| 摘要 |
1,215,171. Self-tapping screws; making of self-tapping screws. G.K.N. SCREWS & FASTENERS Ltd. 2 Jan., 1969 [9 Jan., 1968], No. 1346/68. Headings B3A and B3N. A self-tapping screw has a point formation 13 which comprises planar piercing faces 15 and drill flutes 16, each drill flute has a leading side wall in the wall of the flute that faces the direction of rotation when the screw is rotated clockwise, and a trailing side wall, the two trailing side walls lying in spaced parallel planes on opposed sides of the point formation, the outer edge of the leading side wall is contiguous with the edge of the adjacent piercing face whereby said outer edge constitutes a shearing and piercing edge when the screw is impacted in the direction of its axis and rotated about its axis. Each shearing and piercing edge comprises two parts 19, 21 which form an intermediate point 20 which is on a larger diameter than the diameter of shank 10. The point formation 13 is manufactured by reducing one end of a cylindrical blank and then using appropriate dies in a pinch pointing operation. The screw thread is then rolled on shank 10. In a modification the reducing operation is eliminated but a rolling operation is needed on the point formation such that a thickened part is formed on each leading edge (see Fig. 6, not shown). |
