adhesive must wet the adherend, implying the common-sense idea of a thin film of liquid spreading uniformly without breaking into droplets on the surface (Fig. 3.3). The water break-free test is the simplest approach to a qualitative visual assessment the thermodynamic approach to wetting allows quantitative study. 

Before actual bonding, the subjective water-break test or the quantitative and objective contact-angle test may be carried out. After bonding, the effectiveness of surface preparation may be determined by measuring the bond strength and determining the mode of the failure of the adhesive joint. 

This test depends on the observation that a clean surface (one that is chemically active or polar) will hold a continuous film of water rather than a series of isolated droplets. This is known as a water-break-free condition. A break in the water film indicates a soiled or contaminated area. Distilled water should be used in the test, and a drainage time of about 30 seconds should be allowed. Any trace of residual cleaning solution should be removed or a false conclusion may be made. If a water-break-free condition is not observed on the treated surface, it should not be used for bonding. The surface should be re-cleaned until the test is passed. If failures continue to occur, the treatment process should be analyzed to determine the cause of the problem. ... 

If a chemical surface treatment in required, the process must be monitored for proper sequence, bath temperature, solution concentration, and contaminants. If sand- or grit-blasting is employed, the abrasive must be changed regularly. Fresh solvents for cleaning should he on hand. Checks should be made to determine if cloths or solvent containers have become contaminated. The specific surface preparation used can be checked for effectiveness by the water-break-free test. After the final treatment step, the substrate surface is checked for its ability to form a continuous film of water when deionized water droplets are applied to the surface. After the surface treatment has been found to be adequate, precautions must be taken to assure that the substrates are kept clean and dry until the bonding operation. The adhesive or primer should be appUed to the treated surface as quickly as possible. 

Thirdly, a water break test should then be carried out by spraying distilled or deionized water on to the prepared surface (Surface characterization by contact angles -polymers and Wetting and spreading). Careful abrasion is needed until a continuous layer of water remains for 30 s without any breaks. Once dried, the surface will then be ready for bonding. 

All matrix resins and adhesives absorb some moisture, and a dry surface is necessary before bonding if strong and durable joints are to be made. The surface should then be dried with radiant lamps or hot air blowers for about 3 h at the intended bonding temperature or to the standard specified in the SRM for the component. The prepared surfaces should not be touched by hand or anything else from the time of the water break test to the time of application of the adhesive. Bonding should take place as soon as possible after drying or a suitable primer should be applied within about 4 h. Once the primer is dry, the part can be stored in a sealed plastic bag for several months prior to bonding. 

Conversion coated or etched aluminium surfaces are generally free from organic contamination and easily wetted. A water break test is commonly used to establish that a clean surface has been generated. Such pre-treated surfaces have been described as forming a... 

The specific surface preparation can be checked for effectiveness by the water break-free test. After the final treating step, the substrate surface is checked for a continuous film of water that should form when deionized water droplets are placed on the surface. 

The effect of the water break test is generally due to the fact that greases, oils, and other contaminants have a low surface energy (surface tension less than water) so that a water droplet will bead up and show an incomplete film when applied to surfaces where these contaminants are present. The water break test is sometimes used after surface treatment and before adhesive bonding or coating to determine the adequacy of the surface treatment. 

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