Casting Foundry Technology Researching And Optimizing For Ductile Iron Inlet Casting Cylinder Of Heavy-duty Gas Turbines

Heavy-duty gas turbine is a kind of power generation and power equipment with high working temperature,high thermal power conversion and high output power.The research and development of heavy-duty gas turbine is regarded as one of the important symbols of national high-tech strength by science and technology and industrial circles,both at home and abroad.Inlet casting cylinder is an important component of the front end units of heavy-duty gas turbine units to introduce air evenly,which belongs to large load-bearing and pressure bearing components,with very high mechanical properties,compact structure and nondestructive testing and other requirements.In addition to the casting characteristics of generals ductile iron castings,inlet casting cylinder castings have the special structures of local thick and large section and the distribution of multiple isolated hot spots,which determines there are a lot of casting technical difficulties and they are easy to produce typical casting defects,such as porosity and shrinkage,and surface slag inclusion.Such defects directly affect the operation safety of the unit,and even cause serious accidents in the later generation operation.This paper adopts the theoretical analysis of the defects formation mechanism,the experimental study of the process scheme and the MAGMA simulation of the design results and so on,and forms the optimized technical scheme of inlet casting cylinder casting,through the practice verification of the control group of the technological measures.This paper made the experimental blocks of different chemical components,adopted the methods of UT detection and physical anatomy to confirm the volume of shrinkage and porosity defects,sdutied the influence tendency of Si elements on the graphite morphology with thick and large cross-section,analyzed the detection results of mechanical properties and metallographic examination,and finally confirmed the optimum carbon equivalent range is 4.4 to 4.7%and C is about 3.7 wt.%and Si is about 2.8 wt.%in the composition of the casting.This paper also analyzed the display defects of MT detection of superstandard magnetic marks on the surface of the castings with SEM,EDS and so on,confirmed the surface defect of the castings was a single oxidation clip caused by the aggregation of SiO₂?MgO?Al₂O₃,analyzed the effect of different types of pouring systems,compared and studied the principle and effect of the slag-avoidance in the casting process and finally formed the unique steppted slag-avoiding pouring system project of the cylinder to prevent the slag inclusion defect on the surface of the cylinder effectively.In this paper,the CAD modeling and MAGMA simulation are used to study the riser filling and cold iron chilling scheme to form the temperature gradient conforming to the cylinder solidification,and fully realize the solidification technology scheme composed of main proportional solidification and assisted"sequential solidification+proportional solidification",so as to ensure the bulk density of the castings.After the process optimization,The weight of Inlet casting cylinder is12500kg,and the technological output rate increases from 80.9%to 88.7%,Compared with other large ductile iron castings of the same kind,it has higher economic benefits.Up to now 12 pieces of the inlet cylinder castings have been produced,the qualified rate of the inlet cylinder castings reaches 100%,and the casting quality reaches the leading level of the industry.On the basis of theoretical and practical research,this paper determined the optimum chemical composition of the castings,designed the staircase dregs pouring system,proposed the solidification scheme combined by the proportional solidification and the sequential solidification and finally formed the core casting technical scheme of the thick and large cross-section ductile iron castings.The relevant experimental results have important guiding significance for the research of high-end ductile iron casting,and promote the core competitiveness of our company in the manufacturing field of ductile iron castings.