Volume 5, Issue 6 (June 2008)
It has been suggested that gas quenching of a single component or single layers of components that have been heated in vacuum or conventional atmosphere furnaces can achieve higher quenching rates than those possible with conventional multi-component gas quenching. Such treatments could meet the need for a clean, non-toxic quenching medium that leaves no residues to be removed after processing. The processing of single components gives the operator complete control of quenching intensity, both locally and overall. Moreover, the quenching rate may be changed during the quenching cycle. Extensive computational fluid dynamics modeling of cooling using nitrogen jets has shown that an array of high velocity gas jets close to the surface of a part can cool it at a speed similar to oil. The optimum conditions were: an approximately uniform nozzle field with the jets four to eight times their own diameter apart, at a distance from the part to be quenched of a quarter of the diameter of the jets; and a jet velocity of 100 m/s (224 mph). When these optimized conditions were applied to an idealized gear form, the model suggested that it would be fully hardened if a nitrogen/hydrogen mixture was used.Calculation indicated that in this type of nozzle field, the part would float between the arrays of jets, eliminating the need to fix it. The model was validated using a physical test rig and was found to give results very close to reality, so it could be used to predict cooling behavior. The test rig was also used to quench carburized gear blanks. The hardness profiles produced by quenching in different gas mixtures were compared to those from oil quenched samples, the results confirming the original modeling.