Page 96 - QRedition5.0 062021

Quality Requirements Edition 5.0 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 Take a cooled (20 C) sample of the pickling bath solution into a 100 ml measuring flask
0
and top up to the mark with distilled water. 10 ml of this solution ( = 1 ml original ) are to

Explanation be pipetted in an Erlenmeyer flask. After an addition of about 100 ml distilled water, about
Customary emulsifying degreasing is based on the emulsification of oily or greasy residues 5 g Ammoniumsulphate and 5 drops Bromocresol green, titrate with 0.1 n NaOH until the
in blends of hydrocarbons under the addition of surfactants or wetting agents. These are colour changes from orange to blue.
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 ml consumption 0.1 n NaOH x 4.9 = g H SO / l pickling solution
2 4
active or non-ionogenic surfactants. Due to skillful combinations optimal degreasing

results for each, oil, grease and emulsions are achieved by the manufacturers of degreasing Required reagents:
agents. Ammoniumsulphate
Bromocresol green

The multiplicity of combinations in degreasing agents does not permit to name a simple 0.1 g Bromocresol green dissolved in 100 ml ethanol
and in general valid analysis for enamelling works. For controlling the degreasing baths 0.1 n caustic soda solution
manufacturers of degreasing agents issue obligatory processing guidelines.

Because of the complicated control of degreasing baths it is recommendable to register
on a daily basis the m - surface throughput and its degree of fouling. A good general view
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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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