During the production of galvanized welded wire mesh, the uniformity of the zinc layer thickness is a key indicator of its corrosion resistance and service life. If the zinc layer is unevenly distributed, thin areas may corrode preferentially in humid environments, reducing the overall protective capability of the galvanized welded wire mesh. Excessive thickness in areas may cause the zinc layer to crack or detach, also affecting product quality. Therefore, a comprehensive control system is required, from process design to equipment selection, to operating procedures and quality inspection, to ensure zinc layer uniformity.
The stability of the zinc bath composition is fundamental to controlling zinc layer uniformity. In galvanized welded wire mesh production, the zinc bath typically consists of pure zinc with small amounts of elements such as aluminum and magnesium. The addition of aluminum inhibits excessive growth of the zinc-iron alloy layer and improves zinc layer adhesion, while magnesium enhances the zinc layer's corrosion resistance. Excessive impurities in the zinc bath or an imbalance in the element ratio can lead to poor fluidity and uneven zinc layer thickness on the steel wire surface. For example, excessive iron content accelerates corrosion in the zinc pot, producing large amounts of zinc slag. This slag adheres to the surface of the galvanized welded wire mesh, forming bumps or depressions and disrupting the uniformity of the zinc coating. Therefore, during production, the zinc bath composition must be regularly tested, and its stability maintained by adding alloying elements or filtering the slag.
The quality of steel wire pretreatment directly impacts the adhesion of the zinc coating. Before galvanizing, the steel wire surface may harbor residual oil, rust, or scale. These impurities can hinder the bonding of the zinc bath to the substrate, resulting in incomplete zinc coating or uneven thickness. Pretreatment typically includes pickling, water washing, and flux treatment. Pickling removes surface rust, but the acid concentration and immersion time must be controlled to avoid excessive corrosion and increased surface roughness. Water washing thoroughly removes any residual acid to prevent it from entering the zinc bath and contaminating the zinc bath. Flux treatment enhances zinc adhesion by forming a protective film on the steel wire surface. If pretreatment is incomplete, even with optimized process parameters, it will be difficult to ensure uniform zinc coating on the galvanized welded wire mesh.
Precise control of hot-dip galvanizing process parameters is crucial. Molten zinc temperature, immersion time, and wire lifting speed are the three key parameters that influence zinc coating thickness. Excessively high molten zinc temperature reduces its viscosity, resulting in a thinner zinc coating; excessively low temperatures impair the fluidity of the molten zinc, leading to an overly thick coating. The immersion time must be adjusted dynamically based on the wire diameter and molten zinc temperature. Too short a time results in incomplete zinc coating, while too long a time may cause the zinc coating to sag. The wire lifting speed must be aligned with the fluidity of the molten zinc. Too fast a speed can cause the molten zinc to separate from the wire before it fully adheres, while too slow a speed can cause the zinc coating to accumulate due to gravity. During production, the optimal parameter combination must be determined through experimentation, and a strict process card system must be established to ensure consistent operation.
The commissioning and maintenance of air knife equipment is crucial for achieving uniform zinc coatings. The air knife uses high-pressure air to scrape excess molten zinc off the wire surface. The air knife's opening, pressure, and distance from the wire directly influence the thickness of the zinc coating. An excessively large opening or insufficient pressure will result in incomplete zinc removal, resulting in an excessively thick zinc layer. An excessively small opening or excessive pressure may result in excessive zinc removal, resulting in a thinner zinc layer. The distance between the air knife and the steel wire must be maintained within a reasonable range. Too far will result in insufficient zinc return, while too close may cause scratches on the air knife due to wire vibration. Regularly calibrating air knife parameters and cleaning the air knife nozzle can prevent uneven zinc layers caused by equipment wear or blockage.
The effectiveness of the cooling process influences the final appearance of the zinc layer. Galvanized welded wire mesh undergoes a cooling process after leaving the zinc pot. Excessive cooling can increase internal stress in the zinc layer, causing cracking or shedding. Excessive cooling can cause residual zinc fluidity, leading to sagging. A combination of water and air cooling is commonly used in production. Water cooling is used to quickly reduce the wire temperature, followed by air cooling to evenly distribute heat, ensuring a slow solidification of the zinc layer. Furthermore, the cooling water must be replaced regularly to prevent impurities from adhering to the wire surface and affecting the zinc layer quality.
Quality inspection and feedback mechanisms ensure continuous improvement. During production, zinc layer thickness is monitored using a combination of online and offline testing. Online testing uses X-ray fluorescence spectrometers to measure the zinc layer thickness in real time, while offline testing uses magnetic thickness gauges to spot-check samples. This test data is promptly fed back to the production department, who then isolate and analyze any galvanized welded wire mesh with thickness deviations, adjusting process parameters accordingly. Through a continuous quality improvement cycle, the uniformity of the zinc layer thickness can be gradually improved, ensuring that the galvanized welded wire mesh meets the corrosion resistance requirements of various application scenarios.
