Rusting of steel raw materials, especially cold-rolled/galvanized coils, is a very common defect. Not only steel mills, steel traders, manufacturers, end products, but also auto insurance companies hate it.
White rust on galvanized sheets is generally caused by water pollution.
Water is a common pollutant in the supply chain stages of manufacturing, processing, storage and transportation, and use of galvanized coils. How to distinguish pollutants and thus classify white rust is of great practical significance for determining obligations, insurance claims, and follow-up improvements.
Classification of the shortcomings of white rust in galvanized sheet coils
The classification of white rust can be roughly divided into two categories: manufacturing pollution and storage and transportation pollution.
Manufacturing environmental pollution refers to white rust caused by water pollution during processing. Classic cases such as:
1. White rust caused by the residual leveling fluid of the hot-dip galvanizing line leveling machine;
2. The hot-dip galvanizing line should cut off the white rust caused by condensation water in the production and processing line;
The characteristics of white rust caused by manufacturing pollution are closely related to the two process characteristics of "steel chain movement" and "thorough completion".
Environmental pollution during storage and transportation refers to the water pollution caused by coiled steel/thick steel plates after packaging. Classic cases such as:
1. The coiled steel/thick steel plate was not covered with a raincoat during transportation, causing the packaging to leak;
2. Coiled steel/thick steel plates are soaked in ship warehouses, or caused by heavy rainstorms in southern China in the summer and warehouses being soaked;
The determination details of white rust caused by storage and transportation pollution are similar to those of friction black spots. Understanding the determination details of friction spots will also grasp the determination details of storage and transportation white rust. (Detailed description of friction black spots)
Why is white rust caused by environmental pollution during storage and transportation?
Isn't its appearance close to the edge of the hot-rolled strip?
Generally, the white rust caused by environmental pollution in storage and transportation has a small distance from the edge and a clear outline, while the outline is blurred at the other end.
This is often used by midstream and downstream or storage and transportation companies as evidence of refusal to recognize storage and transportation pollution. In fact, it is a typical feature of white rust caused by storage and transportation pollution.
Affected by capillary action, water will be slowly sucked into both sides of the hot-rolled strip after the top is polluted. Later, when the water pollution is removed, the water at the edges will be sucked in again, and the top will be in contact with the environment, close to the tops of both sides. Some of the water will evaporate.
Then there is this kind of appearance with a little gap from the end but clear contours.
