Pretreatment

tl_files/slike/vsebina/Predobdelava_I.jpgBefore powder coating, each item is treated with an appropriate process of chemical pre-treatment. The selection of the process depends on the material and the intended use of the product. 

Phosphating is mostly used for iron and iron alloys. By using this technique, a bluish phosphate film is formed; this layer forms an excellent pre-coating base, because it provides excellent paint adhesion and effective corrosion protection. Phosphate is also suitable as a pre-treatment for aluminium products that are not exposed to the weather or chemicals, such as indoor aluminium furniture.

Chromating with sixvalent chromium is indispensable in the coating of aluminium façade elements and windows, doors etc. This technique forms a yellow film on aluminium, which considerably improves corrosion protection and paint adhesion of the material surface. A similar effect can be noticed on zinc steel.

On 1st July 2006 the RoHS directive came into force; it prohibits the use of some dangerous substances, including sixvalent chromium in electric and electronic products. However, a significant part of our products falls into this group; thus, passivation with trivalent chromium was introduced in the pre-treatment process. Passivation forms a colourless film, which significantly improves corrosion protection and paint adhesion on aluminium and aluminium alloys surfaces. In terms of quality it is comparable to chromating with sixvalent chromium.

Chromating and passivation effects on aluminium and aluminium alloys are additionally improved with previous etching.


Materials and pretreatments overwiev:

  Degreasing
Phosphating
Etching
Chromating with Cr6+
Passivation with   Cr3+
Aluminium  o o o
o
o
Steel  o o
x
x x
Galvanized steel
 o x
x o o
Stainless stell
 o x o x x
Al-alloys  o x o o o
Zn-alloys  o x x o o
Mg-alloys  o x x o o
Fe-alloys  o o x x
x

 

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