| Injector is a key component of diesel engine supplying system. A lot of troubles occur on the injector during service, such as leaking oil, blocking of injector. Leaking-oil of injector would lead to catastrophic accident. Perfect design and accurate machining, suitable surface treatment and appropriate assemble would prevent occurrence of leaking-oil of injectors. In this paper, two typical failed injectors occurring leaking were investigated. Injector1:leaking at thread; Injector2:cracking of oil-hole.Macro and micro fracture morphology of the cracked injector was observed by stereo microscopy and scanning electron microscopy (SEM) to assess failure mechanism and causes. Macrostructure and microstructure of the failed injector was observed by SEM and optical microscope (OPM) to analyze the influence of intrinsic properties of material on the failure of injector. By measuring sizes of important portion of the failed injector, and observing machining modes at important location of the failed injector, and comparing with the unfailed injectors, the influence of the factors of design and machining modes, etc. on the leaking failure was discussed. According to the specific structure of the injector, a new measure method of axial pressure of injector was developed, which makes measurement accuracy improve significantly. The friction coefficient obtained by relationship of axial preloading force and torque. The main factor responsible for leaking of injector2is obtained the stress distribution of injector body in the operating condition by using Finite element analysis (FEA). It is performed to determine the influence of the mechanical factor on the leaking failure of injector.The main results are concluded as follows:1. No crack was found on the leaked injector1, and without obvious plastic deformation after unloading. However, after assembly, the cap of injector was out of roundness at its thread. The axial preloading pressure of the failed injector was much smaller than that of unfailed injector. The failure mode of injector1is deformation of out of roundness on the thread of cap of injector. The hardness of matrix of cap and body of the failed injector is only60～70%of hardness of the unfailed injector. The axial pressure of the injectors is raised by about80%with increasing hardness. The low hardness of cap and body of injector is mainly responsible for the leaking failure injector. 2."White layer", re-cast layer induced by electric-discharge machining (EDM) was found on the surface of the transverse hole of the injector and a lot of radial micro-cracks are present within the re-cast layer. The crack initiated from the interface between the centre hole and the transverse hole. The failure mode is multiple origins and high-cycle fatigue fracture. The FEA results indicate that the crack origin is not situated at the region with the maximum stress. Thepresence of the re-cast layer with many radial cracks induced by EDM is mainly responsible for the failure of injector2. |
