| 摘要 |
1,111,995. Shaft and rod couplings; screwthreads. SANDVIKENS JERNVERKS AKTIEBOLAG. 21 May, 1965 [29 May, 1964], No. 31705/65. Headings F2G, F2Q and F2U. A drill rod coupling comprises a rod element with a multi-start screw-thread having rounded flanks and flattened crests, the centres of curvature of the flanks being at a greater distance from the longitudinal axis of the coupling than are the thread portions which are most remote from the coupling axis. The thread profile is symmetrical, the flank angle (v) (Fig. 1, not shown) being between 90 and 140 degrees, and preferably between 100 and 120 degrees. The flanks may be arcuate or of compound curvature. The bottom portions of the thread may be arcuate or, as shown, 25, 26, flattened, with fillet radii r joining the flattened portions to the flanks, the bottom portions being spaced apart from the inter-engaging flattened crests. The axial lengths of the flattened crests 22, 24 are between 0À05 and 0À4, and preferably between 0À1 and 0À3, times the axial distance between the centres of two adjacent crests. The lead angle is between 5 and 14 degrees, and preferably between 7 and 11 degrees. The thread form is stated to substantially reduce the torque required to unscrew the coupling. The whole of shaded section 31 may be worn away before the thread loses its effectiveness. |
