| OCR Text |
Show 4 1) After surface degreasing, the steel sheet was pre-oxidized in the electric furnace and an oxidized layer about 27g/m2 weight (5microns thick) formed. 2) The temperature in the furnace was kept at 1250°C. 3) A thermocouple was welded to the steel sheet at the opposite side of blowing, and was inserted from the top of the furnace. 4) W h e n the temperature of the steel sheet rose to between 600 and 900°C, the steel sheet was dropped into the non-oxidizing cooling compartment. 5) After cooling to room temperature, a 5 0 m m wide x 60mm long sample was cut out from steel sheet. 6) After measuring the sample weight, the sample was pickled with hydrochloric acid and then the weight was measured again. 7) The weight of reduced iron oxide was determined from the weight difference before and afterthe pickling and from the iron concentration analysis in the pickling solution. The range of the combustion conditions in which reduction occurs is shown in Figure 5 for experiments conducted at an air ratio of 0.85 without air preheating. Within the range of C O concentration from 1 to 5 % in the furnace, S N M burner can reduce at about a steel sheet temperature of 900°C or less. Figure 6 shows the relation between the heating time and the weight of reduced iron oxide. At the beginning of the heating, the reduction reaction rapidly proceeds. Later, reduction progresses slowly. The weight of reduced iron oxide increased as the air ratio lowers within the range from 0.82 to 0.9. Figure 7 shows the relation between the temperature of the preheating air and the weight of reduced iron oxide. While the weight of reduced iron oxide is not affected by the preheating air temperature at a steel sheet temperature of 800°C, the weight of reduced iron oxide shows a tendency to increase with the preheating air temperature high at a steel sheet temperature of 500°C. 3.3. Improvement of reducing capacity by oxygen enrichment Next, to examine the effect on the reducing capacity of oxygen enrichment, the reducing and direct-fired flame heating in the open air was tested. The test apparatus consisted of the direct fired heating part in the open air and the non-oxidation cooling compartment as shown in Figure 8. Steel sheet attached to the cooling compartment was heated by S N M burner. A S N M burner had been installed in this apparatus, and the distance between the burner and the steel sheet was maintained at 300mm. Coke oven gas was burnt as a fuel at a combustion rate of 70kW, a 30-90% oxygen concentration range in air after oxygen enrichment, and a 0.4-0.8 air ratio range. In a 0.2m wide x 0.8m high x 0.4m long steel compartment, nitrogen gas was blown in as a non-oxidizing atmosphere at blowing rate of 50Nm3/hr. Hot strip mill steel sheet of low carbon was 300mm wide x 300mm long x 5.6mm thick and has oxidation of about ten microns on the surface. |
