| 摘要 |
1,008,720. Self tapping screws; thread rolling. ILLINOIS WORKS TOOL Inc. April 3, 1962 [April 3, 1961], No. 26199/65. Divided out of 1,008,718. Headings B3M and B3N. A self tapping screw comprises a shank 14 extending from the head 12 and having thread convolutions 20 rolled thereon. The thread convolutions are formed with enlargements 32 which have side portions 36 and 38 which bulge laterally from the flanks 26 and 28 of their respective convolution. The enlargements are equally spaced circumferentially and extend radially beyond the normal height of the convolution crest. The end of the shank may be tapered so that together with the thread form described the passage of the screw is facilitated into an unthreaded aperture. The thread convolutions are rolled on the screw shank by feeding blanks 40 between die blocks 46 and 48 which move parallel relatively to each other rolling the blank therebetween. Each die block is formed with thread rolling grooves 50 and ribs 52 with recesses 62 in the groove bottoms 58 to form the thread described above. |
