2 October 2017

Did you know that some sellers of gratings offer their customers “galvanized” products instead of hot-dip galvanized fasteners?  

The information below gives a concept on why it is so important to be aware of the difference and avoid buying such products./strong>

Zinc coating of fasteners instead of hot-dip galvanizing is carried out for two reasons - cost reduction or the lack of technical feasibility for hot-dip galvanizing.

In some cases, this fact is simply kept silent, hoping that the buyer will not notice the difference; in other cases, the client is deliberately misled by telling him that galvanization and hot-dip galvanizing give the same protection against corrosion.
Therefore, we suggest that you figure out the difference between these methods of anti-corrosion protection and why it is necessary to use exclusively hot-dip galvanized hardware for attaching the gratings.
Due to the fact that in the days of the USSR anti-corrosion protection of metal by hot-dip galvanizing was not widespread, today there are frequent cases when consumers mistakenly equate the concepts of galvanization (in common terms “galvanization”) and hot-dip galvanizing. In fact, hot-dip galvanizing and galvanization are completely different processes, giving very different protection against corrosion.

Galvanization - is a method of coating a metal by some other metal using the process of electrolysis. In industry galvanization is used to strengthen the metal surface of products and protect them against environmental influences, such as corrosion. Products are usually galvanized with zinc, copper, chromium, nickel.
Hot-dip galvanizing - is coating a metal (usually iron or steel) with a layer of zinc to protect it from corrosion by immersing the product in a molten zinc bath at a temperature of about 460 °C.

Briefly, the technology of hot-dip galvanizing of fastening elements is as follows. After degreasing, rinsing, etching and re-rinsing, the products in the drum are immersed in a bath (usually ceramic) with molten zinc. The rotation of the drum provides a flow of zinc mass relative to the products to fill all pores and microcracks. The drum is then removed from the bath and spun to remove excess zinc by centrifugation. However, excess zinc still remains on the internal thread (on the nuts), therefore, the internal thread is machined after galvanizing. The lack of coating on the female thread does not affect the corrosion resistance of the joint if the nut is used with a hot-dip galvanized bolt or hairpin. Due to the high reactivity of zinc in relation to iron at temperatures up to 70 °C, zinc itself covers uncoated and damaged parts of the product at a rate of about 2 mm per year. In this case, due to the potential difference between zinc and iron in a natural humid and acidic environment, zinc from external thread of the bolt is transferred to the sections of internal thread of the nut that remained uncoated during the galvanizing process.

Advantages of hot dip galvanizing:
1. Corrosion resistance is 5-7 times higher than galvanized fasteners and is close to the resistance of stainless steel.
2. The coating restores itself on damaged areas.
3. The coating is more resistant to chipping on impact than similar corrosion-resistant polymer paints.

On the photo you can see the degree of corrosion of hardware after being kept for 5 days in solutions of NaCl, HCl, and in water. The first two rows represent ordinary galvanization, the bottom two rows are for hot-dip galvanized products.

This issue is especially relevant in case of using electroplated hardware for attaching hot-dip galvanized metal structures. In this case, despite the excellent protection of the structures themselves, it is the fastenings that after a while become the core of corrosion, spreading it over the entire nearby area.
Thus, we recommend you to be careful when considering commercial offers from unverified suppliers and before purchasing always specify a method of protecting hardware from corrosion, and even better, ask for a quality certificate on hot-dip galvanizing process.
If you need any information or advice on the methods of attaching the grating or options for anti-corrosion protection, you can always contact our managers and technical consultants.

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