Water break test

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... 

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. 

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. 

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 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. 

Whereas actual measurements of contact angles are usually made in science laboratories, the principles are exploited in the water-break test and in the use of liquids of different surface tensions to assess the printability of polyolefins. 

The water-break test is a simple method to check that a metal surface is clean. A few drops of distilled water are placed on the surface, or alternatively the sample can be drawn from a bath of water. If the water does not break into droplets then... 

The water break test may be used to detect oily residues not found by other means. The surface is wetted with a spray of clean water. The water should form a thin layer and remain unbroken for at least five seconds. Beading of the water droplets indicates the presence of oil contaminants, and recleaning is required. This method is generally limited to horizontal surfaces. 

Regardless of the metal pretreatment used, it is important to maintain as much control over the process as possible in order to assure consistently good results. Lubricants and anticorrosive oils that contain chlorinated paraffins or silicone should be avoided, as they can interfere with adhesion. All degreasing solvents and cleaning solutions must be kept clean and free of contamination. Grits and abrasives must be kept clean and periodically changed. Rinse water and drying air must be checked frequently for purity and kept free from oils. A simple test to measure the effectiveness of the metal pretreatment is called the water-break test. In this test, the prepared metal part is dipped briefly in... 

Standard Test Method for Hydrophobic Surface Films by the Water-Break Test, 2002. 

Chemical cleanliness can be determined in a variety of ways. Wetting is often tested using a water break test or more analytically in terms of contact angle, with a low value being desirable. 

On many nonporous surfaces, a useful and quick method for testing the effectiveness of the surface preparation is the water-break test. If distilled water beads up when sprayed on the surface and does not wet the substrate, the surface-preparation steps should be repeated. If the water wets the surface in a uniform film, an effective surface operation has... 

Carbon fiber-epoxy composites (A) Solvent wipe (MEK, toluene, trichloroethylene, etc.) (B) Use peel ply during initial curing. (C) See Ref. 15 for the effect of abrasion procedures. See also Refs. 16 and 17. (A) Lightly abrade with medium-grit emeiy paper. Avoid exposing the reinforcing fibers. (A) Wipe with solvent. Check surface by water break test. Retreat, if necessaiy. 

In metal bonding the issue of wetting is easily settled. Clean metal surfaces have extremely high critical wetting tensions, in the order of several hundred dynes/cm. As a consequence, adhesives with a typical surface tension of 35 dynes/cm have little trouble wetting metal surfaces. If wetting problems occur, it is almost always the result of contamination on the substrate surface, a condition that can be quickly checked with the water break test. If water with a surface tension of 73 dynes/cm wets the surface, it is a safe assumption that no problem will be encountered with lower surface tension adhesives. 

Irrespective of the degreasing method used, the water-break test is a simple method to determine whether the surfaee to be bonded is clean it is best suited to metals. The surfaee may be assumed to be free of contamination if either a few drops of distilled water, whieh have been applied to the adherend, wet and spread or if, on drawing the substrate from out of an aqueous medium, the water film does... 

In virtually all cases where chemical pretreatment has been used, the water-break test can be used to confirm the effectiveness of the process. 

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