| 摘要 |
<p>A breakable composite drill screw comprises a first shank made of a metal unsusceptible of hardening, a driving head (13) extending from one end of the first shank and engageable with a screw driving tool, a second shank made of another metal susceptible of hardening, the second shank being fixedly adjoined to the other end of the first shank thereby to provide a break zone (16) at said other end, a drill bit (21) formed by cold forging at an end of the second shank, and a continuous thread (23, 23a) formed by thread-rolling to extend around the outer cylindrical peripheries of both the first shank and the second shank with the portion extending from the break zone (16) to the drill bit (21) being hardened or quenched, the shanks being adjoined at their engaging surfaces to each other by a projection-welding technique making use of a welding lug protruding from one or other of the engaging surfaces, and the lug forming the break zone (16).</p> |
