MF47-3.05
11
Connect the electrical supply with the side cover off. Take care! Set the furnace temperature to
maximum. Allow the furnace to start heating up.
Measure the current through the element circuit. This is done with the clip-on meter around one
pair of thick cables on the left-hand side of the transformer (as seen when facing the control side of
the furnace).
Adjust the potentiometer on the face of the thyristor unit. Adjust it slowly to the right (clockwise)
to increase the current, pausing to allow the time for response at the meter. Keep adjusting to
obtain an ammeter reading of between (149 to 150 A for HTF 17) or (139 to 140A for HTF 18).
This adjustment should be set up within the first 5 minutes of heat up from ambient and should
finally be checked when the furnace temperature is approximately 100°C below its maximum
temperature. Make further adjustment if necessary at this temperature.
Disconnect the electrical supply to ensure safe replacement of the side panel. See Section 3.1
before disconnecting the power supply.
5.5
Temperature Controller Replacement
2132, 3216, 3508 etc. Ease apart the two lugs at the side; grip the instrument and withdraw it from
its sleeve; push in the replacement.
5.6
Fuse Replacement
Access to internal fuses is by removal of the furnace side cover (see 5.3). See section 8.1 for
details of fuses fitted.
5.7
Thermocouple Replacement
Disconnect the furnace from the electrical supply, and remove the furnace back panel (1700
models) or top cover (1800 models).
Make a note of the thermocouple connections.
The negative leg of the thermocouple is marked
blue.
The “compensating” cable for 1700 & 1800°C thermocouples is plain copper.
Disconnect the thermocouple from its terminal block.
Undo the screw to release the thermocouple sheath; withdraw the sheath, and shake out any
fragments of thermocouple.
Re-assemble with a new thermocouple observing the colour coding, ensuring that the
thermocouple is not twisted as it is being inserted and that the metal tag is bent back, or the screw
inserted, to grip the sheath.
5.8
Element Installation & Replacement
Safety Warning:
Molybdenum disilicide elements form a glazed surface when heated. Internal
stresses can form through heating and cooling which render the glaze fragile. The
glaze can sometimes splinter into a shower of sharp particles when handled. Always
wear eye protection when handling the elements.
Handle the heating elements with extreme care as they are
very fragile
. Also, avoid touching the
heating surface (the thin part of the element), as the material is susceptible to corrosive damage
from skin contact.
Initial Installation
:
The elements, clips and braids are packed separately. Handle them carefully while unpacking.
Fit the insulation blocks to the elements. Locate the clamps over the elements, and tighten
carefully. The length of element above the fixing clamps should be as follows:
1700° models: 42mm
1800°C models: 45mm
Lower the elements into position, and connect the braids according to the scheme shown below,
using the clip tool provided. The braids must be held tightly to the element as the clips are fitted:
