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12 Maintenance
Preventive rather than reactive maintenance is to be preferred. The type and frequency
depends on furnace use, the following are recommended.
12.1
Cleaning
Soot deposits may form inside the furnace, depending on the process. Remove these by
heating to above 750°C for 1 hour.
The furnace outer surface may be cleaned with a damp cloth. Do not allow water to enter
the interior of the case or chamber. Do not clean with organic solvents.
The mating surfaces and fins of the MW door choke must be kept clean. Ensure that they
do not get contaminated with foreign objects such as small pieces of metal and insulation
dust. These are likely to cause arcing.
12.2
Decontamination
If hazardous material is spilt onto or into the furnace, a responsible body must ensure that
appropriate decontamination is carried out. If there is any doubt about the compatibility of
cleaning or decontamination agents with parts of the furnace or materials contained in it,
contact Carbolite.
12.3
Regular microwave safety checks
Regular checks should be made for levels of microwave leakage, Carbolite recommends a
weekly check. Areas to check are; around the door edge, door handle recesses, across the
top, fan inlets and exhausts, around the edge of the back panel. The maximum allowable
level of leakage is 5mW/cm2 when measured in accordance with BS EN 60519-6:2002 part
6.1.
12.4
Check the operation of the door safety interlocks
To check that the radiant heating circuit is disabled when the door is opened: Close the
door. Make sure the MW power is turned off. Raise the Setpoint temperature so the heating
circuit should come on, the heat light(s) on the control panel should glow amber. Open the
door. The heat light(s) should go off, indicating that power to the elements has been
isolated.
To check that the door can not be opened when the MW power is on: Close the door. Lower
the Setpoint temperature to -20°C so the radiant heating does not come on. Set the MW
count down timer to 8 seconds. Start the timer and try to open the door. It should not be
possible to open either latch. At the end of 8 seconds the locks should release allowing the
door to be opened.
12.5
Thermocouple sheath aging
Eventually the foil on the thermocouple sheath protecting the thermocouples from
microwave will deteriorate and holes will appear. Large holes in the foil will cause
temperature measurement errors, difficulties in stabilisation at Setpoint temperature and
possible damage to the thermocouple. The integrity of the shielding can be tested as
follows:
• With the microwave power turned off, set the Setpoint temperature to 500°C. When the
MF 55-GB 1.21
MRF 16/22
39
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