| 摘要 |
1288241 Self tapping screws LAMSON & SESSIONS CO 3 Nov 1969 [20 Nov 1968] 53689/69 Headings B3M and B3N [Also in Division F2] A thread forming fastener comprises a body having an inwardly tapering portion at one end of its shank and a thread convolution on the tapered portion, the convolution having a plurality of wide flank portions 20 for forming the flanks of a thread and a plurality of high crest portions 22 for forming the roots of a thread, the wide flank portions having from the root to the crest of the convolution a greater flank width than the high crest portions, the high crest portions having a greater crest height than the wide flank portions, and the high crest and wide flank portions being arranged alternately on the convolution. A similar construction may be used on a lockthreaded fastener (see Division F2). The tapping thread is formed by a rolling die 60, Fig. 7. The die has a plurality of grooves 62, corresponding to a standard thread on a main body portion 60 for forming threads on a cylindrical part 18 of a shaft, or an outwardly sloping portion 68 for continuing the thread convolutions on a tapered portion 12 of the shaft and trapezoidal inserts at the trailing edge 72 for forming the wide flank portions 20. In use the trapezoidal inserts are stated to apply a radially-inwardly directed pressure to portions of the crest of the standard thread formed on the tapered end 12 of fastener 10, thereby reducing the crest height and increasing the flank width thus providing the wide flank portions of the thread. |
