Simulation And Optimization Of Heating Process Of Low Pressure Vacuum Carburizing Furnace

Low pressure vacuum carburizing,with characters of high efficiency,energy saving and low emission,is a green heat treatment technology,which can realize precision production,efficient production,clean production,economic production,intelligent production.So it has become the key popularized carburizing technology for heat treatment industry.Vacuum heating process,as the first step of low pressure carburizing,is the prerequisite for high quality carburization.Radiation heat transfer has an obvious thermal hysteresis phenomenon.Thermal radiative heat transfer is closely related to relative position between two objects.Therefore,the antiquated way,using experiment results and traditional experience to guide the equipment design and process formulation,can hardly meet the increasingly stringent requirements of heat treatment production.In this paper,numerical simulation method is used to establish virtual production platform of heating process in low pressure vacuum carburizing furnace.The influence of heater structure parameters and configurations of arrays of workpieces on temperature field are researched,and the effects of heating parameters on temperature difference are analyzed,which can provide theoretical guidance for equipment design and process optimization.The main research work and achievements are as follows:(1)The simulation platform of heating process for low pressure vacuum carburizing is established.The nonlinear variation of thermal parameters,such as heat conductivity and heat capacity are taken into account.The virtual heating furnace temperature can be precisely controlled by PID algorithm,which lays the foundation for the virtual production of low pressure vacuum carburizing heating process.(2)The vacuum heating processes with different heater structure parameters are simulated systematically.The change of the radiation intensity of the heater and the change of the radiation angle coefficient,which are caused by the change of the number,length and distribution radius of the graphite tubes,are analyzed.The effects of the above key structure parameters on the surface heat flux of workpieces and the temperature distribution of effective heating zone during heating process are studied,which can provide guidance for the design and optimization of heater structure.(3)The effects of the arrays of workpieces on the temperature field of vacuum heating process are studied systematically.Considering the typical shape of low-pressure vacuum carburizition heat treatment workpieces,the circular rod and the circular plate are selected for the study.The temperature curve,temperature difference curve and temperature distribution contour of circular bar and circular sheet under different arrangements are analyzed,and the influences of workpiece arrangements on heating efficiency and temperature uniformity are researched,which can provide guidance for the arrays of workpieces in actual production.(4)Virtual production of different heating processes are conducted on the simulation platform.First,simulating the full power heating process,then the temperature uniformity of the heating process is analized.It is proved by experiment that full power heating can cause excessive temperature differentials of the workpiece.The heating curves of numerical simulation are agreed well with the experimental results.By simulating the temperature fields of vacuum heating process at different heating rates and preheating temperatures,the influence rules of these heating parameters on maximum temperature difference of workpieces are explored.The heating process of the workpiece with the effective thickness of 40 mm was optimized.