9th January 2025
It’s a hot potato in the industrial coatings world; the debate between Hot Zinc Spray (HZS) and hot dip galvanising (or galvanising) is a persistent one. Both methods involve the application of zinc to protect the metal from corrosion, but they differ significantly in process and outcomes. Understanding these differences, aligned with international standards like EN ISO 14713, is crucial for making an informed choice.
The Science of Zinc Coating
Zinc, a naturally occurring element, is known for its ability to protect metal against corrosion. When applied to steel or iron, zinc acts as a protective barrier. If the underlying metal is exposed, zinc sacrifices itself by corroding first, a process known as cathodic protection. This property is central to both HZS and hot dip galvanising.
Hot Zinc Spray (HZS): Overview and Variants
Hot Zinc Spray, also known as Hot Zinc Thermal Spray or Hot Zinc Arc Spray, involves propelling molten zinc onto a prepared surface. It’s a versatile technique that can be applied to complex structures.
Pros:
- Versatility: HZS can coat a wide range of shapes and sizes.
- Controlled Thickness: The thickness of the zinc layer can be precisely controlled.
- Minimal Distortion: It causes less distortion to the substrate compared to hot dip galvanizing.
Cons:
- Labour-Intensive: Requires more manual labour and expertise.
- Surface Preparation: The substrate needs shot blasting preparation.
Hot Dip Galvanising: Process and Characteristics
Hot dip galvanising involves immersing the metal in a bath of molten zinc. It forms a metallurgical bond with the substrate, creating a robust coating.
Pros:
- Durability: Offers a thick, uniform coating that’s highly durable.
- Comprehensive Coverage: Ensures complete coverage of the item, including recesses and sharp corners.
- Cost-Effective for Large Batches: More economical for large quantities.
Cons:
- Size Limitation: The size of the galvanising bath limits the size of the items that can be coated.
- Potential Distortion: The high temperatures can cause warping, especially in thin materials.
- Fettling: if you are looking for a smooth topcoat this will need to be fettled, meaning taking off some of the galvanize protection you have just paid for.
Comparing the Two Methods
While both processes effectively protect the metal from corrosion, their suitability varies based on project requirements. HZS offers more versatility and precision, making it ideal for complex structures and specific thickness requirements. Hot dip galvanising, on the other hand, is more suited for large batches of smaller items where uniformity and cost-effectiveness are priorities and the end aesthetic finish is not important.
EN ISO 14713 and Its Relevance
EN ISO 14713 is a set of guidelines that provide recommendations for protecting iron and steel against corrosion through zinc coatings. It outlines the principles of selecting an appropriate zinc coating for different environments and ensures that the selected process meets the required durability and quality standards.
Conclusion
Choosing between Hot Zinc Spray and hot dip galvanizing depends on various factors, including the size and complexity of the items, the required thickness of the coating, production scale, and cost considerations. Both methods align with international standards like EN ISO 14713, ensuring that, regardless of the choice, the zinc coating will effectively protect against corrosion. By understanding the pros and cons of each, users can make an informed decision tailored to their specific needs.
At NSP coatings, we prefer to use Hot Zinc Spray to protect our jobs; we find it has a superior finish and results in a much better topcoat and, ultimately, a better finished coated product. We also offer a 60-year guarantee on our specific process, so if you want to find out more, just ask.
