What happens when the joint clearance is too little in brazing?

• A. It increases capillary flow.
• B. It eliminates the need for flux.
• C. It hinders capillary flow.
• D. It improves wetting.

Answer: (C)

Capillary action is what pulls the molten filler metal into the joint during brazing. If the joint clearance is too small, the path for the liquid metal becomes restrictive: there isn’t enough space for the filler to flow between the surfaces, so the capillary flow is greatly hindered. The result is incomplete filling, possible voids, and a weak joint. Flux still helps by removing oxides to promote wetting, but it can’t overcome the physical restriction of an overly tight gap. With the right clearance, wetting and flow occur more readily; too small a gap disrupts that process rather than aiding it.