| 摘要 |
Disclosed is an apparatus for heating glass rod, in particular an apparatus comprising an induction furnace for drawing glass optical fibers from a preform. The induction furnace comprises an inner zirconia susceptor tube (12) surrounded by a radially-spaced annular insulating region of magnesia refractory grog (13), i.e. grain, within a silica beaker (11), i.e. containment vessel. While the magnesia grog has a melting point similar to that of commonly used zirconia grog, and thus can also be used up to temperatures of ca. 2300 DEG C, the electrical conductivity of magnesia is substantially lower, enabling it to withstand higher RF power from the induction coil. Moreover magnesia is more soluble than zirconia in silica, reducing the likelihood of particulate contamination of the silica-based glass fiber compared with that which occurs when using the standard zirconia grog insulation of the prior art. The magnesia grog (13) may be radially confined by an inner magnesia tube (14), spaced form the susceptor tube (12), and by an optional outer layer of aluminosilicate insulation (17) within the silica beaker (12) and may further comprise refractory felt discs (19) for upper and lower confinement. |
