| 摘要 |
1494015 Thread-forming screws INDUSTRIAL FASTENERS CORP 28 Oct 1975 [14 Nov 1974 17 Sept 1975] 44378/75 Heading B3N A thread-forming screw is formed by rolling a thread on a blank, such as shown in Figs. 2, 5 and 9, having a plurality, e.g. seven, of flat sides at least on a transition portion 20, Fig. 2, so that flat areas are provided on the thread crest, Fig. 1, and adjacent flat areas intersect to form sharp longitudinal edges 9. In Fig. 1 also the groove root is of constant diameter and the edges 9 raised ends 8. The transition portion 20, Fig. 2 merges along inclined flat surfaces 30, 31... into the shank and the flat sides of the transition portion may be of different lengths so that the ends of the inclined flat surfaces define a broken right-hand, Fig. 5, or left-hand, Fig. 6 (not shown), spiral or are randomly arranged, Fig. 7 (not shown). The pilot end of the screw need not have flat sides and may be "conical", Fig. 9. The tapered screw end may be inclined at an angle of 5-13 degrees to the axis and the inclined flat surfaces 30, 31... may be inclined at a greater angle, e.g. 12 degrees. |
