Making Fire from Water – The Safe Flame Project


Making fire from water is a seemingly insoluble contradiction – but in 2014 the project will hit the markets.

Instead of propane or acetylene, hydrogen is burnt, which in turn is produced from water in an electrolyzer. Also, the oxygen for the combustion arises from the chemical decomposition. The portable unit requires a standard 220 volt outlet and plenty of water. Therefore, no pressure cylinders for fuel gas and oxygen are required.


In addition, the flame burns much more smoothly and the hot spot is located outside of the burner head. The first tests, brazing aluminum, have been completed successfully.

The Safe Flame project is supported by the EU and actively supported by 11 partners, including EABS (The European Association for Brazing and Soldering).

Solvay supporting EABS technical awareness days for the joining of aluminium and copper piping in the huge global HVACR market. These will commence in January 2014 and run through out the year and will include ALL flames for brazing Al/Al, Al/Cu and Cu/Cu together with appropriate brazing alloys and fluxes.

For further information either contact Solvay or EABS.


A video and more information can be found on


Wastewater Treatment of Flux Slurry

In recent years, the topic of what to do with wastewater from fluxing operations has gained a lot of attention in light of heightened environmental awareness and compliance. Years ago, wastewater from cleaning slurry booths, waste flux slurries etc. were simply diluted and dumped down the drain. Some manufacturers are still following this practice, but it is become less and less common. Today, the heat exchanger manufacturers are faced with what to do with wastewater more and more.

Some manufacturers collect the waste slurries and effluent from cleaning out the fluxing stations and allow the flux to settle out. The water phase is then decanted and collected until a sufficient volume is collected. At that point, a waste disposal company is called in to collect and treat the contaminated water. This is an expensive, but in many cases a necessary option. If the collected water is relatively clean and not contaminated with oil, it may be reused to top up flux slurries. The only problem here is that one must be certain that there are no other contaminants in the wastewater other than flux ions. If there are other contaminants (and there almost certainly will be), tests should be performed to ensure that these will not in any way interfere with the brazing process.

Solvay Fluor also developed a continuous process to reuse and recycle wastewater in a fluxing operation. It is based on the principles described above, only in a continuous fashion:
Lauzon, D.C., Swidersky, H.W., “Methods for Eliminating Wastewater from Flux Slurries in Non-Corrosive Flux Brazing”, VTMS 2001-01-1764, pp 649-654, 2001.

Dumping and Recovery of Flux Slurry

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.

Spilled Flux

Flux powder on the plant floor should be collected by vacuum cleaners equipped with high efficiency particulate air (HEPA) filters, dedicated central vacuum systems or a wet vacuum system. Avoid sweeping and the use of compressed air. Small wet spills may be mopped up. To remove large spills the floor should be hosed down with water. Waste and contaminated water must be disposed of in accordance with local regulations.

Water Quality for Flux Slurry

De-ionized (DI) or reverse osmosis (RO) water is recommended to make up the flux slurries. This is to avoid long-term accumulation of mineral deposits in the flux delivery system that can cause blockage of nozzles and/or inadvertently drop on the heat exchanger. Furthermore, local plant or city water may contain ppm levels of contaminants such as chloride and copper that are detrimental with respect to corrosion performance. Other contaminants may also be present which can affect brazing. Furthermore, to avoid any seasonal variations in water quality, to avoid variations in water quality between manufacturing locations and so on, it is highly recommended that DI or RO water is used to make us flux slurries.

Water analysis recommended

In general, it is difficult to comment on potential effects of trace impurities in the flux slurry water without knowing more details about the character of the contamination. There may be only very little influence on the brazing results even with 1,000 μScm-1 conductivity. However, it is necessary to perform a chemical analysis of the water for further evaluation in each case.

The use of de-ionized water has always been recommended to prevent scale build up in the flux delivery system. Reverse osmosis (RO) water is also used successfully. There are no recommendations on conductivity or maximum hardness values (except those related to the calcium levels as listed below). The only reference Solvay Fluor can provide is the conductivity of the de-ionized water used at our Technical Services and Analytical Department in Hanover, which is below 0.2 μScm-1.

As far as we know, no scientific study was yet conducted to determine water quality requirements for aluminum brazing. In collaboration with Alcan, Solvay Fluor has established guidelines for maximum impurity limits for water quality based on contamination which might interfere with brazing or cause discoloration of the brazed parts:

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For Chloride a maximum of 0.02% is specified (corrosion problems). Based on experiences at some customer locations with post braze odor in the past, Sulfates should be below 0.02%. Phosphates can cause problems with post braze odor too, due to the potential formation of PH3. Silicates are known to interfere with flux activity. Borates and Silicates can cause black spots on post braze flux residue.

Residual hydrocarbons on all aluminum surfaces should be limited to the lowest level possible, due to the potential formation of carbonaceous residue and the long term corrosion problems caused by this residue. The same applies to all other carbon containing trace impurities in the system.

Most of the above information refers to flux and flux slurry contamination. However, it also relates to other additives and chemicals in the process, particularly when those additives cannot be,- or are not-, removed from the fluxed component prior to reaching brazing temperature.