On-Line Melt Thermocouple Calibration

Iron and Steel Foundries

In iron and steel foundries, where continuous casting furnaces are used. It is essential to ensure, that before the casting process commences the melt temperature of the metal is within a predefined a temperature band. In most furnaces it is not practicable, due to the high temperature and corrosive nature of the materials to place a thermocouple permanently in the melt.

In practice, the furnace is heated up using either resistive or induction heaters. The control thermocouple is usually placed in the wall of the furnace and is connected to a temperature controller, which then regulates the power to a heater via a thyristor or contactor switch. When the furnace wall has been up at temperature for enough time to allow the melt temperature to stabilise the operator dips a thermocouple into the melt and depending upon the temperature reading, decides whether or not to start the casting process. Often due to the physical size and insulation characteristics of these furnaces, large temperature differentials between the melt and wall thermocouples exist.

2604 Solution

• Controlled Temperature Ramp-Up
• Automatic Dip Thermocouple Calibration
• Retransmission of Melt and Furnace Temperature

The 2604 controls the temperature of the furnace in the normal way, ie using the wall thermocouple for control. In addition the dip thermocouple is also connected to the controller. The heating up operation, which can be a controlled setpoint ramp, is identical to previously described until the furnace comes within about 100oC of the setpoint. At this point the operator will take a dip temperature reading and compare it against the current furnace wall temperature.

The operator will then press an “auto calibration” button which will make the furnace wall temperature measurement equal to the dip temperature, therefore making the temperature controller think that the wall thermocouple is actually in the melt. At any time during the process this procedure can be repeated.