Method for producing a substrate tube of quartz glass
A method for producing substrate tubes of quartz glass includes continuously supplying a hollow cylinder of quartz glass to a heating zone, softening the hollow cylinder zonewise in the heating zone, and drawing off a tubular strand from the softened portion. The hollow cylinder has an outer diameter C a , an inner diameter C i and an inner bore. The tubular strand has an outer diameter T a and an inner diameter T i . The following parameters are applicable to the hollow cylinder and the tubular strand: C a >180 mm, C r >3 with C r =C a /C i , T r <1.6 with T r =T a /T i and C i /T i <2.5. The blow pressure in an inner bore is adjusted to a value in the range of 4 to 10 mbar. Substrate tubes, obtained by cutting the tubular strand to the desired length, serve as semi-finished products for the manufacture of preforms for optical fibers.
1. A method for producing a substrate tube of quartz glass, comprising:
continuously supplying a hollow cylinder of quartz glass to a heating zone ( 3 ), the hollow cylinder having an outer diameter C a , an inner diameter C i , an inner bore and a wall thickness of at least 62.5 mm;
zonewise softening the hollow cylinder in the heating zone ( 3 ); and
drawing off a tubular strand ( 12 ) from a softened portion of the hollow cylinder, the tubular strand ( 12 ) having an outer diameter T a and an inner diameter T i ,
wherein a blow pressure is produced in an inner bore ( 13 ) is in the range of 4 to 10 mbar, and
wherein the following parameters are applicable to the hollow cylinder ( 4 ) and the tubular strand ( 12 ):
C a >180 mm,
C r >3 with C r =C a /C i ,
T r <1.6 with T r =T a /T i ,
C i /T i <2.5, and
C r /T r >1.88.
2. The method according to claim 1 , wherein the blow pressure is in the range of 6 to 8 mbar, and wherein the following parameters are applicable to the hollow cylinder:
Ca< 300 mm, and
C i /T i <2.
3. The method according to claim 1 , wherein the following parameters are applicable to the tubular strand:
28 mm< Ta< 50 mm, and
T r <1.3.
4. The method according to claim 1 , wherein the following parameters are applicable to the hollow cylinder and the tubular strand:
3.5< Cr< 4.5, and
C r >T r +2.4.
5. The method according to claim 1 , wherein the inner bore of the hollow cylinder has an inner wall that has a surface roughness defined by a roughness value R z >1 μm.
6. The method according to claim 1 , wherein the hollow cylinder has an outer wall that has a surface roughness defined by a roughness value R z >4 μm.
7. The method according to claim 1 , wherein a heating tube ( 1 ) is used that comprises a circular heating space ( 3 ) which is bounded by an inner wall and which defines a heating space volume V Heiz within which the hollow cylinder ( 4 ), a drawing bulb ( 11 ) and the tubular strand ( 12 ) occupy a cylinder space volume V c , where V Heiz >2.5×V c .
8. The method according to claim 7 , wherein an annular gap with a mean gap width in the range of 15 mm and 25 mm remains between the inner wall of the heating zone and the hollow cylinder ( 4 ).
9. The method according to claim 7 , wherein the heating tube ( 1 ) has a length L between 150 mm and 200 mm.
10. The method according to claim 1 , wherein the outer diameter T a of the tubular strand is in the range of 28 mm to not more than 35 mm and a throughput volume is in the range of 10 to 20 kg/h.
11. The method according to claim 1 , wherein the outer diameter T a of the tubular strand is in the range of 35 mm to 50 mm and a throughput volume is in the range of 20 to 30 kg/h.
12. The method according to claim 1 , wherein the tubular strand is drawn off at an elongation ratio of less than 150.
13. The method according to claim 1 , wherein the tubular strand is drawn off at an elongation ratio in the range between 50 and 130.