LT-1 METAL-CERAMIC PROTECTING TUBES
- Superior oxidation resistance
to 2200°F.
- Thermal conductivity comparable
to that of stainless steel.
- Good resistance to wetting
by most molten metals.
Order Marlin Part Number:
LT-1
LT-1 is hard, abrasion-resistant and dense. It is a slip-cast
composite of two compatible high temperature materials, chromium
and aluminum oxide. LT-1 has excellent oxidation resistance and
also resists wetting by many metals and alloys, as well as basic
furnace slags. The chromium-metal phase takes on a very tightly
bonded layer of chromium oxide which, together with the naturally
inert nature of the alumina, provides this material with its remarkable
resistance to oxidizing atmospheres over 2200°F, good corrosion
resistance, and the ability to resist wetting by molten metals.
High thermal conductivity and the resultant excellent sensitivity
to temperature changes accounts in part for its demand in the
high temperature pyrometry field as a thermocouple protection
tube.
LT-1 has good strength at temperatures where many high-temperature
metals melt. Above about 2800°F, it begins to soften and becomes
plastic. LT-1 thermocouple protection tubes have, however, been
used successfully for dip immersion at a temperature of 3000°F.
In use or service care must be taken to avoid conditions of extreme
thermal shock, extreme thermal gradients, mechanical shock, and
impact. Although LT-1 is superior to ceramics in all of these
properties, it is less resistant to shock and impact than the
metallic alloys. Therfore, a standard thermocouple protection
tube should be preheated to about 900°F before immersion in molten
metal at 2000°F or higher. Whenever practical the following preheat
procedure can also be used: Hold the tube immediately above
the molten metal for approximately one minute before immersing.
In tests conducted, this procedure proved to be adequate to prevent
thermal shock failure.
LT-1 exhibits good resistance to wear under conditions of sliding
friction as well as resistance to abrasion at high temperatures.
The hardness of this material (Rockwell C37) is more indicative
of the crushing strength of the material than its true hardness
because the individual particles have a greater hardness than
the combined body.
LT-1 is less porous than most compacts. There is no significant
passage of gases through the body at high temperatures, except
under high vacuum. For the usual industrial application, it is
sufficiently impermeable.
Tolerances and Specifications
I.D. Size
Will pass a 33/64 inch diameter x 2 inch long probe through
the full length of the tube.
Straightness
Tube to be straight within 3/16 inch per foot of length as measured
chord to arc.
Note
For use with B & S Wire Gage 8 or smaller.
A ceramic primary tube is required when noble metal thermocouple
is used.
Connecting Fittings
- Standard 3/4" conduit fitting, malleable iron with 3/4"
N.P.S. thread.
- Thermocouple Protecting Tubes can be supplied without fitting.
- Specify with suffix "O" e.g., LT-1-12-0.
| TYPICAL
PHYSICAL PROPERTIES |
| PROPERTY |
UNITS |
VALUE |
LENGTH
(inches) |
WEIGHT
PER TUBE
(pounds) |
| Thermal
Conductivity |
BTU-ft/ft2-hr/°F |
17 |
9 |
0.56 |
| Coefficient
of Thermal Expansion |
in/in/°F |
5
x 10-6 |
12 |
0.75 |
| Density |
gm/cc |
5.8 |
18 |
1.20 |
| Flexural
Strength |
psi |
45,000 |
24 |
1.75 |
| Compressive
Strength |
psi |
110,000 |
30 |
2.00 |
| Hardness |
Rc |
34 |
36 |
2.60 |
| Chemical
Composition |
Weight
% |
77%-Cr
23%-Al2O3 |
- |
- |
RECOMMENDED APPLICATIONS:
- Molten copper and brass to 2100°F intermittent and continuous
immersions.
- Corrosive SO2 and SO3
gas (to 2200°F) and SO3 and
HF gas (to 2000°F).
- Open hearth furnace checker chambers to 2200°F.
- Steel mill soaking pits to 2200°F.
- Pelletizing chamber of Taconite refining operation to 2100°F.
- Molten zinc to 1600°F.
- Molten lead to 650°F.
- Basic steels and slags to 3000°F (intermittent) and 2200°F
(continuous in open hearth and general foundry practices).
- Calcining kilns to 2200°F.
- Barium titanate (barium oxide service) to 2200°F.
- Magnesium oxide calcining kilns.
- Fluid bed cement process with severe corrosion and temperature
to 2200°F (fluid method of producing builders cement).
- Gas and ethylene cracking atmosphere.
- Atmosphere directly upon burning sodium (1800-2200°F).
- Oil fired furnace chambers.
- Atmosphere directly above molten glass in an open hearth
glass furnace.
- Molten silver solder.
- Molten tin.
- Borax flux.
- Copper matte.
- Boiling sulphuric acid - 97%.
- Blast furnace stove dome and bustle pipes.
NON-RECOMMENDED APPLICATIONS:
- Molten aluminum.
- Cryolite.
- Tin (stannous) chloride (750°F).
- Acid slag.
- Carbide slag.
- Molten glass.
- Boiling sulphuric acid - 10%.
- Carburizing atmospheres.
- Nitriding atmospheres.
- Barium chloride salt bath.
- Sodium Nitrate - nitrate salt bath.
For more information regarding
Protecting Tubes and Thermowells,
Consult your Marlin Catalog, pages D-0 to D-13.
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