Bolts are super important in many industries. They connect different parts in railway building, crane making, ship construction and structural engineering. To make bolts work better and last longer, galvanized coatings are a widely-used and crucial treatment. The two most common galvanized bolt coating methods are hot-dip galvanized and cold galvanized (also known as electro-galvanized). This article explores the key differences between these methods to help you choose the best galvanized bolts for your specific needs.
1. Principle Differences
Hot – dip galvanized bolts are put into molten zinc which is heated between 450 – 500°C. During this process, zinc reacts chemically with the steel surface. This forms a tight and long – lasting zinc – iron alloy layer. This coating is really good at resisting corrosion. It’s perfect for tough environments like coastal areas and industrial sites.
Cold galvanized bolts, on the other hand, get their zinc coating through an electrolytic process at room temperature. A thin layer of zinc is deposited on the bolt surface. This makes the surface smoother and shinier. But this method mainly gives basic corrosion protection. It’s suitable for less corrosive environments.
2. Production Process
The hot dip galvanizing process consists of several steps. First the bolts are given a surface pre-treatment including degreasing, pickling and fluxing to remove oil, rust and oxides. The bolts are then dipped into molten zinc to ensure a strong bond between the zinc and the steel. Once cooled and passivated, the bolts are subjected to rigorous quality checks to comply with industry standards.
In contrast, the cold galvanizing process is simpler. After cleaning, the bolts are immersed in a zinc salt solution, where zinc ions are deposited onto the surface of the bolt by electrolysis. This process produces a thin, uniform coating of zinc with a polished appearance.
3. Coating Thickness
Hot – dip galvanized bolts have a thicker zinc layer. Usually, it’s between 30 and 60 microns. For special uses, it can be up to 100 microns. This thick coating greatly improves corrosion resistance. So the bolts are very durable and great for outdoor or marine environments.
Cold galvanized bolts have a thinner coating, usually between 5 and 15 microns. Although their surface looks better, this thin coating isn’t as good at preventing serious corrosion. So, they are mainly used indoors or in places with low requirements.
4. Appearance
Hot-dip galvanized bolts have a rougher surface with a matte silver-gray color. Minor surface imperfections are common, but these bolts are durable and suitable for large structural projects where functionality matters more than appearance.
Cold-galvanized bolts offer a smooth, shiny finish. They can also be passivated for colored coatings：like green-yellow or white-green. Be more suitable for decorative applications.
5. Adhesion and Durability
Hot-dip galvanized bolts form a strong chemical bond between the zinc and steel, ensuring long-lasting adhesion and durability. They perform well in highly corrosive conditions without compromising connection strength.
Cold-galvanized bolts have weaker adhesion and durability. They’re better for indoor use, where they face minimal exposure to corrosion.
6. Corrosion Resistance
Hot – dip galvanized bolts are really good at resisting corrosion. The zinc coating acts as a physical barrier and also provides electro chemical protection. Even if the coating gets a little damaged a layer of zinc carbonate forms to stop rust from spreading.
Cold galvanized bolts can give basic corrosion protection. They are good for dry indoor environments. But because the zinc layer is thin they are easy to get damaged in wet or chemically corrosive environments.
7. Cost Differences
Hot-dip galvanizing is more expensive due to its complex process and thicker zinc coating.
Cold galvanized bolts are more cost – effective. The production process is simpler and the coating is thinner. They are great for projects with a tight budget and limited exposure to bad environments.
Hot – dip galvanizing is more suitable for environments that need high corrosion resistance. Such as railway construction, highway guardrails, shipbuilding and steel structure projects.
Cold galvanizing is better for applications that focus on appearance. Such as car parts or indoor – used electronic products. It’s very important to choose the right galvanizing type according to your specific needs and the environment where the bolts will be used.
At GloryTrack, we supply bolts and accessories with hot-dip galvanization, including rail fasteners, clamps, and other components. We specialize in manufacturing all types of bolts and can customize them to your specifications. If you’re interested, feel free to reach out!