As manufactured, a non-corrosvie K-Al-F-type flux typically is a mixture of potassium tetra-fluoroaluminate (KAlF4), and also contains potassium penta-fluoroaluminate (K2AlF5). K2AlF5 exists in different modifications: potassium penta-fluoroaluminate hydrate (K2AlF5 · H2O), and hydrate-free (K2AlF5). During the brazing process, the material undergoes essential physico-chemical alterations. While the chief component, KAlF4, is simply heated up, the compound […]
Process related causes The service life of a heat exchanger may be shortened due to corrosion caused by process related events. Some examples are listed below: Excessively high brazing temperature or too long time at temperature will lead to excessive Si diffusion in the core. Si diffuses along grain boundaries and this can increase the […]
In its simplest form, a slurry is held in a reservoir tank and continuously agitated to prevent settling. The slurry is pumped, usually with air-diaphragm pumps to the flux slurry cabinet where the heat exchangers moving on a conveyor are sprayed with the slurry. After spraying, the excess flux slurry is blown off in a […]
NOCOLOK® Sil Flux brazing is a technique, which eliminates the need for clad brazing sheet or conventional Al-Si filler metal. Sil flux brazing uses filler metal generated in-situ to effect brazing. The mechanism for creating this filler metal in-situ is described below: One of the surfaces to be joined is coated with a mixture of […]
The general appearance of NOCOLOK® brazed parts can range from relatively bright to light grey depending on the flux loading and furnace dew-point. When either is increased excessively over recommended levels, the appearance moves towards the grey colour. The flux residue usually can not be seen by the naked eye, however, it is visible under […]
Very often, heat exchanger manufacturers increase the flux loading on components to be brazed to compensate for furnace atmosphere or other process related deficiencies. The flux is an excellent “band-aid” and can be used as such, but only while the true problems are located and rectified. Long term use of higher than recommended flux loads […]
The theoretical amount of flux required to dissolve a 100 Å oxide film is about 0.02 g/m2 (1 Å = 10-10 m = 0,1 nm). For a 400 Å film, still only 0.08 g/m2 flux is required. These do not take into account losses to moisture, oxygen or poisoning of the flux by Mg alloy […]
Based on currently available information, there is no simple cleaning method for flux residues by washing or dissolving – i.e. there is no suitable solvent or chemical solution – without attacking (corroding) the substrate material as well. Mechanical Cleaning Usually, removal of flux residue can only be done by mechanical means. From solid surfaces and […]
Dust and dirt, condensates, lubricants and oils must be thoroughly removed. If the metal work pieces are poorly prepared, the flux will not spread evenly and the flow of filler alloy will be haphazard: it will either not spread properly or will discolour. The consequence would be an incomplete joint. The first step is therefore: […]
When brazing aluminum to stainless steel using: a) NOCOLOK® Flux and Al-Si filler alloys are suitable or b) alternatively CsAlF-Complex flux (melting range between 420 and 480°C) and Zn-Al filler alloys. Regarding a): Brazing of aluminum to stainless steel works both with NOCOLOK® Flux + Al-Si filler alloy and with NOCOLOK® Sil Flux. After the […]