| 摘要 |
1,022,355. Self tapping screws; producing screws; rolling. RESEARCH ENGINEERING & MANUFACTURING Inc. Aug. 31, 1962, No. 33444/62. Headings B3A, B3M and B3N. A self-tapping screw which forms threads in a parent body by a swaging action comprises a driving head at one end, a main shank portion of cylindrical cross-section, and a work entering end having an arcuate polygonal cross-section. A typical cross-section 36 in the arcuate lobular portion has lobes with a radius 37 which is less than half the width of the cross-section. The lobular portion can extend part way along the shank in which case it merges smoothly with the cylindrical portion. A screw (Fig. 1, not shown) is produced by extruding a lobular portion on a headed blank, and rolling the blank between reciprocating dies. One die (Figs. 8 and 9, not shown) includes a portion 44 which is inclined relative to the surface of the remainder of the die and has a smooth lobular surface for producing the lobed effect on the screw. A similar die (Fig. 11, not shown) is used to produce screws having a lobular shank portion. The threads on the work entering portion do not need to be completely formed during the rolling step. |
