Cost reduction and component design improvement to increase the performance and durability of the exchangers has led the automotive industry to switch from electro-welded to folded tube technology. Due to the brazing of the tube, the amount of flux in contact with the coolant has increased. Process improvements have been carried out in order to decrease drastically the amount of flux used. In this study, the interaction between the residual flux and the coolant was studied in order to assess the impact on the performance of the coolant, especially for corrosion protection. Several experiments were set up in order to characterize the properties of three types of coolant with organic and mineral inhibitors containing flux used in controlled atmosphere brazing. The impact of coolant ageing was also studied by measuring the properties difference between new and worn coolant. The first and second series of experiments showed that there is not evidence of precipitation of the coolant's inhibitor package with the cumulative addition of flux residue, up to 3.0 g flux residue/kg of coolant; the destabilization and subsequent precipitation of the coolant inhibitor package is pH driven. The limit might be found in the range of pH-values of 5.6 to 5.9. The third series of experiments showed: 1. A significant reduction of the silicates concentration caused by the flux residues as the most important factor for depletion, but also a significant depletion even without flux. 2. No significant depletion of organic corrosion inhibitors, which means that perhaps other parameters included in the cooling circuit, other than the presence of flux could be responsible for the depletion reported. 3. Nitrates, Borates and Molybdates do not change in concentration after ageing, which means also that other parameters could be involved for their depletion. 4. The pH changes only slightly, mainly due to the flux additions. This shows the stability of the coolants maybe by the presence of buffer solution. The best way to prevent silicate depletion is the reduction and control to the level of < 2 g/m2 of the flux residues inside the folded tube, which has been already implemented, but further work will be necessary to determine the mechanisms of this phenomena.
Study of the compatibility of the CAB flux and commercial cooling fluids
Untersuchung der Kompatibilität des CAB-Flussmittels und handelsüblicher Kühlflüssigkeiten
2007
11 Seiten, 5 Bilder, 6 Tabellen, 3 Quellen
Aufsatz (Konferenz)
Englisch
Kühlflüssigkeit , Kompatibilität , Flussmittel , Wärmetauscher , Kostensenkung , Automobilindustrie , Rohr , Falzen , Hartlöten , Kältemittel , Korrosionsschutz , Inhibitor (Hemmstoff) , Experiment , Ausscheidung , pH-Wert , Molybdat , Nitrat , Borat
C640/062/2007 Study of the compatibility of the CAB flux and commercial cooling fluids
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