Content

• Steps
• Method 1 of 4: Hot Dip Galvanized
• Method 2 of 4: Electroplating
• Method 3 of 4: Diffusion Galvanizing
• Method 4 of 4: Spraying
• Tips
• Warnings

Galvanizing or galvanizing steel consists in applying a layer of zinc on its surface to protect the metal from corrosion. For the first time, zinc was used as a structural material during the destruction of Pompeii, but its first use for galvanizing steel (more precisely, iron) dates back to 1742, and this process was patented in 1837. Galvanized steel is used for gutters and downpipes, roof gutters, and external fixings and nails. There are several technologies for galvanizing steel: hot-dip galvanizing, electro-galvanizing, diffusion galvanizing, spray metallization.

Steps

Method 1 of 4: Hot Dip Galvanized

1. 1 Clean the surface from dirt. The surface of the steel must be completely cleaned before proceeding. The cleaning method depends on what exactly needs to be removed from the surface.
   • Use a mild acid, hot alkali, or biological cleaner to remove dirt, grease, oil or paint stains.
   • To remove asphalt, epoxy, vinyl, welding scale, use sandblasting or other abrasive blasting.
2. 2 Pick out the rust. This is done with hydrochloric acid or hot sulfuric acid; acids remove rust and scale.
   • In some cases, abrasive cleaning is sufficient to remove rust, in others a combination of this treatment with acid etching is necessary. Sometimes an abrasive with coarse particles is used, for example, steel is blown with a jet of air with coarse shot.
3. 3 Place the metal in the flux. In this case, use a zinc ammonium chloride solution as the “flux”, which removes the remaining rust and scale and protects the steel from new rust before it is galvanized.
4. 4 Dip the steel into the molten zinc. The molten zinc bath must contain at least 98 percent zinc and be kept at 435-455 degrees Celsius (815-850 degrees Fahrenheit).
   • When steel is immersed in a zinc bath, iron reacts with zinc, and a whole set of alloys is formed in the surface layers, up to pure zinc on the surface itself.
5. 5 Slowly remove the galvanized steel from the molten zinc bath. Most of the excess zinc will drain off the part; what remains can be cleaned with ultrasound or with a centrifuge.
6. 6 Refrigerate galvanized steel. Cooling will stop the galvanizing reaction, which only occurs at elevated temperatures when the steel is immersed in a molten metal bath. There are several ways to cool steel:
   • Immerse the metal in a passivation solution containing potassium hydroxide.
   • Dip the steel into the water.
   • Cool the steel in the air.
7. 7 Examine galvanized steel. After the metal has cooled, check to see if the coating looks good, is not flaking, and is thick enough. There are many ways to test the quality of zinc coating on steel.
   • Standards for hot-dip galvanizing and quality control of the resulting coating can be found in GOST 9.307-89.

Method 2 of 4: Electroplating

1. 1 Prepare the steel in the same way as before for hot dip galvanizing. The metal surface should be cleaned of dirt and rust before starting the galvanizing process.
2. 2 Prepare zinc electrolyte. Typically, this is a zinc sulfate or zinc cyanide solution.
3. 3 Dip the steel into the electrolyte. The reaction of the solution with the metal will begin, as a result of which a layer of zinc will be deposited on the surface of the steel. The longer the steel is in the electrolyte, the thicker the coating will be.
   • Although this method provides better control over the thickness of the coating compared to hot-dip galvanizing, it generally does not allow relatively thick coatings.

Method 3 of 4: Diffusion Galvanizing

1. 1 Prepare the steel in the same way as for other galvanizing methods. Clean the surface with an acid solution or, if necessary, sandblasting and remove any rust.
2. 2 Place the steel in a closed container.
3. 3 Cover the steel tightly with zinc powder.
4. 4 Heat the metal. This will melt the zinc powder and leave a thin coating on the surface of the steel upon cooling.
   • This method is good for coating parts with complex shapes, since the coating is uniform in thickness and in hard-to-reach places. It also works well for relatively small steel parts.

Method 4 of 4: Spraying

1. 1 Prepare the steel in the same way as for other methods. Clean surface from dirt and rust before applying the coating.
2. 2 Spray on a thin coating of molten zinc.
3. 3 Heat the metal to ensure proper adhesion.
   • The zinc coating obtained by this method is more ductile and less susceptible to cracking and peeling, but has less resistance to rust formation under the coating compared to other methods.

Tips

• Galvanized steel can be further protected against corrosion by painting it with paint containing zinc dust. Zinc-based paint can also be used in place of the above galvanizing methods.
• The painting gives the galvanized steel a bright sheen.
• Galvanized steel is highly resistant to corrosion from concrete, lime, aluminum, lead and naturally zinc.
• Galvanization is a type of what is called cathodic protection, when the metal to be protected acts as a cathode in an electrochemical reaction, and the protective metal acts as an anode, that is, the anode material performs protective functions, corroding instead of the base material. Metal coated with a sacrificial anode layer is often referred to as anodized metal.

Warnings

• Galvanized steel is harder to paint than non-galvanized steel.
• Zinc coating on galvanized steel is susceptible to acid and alkali (base) corrosion. Especially harmful in this respect are sulfuric and sulfurous acids, which can form when hydrogen sulfide and sulfur dioxide are mixed with rainwater (acid rain), especially if this water interacts with moss or lichen. Rainwater can also react with the zinc coating to form zinc carbonate.Over time, zinc carbonate becomes brittle and eventually flakes off, causing the inner layers of the coating or even the base metal to corrode.
• Galvanized steel has low resistance to corrosion when in contact with any metal other than aluminum, lead, tin, or zinc. It is especially susceptible to corrosion when interacting with iron, non-galvanized steel, copper, and chlorides and sulfates, which are often found in cement.
• Zinc-coated steel has reduced fatigue resistance because the zinc coating expands significantly when heated and contracts when cooled.