KnowledgeBase » HDG Process

Why does the galvanized coating thickness depend on the steel thickness?

The hot-dip galvanized coating is an inter-metallic layer of iron and zinc, meaning the zinc and iron react and diffuse into one another to create the galvanized coating. If more iron is available to react with the zinc, a thicker coating can develop. Thicker pieces of steel tend to develop
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Batch Hot-Dip Galvanizing Production Process

The batch hot-dip galvanizing process, also known as general galvanizing, produces a zinc coating on iron and steel products by immersion of the material in a bath of liquid zinc. Before the coating is applied, the steel is cleaned to remove all oils, greases, soils, mill scale, and rust. The cleaning cycle usually consists of a degreasing step, followed by ...
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How is zinc added to the galvanizing kettle?

Zinc is added to the kettle in three primary ways, depending on the amount of zinc being added to the kettle. When a large amount of zinc is added to the kettle it is usually in the form of ingots, which are commonly known as zinc pigs. Zinc pigs are simply chained to a crane and then slowly lowered into the galvanizing kettle until they melt. When smaller amounts of zinc are added to the kettle, such as in 25 kg blocks or zinc pellets, they c...
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Can 4130 steel be successfully galvanized?

4130 steel is a chromoly steel. Steels of this chemistry have presented some adherence problems in the past when galvanized. The galvanized coating developed in some areas but not others. It would be best to try galvanizing a small sample of steel with this chemistry to determine the results before attempting to galvanize a large structure....
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Why is lead added to the galvanizing bath?

Lead is not purposely added to galvanizing baths, rather it is an impurity in zinc. Different types of zinc have different levels of lead. The specified lead maximums for the various types of zinc can be found in ASTM B6. Lead does have the beneficial effect of decreasing the surface tension of zinc, which allows it to flow off the steel easier as it is being removed from the kettle. This creates thinner galvanized coatings that have l...
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How long does it take to convert Chromium VI to Chromium III on galvanized steel?

Some galvanized steel is dipped into chromium quenches after hot-dip galvanizing. The chromium creates a passivated surface on the galvanized coating that prevents wet storage stain and white rust on the galvanized coating for a short period of time after galvanizing. After reacting with the zinc when the newl...
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How can hot-dip steel be dulled or deglared?

Some types of steel come out of the kettle with a matte gray finish and others come out of the kettle with a bright and shiny finish. The type of finish you will get depends on the chemistry of the steel. There are some chemical treatments that can dull the finish such copper sulphate solutions and zinc phosphate solutions;...
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Continuous Sheet Galvanizing Production Process

The continuous hot-dip coating process is a widely used method originally developed over fifty years ago for galvanizing of products such as steel sheet, strip, and wire.  The molten coating is applied onto the surface of the steel in a continuous process.  The steel is passed as a continuous ribbon through a bath of molten zinc at speeds up to ...
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Flux Inclusions

Flux inclusions can be created by the failure of the flux to release during the hot-dip galvanizing process. If this occurs, the galvanized coating will not form under the flux spot.  If the area is small enough, it can be cleaned and repaired. If the flux inclusion covers a large area, then the part must be rejected.  Flux deposits on the interior of a hollow part, such as a pipe or tube, as seen in the image to the right, cannot ...
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What should centrifuge baskets be made of?

Centrifuging baskets are commonly made out of Haynes 556 alloy. This steel does not pick up as much zinc as other types of metals, but it does tend to be rather expensive....
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