Oval Jib Dynamic Characteristics And Lightweight Design

Nowadays, cranes have been the necessary equipments to realize the material transportation mechanization. Jibs are of key importance as the major loading component. As a result, the jib design has a direct influence in loading capacity, practical applicability and safety and reliability of the crane. And the developing tendency of large-scale and high-speed of crane intensifies the dynamic response of gantry crane in hoisting process.The thesis took the jib of a large-tonne double rotation railway rescue crane as the research target, and explored the dynamic characteristics and light-weight technology of the jib structure. Details are as below:Build a parametric model of a new type symmetrical elliptical section jib and accomplished the Finite Element Analysis (FEA). Linear stress treatment, from the resulting graph can be seen in the contact position is the cause of stress mutation. Goal Driven Optimization module is used for lightweight design. Studied the correlation and sensitivity between the input and output parameters. The results show that: the greatest impact of the stress is the long, short axis of the elliptical section and the bottom plate thickness. The jib weight decreased 27.97%, lightweight design effect is significant.In order to study the three working conditions of telescopic jib railway crane, load hoisting suddenly from the ground, hoisting from hung motionless and uniform hoisting braking, real dynamic property, the theoretical formula of the dynamic load was derived by damping coefficient was introduced into the momentum equilibrium equations. The theoretical formula of the load and the load curve is deduced.Modal analysis gives the jib former sixth-order mode shapes and natural frequencies. Harmonic frequency response analysis gives the graph of amplitude, frequency and phase angle. The results show: in the amplitude plane 2.8Hz and 16.4Hz, in the Swivel plane 2.2Hz and 12.5Hz are the resonance frequency, which corresponds exactly the same of natural frequencies in the modal analysis, also indicates the modal analysis and harmonic response analysis is correct. And the resonance frequencies are analyzed and compared, the results showed that the amplitude plane of the second-order natural frequency is most likely to occur.Giving a method for solving the transient dynamics of the jib, Studied affecting of the ratios of the frequency and the jib load natural frequency on the jib’s maximum stress, and draw a graph of the relationship. Curve reflects the frequency ratio between 0.6 and 1.4, the arm stress is very large and the ratio of 1:00 reach peak. By contrast the resonance and non-resonance case, the results show that:in the resonance range, even if the load amplitude decays rapidly, the jib amplitude will also rise rapidly; and the maximum stress easily exceed the material yield limit.Exponential decay function is used for analogy the jib unloading process. Studied the relationship between the maximum stress, which caused by vibration, and the uninstalling time. And different vibration curves were analyzed. The results showed that: When unloading time spent less than 0.1s, The maximum stress will be greater than the maximum static analysis stress, which may exceed the allowable stress values, and boom may be destruct. Between 0.1-0.3s, stress drop very quickly, and leveling off. Therefore, we should be possible to extend the unload time, reduce vibration.