Conax designed a dual-seal thermocouple to save production load when thermocouple sheath fails during a production run.

Industry:  A global manufacturer of specialty glass and high-purity products for the semiconductor industry.

Challenge:  Large graphite lined vacuum furnace operating at 1500˚ carry large loads for heat treatment.  If a thermocouple sheath fails during operation, atmosphere can leak into the furnace causing loss of entire load.

Solution:  Conax provided a tungsten-coated molybdenum thermocouple sheath to protect the molybdenum sheath from the graphite liner.  Because the coating increases the sheath diameter, a split fitting was designed onto one side of the COMBO fitting.  The other side was designed with a TG fitting for sealing on the individual TC wires.  In this design, if the sheath breaks or develops a leak during a furnace run, vacuum is not lost in the furnace and the load may finish the heat treating cycle unaffected.

Impact:  Since implementation of the new COMBO fitting thermocouple, there have been no lost production loads in any of the furnaces.  Additionally, the COMBO fitting may be reused to build new replacement thermocouples when needed.