KnowledgeBase » Appearance
ILZRO Classifications of Sandelin Steels
Research carried out by the University of Cardiff in Wales for ILZRO (International Lead Zinc Research Organization) project took an in-depth look at the problem of silicon reactivity and included phosphorous as a reactive element also. The researchers varied the weight percentage of silicon and phosphorous and then assessed the reactivity of the steel at different galvanizing temperatures. This work led to a table of reactivity clas...
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Weld Slag Clean Up Requirements for Galvanizing
When welded structures are hot-dip galvanized, the weld area cleanliness significantly affects the quality and appearance of the galvanized coating around the weld. If a coated electrode (i.e. a flux-coated welding wire/rod/stick) is used during welding, all welding flux and slag must be cleaned prior to galvanizing or the ...
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How to Clean Wet Storage Stain
Treatment of wet storage stain begins with drying the galvanized surface. As long as water remains on the zinc surface, and airflow is limited, the corrosion mechanism responsible for wet storage stain will continue, and can damage the zinc coating and underlying steel.
After the galvanized surfaces are dried, the treatment processes differ dependi...
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Wet Storage Stain vs. White Rust
Many people perceive wet storage stain to be the same as white rust and use the two terms interchangeably, but they do have distinct differences.
Wet storage stain is the commonly known problem of white surface oxide formed on newly galvanized ste...
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How to Prevent Wet Storage Stain
Prevention of wet storage stain includes not tightly stacking newly galvanized products on top of one another, removing standing water, and providing adequate air flow over the zinc surfaces.
Newly galvanized articles should be stored under cover in dry and well ventilated...
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Visual Observations for Finish and Appearance
The image to the right shows products with connected galvanized pieces that have different appearances. The appearances of these pieces differ greatly from one another due to the steel chemistry of the different sections of the parts; however, all of these products continue to have an equal amount of corrosion resistance throughout and meet the specification.
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Reasons for Different Appearances
The amount of silicon added during the steel-making process can create differences in the appearance of galvanized products. The Sandelin Curve, as seen in the image to the left, compares zinc coating thickness to the mass percentage of silicon in the steel. The recommended silicon composition is either less than 0.04% or between 0.15% and 0.25%. Any steels not within these ranges are considered reactive steels and can be expected to form th...
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Bare Spots
Bare spots, uncoated areas on the steel surface, can occur because of inadequate surface preparation. Bare spots may be caused by welding slag, sand embedded in castings, excess aluminum in the galvanizing kettle, or lifting devices that prevent coating formation in a small area. To avoid bare spots, (left) the galvanizer must ensure surfaces are cle...
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Chain and Wire Marks
A type of surface defect occurs when steel is lifted and transported using chains and wires attached to overhead cranes. Lifting devices can leave uncoated areas on the finished product that will need to be renovated. Superficial marks, like those seen in the image to the right, left on the galvanized coating from the lifting attachments are not grounds for rejection unless the marks expose bare steel; in such a case, the galvanizer must rep...
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Why is steel chemistry important in the hot-dip galvanizing process?
Galvanized coatings are formed by a chemical process during which steel and zinc metallurgically bond, forming a series of corrosion-inhibiting, highly abrasion-resistant zinc/iron alloy layers.
Galvanized coatings are specified for their corrosion resistance. While a gray or matte appearance may occur, the corrosion protection afforded is no different than that provided by shinier galvanized coatings. The corrosion resistance of matte...
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