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Carbon steel fasteners used for construction are rarely sold raw, without any form of surface treatment. Surface treatment refers to the additional process applied to the surface of fasteners to bring about certain functions. The functions surface treatment may bring vary from rust prevention, wear resistance, temperature resistance, lubricity or merely decorative. CORROSHIELD® fasteners are available with a wide range of coating options for various applications and environment. As the name suggest, our focus is on rust prevention. CORROSHIELD® is the flagship brand of Engineering Edge (S) Pte Ltd in Singapore, and we have been manufacturing corrosion performance fasteners since 1989. In this article, we are pleased to share information about common coating used on smaller diameter construction fasteners.
Corrosion is a permanent deterioration of metal as a result of chemical reactions between it and the surrounding environment. For corrosion to happen, surrounding elements such as oxygen, moisture and impurities are present. Then an electrochemical reaction takes place as metal is returned to its natural state as iron oxide, or rust. Corrosion can happen because of weathering or chemical attacks.
There are international standards that provide guidelines in an attempt to govern the quality standards of coatings that are applied onto fasteners. Some of them are:
However, coating technology is evolving faster than any international standards can pen down. The evolution is moving rapidly towards nanostructures and nanomaterials, or smart factory to accelerate outputs and definitely quantum leaps in corrosion performance.
Today, there are several fastener coatings options available in the market. Too much to name in this single article. Every coating has its function and has a limit to its corrosion performance. Here are some of the more common ones that is used on smaller diameter fasteners.
Electroplating uses the power of electricity to deposit metal on the surface of various types of objects. In the case of fasteners, zinc is commonly deposited onto the surface to provide that protection. Corrosion protection achieved by electro zinc plating is very much dependent on the thickness that is applied. Electro zinc plating is one of the most economical ways of providing fasteners with corrosion protection. However, like all coatings, it has its limitations. Electro zinc plating is more suitable for small diameter fasteners, and one cannot plate too thick without bringing on the dangers of hydrogen embrittlement.
Organic coatings are made up mainly of additives and can be applied onto various surfaces. It can be monolithic consisting of one coat or two or more layers of coatings. Some critical manufacturing control parameters when applying organic coatings onto fasteners are viscosity control, evaporation for film formation, film adhesion and coating durability. The effectiveness of organic coatings is dependent on their chemical inertness and impermeability. The corrosion protection of fasteners provided by organic coatings relies on the capability to form highly resistive pathways between anodic and cathodic sites on the fastener surface.
Mechanical plating, unlike electro plating, does not use electricity or high temperature to plate a fastener surface. Instead, it is done in room temperature and uses kinetic energy to deposit coatings onto the fasteners. The process uses a rotating tumbling barrel to provide the mixing action. The fasteners are mixed with glass beads, water, surface preparation chemicals, promoter chemicals and metal powders within the tumbling barrel. The rotation causes metal powder to impact the surface of the fasteners thereby mechanically depositing the coating onto the surface.
E-Coating is also known as electrodeposition of coatings. It is a combination of Electroplating and Organic Coating mentioned above. In e-coating, the fasteners are dipped into a tank of coating materials like resins, pigments, and additives. These coating materials are mixed in water and circulated, and the fasteners are then immersed into the bath. Electrical currents are passed through the bath and as coating materials become insoluble, they adhere to the surface of the fasteners forming a layer of film.
Selection of fasteners with the correct coating type and grade can be a daunting task for any fastener buyers. This is made worse by the fact that there is very little knowledge and loads of misinformation issued by other fasteners sellers. However, fastener buyers can now positively identify the correct coating to be specified on their fasteners by speaking to Engineering Edge. Let us help you out with our 20 over years of experience in corrosion performance fastener. Our experts are ready to help you out and offer you obligation free information at info@engineering-edge.com.
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