Galvanize iron

Galvanizing of iron and iron alloys is a commonly used method of protecting these parts against corrosion. There are different methods of galvanizing. In this article, you will learn all about these processes, as well as why iron and iron alloys are even galvanized.

What is rust?

To better understand the principle of galvanizing, it is important to grasp the process of rusting. Simply put, base metals quickly lose their electrons, causing rust. The task of a zinc layer on iron consists of two areas. On the one hand, the zinc layer forms a protective layer and the iron component.

The tasks of zinc coating on iron

At the same time zinc oxidizes. Similar to aluminum, a solid oxide layer forms only on the surface. Thus, the iron component is very well protected against corrosion. But if it comes to a mechanical damage of the zinc layer, the zinc layer acts like a sacrificial anode. Although the iron or the iron alloy loses electrodes quickly, the zinc also gives off some of the iron. This significantly slows down the process of corrosion.

The different methods of galvanizing

There are different methods for galvanizing. Some of these differ significantly from each other. The typical methods of galvanizing are:

  • Hot dip galvanizing (discontinuous and continuous galvanizing)
  • Zinc spraying
  • Galvanizing
  • Sherardizing
  • Zinc coatings

Hot dip galvanizing of iron

Individual workpieces are immersed in a zinc melt (the melting point of zinc is around 450 degrees Celsius). Layer thicknesses of 50 to 150 microns are achieved. This is the discontinuous or piece process. This contrasts with the continuous hot-dip galvanizing, most likely to refer to assembly line galvanizing.

Semi-finished products such as sheets are hot-dip galvanized in one (endless) passage. However, depending on the speed, among other things, only zinc layer thicknesses of 5 to 40 microns are achieved, which is why this galvanizing is less efficient and lasting.

The spray-galvanizing of iron

This method of galvanizing is similar to hot dip galvanizing. Zinc is melted in a flame and thrown with compressed air onto the workpiece. Due to the process, a lot of air is included, so prefers pore formation. As a result, spray-galvanized surfaces are very absorbent. When painting a lot of paint is needed.

The galvanic galvanizing of iron

You can also use this procedure at home. As the name suggests, it is an electrolytic process. The workpiece (for example, an iron nail) is pretreated. For this you have to grind the iron. The workpiece must be absolutely clean (grease), which is why you now need to clean the iron.

From a charger, clamp the positive pole on the nail. An aqueous solution with ammonium citrate, ammonium chloride and zinc sulfate is prepared. Now comes the iron part with the positive terminal in the liquid. A zinc plate is connected to the negative terminal and also comes the solution. The charger is now set to 6V.

The sheradizing

The workpieces to be galvanized come together with zinc powder in a drum, which is heated up to 500 degrees. As a result, the zinc combines with the metal of the workpieces - it creates its own phase. The corrosion protection is enormously high, also the mechanical resistance speaks for itself. However, the weldability is limited by the formation of another phase.

The zinc flake coating

Zinc flakes (and partially aluminum flakes) in a dispersion are applied to the parts to be galvanized in a dipping and spinning process. Subsequently, the dispersion is baked at around 180 to 350 degrees Celsius. This method does not produce pore-proof galvanizing, which is why the coating must be provided with additional protection, for example a silicate enamel.

Tips & Tricks

Iron can be processed in a variety of ways, but depending on its shape, it also has limitations, for example when welding iron.

Video Board: Hot Dip Galvanizing- Dipping Process....... in action