PRETREATING AGENT AND PRETREATMENT FOR PAINTING OF STEEL MATERIAL

摘要

PURPOSE:To enable electrodeposition painting having excellent direct adhesion without forming a phosphate film in the stage of cooling a steel material which is brazed at a high temp. by cooling the steel material by a specifically composed aq. soln. CONSTITUTION:A steel material on which a brazing filler metal is set is placed on a tray 2 and is carried by a conveyor 1 into a preheating chamber 5 where the steel material is preheated. The preheated material is fed to a heating furnace 3 into which denatured gas such as decomposed ammonia or gaseous N2 is introduced through a gas conduit 4 and is heated to 1,100-1,150 deg.C to braze the steel material. The brazed steel material is fed into a cooling chamber 6 and is subjected to oxidation-free cooling down to 570-720 deg.C at which the deformation of the material is obviated even by the succeeding quick cooling. The steel material is then dipped in the pretreating agent for painting in a cooling tank 10 underneath a cooling chamber 9 and is thus cooled quickly. The treating liquid is a soln. contg. 1-13% hydroxycarboxylic acid such as malic acid, tartaric acid or the like and 1-13% glycol ether such as diethylene glycol or the like. The steel material removed from the treating liquid permits immediate cation type electrodeposition painting without washing.