1.Will insufficient cleanliness of the substrate surface affect the shedding of the zinc layer?
Cause: Before galvanizing, residual grease, iron powder, or scale may remain on the steel strip surface. These contaminants prevent direct contact between the zinc solution and the pure steel substrate, forming an isolation layer. This results in poor coating adhesion and easy detachment.
Prevention:
Strengthen the pretreatment process: Ensure that each step, including degreasing, pickling, rinsing, and fluxing, is thorough and effective.
Regularly check and replace the treatment solution to ensure its cleanliness and concentration.
Ensure that the steel strip surface is completely clean and a good fluxing film is formed before entering the zinc bath.
2.What impact does improper control of process parameters have on zinc layer shedding?
Causes:
Improper zinc bath temperature: Excessively high temperatures can result in an excessively thick and porous iron-zinc alloy layer, making it brittle and susceptible to flake-off in powder form when bent or impacted. Excessively low temperatures can affect the fluidity of the zinc bath, leading to uneven coating.
Improper line speed: This affects the reaction time between the steel substrate and the zinc bath.
Improper air knife control: Instability in the air knife's pressure, distance, and angle can lead to uneven zinc coating thickness, resulting in high internal stress at the interface between thick and thin layers and prone to cracking and flake-off.
3.What are the issues with the chemical composition of the steel matrix?
Cause: Excessive levels of elements like silicon (Si) and phosphorus (P) in steel (such as those from high-strength steel) can lead to the "Sandelin effect," causing the iron-zinc alloy layer to grow abnormally, resulting in a gray, dull coating with poor adhesion that easily flakes.
Prevention:
For known "reactive steels," galvanizers may need to adjust their processes, such as lowering the zinc bath temperature, increasing the cooling rate, or using specialized zinc baths like zinc-nickel alloys, to suppress overreaction.
When purchasing steel coils, clarify their chemical composition and suitability for galvanizing.
4.How to prevent it during processing and use?
Excessive Deformation or Bending
Cause: During stamping, bending, or roll forming, if the bend radius is too small, the zinc layer can crack or even peel due to stress exceeding its limit.
Prevention:
Strictly adhere to the processing equipment's recommended processing parameters for galvanized sheet metal, especially the minimum bend radius.
For parts that require significant deformation, choose a more ductile coating (e.g., pure zinc versus alloyed coating).
Severe Mechanical Scratches
Cause: During lifting, transportation, uncoiling, and processing, strong friction with sharp metal components (such as wire rope, equipment edges, and welding slag) can directly cut or scrape the zinc layer.
Prevention:
Use dedicated nylon slings or C-hooks when lifting; avoid using wire rope.
Keep production line rollers and work surfaces clean and free of hard foreign objects.
Handle with care and avoid dragging.
5.How to prevent problems during transportation and storage?
Improper Packaging and Strapping
Cause: Overtightening of the strapping or vibration during transport can cause the strapping to dig into the edges of the coil or sheet, cutting and abrading the zinc layer. Sliding between layers can also cause friction corrosion and scratches.
Prevention:
Use appropriate corner guards or cushioning materials to protect the edges and surface of the coil.
Ensure the strapping is appropriately tight and secure to prevent loosening during transport.
Keep the strapping flat during storage to prevent slippage between layers.