Uniformity Of Zinc Layer Of Galvanized Steel Wire

The uniformity of the zinc layer affects the corrosion resistance and service life of the product, and should be included in the standard for testing and assessment. The coating uniformity η or the average value H and the standard deviation S of the coating thickness can be used to evaluate the uniformity of the coating. In the hot-dip galvanizing process, necessary measures should be taken to improve the uniformity of the galvanized layer.

The quality of the galvanized layer can be evaluated by the weight of the zinc plated on the substrate, the bonding force between the galvanized layer and the substrate, and the uniformity of the coating. The uniformity of the zinc layer is an important quality indicator of the zinc coating. In general, the corrosion always starts at the thinnest part of the zinc layer and spreads around, resulting in rust, broken wires and affecting the service life. For the coating weight and bonding force, each standard has clear regulations, but the uniformity is different. In the 1970s, the ISO standards and the standards of various countries in the world generally stipulated that the copper sulfate test should be used for inspection. By the 1980s, with the exception of Japan and the former Soviet Union, ISO standards and standards around the world no longer adopted this method. Although our country retains this method in some standards such as GB/T15393-94 "steel wire galvanized layer" in the form of "can be carried out by mutual agreement", most of them are no longer adopted. However, the old zinc coating uniformity detection method has been abandoned but no corresponding new methods have been established. In addition, there is no uniform definition and requirement for uniformity, so that some producers do not monitor and detect the uniformity of the coating well. , So as to affect the further improvement of product quality.

For galvanized steel wire, the requirement of coating uniformity is that the coating is uniform in the transverse (radial) cross-section, and the coating of each cross-section of the steel wire in the longitudinal (axial) direction is almost the same. The local zinc layer buildup (commonly known as zinc tumor) on the surface of the steel wire caused by the jitter of the steel wire, the fluctuation of the zinc liquid level, and the surface scum in the plating pot, etc., should be eliminated by correcting the tooling and standardizing the operation. Regardless of these random and irregular zinc layer accumulations, in the case of determining the tooling, stabilization process and the same operating specification, the zinc layer of each section of the steel wire will not have much difference, so you can choose one that is perpendicular to the steel wire and The cross-section of the zinc-free layer is evaluated for the uniformity of the coating.

Measures to improve the uniformity of the steel wire galvanized layer: The reasons for the uneven coating of the steel wire hot dip coating process are: (1) The wire lead is not perpendicular to the zinc liquid surface, so that the plating solution brought out when the steel wire is drawn is under its gravity when it is not solidified. Under the action, it will not be able to drip down evenly along the circumference of the steel wire, causing the coating to deviate from the geometric center of the steel wire after solidification; The difference in the various directions of the steel wire circumference; (3) The zinc liquid level fluctuates and the steel wire jitters, and the zinc liquid level scum sticks to the surface of the steel wire. The zinc scraping and the zinc layer deform unevenly. In severe cases, even the partial pure zinc layer is completely lost.

Measures to be taken: Improve the design and adjust the tooling to ensure that the steel wire positioned by the pressure shaft and the lead roller of the lead frame is perpendicular to the zinc liquid surface. When the pressure shaft is worn, the position of the wire roller must be adjusted in time or the pressure shaft must be rotated to ensure that the steel wire is perpendicular to the liquid surface. The charcoal particles to be wiped should be uniform and firm. Zinc should be added far away from the lead and slowly pushed in. The position of the pressing shaft and the operating surface of the zinc pot should not be too close. It is better to have a tension control device on the production line to prevent the zinc liquid level from fluctuating.