| 摘要 |
1374628 Self-tapping screw R J EVANS 27 Oct 1971 [9 Nov 1970] 50011/71 Heading B3N [Also in Division F2] A self-locking screw 11 has a displaced or widened thread portion 30 such that as the screw is engaged in a nut 40 whose thread grooves are wider than the screw threads 16 (except for the portion 30) and whose minor thread diameter, prior to insertion of the screw, is less than the diameter across the roots 26 of the screw shank (apart from lead and ramp portions 18, 20 adjacent thread portion 30), material from the crests of the nut thread is displaced into the flank clearance, as at 50, to lock the nut and screw. When the screw is withdrawn the flank 34 of the portion 30 engages and reworks the displaced material 50, forcing it back to the crests of the nut thread, thereby enabling the nut and screw assembler to be used several times. Moreover initially the screw 11 may be self tapping so that when inserted in a suitably bored hole it simultaneously taps the bore of the hole and displaces the material of the crests into the flank. The material is forced back to the crest on withdrawal of the screw. The thread portion 30 may be enlarged as shown at 30 in Fig. 3 or displaced along the axis of the screw as shown at 30A in Fig. 5. Alternatively the angle of the flank 34B of the thread may be such that the flank is less steep and if desired its opposite flank 36B move stays Fig. 6. A further arrangement ensures that the displacement causes material in the groove of the nut to be moved to the crest where its root of the srcew moves it back between a groove of the unit and flank of the screw, Fig. 7 (not shown).In addition the screw may have an enlarged root portion at the outer end which provides additional resistance to the disengagement of the screw and nut, Fig. 8 (not shown). The enlargement of the portion 30 may be of the lower portion only of the thread, Fig. 9 (not shown), or the steepness of the flank may be increased to provide the widened potion, Figs. 11 and 12, not shown.
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