From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The nitrogen hardening process observed at the Aubert & Duval plant, detailing its application on automotive and aero parts.
| Identifier | ExFiles\Box 22\1\ Scan309 | |
| Date | 1st October 1928 guessed | |
| contd :- -2- We then went over the plant of Aubert & Duval who are the Paris licencees of the process and have done Hispano's development work. We there found being treated gears of every description - rear axle pinions, and crown wheels, aero spur gears, water pump spindles etc.etc. We were told that Hispano's had standardised rear axle gears in the steel though we did not see them in the Works. Numerous parts have been standardised by Citroen, Voisin, Amilcar etc. in the steel. Small parts are only treated for two or three hrs. where the depth of hardness required is not great. The explanation they gave of the process now being applicable to gears was that they do not make gears ultra hard, though much harder than case-hardened steel and that the pene- tration of the nitrogen gives a gradual decrease in hardness from the surface to the soft set steel i.e., there is no abrupt dividing line (see sketch). The toughness of the skin can be gauged from the fact that they are making drop forging dies of the steel and Citroen's have already got results which shew an increase in life of the dies of more than 100%. Machining the dies is also simplified as original metal which is softer than normal die steel can be used. We saw quantities of standard Hispano clutch plates being nitrogenised. A feature of the process is that the steel 'grows' to the extent of .01 mm. for .5 mm. depth of hard skin which is about the max. required. They have sufficient experience to be contd :- | ||