Automating Zinc Ash Removal from Galvanizing Vats in Hot-Dip Galvanization Plants

Workers in the hot-dip galvanization industry are exposed to high safety and health risks during the galvanizing process, especially when they are removing zinc ash manually.

In hot-dip galvanizing, items to be galvanized are submerged in a galvanizing vat with molten zinc that is approximately 450° C hot. Reaction products produced during this ten-minute process can affect the quality of the zinc coating adversely. In particular, the zinc ash produced by the vaporization of flux must be removed manually. Workers use mechanical skimmers to remove the ash, something associated with risks, such as falling into the vat and inhaling fumes.

Since automation can lower these risks substantial and reduce the staff required, Fraunhofer IFF developed and tested robot-based solutions together with the Berufsgenossenschaft Holz and Metall (BGHM, German Social Accident Insurance Institution for the Woodworking and Metalworking Industries) and IEHK Steel Institute at RWTH Aachen University for use in hot-dip galvanizing.

The automated solutions center around various removal tools guided automatically over the surface of the zinc bath by a six-axis industrial robot on a linear axis. Both mechanical and gas-based removal tools can be used.

The mechanical tool is modeled after the industry’s typical hand-guided tools which use pulsating motions to move zinc ash on the surface. The gas-based tool, on the other hand, uses a targeted fanned stream of compressed air to move the ash, avoiding direct contact with the surface. Weight, dimensions, heat resistance, stability and modularity are some of the important tool design criteria.

The tools’ optimal design was ascertained from theoretical calculations and preliminary functional tests on a 1:1 scale model in the Fraunhofer IFF technology center. The practicability of both removal tools was tested and proven in removal tests in a real-world industrial galvanizing vat.

The mechanical tool removes the zinc ash completely. The tool’s motion profile comprises slow and pulsating motions.

The gas-based process uses gas to move the zinc ash, the magnitude of the gas flow rate gas pressure being crucial to the efficiency of ash movement. Additional tests using nitrogen as the pressure medium revealed that it oxidized the surface of the zinc less than compressed air did.

The technical feasibility of both system’s has been generally demonstrated and can be incorporated in industrial solutions in the future. Current studies have revealed that removal results are somewhat better when the mechanical tool is used than when the gas-based one is.

Robotics consequently make it possible to automate zinc ash removal at industrial scale. In addition to a significant gain in efficiency, employees’ health risks can be lowered significantly. Closer human-robot collaboration will give future applications even more optimization capability and additionally increase employee safety.