Hitachi Construction Machinery Co., Ltd. (HCM; Taito-ku, Tokyo (headquarters); Kotaro Hirano, President and CEO) and the National Institute for Materials Science (NIMS; Tsukuba, Ibaraki; Kazuhito Hashimoto, President) have jointly developed a method for evaluating the reusability of toothed gears formerly used in construction machinery.
This method can be used to quantitatively evaluate the reusability of used toothed gears based on threshold values during the parts remanufacturing process. Wide adoption of the method is expected to reduce the number of used toothed gears that are scrapped, cutting CO2 emissions and industrial waste and promoting recycling.
HCM has been providing parts remanufacturing services to customers who use construction machinery (e.g., hydraulic cylinders, hydraulic pumps and drive equipment) equipped with genuine HCM parts. HCM collects used parts that need repair or are subject to scheduled replacement. The collected parts are then disassembled, serviced to restore them to a level almost equivalent to new and reinstalled in customers’ machinery with a warranty.
During the parts remanufacturing process, the reusability of certain parts (e.g., reduction devices composed of multiple toothed gears that mesh together) and individual components needs to be assessed to determine the level of processing and repair required. Traditionally, the reusability of used toothed gears has been assessed by estimating their remaining service lives through a visual inspection (e.g., the severity of superficial and frictional damage). However, the development of more objective, quantitative evaluation methods using numerical thresholds had been anticipated.
HCM’s Life Cycle Support Operations Group and Remanufacturing Promotion Division, and NIMS’ Environmental Fatigue Property Group (Research Center for Structural Materials) launched a collaborative research project in 2019 and jointly developed the new reusability evaluation method. The joint group removed and disassembled reduction devices from construction machinery that had operated for different durations. A series of tests were then conducted in which toothed gears were irradiated with x-ray radiation to measure changes in their surface layer microstructures. As a result, the group found correlations between changes in metallographic structures due to accumulated fatigue and changes in residual stress.
Taking this correlation into account, NIMS quantitatively measured changes in surface layer microstructures while HCM compiled data on remanufactured parts. The data they collected was then integrated to determine threshold values for damage to toothed gears. Using these thresholds, it is now feasible to determine whether used toothed gears are reusable. This method is estimated to have the potential to cut the CO2 emissions from a very large hydraulic shovel by 14 tons over its service life by reducing the number of toothed gears scrapped during scheduled parts replacements.
This method has been piloted at HCM plants in Tsuchiura and Hitachinaka since January 2021 and is scheduled for full adoption some time during the 2021 fiscal year. HCM also plans to eventually expand the method to HCM groups overseas that remanufacture construction machinery parts. HCM and NIMS will continue to collaborate to jointly increase the accuracy and speed of the reusability evaluation process through combined use of AI and remanufactured parts databases.
