Hot-dip galvanizing and galvanizing
While you as a do-it-yourselfer can galvanize parts yourself, hot-dip galvanizing is only possible for specialist companies. There are big differences between the processes and the resulting zinc layer.
That means hot-dip galvanizing
When it comes to galvanizing, iron and steel are protected from corrosion by a coating of zinc:
- For hot-dip galvanizing, the parts are thoroughly cleaned and then pickled in hydrochloric acid to remove rust and similar deposits.
- After pickling, the acid is rinsed off the iron and bathed in a flux (fluxing). The parts are placed in a mixture of an aqueous solution of zinc chloride and ammonium chloride. A thin zinc coating is already formed. The flux also ensures that the liquid zinc can be better distributed on the part.
- The actual hot-dip galvanizing takes place by dipping the parts in liquid zinc. Since zinc doesn't turn into a liquid until it reaches 419 ° C, this isn't a job you can do at home. In the hobby area, you should refrain from handling large amounts of melt in this temperature range. The process itself is actually simple, the part is immersed and remains in the liquid zinc until it has reached the temperature of the bath.
- Then the part is removed and it cools down. This often results in ridges or points that now have to be removed.
Galvanizing gives steel parts excellent protection against corrosion. There is …
Hot-dip galvanizing does not produce a pure layer of zinc, but various alloys of iron and zinc. Only the surface is pure zinc. Due to the different alloys, this galvanizing creates a surface structure.
Galvanic zinc plating
- The pretreatment is little different from that for hot-dip galvanizing; the parts must also be clean, free of grease and rust.
- For galvanizing, the parts are placed in a zinc tetrolyte, the workpiece must be connected to a cathode (minus). If you have a suitable electrolyte, you can also galvanize in this way in the hobby area.
In contrast to hot-dip galvanizing, the result is a coating made of pure zinc, not alloys. The surface is smooth. Structures are not created in the process.
The sense of galvanizing
- Immediately after galvanizing, the surface is shiny and silvery, after a while it turns gray. Connections are formed with the oxygen and carbon dioxide in the air. The dark gray layer is zinc oxide and zinc carbonate. This development is desirable, while the white rust that forms when the air supply is reduced contains a great deal of zinc hydroxide and is undesirable. For example, in order to prevent white rust from forming in the harsh sea climate, galvanized parts must be additionally protected.
- All methods of galvanizing make use of a special effect that occurs when different precious metals are connected to one another in an electrically conductive manner. In this case, the base metal will corrode and prevent the corrosion of the noble metal. One speaks of a sacrificial anode. Since iron is more noble than zinc, zinc is the sacrificial anode of iron.
- In addition to the greater layer thickness of the zinc and better adhesion, hot-dip galvanizing also has the advantage of that no hydrogen is produced during the coating, as is always the case with galvanic processes is. If you are into electroplating, it is imperative to avoid sparks, as the hydrogen can explode. If you galvanize hardened parts, the hydrogen can also lead to embrittlement.
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