Patent ID: 8015845

Claim:
A glass tube processing method for performing chemical vapor deposition or diameter shrinkage of a substrate glass tube, the method comprising 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, the heating element having a void part at a part of the heating element, the part being inside of the induction coil, and the void part passing through an inner circumference side and the outer circumference side of the heating element; measuring a temperature of an external surface of the substrate glass tube through the void 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 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 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.