Optimized process control in the anti-corrosive metal pretreatment based on fluoride-containing baths

A method for anti-corrosive treatment of metallic surfaces, in a serial operation, comprising steps of:

• a. contacting in a serial operation a plurality of metallic surfaces of components comprising zinc and/or iron with a passivating aqueous pretreatment solution located in a system tank at a temperature of less than 50° C., the passivating aqueous pretreatment solution comprising one or more water-soluble compounds of the elements zirconium and/or titanium and one or more water-soluble compounds that represent a source for fluoride ions, for a time such that a layer coating of 0.1 mmol/m2 to 0.7 mmol/m2, based on the elements zirconium and/or titanium, results on the metallic surfaces of zinc and/or iron;
• and,
• b. during the anti-corrosive treatment, discarding a portion of the passivating aqueous pretreatment solution of the system tank and replacing said portion with, in sum, at least equal parts by volume of one or more replenishment solutions by addition into the system tank such that concentration of the elements zirconium and/or titanium in total in the passivating aqueous pretreatment solution in the form of water-soluble compounds is maintained at 0.05 mmol/L to less than 0.8 mmol/L, and a molar ratio of a total amount of fluorine in the form of water-soluble compounds that represent a source for fluoride ions to a total amount of the elements zirconium and/or titanium in the form of water-soluble compounds in an added total volume of replenishment solutions is less than the same molar ratio in the passivating aqueous pretreatment solution, but no less than 4.5, and a discarded amount of passivating aqueous pretreatment solution in liters per serially treated square meter of metallic surfaces of zinc and iron exhibits at least a value according to Formula I:
• VW
• =
• z
• E
• -
• 2.4
• 2.8
• ⁢
• ⁢
• mmol
• ⁢
• ⁢
• L
• -
• 1
• -
• c
• B
• Me
• ⁡
• (
• z
• E
• -
• 6
• )
• ·
• 10
• -
• 1
• ⁢
• ⁢
• mmol
• ⁢
• ⁢
• m
• -
• 2
• (
• I
• )
• where
• VW:
• discarded amount of pretreatment solution in L/m2;
• CBMe:
• concentration of zirconium and/or titanium in the pretreatment solution in mmol/L;
• ZE:
• molar ratio of the total amount of fluorine in the form of water-soluble compounds that represent a source for fluoride ions to the total amount of the elements zirconium and/or titanium in the form of water-soluble compounds in the added total volume of replenishment solutions, with the proviso that the following applies:
• z
• E
• <
• 2.8
• ⁢
• ⁢
• mmol
• ⁢
• ⁢
• L
• -
• 1
• c
• B
• Me
• +
• 6.