butt-weld in the downhand position

例句：

1. 1. The car was butt-welded together to make it stronger.
   这辆车是用臀部焊接在一起，使其更坚固。
2. 2. The construction workers used butt-welds to join the beams together.
   建筑工人使用臀部焊接来连接梁。
3. 3.The butt-weld was visible through the crack in the wall.
   但头焊接在墙上的裂缝处可见。