Page 99 - 20250602 EEA QM Edition 6.0

Quality Requirements Edition 6.0 European Enamel Association

8.2 Examination of metal pre-treatment 8.2.1.2 Determination of acid concentration, sulphuric acid pickling

8.2.1. Control of the sheet steel pre-treatment
Analysis instructions:
8.2.1.1 Testing of degreasing baths
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Take a 10 ml cooled (20 C) sample of the pickling bath solution into a 100 ml
Explanation measuring flask and top up to the mark with distilled water. 10 ml of this solution (= 1
ml original) are to be pipetted in an Erlenmeyer flask. After an addition of about 100 ml
Customary emulsifying degreasing is based on the emulsification of oily or
distilled water, about 5 g Ammonium sulphate and 5 drops Bromocresol green, titrate
greasy residues in blends of hydrocarbons under the addition of surfactants or
with 0.1n NaOH until the colour changes from orange to blue.
wetting agents. These are mostly long catenary organic compounds possessing a
lipophilic (on-grease accumulating) and a hydrophilic (on-water accumulating) part of
a molecule. There are anionic or cationic active or non-ionogenic surfactants. Due to ml consumption 0.1 n NaOH x 4.9 g H2SO4 / l pickling solution
skilful combinations optimal degreasing results for each, oil, grease and emulsions
are achieved by the manufacturers of degreasing agents.
Required reagents:
The multiplicity of combinations in degreasing agents does not permit to name a
Ammonium sulphate
simple and in general valid analysis for enamelling works. For controlling the
degreasing baths manufacturers of degreasing agents issue obligatory processing Bromocresol green
guidelines. 0.1 g Bromocresol green dissolved in 100 ml ethanol

0.1 n caustic soda solution
Because of the complicated control of degreasing baths, it is recommendable to
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register on a daily basis the m - surface throughput and its degree of fouling. A good
general view about the efficiency of degreasing baths results from the quantity of
degreasing agents used, the surface throughput and the degree of fouling.

Quick-test of degreasing baths

In order to check the effectiveness quickly, the following small-scale test should be
carried through several times per day.

A degreased component out of production is to be immersed for about 30 sec. into
the pick- ling bath (e.g. hot, 9 % sulphuric acid) and consequently rinsed with cold
water. The water film on the surface must remain closed and should not pull apart.

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