Learn about thermal spray anti-corrosion for bridges
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Thermal spraying technology is a method that uses a heat source to heat spraying materials such as metals, non-metals, and ceramics, atomizing the molten particles, spraying them, and depositing them on the surface of a substrate to form a special surface coating. There are mainly three types of heat sources used for spraying: the first is the arc heat source, the second is the plasma heat source, and the third is the gas heat source. Thus, thermal spraying is divided into arc spraying, plasma spraying, and flame spraying; among these, flame spraying and arc spraying are the main ones used in the field of corrosion prevention. 1 Flame spraying: Flame spraying is a method that uses the combustion of flammable gases as a heat source to melt and atomize metal wires or powders, which are then sprayed onto the surface of the substrate. In Europe and North America, the early thermal spraying methods used for corrosion protection of steel bridges were oxygen-acetylene flame spraying, which achieved excellent corrosion protection results. In 1965, our country applied flame zinc spraying followed by the use of wear-resistant paint to protect the upper decks of the steel girders of the Nanjing Yangtze River Bridge; inspections 13 years later showed good results. However, flame spraying has a low production efficiency, which severely limits the processing time for steel bridges; therefore, anti-corrosion coating is applied only to areas of the steel bridges that remain submerged in water for long periods, to shaded areas, and to the main load-bearing components. If oxygen and acetylene flame spraying is used for the anti-corrosion treatment of the entire bridge, issues such as a conflict between the efficiency of the anti-corrosion process and the project timeline, as well as a conflict between the long-term adhesion of the coating layer and its strength of bond to the surface, may arise. As a result, there are no examples in China of large-scale use of flame spraying for the anti-corrosion treatment of steel bridges. 2 Arc spraying: The principle of arc spraying for corrosion protection involves using arc spraying equipment to heat, melt, atomize two charged metal wires (such as zinc, aluminum, etc.), and then spray them to form a corrosion-resistant coating. This is combined with an organic sealing coating to create a long-lasting composite anti-corrosion layer. The notable features of this coating are: 1) it has a very long service life in terms of corrosion resistance, with a lifespan of over 50 years; moreover, no additional anti-corrosion maintenance is required during its 30-year usage period ； For maintenance 30 years later, it is only necessary to apply a sealing coating over the arc spray coating; there is no need for re-spraying, thus achieving corrosion protection in just one step with a long-lasting effective coating. (2) The arc spray coating exhibits excellent adhesion to the metal substrate; the metal spray coating bonds with the base metal through mechanical interlocking and micrometallurgy, ensuring that the anti-corrosion coating remains intact, does not peel off, and maintains a strong bond under slight bending, impact, or collision. This level of durability is unattainable by any other type of surface anti-corrosion coating. (3) The anti-corrosion principle of arc spraying zinc and aluminum coatings is cathodic protection; in a corrosive environment, even if the protective coating is partially damaged, it still functions by sacrificing itself to protect the steel substrate. The area ratio of the coating (anode) to the steel substrate (cathode) is ≥1; whereas for zinc-rich coatings, the anode-to-cathode ratio is also
Thermal spray anti-corrosion for bridges essentially means applying a metal coating to the bridge surface to prevent rust. There are mainly two methods: one is flame spraying, which uses the combustion of acetylene and oxygen to generate high temperatures, melting zinc or aluminum wires before spraying them onto the bridge deck. This method works well; for example, it was used on the Nanjing Yangtze River Bridge, and after 13 years, inspections showed that its rust prevention effect remained excellent. However, the downside is that its speed is too slow, which can affect the construction timeline of bridges; therefore, it is generally used only in areas prone to water accumulation and rarely on a large scale. Another method is arc spraying, which is more commonly used and more efficient. It melts two metal wires (such as zinc and aluminum wires) through an arc, and sprays the resulting material directly onto the bridge deck to form a protective layer. This coating is particularly durable and can last for over 50 years, with virtually no maintenance required during the first 30 years. Moreover, it is very firmly attached to the bridge deck, so it doesn’t easily fall off even under impact. What’s most remarkable is that even if the coating is damaged, it can continue to protect the steel beneath from rusting, as if through \"self-sacrifice\". Overall, arc spraying is now the preferred method for bridge anti-corrosion, as it is durable and efficient, and can provide long-term protection for bridges. .