Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Patent
1998-03-03
2000-04-11
Vincent, Sean
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
65 2911, 65 2919, 65384, 65414, C03B 2000
Patent
active
060475641
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the production of quartz glass bodies by deposition of SiO.sub.2 particles on the mantle surface of a cylindrical carrier rotating about its longitudinal axis and forming an elongated porous preform, where the SiO.sub.2 particles are formed in a plurality of hydrolysis burners which are arranged in at least one burner row disposed parallel to the longitudinal axis of the carrier and between turnaround points at which points the direction of burner movement is reversed, where the burners move at a preset translational speed forward and back, and by the sintering of the preform.
DISCUSSION OF PRIOR ART
Such a process is described in EP A1 0 476 218. In the known process, SiO.sub.2 particles are deposited in layers by flame hydrolysis burners on a horizontally oriented substrate rod which rotates about its longitudinal axis. The burners are installed equidistantly 10 cm apart on a burner block extending parallel to the longitudinal axis of the substrate rod. The burner block is moved back and forth along the porous cylindrical preform which is being formed during the SiO.sub.2 particle deposition, and between a left and a right turnaround point. The amplitude of the translational motion is lesser than the length of the preform. Due to the slowing down of the translational motion of the burner block at the points of directional reversal an overheating of the preform surface takes place and with it a localized axial density variation develops. This creates areas of differing reactivity of the preform which make themselves known especially during subsequent chemical reactions in further treatment of the preform and which can result in non-homogeneousness of the quartz glass body after the sintering of the preform.
EP A1 0 476 218 proposes to solve this problem by continuously relocating the turnaround points of the burner block motion in relation to the preform and thus distributing them evenly over the preform. For this purpose both the left and the right turnaround points are relocated by a few millimeters at every burner pass.
However, this merely results in an even distribution in the preform of the localized density variations which develop at the turnaround points. In addition, the complicated translational motion of the burner blocks in this known process requires a high expense related to the apparatus and the controls.
SUMMARY OF THE INVENTION
Therefore the object of the present invention is to make available an easily implemented process which would make possible the production of a preform largely free of localized axial density fluctuations.
Based on the process described above, the object is accomplished according to the invention in that the base value of the surface temperature of the preform being formed is kept in a range between 1,050.degree. C. and 1,350.degree. C., that the average peripheral velocity of the preform is kept in the range between 8 m/min and 15 m/min and that the average translational velocity of the burner row is kept in a range between 300 mm/min and 800 mm/min.
The surface temperature of the preform is measured at the point of flame impingement of one of the central hydrolysis burners in the burner row. A "Infratherm IN 4/5" pyrometer made by IMPAC and having a measurement wavelength of 5.14 .mu.m is used for this purpose. The measurement area is approximately 5 mm at a distance of the pyrometer from the preform surface of 30 cm at a temperature between 500.degree. C. and 1,300.degree. C. The burner flame impingement point has a somewhat greater diameter of about 15 m. When the pyrometer is properly adjusted the measurement point is within the flame impingement area. A mis-adjustment results in a measured value that is lower than the actual temperature. The measured temperature resulting from correct adjustment will be used as the surface temperature hereinafter.
This temperature value substantially determines the density of the porous preform. A deposition of SiO.sub.2 particles at the indicated temperatur
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Ruppert Klaus
Schaper Hartwig
Heraeus Quarzglas GmbH
Tiajoloff Andrew L.
Vincent Sean
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