GB1072578A - Screw thread system - Google Patents

Abstract

1,072,578. Rolling threads; taps. STANDARD PRESSED STEEL CO. June 5, 1964 [June 6, 1963], No. 23472/64. Headings B3M and B3N. [Also in Division F2] Fatigue life of mating screw-threaded components is increased by (a) relieving the pressure flank 19 of the external thread so that no flank contact occurs from the root to at least the pitch line 14 of the internal thread; (b)forming the internal thread with a progressively longer lead than that of the external thread when unloaded; and (c) correcting the true pitch diameterof either or both threads to prevent interference when unloaded. Under load, thread deflection causes the differential lead to be absorbed into full length contact. Features (b) and (c) form the subject-matter of Specification 1,032,814. In -Fig. 1, the internal thread flanks are straight and conventional. The external flanks are symmetrical-involute and the radius 19 of the above-pitch-line relief is four times thread height, the root radius 18 being twice thread height. An asymmetrical external thread, Fig. 2, not shown, has an unloaded flank which is straight and parallel to the adjacent internal flank. In Fig. 4, not shown, both thread forms are conventional but the internal thread has a flank angle of 60 degrees, the external 64-70 degrees. The internal threads are cut by a tap (Fig. 8, not shown), whilst the external threads are rolled by flat dies (Figs. 5 and 6, not shown) or cylindrical dies (Fig. 7, not shown), having ribs complementary to the required external thread profile.