Patent ID: 7637125

Claim:
A glass tube processing method for performing chemical vapor deposition or diameter shrinkage of a substrate glass tube comprising the steps of: relatively moving a heating furnace which is an induction furnace including a heating element annularly enclosing the circumference of the substrate glass tube and an induction coil in the circumference of the heating element in a longitudinal direction of the substrate glass tube, the substrate glass tube having an outer diameter of 30 mm or more, a wall thickness of 3 mm to 15 mm, and an ovality of the outer diameter of 1.0% or less, wherein a ratio ID/Od between the outer diameter Od of the substrate glass tube and an inside diameter ID of the heating element is in the range of 1.1 to 5.0, and a speed of the relative movement of the heating furnace is at 10 mm/min or higher, measuring a temperature of an external surface of the substrate glass tube through a void part provided at a part of the heating element, the part being inside of the induction coil using a temperature measuring device provided outside the heating element, and adjusting the amount of heat generation of the heating element based on the measured temperature such that a distance along a longitudinal direction of the substrate glass tube from a place of the maximum temperature of the glass tube to a place in which a temperature lowers by 30° C. than the maximum temperature is at 20 mm or longer and a difference between the maximum temperature and the minimum temperature in a circumferential direction of the substrate glass tube is at 200° C. or lower, wherein the void part is a plurality of holes which are formed and arranged not to align in any of the same circumferential direction or the same longitudinal direction of the heating element, an opening area of the inner circumference side per one hole of the holes is 1000 mm 2 or less, and the total opening area of the inner circumference side of the holes is 50% or less an area of the inner circumference side of the heating element located inside the induction coil.