دانلود رایگان مقاله تحقیقات در شکست شفت فن کششی ناشی در دیگ بخار قدرت

ABSTRACT

The failure of the induced draft fan’s shaft in a power boiler was been analyzed. The performances of material applied satisfied the design requirement. The order torsional vibration showed anomaly at the shaft’s smallest diameter for the design condition and the actual radius of that chamfer less than the design radius caused more significant stress concentration. The additive effect of the abnormal torsional vibration and the higher stress concentration induced the microcrack’s initiation along the network pearlite’s interface. The vibration and the alternating torsional loading in the induced draft fan’s service led to crack growing along the different direction and fracture presenting the typical ratchet-like characteristic.

5. Conclusion

The failure of the induced draft fan’s shaft in a power boiler was been investigated. The material’s composition and mechanical properties satisfied the design requirement. The shaft’s torsional fatigue strength revised based on the ultrasonic fatigue experiment’s result confirmed the material applied was secure enough for the normal operation of the shaft. The finite element simulation based on the shaft’s design size showed the stress concentration was remarkable at the shaft shoulder’s chamfer (the radius was 5 mm), while the actual radius (2 mm) of the shaft shoulder’s chamfer caused more significant stress concentration, so the radius the shaft shoulder’s chamfer must reasonable and accurate during the process. The order torsional vibration appeared anomalous when the shaft’s speed was in the critical speed. The higher stress concentration and torsional vibration induced the microcrack’s initiation along the weak interface of the ferrite and the pearlite due to the network pearlite’s formation; meanwhile the vibration in the induced draft fan’s service led to crack growing along the different direction. The effect of the alternating torsional loading made fracture presents the typical ratchet-like characteristic.