Film galvanizing

from Wikipedia, the free encyclopedia

Film galvanizing is the application of a metallic zinc coating to iron or steel without the action of heat . A zinc film with at least 96% zinc is applied. A zinc coating prevents the reaction of iron or steel with its environment by means of cathodic protection. The oxidation of the metals is prevented.

properties

After application, the galvanized film forms a matt metallic gray protective layer. During the course of weathering , weather-resistant protective layers made of zinc oxide and basic zinc carbonate form - the protective layer turns dark gray. The protective layer corrodes due to atmospheric influences - the layer thickness of the galvanized film decreases.

Since the zinc compared to more noble metals - z. B. Iron - serves as a sacrificial anode , to a certain extent it can also protect adjacent, bare iron from corrosion, as long as there is a galvanic connection between the two metals.

The durability of the corrosion protection depends on the layer thickness of the galvanized film and the atmospheric conditions.

application

The galvanized film is applied like a paint system by brush, roller or spray application. A stable, dust and grease-free subsurface must be created. A degree of purity according to SA 2.5 (ISO 8501-1) should be guaranteed. The thickness of the layer to be applied depends on the required duration of protection, the exposure to corrosion and the thickness of the zinc layer that is still present in the case of galvanizing. A top coat is not required.

Term of protection

Taking into account the existing layer thickness and the corrosion erosion due to atmospheric influences, the duration of protection of the galvanized film can be derived. Film galvanizing fulfills the requirements according to ISO 12944-6:

  • A layer thickness of two times 60 µm fulfills C4-High, C5-I-Medium and C5-M-Medium.
  • A layer thickness of two times 90 µm meets C5-I-High and C5-M-High.

C5-M-High means: A protection period of more than 15 years, in coastal and offshore areas with a high salt load , buildings with almost constant condensation and with high levels of air pollution.

Compared to other corrosion protection systems

Film galvanizing protects more noble metals in the voltage series by serving as a sacrificial anode to them . The substrate is protected from corrosion until the sacrificial anode is completely corroded or used up. This cathodic protection means that the corrosion protection remains in place even if the zinc surface is slightly damaged. Film galvanizing is therefore to be classified as an active cathodic system.

Compared to film galvanizing, a color system results in poorer protection against corrosion. Both methods are identical in the application, but differ significantly in their protective function. A color system is not to be classified as a cathodic system. Even zinc dust paints usually do not offer any active protection, as the binders used isolate the zinc particles. Through the use of special pigments and binders, paints and varnishes only offer passive barrier protection by preventing the effects of atmospheric influences on the substrate. Passive systems are applied in accordance with standards with thick layers in order to be able to guarantee long-lasting corrosion protection.

Areas of application

The areas of application for film galvanizing are:

  • On new or existing constructions without galvanization.
  • To improve other galvanizing processes.
  • On weathered or damaged structures (galvanized).
  • In areas that have been damaged by welding, cutting or transport.

Web links