hollowadj.空的；空洞的；凹陷的；虚伪的；(声音)沉闷的n.山谷；洞；窟窿vt.挖空vi.形成空洞adv.完全地；彻底hollow key空心键,空底键,鞍形键

1. It can also get the same result by raising the tube billet's heating temperature and prolonging its heating time.
   适当提高管坯加热温度和延长加热时间，均能显著减少穿孔毛管的外折缺陷，提高金属收得率。