Method of manufacturing vitreous silica crucible
There is provided a method of manufacturing a vitreous silica crucible having non-bubbles on the inner surface without necessitating new apparatuses for grinding and polishing and without damaging the productivity. According to the present invention, there is provided a method of manufacturing a vitreous silica crucible including the processes of: gathering a vitreous silica layer containing residual bubbles existing in a near-surface region of the transparent layer of the vitreous silica crucible by controlling the number of rotations applied to the vitreous silica crucible in a state that an inner surface side of the vitreous silica crucible is fused by arc heating; and moving a portion of a non-bubble layer in the surface of the transparent layer exposed by movement of the residual bubble-containing layer to cover a region in which bubbles have gathered with the non-bubble layer.
1. A method of manufacturing a vitreous silica crucible comprising the processes of:
(1) supplying silica raw material powder into a rotating mold to form a crucible-shaped molded body;
(2) arc heating the crucible-shaped molded body while rotating the crucible-shaped molded body and depressurizing from an inner surface toward an outer surface the crucible-shaped molded body to form a cylindrical vitreous silica crucible having a bottom portion and a wall portion extending from the bottom portion and the crucible having a transparent layer on an inner surface side and a bubble-containing layer on an outer surface side;
(3) gathering a vitreous silica layer containing residual bubbles existing in a near-surface region of the transparent layer of the vitreous silica crucible by controlling the number of rotations applied to the vitreous silica crucible in a state that an inner surface side of the vitreous silica crucible is fused by arc heating; and
(4) moving a portion of a non-bubble layer in the surface of the transparent layer exposed by movement of the vitreous silica layer containing residual bubbles to cover a region in which bubbles have gathered with the non-bubble layer;
wherein the process (3) of gathering a vitreous silica layer comprises the processes of:
(A) moving, toward the bottom portion, a vitreous silica layer containing residual bubbles existing in a surface of the transparent layer of the wall portion by controlling the number of rotations applied to the vitreous silica crucible in a state that an inner surface side of the wall portion is fused by arc heating;
(B) moving, radially outward, a vitreous silica layer containing residual bubbles existing in a surface of the transparent layer of the bottom portion by controlling the number of rotations applied to the vitreous silica crucible in a state that an inner surface side of the bottom portion is fused by arc heating;
wherein the process (A) comprises the process of controlling the number of rotations to adjust the acceleration in the wall portion to be 13 m/s 2 or less,
wherein the process (B) comprises the process of controlling the number of rotations to adjust the acceleration in the wall portion to be 17 m/s 2 or more, and
wherein the process (4) comprises the process of controlling the number of rotations to adjust the acceleration in the wall portion to be 12 m/s 2 or more and 20 m/s 2 or less.
2. The method of claim 1 , wherein the arc heating in the processes (2) to (4) is carried out at 1800 to 2600 degrees C.
3. The method of claim 1 , wherein the process (1) comprises the processes of:
supplying natural silica powder into the rotating mold to form an outer layer, and
supplying synthetic silica powder on the outer layer to form an inner layer.