The Impact of Residual Flux Requirement of Automotive New Energy Cooling System on Fluxing
The traditional aluminum brazing process for radiators for automobiles is complicated, including processes such as cleaning and degreasing, fluxing (spraying), drying, and brazing. No matter whether solid wire or flux-cored wire (brazing ring) is used in the production process of automotive piping system, flux will be used and some internal flux residue will be formed. Especially when using chlorine salt flux, timely cleaning after brazing is essential. In the current environment of strict national environmental protection inspection in China, the cost and risk of using chlorine salt fluxes are becoming increasingly unbearable.
The traditional brazing spraying process has less effect on the flux and production of common radiators. However, for new energy battery cooling systems, the residual flux may dissolve slightly in the coolant and react with the coolant, increasing the conductivity of the coolant, and possibly accelerating corrosion in the case of excessive use. For example, in new energy vehicles, in order to maintain the safety and stability of the battery system, the conductivity of the coolant is usually limited. Some companies require the conductivity of coolant in pure electric systems: <20 μs/cm, and the conductivity of fuel cell vehicle coolant: <8 μs/cm.
When brazing aluminum parts, the use of chloride-containing corrosive flux and excessive spray flux will cause excessive flux residues that are difficult to clean (especially in the internal circulating system of the radiator), which will cause The following risks:
1. After brazing, the flux remaining inside and outside the brazing will dissolve with the coolant in the liquid cooling system to generate K+. The appearance of K+ will increase the system conductivity and reduce the safety performance of the entire vehicle system. The performance and quality surely have a negative impact in hence.
2. If corrosive flux is used, chloride ions will be precipitated during the operation of the brazed joint, which will cause corrosion of the brazed joint, thereby shortening the life and reliability of the brazed joint.
Therefore, in view of the special requirements of the new energy system for the flux residues of the cooling system and the connecting pipeline, we must consider reducing the flux residues from various aspects. E.g,
1. Use environmental friendly flux which is easier to dissolve and clean;
2. Improve the fluxing process. The traditional dipping and spraying processes that cause overcoating (spraying) shall not be applied for the fluxing of heat exchangers used for new energy cooling system. Instead, atomizing spray on components before assembly or online atomizing spray shall be applied.
3. Flux-cored wire is used instead of solid brazing ring + externally flux paste (uneven, excessive), by which the amount of fluxing and thus the residual flux is strictly controlled.
Once the overall flux amount during the manufacturering of heat exchangers are strictly controlled, the total dissolved residual flux in coolant could be well controlled into an acceptable safety level accordingly.
Compared with traditional spraying or even high-pressure spraying, the flux atomization spraying process has the following advantages:
1. Total spraying amount is strictly controllable
2. Atomization particle size is strictly controllable
3. Controllable spray path/field
4. No nozzle clogging, no dripping
5. No moving parts, low failure rate and maintenance
6. Titanium alloy nozzle, no risk of corrosion
