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US-12623946-B2 - Device for producing glass tubes by a Vello or down-draw method, method for producing glass tubes by a Vello or down-draw method and glass tubes

US12623946B2US 12623946 B2US12623946 B2US 12623946B2US-12623946-B2

Abstract

A glass tube has a center axis, where for the glass tube a specific cross-sectional plane is defined which includes the center axis and which is parallel to the center axis. Within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected first axial position x1 and second axial positions x2 along the center axis, respectively, the following relation is 60 or smaller: |(d2−d1)/(x2−x1)|*(10{circumflex over ( )}6 mm)/d1.

Inventors

  • Stephan Tratzky
  • Volker Trinks
  • Jürgen Eckl
  • Thomas Männer
  • Thomas Zimmert

Assignees

  • SCHOTT AG

Dates

Publication Date
20260512
Application Date
20230511
Priority Date
20220512

Claims (20)

  1. 1 . A glass tube having a center axis, wherein for the glass tube a specific cross-sectional plane is defined which comprises the center axis and which is parallel to the center axis, wherein, within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected first axial position x1 and second axial positions x2 along the center axis, respectively, the following relation is 60 or smaller: |( d 2− d 1)/( x 2− x 1)|*(10{circumflex over ( )}6 mm )/ d 1.
  2. 2 . The glass tube of claim 1 , wherein at least one of the following is satisfied: (i) a relative change of the outer diameter multiplied with a length of the tube is 50 or less; (ii) a ratio d1/d2 multiplied with a length of the tube is 1400 or greater; (iii) a relative change of the outer diameter multiplied with the length and the outer diameter d1, respectively, of the tube is 14000 or less; or (iv) the ratio d1/d2 multiplied with the length and the diameter d1, respectively, of the tube is 800000 or greater.
  3. 3 . The glass tube of claim 1 , wherein a distance between x1 and x2 along the center axis is (i) half of the total length of the glass tube or less or (ii) 400 mm or more.
  4. 4 . The glass tube of claim 1 , wherein d1 and d2 are each 80 mm or more.
  5. 5 . The glass tube of claim 1 , wherein the first axial position and the second axial position are each at a distance of at least 5% of a length of the glass tube from a respective end of the glass tube.
  6. 6 . The glass tube of claim 1 , wherein the glass tube has a length of at least 0.50 m.
  7. 7 . The glass tube of claim 1 , wherein the glass tube has at every position a wall thickness which is between 0.3 mm and 20 mm.
  8. 8 . The glass tube of claim 1 , wherein the outer diameter d1 and the outer diameter d2 are each greater than 100 mm.
  9. 9 . The glass tube of claim 1 , wherein at least one of the following is satisfied: the relation is 50 or smaller; the relation multiplied with a length of the tube is 90000 or smaller; or the relation multiplied with the length and the outer diameter d1, respectively, of the tube is 40000000 or smaller.
  10. 10 . The glass tube of claim 9 , wherein at least one of the following is satisfied: the relation is 20 or smaller; or the relation multiplied with the length and the outer diameter d1, respectively, of the tube is 10000000 or smaller.
  11. 11 . A glass tube having a center axis, wherein for the glass tube a specific cross-sectional plane is defined which comprises the center axis and which is parallel to the center axis, wherein, within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected axial positions x1 and x2 along the center axis, at least one of the following is satisfied: (i) a relative change of the outer diameter, ❘ "\[LeftBracketingBar]" d ⁢ 2 - d ⁢ 1 d ⁢ 2 ❘ "\[RightBracketingBar]" , with d2>d1, is 0.035 or less; or (ii) a ratio d1/d2, with d2≥d1, is 0.95 or greater.
  12. 12 . The glass tube of claim 10 , wherein at least one of the following is satisfied: (i) the relative change of the outer diameter, ❘ "\[LeftBracketingBar]" d ⁢ 2 - d ⁢ 1 d ⁢ 2 ❘ "\[RightBracketingBar]" is 0.025 or less; or (ii) the ratio d1/d2 is 0.99 or greater.
  13. 13 . The glass tube of claim 10 , wherein at least one of the following is satisfied: a relative change of the outer diameter multiplied with a length of the tube is 50 or less; a ratio d1/d2 multiplied with a length of the tube is 1400 or greater; a relative change of the outer diameter multiplied with the length and the outer diameter d1, respectively, of the tube is 14000 or less; or the ratio d1/d2 multiplied with the length and the diameter d1, respectively, of the tube is 800000 or greater.
  14. 14 . The glass tube of claim 11 , wherein a distance between x1 and x2 along the center axis is (i) half of the total length of the glass tube or less or (ii) 400 mm or more.
  15. 15 . The glass tube of claim 11 , wherein d1 and d2 are each 80 mm or more.
  16. 16 . The glass tube of claim 11 , wherein the axial positions x1 and x2 are each at a distance of at least 5% of a length of the glass tube from a respective end of the tube.
  17. 17 . The glass tube of claim 11 , wherein the glass tube has a length of at least 0.50 m.
  18. 18 . The glass tube of claim 11 , wherein a glass of the glass tube has the following Vogel-Fulcher-Tamman (VFT) constants: A ranging from −5.0 to 0.0; B ranging from 4000 to 12000; and T 0 ranging from 1° C. to 250° C.
  19. 19 . The glass tube of claim 11 , wherein a glass of the glass tube is a borosilicate glass.
  20. 20 . The glass tube of claim 11 , wherein a glass of the glass tube comprises the following components in weight percent (wt.-%): SiO 2 50-90; B 2 O 3 0-20; Al 2 O 3 >0-18; Na 2 O 0-15; K 2 O 0-5; Li 2 O 0-2; CaO 0-15; BaO 0-6; ZrO 2 0-5; TiO 2 0-5; and Fe 2 O 3 0-3.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. EP 22173006.2 filed on May 12, 2022, which is incorporated in its entirety herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for producing glass tubes by a Vello or down-draw method, to a method for producing glass tubes by a Vello or down-draw process and to glass tubes. 2. Description of the Related Art Glass tubes with large outer diameters are generally drawn using the Vello or down-draw method. In this process, a molten glass flows over a shaping body comprised by a shaping mandrel. The glass drawing strand forming at the break-off edge of the shaping body is drawn downwards by a drawing machine and cools during the process. Once the glass drawing strand has reached a predefined length, a tube section of predefined length can be cut off from the glass drawing strand and fed to horizontal end processing. Due to the vertical orientation of the drawing process, in addition to the forces exerted by the drawing rollers of the drawing machine, the dead weight of the glass drawing strand also acts on the strand and tube forming process, which varies continuously due to the cutting off of individual sections at the end of the glass drawing strand. The variation of the glass drawing strand weight in this way continuously influences the outside diameter and wall thickness of the glass drawing strand when it is formed in the area of the break-off edge of the shaping body. In the case of the Vello or down-draw method, this leads to an oscillating course of the outside diameter along the tube axis. The length of an “outer diameter oscillation” can correspond to the length of a tube section. The amplitude of the “outer diameter oscillation” is a measure of the geometric quality of a produced glass tube. Therefore, there is a general desire to further reduce the amplitude of the “outer diameter oscillation” and thus the outer diameter variation as a whole. What is needed in the art is ways which allow producing glass tubes having large outer diameters of highly uniform outer diameter and to provide glass tubes of high quality. SUMMARY OF THE INVENTION In some exemplary embodiments provided according to the invention, a glass tube has a center axis, where for the glass tube a specific cross-sectional plane is defined which includes the center axis and which is parallel to the center axis. Within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected first axial position x1 and second axial positions x2 along the center axis, respectively, the following relation is 60 or smaller: |(d2−d1)/(x2−x1)|*(10{circumflex over ( )}6 mm)/d1. In some exemplary embodiments provided according to the invention, a glass tube has a center axis, where for the glass tube a specific cross-sectional plane is defined which comprises the center axis and which is parallel to the center axis. Within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected axial positions x1 and x2 along the center axis, at least one of the following is satisfied: (i) a relative change of the outer diameter, |(d2−d1)/d2|, with d2>d1, is 0.035 or less; or (ii) a ratio d1/d2, with d2≥d1, is 0.95 or greater. In some exemplary embodiments provided according to the invention, a method for producing glass tubes by a Vello or down-draw process includes: flowing a glass melt from a melt feeder, through an outlet opening of the melt feeder and over a shaping body thereby forming a hollow glass drawing strand. The shaping body has a first part extending from a lower end of a shaft in axial direction along a length X and having a conical outer surface, and a second part extending from a lower end of the first part in axial direction along a length Y and having a cylindrical outer surface with an outer diameter Z. A ratio X/Z is between 0.1 and 0.5 and a ratio Y/Z is between 0.02 and 0.35. BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: FIG. 1 illustrates a schematic cross-sectional view of an exemplary embodiment of a device provided according to the invention; FIG. 2 illustrates a flow chart of an exemplary embodiment of a method provided according to the invention; FIG. 3A illustrates a schematic of an exemplary embodiment of a glass tube provided according to the invention; FIG. 3B illustrates a cut view of the glass tube of FIG. 3A within a specific cross-sectional plane; FIG. 4A illustrates a schematic of an exemplary embodiment of a glass tube provided accor