Soldering aluminium ribs to cooling tubes in motor car radiator - with preliminary conditioning to prevent electrochemical corrosion

Ribs are soldered to cooling tubes in a motor-car radiator by immersing the assembly in a hot (250-300 degrees C) bath contg a mineral oil, if aluminium ribs are used. They must be suitably pretreated and coated with a protective layer contg stearin, the cooling tubes are coated with one or two layers of a low melting alloy and opt with a protective layer contg stearin. Method is improved in that, in order to prevent electrocorrosion between the aluminium ribs and the rubes made from another metal, the aluminium ribs are immersed for 10-30 sec in an aq. bath (40-60 degrees C) contg. 20-40% NaOH 10% ZnCl2 and 5% urea. Then the ribs are washed, dried, and immersed in a trichloroethylen bath contg. 10% of alcohol and 10% of stearin (technical grade) or a bath contg. 25% of stearin, 25% of alcohol (technical grade) and 50% of a mineral oil. The ribs are then coated with a protective layer. The cooling tubes are covered with a low-melting alloy and then with a suspension contg. 13% of stearin (technical grade), 13% of alcohol (96%), 26% of a mineral oil and 48% of a 75:25 to 90:10 Sn-Zn alloy powder. The assembly is then immersed in a hot bath (as described above). The electrochemical corrosion between different metals is prevented. The process is simple and inexpensive.