Protecting Tubes – 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
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 is used.
- 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.