Strength testing of retired main hoist ropes of multi-bucket wheel excavators
The paper presents the results of strength testing of hoist ropes which were removed from main hoists of multi-bucket wheel excavators due to loss of their diameter. The important factor was that none of those ropes were removed due to reaching the maximum number of broken wires per existing discarding criteria. All tested ropes were 8-strand with IWRC (independent wire rope core) of either WS (Warrington-Seale) or F (filler) construction and diameter of 42, 60 and 72 mm. The segments were selected for testing such that comparison between ropes with various degrees of deterioration with non-deteriorated rope was feasible. After un-stranding of each rope segment, diameters of all single wires were measured and each wire was then tested for tensile strength, and for torsion (number of twists). Prior to those tests, each wire was identified by its location in strand and layer of strand. The results were then statistically evaluated. The comparison of results for wires of the same diameters allowed to determine the wear distribution in all strands and layers. The main objective of this program was to verify the discarding criteria based on rope diameter loss only, when no other wear symptoms are visible. As a result of the test program described herein, we have defined these criteria as diameter loss of 8% of rope nominal diameter. At such diameter loss, the loss of rope breaking strength in no case has exceeded 15%. The author believes that the presented results are quite novel and the defined discarding criteria will find broad application for heavy-duty hoists installed in strip mining excavators, marine cranes, gantry cranes, etc.