Horizontal heat treatment device

A method of manufacturing a flame-resistant fiber bundle that heat-treats a carbon fiber precursor fiber bundle by a horizontal heat treatment device to manufacture a flame-resistant fiber bundle,

• wherein the horizontal heat treatment device is a horizontal heat treatment device that continuously heat-treats a continuous flat object, while transporting the object within a heat treatment chamber in a horizontal direction,
• a seal chamber connected to an exhaust fan is connected to each of object loading opening and unloading opening of the heat treatment chamber, and the seal chamber is configured so that the object can pass through the seal chamber in the horizontal direction,
• a passage having a rectangular cross-section is connected to an opening of the object loading opening and unloading opening of each seal chamber located on a side opposite to the heat treatment chamber, and the passage is configured so that the object can pass through the passage in the horizontal direction,
• the seal chamber is located between the heat treatment chamber and the passage,
• the object loading opening of the passage connected to the seal chamber object loading opening is an object loading opening of the heat treatment device, and the object unloading opening of the passage connected to the seal chamber object unloading opening is an object unloading opening of the heat treatment device,
• a pair of nozzles configured to eject the gas is provided at upper and lower positions of each passage,
• a gas ejection opening of each nozzle has a rectangular shape,
• in each passage, the pair of nozzles provided in the passage ejects gas toward a center in the vertical direction of the passage, and toward the object loading opening or the object unloading opening of the heat treatment device included in the passage,
• in each passage, the gas ejection opening of each nozzle provided in the passage is parallel to a long side direction of the loading opening and the unloading opening of the object of the passage, and has a length equal to a length of the long side, and
• in each passage, a distance d, which is greater than 0, between the gas ejection opening of the pair of nozzles provided in the passage and the object loading opening or the object unloading opening of the heat treatment device included in the passage, and a height Dn of the passage satisfy a relation of 2 mm≤d<0.75 Dn,
• the method comprising:
• setting a negative pressure in the seal chamber using the exhaust fan;
• and
• ejecting the gas from each nozzle so that a relation of V≤−30×P+21 is satisfied, when an amount of gas ejection of each nozzle provided in the passage per long side 1 m of the loading opening and the unloading opening of the object of the passage is expressed as V (m3/h), and a gauge pressure in the seal chamber connected to the passage is expressed as P (Pa) in each passage.