Reference measurements in gas carburizing atmospheres: part

The most important parameters for the control of carburizing processes are the temperature and the C-potential of the atmosphere. Temperature is normally measured by means of thermocouples. For the control of C-potential the measurement of oxygen partial pressure of the furnace atmosphere by in-situ O2-probes and Lambda probes (L-probes) became accepted. The thermocouples as well as the probes for measurement of residual oxygen gradually lose in accuracy. Therefore, reference measurements for adjustment of temperature and C-potential are essential for an exact control. In the first part of this article [1] the reasons for incorrect measurements with thermocouples and O2-probes, respectively L-probes have been explained. The appropriate reference measurements with calibrated thermo couple and gas analysis for correction of these faults were also described. Furthermore, it was explained what has to be observed with these reference measurements and which information is given, thereby, about the furnace atmosphere, especially with the gas analysis by means of a gas analyzer. Within part 2, following now, following additional reference measurements for C-potential will be presented: reference measurement with a second O2-probe or L-probe, dew point measurement and foil test. The advantages and disadvantages of theses reference measurements will be also discussed.