Study On Thermal Analysis System And Evaluation Of Melt Quality Of Compacted Graphite Iron

Compacted graphite iron(CGI)has a good comprehensive performance and is widely used in industry,especially in automobile industry.However,the production process of CGI is complicated.In the actual production process,the thermal analysis technology is usually used to detect the effect of molten iron modification and inoculation,to achieve the quality of cast iron control.China has not developed the thermal analysis technology of large scale production of CGI.Aiming at this problem,this paper designed a thermal analysis experimental platform system,and studied the method of evaluating the melt quality of CGI.According to the requirement of thermal analysis experiment,a thermal analysis experiment platform system was designed.The system can realize multi-channel temperature data acquisition,real-time display and storage,the calculation of characteristic values,and the view of historical data.The system is calibrated to meet the requirements of the thermal analysis experiment.By using the combined filtering method to remove the interference signal in the experimental data,and using the reasonable data processing method to calculate the thermal analysis characteristic value.The effect of rare earth magnesium and sulfur on the graphite morphology of cast iron was studied by using the control variable method.With the addition of rare earth magnesium,the graphite morphology transformed from the flake to vermicular,then to spheroidal,the percentage of vermicular graphite increases first and then decreases.At the same time,the sulfur in the molten iron will consume the magnesium element in the vermicular agent.There is a close relationship between the characteristic values of the thermal analysis and the graphite morphology of cast iron.According to the characteristic value can distinguish four stages of the thermal analysis samples: the flake graphite,the nodularity is less than or equal to 20%,the nodularity is more than 75%,and the nodularity is between 20% and 75%.The regression relationship between the lowest eutectic temperature(TEU),the eutectic recovery temperature(?Te)and the nodularity was established.Because of the large error in the prediction nodularity by using regression relation,this paper studies how to judge the melt quality of CGI by curve identification.The relationship between the similarity of thermal analysis curves(M)and the difference of percentage of vermicular graphite of the thermal analysis samples(?V)was established.When M <3,?V?5% and the graphite morphology of the thermal analysis samples after solidification are close.