Construction of large centrifugal separator drums requires threaded connections of individual parts. For example, leak-proof assembly of the separator plates and the drum covers is effected by joining the internal thread of the large stay ring with the top cylindrical part of the SAOG [1] separator drum body. Large square of trapezoidal threads with the following specifications: pitch S = 12 ram, spiral height h = 6 ram, average diameter dav = 400-600 mm, threaded angle = 30 ~ and curvature radius of the chamber at the thread root r~ = 0.25 mm are usually used for threaded connections of drum parts.Drum parts have been destroyed during separator operation due to stress concentration in the thread [2]. The accepted method for strength design of centrifugal separator drums [3] does not consider stress concentration in threaded parts of the drum.The problems of stress concentration in threaded joints with standard small thread as a function of s/r 1 are examined in detail in [2].This work was carried out to investigate stress concentration coefficients in ring internal thread connections with the cylindrical body of separator drums as a function of various factors, arising during operation.Leading on the threaded connection is axisymmetricaL We will, therefore, examine the equilibrium of one spiral threaded on the internal surface of the top cylindrical part of the drum body (Fig. 1).In this case, the problem of peripheral stress distribution is reduced to the surface contact problem of the elasticity theory. We select a coordinate system x-y in plane z. The origin of this system is placed on the root periphery in the center of the chamfer (radius rl) between thethread spiral and the root.We assume that functionconformally represents the thread profile section including the spiral and the root over half-surface ~. Using the technique developed in [4], we determine the stress function as two complex potentials: g, mm A 8 Fig. 1. Design sketch for a thread spiral.
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