Production process of Galvanized Steel
Galvanizing (or galvanization) refers to the procedure of coating steel and iron with a layer of zinc. The process was named after the Italian scientist Luigi Galvani, whose primary field of study was bioelectricity and muscle stimulation by an electric current. In chemistry and physics, galvanism refers to the induction of electrical currents from a chemical reaction.
The most common method of galvanizing steel is called hot dip galvanizing.
First, the steel sheets are cleaned in a caustic solution to remove any dirt. After it is rinsed off, the steel is passed through an acidic solution to strip off mill scale (flakes of iron oxides). The steel is then further cleaned by a flux, a chemical cleaning agent, such as ammonium chloride so that the iron can bond better with the zinc molecules in the next step.
After drying off, steel sheets are passed through a metal bath of molten zinc at temperatures around 840°F (450°C). The iron molecules bond with the zinc on the surface of the steel. Following the quenching of the hot sheets, they are taken back to the atmosphere, where the zinc forms zinc oxides (ZnO) as a result of reacting with oxygen (O2). The zinc oxides then react with the carbon dioxide in the atmosphere (CO2) to form a robust layer of zinc carbonate (ZnCO3) that acts as a shield to corrosion.
The coatings of hot dip galvanizing can vary depending on the purpose of the steel sheet. For example, thinner layers of hot dip galvanized steel are applied to automobile parts where paint is to be applied on top.
Benefits of Galvanized Steel
In the manufacturing industry, corrosion resistance of metal valves, machines, plants and tools is a crucial part. Generally, there are two ways to achieve this. The first one is to have inventory that is made of stainless steel (either austenitic or ferritic). The second one is to use a protection coating on regular steel. Galvanized steel, of course, falls into the second category and is used for its many benefits:
- Lower costs: Compared to stainless steels, the process of galvanizing is more cost-effective and can be performed on already existing and damaged steel parts. If one were to decide for the stainless steel (or different metal) solution, they would have to substitute their inventory. From an economical point of view, galvanized steel is much more beneficial.
- Longevity: Depending on the environment the galvanized metal is exposed to, its life expectancy can be up to 75 years. Additionally, metals that are put through the galvanization process are low maintenance and are therefore less expensive long term.
- More protection: Even when galvanized steel is damaged, the protection holds up. The zinc molecules form zinc carbonates, providing sacrificial protection.
Difference to Boronizing
Although both galvanized and boronized steel form a protective surface layer on the steel, they are quite different. Boronizing (or boriding) is a method of case-hardening and provides superior results in corrosion resistance. Furthermore, galvanization only improves properties of corrosion resistance, whereas boronizing (with BorTec) improves high temperature stability, hardness and many other mechanical properties.
However, galvanizing can be a fit solution for industries that have low demands on steel that do not need anything other than improved corrosion resistance. For every other demand and wishes, you can contact us here and get to know more about our boriding technique with Borocoat®.