MAINTENANCE

 

Furnace conditioning:

The destructive effect of carbon and temperature at high levels is conceded by manufacturers who normally instruct in the art of “gentle burnout”. SSi engineers have developed an even gentler routine that shortens or eliminates the time required to “season” the furnace after a burnout has been completed. The recommended routine for burnout is to set the temperature to 1500°F (815°C), discontinue the carrier gas, and start to add air at a rate that will not cause a large increase in temperature. A flow rate of about 10% of the normal flow of carrier gas has been found adequate. Eventually, the Gold Probe™ output will fall to 200 mV. At this point, discontinue the air and observe the probe output. If the output rises above 250 millivolts in less than 15 minutes, turn the air on and repeat the routine until the mV level remains below 250 for more than 15 minutes. Burnoff is complete.

 

 

The reason this technique is superior is that the carbon retained in the pores of the refractory is what constitutes “seasoning”. Complete burnout, however gentle, removes this carbon and requires that it be added during a Monday morning start-up seasoning routine, in order to achieve operating levels.

Probe conditioning:

While periodic furnace burnout is desirable, the process by which solid carbon or ‘soot’ is deposited continues in the probe, and must be remedied more frequently to keep the probe in peak operating condition. SSi technical staff has pioneered in techniques to achieve this. Soot deposition occurs in two critical locations; the annular space between the sheath and the measuring surface and at the measuring junction between the zirconia and the contact point with the sheath, which is the measuring electrode. The probe is burnt out by the flowing air into this space through the burnout fitting provided. The flow of air must be set at a rate that allows a temperature  rise of no more than 100 degrees Farenheit (38 degrees Celsius). If possible the flow should be set high enough to overcome the effect of the work chamber fan and drop the output voltage well below 200 MV. Conducting this process for a 90 second period before or after each batch, or every six to twelve hours in a continuous furnace, will provide adequate conditioning in most cases.