Cylindrical sheath for pyrometric rod and its fabrication - using silico-calcareous material autoclaved and heat treated

摘要

The sheath (4) for a pyrometric rod for plunging in a bath of molten aluminium zinc, or one of their alloys, is made of a silico-calcareous material which contains a pliable mineral and which has been autoclaved and heat treated to a temperature of at least 500 degrees C. The sheath has an annular cylindrical transverse cross-section of external dia. of the order of 45 mm and internal dia. of the order of 21 mm. The pyroelectric rod has an armature formed from a metallic tube (2) around which the sheath fits and inside which the thermocouple is loged. A coupling section is screwed into a threaded extremity (2a) of the tube. The sheath is fabricated by rounding off the outside of an elongated back of silico-calcoreous material and drilling a hole of appropriate diameter inside it. The sheath is then treated in an autoclave and then progressively heated so that the temperature rises by about 50 degrees C. per hour as far as 550 degrees C. where it is maintained for an appropriate duration.