Apparatus for continuously measuring temperature of molten metal and method for making same

An apparatus for continuously measuring the temperature of molten metal comprising a thermocouple unit and an immersion protection tube unit, wherein:

• said thermocouple unit comprises a thermocouple temperature sensing element comprising a platinum-platinum/rhodium alloy thermocouple and terminals connected therewith, an insulator which contains said thermocouple, a porcelain protection tube into which said insulator is inserted, a terminal box having a housing which contains said terminals and provides a cylindrical part extending downward therefrom, and an extension sleeve screwed into said cylindrical part with which the upper part of said porcelain protection tube is held;
• said insulator provides its upper part with fixing means which is fixed to said terminal box so as to suspend the insulator without engaging said porcelain protection tube;
• said immersion protection tube unit comprises a protection tube, a holding sleeve into which the upper part of said protection tube is inserted and fixed by a fire-resistant adhesive member, and a connecting sleeve connected with said holding sleeve;
• said protection tube of said immersion protection tube unit comprises a sintered alumina-graphite protection tube of less than 8 wt % SiO.sub.2 formed from a resin type binder of a high carbonization yield, a graphite powder, a powder of a material selected from the group consisting of:
• SiC derivatives, Si derivatives, ZrO.sub.2 -SiO.sub.2 derivatives, Al.sub.2 O.sub.3 -ZrO.sub.2 -S10.sub.2 derivatives, and mixtures thereof;
• and substantially granular and/or powdered alumina;
• said porcelain protection tube of said thermocouple unit is detachably inserted into said alumina-graphite protection tube of said immersion protection tube unit with said cylindrical part of the terminal box being in contact with said connecting sleeve of said immersion protection tube unit and with said extension sleeve of said thermocouple unit being detachably inserted into said connecting sleeve of said immersion protection tube unit, a clearance being provided between the end of the porcelain protection tube and the inside end of the alumina-graphite protection tube so as to accommodate their differing rates of thermal expansion;
• and
• a fixing means detachably fixes said extension sleeve and said connecting sleeve with each other to allow easy removal of said thermocouple unit from said immersion protection tube unit.