Porous glass base material manufacturing apparatus, method for manufacturing porous glass base material, and method for manufacturing glass base material for optical fiber

A porous glass base material manufacturing apparatus that releases gas of organic siloxane raw materials into the flame of a group of burners that moves relative to a starting base material along the longitudinal direction of the starting base material rotating around a rotation axis along the longitudinal direction to form soot of porous glass particles on the surface of the starting base material, comprising:

• a vaporizer that vaporizes liquid raw materials containing organic siloxane in a liquid state supplied from a raw material tank to make a raw material mixed gas mixed with raw material gas and carrier gas;
• and
• a raw material gas pipe that supplies the raw material mixed gas to a burner of the group of burners,
• wherein the raw material gas pipe is insulated and kept warm by double insulation, which is a combination of an inner layer heat-insulation material provided on the outside of the raw material gas pipe and an outer layer heat-insulation material provided on the outside of the inner layer heat-insulation material,
• wherein an insulation material with a heat resistance temperature of 160° C. or higher and a thermal conductivity greater than that of the outer insulating material is used for the inner layer heat-insulation material, and
• an insulation material with thermal conductivity of 0.05 W/m/K or less (at 20° C.) and a heat resistance temperature lower than that of the inner insulating material is used for the outer layer heat-insulation material.