In modern industrial production, hot-dip galvanised steel coils are indispensable in many areas due to their excellent corrosion resistance and processing properties. However, different application scenarios place different requirements on the surface treatment of hot-dip galvanised steel coils. This paper collects some information to analyse the common types of surface treatment of hot-dip galvanised steel coils and their characteristics, in order to provide a reference for selecting the appropriate surface treatment process.
No treatment
Without chemical passivation, oiling and coating of fingerprint-resistant film and other surface treatments, this type of product is susceptible to surface defects such as white rust, scratches and friction marks during handling, storage and use. This type of surface reduces the stress of subsequent degreasing and cleaning and reduces energy consumption and carbon emissions.
Oil Only
This surface treatment reduces the development of white rust on the surface of the product during transport and storage, and the rust preventive oil applied is not generally used as a rolling oil or stamping lubricant for subsequent processing. Oiling is the most common basic surface treatment, with good versatility and adaptability, but the protection is obviously not as good as subsequent surface treatments with a skin film.
Chromate passivation and chrome-free passivation (organic)
This surface treatment reduces the development of white rust on the surface of the product during transport and storage. In the case of chromium-free passivation, hexavalent chromium, which is harmful to human health, is limited in the passivated film (in accordance with the RoHS directive). The passivation film also reduces the friction between the material and the mould and has a certain lubricating ability, although the main purpose is still corrosion protection and lubrication is only an incidental property.
Chromate passivation + oiling and Chrome-free passivation (organic) + oiling
This surface treatment further reduces the development of white rust on the surface of the product during transport and storage. In the case of chromium-free passivation, hexavalent chromium, which is harmful to human health, is limited in the passivation film (in accordance with the RoHS directive). Re-oiling of the passivated film is commonly used for exporting overseas orders, especially in South East Asia, and is a very effective method of preventing corrosion from shipping in the tropics.
Chrome Free Fingerprint Resistant
This surface treatment reduces the development of white rust on the surface of the product during transport and storage, while the fingerprint-resistant film improves the resistance to perspiration stains on the surface of electronic or electrical products. Chromium-free fingerprint-resistant coatings limit hexavalent chromium, a substance that is harmful to human health (RoHS compliant). Fingerprint-resistant coatings are commonly used in the manufacture of home appliances to prevent corrosion of parts caused by sweaty fingers during assembly and maintenance use. Fingerprint-resistant films also provide some press lubrication.
Self-lubricating
This surface treatment can reduce white rust on the surface of the product during transport and storage, while the self-lubricating film can better improve the forming properties of the steel plate. Combining rust prevention and lubrication, it belongs to the category of skin film.
Inorganic Solid Lubrication
The solid lubrication film produced by this surface treatment can improve the forming performance of steel plate. This surface treatment in different manufacturers have different definitions, check some information, found that some manufacturers of inorganic solid lubrication is essentially a pre-phosphate surface treatment. The process has good surface hardness, excellent stamping lubrication, but slightly less rust resistance.
Chrome-free and highly conductive fingerprint resistant
This surface treatment reduces the production of white rust on the surface of the product during transport and storage, and restricts chromium, which is harmful to human health. At the same time, the highly conductive fingerprint-resistant film further improves the grounding performance of the part, thus enhancing the EMC performance (Electromagnetic Compatibility) of the electronic or electrical product. It is usually used in OA products, such as photocopiers and printers.
The above are some common types of surface treatments, in addition, there are some relatively niche surface treatments, such as: chrome-free self-lubrication, chrome-free inorganic passivation, inorganic self-lubrication, easy-to-machine self-lubrication and so on.
In manufacturing, the surface treatment can be applied either when the raw material is purchased or after the part is made, and the choice needs to be analysed in the context of the actual application.
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