Structure Optimization And Mechnical Performance Experiments Of The Large-Scale Bucket Wheel Machine

A bucket wheel stacker/reclaimer is a kind of large-scale buck material transporting machines. As a large-scale steel structure, not only the stiffness designs and strength designs have to be considered, but also the static and dynamic balance stability, which is more important and is the first things to be considered. It is conservative for designers to compute the experience formula and determine the dimension of the structure by experiences. As result, more materials are used to satisfy the strength and the stiffness but make the structure heavier. The bucket wheel machine is a large-scale steel structure which has a big weight and the method of thicker material and amplified structure dimension and added weight used to solve the problem of the stiffness and the strength problems is limited. A bucket wheel machine's design is different from the former ones and the design experience has not too much helps. The finite element method, a numeric method, can simulate a variety of physic area and helps the steel structure design a lot.As an assistant measure, the finite element method has been applied and developed for years and now it can do not only the static analysis but also the dynamic analysis. Designers can optimize and reanalyze the design scheme by using the finite element method, which can supply the reliable analysis results. The time and cost have been saved.This dissertation is based on the finite element method and the mechanics basic theory, applying the Algor 16, the large finite element software, to simplified the steel structure of the original design. The mechanical performances under several normal and utmost working state have been analyzed by adding the boundary displacements conditions after settling the model. The results suggest that the machine's balance stability is not very reasonable. The range of the upper metal structure gravity center is from 3435 mm to–1010 mm. The radius of the slewing bear is 2484 mm, whose center is in the origin point of the finite element model. The slewing bear is mainly for resisting the press, however, the maximum value of the gravity center in front of the slewing center is bigger than the slewing bear radius, and the moment for resisting turning over is out of the bear design index. The bear's front part is mainly pressed and the backward part is mainly pulled, which is not reasonable and is easy to mar the bear. The difference between the max pulling force and the max pushing force is very big and is not fit for choosing the type of the machine. As a result, the gravity center of the upper metal structure should be adjusted.While the counter weight increases, the stress of the structure will increase too, which make it necessary to strengthen the structure. Though the analysis, it is founded that the strength and stiffness of the boom is big and its weight is 55.7 tons, which can be reduced to adjust the gravity center. The weight of the boom is reduced from 55.7 tons to 39.6 tons, after changing the shape of the boom cross section from box-type to I-type, with the thickness constant. After reanalyzing, the range of the upper structure gravity center is from 2316 mm to–2386 mm, the range of the hydraulic cylinder force is from -97.7 tons to 86.2 tons. The gravity center and hydraulic cylinder force have been improved. Because of the change of the boom, the strength and stiffness of the boom have been reviewed: the maximum stress of the boom is 110.9 MPa in the load caseⅣin which the boom is lifted; The deflection of the front is–29.9 mm and the middle is 25.9 mm, the torsion stiffness of the boom as a single cantilever independently is 0.00044, when the boom is assembled in the whole structure, its torsion stiffness is 0.00016. The strength and stiffness is adequate. The maximum stress of the whole upper structure is 171.2 MPa in the load case I in which the boom is elevated and the stress and displacement of every part is in the safe area. The lower structure is computed by adding the force, which is calculated from the upper structure analysis and the results are reasonable. This optimization design has been applied in the engineering, which not only optimizing the machine's mechanical performance but also saving the materials.In order to inspect the machine's mechanical performance further, the experiment has been done after the installment of the machine. The testing method and the theory calculation are the two ways to solve the engineering problems. Through the testing data, the finite element model was reanalyzed and the more reliable theory calculation can be achieved and help to make correct decisions.Because of limitations of the working conditions, the regular testing method cannot guarantee the precision of the data and cost a lot. For this reason, according to the structure's mechanical performance, the characteristic of the irregular method and the math calculation, a testing scheme has been made. The Static pulling force of the tie rods is calculated by adding a side perturbation to the rods; the machine's dynamic mechanical performance is achieved by supervising the dynamic strain, which is linear to the stress and the stress is linear to the structure load. These methods are easy to be achieved and can be generally applied. The testing results are close to the finite element analysis results and are reliable. Especially, the dynamic stress testing, which distinguished the cutting force from distinguishing the original stress, has an important meaning to the designs and researches on bucket wheel machines.Through the testing data, it can be found that the gravity center in the static and dynamic experiments is behind the counterparts of the finite element analysis calculation, and the two machines'static gravity center is near, which indicates that the testing scheme is reliable. The static and dynamic gravity center has big differences, when the machine is unloaded and the boom of the upper structure is lifted to the limitation. However, it changes around the original point and the magnitude is not very big, so the machine is safe. And it can be judged that the counter weight is smaller than the design value, which is a problem always in the installment of the bucket wheel. The max inertia coefficient is 1.09. The cutting force, which is tested and calculated from the dynamic wheel pressures and the tie rods pulling force testing, is 6.3 tons, smaller than the design value. All data above show that the general performance of the bucket wheel is satisfied and it is safe and reliable in the running process.This dissert shows the important functions of the finite element method in the structure optimizations, which saves the time and money. In the mean time, it also shows the important functions of the experiments in the aspect of reflecting the practical conditions. They help each other, complement each, and should be both applied in the practical engineering problems.