1. Process Parameter Factors
(1) Uneven temperature field
Large temperature difference inside the furnace, and unsynchronized heat absorption and heat dissipation between the seal strips, fins and separators. This causes some local areas to reach the brazing temperature first, making the brazing filler melt and flow in advance; while other areas lag behind with high viscosity and poor fluidity, eventually resulting in uneven filler flow.
(2) Excessively high temperature / Long holding time
Over-melting of brazing filler metal and sharp drop of surface tension lead to excessive wettability. The brazing filler spreads randomly along the seal strip surface, causes material loss and forms bead accumulation. Meanwhile, base metal erosion and gap distortion occur, further disturbing the flow uniformity of the brazing filler.
(3) Low temperature / insufficient holding time
The brazing filler cannot melt thoroughly with high viscosity and weak capillary force, resulting in incomplete filling, flow interruption and cold solder joints at the seal strips, especially at the corner positions.
(4) Improper heating and cooling rate
Too slow: The liquid brazing filler stays in molten state for a long time, aggravating gravity flow and excessive spreading.Too fast: A large internal and external temperature difference is formed, leading to unsynchronized filler flow.
