Table of Contents
Advertisement
MRF 16/22
measured temperature reaches the Setpoint temperature, allow to dwell for 30 minutes.
• Apply 100% microwave power for 5 minutes. While the microwave power is on record the
maximum to which the measured temperature rises.
• When the microwave power turns off, the measured temperature will drop below the
Setpoint temperature then rise back up to it. Record the minimum to which the measured
temperature drops.
• Repeat this test again at 1000°C.
At 500°C the maximum allowed change of measured temperature above or below the
Setpoint is 10°C.
At 1000°C the maximum allowed change of measured temperature above or below the
Setpoint is 5°C.
If the change in temperature exceeds the above limits then replacement of the microwave
shield foil is recommended. [See section 13.7 for replacement].
12.6
Other electrical components
Regular visual or electrical checks should be made on the condition of the supply cable, and
all internal fuses and visible internal cables should be inspected periodically.
12.7
Element glaze
Depending on use the heating elements may lose their glaze and gain a rough appearance.
They should be checked from time to time. The glaze may be restored by heating the
furnace up to 1500°C without load, for 2 to 4 hours.
12.8
Pesting
The furnace is fitted with Molybdenum Disilicide elements which are susceptible to pesting.
Pesting can be seen as a yellowish crystal growth on the surface of the element. It occurs
when the element surface temperature is in the region of 450°C and is caused by the air
oxidising with the Molybdenum in the element compound. Under normal operating
conditions (above 800°C) pesting is not a problem and can often be seen occurring
naturally on the element terminals.
Running the furnace for prolonged periods at temperatures below 600°C will cause pesting
to occur on the element surface and will eventually damage the elements.
Heating on a slow ramp rate or dwelling at temperatures below 600°C for short periods will
not cause pesting providing the furnace is run above 1500°C at regular intervals to
recondition the element surfaces. [See section 12.5].
Large amounts of pesting occurring on the element terminals must be removed in
accordance with good health and safety practices.
12.9
Temperature calibration
After prolonged use the controller and/or thermocouple could require recalibration. This is
important for processes which require accurate temperature readings or which use the
furnace close to its maximum temperature. The thermocouples can not be calibrated in the
MRF 16/22. The thermocouples must be removed and calibrated by comparison.
40
MF 55-GB 1.21
Advertisement
Table of Contents
