Modelling of High Speed Gas Quenching

Gas quenching has been used in vacuum furnaces for many years and its characteristics for bulk quenching of components are well known. More recently the use of gas quenching applied to single or small groups of components that were heated in either vacuum or conventional atmosphere furnaces has been proposed. Gas quenching may be seen as meeting the needs of modern ”batches-of-one” processing for ”just-in-time” manufacturing. It is clean, non-toxic and leaves no residues to be removed after processing. If this process is to be possible then heat extraction rates equivalent to those obtained from a medium quench oil must be achieved uniformly at the surface of real components. There are several strategies for meeting this aim: first, conventional high pressure quenching; second, moderate velocity quenching utilising a high heat transfer coefficient gas such as helium; and third, high velocity quenching utilising a gas with lower thermal efficiency. The implementation cost for the first strategy is high as is the running cost of the second unless high cost gas recycling equipment is considered. In the third, overall costs can be minimised by using a low cost gas such as nitrogen without the need to recycle. It is this third strategy which is the subject of this paper. Computational Fluid Dynamics (CFD) was used to determine if indeed the process could achieve the required results and then to optimise the process parameters off-line. Implementation of a feasible process will then be carried out in the field.