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Corrosion mechanisms in the wood industry, especially caused by tannins
Author(s) -
Winkelmann H.,
Badisch E.,
Roy M.,
Danninger H.
Publication year - 2009
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200805016
Subject(s) - corrosion , tannin , blade (archaeology) , metallurgy , materials science , pitting corrosion , grinding , composite material , engineering , structural engineering , chemistry , food science
In order to improve the lifetime of cutting knives in the wood processing industry, a study has been undertaken to find out which wear process is primarily responsible for the reduction of the lifetime of steel blades. The examination of damaged surfaces of the cutting tools reveals mechanical damage at the cutting edges on one hand, but on the other hand pitting corrosion can be detected. It turned out that the corrosion impact reduces the lifetime of the cutting tools more than the mechanical loading, because a mechanically damaged steel blade can easily be repaired through grinding. But once the blade is subjected to pitting corrosion, it becomes useless because whenever the blade is reground, new holes due to pitting corrosion come to the surface again. Further investigations showed that the corrosiveness of different wood types is responsible for a major part of the damage, and that different woods have a different corrosive impact. One important goal of the present investigation is to learn more about the corrosive agents of different woods. It is revealed that tannin, a water‐soluble acid, which can be found in all woods in different concentrations, is responsible for the main part of the corrosive attack. In view of the above, the corrosion mechanism of steel blades caused by tannin is analyzed. During the cutting processes in the industry the blade temperature is increased. Thus, it is aimed to evaluate the influence of higher temperatures on tannin and the pH value of the acid. It is also revealed that the additional mechanical stress has an important influence on the corrosion process. The investigation could satisfactorily show the lowering of the pH value of tannin acid at higher temperature, which leads to increased corrosion. It is also revealed that the additional mechanical stress causes off stripping of tannin–Fe complexes from the steel surface, there the steel was not able to build a protective layer yet. That also leads to a further increase in corrosion.