| 摘要 |
565,855. Self-tapping screws. AMERICAN SCREW CO. May 26,1943,No. 8441. Convention date, June 25, 1942. [Class 83 (iii)] Relates to self-tapping screws, more particularly for use in synthetic plastic materials, and consists in forms with the crests of threads following a polygonal contour, in crosssection, with rounded corners. The pilot holes in the plastic material have a diameter equal to the maximum diameter A at the root of the threads. Figs. 1 and 3 show a screw of substantially square cross-section with rounded corners 14, the thread being of V-section 16 and of uniform depth. The thread is formed by rolling between dies shaped either to conform to or to produce the polygonal cross-section. In a modification, the thread is cut on the polygonal blank by ordinary circular dies, resulting in the production of flats 23, Fig. 5, at the middles of the sides of the polygon. In a further form, the core may be circular at the bottom of the thread which varies in depth to give the polygonal effect over the crests. The number of sides may vary. A screw of elliptical crosssection may give the effect of two corners. The leading end of the screw is tapered to facilitate entry, the crests in the tapered part being flattened. |
