The production method of fused quartz glass can be: electrically fused, flame fused, plasma fused and electric-arc fused. The raw material can be natural quartz sand SiO2 and synthetic chemical-silicon tetrachloride(SiCl4). The combination of production methods and raw material composes the main 6 types of our quartz glass: EN (electrically fused natural quartz) series; FN (flame fused natural quartz) series; PN (plasma fused natural quartz) series; FS (flame fused synthetic quartz) series; PS (plasma fused synthetic quartz) series; AN (electric-arc fused natural quartz) series.
Electric fusion is the most commonly used melting process for manufacturing quartz glass. This process uses resistance Heaters to melt natural quartz sand into quartz glass tube, rod, blocks etc.. There are two methods of electric fusion, continous fusion and batch fusion. In the continous process, quartz sand is continuously poured into the upper part of tungsten crucible surrounded by electric Heaters elements. The inside crucible is maintained in a neutral or slightly reduced atmosphere that keeps silica from reacting with the refractory metal while the silica is melted inside. The melted quartz exits at the forming part at the bottom of crucible which is shaped into tube, rod and so on. The OH can be reduced by annealing. In the batch fusion process, several tons of raw material are placed inside a refractory vacuum chamber containing graphite Heaters elements to produce tube, rod and so on. The OH is usually below 2ppm. The low OH makes electrically fused quartz glass has high infrared transmission. The electrically fused quartz glass usually has certain bubble and drawing line on glass surface.
Flame fusion is a 2-step process. The first process is the natural quartz sand or synthetic SiC14 is melted in hydrogen/oxygen (H2/O2) flame into a solid round ingot. The second process is to further shape the ingot into various shape and dimension. Flame fused quartz glass contains a adundant amount of hydroxyl (OH) as a result of the direct contact between the H2/O2 and the silica raw material. This OH content can not be reduced by annealing and its presence lowers the viscosity and infrared transmission. The flame fused quartz has no drawing line and very low bubble content.
Plasma fusion is a 2-step process. The first process is the natural quartz sand or synthetic SiCl4 is melted in plasma flame into a solid round ingot. The second process is to further shape the ingot into various shape and dimension. Plasma fused quartz has low OH usually below 5ppm, so it has good infrared transmission. The plasma fused quartz has very low bubble content and has no drawing line.
Electric-arc fusion is the commonly used process for manufacturing crucible which is used to grow monocrystalline silicon ingot.