Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 63 of 707

Figure 7: Bath monitoring with a mobile measuring instrument during cleaning processes. surface tension measure- ment values (see Fig. 6). Afterward, a reference curve based on different reference samples with known surfactant concen- trations can be developed. The surfactant concentra- tion of a measured surface tension in the process can be determined using the reference curve. For economical process management and high process reliability, the sur- factant concentration has to be kept within the given limits. Figure 8: Continuous cleaning bath control. According to specific process conditions, hand- held tensiometers for a peri- odical measurement or process measuring tech- nique for continuous mon- itoring can be used for analysis, as well as monitor- ing the process parameter surface tension. In order to realize efficient measurements during the process or in the labo- ratory, measuring instruments have to be reliable, quick, and easy to operate. The realization of those characteristics were essential for the development of a new hand-held tensiometer, the SITA DynoTester. The surface tension and the tem- perature of the cleaning solutions are measured by pushing one single button. Parameters as bubble lifetime or average determination are predefined and can only be changed in the administrator mode. These characteristics minimize the risk of operating errors. The measuring results can be saved in 25 storage spaces in the device for lat- er evaluation. The integrated power supply allows a mobile use of up to 10 hours and ensures high flexibility. The adjustable average determination increas- es the reliability measurement results in non-homogeneous liquids—for example, in emulsions. One measurement can be carried out within 10 seconds depend- ing on the chosen bubble lifetime. Therefore, the SITA DynoTester is a new, eco- nomical alternative for the measurement of process parameter surface tension. Figure 7 shows the results of periodical measurement of cleaning baths in a plant. The diagram of the surface tension values shows stable conditions with- in the process baths and over the bath lifetime. In the last rinsing bath, the sur- face tension reaches the same value of water, which means that the surfactant con- centration decreases to zero. Continuous bath monitoring requires measuring samples representing the actual condition of the bath that can be assured by using a bypass. Samples for 62

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