Manufacturing silica crucible by fusion of quartz powder in porous mold connected to aspiration system, comprises perfoming primary fusion of quartz powder into dense silica layer, and performing secondary fusion of quartz powder

摘要

The process of manufacturing a silica crucible by fusion of quartz powder (2) in a porous mold (1) connected to an aspiration system, comprises perfoming primary fusion of the quartz powder into a dense silica layer by forming a dense silica skin on inner side of the crucible, and performing secondary fusion of the quartz powder into porous silica layer outside the crucible under second plasma intensity and second aspiration intensity. The mold is rotated around a vertical axis. An air plasma heating the gas is created inside the mold by the electrodes forming an electric arc. The process of manufacturing a silica crucible by fusion of quartz powder (2) in a porous mold (1) connected to an aspiration system, comprises perfoming primary fusion of the quartz powder into a dense silica layer by forming a dense silica skin on inner side of the crucible, and performing secondary fusion of the quartz powder into porous silica layer outside the crucible under second plasma intensity and second aspiration intensity. The mold is rotated around a vertical axis. An air plasma heating the gas is created inside the mold by the electrodes forming an electric arc. The dense silica skin is obtained under first plasma intensity and first aspiration intensity in the mold. The first plasma intensity is greater than the second plasma intensity, and the first aspiration intensity is greater than the second aspiration intensity. A cover with an opening is placed above the mold. The electrodes cross the opening during the formation of the dense silica skin. A gas stream is forced to pass through the opening towards inner side of the crucible. An area of the cover or a distance between the cover and the crucible is larger during the formation of the porous silica layer and dense silica skin. The cover is opened or elongated from the crucible during first aspiration intensity after the formation of dense silica skin and before the second aspiration intensity. The gas (70 vol.%) is introduced inside the crucible using an injector during the formation of dense silica skin. During the formation of the dense silica skin, an area of the cover opening represents 20-70% of the area of the final crucible. The plasma arc is initiated in the air by the electrodes placed over the cover, where the electrodes are then lowered through the opening of the cover to form dense silica skin. The first plasma intensity is changed to the second plasma intensity after the pressure in the aspiration system passes 100 mbars. The second aspiration intensity is zero. An independent claim is included for a device for manufacturing silica crucible.