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BehrOxal®~Chrome-Free Coating for Aluminum Surfaces Based on a Newly Developed Spraying Technology
Published May 20, 2007 by Institution of Mechanical Engineers in United Kingdom
Under the End of Life Vehicles Directive (2000/53/EC), as from 1 July 2007 it will not be permissible for any vehicle component to contain chromium with a valency of six (Cr VI). This paper presents an environment-friendly corrosion protection coating for aluminum evaporators based on an innovative spray application as a qualitatively equivalent substitute for yellow chromate coating. Moreover, the micro-fissures that typically form with the yellow chromate process lead to an accumulation of corrosion-promoting contaminants on the surface, for example de-icing salt. In contrast, the new coating forms a closed homogeneous oxide layer without any fissures and consequently without starting points for fouling and corrosion.
The chromate coating surfaces tend to be hydrophobic. The water vapor condenses on these in spherical droplets that do not drain easily. On the new coating, though, first flat droplets are deposited and then, when they conjoin, a thin film forms that readily runs off the surface.
The water film has a self-cleaning effect that partly washes away pollution and odorous substances. This also applies to substances originating from within the vehicle. Additionally, the new coating exhibits low intrinsic odor.
The results of the corrosion tests and measurements of the contact angle in relation to the hydrophilic properties of the new coating compared to yellow chromate will be presented as well as the newly developed odor test bench. Furthermore, this paper will highlight the benefits of the newly developed process regarding its integratability in the production line and the reduced use of process chemicals and waste water due to the application of a spraying technique instead of a conventional immersion process.