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7.3 Cleaning and care of galvanised surfaces
Excerpt from DIN EN ISO 1461: "Zinc coatings on steel using hot-dip galvanising"
"The main purpose of the zinc coating is to protect the iron and steel material lying
underneath from corrosion. Considerations of aesthetics and decorative properties
should take second priority.... It should be observed that "roughness" and "smooth"
are relative terms and the roughness of piece galvanised coatings can differ from
continuous hot-dipped galvanised products, as for example continuous hot-dipped
galvanised sheet metal, pipe and wire.
In practice it is not possible to specify a definition for the uniformity and the surface
qualities of zinc coatings. The occurrence of dark or light areas (e.g. lattice pattern
or dark-grey areas) or a slight surface unevenness is no reason for rejection. The
formation of (white or dark) corrosion products, mainly consisting of zinc oxide
(occurring from storage in damp conditions after the hot-dip galvanising), is no
reason for rejection as long as the required minimum thickness value of the zinc
coating is still present.
For touch-up work: "The sum of the areas without coating that must be touched-up
must not exceed 0.5% of the total surface of a single part. A single area without
coating must not exceed an area of 10 cm
The touch-up work should be done through thermal spraying with zinc (e.g. ISO
2063) or through a suitable zinc powder coating, where the zinc dust pigment must
comply with ISO 3549 within the practical limits of such systems, or using suitable
zinc-flake coating or zinc paste. .. A sufficient corrosion protection must be ensured
on the touched-up areas." The touch-up work must always be at least 100 µm thick.
Excerpt from GSB ST 663: Visual assessment of the surface:
Source: Quality and inspection regulations for industrial hot-dip galvanising, part 663:
"International quality guidelines for part coating on steel and hot-dipped galvanised steel"
"The assessment of the decorative appearance of the surface in regards to
uniformity of colour and structure must be done without auxiliary aids; for external
parts at a distance of at least 5 m, for interior parts at a distance such as at least 3
m vertical with diffused lighting. All parts must basically match in gloss, colour and
structure. Foundation unevenness, for example scratches, grinding marks, corrosion
scars and welding seams have no significance in the assessment of the coating
quality."
Influence factors for discolourations of the surface
Source: Hot-dipped galvanised: Newsletter for users no. 5
The protective effect of the durable hot-dipped galvanising is based on the
formation of cover layers which, due to weathering influences in the course of
weeks or months, occur on the galvanised surface. The cover layers mainly occur
from basic zinc carbonate. If the zinc surface is sprayed with water over an
extended period or if the air access and thus the presence of CO2 insufficient, then
UNI LIFT 6500 - 8000
Operating instruction and documentation
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UNI-LIFT 6500 - 8000
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