Deep rolling of antimicrobial coated inner pipe-surfaces

Florian Vogel, Institute of Machining Technology / TU Dortmund, Dortmund, Germany
Dirk Biermann, Institute of Machining Technology / TU Dortmund, Dortmund, Germany

The wastewater-system in airplanes is an assembly with an increased maintenance requirement. Especially at design related constrictions and junctions of the wastewater-pipes, adherences of microorganism in the form of biofilms can occur. This results in such a reduced cross section of the respective parts that foreign objects often clog the nearly 60 m long pipe-system. Due to the system-length and the comparatively complicated accessibility, the localization and the removal of congestions takes a lot of time. A replacement of the whole assembly is often necessary. In addition to that, maintenance results in a high amount of downtime costs.

For preventing such adherences of biofilms on the inner pipe-surfaces, the application of a novel antimicrobial coating was investigated. The coating was based on a galvanic silver top layer in which microporous ruthenium-particles were incorporated. Thus, a highly efficient physical contact-catalyst is generated that kills the microorganisms near the coating. Because of the different standard electrode potentials of silver and ruthenium, a micro-electric field is developed in contact with water. This effect results in a depolarisation of the electric loaded germ membranes of the microorganisms. Thus, dissolution of the membranes occurs. Furthermore, due to an electrochemical-catalytic reduction of the oxygen solved in the water, reactive oxygen-species are generated, which also kill the microorganisms. Additionally, the organisms are oxidized when they get in contact with the micro-anodes.

The present investigation deals with the implementation of a deep rolling process to enable an additional treatment of the coated surfaces. Therefore, a hydrostatic tool with two rolling-balls and a maximum pressure of pmax = 200 bar was used. The investigations have shown that the deep rolling treatment of the antimicrobial coated pipe-surfaces offers several advantages. On the one hand, the adherence and the hardness of the coating are increased by the deep rolling process. On the other hand, the roughness of the top-layer is decreased down to Rz < 1 µm. Furthermore, special tests of deep rolled samples on microbial cultures verified that a high antimicrobial efficiency is given until a rolling-force of FW = 150 N. It is demonstrated that deep rolled, antimicrobial coated pipe-surfaces represent a sustainable and efficient method for an active prevention of microbial adherences.

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