PURPOSE: To considerably inhibit the shrinkage and to reduce a change in the outside diameter by slowly vitrifying moving rodlike oxide powder deposited in a powder depositing process with a plurality of heat treating units arranged in succession along the moving direction.
CONSTITUTION: Oxide powder produced with gaseous starting materials and an oxyhydrogen flame sprayed from a burner 5 having a multitubed structure is deposited on the lower end of a rotator 6 to form rodlike oxide powder A. The rotator is slowly moved upward in synchronism with the deposition speed of oxide powder, and the powder A enters a heat treating unit 7, where it is subjected to primary heat treatment. Since the heat treatment is carried out at a low temp. such as ≤ about 1,200°C, the shrinkage rate of the rodlike oxide powder A is low. Next, the powder A enters a heat treating unit 8, where it is thoroughly vitrified by secondary heat treatment. This heat treatment is carried out at ≥ about 1,300°C, yet the shrinkage rate of the powder A is low since the powder has been subjected to the primary heat treatment.
OGURA KUNIO
YOSHIDA KAZUAKI
KUROBA TOSHIAKI
SHIBUYA SEIJI
FURUKAWA ELECTRIC CO LTD