Contact Finite Element Analysis Of Hoister's Cracked Shaft Gear In Large Mining Excavator

The mining excavator is widely used in opencast mining. It plays an important role in the national economy. The request of reliability and the security of drive equipments are getting higher and higher accompany with the development tendency in mining excavator to high speed, the heavy load, low noise, high reliability, precise treatment and complication presently. Namely not only requests the equipment to be able to transmit higher power and bigger load, but also the transmission system itself must have the good reliability, thus it can reduces operation cost of mining excavator and enhances the security of equipment in operation process.The lifting mechanism is an important power transmission mechanism of the mining excavator. The gear shaft is the most critical components in the promotion drive process; it often has many breakdowns in the practical work process. The gear shaft in the periodic load, the random load function work status, the crack caused by gear teeth fatigue is the main failure form; the existence of teeth fatigue crack brings the huge latent threat to the security of mining excavator system. The breakdown of lifting mechanism which caused by the shaft gear crack growth and the fracture will affect the security and reliability mining excavator directly, and cut down the production efficiency, and even lead break accident to the teeth or the axis, create heavy loss to the industrial production and the society.According to the features of gear, the gear teeth root has the bending stress, the teeth surface has the contact stress in the power transmission process, between the teeth surface the relative sliding friction will create teeth surface abrasion. Because of the attrition, the main gear failure form is teeth crack and break caused by the bending moment function makes permanent, the surface fatigue peeling caused by the contact stress function and gear fatigue wear caused by friction. The existence of gear crack will causes the uneven gear teeth load in meshing process, increases the teeth root crack stress concentration level, makes the teeth root crack to expand rapidly, finally causes the teeth break accident seriously. Looking from the developing process of gear crack, the failure period is a gradation process from beginning the fatigue crack appears to the end when the teeth break. Therefore, it is necessary to carries on the analysis and the appraisal to the root bending stress of gear teeth and the contact stress of teeth surface in order to avoid the gear teeth break, teeth surface damage and plastic deformation industrial accidents which caused by gear crack.The research on gear system and the analysis of gear teeth damage, monitor and diagnosis have become the hot spot in domestic and abroad at present. Many research concentrate mostly in discussing one kind of new identification and the diagnosis method, the problem on the structural strength analysis, dynamic characteristics analysis, and gear mesh impact and collision in transmission after gear teeth crack exist is to be further explored in the future.This article carries on the method study of early fatigue crack monitoring in view of the gear shaft and makes the static contact analysis and the dynamic contact analysis of lifting mechanism main shaft whether there is crack based on finite element analysis method, when compares change rule of teeth root stress and the strain, and make effective attempt on dynamic contact analysis to compact gear and gear contain crack using finite element analysis software. The results provide reference information relating to gear teeth damage monitor and diagnosis, and this analysis results also have positive significance to solve the problem about gear mesh impact and collision in transmission. The work which mainly does is as follows:Firstly, this paper introduced the significance of gear shaft teeth root bending stress and teeth surface contact stress analysis in mining excavator; The current situation and developing tendencies of gear crack analysis at home and abroad, The finite element method about contact question, as well as the obtained achievement of gear contact analysis.Secondly, a three-dimensional model of helical gear is set up using Pro/E software. Gear modeling is convenient using this method. Using the parameter tool to carry on the modeling of the involutes cylinder gear, this model can generate helical gear in a flexible way.This paper use the Pro/E parameterization characteristic modeling method, carries on the parameterization modeling of the helical gear, has solved the redundant modeling problem of contour highly similar gears, and completes the assembly of lifting mechanism.Thirdly, this paper introduced the elementary theory in contact problem, the numerical solution and the finite element solution of contact problem which most widespread in practical project. Elaborated the principles of several algorithms in the ANSYS contact analysis method, discussed the issue of key contact parameter value and the influence to computation which need pay attention to in the application. This paper also introduced the basic step of ANSYS contact analysis method and how to establish the real constant and some interrelated key words. Based on the discussion about contact algorithm, this paper uses ANSYS's data exchange connection, established the gear contact finite element model exported from Pro/E to the ANSYS finite element analysis software, makes the static contact analysis in two kind of situations separately, according to needs while the shaft gear whether there is a crack in gear teeth. Obtained the situation of stress and strain change in gear teeth a pair of teeth and three pairs contact engaged in meshing; Then drawn up the teeth root bending stress curve along the teeth width direction in change of intact gear teeth and cracked gear teeth using the calculated results, showed may exceptional phenomena of the gear teeth root stress, so this method revealed that it's possible to examine when the gear teeth had a crack.Fourthly, this paper carried on the three-dimensional gear dynamic contact finite element analysis using ANSYS11.0 and completed the dynamic contact analysis separately of the shaft gear whether there is a crack, had demonstrated intuitively and clearly of the gear stress distribution in the situation of gear teeth dynamic engagement conditions in various positions accompanied with time run over. Obtained the change rule of teeth root stress in the gear teeth meshing process. And compared the difference of stress strain between the normal teeth root and teeth root with a crack, this results can provides a effective analysis method and the detection basis for the detection of gear crack.This paper compared the difference of teeth root stress and strain change when there is a gear teeth crack, carried on a beneficial attempt about the method of gear crack detection through finite element analysis. Next step will test this method through the strain measurement technique.