Carbolite GHA Installation, Operation & Maintenance Instructions Manual page 12

G range
separate the cylindrical body from the base, or remove some guards under the protruding ends of
the body. For the versatile models it will be necessary to dismount the furnace from its stand, and
remove the mesh terminal cover.
Disconnect the furnace from the supply, and separate the furnace body and/or remove covers and
guards as necessary.
Make a note of the thermocouple connections. Type N colour codings are:
negative
white
Disconnect the thermocouple from its terminal block.
Withdraw the thermocouple from the end of the furnace: ensure no broken bits remain.
If the thermocouple is supplied straight or coiled, bend it carefully to match the shape of the
original (working from the terminal end). Should the length differ from that of the original this
will usually not be important provided that the thermocouple tip is within a tube diameter's
distance from the furnace centre. End zone thermocouple tips should be about two-thirds of the
way along the end element.
Insert the new thermocouple into position, restoring any removed porcelain spacers, and ensuring
correct polarity.
Re-assemble the furnace.
5.6 Element Replacement
Please see safety note 5.2 - please wear a face mask.
Disconnect the furnace from the electrical supply.
Remove all outer guards, meshes and terminal covers from the furnace body. For a horizontally
mounted furnace remove the furnace body from its base; to reach the bolts or screws that fix the
body to the base, remove the back panel from the base.
Disconnect all electrical leads from the terminal blocks on the furnace case. Note the colours and
positions of the connecting leads to enable correct reassembly. Take care not to crack porcelain
terminal blocks - use two spanners where appropriate.
Remove the thermocouple(s).
Lay the furnace body horizontally with the split in the cylindrical case uppermost. Remove the two
metal end-caps from the body. Undo the self-tapping screws that hold the terminal strip to the case
join. The case will spring open slightly. Remove the ceramic board disc from one.
Cut through the outer wrap of blanket insulation. Note
how the element tails are connected and disconnect all
of them. Lift out the elements through the end of the
cylindrical case.
Check the cylindrical case and clean out as appropriate.
Remove any insulation sleeving from the tails of the old
element and fit to the replacement element.
Slide in the new element(s). Close up the furnace again,
refitting the terminal strip and the end-caps. Any cut
made in the insulation should close up completely: if
the insulation appears loose or damaged in any way,
please contact our service division.
Reverse the rest of the disassembly process. Take care to make all connections to the correct
terminals. Do not overtighten the connectors in porcelain terminal blocks.
Let the furnace heat up at its maximum rate to 900°C without interruption, and then soak for 1
hour. Fumes may be emitted: this should be done in conditions of good ventilation.
12
positive (type N)
pink
Note on Elements
The end and centre elements look the
same but have different wattages. On
standard models the two end elements
are 1170W, and all the centre
elements are 780W. Ensure that
elements are correctly replaced.
MF48 -1.18