An extensive modelling study of cooling by means of nitrogen jets showed that an array of high velocity gas jets close to the surface of the part could produce cooling at about the same rate as oil. The optimum conditions required an approximately uniform nozzle field with the jets very close to the part and a gas velocity of 100 m/s. When these optimised conditions were applied to an idealised gear form, the model suggested that it could be fully hardened when a nitrogen-hydrogen mixture was used. Calculation suggested that in this type of nozzle field the part would float between the arrays, eliminating the need for fixturing. Up to this point all the work had used CFD modelling. This type of modelling dramatically reduced the time taken to discover the optimum conditions but it had not been validated by experiment. Before it could be given a commercial application, the model had to be validated using a physical test rig. This showed that the model gave results very close to reality, which could predict the behaviour of production parts.
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