Resolving Dimensional Problems - Delta Controls HTX Installation, Operation & Maintenance Manual

2.8 Resolving Dimensional Problems

Carefully measure the nozzle and refractory dimensions and compare them to the dimensions on the
front cover of this manual. Dimensional discrepancies are commonly caused by the following conditions:
A. Nozzle inner diameter is not as specified – If the nozzle I.D. is too small, the hard
packing rings will not fit. These rings can be cut down to size. This is best done in a
lathe with a tapered arbor to fit the center hole. Use a dust collector when cutting these
rings to avoid breathing the dust.
B. Nozzle height is not as specified – If the nozzle is too tall, the thermocouple will not
extend all the way into the vessel and may report erroneously low temperatures. If the
nozzle is too short, the thermocouple may contact the bottom of the refractory thermowell
causing it to break. (See Note "D", below). Contact Delta Controls to arrange for a
thermocouple correctly sized for the installation.
C. Incorrectly specified thermocouple dimensions – The design intent is for the
thermocouple element tip to be positioned even with the refractory hot face, and for the
HRW Refractory Thermowell to extend approximately 1 inch (2.5 cm) past the refractory
hot face. If these conditions are not met, the result may be inaccurate measurement and/or
breakage due to mechanical interference or thermal shock. Contact Delta Controls to
arrange for a thermocouple that is correctly sized for the installation.
D. Refractory has entered the base of the nozzle – The top surface of the refractory
should be even with the inside surface of the vessel shell. If it is not, the HRW Refractory
Thermowell will not rest at the proper position and may cause it to be broken when the
thermocouple is inserted into the nozzle. If there is refractory material inside the base of
the nozzle, it must be removed to restore a flat surface that is even with the inner surface
of the vessel shell.
E. Refractory is not installed at the specified thickness – If the overall refractory is thicker
than specified, the thermocouple will not extend all the way into the vessel and may report
erroneously low temperatures. If the refractory is thinner than specified, the thermocouple
will extend past the refractory hot face. This could increase the possibility of breakage due
to thermal shock. Contact Delta Controls to arrange for a thermocouple that is correctly
sized for the installation.
F. Refractory firebrick has separated from the insulating castable – It is not uncommon for
the firebrick to sag and form a gap between the firebrick and the castable or insulating brick.
Often, thermal expansion will cause this gap to close by itself when the furnace reaches
operating temperature. If this is the only cause of dimensional discrepancy, thermocouple
installation may proceed.
G. Refractory has separated from the vessel shell – This condition is not common, but it
is possible for a gap to appear between the insulating refractory and the vessel shell. The
result is that the thermocouple may not extend far enough into the vessel to reach the
refractory hot face and may report erroneously low temperatures. In general, this gap will
not close up at operating temperatures. The thermocouple must be re-sized to account for
the gap. Contact Delta Controls to arrange for a thermocouple that is correctly sized for
the installation.
Pre-Installation 9