5-10
hex nuts turn them firmly until resistance is felt using a nut driver and
then stop, this compresses the electrode springs to the correct height and
tension.
• Cycle the furnace to operating temperature several times and verify that
heating rates are as expected for the selected profile.
• Procedure complete.
5.3.2 Thermocouple Replacement, SST #35229
• Run a vacuum leak down check and record the change in vacuum level
over a 5-minute period starting from the lowest reading that the furnace
can obtain.
• Referring to the pictorial drawing “ Thermocouple Installation” in Section
5.4, hold the TC sealing plug, item 1, with one wrench and loosen the lock
nut and TC sealing screw, items 3 and 4, with a second wrench. Remove
the TC sealing screw, lock nut, thermocouple, and O-ring from the
chamber. Slide the TC sealing screw, lock nut, and a new O-ring, item 2,
onto the new thermocouple and reinstall in the reverse order of removal.
Tighten the sealing screw carefully until the O-ring grips the TC shaft and
locks it in place. When properly tightened the TC will rotate easily, but
will not slide in the fitting; if the sealing screw is too tight the O-ring and
TC can be damaged. Tighten the locknut with a wrench, making sure that
the sealing screw remains stationary. If the TC sealing plug, item 1, turns
at any time during removal or installation of the TC it should be
completely removed from the chamber, cleaned and resealed with SST #
33643 thread sealant.
• Repeat the vacuum leak down check and verify that the TC installation has
not affected vacuum integrity.
• Select a familiar profile and run the furnace observing that the temperature
control system is working correctly.
• Note: If the machine is equipped with the MT-2 option a small ceramic
bead is to be installed on the control thermocouple as a visual aid in
distinguishing it from either of the reference thermocouples. Install the
bead about two inches from the end of the thermocouple and bend the
thermocouple shaft slightly as required to retain the bead in place. Three
additional beads were shipped with the MT-2 option; if additional beads
are required they can be ordered directly from SST, (P/N 35378).
• Procedure complete.
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