Temporary Corrosion Protection
According to the World Corrosion Organization, the economic damage caused by corrosion worldwide amounts to more than € 2 billion annually. How can products be protected against corrosion?
DIN EN ISO 8044 defines corrosion as the reaction of a metallic material with its environment, which causes a measurable change in the material and can impair the function of a metal component or an entire system. In most cases the reaction is of an electrochemical nature, in some cases it can be of a chemical or metal-physical one. The standard defines 37 different types of corrosion. The best-known examples are surface corrosion, crevice corrosion, contact corrosion, pitting corrosion, intercrystalline corrosion, stress corrosion and condensation corrosion. Corrosion causes damage running into billions, but for thermodynamic reasons it cannot be prevented in principle, it can only be delayed.
Different Types of Corrosion Protection
Active Corrosion Protection
Corrosion is reduced from the outset by selecting or combining suitable materials (e.g. certain stainless steels). This method often fails due to economical (expensive materials) but also due to technical reasons (lack of mechanical properties). Corrosion protection planning and design also ensures active corrosion protection, for example by avoiding gaps, joints, direct contact between different metals (keyword: contact corrosion, contact elements) as well as the separation of ferrous and non-ferrous metals during production. The same applies to storage and transport conditions — constant temperatures, low humidity, avoidance of condensation and contact with aggressive media (salt, hand perspiration etc.) as well as the choice of suitable packaging are important factors.
Passive Corrosion Protection
This is generally defined as the application of a separating layer. In the case of iron and steel, these are usually galvanically applied metallic coatings (e.g. zinc, nickel, zinc alloys), organic coatings (e.g. paints, varnishing), as well as non-metallic coatings (e.g. enamelling, gas nitriding, burnishing and phosphating, but with subsequent oiling or varnishing).
Temporary Corrosion Protection
The aim of temporary corrosion protection is to achieve a sufficient corrosion protection effect during the production process, storage and transport of the components. It includes oil-containing and watery media. The maximum corrosion protection period is approximately two years, depending on the application. The durability strongly dependents on the ambient conditions as well as the type of corrosion protection: it increases significantly in comparison with watery media to those containing oil (e.g. Surtec 590). In the case of oil-based corrosion protection agents, removal from the surface of the part is more difficult than in the case of watery media, which is why these are no longer permitted in some areas.
Temporary Watery Corrosion Protection
In most cases, these materials are adducts of fatty acids and amines. They are salt-free and create a mildly alkaline to alkaline environment on the component surface. Either the cleaner itself already contains a temporary corrosion protection or the application takes place in the rinsing baths, allowing the corrosion protection to dry on the surface. Subsequent processes such as hardening are not negatively affected, as the corrosion protection evaporates completely at temperatures above 200 °C. The corrosion protection is then completely removed.
Depending on the material, storage conditions and water quality, corrosion protection times of two weeks to six months can be achieved. Requirements for good watery storage corrosion protection:
- Preparation in demineralized water (deionized water)
- Cleaning and rinsing baths <10 mg/I Chloride
- Fast and complete drying after cleaning or passivation, vacuum drying for complex geometries
- Parts that go directly to assembly must be stored dry and in dry ambient air or packed cooled in corrosion protection paper.
This is particularly important in the summer months, which are characterized by warm air with high humidity.
In summary, it is safe to say that an influence on corrosion protection does not start directly after a cleaning process but already during the construction of the parts. This shows how important it is to consider the entire manufacturing process right through to transport. In this way, problems can be detected promptly, complaints regarding corroded parts can be minimized, or even completely avoided.
This article was first published by MM MaschinenMarkt
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