Hot Dip Galvanizing And Fasteners

For people what death means is corrosion for metals and is inevitable. All metals are afraid of corrosion. It is the most insidious enemy that bridges are destroyed, underground pipes become useless, gross domestic productions are wasted and accidents occur, and shiny metals, sometimes internally or externally, face this problem. This much drama is enough, but if we take it from a chemical point of views, what is this corrosion?
Corrosion is a process in which metals return to their natural oxidation state prior to fabrication. Corrosion can mainly be explained as the formation of voltaic or galvanic cells by losing the functional stability of the metal and acting like an anode.
Metals and all materials that can be transformed into metal (e.g.; plastic) serve the purpose that we can distinguish in two main titles. The first aim is the decorative coating which has satisfactory properties in terms of colour, pattern and brightness. Since there is no need and demand, there is limited corrosion resistance. The second one is the functional coating and the functional coating has led to a great war against corrosion.

Examples of functional coatings include galvanizing, phosphating, spray zinc plating and chrome plating. It includes coating types and is in the pursuit of producing products that will provide more durability of 30 to 40 years.
The recorded date of the galvanization method is based on the 1740s. In 1742, a French chemist, P.J. MALOUIN prepare a presentation to the French Royal Academy, he dipped the iron into the molten zinc to show about the dipping coating method. Thirty years later, Luigi GALVANI, the chemist who gave name the galvanizing, discovered more about the electrochemical reactions between metals. In 1829, GALVANI’s research was progressed when FARADAY discovered the zinc as a *sacrificial anode in a salt water with iron pins. Zinc was dissolved and protected iron from corrosion. In 1836 French engineer SOREL took the galvanization process as a research Project and GALVANI’s research continued to progress. When it came to 1850, The British Galvanizing Industry used 10,000 tons of zinc per year to protect the steel. In 1870, the first galvanizing plant was established in the United States. Since then, the galvanization method has been used as a protection in all industries where iron and steel exist. Hot-dip galvanizing is a proven application in numerous applications around the world and has a growing track record of success.
Galvanizing is a process that aims to protect and make stainless iron and steel with zinc coating. The most commonly used zinc coating processes in steel and iron are; hot dip galvanizing, electro galvanizing and zinc spraying. The most popular of these three is the hot-dip galvanizing process. The materials to be coated in the molten zinc at 870 ° F are immersed and the material is metallurgically coated as zinc or zinc iron alloy.

The most critical choice in the design and manufacturing of the fasteners is how to protect the fasteners. Because if the fastener is corroded, it means the whole structure is in danger. It has been a long-lasting and maintenance-free preservative and always advantageous method in the war against corrosion caused by hot dip galvanizing fasteners.
Hot-dip galvanized fasteners, whether in atmospheric conditions or salt water, have always demonstrated maximum corrosion resistance. If iron and steel are left without passivation, that is, if it is left unprotected, the corrosion itself will be exposed as black spots and then as white rust and finally as red rust. A thinly applied layer of zinc forms a layer which retains metal and is an effective protection method despite being highly economical. When the zinc-plated metal forms a layer with hot-dip galvanizing on it, it acts most effectively as a physical and cathodic barrier for the steel underneath.


As with any coating system, this coating system also includes surface cleaning in the first place. The secret to having a long-lasting and durable coating is to prepare the surface for the coating to be made. As long as the steel is not completely cleaned, there is no metallurgical reaction between zinc and steel. So the coating does not stick to the material. To avoid this, the coating preparation process for well-coated fasteners includes a plurality of dip cleaning.
Alkali Cleaning - A hot alkaline solution is often used to remove dirt, paint stains, and organic contaminants such as oil on the metal surface from the metal surface. Epoxies, vinyl, asphalt or welding slag, burrs on the metal surface must be removed by sand blasting or other mechanical means before galvanizing. It is usually the manufacturer’s responsibility to remove these materials.
Acid Pickling - Burr and rust are removed from the steel surface by acidification at room temperature and generally by acidic solution containing hydrochloric acid.
Fluxing- Fluxing is the final surface preparation step in the galvanizing process. Flux treatment removes oxides and prevents the formation of more oxides on the surface of the metal before galvanizing and encourages the bonding of zinc to the steel or iron surface. In the dry galvanizing process, steel or iron materials are immersed in an aqueous solution of zinc ammonium chloride. The material is dried after flux treatment. It is then immersed in molten zinc and cooled. Quality control procedures are then carried out and the material is made suitable for sale and use.

Hot Dip Galvanizing- In this step, the material is placed in perforated metal baskets and completely immersed in a bath containing 98% pure molten zinc. Bath chemistry is determined by the American Association of Tests and Materials A 123. The bath temperature is maintained at about 870 Fahrenheit. The materials to be coated are immersed in the bath for long enough to reach the bath temperature. The materials are slowly removed from the galvanizing bath and clarified from excess zinc. 

The chemical reactions that result in the formation and construction of the hot-dip galvanized coating continue as long as they are removed from the bath as long as these materials are close to bath temperatures. The coated materials are air cooled after removal from the coating bath.
Advantages of hot dip galvanization;

• Provides a homogeneous and uniform coating so that the inner surface and sharp corners of the material can be easily coated,
• Provides superior protection and durability due to its self-repair and high resistance due to a surface which provides cathodic protection.
• Long life, low cost and nature friendly. The materials used in the process can be re-used. Zinc is a 100% recyclable material. 30% of the zinc metal used in the world is recycled every year. In addition, the hot-dip galvanized coating completely disappears when it reaches the end of its useful life. In this issue we talked about corrosion and its effects, and hot dip galvanizing, which is perhaps one of the best methods to prevent corrosion. The process of hot-dip galvanizing still continues to hold the battle with the leading flag in terms of cost and sustainability. You can write to us which method you prefer in your fight against corrosion.
*A metal or alloy which is more electrochemically active is contacted with a more precious metal article to be protected to form a corrosion circuit. In this case, the active metal enters the anode position and is corroded and accelerated over time. Meanwhile, corrosion of the other metal is prevented. The material that is connected to the electric circuit and serves as the anode is called the sacrificial anode.


Date : 27.11.2018