In the hot-dip galvanizing process, steel components are immersed in molten zinc and receive a zinc coating that provides long-lasting protection against corrosion.

The discontinuous galvanizing of individual pre-fabricated steel components (called Stückverzinken in German) is by far the most commonly used version of the hot-dip galvanizing process. After being pre-treated (cleaning/rinsing, pickling/rinsing, fluxing, drying), the steel components are immersed in a bath of molten zinc (containing various percentages of lead and aluminium). The standard version of this process strives for a bath temperature of approximately 450° C.

Diffusion reactions during the immersion process result in the creation of iron-zinc alloy phases on the surface of the immersed workpiece. These are covered by pure zinc when the workpiece is removed from the bath. The layer of zinc ash that builds on the top of the molten zinc is skimmed off before the galvanized workpiece is removed from the bath.

The gasiform emissions (hydrogen chloride - HCl) and dust emissions (zinc chloride/ammonium chloride) that result from the hot-dip galvanizing process may not exceed their respective legal emission limits - this requires special collection, extraction and dedusting systems.

Complete collection of the flue gases is achieved by surrounding the galvanizing kettle with an enclosure equipped with appropriate openings for crane lifting gear and skimming equipment. The required exhaust gas flow rate is significantly lower than is the case with a rim extraction system. A turbidity measurement using a frequency converter is used to adjust the extraction flow rate as a function of the galvanizing process sequence and the amount of dust generated during hot-dip immersion. This lowers operating costs.

Rim ventilation systems are used for small galvanizing baths and in situations where the collection of exhaust gas using an enclosure is not possible because of technical production issues. The suction slots are arranged above and along the rim of the zinc bath and depending on the width of the zinc kettle can be equipped with a blower device to improve the collection of the flue gas. The collection level that can be achieved is less than what is possible with an enclosure-based system.

The collected flue gases are cleaned using the proven Impuls filter system. The efficient Impuls cleaning system makes it possible to keep pressure losses and operating costs low.

Clean air leaving the filter can be reused in a downstream heat exchanger for heating purposes or for drying the galvanized part.

Scheuch - the specialist for industrial dedusting technology - delivers plants of this type to customers in Germany, Austria, Egypt, Saudi Arabia, the Czech Republic, Estonia, Azerbaijan, Holland and Russia.