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.

Abstract: The apparatus for continuously manufacturing a calibrated round or profiled glass tube with a predetermined inner profile has a melt feed with an outlet opening for molten glass, a shaping body for forming a hollow drawing bulb from the molten glass, a profile forming body positioned downstream of the shaping body, and a device for changing a distance between the shaping body and the profile forming body to vary a wall thickness of the glass tube. The molten glass from the outlet opening is drawn over the shaping body to form the drawing bulb and the drawing bulb is drawn over the profile forming body so that inner circumferential surfaces of the drawing bulb are deformed while bearing on outer surfaces of the profile forming body to form the predetermined inner profile of the glass tube.

Abstract: In the method molten glass emerges from an outlet opening of a melt feed. The molten glass is drawn over a shaping body so as to form a hollow drawing bulb. According to the invention, the drawing bulb is drawn over a profile forming body positioned downstream of the shaping body so that inner circumferential surfaces of the drawing bulb are deformed while abutting against outer surfaces of the profile forming body to form the predetermined inner profile. The distance between the shaping body and the profile forming body can be changed to vary the wall thickness of the glass tube.

Abstract: The present invention relates to a method and apparatus for continuously manufacturing calibrated round or profiled glass tubes having a predetermined inner profile. In the method molten glass emerges from an outlet opening of a melt feed. The molten glass is drawn over a shaping body so as to form a hollow drawing bulb. According to the invention, the drawing bulb is drawn over a profile forming body positioned downstream of the shaping body so that inner circumferential surfaces of the drawing bulb are deformed whilst abutting against outer surfaces of the profile forming body to form the predetermined inner profile. According to the invention the distance between the shaping body and the profile forming body can be changed for varying the wall thickness of the glass tube.