With continuous use, a flux slurry will eventually become contaminated. So far, there is no data that correlates the level of accumulated contaminants with poor brazing. Therefore, it is better to be on the safe side rather than wait till the number of rejects rise due to a contaminated or dirty slurry. It is therefore recommended that a slurry should be dumped when there is visual evidence of contamination. If there is an oil slick floating on top of the slurry in the reservoir or when it is discolored, the slurry should be dumped and replaced with fresh slurry. Alternatively, to avoid misjudging the quality of slurry visually, the slurry could be dumped at regular intervals, especially if the manufacturer knows that the cleanliness of the heat exchangers entering the fluxing booth is not ideal. Experience will dictate how often the slurry should be dumped.
Note however that some heat exchanger manufacturers almost never dump their flux slurries or if they do it might be only once per year. This is only the case when the heat exchangers are very well degreased prior to entering the fluxing booth and efforts are made to avoid undue contamination of the slurry. Simply keeping the cover closed on the slurry tank reservoir will keep out airborne contaminants and lengthen the slurry life.
What to do with the used flux slurry is treated covered under wastewater.
Flux Recovery – Recycle and reuse?
Around the flux slurry preparation station or around the perimeter of the fluxing booth, there will inevitably be some flux on the floor. The inclination is to sweep up this flux and throw it into the flux slurry reservoir or back into the flux drum. This action should be avoided at all costs. Any flux that falls on the floor should be disposed of promptly. The reason is that there are too many contaminants in a manufacturing environment that can affect brazing or cause other damage. Cigarette butts, paper clips, dust, dirt, oil, paper and so on can all have very damaging effects to the flux delivery system and on the brazed products. If the flux is on the floor, dispose of it and do not reuse it.