The reaction kettle stirring shaft fracture damage cause analysis abnormal happens

Reaction kettle stirring shaft fracture damage cause analysis abnormal happens - 2018 09 - 28 Wang Lisong army yet ( Weihai chemical machinery co. , LTD. ) Abstract: the reaction kettle stirring device, when the design needs to be carried out on the stirring shaft strength calculation, torsional deformation, critical speed, respectively, under the condition of a series of calculation, we can design a meet the requirements of the stirring shaft. But in actual use, found that can occur in meet the design calculation of the stirring shaft fracture phenomenon. In this article, through some case, to appear this kind of problem of stirring shaft is analyzed, put forward the issue to consider in the design in the future, to avoid these problems. Key words: the reaction kettle; Stirring shaft; Fracture; Fatigue 1 preface stirring shaft is the core component in mixing reaction kettle, drive motor power by stirring shaft transmission to the mixing blades, realize the mixing reactor was carried out on the material, the function of the reaction. Found in the actual usage, however, meet the design calculation and checking of the stirring shaft will often appear abnormal damage. 2 problems encountered in the analysis I work with the example of stirring shaft fracture analysis, specific as follows: my company developed 20 cubic polyurethane equipment for a chemical company, need to make through agitator kettle body internal gas to achieve effective concentration, at the same time to make the kettle body catalyst can achieve effective suspension, must have both the role of the mixed reaction at the same time, one of the most critical is to reach the secondary utilization of the gas. Therefore, we select the combination of self-priming blender, stirring shaft with single span shaft structure, supported by sliding at the bottom of the collar. Specific parameters are shown in table 1, structure diagram is shown in figure 1. The equipment in use after six months, the stirring shaft fracture phenomenon. In the stirring shaft fracture after we carefully analyzed, on the diameter of the stirring shaft strength check calculation, because it is a self-priming agitator form, with a hole on the hollow shaft structure of gas-liquid interaction. We are calculated, considering the shaft hole of shaft strength weakened, so appropriate to improve the safety coefficient and so on the theoretical calculation is to meet the design requirements and has certain strength margin. But appears in be used actually four continuous stirring shaft fracture. After the analysis, we found that the stirring shaft broken parts at precisely the imbibition agitator air inlet area, as shown in figure 2. 3 analysis through calculation and analysis, we have eliminated the shaft intensity and material problems. Finally we found that the stirring shaft fracture is caused by fatigue fracture. Because at the bottom of the stirring shaft end float up and down with bearings, bearings for rolling bearing, the bearing for sliding friction, as the typical beam structure, the work, the mixing speed is 260 RPM, add equipment stirring shaft is longer, stirring shaft alignment has certain deviation, self-priming installed on the shaft mixer place opened the vent, you can see by the picture here is weak, easy to produce stress concentration, and the shaft in the process of work, mainly affected by torque, due to the stirring shaft alignment has certain deviation, so the shaft in the working process of the high speed axis will be affected by the bending moment and bending stress caused by bending moment is alternating stress, when the shaft torque size and the direction of constant, so the cycle of torsional shear stress produced by the torque characteristics of static stress, due to the special hole structure to produce stress concentration, make the stress here may be higher than the allowable stress of material, when parts are stress is higher than the fatigue limit, every loading cycle damage to a certain amount of parts, and the damage can be accumulated; When accumulated to the critical value, the damaged parts fatigue damage will occur. According to the theory of linear accumulation of fatigue damage in the application more PAM glen as theorem, every time is the total damage of linear accumulation of fatigue damage, and fatigue fracture of shaft goes through several processes, the first is the initiation of fatigue crack, and then the subcritical extensions, finally happened instability of extension, so six months after the machine is running, the fatigue crack initiation and propagation of gradually, in the absence of obvious plastic deformation and other obvious signs of the fatigue fracture of axial stress concentration, and at the same time four of blender fracture at the same time, so you can see this is caused by fatigue damage accumulation of stirring shaft vulnerabilities in stress fatigue fracture. 4 preventive measures to avoid in the design of future reaction kettle stirring shaft fracture damaged problems, one is the need to consider in the process of design rigor, in the case of design allows the rational selection of safety coefficient larger; 2 it is to advance to the stirring shaft of the fatigue fracture risk in anticipation, and by changing the different processing technology to improve the fatigue properties of materials, combined with the practical situation in the process of analysis and test, the experience accumulation, possibility to do your best to avoid these abnormal cases of stirring shaft fracture risk. In addition, it is necessary to carry out regular maintenance of agitator, a need to check whether the retaining bolt looseness, thereby prevent blender momentum increases, vibrations cause the reaction kettle; Two fixed for blade and keep vertical stirring shaft, the verticality deviation should be in a 0. Less than 4%. Three need to regularly monitor the corrosion of the agitator, loose, deformation and crack defects, etc. Source: shandong industrial technology, 2018, 2