7.0 Repairs and Replacements
7.6
Element Replacement
See section 7.2 - wearing a face mask is required.
The chamber of this type of furnace is formed by winding resistance heating wire on to a
refractory muffle former. In the event of failure, the whole "wound muffle" assembly
must be replaced.
Disconnect the furnace from the electrical supply and remove the furnace back panel.
Pull the chimney out of the top of the furnace.
Make a note of the wiring connections;
"Thermocouple Replacement" above which
refers to the thermocouple colour coding.
Unfasten the electrical connections to the
inner chamber (brick-box) and remove the
thermocouple and sheath (see
thermocouple replacement instructions).
If the connections are secured by
hexagonal nuts, two spanners should be
used to avoid cracking the porcelain
mounting.
Undo any self-tapping screws and hook bolts necessary to release the brick-box.
Support the front of the brick-box as you withdraw it from the case so it does not fall
onto the electrical connections below.
Remove the brick-box lid and top insulating board, noting how it is assembled and
observing the position of the heating element wires (or “tails”).
Pull the element tails out of the terminal block and remove sufficient insulation to allow
access to the heating element. Check and replace damaged insulation.
Fit the new heating element, ensuring that the tails are separated from the element by
at least 25 mm (preferably 50 mm) of insulation – see the image above.
Feed the element tails through the terminal blocks and tighten the clamping screws
using two spanners as before. Cut off excess element tails.
Complete the fitting of the insulation and refit the lid. Do not use any cement unless
supplied by Carbolite Gero, as other types may chemically attack the heating element.
Replace and fasten the brick-box into the furnace case.
Replace the thermocouple and sheath and remake the electrical connections. In
porcelain and brass terminal blocks the brass connector should be slightly loose in its
porcelain support block to allow for expansion.
Replace the back panel and reconnect the electrical supply.
Switch the furnace ON and heat to 900 °C without interruption and then dwell for 1
hour. Some smoke may be observed during this process, which should be carried out in
a well ventilated area.
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