Wet Flux Application

The most common flux application method in CAB is by spraying an aqueous suspension. Constantly agitated flux slurries with concentrations of approximately 5-35 % solids are pumped from tanks to fluxing booths. All aluminium surfaces involved in the brazing process are coated with the slurry, resulting in a uniform flux layer. Excess flux slurry is removed with a high-volume air blow the excess is then collected, recycled and reused in the fluxing booth. 

When wet fluxing is used, the heat exchangers are dried prior to brazing in a separate dry-off oven. Product entering the brazing furnace must be completely dry from water introduced via aqueous cleaning or flux slurry coating. 

Aluminium oxide thickness increases with temperature, time at temperature and particularly in the presence of moisture. Oxide formation will affect clad fluidity [78]. There is only a small drop in braze ability when the oxide thickness increases from 40 to 220 A at 5 g/m flux load. However, there is an appreciable drop in clad fluidity as the aluminium 

Since the early 1990s, some users of CAB technology have successfully implemented dry flux application methods. Based on the principles of powder-paint technology, an alternative application technique was introduced in the brazing industry. 

Particularly when dry fluxing is used in combination with thermal degreasing (i.e. evaporative oils and lubricants), the objective is to completely eliminate or significantly reduce the water consumption in the process. 

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