In addition to standard physical inspection and cleaning maintenance, we suggest that you can minimize flux build up on the interior components and save money at the same time. It is a matter of taking the time to determine the correct amount of flux necessary for your brazing requirements. This is not a difficult process and it can pay dividends over time. S.A. Day’s Technical Sales Representative, Gary Lampka suggests the following:
The Importance of the Proper Coating Weight of Flux
Using the proper amount of flux is important when brazing an aluminum heat exchanger in a controlled atmosphere brazing (CAB) furnace. If there is not enough flux on the parts you may not get proper braze joints. Too much flux & you’re throwing away money as well as possibly contributing to problems in your furnace.
Normally the flux is mixed with water and a little wetting aid and the resultant slurry applied to the heat exchanger either by spraying or dipping. Some manufacturers will use the waterless method of electrostatically spraying the flux onto the core.
The slurry will have a flux concentration of anywhere between 6 – 25% by weight depending on the joint being brazed. Tube to fin brazing (core bake) can be accomplished using concentrations as low as 6%. Generally the rule of thumb is to have 2 grams of dry flux/square meter of core. Tube to header joints generally use higher concentrations.
To determine the coating weight, weigh a core that does not have the headers in place. Put the core through the fluxer. Dry the core & reweigh it. Determine the area of the core. Subtract the weight of the unfluxed core from the weight of the fluxed core. Divide that number by the area of the core to determine the coating weight.
If the coating weight is higher than suggested, you are wasting money because you are using too much flux. Additionally, the excess flux will come off in the braze zone of the furnace causing increased down time for maintenance to remove the build up.
Important things to remember:
- Use the proper flux concentration for the tube to fin & tube to header joints.
After fluxing be sure to blow off excess flux
- Check dry coating weight to be sure that excess flux is not being used.
Once you have established the necessary flux concentration that satisfies the requirements of your particular components, you should begin to see less buildup of flux during your routine maintenance inspections. Although you will most likely not be able to eliminate the number or the timing of your inspections, you may however, find that the actual cleaning will require less time to complete.
Finally, as a manufacturer of our #2805 “Buffalo Flux” for Controlled Atmosphere Brazing (CAB) we work with many furnace operators and we offer the services of our Gary Lampka, S.A. Day’s Technical Sales Representative to assist you, and to answer any questions that you may have. Please note that you do not need to be a current customer to seek our assistance.
For more information visit www.saday.com or simply call us at 888-735-2805.
For more information on CAB Brazing, check out http://www.secowarwick.com/aluminumbrazing.html
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