Main Drive Shaft Of The Heavy Plated Mill Mechanical Analysis And Repairing Experiment Study

Baosteel Company is the first used of the 5000mm width heavy plated mill in domestic, it is also one of the most advanced heavy plated mill in the world. The main drive system of rolling mill in Baosteel company is composed of motor, reducer, distribution box, connecting shaft and couplings etc, it has the characteristics that transmission torque is large, stress is great, impact is big, dimension is strictly limited etc. Since its operation, the main transmission system of Baosteel thick heavy rolling mill repeatedly happens super-large equipment fracture accidents, mainly including: flange transition rounded part fracture, laser repaired joint head fracture, which seriously affected the thick heavy rolling mill normal production and greatly increased equipment repairing and spare parts cost. This paper focuses on main shaft accident in the Baosteel company, carrying out the related research.To solve the thick heavy plated mill's main shaft abnormal fracture problem and improve its repair technology, it is necessary to analyze its main transmission system. This paper combines finite element analysis method with experimental research, discussing unusual cracking reasons of the main shaft , analyzing the failure mechanism of fracture fork head. After finding the failure reason, it is necessary to study laser repair technology and achieved the following research results:First, establishing the mathematical model of the main transmission system. Simulating the mathematical model through MATLAB, calculating the spindle of natural frequencies and torque amplitude factor for the inspection of the design, through the field test data analysis verify the correctness of the mathematical model, it is concluded that the spindle design is reasonable.Second, applying finite element analysis and engineering mechanics method to often fractured flange and fork head. It obtained the calculation results,for the steady rolling torque of 4000 kN?m, 60mm 80mm flange fillet radius have the maximum equivalent stress value 111MPa and 101MPa respectively, Rounded radian of 2mm 80mm 60mm,its safety coefficient is respectively 3.131, 1.4 3.269, thus it can be seen, flange failure due to too small fillet caused by the local stress concentration, and advances improving opinions, after implementing the correct action, the flange fracture has not occurred, fork head analysis get the feedback fork head of the maximum equivalent stress is 361.196Mpa, far from reaching its ultimate strength, fork head fracture should belong to fatigue damage failure, according to fatigue failure theory fork head safety coefficient is 0.303, far from meeting the design requirements, which leads to the fork head failure, proposed reducing mill load improvement measures, to avoid the new joint head rupture.Third, failure mechanism analysis of fractured fork head. Though the disassembly analysis of the fractured fork head, looking for fork head of failure mechanism, Through performing macro and micro morphology analysis, chemical composition analysis, mechanical property testing, microstructure analysis, obtains that the fracture mode for fork head is fatigue fracture, The main reasons of the fatigue fracture besides the fork head design life expectancy is insufficient, the fork head bearing hole working face, the laser cladding of inner surface and local repair caused the defects, these defects caused crack expanding further under periodic stress, The failure mechanism analysis results showed that inappropriate laser caused the ford head fracture, if we can raise fork head hole repairing process, it can greatly improve expected life of the fork head.Fourth, on the foundation of the failure analysis, studying the repair technology of universal joint. According to the joint head materials properties, operating conditions and stress state etc, choose two different parts (fork head and fork head flange) and two different Ni based powder for laser cladding process research, analyze the surface hardness results, residual stress and microstructure detection results, it got the conclusion that DL2 Ni based powder in low residual stress position cladding effect is better, and also got the suitable fork head laser cladding process, through computer tests, the new laser cladding repaired fork head, its service life already amounted to 3 months at present, far longer than previously cladding process 3 weeks using life.Thick heavy rolling mill shaft has the maximum torque (the measured lord is 7000KNm), high stress and under strong impact. Laser cladding as a new technology is different from conventional surfacing, electroplating, spraying process, it has some features and advantages, which are increasingly widely used in industry. By means of application research about laser cladding on big torque and high stress of mechanical parts repairing , it helps to develop laser cladding industrial application, also helps to improve the large mechanical transmission parts repair and remanufacturing technology level.