Method for preform or tube drawing based on its viscosity

A method of producing an elongated strand of a glass component upon which a gravitational force is applied, the method comprising:

• providing an apparatus having a heating zone generating heat and being configured to heat the glass component from which the strand is drawn at a constant speed, the strand having a mass, and a pulling device configured to apply a pulling force to the strand;
• determining the pulling force;
• heating the glass component in the heating zone to create a forming region in the glass component, the forming region exerting a holding force on the strand;
• calculating the gravitational force applied to the strand by determining the mass of the strand multiplied by the gravitational constant;
• calculating the holding force by determining a sum of the gravitational force and the pulling force;
• controlling the holding force by correcting the heat in the heating zone;
• and
• adjusting the pulling force of the pulling device to maintain the constant draw speed,
• wherein a sum of the holding force, the gravitational force, and the pulling force is maintained as zero.

A method of producing an elongated strand of a glass component upon which a gravitational force is applied, the method comprising:

• providing an apparatus having a heating zone generating heat and being configured to heat the glass component from which the strand is drawn at a constant speed, the strand having a mass, and a pulling device configured to apply a pulling force to the strand;
• determining the pulling force;
• heating the glass component in the heating zone to create a forming region in the glass component, the forming region exerting a holding force on the strand;
• calculating the holding force by measuring a stress-induced birefringence in the strand at a point at or below the forming region, determining an amount of force value applied to the strand at the point, which corresponds to the measured stress-induced birefringence, and correcting the force value to account for a gravitational effect of the weight of the strand between the heating zone and the point, wherein the correction of the force value is zero if the point is at the forming region;
• calculating the gravitational force applied to the strand by determining the mass of the strand multiplied by the gravitational constant;
• controlling the holding force by correcting the heat in the heating zone;
• and
• adjusting the pulling force of the pulling device to maintain the constant draw speed,
• wherein a sum of the holding force, the gravitational force, and the pulling force is maintained as zero.