| 摘要 |
The invention pertains to a screw produced by cold rolling, designed to be screwed into plastic material, and having a self tapping thread, the fillets (3) of which are formed, in a sectional view, like a knife blade. The fillet flank surface (6, 8) features an inward curve (5) in its central third and forms an outer thread flank angle ( alpha ) of approximately 30<0 >(between the curve (5) and the crest of thread (27)) as well as an inner thread flank angle ( beta ) (between the curve (5) and the thread root (7)), while the inner thread flank angle ( beta ) in the central portion is substantially equal to or larger than a third of the outer thread flank angle ( alpha ). The invention also relates to a screw, the shank end (34) of which operates as a guide for screwing said screw into a bore (41), while the thread end (32) presents, on the one hand, an end area (36) having a cutting edge (58) for cutting its channel of screw and being oriented askew relative to the radial direction of the screw and, on the other hand, a base line (56) which extends the thread foot edge (60) between a thread flank (49) and the shank jacket (33) and runs in the spiral direction of the screw (32) according to an angle ( beta ) substantially deviating from 90<0>, while the cutting edge (48) extends into the crest (40) of thread. |
