高压气淬均匀性研究

Homogenisation of Heat Treatment Process in High Pressure Gas Quenching

高压气淬具有纯对流传热、易于控制、工件淬火后无需清洗和对环境影响小等优点。然而,典型的气淬设备显示出淬火料盘与工件之间的气流不均匀,导致工件的最终性能产生差异。业已发现,料盘的逆向气流布置是决定局部气流状态和热量传递的关键因素。尽管气流的主要部分在料盘与炉壁之间流动,对淬火过程不起作用,但是由料盘引起的流动阻力所产生的压降决定了淬火冷却强度。采用一种能较快收敛的多尺度模型对工业用高压气淬炉的内部流场进行了模拟,并通过速度测量和气流可视化技术对试验用淬火炉的内部气流进行了试验研究。最后,对圆柱体工件的双室真空炉淬火进行了模拟结果的验证,揭示了不同的逆向流速分布对淬火结果的影响。报道了多尺度模拟方法和流动过程的研究结果,并概述了对气淬工艺优化的指导性建议。

High pressure gas quenching has the advantages of pure convective heat transfer,high levels of control,avoidance of cleaning the quenched parts and low environmental impact.However,typical gas quenching facilities exhibit inhomogeneous flow conditions through the quench load and the parts,resulting in scatter in final properties.The upstream flow profile of the load has been identified as a key factor determining local flow conditions and heat transfer.The intensity of the quenching process is determined by the pressure drop that results from the flow resistance of the quench load,although a significant part of the flow passes between the load and the chamber walls and does not contribute to the quenching process.A simulation of the flow inside a commercial high pressure gas quenching chamber was carried out,using a multiscale model to give faster convergence.An experimental analysis of the flow inside a model quenching chamber through velocity measurements and flow visualisation was also performed.Finally,a quenching run with cylindrical parts in a double-chamber vacuum furnace was used to validate the model results.Various upstream velocity profiles were applied to demonstrate their influence on the quenching result.The multiscale simulation approach and the results of the flow process investigation are reported.Guidelines for gas quenching process optimisation are outlined.