Video courtesy of Everwand & Fell GmbH.
Traditionally, brazing and soldering are distinguished from each other in the following manner:
- Flame soldering of aluminium: T < 450 °C
- Flame brazing of aluminium: T > 450 °C
There are some guidelines which should be followed in order to achieve succesful brazing:
- Joint clearances (ideally 0.1 mm, but min. 0.03 mm and max. 0.17 mm)
- Evenly distributed heat from a soft flame (ideally propane with oxygen)
- Appropriate selection of flux and filler material
- Cleanliness
Flame brazing with an AlSi filler has a narrow process window, approximately 20 °C, and there is a need for good temperature control to avoid scrapping of the joined parts due to overheating.
It's paramount that solar absorbers are brazed with an AlSi filler that does not contain zinc. This is because zinc will become the least noble material in the system and as a result the joint may corrode at high temperatures.
