Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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chemical surface preparation CONTROLLED CLEANING BY MEASURING SURFACTANT CONCENTRATION BY DANIEL SCHÜMANN, SITA MESSTECHNIK GMBH, DRESDEN, GERMANY The process reliability of pretreatment methods is the basis for high-quality products in the production of metal parts with special surface requirements. The cleaning process is the essential step between the finished shape forming and fol- lowing surface treatment and surface coating, respectively. Deficiently cleaned parts cause defects in the surface quality of products, leading to high costs due to consequential damages. Industrial and aqueous cleaning processes of metal parts consist of cleaning and rinsing procedures in several baths (see Fig. 1). First, the cleaning baths remove the contamination of the metal surface, followed by the rinsing baths for eliminating further contamination as well as cleaning agent residues. The cleaning baths have a temperature of 40–80°C (104–176°F). The resulting evaporation of water is compensated by a recirculation of rinsing water. A regeneration circulation ensures stable bath condition due to a continuous removal of bath contamination. Aqueous cleaning processes require optimal and stable conditions of the parameters that influence cleaning results in order to ensure a high process reliability (see Fig. 2). These parameters entail: • concentration of cleaning agent components (builder and surfactant) • bath contamination • bath temperature • agitation The main goal of process management is to continuously monitor the con- dition of the cleaning bath and control the condition in a way that ensures suf- ficient cleaning quality can be achieved by using minimum amounts of water, Figure 1: Example of a cleaning process. 57

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