Capillary Gap Action in Soldering
Liquid filler metal is drawn into tight joint gaps by surface tension, allowing complete wetting and a metallurgical bond.
Physicochemical mechanism of action
Liquid filler metal is drawn into tight joint gaps by surface tension. These tensions arise from the tendency to reduce surface water and minimize surface area. This causes the filler metal to move into gaps or cracks, regardless of gravity.
Metallurgical relevance & risks in brazing
Capillary action is crucial for complete wetting and a metallurgical bond between workpieces. Without it, joint surfaces may be incompletely covered, leading to voids or poor mechanical properties. However, excessive filler metal can penetrate tight gaps and narrow the joint, causing stress and potential cracking.
Workshop practice & instructions
To optimize capillary action, the amount of filler metal should be precisely controlled. Too much can cause joint constriction and stress, while too little prevents complete penetration. Recommended filler metal amounts vary by material and joint type, but generally range from 10% to 25% of the rod diameter.