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Fidrovska N. M., Pisartsov O. S., Nesterenko V. V.
Hoisting and transport equipment, 2020, №1(62)
Current technologies require more and more new standards for the reliability and durability of hoisting ropes. When choosing the design of the rope it is necessary to consider the conditions in which they will be operated and make calculations based on these conditions. The current standard-based method of calculating the ropes does not reflect actual rope operating conditions and does not ensure the required durability. The calculations provided in the course books and reference guides underestimate the impact of the geometric and elastic parameters of the rope sheaves on the durability of the rope. The rope is selected only based on the conditions on extension, while it has been experimentally proved that the wire breakage occurs precisely in most cases when the rope passes through the sheave.
Considering the forces that arise when a rope is rolled on a pulley, the dependence of the tension of the rope wire on the transition point is determined, depending on the radius of the pulley, and the angle of the wire twist. When the rope runs on a pulley, the elongation of the wire on the convex side of the rope, depending on the friction forces, will be distributed to the compression, side on the concave side of the rope. This elongation changes the axial force in the wire.
To ensure the absence of wear of the rope and the sheave, at the point of the rope coming off the sheave, a mathematical relationship has been obtained for the maximum allowable deflection angle of a rope coming off the sheave. The maximum allowable rotation angle of the rope at the point of its detachment from the surface of the sheave has been determined based on the contact of the rope with the sheave rim and prevention of the rope fracture along the edge of the groove rim.
The expansion angle of the sheave groove is determined considering the reduction the torsion of the rope when it is deviated, and its amount has a very significant effect on the durability of the rope. The thesis contains the analysis of the influence of the expansion angle of the sheave groove on the allowable deflection angle of the rope coming off the sheave.
Due to the inflexibility of the rope and the fact that its curvature in the zone of winding on the sheave does not change instantly, but with a certain terminal speed, when the rope winds on the sheave, the contact of the rope does not occur along the entire length of the groove. By applying the law of changing the load of a bent rope, taking into account the frictional force between the sheave and the rope, a formula has been obtained to determine the angle at which the rope comes off the sheave. This provides a more truthful overview of the load of the rope when bent on the sheave.
crane, hoisting mechanism, rope, rope sheave, contact stresses, deflection angle of a rope, durability of rope