Gas Nitriding: Ammonia saving up to 50%
by Stange (comments: 0)
STATE OF THE TECHNOLOGY
Ammonia is used as nitrogen dispenser for gas nitriding. The ammonia reacts at nitriding temperature at the catalytic acting metallic surface in the treatment chamber due to thermal causes in nitrogen and hydrogen. The degree of dissociation of ammonia or the hydrogen content in the furnace atmosphere defines the nitriding effect of the process gas and is specified by the nitriding potential Kn. But only 5 up to a maximum of 10% of the used ammonia react on the active surface in the treatment chamber. The rest of the process gas is unused and usually flared.
In industrial practice gas nitriding processes run with constant set gas quantities or gas potential during holding time. Set values can be changed empirically in several steps during holding time. This practice leads above all to a high NH3 consumption in the run-up nitriding phase with high nitriding potential. But even in the following segments of the holding time the gas consumption is very high with constant set values.
NITRO-PULS© TECHNOLOGY
The utilisation factor could be improved considerably by pulsating and/or time-dependent, cyclic variable nitriding potentials. The setting of the required compound layer phase structure was reached by time-dependent variation of the nitriding potential and the gas flow. This new gas nitriding technology NITRO-PULS© was developed together with the Institute of Materials Engineering TU Bergakademie Freiberg.
For the NITRO-PULS© technology a new control concept of a temporal variation of nitriding potential Kn on basis of a change of the H2 sensor signal was introduced. The temporal variation takes place after the pulse length as well as the pulse break.
Our control concept was successfully tested in practice. The evidence was provided that our concept fulfils the practical requirements.
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