In the fabrication of galvanized trough bridges, zinc consumption primarily originates from zinc layer consumption, zinc ash generation, zinc slag precipitation, and zinc loss during operation. Reducing zinc consumption requires coordinated control from multiple aspects, including process parameter optimization, equipment improvement, operational procedures, and material selection.
Zinc layer consumption is the main component of zinc consumption, and its thickness directly affects the amount of zinc used. The galvanized layer consists of a pure zinc layer and an iron-zinc alloy layer, and its thickness is affected by the zinc bath temperature, immersion time, and the surface condition of the workpiece. If the zinc bath temperature is too high, the iron-zinc reaction accelerates, the alloy layer thickens, and zinc consumption increases; if the temperature is too low, the zinc bath has poor fluidity, resulting in an uneven coating and localized excessive thickness. Therefore, the zinc bath temperature must be controlled within a reasonable range, typically between 435℃ and 445℃, based on the workpiece material and size, to ensure a uniform coating with appropriate thickness. Simultaneously, the immersion time must be precisely controlled; the workpiece should be removed immediately after the zinc bath reaches boiling point to avoid prolonged immersion leading to an excessively thick zinc layer. In addition, the surface roughness of the workpiece also affects the zinc layer thickness. Thorough cleaning is necessary after pickling to remove surface oxides and rust, reducing zinc consumption.
Zinc ash formation is another significant source of zinc consumption. At high temperatures, the surface of the molten zinc easily oxidizes upon contact with air, forming zinc oxide, i.e., zinc ash. Zinc ash not only consumes molten zinc but can also adhere to the workpiece surface, affecting coating quality. To reduce zinc ash, the exposed area of the molten zinc needs to be controlled by adjusting the size of the zinc pot and the placement of the workpieces to reduce the airflow speed on the liquid surface. For example, using a fast-in, slow-out operation reduces the residence time of the workpiece in the molten zinc, lowering the probability of oxidation. Simultaneously, a protective layer can be applied to the surface of the molten zinc, such as by adding aluminum or rare earth elements, forming a dense oxide film to inhibit zinc ash formation. Furthermore, regularly cleaning zinc ash to prevent it from mixing into the molten zinc is also an effective measure to reduce zinc consumption.
Zinc dross precipitation is equally important. Galvanized trough bridge zinc dross is mainly formed by the reaction of iron ions with zinc, precipitating at the bottom of the zinc pot and reducing the effective components of the molten zinc. Sources of iron ions include residual rust on the workpiece surface, iron salts in the pickling solution, and iron impurities in the flux. Therefore, it is crucial to strengthen control over the pretreatment process, ensuring thorough pickling and rinsing to remove surface iron salts. The flux should be regularly tested for iron ion content and replaced or purified promptly to prevent iron ions from entering the zinc bath. Furthermore, the choice of zinc pot material also affects zinc dross formation. Using a dross-free internal heating zinc plating process can reduce radiation to the zinc bath surface during heating, thus reducing dross formation.
Zinc loss during operation also requires attention. Improper lifting and lowering angles, or excessive speed, can cause zinc molten metal to splash or remain on the workpiece surface, resulting in zinc loss. Therefore, standardized operating procedures are necessary, employing a fast lowering and slow lifting method to ensure smooth immersion and removal of the workpiece from the zinc bath. Simultaneously, splashed and fallen zinc fragments should be promptly recovered to avoid waste. For example, a recovery device can be installed around the zinc pot to collect zinc ingots formed from dripping zinc molten metal, which can then be remelted and reused.
Material selection and equipment improvement are also key to reducing zinc loss. Using high-purity zinc ingots reduces impurity content and zinc dross formation. Adding zinc-nickel alloys or multi-element alloys to the molten zinc refines the coating grains, reduces zinc layer thickness, and improves corrosion resistance. Furthermore, using an internally heated galvanizing pot directly transfers heat to the molten zinc, reducing heat radiation loss, improving thermal efficiency, and slowing the oxidation rate of the molten zinc surface.
Regular maintenance and inspection are equally important. The galvanized trough bridge zinc pot needs regular cleaning to remove zinc dross deposited at the bottom, preventing it from mixing into the molten zinc. Simultaneously, the composition of the molten zinc should be tested, and alloy ratios adjusted promptly to ensure stable performance. Continuous optimization of the production process using tools such as Six Sigma management, identifying and controlling key influencing factors, can further reduce zinc consumption.
