process for the production of phosphatüberzügen fix on iron and steel

摘要

Phosphate coating of iron and steel prior to other coating processes comprises spraying aq. solns. of alkali metal orthophosphates and/or ammonium o-phos. (amm. o-phos) at pH 4.3-6.5 contg. accelerators and 0.05-1 g/l short-chain alkanolamines and 0.01-1.5 g/l non-ionic wetting agents. The accelerators are pref. nitrites, perborates, bromates, molybdates, hydroxylammonium salts or organic nitrates at 0.05-5 g/l. The phosphating process takes place in two steps, the concn. of o-phos. being increased in the second and the wetting agent level decreased. Improved corrosion protection is achieved cf. prior methods.