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

A device for producing glass tubes by a Vello or down-draw method, the device comprising:

• a melt feeder with an outlet opening for discharging a glass melt;
• and
• a shaping mandrel comprising a shaft and a shaping body, the shaft extending through the outlet opening forming an outlet ring between the shaft and a circumferential edge of the outlet opening, so that the glass melt can flow from the melt feeder through the outlet ring and over the shaping body thereby forming a hollow glass drawing strand, the shaping body comprising a first part extending from a lower end of the shaft in an 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 the 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.