Assessing the Bearing Capacity of Hot-Metal Crane Ropes Based on Laboratory Thermal Test Data

Abstract

The article presents an approach to assessing the bearing capacity of the steel ropes of hot metal cranes used at metallurgical enterprises. The rope bearing capacity is assessed based on the data of laboratory thermal tests, which are carried out in two ways. According to the first way, the temperature variation pattern over the rope cross-section is analyzed in subjecting the rope to thermal cycling by means of the contact method with the use of thermocouples and by means of remote measurements using an infrared imager. Recommendations regarding the procedure of carrying out rope temperature measurements under the production cycle field conditions are suggested. The second way implies studying the temperature variation pattern over the rope cross section in subjecting it to a short-term heating, which simulates the burst of flame from the ladle in pouring cast iron into the converter. It has been determined that the temperatures of rope core wires and outer wires of external strands may differ from each other by as much as several hundred degrees. It has been shown that ropes having a denser structure are characterized by better heat transfer between the wires and, as a consequence, feature more uniform temperature distribution over the rope cross-section. An experimental time dependence of the temperature gradient was used for estimating the stresses in wires based on a two-component rod-type analysis scheme. The change in the working rope safety margin under thermal cycling conditions was determined taking into account experimental data on the effect of temperature on the steel strength parameters. It has been shown that the real safety margin of a hot rope is essentially lower than its certified value in the rope delivery state. Possible rope failure cases are analyzed, and the hot rope strength criteria are formulated. A procedure for determining the two-parametric region of the permissible rope operating states on the basis of combined numerical and experimental assessments has been proposed. The suggested procedure makes it possible to determine in advance whether or not safe operation of the rope is possible given the existing technology of pouring cast iron into the converter. A general concept of unsafe operating conditions of hot metal crane ropes is given.