Contact thermometry is still the most successful means of measuring temperatures to enable control of industrial processes.
Its success is, however, largely dependent on how well the sensing element is protected from the process environment. High temperatures, in conjunction with corrosion and abrasion, provide a demanding operating environment which many sensors alone could not handle. This is where a ceramic sheath is essential.
Pyrosales provide a number of ceramic sheaths made from a variety of materials. We can recommend the most suitable type for your application.
Ceramic sheaths made from recrystallised alumina (Alsint, Rubalit, AL23 or KER 799) are the preferred solution for protecting a platinum-based sensor. Recrystallised alumina has excellent thermal conductivity which allows the thermocouple to respond quicker to changing temperatures.
Hexoloy® SA, a silicon carbide material with no free silica, now offers superior chemical resistance in both reducing and oxidising environments, and has been successfully used in mineral processing, non-ferrous melting and refining, high temperature process furnaces and chemical incinerators recuperators.
The corrosive nature of sulphur-containing processes, operating above 1300°C, requires the use of a protection sheath that will stand up to that environment, and Hexoloy® SA has been successfully used in these applications
PyroSheath, a metal ceramic sheath (LT-1®), is another protection sheath suitable for extreme temperatures. It is a composite material made up of chromium and aluminium oxide. This combination of metal and ceramic exhibits excellent resistance to oxidation above 1200°C, and also makes it resistant to wetting by many metals and alloys. The high thermal conductivity makes it superior to ceramics in thermal shock capabilities, but should be preheated before immersion into molten metals.
PyroSheath is suitable for molten copper, brass, zinc and lead. It is excellent in atmospheres containing SO2, SO3, calcining kilns, blast furnace stove domes and bustle pipes, gas and ethylene cracking atmospheres and oil fired furnace chambers.
PyroSheaths are not recommended for use in carburising or nitriding atmospheres, or in molten aluminium, as the chromium phase becomes reactive at elevated temperatures. It has a maximum continuous temperature rating of 1400°C.