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Electrogalvanized process

The zinc plating process, or electrogalvanizing, is a process in which a layer of zinc is adhered to the steel to protect it against corrosion.
Electrogalvanizing is the most widely used method of electrolytic coating of steel. This coating process guarantees reasonable protection against corrosion and a pleasant appearance of the parts at a low cost. The coating is also used to improve the corrosion properties and persistence of the paint.
It is carried out cold by means of electrolysis, the zinc layer deposited on the pieces ranges from 5 to 25 microns and is used when a lower resistance to corrosion and a lower mechanical strength are required, as well as greater aesthetic qualities. That is why it is used especially in interior applications or processes prior to painting to give it greater protection.
It consists of applying zinc to the steel sheet and pickling it by electrodeposition. Unlike other zinc coatings, such as zinc painting, the zinc plating process is continuous and the thickness of the coating is minimal, and like galvanizing, it involves a series of baths and rinses before the zinc bath.


The phases of the zinc plating process

In the zinc plating process, a layer of zinc is applied using electric current. For this, an electrolytic zinc bath is used with two electrodes: an anode (positive pole) and the steel parts that will be coated with zinc as a cathode (negative pole), to which current is applied.

Dissolved zinc is also included in the bath, and is introduced as a concentrate through metering pumps, adding a conductive salt, usually caustic soda (sodium hydroxide/NaOH), to increase conductivity. Under the influence of electric current, the zinc (Zn2+) dissolved in the bath is reduced at the cathode, and then gradually deposited on the surface of the steel component.
During the zinc plating process, the zinc ions present at the cathode collect electrons and are subsequently deposited on the component as elemental zinc:
Zn2 + + 2e¯ → Zn
The quality of the zinc coating depends on all the phases being carried out correctly. It is very important to degrease and pickle the base material very well to achieve the best finish.
The process is carried out with a cyanide-free and environmentally friendly zinc bath. It is very important that the components to be coated are free of impurities. Once the piece is covered with its zinc layer, it is protected by passivation and sealing additional if required, passivation.
These baths are:
1. Chemical degreasing
2. Acid Pickling
3. Chemical degreasing
4. Alkaline zinc bath
5. Rinse baths
6. Passivated
7. Sealing
Several washes and pre-washes are interspersed between each process so as not to drag or contaminate each of the processes.
To obtain excellent product quality, it is important to ensure that the composition of the many baths remains within the specified range. Even a small difference from the process window can significantly reduce quality and lead to more rejects.
Different coating methods can be used depending on the size of the metal parts to be coated. Good current flow is required during the zinc plating process, so smaller parts are galvanized in drums, while larger parts are static galvanized.


Main advantages of zinc plating

Zinc plating is especially used indoors and in other applications that do not require the durability of galvanizing, because it means:
- An extremely thin and uniform layer of zinc that does not overgrow the piece and does not prevent future assemblies.
- It is an electrolytic layer, it is part of the piece, it does not jump, it can be bent, folded without losing the protection.
- Not a very high economic cost.
- Aesthetic and uniform finish that, together with the final passivation, can achieve different colors.

Uses of the zinc plating process

The zinc plating process can be found in a multitude of applications in our day to day, starting with doors, hinges, screws, tubes, various fittings and a multitude of parts inside electrical appliances, machinery, etc.
  •  Automotive industry: engine parts and components, all screws and fixings, as well as assembly parts
  •  Construction and architecture: doors, windows, fences, bars, parts and interior applications in general that need to be protected against corrosion with a better aesthetic appearance.
  •  Fixing devices: screws, nuts, washers, flanges

Applied standards

  •  - Uniform coating.
  •  - It is suitable for small pieces.
  •  - It is governed by the standards UNE EN 12329 (discontinuous) and PNE-Pr EN 10152 (continuous).