Study On The Calculation Method Of The Bending Stress And Test Technology Of The Rack For The Three Gorges Ship Lift

Rack,especially large module rack is used more and more in great engineering equipment,and the module of rack is continuously roughening,for example,the module of the rack used in the Three Gorges Ship Lift already reaches 62.67mm. However,there is not a existing calculation method that can calculate the tooth root bending stress of rack accurately.The tooth root bending stress of rack is calculated by the current standards, which regard the rack as a involute gear with infinite tooth.When the rack module is less than 50mm, the calculation results are basically correct and practical.However, if the module is larger than 50mm, the current standards is no longer suitable because of lack support of test data.Strictly speaking, the current standards are not suitable to calculate the tooth root bending stress of the large module rack accurately. The investigated results show that, the dangerous area of fatigue and crack initiation will move from surface into subsurface when the gear is hardened,therefore,the calculation of root stress inside the profile is very important.Given all that, the study is of great significance,whether on the accurate calculation method of stress on rack fillet curve and internal the tooth, or on the testing technology of rack root stress.The main researches and conclusions are the following:(1)The line section method,broken-line section method and finite element method are contrasting analyzed.Researches show that the line section can only calculate the maximum stress on the fillet curve. The broken-section method is able to calculate the stress on the fillet curve as well as inside the profile, in addition,the broken-section method has a higher calculation accuracy. The finite element method can clearly obtain the distributed regularities of root bending stress,and so it can serve as an important method to analyse the root stress.(2)The current broken-section mathematical calculation model is revised in this paper.To take the stress concentration of root circle into consideration. A new concept named as stress permeability factor is introduced for the first time,and the bending stress and the compressive stress are calculated by integral method. Based on the broken-line section method mathematical model, the factors which influence the calculation accuracy of the tooth root bending stress are analyzed.(3)The factors influencing the tangent angle that at the point the bending stress is maximum are analyzed. The finite element method is used to analyse the impact of tooth profile angle,fillet radius,module,loading position and applied force.The study results show that tooth profile angle,fillet radius,loading position have an important influence on the tangent angle, module and force are hardly linked to the the tangent angle.(4)The influences of meshing stiffness on load distribution between teeth and the most evil loading point are analyzed.The meshing stiffness under different phase is obtained by the analysis of gear-rack meshing processions. When the pitch error is considered, the most evil loading point of the Three Gorges Ship Lift rack is located at the outer point of single pair tooth contact.(5)The stress concentration factor is determined.Using methods of experiment and similarity theory,the calculation method of stress concentration factor is studied,and the finite element method is used to verify the correctness of the similarity theory(6)The test of tooth root bending stress of the Three Gorges Ship Lift rack is performed.According to the control strategy of revolution speed and load, the teeth that need to be tested are determined.A finite element root bending stress model of rack is presented and analysed, then the root bending stress distribution of rack is carried out and the locations of the resistance strain gauges are determined.(7)The data analysis of the Three Gorges Ship Lift rack root bending stress is completed.Based on the root bending stress distribution,the testing point of available data is determined.The testing data is processed by the least squares method, and then the relationship between the torque and tooth root stress is obtained.By the container analysis of test value, analytic value of broken-line section method and numerical value of finite element method,some results are carried out,and the results indicate that the error between analytic value and test value on the root fillet curve is very small,only 5%,and also,the analytic values inside profile are almost consistent with the numerical values.As a result,the study and test show that the test technology used in this paper is feasible,and the results of test and finite element method both demonstrate that the revised broken-line section model which is put forward in this paper is correct.The main contents and conclusions will lay the important foundations for the further research on bending stress of large module rack.