Abstract: A heat treatment apparatus for yarn including a plurality of heat treatment apparatuses provided for a plurality of spindles, respectively, disposed at horizontally spaced intervals. The heat treatment apparatus provided for each of the spindles, includes a heat treatment tube through which at least one yarn passes, and a heat insulating jacket to surround the tube. An orifice having a throttling function is provided upstream of a part which provides communication between the heat insulating jacket and the heat treatment tube, while a nozzle for injecting a heated fluid is provided in the heat treatment tube downstream of the communication part. The throttling orifice is arranged to have a fluid resistance greater than the fluid resistance of the nozzle.

Abstract: This invention relates to a method and apparatus for producing a polyester fiber which cools a plurality of molten polyester fibers from a spinnert 2 to a temperature below a glass transition point, then takes up the fibers by a non-heating first godet roller at a take-up speed less than 4,000 m/min, heat-stretching the fibers between the first godet roller and a non-heating second godet roller 10 inside a normal pressure steam atmosphere (first heat-treating device 8) higher than the glass transition point of the polyester fiber, and heat-treats the fiber by a pressurized steam atmosphere (second heat-treating device 9) higher than 105.degree. C.