Patent ID: 8079233

Claim:
A burner for manufacturing porous glass base material, comprising: a central pipe that is arranged centrally and has a central raw material gas discharge port formed therein; a plurality of pipes that are coaxial with the central pipe and that form annular gas discharge ports between adjacent pipes; and a plurality of small-diameter gas discharge port nozzles that (i) are arranged in one or more rows in a circle coaxial with the central pipe within one of the gas discharge ports other than the central raw material gas discharge port, (ii) have small-diameter gas discharge ports formed therein, and (iii) branch from one main pipe arranged between a pair of pipes forming the gas discharge port in which the nozzles are arranged, at a position that is a prescribed length L from tips of the nozzles, wherein inner diameters of the pipes forming the gas discharge ports positioned farther inward in a radial direction than the gas discharge ports in which the small-diameter gas discharge port nozzles are arranged contract beginning from a position farther on a burner source side than the prescribed length L position, the contraction being greater closer to a burner tip side and within the one main pipe arranged between a pair of pipes forming the gas discharge port in which the nozzles are arranged, and inner diameters of the pipes forming the gas discharge port in which the small-diameter gas discharge port nozzles are arranged and the gas discharge ports that are positioned farther outward in the radial direction than this gas discharge port contract beginning from a position farther on a burner tip side than the prescribed length L position, the contraction being greater closer to a burner tip side.