Numerical Simulation Of High-pressure Gas Quenching Process And Optimization Of Duct Structure

As a kind of “green heat treatment” technology,the high pressure gas quenching has gradually become a dominant technology with its unique advantages such as no oxidation and clean efficiency.However,a faster and more uniform quenching of the whole charge has not been achieved due to the complexity of gas flow.There is no guarantee that meet the requirements of cooling rate and cooling uniformity.And it is easy to have large deformation of the workpiece and different hardness of synchronous furnace.In this paper,the circular nozzle-type high pressure gas quenching furnace used as research object.And its high pressure gas quenching process is analyzed by using numerical simulation method.The aim of this work is to find a method which could improve the quenching effect from the gas quenching process parameters and the structure of the air duct.The characteristics of gas flow and heat transfer in high pressure gas quenching are analyzed,and the boundary conditions of numerical simulation of high pressure gas quenching process are determined.The Fluent software is used to simulate the flow field and temperature field in the process of high pressure gas quenching.The experimental data are verified by wind speed and temperature measurement experiments.The experimental data are basically consistent with the simulated values.The error is within 15%,which confirms the accuracy and reliability of the model,and provides a basis for the subsequent simulation and optimization.In this thesis,the evaluation system of quenching effect is established from two angles of cooling rate and cooling uniformity.Through the single variable control method,the influence of different gas quenching process parameters on the quenching effect is studied.The general rule of the gas quenching process is obtained: Increasing the quenching pressure and velocity can improve the cooling speed of the w orkpiece,but the cooling uniformity will be reduced to a certain extent at the same time.As a result,the suitable technological parameters should be selected by comprehensive economic factors and quenching effect.According to the research literature at home and abroad,the number of nozzles,the diameter of the nozzle and the number of the wind pipe have an important influence on the quenching effect.As a design variable,the standard deviation of the temperature and temperature of the workpiece after quenching 100 s is taken as objective function under definite batch.The response surface model is combined with the response surface test design and the numerical simulation method to build the response surface model.After complete verification of the simulation and variance,it is the model instead of the simulation that can be used to assist in parameter variation for optimization.Considering the cooling rate and the cooling uniformity,the structure of the air duct is optimized.The optimized parameters are obtained: the number of the wind pipe is 8 and the number of nozzle which uniformly distributed on the pipe is 4,the diameter of the nozzle is 24 mm.Compared with the previous structure,the temperature decreased by 17.5% and the standard deviation of temperature decreased by 12.7%.To a certain extent,the structure optimization of gas quenching duct was realized.