Patent ID: 7797965

Claim:
A method for producing tubes of quartz glass, said method comprising: continuously supplying a hollow cylinder of quartz glass to a heating zone and softening a region of the cylinder therein, and drawing off a tube strand at a drawing speed from a softened region so as to form a drawing bulb, and cutting the tubes to length in the form of tube strand pieces wherein the tube strand pieces are separated from the tube strand at a separation point, wherein the hollow cylinder has an inner bore, and wherein the method further comprises maintaining an internal pressure differing from an external pressure applied to an outer surface of the cylinder in the inner bore of the hollow cylinder, and wherein the tube strand has an inner bore, and wherein the method further comprises producing a constriction of the inner bore between the drawing bulb and the separation point, wherein the constriction of the inner bore of the tube strand is produced by softening and plastic deformation of the tube strand in an area of a deformation zone, wherein the constriction acts as a flow obstacle that obstructs gas flow through the inner bore of the tube strand.