Carbolite TZF Series - Manual (Page 11)

STF/TZF
MF08 – 3.24
11
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 a horizontal furnace from its base, or a vertical from its stand and/or
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. The negative leg of the thermocouple is marked
blue. Compensating cable colour codings are:
negative positive (type r)
white orange
Disconnect the thermocouple from its terminal block.
Withdraw the thermocouple from its sheath and remove any broken bits of thermocouple.
Alternatively, withdraw the sheath together with the thermocouple, first disconnecting any screws
which hold the sheath in place.
Insert the new thermocouple (or thermocouple and sheath) into position, restoring any removed
porcelain spacers, and ensuring correct polarity.
Re-assemble the furnace.
5.6 Element Fitting and Replacement
Replacements: read the section on element aging (4.6). If at any time the power limit has been
increased, reset it to its original value (section 8.2), or measure the resistances and recalculate
the limit.
Disconnect the furnace from the electrical supply.
Remove the furnace end guards to gain access to the element connections.
Remember that the elements are fragile and expensive, and that they can be damaged by
contamination: handle them with care and keep them clean.
Replacements: make a note of the actual braid and cable connections to the elements. From rod
elements disconnect the clips with the special tool provided (or with finger pressure, depending on
the type of clip fitted), lift off the braids and carefully withdraw each element. See fig.5.
Carefully insert the new elements into the furnace. Ensure that the rod elements are placed
centrally: the same length should be outside the insulation at each end.
STF: Attach the braids according to the notes made, or according to the appropriate diagram, fig.6
to fig.8. Use the special tools (or finger pressure) to fit the clips. Take care that clips do not touch
each other or any other metal parts.
TZF: The 3 rod elements are connected in series, using braids. The 6 double-spiral elements are
fitted 3 in series at each end, connected by 10mm cable. See fig. 9. In the case of 3-phase +
neutral, each set of elements is connected to a live from an SSR at one end, at to neutral at the
other. In the case of 3-phase delta (no neutral), each set of elements is connected to a live from an
SSR at one end, and a direct live from another phase at the other. The normal phase connections
are A1-C, B1-A, C1-B.
Replace the furnace end guards and connect the furnace to the supply.
If aged elements have been replaced, reset the furnace power limit.
If you have any problems with this procedure, please contact our service division.