Sensor for carbon transfer control during low pressure carburising process

Abstract

The real time control of furnaces for low pressure carburising requires rugged sensors and systems, which provide a signal correlated to the momentary carbon transfer into raw materials. A coulometric solid electrolyte sensor based on stabilised zirconia was developed and tested for this purpose, which enables the continuous titration of a proportion of the exhaust flow with oxygen. Investigation in the laboratory as well as in a single chamber furnace proves that the response time of the measuring system is significantly shorter than that of a H₂ thermal conductivity detector and that an on-site calibration enables the interpretation of the coulometric signal as a direct measure for momentary carbon transfer. The comparison of the online measured integral transferred carbon mass with the offline analysed carbon profiles of the treated workpieces shows good agreement related to the precision achievable.

Keywords:

• Low pressure carburising
• Vacuum carburising
• Pyrolysis of hydrocarbons
• Acetylene
• Measurement of carbon transfer
• Coulometric solid electrolyte sensor

Acknowledgement

The work was funded by the German Federal Ministry of Economy and Technology with the contract no. EP 100441. The authors gratefully acknowledge the support as well as the device related promotion by the ZIROX Sensors and Electronics Ltd, Greifswald, Germany. This paper was originally published in German in HTM J. Heat Treat. Mater. 2013, 68, 69�76 and is reproduced in translated form with permission; the original can be viewed at http:/dx.doi.org/10.3139/105.110181.