Because of the lower rock fragmentation efficiency and defective geometrical shape of chisel bit , sweden has replaced chisel bit with taper connecting cross chisel bit and button bit since the mid - seventies 因一字形釬頭破巖效率低和幾何形狀結(jié)構(gòu)缺陷等問(wèn)題,瑞典從70年代中期就用錐體連接的十字和球齒釬頭取代了一字形釬頭。