LT-1 METAL-CERAMIC PROTECTING
- Superior oxidation resistance
- Thermal conductivity
comparable to that of stainless steel.
- Good resistance to wetting
by most molten metals.
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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
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
Will pass a 33/64 inch diameter x 2 inch long probe through
the full length of the tube.
Tube to be straight within 3/16 inch per foot of length
as measured chord to arc.
For use with B & S Wire Gage 8 or smaller.
A ceramic primary tube is required when noble metal thermocouple
- Standard 3/4" conduit fitting, malleable iron with 3/4"
- Thermocouple Protecting Tubes can be supplied without
- Specify with suffix "O" e.g., LT-1-12-0.
of Thermal Expansion
- Molten copper and brass to 2100°F intermittent and continuous
- 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
- 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
- Molten silver solder.
- Molten tin.
- Borax flux.
- Copper matte.
- Boiling sulphuric acid - 97%.
- Blast furnace stove dome and bustle pipes.
- Molten aluminum.
- 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.
If you do not have a Marlin Catalog - Click