Study On Influence Of Circulation Fan Flow To Bonding Defects In Process Of Full-hydrogen Cover Annealing

This paper introduces specifically the structure of full-hydrogen bell type furnaceand thermal process of cover annealing and the bonding defects appears during coverannealing which has serious impact on the productivity and product quality ofcold-rolled sheet. To reduce the bonding defects, this paper analyzes the mechanismand influencing factors of the bonding defects, and states that the radial stress causedby uneven distribution of temperature is considered to be the main factor leads to thebonding, in the meantime, summarizes the methods used to reduce the bondingdefects.Based on the above analysis, the paper makes mathematical models of coil’stemperature field during earlier stage of cover annealing, analyzes process of heattransfer in bell type furnace and flow distribution in case of different circulation fanflow and different temperature, as well as the relationship between hydrogen and itsphysical property. In order to correct the simulation calculation, an experiment aimedat measuring the temperature of representative spot is to be conducted. Thecomparison between simulation and measure reveals that simulation is believable.At last, to decrease the flow of circulation fan and calculated the temperature fieldof this working condition based on the authenticity of the simulation result so as tocompare the temperature field of the two working condition, and calculate the radialcompressive stress of the coil at its cooling stage according to the temperature fieldswhich may be respectively served as the thermal load respectively and loaded to thestress field. The results show that radial compressive stress is directly influenced bytemperature range between the cold spot and hot spot, and flow distribution within theenclosure can be changed by reducing the fan flow circulation. Thus, temperaturerange between the cold spot and hot spot can be reduced as well as the maximum coilcompressive stress. As the fan flow circulation is reduced to50000Nm3/h from70000Nm3/h, the temperature range between the cold spot and hot spot of the coilcan be decreased to maximum7℃, and the maximum radial compressive stress isable to drop17MPa. A decrease of circulation fan flow is of great effect on reducingthe bonding defects.