Study On The Failure Analysis And Thermal Spray Remanufacturing For Construction Machinery Shaft Parts

Due to the shortage of resources, reduction of product profit, and the inspirationof big potential market, remanufacturing has become an inevitable tendency in thefield of construction machinery. As a kind of high efficient and convenient surfacerepairing technology, thermal spraying is potential for wide application in theremanufacturing for construction machinery.According to this thesis, failure mechanism research of construction machineryparts has been taken on loader, by taking examples of second and third shaft in thegearbox, as well as cross shaft in the driving axle. The result showed that the mainfailure form of construction machinery shaft parts is wear, and the wear process canbeen divided into three periods: friction wear-abrasive wear-adhesive and fatiguewear. The hard abrasive particle in the abrasive wear process is produced in itsfollowing operate process, by the wear dust produced in the friction wear period. Theformation of hard abrasive particle greatly accelerates the wear failure process.Remanufacturing has been carried out on the second shaft, third shaft and crossshaft via HVOF, by utilizing WC-12Co powder, which contains micron size WCparticle. The applied parameters were: C₃H₈（0.75MPa,25L/min）, O2（0.75MPa,250L/min）, N₂（0.6MPa,13L/min,2r/min）, nozzle length（150mm）, spraydistance（265mm）. Surface quality evaluation of the remanufactured coating has beendeveloped via XRD, SEM and microhardness test, et al. The result showed that thecoating mainly consist of WC phase and Co phase, as well as small amount of W₂Cphase; the microhardness of the coating is1107HV_0.1; and the porosity is2.2%; themean tensile strength of the coating is68.12MPa, and the highest tensile strength canreach75.82MPa; and the main fracture mechanism of the coating is intergranularfracture.In order to reduce the thermal spray remanufacturing cost and develop a new kindof engineering coating, carbon nanotube reinforced amorphous Fe alloy compositecoating has been synthesized via Air Plasma Spraying（APS） and the microstructure ofthe coating has been investigated through single splat morphology, as well as fracturemorphology of the coating. The result showed that by the addition of carbon nanotube,amorphous Fe alloy can be strengthened and toughened by the bridging andpulling out mechanisms of carbon nanotube. However, the poor wettability of carbon nanotube caused insufficient bond with amorphous Fe alloy; also the relativeserious erosion of carbon nanotube during plasma spring weakened the fiberreinforcement of carbon nanotube. To solve this problem, more advanced processshould been developed in the future.In order to solve the local repairing problem of construction machinery shaft parts,remanufacturing design has been carried out on the thermal spray frock system. Akind of thermal spray remanufacturing frock and its automatic repair control systemhas been invented, which can make construction machinery shaft parts accomplishlocal, precise and automatic thermal spray remanufacturing process.