Carbolite BLF 18/21 - Manual (Page 5)

BLF
MF23 – 3.11
5
3.0 O PERATION
The instructions for operating the temperature controller are given in a separate manual.
If the furnace is fitted with a time switch, see also the supplementary manual MS03.
If cascade control is fitted, see the supplementary manual MS07.
3.1 Operating Cycle
The furnace is fitted with an Instrument switch. The switch cuts off power to the controllers and
contactor.
Connect the furnace to the electrical supply. The cooling fans should automatically operate.
Check the hearth control switch for correct operation. The spring return switch stops the hearth in
any position, but over-travel is automatically limited. Load the furnace and raise the hearth.
Operate the instrument switch to activate the temperature controller. The controller becomes
illuminated and goes through a short test cycle.
Adjust the temperature controller – see the controller manual.
Set the overtemperature controller to a temperature a little (say 15°C) above the maximum setpoint
of program temperature, according to the instructions in the appropriate manual.
Unless a time switch is fitted and is off, the furnace starts to heat up. The Heat light glows brightly
at first, more dimly as the furnace temperature approaches a program setpoint.
If the overtemperature trip operates then an indicator or message in the overtemperature controller
flashes, and the heating elements are isolated. Find and correct the cause before resetting the
overtemperature controller according to the instructions supplied.
To switch the furnace off, set the Instrument switch to off. The case cooling fans remain on and the
chamber can be unloaded. Leave the fans on until the furnace cools to below 300°C. If the furnace
is to be left off unattended, isolate it from the electrical supply.
3.2 General Operating Advice
Heating element life is shortened by use at temperatures close to maximum. Do not leave the
furnace at high temperature when not required. The maximum temperature is shown on the furnace
rating label and on the back page of this manual. The furnace can be cycled between room
temperature and maximum without a detrimental effect on element life.
On first installing the elements, and on subsequent element replacement, run the furnace at 1500°C
for an hour to create a protective glaze on the element surface.
The thermocouple is intended to sense the temperature near the heating element, but if a large
object is placed in the chamber it may record the average temperature of the object and the
elements, which can lead to overheating of the elements. Allow large objects to gain heat at a
lower temperature and then reset the controller to a temperature close to the desired maximum.
The furnace elements are very susceptible to mechanical shock. Take care when loading or
unloading the furnace chamber. Opening the hearth at high temperatures is not recommended, but,
if it is necessary, keep the hearth lowered for as short a period as possible. The insulation cools
quickly and may crack through thermal shock. Note, though, that the insulation material is
susceptible to some surface cracking arising from high temperature cycling; such cracking is not
detrimental to the performance of the furnace.
Lightweight ceramic fibre insulation can easily be marked by accidental contact. Some fine cracks
may be visible on the surface of the insulation, or may develop in the surface of the chamber due
to the progressive shrinkage of the insulation materials. Cracks are not usually detrimental to the
functioning or the safety of the furnace.