Troubleshooting Fold-line Cracking
折叠处开裂的故障排查
标签：折叠开裂, 退火不足, 折痕过锐, 锤击过猛, 晶界脆化
折叠根部开裂主因有三：退火不足致金属过硬、折痕折得太死（锐角应力集中）、锤击过猛撕裂纤维。排查：若裂在折根，先确认退火是否到位；折弯时用木方做圆角支撑避免死折；锤压改"多遍轻打"而非一锤重压。含杂质多的回收铜更易裂，建议用标准牌号紫铜。
Fold-root cracks come from three causes: under-annealing (metal too hard), an overly sharp crease (stress concentration), or violent hammering that tears fibres. If cracking is at the root, check annealing first; use wood blocks to support a rounded bend, never a dead crease; hammer in many light passes, not one heavy blow. Impure recycled copper cracks more—use standard-grade copper. ---