Capillary attraction in soldering or brazing occurs when the filler metal flows toward the heat.

Capillary attraction in soldering or brazing occurs when the filler metal flows toward the heat.

• A. When the filler metal flows away from the heat.
• B. When the capillary lube is connected to the suction line.
• C. When the filler metal flows toward the heat.
• D. When hot fluid metal rises only to the top of the pipe.

Answer: (C)

Capillary action in soldering and brazing is the tendency of molten filler metal to be drawn into narrow joints by surface tension and good wetting of the surfaces. When heat is applied, the filler metal melts, its viscosity drops, and it wets the metal surfaces more effectively. The capillary forces then pull the liquid into the tiny gaps between parts, directing the flow toward the heated area where the metal is actively molten and can wet and spread along the joint. That wetting-driven pull toward the heated region is what fills and bonds the joint. The other ideas don’t match how capillary action works here: flowing away from the heat isn’t driven by capillary forces in this context; a capillary lubricant and suction line aren’t part of the soldering/brazing process; and hot metal rising to the top of a pipe is a buoyancy/convection effect, not capillary flow into a joint.

Capillary action in soldering and brazing is the tendency of molten filler metal to be drawn into narrow joints by surface tension and good wetting of the surfaces. When heat is applied, the filler metal melts, its viscosity drops, and it wets the metal surfaces more effectively. The capillary forces then pull the liquid into the tiny gaps between parts, directing the flow toward the heated area where the metal is actively molten and can wet and spread along the joint. That wetting-driven pull toward the heated region is what fills and bonds the joint.

The other ideas don’t match how capillary action works here: flowing away from the heat isn’t driven by capillary forces in this context; a capillary lubricant and suction line aren’t part of the soldering/brazing process; and hot metal rising to the top of a pipe is a buoyancy/convection effect, not capillary flow into a joint.