Patent ID: 7891213

Claim:
A vertical drawing method for producing a cylindrical glass body, said method comprising: continuously feeding a glass cylinder to a heating zone having a vertically oriented heating tube; zonewise softening the glass cylinder; drawing a glass strand from the softened glass cylinder; and cutting the glass strand to size to obtain the cylindrical glass body; and an adjusting operation that comprises sensing a value for a first xy-position of a longitudinal cylinder axis of the glass cylinder or of a test glass cylinder in a first horizontal sensing plane, softening the glass cylinder or the test glass cylinder in the heating zone, with the longitudinal axis thereof extending through the heating tube and through the first xy-position in the first horizontal sensing plane, and drawing the glass cylinder or the test glass cylinder arranged in the first xy-position into a test glass strand, and carrying out the following steps once or repeatedly: a) measuring an actual state of a radial circular or annular dimension of the test glass strand, b) determining a deviation between the actual state and a desired state of the circular or annular dimension relative to a magnitude and position of said deviation relative to an inner wall of the heating tube during drawing, c) calculating a corrected xy-position of the longitudinal axis on the basis of a correction factor and the magnitude and position of the deviation, said corrected xy position being such that heating of the glass cylinder extending through the heating tube with the longitudinal axis thereof in said corrected xy-position is improved, d) repositioning the glass cylinder or the test glass cylinder in the heating tube such that the longitudinal cylinder axis extends at least in the first horizontal sensing plane in the corrected xy-position, and e) drawing the glass cylinder or the test glass cylinder in the corrected xy-position to obtain a further test glass strand; and wherein the test glass strand is tubular, and wherein the measurement of the actual state of radial circular or annular dimension of the test glass strand comprises measuring at each of a plurality of measurement points distributed around a circumference of the test glass strand a respective wall thickness of the tubular test glass strand, and said deviation determined is a determined degree of lopsidedness and a determined direction of lopsidedness of the test glass strand.