Optimization Study On Compositions And Casting Processes Of High-pressure Pump/Valve Bodies Based On Simulation

The pump/valve bodies in loaders and excavators sustain high pressure at a temperature that causes expansion and leakage. It is necessary for these castings that there are enough strength, high wear resistance, outstanding heat conductivity and dissipativity, high size stability and compact structure. These pump/valve bodies are generally nodular cast iron castings at present that the strength is high enough, but there are poor heat conductivity and dissipativity, poor thermal fatigue resistance, and lower densification structure. Leakage and short service life are the commonly trouble for these nodular cast iron pump/valve bodies. In this paper, it has been studied base on a casting simulation software MAGMASOFT that effects of alloying elements, melt treatment parameters and casting processes on the microstructure, mechanical properties and residual stress of a gray cast iron pump body and a vermicular graphite cast iron valve body. The simulation analysis results should be foundations for researching gray cast iron pump bodies and vermicular graphite cast iron valve bodies used in high pressure conditions. The optimization results based on simulation analysis should been used in production.For the pump casting of loaders, the casting process is set as sand gravity mould casting: resin sand mould and core, one-mould-two-workpiece structure, bottom pouring, pouring temperature1400℃, stream inoculation. In the simulation, the effects of the basic elements C, Si, S, P and alloying elements Mo, Cu, Cr and Ni on the casting microstructure, properties and residual stresses are studied.Through comprehensive analysis, the effects of each element content on the content of primary cementite, average lamellar spacing, eutectic cell size, eutectic phase fraction, undercooled graphite content, average tensile strength, hardness and residual stress of the castings, thus the suitable chemical composition range of pump body castings is determined as:C3.4%-3.8%, Si1.7%～2.0%, Mo0.5%～1.5%, Cu1.5%～2.0%, Ni0.5%～1.0%, Cr0.2%～0.6%, S<0.08%, P<0.14%. The pump body casting chemical composition is selected as:C3.5%, Si2.0%, Mn0.9%, S0.06%, P0.1%, Cu2.0%, Cr0.6%, Mo1.5%, Ni1.0%. The casting microstrcture, that is obtained with the presetting casting process, is in absence of primary cementite, with the eutectic cell size of702μm, average length of the graphite flake of243μm, eutectic fraction of75%, average tensile strength of426Mpa, average hardness of286HB and the maximum residual stress of30MPa. However, there are shrinkage cavities at the top and center section of the casting. By changing the pouring temperature and types of casting mould and inoculation, variations of the casting microstructure, properties, residual stress, compactness and defects of shrinkage porosity and cavity are invested. The simulation results show that, the optimal casting process for pump body casting is:gravity sand mould casting, shell mould and core, one-mould-two-workpiece structure, bottom pouring, pouring temperature1350℃-1450℃, stream inoculation. The optimal technology is verified by production experiment, in which the pump body casting obtained shows compact microstructure, no shrinkage, eutectic white and crack defects, the pearlite content of90%in the matrix, graphite level5, furnace sample tensile strength of472MPa, hardness of305HB.For the valve casting of loaders, he casting process is set as sand gravity mould casting: resin sand mould and core, one-mould-two-workpiece structure, top pouring, pouring temperature1400℃, stream inoculation. In the simulation, the effects of the basic elements C, Si, Mn and alloying elements Mo, Cu, Cr, Ni and Sb on the casting microstructure, properties and residual stresses are studied. Through comprehensive analysis, the effects of each element content on the content of primary graphite, nodularity, average tensile strength, hardness and residual stress of the castings, thus the suitable chemical composition range of pump body castings is determined as:C3.7～4.0%, Si2.0～2.05%, Mn0.5～0.9%, Cu0.3～0.9%, the optimal contents of Cr, Mo, Ni composition are Mo0.9%, Cr0.6%, Ni1.0%. The chemical compositions of the pump body casting are selected as:C3.8%, Si2.2%, Mn0.7%, S0.02%, P0.01%, Cu0.6%, Cr0.6%, Sn0.05%, Mo0.9%, Ni1.0%, Mg0.01%. The casting microstrcture that is obtained with the presetting casting process is in absence of primary cementite, with the eutectic fraction of99%, average tensile strength of543Mpa, average hardness of311HB and the maximum residual stress of101MPa. However, there are shrinkage cavities at the center section of the casting. By changing the pouring temperature and types of casting mould, variations of the casting microstructure, properties, residual stress, compactness and defects of shrinkage porosity and cavity are invested in the simulation. The results show that, the optimal casting process for pump body casting is: gravity sand mould casting, shell mould and core, one-mould-two-workpiece structure, top pouring, pouring temperature1350℃-1450℃, stream inoculation. The optimal technology is verified by production experiment, in which the valve body casting obtained shows compact microstructure, no shrinkage, eutectic white and crack defects, the nodularity is14%,the pearlite content more than70%.