Development Of Melt Quality Detection System For Compacted Graphite Iron Based On LabVIEW

Compacted graphite iron(CGI)is superior to gray cast iron in high temperature strength and thermal fatigue properties,and its shock absorption ability is superior to that of nodular cast iron.It fills in the gap of mechanical properties between nodular cast iron and gray cast iron,and has been widely used around the world.However,the control of CGI vermicularity requires higher control technology than that of nodular cast iron.It is difficult to stabilize production,which greatly affects the popularization and application of CGI.In this paper,the hardware acquisition module of CGI melt cooling curve,the data acquisition and analysis module based on LabVIEW and the oxygen potential measurement module of melt are combined to form a CGI melt quality detection system based on LabVIEW.The system solves the communication problem between sensors or standard instruments and computers unfamiliar to most foundry workers.A self-made composite sample cup and LabVIEW software platform were used to construct a thermal analysis platform for CGI melt,an oxygen potential measurement platform was built with a hot metal oxygen determinator,and a multi-channel data acquisition hardware system was constructed.Using graphical programming language to complete the predetermined algorithm,the data collected by the data acquisition card are analyzed and processed,and the functions of temperature acquisition and transmission,real-time data display,data analysis,historical data reading and preservation are realized.The differential curve of cooling curve is obtained by substituting differential quotient for differential quotient.The characteristic values of TL,TEU,TEM,TER and TS on the cooling curve of vermicular cast iron were extracted by comparing the cooling curve of cast iron with its first and second differential curves.Five characteristic parameters,TL,TS,TEU,? T and oxygen activity,were selected to establish the mathematical model of melt quality parameters of vermicular graphite cast iron.Regression analysis showed that CEL=13.4857-0.00827×TL,%Si=82.14778-0.07289×TS,%C=-6.20-0.0079×TL+0.0192×TS,and vermicularity =-2275.1+2.027 ×TEU+4.099 ×?T four regression prediction equations.The relationship between vermicularity and oxygen potential of cast iron was studied.The experimental results show that the oxygen activity of vermicular cast iron is closely related to the morphology of graphite after crystallization.When oxygen activity is less than 0.6 ppm,graphite is spherical;when oxygen activity is more than 0.6 ppm and less than 1.7 ppm,graphite is vermicular;when oxygen activity is more than 1.7 ppm,graphite is mainly flaky.The change trend of structure and properties of vermicular graphite cast iron under different holding time was studied.With the prolongation of holding time,the quantity and volume fraction of graphite in vermicular graphite cast iron increased first and then decreased,while the graphite vermicularization rate fluctuated with holding time.The decomposition of sulfide and the burning of Mg and RE lead to the change of the structure and properties of the melt,which is consistent with the predicted results of thermal analysis.