Carbolite TZF Series - Manual (Page 10)

10 MF12 3.12
5.5 Thermocouple Replacement
The coverings and guards which must be removed to gain access to the thermocouple depend on
the model, its orientation (horizontal or vertical), and possibly other options and fittings. It is
usually necessary to separate the furnace from its base or stand. On horizontal models (except TZF
12/38) one outer end-cap should be removed; on TZF 12/38 and vertical models the 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:
current models negative: white positive (type K): green positive (type N): pink
old models negative: blue positive (type K): white positive (type N): orange
Disconnect the thermocouple from its terminal blocks.
Withdraw the thermocouple from its sheath and remove any broken bits of thermocouple.
Bend the new thermocouple carefully to match the shape of the original (working from the
terminal end). Should the length differ from that of the original this is usually not important
provided that the thermocouple tip is within a tube diameter's distance from the furnace centre.
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.
The coverings and guards which must be removed to enable replacement of the wound tube
element depend on the furnace model, its orientation (horizontal or vertical), and other options and
fittings. The general procedure is:
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 which 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 thermocouples.
Lay the furnace body horizontally with the split in the cylindrical case uppermost. Remove the two
metal end-caps from the body. Except TZF 12/38, undo the self-tapping screws which hold the
terminal strip to the case join. The case should spring open slightly. Remove the ceramic board
disc from one end.
Use a sharp knife to cut right through the insulation down to the wire-wound tube element along
the whole length of the body, but do not cut either of the ceramic board end discs. The knife cut
must be in line with the element lead wires. Slide the element gently out through the end of the
furnace body.
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 (where
applicable) 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.