Page 122 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

8.7.2 Valuation of burn-off on enamellings As a result of the firing process, high amounts of iron oxide withdraw the opacifying TiO
from the enamel layer, due to the formation of iron Titanate (needle like crystals). The 2

Definition and cause covering power in the defect area is reduced - as a black line is formed (optical
Burn-offs or burnings are locally limited defects, caused by a too thin applied enamel impairment). In the reach of burnings, corrosive stressed articles do not have a
coating. Due to an excessive oxidation of the metal substrate by firing, the enamel coat complete protection against corrosion. Therefore burnings are to be bound by perfect
processed cutting edges and welding seams.
could not form a regular stratified structure or it has been destroyed by a super saturation

of metal oxides.
Consideration and description

Typical burnings occur on cutting edges or in the reach of welding seams. The thickness of The judgement of the laminar expansion of burnings is performed by naked eye and, as
agreed upon, to be measured out. The dimension of the destroyed surface is to be ex-
the destroyed enamel layer is not measurable with customary types of measuring
pressed in cm .
2
instruments complying to ISO 2178. The determination has to be carried out on cross

sections with the help of a light-microscope.
On difficult accessible containers, equipped with protecting anodes, a measurement of the

The illustrations (Enlargement 50 : 1 resp. 500 : 1) display the result of a poor cutting edge protective current requirement can be an indication for the extent of burnings.
with a direct-on white enamelling.
Test report
To be mentioned in the test report:
kind and origin of the test piece
place and date of the testing
description of defects, number and extent
location of defects on the enamelled article.

Direct-on white enamelling Direct-on white enamelling
on a squeezed-off edge (50 : 1) on a squeezed-off edge (500 : 1)

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